Alignment

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Dial gauge and Alignment

Taking dial gauge reading for calculation of “TIR” (Total indication run out) is not an easy job. When it comes to practical many EXPERTS get confused. In order to understand alignment /TIR it is essential to know about dial gauge and its working.

Dial gauge A dial gauge or indicator consists of components such as bezel, indicating pointers, tool post and clamp, magnetic tool holder and sensor button. Dial indicators are available in many physical sizes and ranges. For most alignment applications the smaller sized indicators should be used to reduce indicator bar sag. Dial indicators should be chosen that have a range of 0.100 inch and accurate to 0.001 inch. Indicator readings, and many other types of readings, are expressed in several units. A reading of 1/1000" is equivalent to 0.001 inch and is commonly expressed as 1 mil.

The dial gauge have two scales. One outer scale marked (0-100) and second inner scale marked (1000).The outer scale (0-100) is to be used when dial gauge needle moves clockwise and inner scale (100-0) when dial gauge needle moves anticlockwise. When sensor of dial gauge is pushed upwards towards dial then needle on the dial moves clockwise and when sensor is moved downwards away from the dial then needle on dial gauge moves in anticlockwise direction. The dial gauge readings when needle moves clockwise are +ve where as when needle moves anticlockwise are - ve (Fig.-2). The movement of the needle should be watched for clockwise or anticlockwise rotation through out the move to avoid any confusion of +ve or—ve sign. All readings should be recorded as viewed from the stationary machine side to define right and left direction at the time of data entry. Backlash Error Check the indicator for backlash error. Press the sensor and then release and note down the dial gauge reading.. Repeat this process two three times. Every time dial gauge reading should be same. If readings differ then change the dial gauge. SAG calculation Dial gauges are coming with standard mounting systems. · For single gauge mounting. · For double gauge mounting. Some time depending on the equipment to be aligned some modification or extension is required in mounting system to carry out the alignment. If length of the tool mounting holder is more or any extension for mounting magnetic tool holder is there then there is more possibility of sagging due to weight. Mounting of the dial gauge on the bracket should be performed carefully so that dial gauge sensor axis is perpendicular to the pipe axis to ensure accuracy. Otherwise it will lead to large errors. It is essential to calculate the sag always before alignment and to be considered during calculation. For calculation of sag mount firmly the magnetic tool holder with gauge on a pipe. Adjust the dial gauge reading to zero with dial gauge sensor tip touching to pipe surface as shown in (figure-4). Now turn the pipe 180 degree and take the dial gauge reading. The difference between these two readings will give you the double of the sag value. So sag=dial reading/2

Taking the readings

After the dial gauge is firmly mounted on the shaft of the machine to be rotated then four locations at the circumference of the shaft or coupling of the stationary machine are required for taking the readings for alignment. These Four locations are at 90 degree rotation of shaft(12, 3, 6, and 9 “O” clock positions) as shown in Fig.-5.Please note that left right directions are marked as seen from the stationary machine side Before any readings to be taken the dial indicators must be set. Adjust the dial gauge in such a way that sensor of the dial gauge is slightly pressed against the circumference of the coupling. Rotate the machine shaft through an entire 360 degree and verify that the indicator sensor tip is in complete contact with the shaft. Now When indicator is at the top location reset the indicator to display zero. This is achieved by rotating the outer bezel of the indicator until the dial face, which is attached to the bezel, shows "0" under the needle. Collect the data by rotating the machine shaft in 90 degree increments and noting the dial indicator readings with their signs (+ or -) at Top, Right, Bottom and Left locations. If only one dial indicator setup is available, the dial gauge mounting arrangement must be relocated to the other coupling or shaft of stationary machine and the sweep should be repeated. Remember, that all readings should be collected while observing from the stationary machine to the moveable machine to maintain right and left consistency. In this case when dial gauge is mounted on stationary machine and readings are taken on machine to be moved then change the sign of readings so obtained. +ve sign to be made –ve and –ve sign to be made + ve. Accuracy Verification Each time the dial indicator is rotated to the top location it should display a reading of zero. If it does not then something has moved during the rotation. Correct the problem and start again. Another test, which can be performed as the data is collected, is to verify that the sum of the top and the bottom readings should equal the sum of the left and right readings. (See fig.-6). While taking dial gauge reading at the bottom portion of the shaft or coupling ,value of sag must be taken in to account. Actual dial gauge reading at the bottom of the coupling (6 “o” clock position) = dial gauge reading -{-(2*sag)} Assuming sag=0 Top+ Bottom reading =0+10 = +10 Right + Left reading =-12+22= +10

