Mechanical Maintenance of Kiln Systems: Global Services - Training © F L Smidth A/S
October 12, 2022 | Author: Anonymous | Category: N/A
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Mechanical Maintenance of Kiln Systems
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Table of Contents
1. DESIGN CONSIDERATIONS
1.1 THE MAIN COMPONENTS....................................................... COMPONENTS................................................................................. .......................... 7 1.2 MECHANICS MECHANICS OF THE KILN KILN SYSTEM ........................................................ .............................................................. ...... 9 1.3 KILN SHELL - THE GLOBAL SITUATION...................................... SITUATION....................................................... ................. 9 1.3.1
Kiln shell - the cross-section geometry influence ...................................... ...................................... 11
1.3.2
Kiln shell - fatigue loading ......................................................... ......................................................................... ................ 13
1.3.3
Kiln shell - weldings............................................................................ weldings................................................................................... ....... 14
1.4 LIVE-RINGS AND SUPPORTING ROLLERS................................ ROLLERS.................................................. .................. 14 1.5 SUPPORTING ROLLERS - KILN CRANK....................................................... CRANK....................................................... 16 1.6 CONCLUSION ..................................................... .................................................................................. ............................................... .................. 17 2. OPERATIONAL ASPECTS
2.1 GENERAL ............................................................ .......................................................................................... ............................................... ................. 19 2.2 PRACTICAL ASPECTS ASPECTS............................... ............................................................. ....................................................... ......................... 19 2.3 PRE-START CONDITIONS .......................................................... ............................................................................... ..................... 20 2.4 START-UP, START-UP, PREHEATING AND SHUT-DOWN PROCEDURES .................. 21 2.5 OPERATING KEY - BARRING OF THE KILN ............................................... ............................................... 24 2.6 COLD KILN START ............................................................ .......................................................................................... ................................ 26 2.7 KILN STOP FOR A LONGER SERVICE STOP ............................................... ............................................... 28 2.8 SHORT STOP ...................................................... ................................................................................... ................................................ ................... 29 2.9 RING OR COATING FALLS..................................................... FALLS.............................................................................. ......................... 29 2.10 CYCLONE BLOCKAGE............................................... BLOCKAGE.............................................................................. .................................... ..... 30 2.11 BUILD UP IN IN RISER PIPE ........................................................ ............................................................................... ....................... 31 2.12 RED RED SPOTS ......................................................... ...................................................................................... .............................................. ................. 32 2.13 KILN FEED FAILURE...................................................................... FAILURE..................................................................................... ............... 33 2.14 KILN MOTOR STOP ................................................................ ....................................................................................... ....................... 33 2.15 ID MOTOR STOP.............................................................................. STOP............................................................................................. ............... 34 2.16 ELECTROSTATIC PRECIPITATOR-FAN STOP STOP........................... .......................................... ............... 34
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2.17 CLINKER TRANSPORT STOP....................................................................... STOP....................................................................... 34 2.18 HAMMER CRUSHER STOP ......................................................... ........................................................................... .................. 35 2.19 ELECTROSTATIC PRECIPITATOR TENSION STOP ................................. ................................. 35 2.20 KILN COAL STOP ............................................................... ........................................................................................... ............................ 35 2.21 CALCINER COAL STOP ........................................................ ................................................................................ ........................ 36 2.22 CHANGE BETWEEN COAL AND OIL DURING RUNNING ..................... 37 2.23 MISSING GRATE PLATE ...................................................... ............................................................................... ......................... 37 3. INSPECTION OF THE KILN SYSTEM
3.1 GENERAL .......................................................... ........................................................................................ ............................................... ................. 39 3.2 INSPECTION....................................... INSPECTION....................................................................... ............................................................. ............................... 39 3.3 METHODS OF EXAMINATION ........................... ........................................................ .......................................... ............. 50 3.3.1
Visual Inspection ................................................................ ........................................................................................ ........................ 50
3.3.2
Dye-penetrant testing................................... testing............................................................... ............................................... ................... 51
4. SHELL OVALITY MEASUREMENT AND CORRECTION
4.1
INTRODUCTION .......................... ........................................................ .............................................................. ..................................... ..... 53
4.2
OVALITY ........................................................ ........................................................................................ ................................................. ................. 54
4.3
CLEARANCE / LIVE-RING MIGRATION......................... MIGRATION .................................................... ........................... 56
4.4
MEASUREMENT OF LIVE-RING MIGRATION ......................................... ......................................... 58
4.5
TERMINOLOGY AND SYMBOLS ........................................................ ................................................................ ........ 61
4.6
INTERPRETING THE MIGRATION.............................................................. MIGRATION.............................................................. 62
4.7
LIVE-RINGS - REDUCTION OF MIGRATION ............................................ ............................................ 63
4.8 LIVE-RING - LUBRICATION.......................................... LUBRICATION...................................................................... ............................... ... 65 5. KILN ALIGNMENT 5.1 INTRODUCTION........................... INTRODUCTION ......................................................... .............................................................. ..................................... ..... 67 5.2 MEASURING OF KILN AXES ..................................................... ........................................................................ ................... 68 5.3 CAUSES FOR MISALIGNMENT ......................................................... .................................................................... ........... 82 5.3.1
Manifestation of misalignment................................................................... misalignment................................................................... 82
5.4 ALIGNMENT TOLERANCES ................................................... ......................................................................... ...................... 85 5.5 ALIGNMENT PROCEDURES ................................................. ......................................................................... ........................ 86 5.6 SAFETY ......................................................... ....................................................................................... .................................................. .................... 107
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6. KILN SHELL TEMPERATURE MONITORING
6.0
INTRODUCTION ....................................................... .................................................................................... ........................................ ........... 109
6.1 Instruments .......................................................... ........................................................................................ ............................................. ............... 109 6.2 Measuring points ....................................................... .................................................................................... ....................................... .......... 110 6.3
Recording of temperature ............................................................ ................................................................................ .................... 112
6.4
Evaluation of results ....................................................... ...................................................................................... ................................. .. 113
6.5
Safety................................................... Safety................................................................................... ............................................................ ............................ 114
7. KILN SYSTEM LUBRICATION
7.1 INTRODUCTION........................... INTRODUCTION ......................................................... .............................................................. ................................... ... 115 7.2 LIVE-RING /SUPPORTING ROLLERS ........................................................ ........................................................ 116 7.3 LIVE-RING /LIVE-RING PADS OR KILN TUBE...................... TUBE ........................................ .................. 118 7.4 SPECIAL CONDITIONS DURING KILN START-UP ................................. ................................. 119 7.5 SUPPORTING ROLLER BEARINGS ........................................................ ............................................................ .... 119 7.6 GIRTH GEAR LUBRICATION............................. LUBRICATION ........................................................... ......................................... ........... 123 7.6.1 Lubrication by means of lubricating lubricating wheel ................................................. ................................................. 123 7.6.2 Spray Spray Lubrication Lubrication ........................................................... ........................................................................................ ............................. 126 7.6.3 Operating principle .......................................................... ...................................................................................... ............................ 127 7.6.4 Lubricants ....................................................... .................................................................................... ............................................. ................ 127 7.6.5 Operation ........................................................ ...................................................................................... ............................................. ............... 128 7.7 PLUMMER BLOCKS AT DRIVE STATION ................................................ ................................................ 132 7.8 THRUST ROLLER ............................................................. .......................................................................................... ............................. 133 7.9 MAIN GEARBOX ........................................................ ...................................................................................... ................................... ..... 135 7.10 SEAL AT INLET ......................................................... ........................................................................................ .................................... ..... 137 7.11 SEAL AT OUTLET ............................................................... ......................................................................................... .......................... 139 7.12 SAFETY PRECAUTIONS .......................................................... .............................................................................. .................... 141 8. KILN COMPONENT FAILURES
8.1 KILN SHELL .......................................................... ....................................................................................... ......................................... ............ 143 8.1.1
Introduction .......................................................... ......................................................................................... .................................... ..... 144
8.1.2
Critical welded seams in terms of stress................................................... stress................................................... 144
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8.1.3
Intervals for examination....................................................................... examination.......................................................................... ... 145
8.1.4
Methods of examination ........................................................... ........................................................................... ................ 145
8.1.5
Inspection and Repair ...................................................... ............................................................................... ......................... 148
8.1.6 8.1.7
Replacement of Plate Section ...................................................... ................................................................... ............. 160 Introduction .......................................................... ......................................................................................... .................................... ..... 160
8.1.8
Measuring and Marking-Out .......................................................... .................................................................... .......... 161
8.1.9
Stiffening of Kiln Shell ........................................................ ............................................................................ .................... 163
8.1.10 Cutting-Out................................... Cutting-Out.................................................................. ............................................................ ............................. 164 8.1.11 Welding ........................................................ ...................................................................................... ............................................ .............. 165 8.1.12 Re-checking Re-checking ....................................................... ................................................................................... ....................................... ........... 167 8.2 LIVE-RING/SUPPORTING ROLLER........................................................ ROLLER............................................................ .... 167 8.2.1
Faults; causes and remedies.............................................................. remedies...................................................................... ........ 167
8.2.2
General description of machining of rollers and live-rings...................... live-rings ...................... 169
8.3 SUPPORTING ROLLER BEARINGS ........................................................ ............................................................ .... 171 8.4 SUPPORTING ROLLER SHAFT AND LIVE-RING .................................... .................................... 180 8.4.1
Supporting Roller Shaft ....................................................... ............................................................................ ..................... 181
8.4.2
Live-rings ........................................................ ...................................................................................... ......................................... ........... 183
8.5 THRUST ROLLERS.............................................................................. ROLLERS........................................................................................ .......... 184 8.6 GIRTH GEAR ........................................................ ...................................................................................... .......................................... ............ 186 9. MAINTENANCE OF KILN DRIVE
9.1 INTRODUCTION ......................... ..................................................... ......................................................... ........................................ ........... 191 9.2 MAIN GEARBOX ........................................................ ........................................................................................ .................................... .... 193 9.3 SAFETY PRECAUTIONS ........................................................ ............................................................................... ....................... 194 KEY TO SKETCHES IN FIGURES 9.2 and 9.3.................................................. 9.3..................................................... ... 194
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DESIGN CONSIDERATIONS A thorough understanding of the mechanical behaviour of the rotary kiln by the maintenance management is a prerequisite of proper mechanical maintenance of the kiln. Fundamental in modern condition based preventive maintenance is the ability to choose the right maintenance activities at the right time. This is, however, only possible if the persons responsible for maintenance planning are able, so to say, to put themselves into the place of the kiln designer. To a certain degree they should be able to understand why the kiln components look like they actually do. Able to understand how the different external physical conditions and the process conditions interact inside the material of the kiln components creating stress, strain and possibly fatigue. Ultimately, they should be able to prescribe relevant corrective actions to be taken to avoid or at least to minimise the consequences of a dangerous operating situation, or even better, to avoid that such a situation develops.
1.1 THE MAIN COMPONENTS The rotary kiln is an elastic body supported at a number of kiln supports. A typical kiln with four supports is is shown on Figure 1.1. 1.1. The basic components of a rotary kiln sup port are:
•
A live-ring, that surrounds the flexible kiln shell thereby se-curing its cross sectional stiffness.
•
Two supporting rollers each carried in two supporting roller journal bearings.
•
A bearing bed-plate, normally a welded steel construction, grouted into a reinforced concrete structure: the supporting pier.
•
To ensure the material flow down through the kiln interior, the rotary kiln is normally installed with a horizontal inclination of approximately 3 per cent towards the outlet.
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Figure 1.1 Four support kiln with planetary cooler.
This circumstance, however, gives rise to an axial force acting on the kiln. The magnitude of this axial force is the above mentioned approximately 3 per cent of the gravitational force on the total mass of kiln shell, refractory lining, coating formation and process material inside. Typically, the order of magnitude of those axial forces reaches to between 60 to 90 tons. Unless properly counteracted such forces are easily able to move the kiln downwards and ultimately to lead it to a fall down from the supporting rollers. Therefore:
at least one thrust roller arrangement is installed and then al-ways on the live-ring nearest to the kiln drive in order to en-sure proper and constant gear mesh.
The above mentioned mechanical kiln support components are the most ex-pensive components of the whole kiln system. Apart from high direct purchase costs they are normally associated with extremely long delivery times. Consequently, in case of failure, they represent great loss potentials in terms of loss of production. Availability of the rotary kiln system is crucial for the achievement of long term plant economy. It is therefore of the utmost importance that the organisations responsible for
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maintenance and operation are closely co-operating in keeping the mechanical conditions of its above mentioned components at an optimum. Insight into the fundamental mechanics of the system is a pre-requisite for achieving this goal.
1.2 MECHANICS OF THE KILN SYSTEM Generally, a component becomes mechanically damaged when the material strength somewhere in the component is surpassed by the value of the actual stress derived from the present mechanical operation condition. There are two sources to the build up of the actual stress-distribution:
• •
the global operating condition the specific cross-sectional geometric conditions of the kiln
1.3 KILN SHELL - THE GLOBAL SITUATION Globally considered the rotary kiln is treated as an elastic beam carried in a number of axially distributed supports. The purpose of the supports in this connection is to carry the inertial loads from the kiln shell proper, the refractory lining inclusive of possible coating formation and the process material inside the kiln. Consequently, an equilibrium is created between these inertial loads and the reactions from the previously supports. The sum of the latter being numerically equal but opposite in direction to the mentioned. For kilns with only two supports a so-called statically determined situation exists where it is relatively simple to calculate the load distribution between the two supports as this distribution depends on the static conditions only. For three or more supports the situation becomes statically indeterminable. This implies that the load distribution between the supports now depends not only on the static conditions but on the geometry of the kiln axis and on the stiffness of the kiln shell as well. This is a very important and unfortunately often disregarded circumstance. From the maintenance point of view this is especially important. It implies that while a flexible kiln is relatively insensitive to smaller changes in the kilns axis, the same changes may be detrimental to a very stiff kiln.
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Figure 1.2 shows the nature of the axial distribution of the max. bending moment and shear force in the kiln shell at a specific kiln axis.
Figure 1.2 Typical bending moments and shear force distribution.
From the figure it should be noted, that the values of the global or longitudinal bending stresses near the support positions could be quite significant. Most rotary kilns are designed to operate at straight kiln axis. The principle of straight axis can, however, in many cases be modified. By displacing the kiln axis in the vertical plane at a supporting pier (either by lowering or raising slightly) it is possible to transfer some of the loads from the heavier loaded bearings to the lighter loaded bearings. This method may be intentionally practised for instance with the aim to even the load capacity utilisation of the supports.
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Example: The percentage load change achieved by lowering one of the supports 10 mm at each of the 3 supports of a Ø5,00 × 80,00 meter kiln is shown below:
Resulting [%] 1
2
3
1 (Lowered)
-4,2
5,8
-4,6
2 (Lowered)
8,4
-11,5
9,1
3 (Lowered)
-4,2
5,8
-4,6
Support Number
1.3.1 Kiln shell - tthe he cross-section cross-section geometry geometry influence
If the kiln cross-section always remained circular, the load distribution would be as shown in Figure 1.2. In reality, however, this is not the case. From an engineering point of view a realistic kiln geometry could be described as an extremely thin-walled tube. Exposed to axial bending, the cross-section of any thin-walled tube will deform. The originally circular cross-section becomes oval. This, of course, is identical to circumferential changes in the radii of curvature i.e. circumferential bending. And circumferential bending again means circumferential circumferential bending stresses. Axial bending, however, is not the only reason for kiln shell ovality. In fact, it is not even the most important reason. Because of the small wall-thickness to diameter ratio the cross-sectional stiffness of the kiln shell becomes insufficient by itself i.e. without the stiffening support from the liverings, to avoid unacceptable ovality (i.e. bending stresses in shell plate) and consequential crushing of the refractory lining. The live-rings have two tasks:
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•
to transmit the inertial loads from the kiln shell, lining, crust and process material to the supporting rollers.
•
to supply cross-sectional stability to the kiln shell.
Figure 1.3 shows a typical cross-section of a kiln near one of the supports. The live-ring is of the so-called "floating" type, which is by far the most frequently used design.
Figure 1.3 Cross section at support
A top clearance is observed between tyre and kiln shell. This implies that a certain ovality and hence circumferential bending stresses are present in the kiln shell. It is obvious, that the greater the top clearance the greater the ovality and bending stresses - and further - the greater the mechanical loading on the lining. At this design, however, top clearance is a "necessary evil". It must be present, but it must be kept within an acceptable limit. To understand the background for the necessity of top clearance presence consider the warming-up phase of a cold kiln.
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It is a fundamental physical law that heat flows from areas with higher temperatures to areas with lower temperatures. As the only source of the live-ring temperature increase is a heat flow through the kiln shell, the temperature of the kiln shell must be higher than that of the live-ring. Bearing in mind, however, that a steel component elongates proportionally with its tem perature increase, this fact implies that the kiln shell diameter increases faster than that of the live-ring during this phase. If not for the existence of a top clearance, such fast diameter -in-creases would have caused a circumferential deformation of the kiln shell under the live-ring. Such a deformation is called a constriction. It would most probably have seriously damaged the lining and necessitated an exchange of the exposed kiln shell section. Even during relatively stable operating periods a certain kiln shell temperature variation can be observed. Consequently, some top clearance should always be present. In conclusion, the size of the top clearance is a balance between on the one side the risk of constriction and on the other side the stresses in the kiln shell material and the mechanical loading of the refractory lining inside. Ovality its equivalent: clearance, creates bending stresses the kiln shellormaterial. Ovalitytop is created between thecircumferential kiln shell and the live-ring as a in result of the geometrical conditions here. The ovality decreases, however, with the axial distance from the live-ring. Experience shows that it has practically disappeared at a distance from the live-ring of approximately 1,5 times the kiln diameter.
1.3.2
Kiln shell - fatigue loading
All the above-mentioned phenomena i.e. ovality, top clearance, bending etc. are fixed in space; i.e. their positions are independent of the rotation of the kiln (top clearance is always to be found in the top, max. bending stress always in the top etc.). This, on the other hand, means that every piece of material in the kiln shell undergoes a cycle of stress variation specific to its position during each rotation of the kiln. The material is said to be fatigue loaded. It has already been mentioned, that the global bending stresses assume their high-level values near the supports. This is, however, also the area where the circumferential ovality bending stresses are present. Consequently, the combined stresses could be expected to be at their highest here.
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1.3.3
Kiln shell - weldings
For obvious reasons the kiln shell is manufactured by welding together a number of circular sections. This implies that by necessity some circumferential weldings are located near the support positions i.e. in areas where the combined (fatigue) bending stress assumes its high level. Bearing in mind that the fatigue strength of the material in the area where two kiln sections have been welded together is only about one third of that of the material itself, it should be understandable why great care is given during kiln erection to the quality of these weldings. From a maintenance point of view, especially the circumferential kiln shell weldings adjacent to the live-rings should be systematically observed. This consideration not being based upon mistrust to the kiln designer but upon the fact that accidental changes during time i.e. of the kiln axis may cause considerable change of the loading situation. It is similar for any welding w elding on the kiln shell where the longitudinal stiffness of the t he shell abruptly undergoes change, for instance cooler console weldings etc.
1.4 LIVE-RINGS AND SUPPORTING ROLLERS When calculating the dimensions of a live-ring the designer will assume it to be loaded wherever it is in contact with other components i.e. kiln shell (supporting pads) and supporting rollers. On the inside surface the contact with the kiln shell (supporting pads) is shown on Figure 1.4 as the area below the two points A and B. Because the kiln shell is extremely flexible compared to the live-ring, it will completely assume the geometry of the latter resulting in a rather straight-forward and, from a maintenance point of view, rather uncomplicated contact pressure distribution. The pressure assumes the value zero at A and B and varies continuously between those two points having its max. values over the sup-porting rollers. Much more attention is, however, to be given to the contact between live-ring and supporting rollers. Here, two rigid cylindrical bodies having opposite curvatures are transmitting high inertial loads over contact areas that are very small compared to the situation at the inside diameter. Concentrated surface loading like this may easily create extremely high stresses in the surface material.
