Gap Measurement and Displacement Between the Kiln Shell and Tire (Kiln Tires)

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OPERATIONS / MAINTENANCE KILNS MECHANICAL MAINTENANCE Code..

Chapter 1 GAP MEASUREMENT (Clearance) AND DISPLACEMENT (Control of Clearance) THE KILN SHELL AND TIRE (Kiln Tires).

BETWEEN

1.1 OBJECTIVE AND SCOPE The objective of this measurement is to count with the necessary information to control displacement and clearance between the kiln tube and tires due that it is fundamental for the refractory life as well as for mechanical conditions. This is a control requiring a lot of caution, and the recommendation is to check at least once per shift. 1.2 METHOD BASIS OR FOUNDATION There are kilns with tires that due to their design are fixed; i.e., they do not have sliding between the kiln tube and tire, but in the FLS kilns (F. L. Smidth) rolling rings of "floating" single type or "migrating" type are used, with certain diameter difference between the kiln tire and the kiln shell (support blocks). The kiln tube and the rolling rings are dimensioned so that D internal diameter, of kiln tire, is a little bit bigger than the d kiln tube external diameter, measured in support blocks (or in the kiln tube). The diameter difference is necessary considering that the thermal expansion is a little bit bigger than the kiln tube. The absolute diameter difference, i.e., the diameter difference between a circular kiln tire and a circular kiln shell, is named 2s. See Figure number 1.1. The diameter difference provokes, during the kiln rotation, a relative movement between the kiln tire and the kiln shell due to the different expanded lengths of both supporting faces. The kiln tire movement, regarding the kiln shell, is named kiln tire displacement.

Figure 1.1. The displacement of the kiln tire in a kiln rotation is classified with the letter V.

CHAPTER 1 Kilns Maintenance Manual

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1.2.1 Importance of Clearance It is important that the clearance between the kiln tube and the kiln tire is maintained within certain values obtained by experimentation. If the kiln tube temperature is suddenly increased, so that the temperature difference between the kiln tube and the kiln tire is substantial, perhaps the clearance between these becomes null or negative. This way represents a possible choking between the kiln and the kiln tire. In case the choking is very pronounced, a permanent deformation called "constriction" (or trumpet) will be produced in the reinforced kiln shell of the kiln tube. The risk of this situation is higher in the kiln tires, above and below the calcinations zone. Consequently, it is important that the relative displacement between the kiln and the kiln tires is controlled. In case of producing permanent deformations on the kiln tube, this can result in, that a diameter extended difference involves difficulties in coating, with the consequent need to reduce the clearance between the kiln tires and the support blocks for the ring due to supplements placed below the blocks. In order to protect the rotary kiln against deformations and / or damages in coating, produced by overheating during service, it is necessary to control strictly and perform, if possible, service corrections to maintain the diameter difference, between the kiln and the kiln tire, within an acceptable level, so that the ovality can be maintained within the admissible maximum and minimum limits. A control of the current diameter difference, during the kiln service, is made in the simplest and most accurate mode in order to measure the kiln tire displacement, the kiln tube relative movement regarding the kiln tires. 1.2.2 Kiln tire displacement Measurement. As previously mentioned, the supports are built so that there will be in the hot kiln a diameter difference from 0 to 3 mm between the kiln tube and the kiln tire. The diameter difference, the clearance between the kiln shell and the kiln tire, provokes, as indicated, a relative movement between these two components. The theoretical diameter difference, 2s, produces a relative movement as follows: Vt = .( 2RL - 2 RO ) RL = Internal radius RO = External radius Vt =  . 2s The relative movement or displacement V, between the deformed kiln shell and the kiln tire, according to acquired experiences will be, 1 1/2 - 2 times the upper clearance d (gap). When dealing with small holes, it will be 1 1/2 times and 2 times in big size kilns. The theoretical and real displacement of kiln tire, are in reality the same, whatever the deformation is. It is not possible measuring the diameter difference in a hot kiln, but, considering that the kiln tire displacement is a function of the diameter difference, this can be indirectly controlled by the kiln tire displacement confirmation. CHAPTER 1 Kilns Maintenance Manual

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1.2.3 Causes of kiln tire clearance reduction A kiln tire in cold status is never fixed seated over the kiln. The technical reasons related to mounting explain the need to have certain clearance, so that the kiln tire can move along the kiln. With the purpose to consider the variable thermal expansions of the kiln shell and kiln tire during the heating period; the kilns suppliers calculate both diameters so that the clearance between the kiln tire and kiln, at service temperature, adopts a minimum value. It would be ideal that the kiln, in hot status, would exert certain pressure over the kiln tire, without being subject to a contraction. This would naturally demand that the temperatures used for calculation would be really reached during the service. It is confirmed, based on experience, that it is practically impossible to anticipate the calculation of the temperatures profile related to a rotary kiln shell. There is always a danger for the kiln when the kiln shell expands with a higher speed than that of the kiln tire. It is easy to understand that this happens when a coating damage occurs under the kiln tire. But it is not clear, on the other hand, a too quick heating condition, i.e. a start within a record time, can also have serious consequences. In this case, the kiln tire is relatively cold and the kiln shell is quickly heated, so that permanent deformations can occur due to the kiln shell contraction. In such cases, the kiln tire internal heating can lead to an inadmissible increase in the kiln tire clearance. Figure 1.2 shows the temperature development of the kiln tire and kiln shell during a kiln facility-heating period. t máx. is the maximum temperature difference, which can occur between the kiln tire and the kiln shell.