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Figure 1.4 Loads on the live-ring.
It is generally important that maintenance people understand the intentions of the designer. At this point, however, it is especially important because without understanding the contact mechanics the rolling surfaces of live-rings and supporting rollers can easily be destroyed by phenomena termed pitting or spalling. The kiln designer imagined or assumed operating conditions where the axis of rotation of live-ring and supporting rollers at each individual support were completely, or at least close to completely parallel. Under this assumption the contact between live-ring and supporting roller will cover the full width of the live-ring and roller and a so-called "line con-tact" is established. In this ideal situation no air gap exists between live-ring and supporting roller and no light is to be seen penetrating the contact zone. In the opposite situation, where light is clearly to be seen in the contact zone between live-ring and supporting roller, a line contact situation does not exist. Consequently, the real contact area has become less than the ideal resulting in increased concentrated surface pressure and increased material stresses. Concerning maintenance, such observations could be an indication that supporting roller adjustments were to be considered.
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1.5 SUPPORTING ROLLERS - KILN CRANK From what is mentioned hitherto it can be understood, that the supporting rollers have two tasks:
•
to carry the inertial loads of the kiln inclusive of lining, crust formation and process material.
•
to establish a specific kiln axis geometry i.e. to ensure a specific distri bution of loads between the supports. supports.
Fulfilling these tasks result in a constant load on each supporting roller i.e. constant load between supporting roller and live-ring. live-ring. The ideal kiln is manufactured to be straight. This straightness, however, can not always be during thewith kiln formation operation.and For lo instance, certain acan ccidental deformations canmaintained occur in connection conn ection loss ss of crust. This accidental be be registered from outside the kiln by study s tudy of the shell circumferential temperature distribution. When accidentally one side of the kiln shell becomes warmer than the opposite side, the warmer side becomes longer too, and the kiln is not straight anymore. Had it been free to deform, it would have taken a "banana shape". In technical terms the kiln is said to have crank. This deformation, however, is hindered by the supporting rollers, which indirectly therefore have a third purpose:
to force the kiln proper to act as an originally straight body.
During this process a force that straightens the kiln and therefore rotates with it is created. The source of this force is variations in supporting roller loads. This phenomenon is inherent in the kiln design. It is important to the maintenance peo ple because the variations created in the supporting roller loads could easily be of the same order of magnitude as the original and constant supporting roller load. Kiln crank is a potential source of mechanically overloading the supporting rollers as such, to the surface load of rollers and live-ring and to the loading of live-rings as such.
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1.6 CONCLUSION At first glance the rotary kiln may give the impression of a coarse and sturdy piece of machinery which does not need much maintenance or care. This is, however, not true. High availability of the rotary kiln is one of the important keys to success of the cement plant. Neglect of care and maintenance, therefore, will certainly lead the total plant economy into great risks. High mechanical availability is ensured only by good and well organised maintenance based on true insight into the mechanics mechanics of the de-sign.
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OPERATIONAL ASPECTS 2.1 GENERAL The SP kiln system with planetary cooler is by far the simplest system in terms of manual operation, because it requires a minimum of instrumentation. On the other hand, precalciner systems are well suited for automatic kiln process control because the degree of calcination of the material before it enters the kiln is fixed. Similarly, material retention time within the system is shorter. The lining life time is longer and the kiln refractory weight of the pre-calcining kiln systems is lower. This means longer operation periods and less down-time for these systems and reduced refractory costs com pared to SP kilns. Generally the maintenance costs are lower for a single-string kiln system than for a double or triple-string system. Furthermore, the risk of cyclone blockage is reduced with fewer cyclones. Consequently, a single-string preheater is always preferable to a double-string preheater for small to medium production capacities, if there are no tower height limitations.
2.2 PRACTICAL ASPECTS There are a number of considerations which must be taken prior to initial start-up. Some of these are obvious, but not always regarded as important as they actually are. Lack of attention to these important points often cause long delays and unnecessary problems during commissioning. Good examples of the above are compressed air and water supply. These are often taken for granted on existing plants where an extension has been built. Their importance is often underestimated and it is overlooked that lack of ( or poor quality) air and water can stop a production line. This is especially the case where new high-tech lines have been added which require higher quality air and water than the existing plant. The air should be free from moisture, oil and grit and be available at the specified quantity and pressure. The water for the gas analysers for example should literally be of drinking water quality. Where industrial water is used in existing plants a new separate line should be installed.
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Other things to be considered in relation to initial start-up are:
•
access to all specified areas such as all material flap gates.
•
ensure that platforms or supports of equipment that will expand when hot, are free to move, e.g. duct supports.
•
all machines should be labelled in a clear neat manner using the relevant codes.
•
ensure clean surroundings especially preheater tower floors which should be swept prior to feed-on in the event of cyclone blockage.
•
ensure adequate lighting everywhere, and again particularly on the preheater tower.
•
ensure drain holes for large fans, as a lot of condensation water will be present from the new castable refractory. refractory.
•
check the locking system on all machine switches.
•
ensure cleaning lances on all preheater floors.
•
ensure adequate cable tray protection in areas where hot material can flow.
•
ensure an adequate number of two-way radios are available.
•
note that some steam release holes may be drilled at the top of ducts and cyclones in the preheater tower.
2.3 PRE-START CONDITIONS •
tools and foreign objects removed from all plant machines
•
ducts and cyclones clear and clean
•
all doors and hatches closed
•
all dampers closed
•
electrical and mechanical departments give clearance to start
•
sufficient raw meal available for continuous operation
•
sufficient fuel available
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• •
compressed air and water ensured barring device checked
Precondition for flame on: It is judged that feed can commence immediately after preheating is completed.
2.4 START-UP, PREHEATING AND SHUT-DOWN PROCEDURES Figure 2.1 presents a graphic illustration of the heating and start-up procedure for an ILC kiln with calciner.
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Figure 2.1 Heating and start-up procedure for kiln with calciner, type ILC.
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The exact step-by-step procedures, however, vary depending on the kiln system type and equipment lay-out. Nevertheless, the principles involved can best be understood by use of an example of an "Operating Key" prepared for a modern kiln system of the InLine- Calciner ILC type. It is a five stage, 2000 tpd clinker capacity dry process kiln system with grate primarily erating Key" on thecooler, following page. coal fired with provision for oil firing (see the "Op-
Figure 2.2 5-Stage ILC Kiln System
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2.5 OPERATING KEY - BARRING OF THE KILN The following guidelines apply in a situation when a kiln stopped in hot condition is to be barred: A) As long as the kiln is hot, the barring operation must not be stopped for more than 10 minutes. B) If the axial position of the kiln should cause the alarm to be tripped, barring must must be continued until the correct position has been reestablished. C) If the kiln shell is exposed to strong external cooling, for instance due to heavy rainfall, continuous barring is required.
An example of barring programs is given below (see also Figure 2.1).
Barring programs programs The barring programs are divided into stages of 100° rotation. This is done to ensure variations in the position of the kiln during standstill.
Barring during during drying-out of the lining prior to initial start-up start-up
Hours 0–1
No barring
1 – 48 48 – 66
Approx. 100° every 15 minutes Approx. 100° every 10 minutes
66 – 72
Continuous barring
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Barring during during normal start-up of cold kiln
Hours 0– 1
No barring
1 – 14
Approx. 100° every 15 minutes
14 – 22
Approx. 100° every 10 minutes
22 – 24
Continuous barring
Barring during during stoppage and shutdown shutdown of kiln
Hours 0– 1
Approx. 100° every 10 minutes
1 – 24
Approx. 100° every 15 minutes
24 – 48
Approx. 100° every 30 minutes
48 –
Barring must be performed to required extent if rendered necessary by any of the conditions mentioned previously.
Braking of the kiln kiln When the barring operation is stopped, the kiln is automatically braked and maintained in an arbitrary position. The kiln could be weighted unevenly. This factor must be taken into account when the brake is slackened.
Special conditions during kiln start-up The positions of the supporting rollers may have changed considerably during the initial start-up of the kiln after erection or during start-up after major repair. There is therefore a risk that such a high axial load on a bearing liner collar may occur that overheating of the bearing can develop before it is possible to adjust the bearing to the correct position.
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For kiln starts of this kind all roller paths must be covered with oil (dosage by oil can). The oil layer must be maintained during the entire adjustment period. It is thus ensured that the axial force is reduced because of the lower friction between supporting rollers and tyre. When the start-up procedure has been completed, the oil layer shall be removed from the rollers.
2.6 COLD KILN START Pre-start conditions: conditions:
•
Raw meal stocks at least for 24 hours.
•
Oil, coal, gas, water and compressed air ready to use.
•
Instrumentation checked and OK.
•
Ducts and cyclones clear and clean.
•
All dampers closed.
•
Stop Electrostatic Precipitator and cooling tower dust transport.
•
Before kiln feed, switch over the filter dust to the kiln elevator.
Light Up:
•
Open for the gas to the pilot burner.
•
Start recirculation of oil to the burner platforms.
•
Start oil pre-heaters.
•
Heat the oil to a viscosity of 2° Engler.
•
Start the pilot burner.
•
Start the Electrostatic Precipitator-fan on lowest speed.
•
Open the Electrostatic Precipitator-fan damper to 100%.
•
Open the ID-fan damper to approximately 10%.
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•
Start the primary air fan.
•
Start the oil burner.
•
Adjust the draft in the kiln to correspond to 5 – 10% O 2.
•
Give primary air to form a clean and correctly formed flame without blowing it out.
•
After the flame has stabilised (2 – 3 hours after ignition) start the cooling air fans and the cooler excess air fan in Auto.
•
Adjust the kiln hood pressure to about 0,2 – 0,4 mbar. If you cannot reduce the kiln hood pressure low enough, start more cooling fans and eventually give more air in the last part of the cooler, so you obtain a balance between what goes to the kiln and what goes to the excess air fan. If the excess air fan is pulling too much, it will be observed as the flame is coming backwards in the kiln
•
Follow the barring program for the kiln
•
Follow the heating up curves in the pre-heating program. (See Figure 2.1). •
Start the clinker transport. Feed elevator and filter transport
•
Start the grate cooler and all cooling fans.
•
Start the kiln motor on minimum speed.
•
Start raw meal extraction if the kiln feed tank is not full.
•
Start the ID-fan with closed damper when the lower stage cyclone exit gas temperature is about 700°C.
•
Put the control of the pressure after the ID-fan in automatic
•
3 minutes after the ID-fan started, start the Electrostatic Precipitator
high tension. • Start the kiln feed. •
When you can see the indication of feed on the kiln feeder and the increase of Amps on the kiln feed transport, open the ID-fan damper to approximately 50%.
•
Increase the oil in the kiln as required.
•
Adjust the draft in the kiln between 1,5 – 3% O 2
•
Increase the kiln speed in accordance with the kiln feed/speed program.
•
Start the cooling tower water spray.
•
Start firing the calciner.
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•
Put the set point at approximately 890°C in the calciner and bring the temperature of the final stage cyclone exit gas up to this level and then put the controller in automatic mode. mode.
•
Run the clinker cooler at minimum speed.
•
Have the cooling fan dampers at 10%
•
When the kiln feed reaches approx. 60% of the nominal production, the cooler grate speed can be put in automatic control. The cooling fan air flows will at this production level be around 75% of the flow at full production depending on the actual grate plate temperature.
•
Increase the kiln production production in synchronisation kiln speed/kiln feed.
•
Use the tertiary air damper to distribute the gases between the kiln and the calciner. Kiln oxygen 2 – 3%. Calciner 2,5 – 3,5 O2.
2.7 KILN STOP FOR A LONGER SERVICE STOP •
Stop the coal dust supply to the coal dust bins. The coal dust bins should be emptied when the kiln is shut down.
•
Stop the raw meal extraction in such a way that the Schenck and coal bins are emptied at the same time (calculate consumption) or use oil when the coal bins are empty.
•
If the kiln is aimed for rebricking, you can reduce the kiln feed gradually without reducing the kiln speed to reduce the material bed in the kiln. This has to be started approximately 8 hours before the shut down. In a to clinker bedto level reducing procedure, special attention has to be paid the kiln prevent overheating. overheating.
•
When the coal and kiln feed bins are empty, stop the ID-fan. The interlocking will then stop the kiln department.
•
Bar the kiln according to the barring program.
•
Cool down the kiln by natural draught. If you cool down too fast, the retraction can cause damages to the castable and bricks.
•
Keep the clinker transport and filter transports running so as not to get accumulation of material in the transports.
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2.8 SHORT STOP •
Stop the ID-fan
•
The interlocking will then stop the kiln feed. Reduce the kiln speed to minimum (0,15 RPM). Close the ID-fan dampers; close all the clinker cooling fan dampers; close the tertiary air damper.
•
Reduce the primary air damper to approximately 30%.
•
If the stop is longer than 30 minutes, open the ID-fan damper between 10 – 20% and maintain oil or coal to the kiln, to keep the kiln in 'ready to go position'.
•
If coal or oil is not added to the kiln, go over to barring device and bar the kiln every 10 minutes, 110°.
•
Keep cooler, clinker transport and filter transport running to avoid material accumulations.
2.9 RING OR COATING FALLS
Indications:
•
Abrupt change on the torque curve.
•
The material will flush through the kiln and cool the burning zone
•
NOx reduces
•
Secondary air temperature increases due to more load on the grate. Tertiary air temperature increases due to extra load on the grate
•
Under-grate pressure increases
•
The automatic control on the grate speeds up the cooler
•
After a while, the clinker temperature goes up
•
After a while, the excess air temperature goes up
•
The cooling fan dampers open more than normal
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Action:
•
If the ring or coating fall is of minor disturbance, just let the cooler
automatic control take care of it. • The under grate pressure goes too high, the plate temperature climbs too high (500°C) and the excess air temperature is increasing despite full water injection then reduce the kiln speed for 5 – 10 minutes to ease the pressure on the grate.
2.10 CYCLONE BLOCKAGE
Indications:
•
The material temperature goes down in the blocked cyclone
•
The gamma ray indicators blocked with alarm
•
The cyclone pressure gives low alarm
•
The gas temperature in the cyclone below increases
•
The calciner temperature increases fast
Action:
•
Stop the ID-fan immediately. The interlocking will then stop the rest of the installation
•
Start cleaning as quick as possible because the longer the material is in the cyclone, the harder it will be to get it out
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Caution:
•
Always use protection equipment while working in the cyclones or riser
pipe • Always open the small holes first to prevent hot material from flushing out •
Always open the upper part or the cyclones first until you have located the size of the build up
•
Make sure the air blasters are stopped and manually released, before starting work
(See also separate INSTRUCTIONS FOR CYCLONE BLOCKAGES )
2.11 BUILD UP IN RISER PIPE Indications:
•
The under pressure in the whole cyclone tower increases
•
The oxygen level in the kiln goes down
•
The ID-fan RPM has to be increased
•
The tertiary air damper will be more and more closed to preserve the normal oxygen levels
Action:
•
Clean the riser pipe
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2.12 RED SPOTS
There are normally three different reasons for red spots on the kiln shell: •
Bricks fall out
•
Bricks are melted out
•
Bricks are worn out
If the bricks fall out in the burning zone, it has to be decided from case to case if the kiln is to be stopped or not
Example I:
The kiln is softly red in the normal coating zone Action: Put cooling air on the spot and continue to run the kiln as normal
Example II:
The spots are yellow and over a large area. Action: Stop the kiln and cool the spot. Bar the kiln continuously. Cool down the kiln and go in for repairs.
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2.13 KILN FEED FAILURE
Indications: •
Alarm for kiln feed tank under weight
•
t/h kiln feed reduces
•
Kiln feed elevator amps reduces
•
Calciner temperature increases
•
The pre-heater exit temperature will trip the kiln ID-fan at 425°C
Action:
•
Cut down the coal drastically in the calciner and kiln
•
Reduce ID-fan damper opening and speed.
•
Reduce the kiln speed to minimum or in synchronisation with present kiln speed
•
If complete kiln feed failure, stop the ID-fan which will stop the kiln department
2.14 KILN MOTOR STOP Action: Action:
The interlocking will stop the kiln department
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2.15 ID MOTOR STOP
Action: The interlocking will stop the kiln department
2.16 ELECTROSTATIC PRECIPITATOR-FAN STOP Action:
The interlocking will stop the kiln department
2.17 CLINKER TRANSPORT STOP Action: Action:
The interlocking will stop no. 3 grate at once. After 5 minutes no. 2 grate will stop. Further 5 minutes will stop no.1 grate and further minutes will reduce the kiln speed. When the goes down to minimum speed, stop the ID-fan and the interlocking will stop the kilnkiln department.
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2.18 HAMMER CRUSHER STOP Interlocking Action: Action:
•
The no. 3 grate stop at once No. 2 grate after 5 minutes No. 1 grate after further 5 minutes minutes
•
The kiln slows down to minimum speed after further 5 minutes
Your action:
•
Stop the ID-fan and the interlocking will stop the kiln department
2.19 ELECTROSTATIC PRECIPITATOR TENSION STOP
Action:
Find out the reason as quick as possible. If you cannot get the high tension on quick enough, the result will be considerable added expenditures, so you better stop and re pair.
2.20 KILN COAL STOP
Action:
The interlocking will stop the calciner coal
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Your action:
Stop the ID-fan and the interlocking will stop the kiln department. If there is something wrong with the kiln coal, coal, then start the kiln oil pum pump, p, the kiln oil preheater preheater and start oil to the kiln. Start up the kiln as usual.
2.21 CALCINER COAL STOP Indications:
Calciner temperature decreases rapidly
Action:
If the calciner coal cannot be restarted in few seconds:
•
Reduce kiln speed/kiln feed to approximately 80 – 90 t/h.
•
Reduce the draught to approximately 40 – 50 RPM on the ID-fan or to fit with 2 – 3% O 2 in the kiln.
•
Close the tertiary air damper
•
Start calciner oil pump
•
Start calciner oil pre-heaters
•
Cancel alarms on local oil panel
•
Start the oil to the calciner
•
Increase the production as normal again
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2.22 CHANGE BETWEEN COAL AND OIL DURING RUNNING The heat value of l ton of coal is equal to approximately 0,67 – 0,75 m 3 of oil. The heat 3
value of l m of oil is equal to approximately 1,3 t of coal. When you want to change, do it gradually. Always taking off before putting on.
Example: 4 t/h coal in the kiln to be exchanged to oil Example:
•
Reduce coal to 3 t/h
•
Increase oil to 0,75 m /h
•
Reduce coal to 2 t/h.
•
Increase oil to 1,5 m /h
•
Reduce coal to 1 t/h
•
Increase oil to 2,25 m3/h
•
Stop coal
•
Increase oil to approximately 3 m3/h after adjust with oil, so the oxygen level will be the same as with coal
3
3
2.23 MISSING GRATE PLATE
Indications: •
The cooling fan damper in the department where the plate is missing will be on a lower position than normal
•
The under-grate pressure in the same department will be lower than normal level
•
The material level in the under-grate compartment will give high alarm
•
Visual observation will indicate big amount of clinker falling through
•
Accumulation of clinker on the grill cover over fine clinker compartment
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Action:
• •
If the plate is completely gone in grate no. I, II or III, stop and repair If the amount of clinker falling through is minor, increase the air in the present compartment and repair at next next stop
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INSPECTION OF THE KILN SYSTEM
3.1
GENERAL
The rotary kiln is the central machine in a cement manufacturing plant. A high availability, a high run factor, i.e. a stable mechanical function of the rotary kiln over a period as long as possible is essential for the overall economy of the plant. Spontaneous stop of the kiln will not only cause expenses in terms of spare parts and repair costs but will also cause loss of production which can be difficult to retrieve. The run factor is particularly dependent on the condition of the lining, the lifetime of which is related to the mechanical condition of the kiln system. In order to determine the mechanical condition it is necessary to carry out regular inspection of the individual components of the kiln system to be able to discover, m monitor onitor and rectify any fault or development of wear wear which would eventually lead to a uncontrolled, spontaneous stop of the kiln.
3.2
INSPECTION
The components to be inspected during normal operations of a kiln are as follows: •
Supporting rollers and Bearings
•
Live-rings
•
Thrust roller(s)
•
Drive station inc. Barring device
•
Kiln shell
•
Seals at in- and outlet.
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During a shutdown of the kiln further inspection i nspection can be carried out:
•
Inclination of supporting rollers
•
Inspection of pinion and girth gear for drive station
•
Inspection of girth gear mounting
•
Inspection of internals in cooler and kiln if relevant (together with production department)
•
Drive station
•
Kiln shell, crack detection.
In the following, the inspection of the above mentioned components will be described in general. It is also necessary, however, to study the relevant instruction from the partici pant's own plant in detail in order that the inspection of the equivalent components is carried out as prescribed by the supplier. All the observations observations made shall be recorded every time an inspection inspection has been carried carried out so that comparison between the observations can be made and any onset of a development can be detected. The inspection comprises: co mprises:
Supporting Roller and Bearing
•
Control of graphite lubrication
•
Condition of roller path (pitting /facets / fish scaling / wear / other)
•
Temperature of roller path Check the direction of the reaction between supporting roller and livering (Contact / no contact between thrust plate (2) and bearing liner (1) see Figure 3.1 and for a more detailed explanation explanation refer to section 5.1. 5.1.2) 2)
•
Distribution of oil over the journal surface of the side where the journal leaves the liner.
•
Oil level in gauge (3)
•
Oil scraper (4) where relevant
•
Cooling water supply
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It is also essential to check the general cleanliness around the supporting rollers. If the bases are not kept clean and free from oil spillage the actual inspection will suffer. The inspector will not be able to perform his job correctly if he cannot move move around freely.
Live-ring
•
Condition of roller path (Pitting / facets / fish scaling / wear / other)
•
Live-ring migration The relative movement between live-ring and kiln as described in detail in Section 4 of this chapter.
•
Live-ring position in relation to the retaining rings
•
Condition of the retaining rings
• •
Condition of supporting blocks Lubrication between live-rings and supporting blocks/kiln.
Drive station
Inspection of the Drive Station including Barring Device is described in detail in section 9 of this chapter.
Thrust Rollers
•
Control of graphite lubrication
•
Condition of contact face (Pitting/facets/fish scaling/wear/other)
•
Oil level
•
Oil pressure
•
Hydraulic system where relevant (Pressure / leaks / level in tank).
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Kiln Shell
As a result of mechanical or thermal overloads fatigue symptoms may appear in the welded joints. Fatigue cracks always begin as micro-cracks in connection with notch effects, and inspection of kiln and cooler is therefore important. The following weld seams should be examined for fatigue cracks: •
circumferential seam between the kiln support section and the transition section and between the transition section and the adjoining section - see Figure 3.2
•
welds at manhole reinforcement frame - see Figure 3.3
The planetary cooler suspension is exposed in the same way as the kiln and cooler tubes. Its critical areas must therefore also be examined visually. During normal operation of the kiln it is of course not possible to carry out a detailed examination for cracks. Thorough crack detection will be described later in this section.
Figure 3.2 Transition and adjoining sections
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Figure 3.3 Kiln shell welding check
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Seals at inlet - and outlet end
There are numerous different designs of sealing arrangement between the rotating kiln and the stationary smoke chamber to be found. In the inspection programs, however, there are similarities:
•
Control of contact between rotating and stationary parts
•
Control of free movement
•
Inspection of wear parts
•
Lubrication
Pneumatic system (if relevant). relevant).
Similar for the sealing arrangement in the outlet end: The inspection programs will be similar to the seal in the inlet end irrespective of the cooler type (i.e. grate cooler or planetary cooler): •
Control of contact
•
Control of free movement
•
Inspection of wear parts
•
Lubrication
• •
Pneumatic system (where relevant) Seal cooling system ( where relevant).
The following inspections can be carried out during kiln stop:
A. Measuring of supporting roller inclination B. Inspection of teeth and girth gear mounting for drive station C. Inspection of interior of the kiln and cooler cooler (where relevant) D. Crack detection.
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Re. A: A: The inclination of the supporting rollers can be measured by means of an instrument as shown in Figure 3.4.
Figure 3.4 Supporting roller inclination instrument
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Figure 3.5 Supporting roller inclination instrument
If the contact between rollers and live-ring is not correct a cause could be that the roller inclination has changed. Through inclination measurement it is possible to calculate the required correction to the inclination.
Description and mode mode of operation
The inclinometer (see Figure 3.6 and 3.7) consists of a magnet holder (09) hinged to a spirit level holder (02) by means of a pivot (08). Both holders are made of silumin. The magnet holder supports two cylindrical magnets (10) and an adjustable stop bolt (13) fitted with a ball point The stop bolt is locked with the screw (04). The spirit level holder is fitted with a micrometer calliper (05). A spring (11) holds the micrometer calliper against the ball point of the stop bolt. Two large spirit bubble levels (03) and (04) (04) are used to measure the horizontal and ververtical plane deviations. The spirit bubbles can be adjusted using the screws (06). {Figure 3.6 is lacking – impossible to copy and transfer from original document}
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Figure 3.7 Inclinometer
The small spirit bubble levels (01) and (07) are directional spirit levels used to check the position of the inclinometer on the surface. When using the inclinometer on round surfaces, e.g. journals, the magnet holder can be fitted with a supporting bridge, see Figure 3.4. This is attached to the magnet holder with a dovetail (12). The exact gap between the micrometer calliper and the pivot (08) is 100 mm. The millimetre graduation of the micrometer calliper is equal to the inclination rate therefore 1 mm on the scale corresponds to 1% inclination.
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Example:
0,002 mm on the micrometer scale is an inclination of 0,002% or 0,02 mm per 1000 mm. The measuring range of the micrometer calliper is 0 – 25 mm, but the hinge between the magnet holder (09) and the spirit level holder (08) limits the actual physical measuring range to 0 – 20 mm (± 10 mm). When measuring the inclination of a loaded supporting roller, insignificant variations between the measurements on the two shaft ends may occur due to the deflection of the supporting roller. This is not unusual, compensation for this discrepancy is obtained by using the average measurements when computing the inclination incl ination rate.
An Example of Inclination Inclination Measurement: Measurement:
To measure the inclination of an unloaded supporting supporting roller that is to be adjusted for an inclination of 4% is as follows:
Measurement on the shaft end against the kiln outlet results in
R SUB i ~ = ~ {14,060 ~ + ~ 14,066} OVER 2 ~ = ~ 14,063
Deviation from 10,000 is
10,000 – 14,063 = - 4,063
Measurement on the shaft end towards the outlet of the kiln results in
R SUB o ~ = ~ {5,940 ~ + ~ 5,936} OVER 2 ~ = ~ 5,938
The deviation from 10,000 is
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The resultant supporting roller inclination is therefore; R SUB m ~ = ~ {14,063 ~ + ~ 5,938} OVER 2 ~ = ~ 4,063 %
Where: R i
=
Supporting roller inclination at shaft end nearest to kiln inlet
R o
=
Supporting roller inclination at shaft end nearest to kiln outlet
R m
=
The resultant supporting roller inclination
Re. B. Inspection B. Inspection of girth gear mounting for drive station.
This is covered in Section 3.9 of this training material.
Re. C. Inspection C. Inspection of interior of the kiln and cooler.
The interior shall be inspected together with the production department. The production staff can decide if the interior can meet the production demands whereas the maintenance department can assess the actual mechanical condition. A chain should be replaced when the chain weight has been reduced by 50% or when individual links have become worn to approx. half thickness. Chain wear is often heaviest on the chain links closest to the suspension points, but may also occur elsewhere on the chain. No general specifications can be given on the service life of a chain system. A worn-out cross system will have negative impact on the thermal economy. If this is acceptable, it will be reasonable to examine examine and possibly also repair the cross system in connection with kiln shutdown of appropriate duration. Where temporary repair work is undertaken, loose parts must be removed, and where required, damaged cross plates over the arched section of the brick lining are cut off. Based on an evaluation of the efficiency and condition of the cross system repairs can be planned so that the necessary replacement sections are held available during scheduled shutdown s hutdown of kiln.
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Re D. Crack D. Crack Detection
A thorough crack detection can only be carried out during a planned stop. To some extent, the frequency of the periodical examination of the welded seams should depend on the operating conditions of kiln. Where normal operating conditions apply, an interval of two years would seem appropriate. If the kiln has been in operation for more than 5 years, howe however, ver, a visual inspection of the welded seams once a year is recommended. Where operational irregularities may have increased the stress loading on the welded seams, an additional inspection of those welded seams which have been exposed to exceptionally severe stresses should be made. Any repairs by welding must be re-checked after 6 months of operation.
3.3
3.3.1
METHODS OF EXAMINATION
Visual Inspection
The visual inspection of the kiln welds constitutes the simplest and, at the same time, the most important form of examination as to the condition of welds. In connection with the visual inspection, an initial check-up should be made without removal of rust and dirt from the welded seam, since it is quite often easier to identify a possible crack formation with the welded seam un-cleaned. After this initial inspection, the surface of the welded seam is carefully cleaned using a hammer and a wire brush, and grinding may also be required. In connection with the subsequent visual inspection, it must be remembered that many "irregularities" in weld may resemble cracks. It is recommended that the cleaned c leaned welded seams are also dye-penetrant tested, or, better still, subjected to a magnetic particle examination.
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3.3.2 Dye-penetrant testing
The dye-penetrant is a into liquid with a cracks, strong colour which, when applied a metallic surface, penetrates possible and by(red) means of a "developer" thetoevidence of cracks is increased.
Procedure:
A. Remove grease, dust and scale from the surface B. The dye-penetrant liquid to be applied by painting or spraying to the cleaned area in a uniform layer. C. The dye-penetrant liquid must be allowed time to penetrate into possible cracks. 10 minutes will be sufficient at temperatures from 0 to 60° C. D. Carefully remove any excess dye-penetrant liquid. If the liquid is watersoluble, water should be used, otherwise use the relevant solvent. E. The dye-penetrant liquid must never be removed by "flushing"; always wipe off the liquid by means of a lint-free cloth. F. Wait until the surface has dried, and then apply a thin layer of "developer", which is a high-absorbent white powder, suspended in a volatile solvent. G. After evaporation of the solvent, possible cracks will take on a stronger appearance in the form of red lines li nes against the white background.
NOTE! If the cracks are filled with grease, oil etc. this crack detection method cannot be ap plied. In such cases a magnetic particle examination examination is required.
Where the cracks are extremely deep, the dye-penetrant liquid may penetrate so far into the crack that it cannot be seen on the "developer". Therefore, it must always be ensured that sufficient dye-penetrant liquid is applied and that it is given reasonable time to penetrate. At temperatures below 0°C the plate requires pre-heating with a gas burner or a hot-air blaster before the dye-penetrant liquid is applied. For any further information i nformation see ISO 3879-1977.
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Magnetic Particle Examination Examination
Magnetic particle and magnetic powder examinations are performed by covering the area to be examined for surface cracks with a ferromagnetic indication material (magnetic powder). A magnetic field is then generated in the area in at least two directions with the highest attainable degree of perpendicularity relative to one another. The indication material will now accumulate in possible cracks, and will thus disclose even minute defects in the surface region, and defects extending to 3 mm below the surface proper. To facilitate the identification of cracks, a light contrasting colour should be applied to the area to be examined by painting before the examination is conducted. The equipment needed (in addition to the consumables) is a hand-held yoke for magnetic detection, see Figure 3.8.
Safety Aspects
When the inspection around the kiln takes place it is most essential that the personnel performing the inspection shows extreme carefulness to avoid coming into contact with any of the moving or hot parts of the kiln. Only personnel with the appropriate authority shall be allowed to perform the inspection and be allowed to remove any guard and protection to enable the inspection to be carried out. And they must be held responsible for replacing any guard or protection which has been removed. The personnel must wear personal safety equipment such as helmet, shoes and clothes that fits. Any kind of loose hanging clothes or scarves shall be avoided as these can be caught by the moving machinery and be the cause for fatal damage. Not only the personnel but also the machinery shall be protected against any damage during the inspection. When an inspection cover is removed it must be done in such a way that no dust or dirt will find its way into the machine. For instance, it will be extremely harmful if clinker dust entered into the supporting roller bearings each time the cover w was as removed.
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SHELL OVALITY MEASUREMENT AND CORRECTION
4.1
INTRODUCTION
Kilns can be designed to have single "floating" or "migrating" types of live-rings with a certain diameter difference between live-ring and kiln shell (supporting blocks). Kiln tube and live-rings are dimensioned so that the inside diameter (D) of a live-ring is somewhat bigger than the outside diameter (d) of the kiln tube, measured on the livering pads(or the kiln tube). The diameter difference is necessary, because of the larger thermal expansion of the kiln tube. The absolute diameter difference, i.e. the diameter difference between a circular livering and a circular kiln shell is designated 2s. See Figure 3.1.
Figure 3.1 Kiln shell in live-ring.
As the kiln rotates, the diameter difference will cause a relative movement between livering and kiln shell due to the different developed lengths of the two joint faces. The live-ring movement relative to the kiln shell is called live-ring migration.
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The live-ring migration during one kiln revolution is designated by the letter V V..
4.2
OVALITY
Since kiln tube and live-ring are not absolutely rigid, the weight of the parts will lend them a certain elasticity in the cold as well as in the hot state.
Figure 3.2 Ovality. Ideal and real conditions.
The left half of Figure 3.2 shows what it would look like if kiln tube and live-ring were absolutely rigid, whereas the right half of the figure - somewhat exaggerated - shows how the parts are exposed to elastic deformation in practice. The deformation is largest under the live-rings and reduced fast as the distance from the supports increases. The deformation is normally referred to as the ovality of the kiln. The term ovality is often used in different senses. It is therefore important to stick to a
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defined terminology and defined symbols when dealing with the relationships mentioned herein.
Figure 3.3 Elastic Deformation
The elastic deformation (ovality ) ωo of the kiln shell can be expressed as the difference between the horizontal and vertical diameter of the kiln tube during the elastic deformation i.e.
ω 0 = d 0v − d 0l The relative ovality ω0r of the kiln is expressed in percent and derives from:
ω 0 r =
d 0 v − d 0 l
d 0
⋅ 100
[%]
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To take an example, FLS kilns are normally dimensioned to have a relative ovality of approx. 0,3% during normal operation corresponding to a live-ring migration of approx. 10 mm.
Figure 3.4 Live - ring migration.
4.3
CLEARANCE / LIVE-RING MIGRATION
It is important to keep the clearance between kiln tube and live-ring within certain em pirically established values. If the kiln tube temperature becomes extremely high, so that there is a large temperature difference between kiln tube and live-ring, the clearance between them may become zero. If the temperature of the kiln shell rises any higher the shell on both sides of the live-ring will expand further resulting in a permanent deformation called "constriction". When the kiln shell temperature goes back to normal and the th e shell contracts correspondingly the clearance between the live-ring and the kiln becomes excessive. See Figure 3.5.
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Figure 3.5 Constriction of kiln shell
This risk is highest at the live-rings before and after the burning zone. Therefore it is important to check the relative migration between kiln and live-rings. In case of permanent kiln tube deformations an increased diameter difference may cause lining troubles, and it may become necessary to reduce the clearance between life-ring and live-ring blocks by inserting intermediates under the blocks. To protect the rotary kiln against deformations and/or lining damages caused by overheating during operation, it is necessary to carefully check and, if possible, make operational corrections so as to keep the diameter difference between kiln and live-ring at an acceptable level, so that the ovality is maintained within the permissible max. and min. limits. A simple and accurate check of the actual diameter difference during kiln operation is made by measuring the live-ring migration i.e. the relative kiln movement in relation to the live-rings.
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4.4
MEASUREMENT OF LIVE-RING MIGRATION
The kiln supports are designed so that there will be a minimum diameter diff difference erence between hot kiln tube and live-ring. live-ring. As an example, this is 0 – 3 mm on an FLS kiln. As mentioned, the diameter difference or clearance between kiln shell and live-ring causes a relative movement between the two components. The theoretical diameter difference 2s causes a relative movement which is
V = π ⋅ ( D L − D 0 )
2 s = ( D L − D 0 )
V = π ⋅ 2 s as shown on Figure 3.4 This relative movement V between the deformed kiln shell and the live-ring will as a rule be one and a half to twice the top clearance δ. One and a half for large kilns (D0 > 4 m) and twice for small kilns (D0 < 4 m). The theoretical and the actual live-ring migration are, of course, the same irrespective of the deformation. It is not possible to measure the diameter difference on a hot kiln, but since the live-ring migration is a function of the diameter difference, same can be checked indirectly by checking the live-ring migration. Automatic equipment for monitoring and controlling the live-ring migration can be installed. If such equipment is not available, it is possible to measure the live-ring migration manually. The simplest way of measuring the live-ring migration is to plot corresponding marks on live-ring and kiln tube. After the kiln has completed for instance 10 revolutions, measure the displacement between the marks, after which the mean migration can be calculated easily. Clearance δ can then be found by dividing V by 1,5 to 2, that is
δ =
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Dividing the mean migration V by π results in
V π
= 2s
that is, the theoretical clearance for circular kiln tube /live-ring. A more practical method of measuring V, for instance, during the start-up period, is to use measuring instrument as shown on Figure 3.6.
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Figure 3.6 A practical method of measuring V.
The measuring instrument consists of a frame (02) which is placed on one of the sup porting blocks by means of magnet base (01). The frame supports a spring-loaded, horizontally placed pencil (03) which is pressed against a piece of paper attached with adhesive tape to a plate (04), which is fixed to the live-rings by means of magnet blocks.
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Figure 3.7 Kiln revolution curves
As the kiln rotates, the pencil will scribe a curve as shown in Figure 3.7. The shown curve corresponds to five kiln revolutions, and the values V and measured directly on the curve.
δ can
be
As mentioned previously, it is important that the clearance between kiln shell and livering is kept within certain values. If, during kiln start-up, the pencil begins to scribe ever smaller curves, this means that V and δ approach zero, and interference may be required in order to avoid the before mentioned "constriction".
4.5
TERMINOLOGY AND SYMBOLS
s 2s
Theoretical radial clearance Theoretical top clearance / diameter difference
V
Relative movement between kiln tube and live-ring per kiln revolution (Live-ring migration)
δ
Actual top clearance with hot kiln
ω0
Absolute kiln tube ovality
ω0r
Relative kiln tube ovality
DL
Inside diameter of live-ring measured on vertical plane
D0
Outside diameter of kiln measured on kiln shell or supporting blocks on vertical plane
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d01
True inside kiln diameter measured on vertical plane
d0v
True inside kiln diameter measured on horizontal plane
4.6
INTERPRETING THE MIGRATION
Generally, relative ovality corresponding to live-ring migration of 10 – 15 mm will not have any harmful effect on the kiln lining. However, if the live-ring migration exceeds approx. 20 mm, this indicates that the ovality of the kiln shell has reached a size which will most probably contribute to a reduction of the life of the lining. Such an increase in the ovality will also add to the stresses in kiln shell and welds, and this may contribute to crack formation. Consequently, it is recommended that the measuring of the live-ring migration and of the related temperatures on the surface of the live-rings and on the kiln shell on both sides of the live-rings to form an integral part of the normal, preventive maintenance program. In doing so, it will be possible to follow the variations in the live-ring migration and take the necessary steps to meet any problems.
Normally, an increase in the live-ring migration migration is caused by:
Wear on the supporting blocks where such do not exist, on the kiln shell itself , caused by ineffective lubrication between live-ring and livering supporting blocks, which can, e.g. be the case when the environment at the live-ring is very dirty. To ensure effective lubrication, it is necessary to use:
•
correct Lubricant,
•
correct Lubricating method,
•
correct Lubricating frequency, as will be described later in this section.