CHAPTER 1 Kilns Maintenance Manual

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752 [0F] 572

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392 Rolling Ring

212

Hours

Figure 1.2 T = Thermal stress with obstructed expansion t max = Maximum temperature difference between the kiln tire and cover t s = Operation temperature difference t = Expansion Coefficient Temperature curve of kiln tire and kiln shell during a kiln-heating phase A kiln shell permanent contraction will be produced below the kiln tire when the thermal stress  T for a kiln shell impaired expansion exceeds the elasticity limit  F. sT = E . t . t max < F This can be the case when the required clearance in cold status sth is little or zero. In the same way, whenever the maximum temperature difference  t max is too high due to an excessively fast heating situation.

1.3 METHOD DEVELOPMENT 1.3.1 Equipment and tools to be used F.L. Smidth supplies automatic equipment for kiln tire displacement surveillance and control. In case that such equipment is not available, it is possible to measure the kiln tire displacement manually.

One of the most utilized methods in Cemex is the use of Displacement and Gap Meter (Figure 1.3). This measurement appliance is composed by a bracket (02) that, through a magnetic base, is placed on one of the support blocks. The bracket supports a recording needle (03), under a spring and in horizontal CHAPTER 1 Kilns Maintenance Manual

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position, pressed against a piece of paper that is, through the usage of adhesive tape, fixed to a plate (04), that in turn, is fastened to the kiln tire by magnetic blocks. Additionally the measuring can be made by a manual method, which is described in the procedures section. 1.3.2 Periodicity The measuring operation of the kiln tire (tire) displacement and gap is a control requiring the most caution, and the recommendation is to check it at least once by shift. When dealing with kiln starts, the measuring operation must be more intensive, i.e. measuring two or more times per shift. 1.3.3 Procedure, calculation methods and results 1.3.3.1 By the displacement and gap-measuring appliance. Placing coupled marks in the kiln tire and in the kiln tube can perform, in a very easy way, the simplest kiln tire displacement measuring method. Whenever the kiln has been spinning, for example, 10 rotations, the displacement between marks is measured, in this way, the average displacement calculation is possible. The clearance  can consecutively be found when dividing V by 1.5 - 2, i.e.: V  = ------------1.5 a 2 If the displacement average V is divided by  , the result is : V/ = 2s, it means The theoretical clearance in the circular kiln tube / kiln tire. 1.3.3.2 Using the displacement and gap meter. A method even more practical for measuring V and  , utilized by CEMEX, is performed with a single appliance named: displacement and gap meter, shown in Figure 1.3, described as follows: The appliance is placed as illustrated in Figure 1.3 and during the kiln rotation; the recording needle will draw a curve, as illustrated in Figure 1.4, corresponding to the kiln base where the kiln is to be measured. The curves shown are equivalent to 5 kiln turns or rotations illustrated in Figure 1.4, the values V and S can be directly measured in the curve.

CHAPTER 1 Kilns Maintenance Manual

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As previously mentioned, it is important that the clearance between the kiln shell and the kiln tire is maintained within determined values.

Figure 1.3

Figure 1.4 If the recording needle, during the kiln starting process, begins to draw smaller and smaller curves, means that V and S tend to null value, and it can be necessary to participate in order to prevent "constriction".

1.3.4 Interpretation of results. Gap Adjustment CHAPTER 1 Kilns Maintenance Manual

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As previously mentioned, the big deformations are observed in the zone of the kiln tires having an important clearance. In order to reduce deformations, it is necessary to reduce the kiln tire clearance by lower shimming of kiln tires wear pads, provided that it is constructively possible (kiln tire wear pads are screwed). In such case, the thickness of plates to be placed must be determined. The safest method for this purpose is the following: - Daily determination of a relative movement U and / or during a period sufficiently long (3 months). - The minimum value U and / or V occurring within this period must serve to determine the mean clearance of the kiln tire. - The supplementary plates thickness is obtained from the mean clearance of the kiln tire s th and / or . U sth = ------- - As a safety factor regarding the big thermal expansions, the supplementary plates thickness will be dimensioned so that the clearance in service status is within the order of 3 mm. Therefore, the thickness for the supplementary plates is the following: sth - 3 tB = ------------- mm 2 1.3.5 Safety aspects In order to measure the kiln tire gap and the displacement, the activity must be executed with the kiln running and in hot condition, as previously mentioned, thereby special caution and attention must be paid to prevent damage by burning or by touching the equipment in motion. 1.3.6 Condemning or permissible limits The relative movement or displacement V, between the deformed kiln shell and the kiln tire, must be according to the acquired experiences, 1 1/2 - 2 times the upper clearance d (gap). When dealing with little kilns, it will be 1 1/2 times and 2 times for big size kilns.

1.4 COMMENTS AND OBSERVATIONS As previously mentioned, it is very important to have kiln tire gap and displacement control, this procedure is therefore classified as general observance and mandatory. CHAPTER 1 Kilns Maintenance Manual

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1.5 ATTACHMENTS AND USED FORMS The form used to record information is free, it means the wanted information can be utilized according to each plant needs. 1.6 REFERENCES - Control of clearance between the kiln tube and the kiln tires, Manual F.L. Smidth 19124-01. - Recommended Procedures for Mechanical Analysis of rotary kilns, Book of Robert P. Chapman (Fuller Company).

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