•
Constriction as described previously in this section.
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4.7
LIVE-RINGS - REDUCTION OF MIGRATION
If the kiln has a constriction, it may be impossible to do a proper lining work resulting in an unacceptably short life of the lining. In such a situation, the kiln section in question should be replaced. In case the live-ring migration increases due to wear to such an extent that the ovality and bending stress values approach an unacceptable level, corrective action should be taken to reduce the ovality in order to avoid a real breakdown. The choice of method depends on the type of kiln shell: with or without w ithout live-ring supporting blocks.
Kiln Shell with Live-ring Live-ring Supporting Blocks: Blocks:
For this type of kiln shell, the clearance between supporting blocks and live-ring is reduced by inserting shims between the live-ring pads and the kiln shell.
Figure 3.8 'Reversed Kiln Section'
The mean thickness "t" of such shims is calculated according to the following formula where "v" is the live-ring migration:
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t =
(v − 10 ) 2 ⋅ π
(" t " and " v" in mm )
By inserting shims the mean thickness of which is "t" mm, the live-ring migration will be reduced to 10 mm per per revolution of the kiln. Before deciding on the thickness of the shims to be inserted under the live-ring supporting blocks, the following measuring program should be carried out:
•
Live-ring migration
•
Temperature on the surface of the live-ring
•
Temperature on the kiln shell on the inlet side and on the outlet side of the live-ring.
These measurements are to be taken at least twice every 24 hours for a period of 2 – 3 weeks. Moreover, the condition of the lining and the stability of the coating in the kiln area in question should be evaluated.
Kiln Shell without Live-ring Supportin Supporting g Blocks:
In order to reduce the live-ring migration of this type of kiln shell, one of the following three solutions can be chosen:
•
The heavy kiln section at the live-ring in question can be replaced so that it will have a live-ring migration of approx. 10 10 mm.
•
Mounting of a new live-ring with larger inside and outside diameter permitting supporting blocks blocks to be mounted on the existing kiln section.
•
Mounting of a new, "reversed" kiln section as shown in Figure 3.8 below. The existing live-ring can be used for this kiln section which is supplied with live-ring supporting blocks.
However, the latter solution necessitates very careful lining work in the diameter transition zones of the kiln. It will be necessary to cut the bricks to size between the cylindrical and the conical sections. Therefore, before choosing this solution, it is recommended
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to make sure that the lining installation company is capable of doing this kind of work in a satisfactory manner.
4.8
LIVE-RING - LUBRICATION
In connection with maintenance of the live-rings, choosing the correct lubricating method is of paramount importance in the following two places:
1) The contact faces between live-ring and supporting blocks or kiln shell 2) The contact faces between live-ring and side guides
The following lubricants are suitable for the purpose: Producer
Product
Chesteron
Nickel Anti-Seize Compound
Klüber Lubrication
Grafloscon SY-20
Molub-Alloy
491-C
Never-Seez Comp. Corp
Never-Seez
Paul Products Ltd.
PBC
Reiner Chemische Fabrik
Ceplattyn HT
Lubrication should be carried out by means of a pump to ensure that the lubricant is distributed over the entire contact face. Lubricant should be applied once or twice a month.
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KILN ALIGNMENT
5.1
INTRODUCTION
The purpose of performing a kiln alignment is to establish:
•
Correct mechanical balance of the kiln, kiln, meaning that the axial thrust of the kiln is absorbed both by the supporting rollers and by the thrust rollers so that the supporting rollers absorb from 10 to 50% of the axial thrust and the thrust rollers the remainder remainder during the kiln operation.
•
Optimum load distribution on the kiln supports supports,, meaning that the radial load on each individual supporting roller is within the limits defined at
•
the dimensioning of the kiln. Good mechanical operating condition of condition of the kiln system.
In order to attain the above objectives, the following requirements are necessary:
•
The kiln axis must be adjusted correctly.
•
The adjustment (skewing and inclination) of the supporting rollers must be correct.
•
The roller paths of the supporting rollers and the live-rings must be truly cylindrical.
The adjustments to the supporting rollers which are required to obtain the above mentioned conditions are attained through inspection and measuring activities and supplemented with calculations of the present loads on and stresses in the kiln shell, live-rings, supporting rollers, and supporting roller bearings. These calculations are based on the measurements made and on the weight of the lining and coating ascertained or according to information received from the plant and on the weight of the existing kiln internals.
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5.2
MEASURING OF KILN AXES
The actual kiln axis, i.e. the centre of rotation for the kiln tube proper at each support is determined through 2 sets of measurements viz.:
1) Measuring of the vertical axis 2) Measuring of the horizontal axis
By processing the measurements the position of each kiln centre in relation to a straight line is obtained and will be shown as a deviation from the straight line in the horizontal as well as the vertical plane. It can then be calculated by how much each supporting roller should be moved to bring the kiln axis into the correct position. Most rotary kilns are designed to operate at straight kiln axis. The principle of straight axis can, however, in many cases be modified. By manipulating the vertical component of the kiln axis the load distribution between the supports can be altered. This method may be intentionally practised for instance with the aim to even the load-capacity utilisation of the supports. Please refer to page 5. The measurements can be taken when the kiln is in operation, which is to be preferred as these represents the "live" kiln or when the kiln is stopped and cold. The attached forms will explain both situations.
Re 1. Measuring of vertical axis.
The measurements required to determine the vertical kiln axis are shown on the attached t he following information: forms A forms A - B - B x and C . Each form comprises the
A
Adjustment, wear, and temperature effects at kiln supports as compared with erection measurements.
and B B B and B x
Relative differences in elevation between foundation plates as compared with erection measurements, including any correction resulting from unevenness in foundations.
C
Vertical deviation of kiln axis to a horizontal line.
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The entries and calculations on the individual forms are:
Form A
Line 1 Statement of working temperatures.
Lines 2 to 12 inclusive inclusive Statement of mechanical condition as compared co mpared with erection measurements.
Line 13 Denotes centre displacement between kiln shell and live ring. This value can be specified in three ways as described at head of sheet under Items 1, 2, and 3. Item 1
is used for a known, measured, cold, top clearance. The resultant specification will correspond to a "cold" kiln axis.
Item 2
is used for a known, measured, cold top clearance together with theoretical or normal temperatures supplied by the plant. The resultant specification will correspond to a theoretical "hot" kiln axis.
Item 3
is used when the relative movement between kiln shell and live ring (live ring migration) during operation is known. The resultant specification will correspond to a "hot" kiln axis.
Line 14 Denotes the extension in live-ring radius resulting from working temperatures. This line is only used when Items 2 or 3 have been used in Line 13, in other words when the kiln axis is measured in the hot state. This line is not completed if the live-ring and supporting roller diameters are obtained using circumference measuring equipment.
Lines 15, 16 and 17 17 Here the values on the sheet are added together, and compared with the erection measurements. The resulting difference shows how much the individual kiln supports deviate from a straight line.
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Figure 5.1 Alignment of kiln - Vertical level. Form A.
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Sheet B and B x
Base plates. Elevation differences differences 1. Purpose The purpose of levelling is to make sure that the difference in the elevation of the base plates is as specified on the kiln position drawing.
2. Measuring principle Use a levelling instrument.
First check whether the base plates are transversely horizontal. Sight the instrument on the front two corners the corner base plate, placingThe the alignment levelling staff thebe front the base plate - directly beforeofthe curvature. rod on must theofsame distance from the centre line of the base plate in both measurements. Note any deviation from the horizontal plane in the spaces at the head of the sheet, printing the value opposite the highest corner. Number the corners 2 and 3 in accordance with the numbers of the elevation bolts. Now level the base plates. Place the instrument between two supports, as shown on sheet, and position the levelling staff as shown in the figure above. Local conditions will determine where the instrument can be positioned - whether to the right or to the left of the kiln - but alignment of the two adjacent supports must be performed from the same position.
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Completion of sheet B and B x
Sheet B x
Column 1
POSITION OF INSTRUMENT INSTRUMENT
State here whether the instrument was placed to the right (RH) or left (LH) of the kiln during alignment (viewed from burner's platform).
Columns 2-4
Enter the value measured in one of the lines in Column 4, according to the corner (2 or 3) at which the levelling staff was positioned, the kiln support number (in Roman figures) and the direction of sighting (towards the outlet opposite B and towards the inlet opposite F).
Column 5
0,5 ⋅ DIFF Enter here any difference in elevation between the corners of the base plate. Multiply this difference by 0.5, and write this value opposite corners 2 and 3 in Column 5. When measuring as shown in the example, the value must be shown with a plus sign opposite the top-most corner, and with a minus sign opposite the bottom corner. As can be seen from the example, base plate I is highest (4 mm) on the left-hand side (corner 3), and support II is highest (3 mm) on the right-hand side (corner 2). This half value with its plus or minus sign is entered in Column 5.
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Column 6
ELEVATION ON ON BASE PLATE CENTER LINE. Enter here the value measured (Column 4) after aft er correction with the value in Column 5.
Column 7
ELEVATION DIFFERENCES DIFFERENCES ACCORDING ACCORDING TO POSITION DRAWING. The difference between the elevations on the position drawing is found by means of the H+ measurements which indicate the height of the base plates above the horizontal sighting line.
Column 8
ELEVATION DIFFERENCES DIFFERENCES FOUND AFTER AFTER ERECTION. The actual measured difference in elevation is obtained from the difference between the B and F measurements. BI – F II gives the difference in elevation between base plates I and II. BII – F III gives the difference in elevation between base plates II and III, and so on.
Column 9
DEVIATIONS DEVIATION S FROM POSITION POSITION DRAWING. DRAWING. This deviation is obtained from the difference between Column 8 and Column 7, i.e. h 1 – h, preceded by a plus or minus minus sign as appropriate.
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Figure 5.2 Alignment of kiln - Levelling of base plate Form B x
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Figure 5.3 Correction related to inclination of foundation.
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Figure 5.4 Alignment of kiln - Levelling of base plates Form B
Checking Alignment has been performed correctly if
A=B=C
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where A is the difference between the sum of B measurements and the sum of F measurements (Column 6). B is the difference between the sum of positive and the sum of negative differences in elevation. (Column 8). C is the sum of the differences in elevation on the position drawing, plus the sum of the plus/minus deviations (Column 7 + Column 9). The found values h, h 1 and h1 – h from column 7, 8 and 9 to be transferred to sheet B.
Sheet B The values from sheet B x are converted to vertical deviation in relation to a horizontal line.
Sheet C The sum of the values from Sheets A and B gives the deviation of the kiln axis from a horizontal line. Before plotting a curve, select a zero point on the foundation as a basis. The vertical deviations of the resulting kiln axis to a horizontal line are obtained by scale marking the elevation deviations and length characteristics on the curve.
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Figure 5.5 Alignment of kiln - Vertical level Form C
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Re: 2 Measuring of horizontal horizontal axis
See attached form D.(Figure 5.6) The levelling instrument is placed at foundation no. I and a line of sight is established along the kiln. The line of sight shall be as close as possible to a line parallel to the kiln axis. From the actual line of sight the distance to the kiln centre is found by measuring the distance to the supporting roller as shown on form E (Figure 5.7) and then adding the supporting roller radius + the relevant Cright or Cleft from Form A. Name these distances CI to CV respectively. A line parallel to the kiln axis is then constructed as follows: At foundation V a distance equal to CI is marked from the kiln centre towards the line of sight and a line parallel to the straight line between the centre at foundation I and the centre at foundation V can be drawn. The deviation ofby themeans line of from triangles. the parallel line d II - dIIIat -foundation dIV is calculated each foundation of sight equilateral The deviation V is CVfor – CI. When subtracting dII – V from CII – V respectively the result is equal to the distance from the parallel line to the kiln centre. Name these distances P II – V respectively. To find the deviation in the horizontal plane of each kiln centre from the straight line between foundation I and foundation foundation V simply subtract CI from PII – PIII – PIV and PV.
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Figure 5.6 Alignment of Kiln - Horizontal Alignment Form D
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Figure 5.7 Alignment of kiln - Horizontal Alignment Form E
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5.3
CAUSES FOR MISALIGNMENT
When a new kiln is installed it complies with the following instructions from the sup plier:
-
The kiln axis is correct (i.e. straight in the horizontal plane but not necessarily straight in the vertical plane due to load distribution on the sup porting rollers).
-
Correct inclination of supporting rollers.
-
Correct centre distance between the two t wo rollers on the foundations.
-
Correct axial force between supporting rollers and live-rings.
-
Correct mesh between pinion(s) and girth gear.
During operation of the kiln, critical situations can have necessitated an adjustment to the kiln system and perhaps an uncontrolled movement of the supporting rollers was the result. Uncontrolled movement of the supporting rollers can be the cause for wear on the faces for both the supporting rollers and for the live-rings which eventually will require machining of the faces to restore the true cylindrical form of the rollers and rings. A movement of the supporting rollers or a machining of the rollers and live-rings will of course result in a misalignment of the kiln. Other causes for misalignment can be a settling of a foundation. This can occur when the subsoil or piling were not as strong as anticipated. The foundation could also tilt which would introduce misalignment. Wear on a bearing liner can also cause the inclination of the supporting roller to change.
5.3.1 Manifestation of misalignment
If the misalignment is the cause of incorrect contact between supporting rollers and liverings it can often be seen on the rolling surface. The area of greatest pressure can often be seen as an intense bright coloured area against a contrasting dull colour of the remaining surface.
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Figure 5.8 Support Bearing.
If the skewing of the supporting rollers is too much the rolling faces can show signs of "fish-scaling" or even pitting and other damage due to too high contact pressure between the faces. A lead wire print of the contact will also reveal the misalignment. Misalignment can also be detected in the supporting roller bearings. Normally the sup porting rollers should slightly push the live-rings towards the inlet end of the kiln. The reaction is such that the supporting roller is pressed downwards towards the kiln outlet end with the result that the thrust plate on the supporting roller shaft rests against the collar of the bearing liner as shown in Figure. 5.8. This can be observed through the observation openings in the bearing housing. If the contact between the thrust plate and bearing liner is seen at the "wrong" side it is a sign that the direction of axial pressure between the supporting roller and the live-ri live-ring ng has changed. See Figure 5.8. The change of direction could be caused by adjustment of the supporting rollers or it could be due to operational change.
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Figure 5.9 Contact/No contact Bearing liner & Thrust plate
Even if the direction of pressure is still the same it is extremely important to follow any changes in the temperature on the axial thrust collars. A change may indicate a change in the operating conditions. conditions. If the temperature temperature on a thrust collar is found to be more than 2°C higher than the temperature on the adjacent journal this normally indicates that too large an axial thrust is transferred via the supporting roller bearings at the risk of their running hot. The temperatures of the supporting roller bearings are measured by means of a contact thermometer. Three temperature measurements are made on each supporting roller bearing, two measurements on the journal, approximately 150 mm from the supporting roller and approximately 30 mm from the thrust collar and one measurement on the axial thrust collar.
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Warning Please ensure that the probe is not hit by the moving parts. In cases where the temperature difference becomes more than 2°C corrective action should be taken as soon as possible in order to ensure that temperatures revert quickly to normal. Further, a misalignment can cause the pressure between live-ring and live-ring guides to become too high with great wear wear as a result. Normally the vertical centre-lines of the kiln live-ring and the thrust roller should be on the same vertical plane. At this condition the relative movement is one of pure rolling action. If however, the live-ring vertical centre-line is displaced relative to the thrust roller vertical centre-line, the relative movement will be a combination of sliding and rolling, as the direction of the velocity of the live-ring at the area of contact will not be the same as that of the thrust roller (see Figure 5.8). This will be clearly seen from the wear pattern on the thrust face. If the girth gear has been lowered due to a movement of the nearest supporting rollers there is a risk that the teeth will be damaged when the root clearance is reduced.
5.4
ALIGNMENT TOLERANCES
When a kiln is aligned, either during the initial installation or as a part of a maintenance program the aim is to have the kiln axis in the correct position when the kiln is operating in normal production. In the introduction to this chapter it was mentioned that the required adjustments to the kiln were attained through inspection and measuring activities, (when the kiln is operating) supplemented with various calculations. The adjustments are dependent on the accuracy of the measuring system and the accuracy of the other information used in the various calculations. Using modern measurement techniques which incorporate the use of laser beams, it is possible to keep the average deviation of the actual kiln axis from the correct, theoretical kiln axis within:
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and
± 1,5
mm
± 2,5
mm
in the horizontal and in the vertical plane respectively.
5.5
ALIGNMENT PROCEDURES
Three sets of procedures shall be followed when aligning a kiln:
1) Adjustment of supporting rollers, horizontally
2) Adjustment of supporting rollers, vertically 3) Axial thrust control.
To obtain a good result when aligning a kiln, a prerequisite is that the supporting rollers and live-rings are truly cylindrical. If the faces are not cylindrical the reaction between rollers and rings will be uncontrollable. On the following pages are shown how the information about adjusting a 4 support kiln is received from the specialist performing the inspection and measuring. Below in Figure 5.10 shows the correction at support no. III which is required to bring the kiln centre into the correct alignment.
Example: Kiln Axis Adjustment It has been determined that the kiln centre axis is to be lifted 4 mm and moved 6 mm to the left. This can be achieved by adjusting the supporting rollers. The following exam ple will show two possibilities for achieving this goal. The first method for achieving this is the most practical. The second method is slightly more precise but would proba bly not be used because it is less practical. Figure 5.10 shows the adjustments as vectors below the drawing of the kiln supported by the rollers. Adjustment 1 and 2 gives a total movement of 12 mm in order to both lift and move to the left. Adjustment 3 and 4 give a total movement of 0 mm in order to both move to the left and lift. lift.
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Figure 5.10 Kiln axis adjustment.
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Figure 5.11 will further illustrate how our goal is achieved through these movements.
Figure 5.11 Two options for achieving the desired kiln axis adjustment.
It is the first option which has been illustrated in Figure 5.10. This is because it is theoretically simpler since the left roller does not require any movement (vector sum = 0). The second option requires a 1mm movement for the left roller (vector sum = 1). This is less practical as it is difficult to move the roller precisely 1mm. Both options can be accepted since the error associated with both options is negligible.
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In the same figure is also shown that the inclination of both supporting rollers shall be corrected by inserting a 1,4 mm shim under bearing housing no. 4 and a 0,6 mm shim under bearing housing no. 1.
Re: 1: Adjustment of supporting supporting rollers horizontally
The horizontal adjustment can be performed while the kiln is in normal operation. Normally there will be an adjustment screw at each bearing housing that can be used for displacing the housing, but in many cases a set of hydraulic jacks are preferred as shown in Figure 5.13 to force the bearing housing towards towards the centre of the kiln. If the bearing housing is to be moved outwards there is no need for the jacks. As shown in Figure 5.13 the jacks are placed between the block bolted to the foundation plate and the bearing housing. A clock gauge is placed on the inside of the bearing house when the bolts holding the housing to the foundation are loosened. The movement of the bearing housing can then be observed when the jacks are worked. If two sets of jacks are available then both bearing houses can be moved simultaneously. Otherwise it is necessary to alternate the jacks between the two bearing houses and only move a few millimetres at a time. It is essential that the temperature of the supporting bearings are checked during the operation to prevent overheating. When the supporting roller is being moved the adjustment screw shall follow. When in position the bolts holding the housing shall be tightened and also the adjusting screw.
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Figure 5.12 Correction of Roller Inclination
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In case the supporting roller is to be moved outwards the bolts shall be loosened and then the adjusting screw be slackened. Normally the supporting roller will be moved by the load from the kiln. Again the movement is to be observed using a clock gauge.
Figure 5.13 Hydraulic Jacks
Re 2: Adjustment of supporting rollers rollers vertically
It is very important for kilns with a hydraulic thrust device and semi-rigid supporting rollers that the indications of the supporting rollers are absolutely correct. The centre lines of the supporting rollers must, in principle, be parallel with the kiln axis/live-ring axis, both in the vertical plane and in the plane of inclination. The result will be clean rolling between supporting rollers and live-ring without any axial reaction. In actual practice, a deviation of up to 0,02 % is preferred in the vertical plane. The angles of inclination will be different for two rollers on the same foundation as shown in Figure 5.14.
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Figure 5.14 Vertical Kiln Alignment
The reason that two rollers on the same foundation should have different inclinations is to ensure that the supporting rollers do not force the kiln in a downward direction. The base plate on which the journal bearings stand, is set up with an inclination which corresponds to the theoretical inclination of the live-ring. The live-ring inclination in the vertical plane can be adjusted by inserting a shim between journal bearings and base plate. The inclination of the supporting rollers can be measured using an inclinometer as shown in Figures 3.4 and 3.5 and the results entered into the table as shown in Figure 5.13. By following the procedure as shown in the table the thickness of the shims required to obtain the correct inclination will w ill be determined.
1) Determine the kiln indication K i (%) 2) Determine for each support roller the deviation of inclination indicated on the position drawings of the kiln.
∆i
(%) as
3) Calculate the live-ring inclination at each support, LT
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4) Calculate the theoretical maximum roller inclination RTL for left hand roller and RTR for right hand roller.
RTL = LT – 0,02% for for clockwise rotation (as seen from burner burner platform).
RTL = LT + 0,02% 0,02% for anti-clockwise anti-clockwise rotation
RTR = LT + 0,02% for clockwise rotation
RTR = LT – 0,02% for anti-clockwise rotation
5) Measure for each roller the actual % inclination at the inlet (R i%) and outlet (R o%) ends of the kiln. 6) Calculate for each roller the mean roller inclination (R m%) 7) From the erection drawings, obtain the centre to centre distance, A, for the left and right hand rollers of each pier support. 8) Calculate the deviation of inclination Y1% and Y2% for both left and right hand rollers.
LEFT HAND ROLLER
RIGHT HAND ROLLER
Y1 % = R m - LT
Y1 % = R m - LT
Y2 % = R m - RTL
Y2 % = R m - RTR
If Y1 and Y2 have opposite signs or if one of the values is zero, R m has the correct value and no correction to the inclination is necessary. Otherwise proceed to step 9.
9) Calculate the theoretically required corrections to inclination t1 and t2 for the left and right hand rollers.
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t 1 mm =
A ⋅ Y 1
t 2 mm =
100
(Left hand roller)
A ⋅ Y 2
100
(Right hand roller)
10) Calculate the algebraic mean t p of t1 and t2 for each roller. Obtain the combination of standard shims that have the thickness closest to t p. 11) Insert the shims as follows: If t1 and t2 are positive(+), position the shims on the outlet side of the roller. This shim thickness is designated t po. If t1 and t2 are negative (-), place the shims on the inlet side of the roller. This shim thickness is designated t pi. 12) Calculate ∆R, the theoretically obtained correction of inclination:
∆ R
% = t p ⋅ 100 A
Where ∆R is negative (-) if t1 and t2 are (+) positive and where positive (+) if t1 and t2 are (-) positive.
∆R
is
13) Determine the theoretically obtained inclination, R g%:
R g % = R m + ∆ R
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14) Repeat steps 5 & 6 to obtain the corrected inclination, R me me%.
Re 3: Axial thrust thrust control
General remarks
When a rotary kiln is equipped with a hydraulic thrust device, its supporting rollers must, in principle, be parallel to the kiln axis so that rolling totally without axial reaction takes place between supporting roller and live-ring. In actual practice this is not possible and the supporting rollers should be positioned so that they all have a slight tendency to force the kiln upwards. The axial reaction resulting from this action must - for the different bearing types and sizes as ssupplied upplied from different sources - be within definite maximum/minimum values. For supplied supporting rollers and their respective bearings can the be FLS measured with the equipment as shown on Figure 5.14 the and axial the forces maximum/minimum values are shown on Figure F igure 5.15.
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Figure 5.15 Measuring Equipment
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Figure 5.16 Axial forces - Maximum & minimum values
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The axial force is transferred to the supporting bearings via a thrust ring on the supporting roller shaft and a corresponding thrust collar on the bearing liner. The direction of the axial force can be checked visually by examining in which bearing there is a clearance between the thrust ring and the thrust collar of the bearing liner. Measurement of axial forces and adjustment of supporting s upporting rollers should only be carried out during normal kiln operation.
Bearings model 1958 1958
With this kind of support there must, when the bearing rollers stand correctly i.e. when they have a slight tendency to force the kiln upwards towards the inlet, be a clearance between thrust plate and thrust collar in all all bearings situated on the kiln's discharge side. Prior to measurements and adjustments, note the supporting rollers which force the kiln upwards and the ones that force the kiln downwards. Reverse the pressure direction of the rollers which force the kiln downwards, and perform the measurement. It should be done according to a definite pattern so that the thrust rollers are not overloaded at any time. Then read the hydraulic pressure on the pressure gauges of the thrust rollers before and after every adjustment. The measurement on the single bearing is performed by following this procedure: Place the measuring equipment on the hinges of the bearing housings. Start the measurement by pumping up the cylinder to the maximum pressure applying to the bearing size in question. If the supporting roller has been adjusted correctly, the pressure in the cylinder will within approximately 10 minutes adjust itself to a value which lies between the maximum and minimum pressures, indicated on Figure 5.15. At the same time, a permanent clearance will have been created at the thrust collars of both the bearings. During one kiln revolution the pressure may vary somewhat because of live-ring eccentricity, etc., and it will therefore be necessary to reckon with a mean value of the pressure readings. If the pumped-up pressure does not drop below the maximum pressure, or if it drops below the minimum, the supporting roller position must be changed according to the instructions on Figures 5.16 and 5.17.
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Figure 5.17 Bearing adjustment, 1958 type-clockwise
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Figure 5.18 Bearing adjustment 1958 type-counter clockwise
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Bearings model 1974 1974
The measuring equipment must also be placed on the bearings situated on the kiln discharge side. With these bearings, on which the thrust plate of the supporting rollers are located between hub and bearing liner, there must be a clearance between thrust plate and thrust collar of bearing liner in the bearings situated on the kiln inlet side . The remaining procedure is as described previously. Directions for corrections are given on Figures F igures 5.17 and 5.18.
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Figure 5.19 Bearing adjustment 1974 type-clockwise
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Figure 5.20 Bearing adjustment 1974 type-counter clockwise
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Control of adjustment
When the kiln alignment has been performed in accordance with the pressurised procedure the distribution between the thrust roller(s) and the supporting rollers of the axial load from the kiln should be as mentioned in the distribution: 10 to 50% on the supporting rollers and the remainder on the thrust roller(s). During the operation of the kiln, the pressure in the hydraulic system for the thrust rollers can be followed and any change in the pressure will indicate a change in the mechanical balance. The contact between supporting rollers and live-rings can be controlled by means of lead wire tests as described in the following:
Figure 5.21 Lead wire test
Lead wire tests are carried out by inserting a piece of ∅ 2 – 3 mm lead wire wi re between the supporting roller and the live-ring while the kiln is rotating. The lead wire is then rolled flat. The shape of the rolled lead wire will give an impression of the pressure conditions between live-ring and supporting roller on the generatrix along which rolling takes place. It is very difficult to assess a single lead wire test since many different factors will have contributed towards the rolled shape of the lead wire.
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The test result can be assessed most easily when two test wires are compared, e.g. rolled before and after a correction of the position of a supporting bearing. The difference between the two test wires will then give a reliable picture of the effect resulting from the correction. Systematic and regular tests can also, when compared to each other and to other regular measurements, give a reliable picture of any changes in the kiln alignment.
Supervision after adjustment
During the first period after adjustment of the supporting rollers, supporting rollers and bearings must be observed closely because of any unforeseen effects of the adjustment. Particularly the bearing temperature must be checked and also the surface of supporting rollers and live-rings should be watched closely until it is ensured that the stable operation of all parts has been restored. It can be difficult to determine, without measuring equipment, how the axial load is distributed on the supporting rollers. A very high load will, normally, manifest itself quickly by the upper bearing of the supporting roller in question becoming hot, and in such a case immediate action must be taken by changing the position of the supporting roller. First the direction of thrust of the supporting roller must be turned until there is a clearance between thrust ring and bearing liner in the upper bearing, and the bearing should then be adjusted back until the clearance occurs again in the lower bearing. In this way it can be ensured that the skewing of the bearing is not larger than necessary, and the bearing temperature should return return to normal.
Please note:
There can arise unfortunate consequences from repeatedly pulling the supporting roller bearings away from the kiln centre-line centre-line thus lowering the kiln centre at this suppo support rt relative to the kiln axis. It will be an advantage if one of the adjustments can be made by a bearing being forced towards the kiln axis.
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Figure 5.22 Supporting roller skewing
If during the operation of the kiln it appears that minor adjustments to supporting rollers are required in the horizontal plane it is then a question of deciding which of the two bearings of the supporting roller has to be moved. Whether it is the upper or the lower bearing will depend on the direction of of kiln rotation. Figure 5.21 shows, greatly distorted, how the supporting rollers have been turned away from parallel; skewed in order to ensure that they will not affect the kiln in the downward direction. Of course, the skewing cannot be seen with the naked eye, but if it is imagined that the skewing of the supporting rollers is established by the rollers being turned on their centres in the plane of inclination, as shown in the figure, it can be seen that correct skewing means that during clockwise kiln rotation (as viewed from the burner's platform), the roller must also be turned (to intersect) clockwise, and when the kiln rotates anticlockwise, the roller must also intersect anti-clockwise. If this is kept in mind, it can always be determined which bearing to move in which direction in order to make the roller pull the kiln upwards. If, therefore, a supporting roller has a clearance in the upper bearing between thrust ring and bearing liner (but not in the lower bearing) as shown in Figure 5.9, the roller does not intersect correctly, as shown in Figure 5.21, but is reversed and it will therefore be necessary to pull the lower bearing outwards (or press the upper bearing inwards) in order to impart the correct skewing to the roller.
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Figure 5.23 Roller does not intersect correctly
5.6
SAFETY
During alignment of the kiln it is necessary to work around the moving machinery. Therefore only personnel who are aware of the hazards of working around the kiln should be allowed to participate in the various alignment jobs. It is therefore of the utmost importance that the personnel involved in the alignment show extreme caution in order not to come in contact with the moving machinery. The personnel shall be issued with the relevant safety equipment including properly fitting work clothes and helmets so that all loose clothing is avoided. All tools required for the jobs shall be in proper working working order to ensure a good result. When measuring the temperature on the supporting roller journal and on the thrust plate care must be shown to avoid the temperature probe being caught by the rotating oil cups.
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KILN SHELL TEMPERATURE MONITORING (MANUAL) 6. INTRODUCTION The physical condition of the kiln shell itself, particularly the preservation of its circular shape while rotating, is one of the most important maintenance parameters when it comes to keeping a high run factor of the kiln system. It is common knowledge that the deformations occurring in the kiln shell while rotating are most significant under and at the live-rings. The deformations, which are transferred to and through the lining, have an extremely large effect on the stability of the coating and on the durability of the refractoryhigh lining. In addition this,and these substantial deformations result in correspondingly stresses in kilntoshell welds, and these stresses can contribute to crack formation. Temperature measuring of the kiln shell is one of the activities which are undertaken in order to keep control of the temperature condition inside the kiln and to detect if any abnormality is under development, that could lead to a deformation of the kiln shell, for instance because of a "hot spot". The kiln shell temperature is normally measured by personnel from the production de partment, between the kiln supports to determine the heat radiation and to detect if a "hot spot" is developing. The temperatures in the vicinity of the live-rings are critical to the mechanical condition of the live-rings and therefore the close observation of these temperatures should be the responsibility of the maintenance department.
6.1
Instruments
A radiation pyrometer can be used for measuring the kiln shell temperature as shown in Figure 6.1 - the probe is used for measuring the live-ring, supporting roller and supporting roller bearing temperature. The distance from the kiln shell to the pyrometer can be from 0.5 m to 1 m but the manufacturers recommendations must be consulted when a pyrometer is taken into use.
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Figure 6.1. Radiation Pyrometer
6.2
Measuring points
The measuring points at each live-ring are shown in Figure 6.2
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Figure 6.2 Measuring points.
The temperatures ti and to represent the temperatures measured at the inlet side of the live-ring and at the outlet side of the live-ring respectively. The temperatures ti and to are measured close to the live-ring pads for the live-ring or, in the case of a support where there are no live-ring pads, close to the side guides and the temperatures are measured on the whole circumference.
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6.3
Recording of temperature
The minimum and the maximum kiln shell temperature are registered for each of the measuring points and can be entered into a table as shown in Figure 3.45. Below is shown a set of temperature readings from an actual kiln:
Temperatures of Kiln Shell
Inlet Side
Outlet Side
Max.
Min.
Max.
Min.
Live-ring I
~ 35
~ 35
~ 35
~ 35
Live-ring II
255
248
290
279
Live-ring III
379
247
312
245
Live-ring IV
261
230
274
241
T (°C)
Figure 6.3 Temperatures at kiln shell
As can be seen from the table, the largest temperature difference was found at live-ring III where the following temperatures (°C) were measured:
Maximum Temperature
Minimum Temperature
Temperature Difference
379
247
132
Figure 6.4 Minimum /Maximum Temperatures
The differences in temperature measured indicate an uneven coating formation in the kiln at support III which could lead to deformation of the kiln shell a "thermal crank"
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6.4
Evaluation of results
The above mentioned thermal crank could result in a situation where the live-ring, during the rotation of the kiln, first lifts from one ssupporting upporting roller and then from the other. This situation should be immediately rectified as each of the two supporting rollers and their bearings would be grossly overloaded and may result in a break-down. Experience has shown that as long as the temperature difference between maximum and minimum at the same measuring point is less than 500°C there will not be any cause for alarm. Another point where it is necessary to be cautious when evaluating the recorded tem peratures is when evaluating the ti and the to temperatures. The perfect condition is when ti = to where the heat expansion of the kiln shell is the same on both sides of the live-ring. If there is a temperature difference the diameter of the kiln on each side of the live-ring will be different, i.e. the kiln is in fact conical under the ring, a situation which could lead to uneven wear of the live-ring pads or the kiln shell. Should the temperature of the kiln shell rise over 400°C it is essential that action is taken immediately to lower the temperature. The strength of the steel will be reduced when the temperature is above 400°C which could result in permanent damage to the shell. If the temperature evaluation shows that the present temperature range can lead to an unacceptable situation, it is recommended that the production department take the ap propriate action so that the conditions conditions inside the kiln are changed. The reason for this could be that the coating should be re-built to create a uniform tem perature at the measuring points. Or perhaps a dam ring has been built half way over the live-ring. If the temperatures are incorrect and the stable mechanical function of the kiln cannot be ensured, it is the production department's responsibility to change the operational conditions.
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6.5
Safety
When kilnout shell aretomeasured it to is necessary forkiln. the personnel thatthe carry thetemperatures measurements be in closemanually proximity the rotating It is therefore essential that the personnel performing the measurements are extremely careful not to come in contact with the rotating parts and only personnel with the appro priate authority shall be allowed to perform perform the temperature measurem measurements. ents.
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KILN SYSTEM LUBRICATION
7.1
INTRODUCTION
To reduce friction and wear in a kiln system it is necessary to follow the supplier's manuals in respect of points to be lubricated, the frequency of lubrication, and the quality and quantity of the lubricants. The differences in the design and operational principles of the various kiln systems also imply differences in lubrication techniques, -points etc. The following description will mainly deal with lubrication of the FLS kiln system, but similar equipment from other suppliers will probably not differ greatly in terms of methodology of lubrication. Irrespective of the supplier, however, one item is common for all when it comes to handling of the lubricants, viz.:are as contaminated any impurity oil in aorlubricant CLEANLINESS as CLEANLINESS damage parts which lubricated by the grease. will very soon
In the kiln system the points to be lubricated will typically be:
1. Roller surface on live-ring and supporting rollers. 2. Contact surface of live-ring and live-ring pads on kiln shell. 3. Special conditions during start-up. 4. Supporting roller bearings. 5. Girth gear (drive station). 6. Plummer blocks at drive station. 7. Thrust roller. 8. Main gearbox. 9. Seal at inlet. 10. Seal at outlet.
Each of these items will be described in turn below in terms of routines, points of special attention etc. The types of lubricants mentioned at the various lubrication points are, for the sake of identification, products from Mobil.
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This does not mean, however, that only products from Mobil can be used for kiln lubrication. But an alternative product must always have the same specific properties required for the purpose. It is most likely, though, that the supplier of the machinery will recommend more products than one, i.e. products from various manufacturers of lubricants. It is therefore recommended to adhere adhere to the ad advice vice given by the suppliers of the machinery.
7.2
LIVE-RING /SUPPORTING ROLLERS
Graphite is to be used for lubrication of the path between between live-ring and supporting roller. Lubrication is effected by a graphite block (99,5% graphite) placed in a frame (see Figure 7.1). The graphite rests (by its own weight) on the path of one supporting roller. Graphite is transferred to the roller path and lubricates it. From the supporting roller the graphite is transferred to the live-ring live-ring and to the other supporting roller. roller. Only graphite must be used in order that a bright and half-dry surface is passed on to supporting rollers and live-ring. (Note the special conditions during kiln start-up. See Section 4.7.) If, in the course of time, graphite flakes flakes develop on live-ring and supporting rollers, these flakes can be wiped off easily with an oil-soaked cloth. The oil must be wiped off again when the flakes have been removed. When about one half of the graphite block has been worn away, the reduced heaviness can be compensated by placing weight, e.g. a piece of iron, on the graphite block. It must be ensured, however, that the shape and position of the weight makes it iimpossible mpossible for it to leave the holder, holder, so that the block cannot g get et stuck between live-ring and sup porting roller or between supporting supporting roller and graphite h holder. older.
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Figure 7.1 Application of lubrication with graphite block.
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7.3
LIVE-RING /LIVE-RING PADS OR KILN TUBE
Because of the live-ring migration, lubrication must be done between the inner inner surface of the live-ring and the live-ring live-ring pads or the kiln kiln tube, and between the flanks of the live-ring and the retainer rings. Careful, thorough lubrication must take place whenever the kiln has been stopped for a prolonged period. During operation the lubrication frequency depends o on n the characteristics of the lubricant (see the supplier's instructions) and the temperature of the livering. According to experience, the lubricant consumption is:
-
For hot live-rings: approx. 50 kg/year per live-ring.
-
For cold supports: approx. 20 kg/year per live-ring.
The following lubricants are recommended for this purpose:
Klüber Lubrication
Grafloscon Suspension-02
Reiner Chemie
Ceplattyn HT
Molub-Alloy
491-C
Chesterton
Nickel Anti-Seize Compound
Achesons Colloids Company
Oildag
Never-Seez Compound Corp. Corp.
Never-Seez
Paul Products Ltd.
PBC
Lubrication should be carried out by means of a pump to ensure that the lubricant is distributed over the entire contact face. Lubricant should be applied once or twice a month. Never-Seez, which is supplied as a paste, can be mixed with oil to improve its flow between live-ring live-ring and live-ring pads/side guides/kiln guides/kiln shell. The mixture mixture ratio is to be approx. 40% Never-Seez and approx. 60% oil, and the oil used must have a high flash point.
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7.4
SPECIAL CONDITIONS DURING KILN START-UP
During the initial or duringrollers start-up after major repair, have changed the start-up positionofofthe thekiln supporting considerably), there is(which a risk may that such a high axial load may occur on a bearing liner collar that overheating of the bearing can develop before it is possible to adjust the bearing to the correct position. For kiln starts of this kind all roller paths must be covered with oil (to be dosed with an oil can), and the oil layer be maintained during the entire adjustment period. It is thus ensured that the axial force is reduced because of the lower friction between supporting rollers and live-ring . For the same reason, there will be a lower effect on the thrust ring of the supporting roller shaft against the collar of the bearing bearing liner, and consequently less risk of overheating. The supporting rollers which deviate most from the correct position can be identified quickly. Bevel edges will appear on the roller path, and small pulses in the bearing can be sensed with the hand placed on the cooling water discharge connection. Lead wire tests can also contribute to the identification of the wrongly adjusted supporting rollers. In this way there will be time enough to make the necessary correction of the roller position without danger of over-heating of a bearing caused by too high axial pressure. When the start-up procedure has been completed the oil layer must be removed from the rollers and the live-rings.
7.5
SUPPORTING ROLLER BEARINGS •
The bearings for the supporting rollers of the rotary kiln are selfadjusting sleeve bearings. The ball race of the bearings ensures that the journal will always be fully supported even if one bearing is displaced relative to the other, either vertically or horizontally.
•
The lubrication principle is hydrodynamic, which means that a supporting oil film is built up between liner and journal during rotation.
•
Because of the low rotary speed it is therefore very important that the difference in diameters between journal and liner should be exactly so large as to give the wedge-effect which is necessary to have the supporting oil film built up under the journal.
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•
In theory, there is a live contact between the roller shaft and the bearing liner. At sufficient rotational speed of the shaft, the oil will be sucked into the wedge-shaped clearance between shaft and liner, so that the shaft is supported by a thin oilbe film. speed and 7.2). temperature this oil film thickness will 0,01Depending – 0,02 mm.on(See Figure
•
So the function of the supporting bearing is highly dependent on the oil viscosity, and it must therefore be emphasised emphasised again that it is very im portant to observe the lubricating instructions instructions closely.
Lubrication of the bearing is effected by the oil cups (01) screwed to the locking ring (02) of the supporting roller journal, lifting the oil from the bottom of the bearing housing to an oil groove (03) which distributes the oil over the supporting roller journal, (see Figure 7.2). In order to prevent oil spill, an oil scraper (04) is mounted as shown on Figure 7.3 to keep the lubricating oil away from the felt seal.
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Figure 7.2 Supporting Roller Bearings
The bearing is cooled by means of continuous water cooling. Cooling is necessary in order to prevent the lubricating oil becoming too warm so that its lubricity is impaired. The cooling water is supplied to the supporting roller bearings through a common sup ply line with branch lines alongside each foundation.
Oil filling: Do not fill more oil into the bearing than indicated by the mark on the oil level gauge, since too large quantities of oil can result in oil spill. The oil must be replaced if metal
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particles or other impurities occur in the oil as well as after any overheating of the bearing.
Oil quality: The selection of oil type depends on the ambient temperature. During kiln start and normal operation at ambient temperatures which are lower than +5°C , use oil such as "Mobilgear 634" or "Mobilgear 636". The best solution is to use synthetic oils which have a low pour point and which can be mixed with mineral oil.
Example: Mobil Oil SHC-639 or 634, both of which have a pour point of –40°C.
During kiln start and normal operation at ambient temperatures higher than +5°C use use oil such as "Mobilgear 636" or "Mobilgear SHC 639". Never mix synthetic and mineral oils, unles unlesss accepted by the oil supplier supplier..
NOTE:
After the initial start-up of the kiln, change the oil after the run-in period, i.e. after 2-3 months. Henceforth the oil must be changed at intervals of approx. 12 months.
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7.6
GIRTH GEAR LUBRICATION
In this section two types of girth gear lubrication will be described:
1. Lubrication by means of lubricating wheel 2. Spray lubrication
7.6.1 Lubrication by means of lubricating wheel
(Refer to Figure 7.3).
The gearing is a double wheel gearing, which consists of a gear rim (01) and a drive (02), intermediate wheel (03) and pinion (04). The kiln drive meshes with the gear rim and with a lubricating wheel (05) , which dips into the lubricating oil in the oil sump (06) of the base plate. Hence the lubricating oil is transferred to the kiln drive which again transfers it to the gear rim. Excessive oil is scraped away from the sides of the gear rim by means of weighted rub ber scrapers (07). (See Figure F igure 7.3). It is important that these scrapers s crapers are kept in good operating condition in order to avoid oil spill s pill on the kiln tube. Oil quality: Gear quality: Gear unit lubricants for industrial open gear units with dip lubrication. Kiln and mill girth gears. May contain MoS2 or graphite, as for example: "Mobiltac MM". Oil quantity: quantity: The gearing is lubricated, as mentioned, by the lubricating wheel (05) transmitting oil from the oil sump to the drive and from there to the gear rims. In order to avoid oil spills, the oil level should not be too high in the sump. The lower teeth of the lubricating wheel should only be immersed half-way into the oil, and refilling should only be done step-by-step and very carefully. The size of the refill can be determined by filling in for instance one litre of o oil il at the lowest permissible oil level. The time lapse until the oil level has again dropped to the low level will then form the basis of a calculation of how much much oil has to be filled in totally. Pinion (04) and intermediate wheel (03). The oil level in the oil sump must be so high that the teeth of the intermediate wheel are submerged approximately half-way into the oil. The quantity must be refilled when required. The teeth of the intermediate wheel are submerged in a separate oil sump in the base plate and keep the pinion lubricated. lubricated.
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The oil quality for the intermediate wheel set is the same as for the pinion and the girth gear. Replacement: Oil sump (06). Drain the lubricating oil through drain cocks (07). Clean Replacement: Oil the oil sump.
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Figure 7.3 Lubrication by lubricating wheel
Supply clean oil to the two separate chambers in the base plate, until the lower teeth of the lubricating wheel and the intermediate wheel are covered with oil.
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7.6.2 Spray Lubrication
General Spray lubrication of the gearing involves that a lubricant is atomised by pneumatic pressure and sprayed towards the gearing so that the lubricant covers the pressure tooth flanks of the pinion with an even and uniform layer. From the pinion the lubricant is distributed to the gear rim. The need for lubrication varies depending on the operating conditions of the gearing. Consequently, the design of the spray system incorporates automatic adjustment of the lubrication rate in order to meet the specific requirements of the actual mode of operation. The spray system proper is available in various makes, though the working principles are basically identical. The same also applies to the supervision and control systems. For the special features of the individual spray system, reference is made to the separate instruction manual from the manufacturer. Structure The spray equipment is built up as two independent systems, A and B. Each system incorporates:
•
One 200 or 180 litre barrel with barrel pump
•
Lubricant filters
•
Dosing equipment
• •
1 or several spray nozzles an electrical control system, and
•
pneumatic equipment.
The barrels are placed on the hollow kiln foundation together with two empty barrels for collection of the used lubricant, which drops through the tubes fitted at the bottom of the base plate and on the gear rim guard. The used lubricant cannot lubricant cannot be be re-used. The dosing equipment is set electrically for the desired dosage. The dosage of lubricant can be varied from 1 – 8 cm3/cm × h, i.e. cm3 lubricant per cm gear rim width per hour.
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7.6.3 Operating principle
The two systems A and B both operate on the principle that the pump feeds the lubricant from the barrel through the filter to the dosing equipment from where it passes to the nozzles. Here it is sprayed towards the pressure tooth flanks of the pinion. The two systems work together so that they are alternately cut in for lubrication of the pinion, but always so that system A - because of wear rate and safety factors - com pletes one working cycle 8 times for for each working cycle completed by system B. During one working cycle a specific amount of lubricant is sprayed corresponding to a 3 3 definite number of cm lubricant per cm tooth width per hour (cm /cm × h). The duration of a working cycle is arranged so that ( during normal operation ) it corresponds to several revolutions of the pinion, which in turn means that all the pressure tooth flanks of the pinion are covered by an even layer of lubricant. In case one of the systems should fail, an automatic switch-over is effected via the electrical control panel, so that the other system takes over the function of both systems while, at the same time, an alarm is triggered.
7.6.4 Lubricants
The following lubricants for the spray lubrication system can be recommended:
Make
Manual lubrication
Lubrication during run-in
Operation
Grafloscon A-SG
Grafloscon B-SG-00
Grafloscon C-SG-O
Ceplattyn 300
Ceplattyn Einlauf
Ceplattyn KG-10
Klüber Lubrication (180 l barrels) Reiner Chemische Fabrik (200 l barrels) The lubricants Ceplattyn 300 and Grafloscon A-SG for manual lubrication must never be used in the spray lubrication system.
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7.6.5 Operation
Prior to barring in connection with erection, the pinion and gear rim must be manually lubricate by applying the lubricant to the teeth by means of a brush. First, clean the pinion teeth carefully so that they are thoroughly clean, (this applies to tooth flanks as well as tooth tip and tooth base). Use a suitable solvent, e.g. Trichloroethylene. Detergents leaving a greasy surface are not fit for use. ((Remember Remember the safety precautions required when using solvents) solvents) Use a stiff brush for application of lubricants to the tooth flanks of pinion and gear rim. As previously mentioned, the lubricant grade must be Ceplattyn 300 or Grafloscon ASG. By using a stiff brush air bubbles in the lubricating film are avoided and besides, a brush is the most effective tool for this operation. If holes in the lubricating film are ascertained after the pinion has been turned a few revolutions, corrective action is required. It is recommended that a lubricant is also applied to the non-loaded tooth flanks as well as tooth tip and tooth base due to the back-run of kiln. In case of switch to an alternative lubricant at some future stage of time, the lubricant applied can be left remaining on pinion and gear rim. It is essential that the pressure tooth flanks are always covered by a lubricant when the kiln is barred. Regarding the amount of lubricant for manual lubrication, the instructions given by the manufacturer of the lubricant must be complied with. w ith.
Lubrication during during run-in The purpose of the run-in of large gearings is to attain the full load by establishing full support between the teeth teet h of the pinion thechanged. gear rim within m minimum inimum time, and without the geometrical shape of the latterand being The use of a run-in lubricant results in a faster smoothing of the surface roughness of the tooth flanks combined with the fact that the lubrication rate is sufficient to avoid a strain which is too heavy on the teeth. During run-in only lubrication system A should be provided with the special run-in lu bricant, whereas system B is charged with a lubricant lubricant designed for normal oper operation. ation. It is of no importance whether both systems are operational simultaneously, since the two lubricants are compatible. During run-in the tooth support must be inspected on a day-to-day basis. The amount of lubricant is adjusted to 8 cm3/cm × h.
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After the run-in procedure has reached the stage where the contact on the tooth flanks is approx. 80%, the barrel containing run-in lubricant in system A is replaced by a barrel containing a lubricant for operational applications.
Lubrication during during operation When the run-in phase has been satisfactorily completed, and after the run-in lubricant has been replaced by the lubricant for operational applications, the gearing must run for 24 hours with 8 cm3/cm × h. If the tooth support is unchanged afterwards, it is possible to reduce the amount of lu bricant gradually in compliance with the directions given by the manufacturer of the lubricant. When the kiln operation has stabilised, the lubrication system operates automatically and the system is capable of operating unsupervised over a long period of time. ti me. The two separate, independent systems offer a high degree of reliability. When the barrel in system A is empty, it must be replaced by the almost filled barrel in system B, and a new barrel is placed here. In this way it is ensured that fresh lubricants are always available in both barrels. barrels. Besides, the stand-by system ( system B) will be able to handle operations for a long period of time when barrel A is empty.
Lubrication during during kiln start-up and and barring During heating or drying out of a rotary kiln the gearing will be subject to strong variations in terms of load rates. In the event of uneven heating of the kiln shell (one side becoming hotter than the other), the shell may deform so that the load on the pinion is not evenly distributed across the entire tooth width, but changes from side to side dependent on the axial wob bling of the gear rim. To ensure an adequate lubrication rate during these extreme conditions, the lubrication system is set for an automatic supply of uninterrupted spraying of lubricant for the first 30 minutes following every start-up. During this period an amount of lubricant corresponding to 16 cm3/cm × h is distributed by continuous spraying. After the 30 minutes have elapsed, the system automatically returns to normal operation with the pre-determined amount of lubricant. During heating and drying-out, the kiln is barred gradually, e.g. in steps of 90° at a time. The lubrication system's response to the barring start-up is similar to that of kiln startup, which means that the pinion is receiving additional lubrication during the process.
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Performance test Check the spray image once a week. The design of the gearing guard is such that it is possible to insert a control plate between spray nozzles and pinion to capture the lubricant discharged. The plate is placed in two guide-ways on the guard, with a piece of paper glued on at either end in order that the t he spray image can be recorded. Proceed as described in the suppliers manual. Then evaluate the spray image. The spray system design entails that the amount of lu bricant supplied to the corners of the teeth exceeds the amount ssupplied upplied to the central half of teeth. Figure 7.4 shows an example of a stationary spray image.
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Figure 7.4 Stationary Spray Image
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7.7
PLUMMER BLOCKS AT DRIVE STATION
The plummer blocks for the drive station shall be charged with oil, for instance "Mo bilgear 629" to the mark on the oil level glass, see Figure 7.5. The oil is lifted from the reservoir in the housing by the lifters (01) and distributed over the journal. It is recommended to replace the oil once a year.
Figure 7.5 Plummer Block
Refilling when required.
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7.8
THRUST ROLLER
The path of the thrust roller is lubricated by a graphite block (01) which is pressed against the path by a counterweight, see Figure 7.6.
Figure 7.6 Thrust Roller
Roller bearings The bearings run in an oil bath. Check the oil level. It must reach up to the mid-way mark on the glass (02). Oil quality: For quality: For example: Mobil Extra Hecla or Mobil 600 W Super Cylinder Oils. It is recommended to replace the oil once annually.
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Bearing bushes for slide shafts
Supply grease through the lubricating nipples (03) (Figure 7.6). There are four nipples for each thrust roller. Grease quality: Universal quality: Universal grease 3 Grease quantity/nipple: quantity/nipple: 10 cm , once a month.
Switch box (See Figure 7.7).
Figure 7.7 Switch Box
This equipment monitors the up and downwards movement of the kiln. Supply grease through lubricating nipples (01). Grease quality: quality: Universal grease 3
Grease quantity/nipple: quantity/nipple: 2 cm , 4 times a year.
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Pressure roller (02) (Figure 7.7)
Supply grease through lubricating nipple (03). Grease quality: quality: Universal grease Grease quantity/nipple: quantity/nipple: 2 cm3, 4 times a year.
7.9
MAIN GEARBOX
Lubrication systems Normally the gear units are lubricated by ordinary dip lubrication. This means that the gear wheels of the gear unit unit is submersed in the oil bath and distribute the oil to tooth meshing and bearings. On large-size gear units oil traps are fitted at the bearings to collect the oil from the gear wheels for onward transmission to the bearings. Check the oil level at least once a week. At standstill the oil level must always reach to the middle of the sight glass or to the marks on the dip stick. Certain gear units incorporate a circulation pump. The installation is designed in such a way that the lubrication is effective for f or both directions of revolution. The pump motor is connected so that it starts when either main or barring motor is cut in. This means that the circulation lubrication will be operational both during normal operation and when barring is effected.
Lubricants The same oil grade must be used everywhere in the gear unit, for instance "Mobilgear 630".
Gear unit, replacement of lubricating oil The initial oil charge of gear unit must be changed after the run-in period. During normal operation the oil is changed at longer intervals depending on the oil grade and the operating temperature.
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During normal operating and temperature conditions the oil grades specified can be used in the gear unit for the number of operating hours stated in the table below.
Operating temperature: temperature: 60 – 65°C Mode of operation
Continuous operation without stop
Continuous operation with moderate number of stops
12h/day
24h/day
12h/day
24h/day
Oil Grade:
2000
1500
1200
1000
Mobilgear 630
to
to
to
to
2500
2000
1600
1400
Intermittent operation
1 year
For gear units with a substantial oil charge, it would be advisable to extract regular oil samples from the gear unit and to have the oil tested at a laboratory in order to determine the time of replacement. Draining of oil is effected through a hole in the bottom of the gearbox.
EXTREME CAUTION IS REQUIRED IN CONNECTION WITH FIRE AND LIGHTS. THE OIL FUMES PRESENT A MAJOR FIRE HAZARD. Remember to drain off the old oil from oil cooler and the external pipe connections and to refill these parts when the fresh oil is charged. Check whether it will be necessary to clean the gearbox of ssediments ediments from the old oil. If required, use plastic scrapers for this operation, never use cloths or cotton waste.
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7.10 SEAL AT INLET With the many designs for inlet seals it will not be possible to describe all the relevant lubrication systems. Only one seal design, a pneumatically operated one, will be described here.
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Figure 7.8 Pneumatic Seal at Inlet
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Wearing rings (01) and (02) The contact faces between wear rings (01) and (02) are lubricated continuously from an automatic centralised lubricator. The grease reservoir of the lubricator must be refilled as required, normally every fourth day. Grease quality: quality: Universal grease.
Suspension parts (07) Supply grease through the lubrication nipples. Grease quality: quality: Universal grease. 3 Grease quantity/nipple: quantity/nipple: 10 cm , 4 times a year.
7.11 SEAL AT OUTLET With the many designs for outlet seals it will not be possible to describe all the relevant lubrication systems. Only one seal design, a pneumatically operated one, will be described here.
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Figure 7.9 Seal at Outlet
Spacer roller (01) Grease to be charged through the grease nipple until a grease bead is formed around the shaft as a dust seal. The lubrication must never be overdone, and the runway and rollers must not come into contact with the grease. Grease quality: quality: Universal grease. To be greased once a week. w eek.
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Travel wheels (02) Dismantle the travel wheels, clean the bearings and fill them halfway with grease. Grease quality: quality: Universal grease. Grease to be replaced once a year.
7.12 SAFETY PRECAUTIONS
Warnings Against Oil and Oil Fumes When handling oil, precautions shall be taken to avoid that the human skin is soaked in the oil as this will lead to rashes and other injuries to the skin. Also oil fumes are dangerous to the health if inhaled. Particularly when a gearbox is opened for inspection immediately after it has been stopped care has to be taken not to inhale the oil fumes. Ample ventilation shall be provided when operating in closed rooms when the oil is still warm and the air is filled with oil fumes. Another hazard with oil fumes is that they are inflammable. Therefore:
WARNING - DANGER!! Oil fumes are highly flammable - there is a danger of explosion. When working on a gear unit with open inspection covers or when draining and charging oil:-
- NO NAKED LIGHTS - NO OPEN FLAMES - NO SMOKING
Check all electrical tools/hand-lamps. These can also ignite oil fumes if faulty.
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Warning Against Cleansing Agents In order to avoid health hazards, unsafe use of chemical cleansing agents and solvents is strongly warned against. They may cause serious s erious poisoning and injuries. When removing oil, grease and tectyle rust inhibitors, ample ventilation is required. The following products are recommended as they are the least dangerous:
1. When cleaning the gear flanges in connection with recording of tooth prints, use a dry cloth only. 2. Chesterton Industrial & Marine solvent, water emulsifying cleaning fluid for light to medium-heavy oil and grease cleaning. Minimum ventilation requirements: 100 m3 air per litre solvent. 3. Solar oil, for removing oil, grease and tectyle rust inhibitors. 4. White spirit for removing tectyle rust inhibitors, etc. 3
Minimum ventilation requirements: 800 m air per litre solvent.
Avoid other types of solvents if possible. Beware of the danger of fire, ignition and explosion as well as the risk of injury to the skin. Always observe the precautions stated on the packing or data sheet of the product in question. vapours rs from the well known cleansing cleansing agent Trichloroethylene are WARNING: The vapou WARNING: extremely poisonous and shall be avoided.
Course Name :
Mechanical Maintenance of Kiln Systems
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KILN COMPONENT FAILURES
8.1
KILN SHELL
This section will deal with two topics:
1) Preventive maintenance for welded seams on a rotary kiln 2) Replacing of a plate section for a kiln tube
In the section on preventive maintenance for welded seams s eams on a rotary kiln. The following items will be described:
Introduction
Critical welded seams in terms of stress
Intervals for examination
Methods for examination
Inspection and repair
Circular seams
Welded seams of the planetary cooler Manholes
Welds at thrust rings of tyres
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8.1.1
Introduction
The rotary kiln is a dynamically loaded construction, which consists of welded plate materials of varying thickness. Due to the size of kiln and its method of operation - rotating on a few supports - the many welds of kiln kiln are subject to immense and varying varying stresses. These stress factors have been taken into account when calculating the welded seams of the rotary kiln. Deviations in the kiln axes from the normal, due to abnormal operating conditions etc. may cause excessive stress loading of certain welded seams. Where any such abnormal operating conditions continue over a long period of time, the risk of crack formations arises, especially in terms of cracks under fatigue, in and around the most critical welded seams in terms of stress loading. Therefore, it is an essential feature of the preventive maintenance of the rotary kiln that the welded seams are inspected from time to time, both visually and through application of the relevant methods of examination . The following pages contain directions as to where and how to conduct this examination.
8.1.2
Critical welded seams in terms of stress
On planetary cooler kilns the welds primarily exposed to stress loading are:
1. All circular seams at the transition between the heavy-duty kiln sections and adjacent seams. Particularly at the supports around the burner zone and at cooler suspension arrangement. 2. Welds at kiln outlet - reinforcement frames . 3. Planetary cooler brackets, various welds. 4. Welds at reinforcement frames around manholes. 5. Fillet welds for the thrust rings of the tyres.
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8.1.3
Intervals for examination
The welded seams of kiln can only be examined in connection with kiln stops of a certain duration. Therefore, the examination must be arranged to coincide with the scheduled kiln stops required for the maintenance of the kiln. To some extent, the frequency of the periodical examination of the welded seams de pends on the operating conditions of kiln. Where normal operating conditions apply, an interval of two years between each major examinations would seem appropriate. If the kiln has been in operation for more than 5 years, a visual inspection of the welded seams once per year is recommended. Where operational irregularities may have increased the stress loading on the welded seams, an additional inspection of the welded seams exposed to exceptionally severe stresses should be made. Any repairs by welding must be re-checked after 6 months of operation.
8.1.4
Methods of examination
Visual inspection The visual inspection of the kiln welds constitutes the simplest and, at the same time, the most important form of examination as to the condition of welds. In connection with the visual inspection, an initial check-up should be made without removal of rust and dirt from the welded seam, since it is quite often easier to identify a possibly crack formation with the welded welded seam uncleaned. After this initial inspection, the surface of the welded seam is carefully cleaned using a hammer and a wire brush. Grinding may also also be required. In connection with the subsequent visual inspection, it must be remembered that many "irregularities" in welds may resemble cracks. It is recommended that the cleaned welded seams are also dye-penetrant tested, or, better still, subjected to a magnetic particle examination.
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Dye-penetrant testing testing
The dye-penetrant is a liquid with a strong colour (red), which penetrates into possible cracks when applied to a metallic surface. By means of a "developer" the evidence of cracks is increased.
Procedure: A. Remove grease, dust and scale from the surface. B. The dye-penetrant liquid shall be applied by painting or spraying to the cleaned area in a uniform layer. C. The dye-penetrant liquid must be al-lowed time to penetrate into possi ble cracks. 10 minutes will be sufficient at temperatures temperatures from 0 to 60°C. D. Carefully remove any excess dye penetrant liquid. If the liquid is watersoluble, water should be used, otherwise use the appropriate solvent.
The dye-penetrant liquid must must never be removed removed by "flushing"; always wipe off the liquid by means of a lint-free cloth.
E. Wait until the surface has dried, and then apply a thin layer of "developer", which is a high-absorbent white powder, suspended in a volatile solvent. F. After evaporation of the solvent, possible cracks will become more evident by the formation of red lines against the white background.
NOTE! If the cracks are filled with grease, oil etc. this crack detection method cannot cannot be ap plied. In such cases cases a magnetic particle particle examination is required.
Where the cracks are extremely deep, the dye-penetrant liquid may penetrate so far into the crack that it cannot be seen on the "developer". Therefore, it must always be ensured that sufficient dye-penetrant liquid is applied and that it is given reasonable time to penetrate.
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At temperatures below 0°C the plate requires preheating with a gas burner or a hot-air blaster before the dye-penetrant liquid is applied. For any further information i nformation see ISO 3879-1977.
Magnetic particle examination examination Magnetic particle and magnetic powder examinations are performed by covering the area to be examined for surface cracks with a ferromagnetic indication material (magnetic powder). A magnetic field is then generated in the area in at least two directions with the highest attainable degree of perpendicularity relative to one another. The indication material will now accumulate in possible cracks, and will thus disclose even minute defects in the surface region, and defects extending to 3 mm below the surface proper. To facilitate the identification of cracks, a light contrasting colour should be applied to the area to be examined by painting before the examination is conducted. The magnetic particle examination must be performed in such a manner that the magnetic field strength in the area examined attains maximum values in the range of 2400 and 4000 A/m (30 – 50 Oersted). The simplest method is to use an electromagnet with a 90° phase shift. For further information see ASTM E 709 or DIN 54130.
Ultrasonic inspection An ultrasonic inspection can be performed in case internal flaws in the welded seam are suspected or where it is desirable to ascertain the depth of crack prior to repair work being done. Similarly, ultrasonic inspections should be performed following major repairs by welding. Normally, an ultrasonic inspection with 4 MHz 45 and 70 angular probes and 2 MHz normal probes will be sufficient. For further reference consult the ANNUAL the ANNUAL BOOK BOOK OF ASTM STANDARDS STANDARDS PART 11 11 or other relevant literature.
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8.1.5
Inspection and Repair
Circular seams Certain circular welded seams will sustain higher stress loads than other welds. The figure below shows a kiln shell for planetary cooler kiln with 4 supports. The heavy-duty kiln sections for supports, cooler outlet and suspension are shown as hatched areas.
Figure 8.1 Kiln shell for planetary kiln with four supports.
On Figure 8.1 these circular seams are marked with triangles.
Inspection The inspection must be made with the kiln shut down, and the stress-critical seams must be examined to full extent.
Repair When a crack is ascertained, assessment as to the most appropriate form of repair is required. Cracks having a length of less than 10 mm rarely have a depth exceeding 3 mm. Such "minor cracks" can normally be removed by grinding only. This form of repair is sufficient if it is possible to remove the crack by grinding or milling without reducing the material thickness by more than 3 – 5 mm or max. 10% of the plate thickness, while attaining, at the t he same time, a ssmooth mooth surface without notch indicators and with a minimum radius of approx. 15 mm. Afterwards a magnetic particle examination must be performed and additional grinding may also be required. Major cracks, i.e. cracks which must be assumed to have a depth of more than 3 mm to be repaired by welding.
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In connection with repairs through welding the following directions must be closely observed.
a. Marking of the crack length Mark off the length of crack by means of centre punches at the two ends of the crack so that the welder is able to identify point where welding is to be commenced. b. Preheating Preheat the area where weld joint is to be applied to 100 – 150°C. c. Gouging The gouging must be carried out with Arc-Air, from the two ends of the crack towards the centre of crack. The thickness of the carbon electrode should be 8 mm, and the welding machine must have a rating of minimum 400 A. The gouge must be so deep that the entire crack is removed. For penetrating cracks the depth of the gouge must correspond to approx. 75% of the plate thickness. At the base, the width of the gouge should be such that there is sufficient space to deposit a sound bottom run. See Figure 8.2. d. Grinding It is very important that the area where the weld joint is to be applied is ground prior to welding. Inadequate grinding may give rise to new crack formations. As a minimum 1 mm must be ground off the surface of weld joint to remove re move the charred layer. The entire weld joint must be metallically clean.
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Figure 8.2 Gouging of crack
e. Examination of gouging The gouge must be subject to a dye-penetrant or magnetic particle examination. Do not forget the sides of weld joint. In case the traces of crack formations have not been fully removed, operations under c , d , and e, must be repeated. Welding must never be performed until all traces of flaws have been removed f. Preheating Preheat to minimum 150°C. This temperature must be maintained throughout the welding operation. After welding, the welded joint must be covered with mineral wool mats or similar items so as to minimise the rate of cooling. g. Welding Welding must be performed with dry basic electrodes conforming to or E 7018. AWS/ASTM: E 7016 7016 or E 7018. Minimum electrode thickness must be 3,25 mm. This requirement also applies to bottom runs as well as to position welding. In connection with
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normal build-up, welding welding electrodes of 5 – 6 mm thickness should be used. For major build-up welding operations where flat down-hand welding can be applied, use e.g. high-efficiency electrodes such as AWS/ASTM as AWS/ASTM E 7028. 7028. As basic electrodes are highly sensitive to moisture, they must be kept in a drying oven at a temperature of 200 – 250°C for at least 3 hours before being used. Moisture deteriorates the coating coat ing of the electrodes w which hich results in a poor quality weld. At the welding point the electrodes must be kept in a heat-retaining bucket at 70 – 150°C.
Through-going Through-goin g cracks Repeat operations under clause a a through g g,, on the inner side of kiln shell.
h. Grinding In order to maximise the durability of the repairs, the convexity must be removed by grinding. Grinding of the finished weld should be performed so that the resultant surface is absolutely smooth, without any notch indicators and with the grinding marks at right angles to the longitudinal direction of the weld. The transition to base material must be as indicated in the Figure F igure 8.3.
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Figure 8.3 Grinding of weld repairs
i. Examination of weld The entire area repaired must be subject to a magnetic particle and ultrasonic examination.
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positions Figure 8.4 Possible weld crack positions
Cracks or junction defects are not allowed. However, minor, unconnected slag and pore inclusions within the weld will usually be accepted.
Welds to the planetary cooler The planetary cooler is a design which comprises a large number of welds and weld terminations. Therefore, there is a risk of crack formations in connection with any operational irregularities. Consequently, the welds must be subject to careful periodical examinations, both visually and by application of dye-penetrant testing and magnetic particle examination. The following Figures show the most likely starting points for possible crack formations in cooler brackets etc., i.e. the points requiring priority in terms of regular inspections. During inspection a record should be kept so as to provide the plant with a track record to indicate point and time of inspection, points where flaws have been ascertained, and location and time of repair work. Directions applying to repairs through welding on the planetary cooler are similar to those applying to the circular seams of the kiln. However, attention is drawn to the fact
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that for repairs on the welds of the cooler brackets it is a fundamental requirement that the weld terminations are very carefully ground.
Figure 8.5 Possible weld crack positions
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Figure 8.6 Possible weld crack positions
Figure 8.7 Possible weld crack positions
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The reinforcement frames at outlet from kiln to planetary cooler may also be exposed to crack formations. When checking the welded seams, attention must be focused on the opening edge. Here cracks may occur in connection with abnormal thermal impacts.
Figure 8.8 Possible weld crack positions
Normally, the cracks will w ill originate from the opening edge at an angle of approx. 45 degrees to a kiln generatrix, as indicated in Figure 8.8.
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Figure 8.9 Possible weld crack positions
Grinding procedure Surface treatment following repair by welding must be performed with great care. Carefully grind and polish the inner welds and the edges of the reinforcement frames with emery cloth No. 60. Grinding should be made in the direction of the welded seams. The ground area must cover as a minimum 200 mm on either side of the inner edges, as shown above: The inner edges must be carefully rounded off (R ≥ 20 mm). After the polishing operation all edges and scratches, which may take the form of notch indicators, must have been removed from the surface of the material . Subject the weld to a magnetic particle and ultrasonic examination.
Manholes The manholes are provided with reinforcement frames, which are welded to the kiln shell, the inner edge of which is welded and ground together with the kiln shell. This results in a solid construction, with a surface free from notch indicators. As it is, immense stresses occur in the kiln shell and therefore the welds of the reinforcement frames must be examined, especially after local lining drop-outs in the area have been experienced.
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Welds at the retaining rings of the live-rings The retaining rings are welded to the live-ring blocks or kiln shell (see Figure 8.10), and they are furthermore reinforced with safety straps which are likewise welded up with fillet welds (see Figure 8.11). All fillet welds must be examined for crack formations, and eventually be repaired by welding as required.
Figure 8.10 Welded Retaining rings
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Figure 8.11 Fillet Weld
On newer kilns, the live-ring is guided by thrust blocks which are bolted on to the kiln shell. The blocks are secured with safety straps which are welded to the live-ring blocks with a fillet weld. This fillet weld must be examined for crack formations.
NOTE! In connection with repair welding near the live-ring, make sure sure that the latter is propro tected against weld spatter spatter etc. Likewise, weld spatter spatter etc. must never be allowed allowed to enter between live-ring and live-ring blocks or kiln shell.
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8.1.6
Replacement of Plate Section
The following items will be described:
8.1.7
Introduction
Measuring and marking-Out
Stiffening of kiln shell
Cutting Out
Welding
Re-checking
Introduction
If local defects occur in parts of the kiln shell, e.g. dents or cracks, which cannot be re paired by welding, the best repair will be replacement of the defective p plate late section. The cause for such defects is most likely that a red spot has been allowed to develop whereby the shell was weakened so much that defects occur. The best way to avoid defects deriving from red spots is to take the necessary precautions as soon as a red spot is detected. d etected. Cutting out part of the kiln shell will weaken it seriously. So it is very important that the kiln shell should be supported thoroughly before repair work is done. If the damage extends over more than 2.5-3 m in the longitudinal direction of the kiln, or over more than one-fourth to one-third of the circumference, replacement will have to be carried out section by section. It is recommended to consult the supplier of the kiln.
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8.1.8
Measuring and Marking-Out
Clean the kiln shell around the damaged area and determine the extent of the damage. Check the spreading of any cracks by means of capillary liquid or Magneto-flux. The ceramic kiln lining must be removed around the damaged place, and preferably (considering the future durability of the lining) on all the circumference of the kiln. As the stiffening girders are to be placed inside inside the kiln in the majority majority of cases, it is the size of the stiffening which determines the size of the lining to be removed. removed. Measure the size of the new plate section and of the cut-out. The distance from any cracks and dents to the edge of the plate section/cut-out must nowhere be less than 200 mm, and the radii of corner curvatures must be at least 100 mm.
Figure 8.12 Marking-Out
It is important that an absolutely identical marking-out of the cut-out and the plate section is obtained (see Figure 8.12). If the conditions and the extent of the damage permit so, it may be of advantage to use a template of thin sheet or e.g. of hard fibre sheet, from which both the cut-out and the plate section can be marked out.
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The size and shape of the template must comply with the tolerances shown in Figure 8.12. After the template has been used in the plate shop for marking out the new plate section; it is to be used for marking out the cut-out in the kiln shell. The procedure could be as follows:
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Place the template over the damaged area inside the kiln and mark off the template circumference. It can be done most easily by turning the kiln so that the damaged area is in bottom position.
•
Use a centre punch to mark off the eight points where the corner curvatures start.
•
Drill eight 5 – 10 mm holes radially through the kiln shell "within" the eight centre marks so that the marks are tangents to the holes. See Figure 8.12.
The holes can form the starting point for marking-out and cutting on the outside of the kiln, and on the inside for placing of stiffeners. If it is not desirable to use this method, method, the new plate section can be made made after measuring on the kiln, and and the cut-out can be marke marked d out on the basis of the fin finished ished plate section, as described in Section 8.1.11. The edges of the new plate section and the cut-out must be chamfered for welding, as shown on Figure 8.13. If the plate thickness exceeds 40 mm, the smallest chamfer must be increased to 8 mm.
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Figure 8.13 Plate joint
The smallest chamfer must be carried out on the side of the plate which is to face towards the stiffening, i.e. normally the inner side so that the largest weld can be made without interference with the stiffening.
8.1.9
Stiffening of Kiln Shell
In order to strengthen the kiln shell during repairs, a stiffening is to be made across the part of the kiln shell which is to be removed. The stiffening is to be made of HE or IPE sections (01) with h = min. 120 mm, as shown on the figure on the following page. The shims (02) create a clearance under the stiffening girders so that cutting the plate can be done without difficulty. See Figure 8.13.
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Figure 8.14 Stiffening using shims
8.1.10 Cutting-Out
If the cut-out is not marked out from the template, marking-out must be done on the basis of the new plate section. Turn the kiln to a position where the new plate section can be laid over the damaged place. Mark out the cut-out by moving a scriber along the edge of the plate section s ection on the kiln shell, and provide the engraved line with centre marks as soon as it has been traced. Be careful with this marking-out in order to ensure that the cut-out and the plate section will fit together as well as possible. Cutting-out is done by flame cutting. A minimum of 2 mm of material must be left for subsequent machining and grinding. The plate edges of the cut-out must be shaped as shown on Figure 8.13. Especially at the corners, it is important that the plate edges are absolutely clean and ground since the risk of future cracking will be highest at these points.
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8.1.11 Welding
Position the new plate section in the cut-out and support it so that the plate edges are flush everywhere. Welding should only be done by experienced and trusted welders who have the necessary certificates or other evidence of competence for this type of w welding. elding. Preheated basic electrodes, AWS/ASTM:A electrodes, AWS/ASTM:A233/A316 233/A316 , are to be used for welding. The plates must be heated to min. 100°C during welding. This temperature must be maintained during the entire welding process. The greatest possible care must be shown during welding to eliminate, as far as possi ble, the risk of cracking caused by welding stresses. Use the correct amperage. Faulty welds, with undercuts, burning or fused slag must not occur. The weld penetration must be deep enough to provide an even and homogeneous connection. Each run must be cleaned carefully with a hand hammer and a wire brush and be peened (hammered) after cleaning in order to counteract shrinkage strains. Before the first run is passed from the opposite side, the throat must be cleaned by grinding and examined for cracks. This applies to the internal runs marked 13 – 19, 38 – 42, and 66 – 75 on the figure on the following page. Welding should ,whenever possible, be carried out in the horizontal down-hand position for better penetration.
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Figure 8.15 Welding procedure
To reduce the welding strains to a minimum, the below method should be used:
A) Tack-weld the plate in sufficiently many places along the entire circumference. B) Carry out welding in the order indicated by the numbers in the above figure, and in the welding direction indicated by the arrow. (Step-back welding). As it can be seen from the above figure, side "a" is finished completely, with the last run outside, before side "b" is started. When side "b" has been finished, sides "c" and "d" are to be welded simultaneously. On completion of the sides "a" and "b", it must be checked whether the tack-welds in sides "c" and "d" have cracked since it is very important that they should have cracked. If it appears that the tack-welds in sides "c" and "d" have been too strong to crack after finish-welding of "a" and "b", the tack-welds must be chipped or ground open open so that strains can be relieved.
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C) The weld must be ground flush with the inner surface. The welding bead can be kept on the outer side, but an even transition without undercut is absolutely necessary.
8.1.12 Re-checking
On completion of welding, it must be checked for cracking by the use of capillary liquid or Magnetoflux as well as by means of ultrasonic waves or X-rays. Local strain relief by heating can, as a rule, not be recommended.
8.2
LIVE-RING/SUPPORTING ROLLER
8.2.1 Faults; causes and remedies.
A number of failures (faults) on the live-ring and matching supporting rollers are interdependent and will be described together as will the procedures for correction of the faults:
Faults: The axial force of the supporting roller on the live-ring acts in downward direction.
Possible Cause: The position of the supporting roller in relation to the kiln axis has changed.
Remedy: For adjustment of supporting roller position, see module 5.
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Possible Cause: Irregular kiln operation, irregular coating build-up, thermal crank ( "banana" kiln), etc.
Remedy: Remedy: The condition may be temporary. So wait for stabilisation of kiln operation. If the problem does not disappear, adjust the position of the supporting roller. See module 5.
Fault: Bright stripes, bevelled edges on supporting rollers and live-ring.
Possible Cause: Wrong position of supporting roller. See discussion in module 5, section 5.1.2. Because of oil on the roller paths there is an axial slide between supporting roller and live-ring. This can be felt like small shocks when the hand is placed on the water discharge connection of the bearings.
Remedy: Check the axial reaction with the axial measuring equipment (see module 5) and make a correction of the positions of the supporting rollers. A temporary remedy will be wiping of the rollers.
Fault: Pittings (small surface craters) in live-rings and supporting supporting rollers.
Possible Cause: Too high surface pressure between live-ring- and supporting rollers.
Remedy: Adjustment of inclination of supporting rollers; if required kiln alignment.
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Fault: Rolling-out of supporting roller.
Possible Causes: Wrong supporting roller position. See module 5 section 5.1.2. Insufficient lubrication. Insufficient cleaning.
Remedy: Carry out machining of the supporting roller which has been worn hollow. See module 8, section 8.2.2. If the live-ring has been worn oblique or convex, it must also be machined. Adjust the positions of the supporting rollers and check the lubrication arrangement.
8.2.2
General description of machining of rollers and live-rings
A supporting roller or live-ring, the surface of which (i.e. roller path) has become worn or has small pittings, can be repaired by machining during operation. Repair should be carried out when the contact face between live-ring and supporting roller has been reduced by 10% or more, or if a supporting roller and/or a live-ring have been worn so conical that it is impossible to obtain the correct roller position. Machining of a support consisting of two supporting rollers and a live-ring must be done in the following order. In the case of small deformations:
1. Finish-turn live-ring. 2. Finish-turn supporting rollers.
In the case of large deformations:
1. Rough-turn supporting rollers. 2. Finish-turn live-ring.
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3. Finish-turn supporting rollers.
There are limits to the amount of material that can be removed from a live-ring or a supporting roller by turning. Normally, it is permissible to remove as much as 25% of the original thickness of the supporting roller path, and as much as 5% of the original thickness of the live-ring. Any transgression of these values will have to be approved by the supplier.
Cutting tool The turning tool consists of a cutting tool with bed, slide and tool post. The spindle is chain driven by a hand wheel or a star wheel, which is activated by the rotating supporting roller or live-ring. This ensures automatic feed in accordance with the rotation of the supporting roller or live-ring. The turning tool is mounted on a frame and has a swivel base used when turning liverings. The frame incorporates standard features such as controls etc. used during the turning process.
Figure 8.16 Turning of live-ring
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Figure 8.17 Turning of supporting roller
8.3
SUPPORTING ROLLER BEARINGS
The supporting roller bearings need daily inspection to ensure that they are functioning correctly. In case the condition changes in the bearing, e.g. the temperatures or the direction of the thrust, it is necessary to determine the reason and to take the appropriate corrective actions. The fault which may arise, and the relevant remedy could be:
Fault: Too high bearing temperature
Possible Cause: Too high axial load on thrust collar of bearing liner.
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Remedy: Check the load by means of the axial measuring equipment. Relieve the bearing of pressure vice.by distributing the axial load evenly between all journal bearings and the thrust de-
Possible Cause: Radiant heat from kiln.
Remedy: Check that the heat shield of the bearing is in position. If necessary, install an extra screen between kiln tube and journal bearing.
Possible Cause: Faulty lubrication and/or cooling of the bearing.
Remedy: (See module 7 on lubrication).
Possible Cause: Excessive heat supply from supporting rollers and live-ring.
Remedy: If the supporting roller path is hotter than 130°C, it will be necessary to cool the sup porting roller. This is, normally, done by raising the water level in the base-plate so much that the sup porting roller is immersed in the water. It should be ensured that the water surface is free from dirty oil and other impurities.
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NOTE: Even if the supporting supporting roller is cooled by immersion in the cooling cooling water, the roller path must be dry when when contacting the live-ring. live-ring. That is, the su supporting pporting roller must must be so hot that the water water evaporates before before it reaches the live-ring live-ring.. Due to the high ssurur face pressure, water water drops between supporting supporting rolle rollerr and live-ring can create create a risk of pitting.
Kilns with a closed cooling water system have an arrangement for cooling of the sup porting rollers which in principle principle corresponds to that shown in the below figure. Through a number of holes in a tube which is mounted parallel to the supporting roller, cooling water is sprayed on to the supporting roller path.
Figure 8.18 Roller cooling water system
Note the position of the tube relative to the direction of rotation of tthe he supporting rollers. It is also here necessary that the cooling water must evaporate before it reaches the live-ring.
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Faults: Running hot.
Possible Cause: Insufficient lubrication, caused either by a leakage at the bottom of the bearing housing or a leakage in the cooling water connection so that the oil is mixed with water, emulsifies and consequently loses its lubricity. Both may be observed through oil level glass. See Figure 8.19.
Figure 8.19 Bearing with oil level glass - item 01
Remedy: Locate the leakage, repair it and renew the oil.
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Possible Cause: Axial pressure too high. The thrust plate of the supporting roller treads too hard on the thrust of the liner, because the supporting roller takes up more of the axial load ofcollar the kiln thanbearing is expected.
Remedy: Place the supporting roller closer to neutral position. That is, pull the upper or lower supporting bearing -depending on the direction of rotation - outwards by means of ad justing screws until the thrust ring pressure against the bearing liner collar has been relieved.
Nevertheless if the bearing temperature remains high, or exceeds 80 – 90°C, it is necessary, in either of above cases, to replace the oil with EP-1000, e.g. Mobil Oil SHC 639. Replacement of liners. If the proper oil is used at the correct bearing temperature, full liquid friction between journals and liners can be obtained. This prevents wear of the liners. There are examples of kilns which have been in service for more than 15 years without any noticeable wear of the liners. Nevertheless if replacement of a liner should become necessary, various conditions must be considered. Normally, the liners are supplied with a bore corresponding to the original diameter of the supporting roller journal, with a suitable large clearance between liner and journal. The clearance (see item 4 on Figure 8.20) between supporting roller shaft and bearing liner is based on the principle of hydrodynamic lubrication of the bearing. Information on the clearance may be obtained from the supplier. In theory, the shaft rests on a line at the bottom of the bearing liner. At sufficient rotational speed of the shaft, the oil will be sucked into the wedge-shaped clearance between shaft and liner, so that the shaft is supported by a thin oil film. Depending on speed and temperature this oil film thickness will be 0.01 - 0.02 mm. Very careful adaptation of the bearing liner is therefore required. The oil film pressure development appears from the Figure 8.20 item 1. For FLS designs, a new liner can be mounted as follows in case of a FLS design:
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Figure 8.20 Oil film pressure development
•
Clean and wipe the new bearing liner and check that it has not been damaged during transport. Remove any dents and scratches by light polishing.
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Check that there is a smooth transition from oil pocket (see Figure 8.20) to supporting face on the radial as well as on the axial supporting face. See above Figure 8.20 (4).
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Dismount the ball socket of the bearing and mount the liner in the ball socket so that the chamfered thrust collar of the liner faces the thrust plate. See (2) on Figure 8.20 and (4) on Figure F igure 8.21 for the socket, liner, (4) on Figure 8.20 for the thrust collar.
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•
Check by means of retainer pieces that the bearing liner is fixed carefully in the ball socket, is flush with same, and that there is no clearance between bearing liner and ball socket. See Figure 8.20 (3).
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Remove any traces of metal from the old liner from the journal of the supporting roller shaft.
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Fit eye bolts at the corners of the ball socket so that ball socket and liner can be suspended with the liner hanging downwards. See Figure 8.21 (2 and 3).
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Figure 8.21 Bearing Shells
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•
Wipe the supporting roller shaft carefully and apply a very thin layer of marking colour along the entire journal length and across a width covering approx. 120°.
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Wipe the bearing liner thoroughly and carefully place the liner fixed to the ball socket, on the supporting roller shaft, using the thrust ring as guide during lowering.
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Reciprocate the liner axially a few times (10 – 20 mm) while resting on the journal. Measure the clearance between liner and journal as shown on Figure 8.21 (1).
•
Lift liner and ball socket away from the journal and examine the contact between journal and liner by inspecting inspecting the colour marking on the liner. If contact shows as a continuous or sporadically broken narrow stripe at the bottom of the liner, the contact obtained is satisfactory. See Figure 8.21 (4) If contact shows only as single dots, remove the high spots on the bearing liner by light scraping. Apply new marking colour to the journal, and repeat the process until a satisfactory result is obtained.
•
Next, check that the transitions between oil pockets and supporting faces faces of bearing liners are smooth. When everything has been checked and found in order, pour the same type of oil as used in the bearing over supporting roller journal and bearing liner, place the roller in position and finish-mount the bearing. To make the bearing oil-tight, smear all joint faces with sealing agent "Tonite" or similar.
Before mounting the bearing top cover, check that clearance "h" is 3-6 mm (see Figure 8.22, highlighted in the circle). This is to ensure that the bearing can adjust itself in the ball socket. Corrections, if any, must be made with shims. Thrust screw (in the highlighted circle) on the other side must touch the top cover during the mea-surement.
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Figure 8.22 Bearing 8.22 Bearing Adjustment
8.4
SUPPORTING ROLLER SHAFT AND LIVE-RING
Failures can occur to supporting roller shafts and to live-rings because of overloading of these parts. The failure can start as a fissure hidden from normal visual inspection, this then develops into a crack which eventually will lead to a rupture resulting in a completely un planned stop of the kiln. To avoid such a stop the supporting roller shafts as well as the live-ring can be examined by ultrasonics whereby any fault can be detected and remedied during a planned kiln stop. The description below covers:
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1) Test of supporting roller shaft 2) Test of live-ring
8.4.1
Supporting Roller Shaft
If a supporting roller shaft ruptures, it can result in extensive damage to liners and bearing housings. At the same time the other supports will be subject to overloading which under ad-verse circumstances can result in further damage. da mage. The possibility of failure can be reduced if the supporting roller shafts are replaced before cracks result in fracture. In order to detect the cracks and determine their position and depth, the supporting roller shafts should be examined ultrasonically at regular intervals. While cracking of supporting roller shafts is not desirable, it is not necessary to replace immediately, provided the condition is monitored on a regular basis. Ultrasonic measurements taken by experienced and qualified personnel will enable the operator to monitor the development of a crack and when necessary the shaft can be re placed.
Equipment The equipment must be of a reputable make, e.g. Krautkrämer or similar, able to scan by impulse echo. It should be provided with a decibel scale and have a range which corresponds at least to the length of the supporting roller shafts which are to be examined. Procedure Ultrasonic inspection of roller shafts can be made while the kiln is operating, however it is preferable to do it during standstill. Inspection should be made twice a year. Inspection must be made from the shaft end, and hence the end covers of the two bearing housings need to be removed. A 2 MHz standard head should be used for inspection. After adjustment of the equipment to the actual shaft length, the head is placed on the end face of the shaft.
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A bottom echo A and an echo from the most remote diameter transition (B) are normally monitored. See Figure 8.23 (top drawing).
Figure 8.23 Ultra sound equipment and diagram
If there is a crack in the shaft, it will usually be situated at C or C1. If a crack is found, its position should be determined on the circumference of the sup porting roller shaft. s haft. This can be done by scanning the shaft end face all the way round. Scanning must be done from both end faces. When the crack location has been fixed, it is necessary to determine its depth. This requires experienced and qualified personnel. It is wrong to use the height of the echo as a measure of the crack depth since the echo height depends on the orientation and reflection ability of the crack.
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Assessment of measured measured results A crack in a supporting roller shaft will develop into a fracture, and it is impossible to decide in advance whether it will happen, or how long it will take before the fracture occurs. A fracture in a supporting roller shaft will always be due to fatigue, and experience shows that the residual area of fracture never exceeds 50% of the cross sectional area. Residual area of fracture means the fracture area created by the actual crack.
8.4.2
Live-rings
Similar to the supporting roller shafts the live-rings can also be examined by ultrasonic equipment to detect if any cracks are developing inside. Figure 8.24 shows a drawing of a "real" crack in a live-ring. This particular crack developed from the "eye" and eventually occurred in the surface as a small fissure. When preparing to repair the fissure by gouging it was quite a surprise to find that it was not only a surface fault, but a fault that extended deep into the live-ring.
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Figure 8.24 Crack in live-ring.
8.5
THRUST ROLLERS
Thrust roller hydraulic system failure. On kilns with two thrust rollers, each of them is dimensioned so that it can separately take up the full axial load of the kiln for a short time. If the hydraulic system fails, the kiln can, therefore, be kept operating until the fault has been remedied.
Live-ring wobbling If the curves that record the hydraulic pressures, i.e. the axial load, vary strongly during one kiln revolution, it is due to the fact that one or more of the live-rings in contact with the thrust rollers, wobble. The pressure variations will depend on the positions of the live-rings relative to each other which can vary during the movement of the live-rings
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Positions of supporting supporting rollers. If the thrust rollers are excessively loaded, or if the kiln is too slow in sliding to bottom position, it is, usually, because the supporting rollers are not positioned correctly. It is important for the operation of kiln and thrust device that the supporting rollers stand correctly. This condition must be checked regularly, and the thrust roller face is lubricated correctly by means of a graphite block.
Positions of thrust thrust rollers. It is important that all the surface of the thrust rollers tread on the live-rings. In cases where only the upper part of the thrust roller surface is in contact with the live-ring, the adjustment can be carried out by placing shims between thrust device and pedestal. It is also very important that the axis of rotation of the thrust roller should be in the same vertical plane with that of the kiln axis. If these conditions are not met, the effect will be the same as with supporting roller skewing, i.e. the thrust roller will either be lifted by the live-ring some distance upwards or it will be forced downwards very hard, as shown in Figure 8.25.
Figure 8.25 Positions of thrust rollers
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This sliding movement will cause the surface of the thrust roller and the corresponding surface of the live-ring to be damaged. This is called the "fish scaling" effect.
8.6
GIRTH GEAR
Gear wheel mesh. Wear of supporting rollers live-rings, bearings, etc., can result in the centre distance being reduced between gear rim and drive. The effect is that the distance between tip and bottom of teeth will become too small (See B in Figure 9.1), i.e. below 6-12 mm (de pending on the kiln size). If this is the case, it will be necessary to re-align the kiln. In severe instances the base plate under the plummer blocks (01 on Figure 8.26) will have to be removed and re placed by a thinner one.
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Figure 8.26 Girth gear
If the position of the above plummer blocks are changed, the proper meshing between pinion and intermediate wheel must also be checked, and plummer blocks (02) possibly adjusted in the same manner. If the tooth contact is not correct, i.e. the teeth do not contact each other across the entire tooth width, one of the plummer blocks (01) may have been displaced in the horizontal plane. The original position of the bearing is marked with a chisel cut in pedestal base and base plate. The positions of the bearings can be adjusted by means of the screws (03). If the bearings are displaced, they may twist in relation to the shaft. Use a feeler gauge
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shaft collar must be identical, and at the opposite end of the shaft the clearances "b" must be identical in order that the liners shall not seize the shaft. When adjusting bearings (01), the tooth contact between pinion and intermediate wheel must also be checked and possibly be adjusted by adjusting bearings. Since it can be difficult to check these dimensions without removing the top part of the bearing, the bearings may also be allowed to align themselves to the shaft. This can be done in the following way: After adjustment of the gear wheel mesh, it is ensured that the adjusting screws (03) only tread lightly against the bearing base, at the same time as the base bolts (04) of plummer blocks (02) are only tightened lightly. The kiln is then turned through a few revolutions, and all screws s crews and bolts are then tightened firmly.
Oil scrapers. Dismount the oil scrapers and examine them. If necessary replace the rubber scrapers. Lubricate the moving parts with grease and remount the scrapers (refer to Figure 8.27).
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Figure 8.27 Oil Scraper
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MAINTENANCE OF KILN DRIVE
9.1 INTRODUCTION This section describes the inspection activities for a kiln drive system as well as for the main gearbox. Please note that only the mere inspection routines for gearboxes are mentioned in this section;. gearbox maintenance is thoroughly dealt with in chapter 6 of this training material. The numbers in brackets ( ) refer to the numbers in the figures. To facilitate reference we have chosen to enclose enclose the sketches (Figures 9.2 9.2 and 9.3) together with a key at the end of this section.
Figure 9.1 Clearances
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Check, by moderate blows with a hammer on the keys, whether pinion and intermediate wheel are fixed on the shafts. Inspect the lubrication. Plummer blocks (06) and (18). Inspect the bearings. Look, listen, and feel for irregularities of any kind. Look for oil spills on the shaft seals.
Oil sump (08). Examine by means of the drain cock (09) whether rain water has penetrated into the oil sump.
Oil scrapers (13). Inspect the oil scrapers. Check that they move easily and keep the sides of the gear rim free from oil. Lubrication wheel (07). (07). Check that the lubrication wheel functions correctly.
Spray lubrication. In case spray lubrication of the pinion and girth gear is used, the spraying pattern shall be checked once per week and corrected if required. required.
Gear wheel mesh. The teeth must be in contact across the entire tooth width. Use a feeler gauge for checking. Examine the tooth flanks for signs of abnormal wear. If the tooth contact is not all right, i.e. the teeth are not in contact each other across the entire tooth width, one of the plummer blocks (06) may have been displaced in the horizontal plane. The original position of the bearing is marked with a chisel cut in the pedestal base and base plate. The positions of the bearings can be adjusted by means of the screws (12). If the position of the bearings is changed, the conditions between pinion and intermediate wheel must also be checked, and bearings (18) possibly be adjusted in the same manner as the other two bearings. If the bearings are displaced, they may twist relative to the shaft. Use a feeler gauge to
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identical, and at the opposite end of the shaft the clearances "b" must be identical in order that the liners shall not seize the shaft. When adjusting bearings (06), the tooth contact between pinion and intermediate wheel must also be checked and possibly be ad justed by adjusting the bearings (18). (18). Since it can be difficult to check these dimensions without removing the top part of the bearing, the bearings may also be allowed to align themselves to the shaft. This can be done in the following way: After adjustment of the gear wheel mesh, it is ensured that the adjusting screws (12) only tread lightly against the bearing base, while the bolts (19) are only tightened lightly. The kiln is then turned through a few revolutions, and all screws and bolts are then tightened firmly.
9.2 MAIN GEARBOX Inspection and adjustment The following inspection and adjustment routines must be carried out once per month:
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Measure the oil temperature in the gear unit.
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Normally the maximum permissible operating temperature is 80°C in the oil bath and 100°C in the bearings for high-speed shaft.
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Look, listen and check for irregularities of any kind. Report on any changes in the sound of the gear unit.
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Inspect for oil spillage at assemblies, covers and shaft seals.
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Check the adjustment of any temperature measuring equipment.
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Check cooling water control, if any.
Checking of condition. The condition shall be checked once per year:
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Inspect the tooth flanks for any signs of abnormal wear.
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Inspect the roller bearings of gear unit for wear.
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Check fastening of all bolts.
9.3 SAFETY PRECAUTIONS When carrying out the inspection procedures on the kiln drive station the personnel must take care not to come into contact with the moving machinery. In the event that removal of protection or guards is required to allow the work to be carried out this must only be done by personnel with the appropriate authority. The same staff is also responsible for the re-positioning of the removed parts. All necessary tools and equipment shall be in order and the personnel must be wearing the issued protective clothing. When inspecting the main gearbox and the covers are opened, great care must be exercised because of the hazards presented by the warm oil fumes.
KEY TO SKETCHES IN FIGURES 9.2 and 9.3 01
Gear rim
02
Gear rim spring
03
Plain bolt
04
Locking plate
05
Drive
06
Plummer block
07
Lubricating wheel
08
Oil sump
09
Drain cock
10
Tight-fitting bolt
11
Shaft for drive
12
Adjusting screw
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13
Oil scraper
14
Lifting cup
15
Countershaft
16
Pinion
17
Intermediate wheel
18
Plummer block
19
Bolts for plummer block
20
Guard for gear rim
21
Drip ring
22
Drip ring
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Figure 9.2 Kiln drive
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Figure 9.3 Oil Scraper
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