Calculations As the dial indicator is moved around the circumference of a coupling or shaft it displays twice the difference between the projected centerline of the indicator's attachment point and the measured shaft centerline. This is true for both the vertical and horizontal readings. This is known as TIR (Total indication run out) Thus, the sum of the vertical and sum of the horizontal readings must be divided by two to represent the actual differences in the two shaft centerlines. Remember to observe the signs of the indicator readings closely to prevent errors in these calculations. Thus actual difference in shaft centre lines (offset) in vertical plane = TIR (vertical)/2 Thus actual difference in shaft centre lines (offset) in horizontal plane= TIR (horizontal)/2 Two vertical offset numbers and two horizontal offset numbers will be obtained; one set representing the readings while the bracket is installed on the shaft of the machine to be moved and another set representing the readings while the bracket is installed on the shaft of stationary machine. Horizontal offset calculations have always remained a point of confusion. Mostly people do mistake in calculating this. This is because of the reason that one side does not start at zero. This is achieved by Adding or subtracting the value equivalent to the value of right hand side reading on both sides ( in left side reading and right side reading ) so that right side reading becomes zero. Let us take the case of Fig.-6 (All readings are in mil) Vertical TIR = 0+10=10 Horizontal right hand side reading is –12 . Horizontal left hand side reading is +22 In order to make right hand side reading zero we shall add +12 on both sides. Now horizontal right hand side reading is =-12+12=0 And horizontal left hand side reading is =+22+12=+34 Therefore horizontal TIR = 0+34=34 So offset in vertical plane is =10/2=5 And offset in horizontal plane is =34/2=17 For more details

· Methods of alignment · Target alignment and angular tolerance · Alignment check without removing coupling

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ALIGNMENT

There are two types of alignment methods: · Face and perif · Reverse alignment Reverse alignment is the most accurate method, but should be used in conjunction with Face and Perif method. Face and Perif method: vertical Alignment (Angular)

Fixed machine

Machine to be moved

D1 F1

Fig. 1

F2

D2 D3 F1=First hold down bolt F2=Second hold down bolt D1=Diameter of the circle made by dial indicator tip when coupling of the fixed machine is rotated 360 deg. (mm) D2=Distance from Pointer of dial indicator to first holding down bolt F1.(mm) D3=Distance from pointer of dial indicator to second holding down bolt F2. (mm) Always align angular misalignment first in both vertical and horizontal alignment. For vertical alignment, zero dial indicator at T.D.C .Rotate through 180˚ and note total indicator reading (T.I.R) and sign. To calculate the amount of shims required under F1 and F2, following method can be used Ratio between D1 & D2,D1 & D3 are required. Example Say: D1 = 50mm D2 = 100mm D3 = 200mm R1=100 /50=2

and R2=200/50=4

If dial indicator reading = +0.2mm Then distance between coupling faces are greater at the top than bottom Add 0.2 X 2= 0.4mm at F1 0.2X 4 =0.8mm at F2 When T.I.R = o.1 or less check for height alignment, as per the fig 2

Machine to be moved

Fixed machine

Fig. 2 F1

F2

Once angular alignment has been achieved, equal amounts of shims can be removed or added as calculated below. zero dial indicator at T.D.C .Rotate through 180˚ and note total indicator reading (T.I.R) and sign. For a minus dial indicator reading ,add shims under m/c to be moved equal to that of the indicator reading. For a plus indicator reading remove shims under machine to be moved equal to that of the indicator reading. HORIZANTAL ALIGNMENT(ANGULAR) Three dial indicators are required. Positions are shown in fig 3

F2

F1

Machine to be moved

Fixed machine

D1

F2

F1

Fig. 3

D2 D3 Method Zero dial indicators (D.I) and rotate through 180°.Note the reading and sign minus or plus. Using fig. 1 find ratio R1 and R2,calculate distances to move m/c at D2 and D3 . Zero dial indicators positioned at feet of m/c to be moved and move machine until indicators read calculated dimensions when T.I.R = 0.1mm or less, horizontal alignment can be checked. Positions D.I as shown in Fig 3 .Zero DI and rotate through 180°.Note indicat or eading and sign. Zero D.I position at feet of m/c to be moved and mov machine until both D.I indicate error previously recorded. (2) REVERSE ALIGNMENT

D1 A

Machine to be moved

Fixed machine F1

Fig. 4

F2

B D2 D3

P

A=clock dial indicator on coupling hub (fixed m/c) B=clock dial indicator on Coupling hub (machine to be removed) F1=First holding down bolt F2=Second holding down bolt D1=Distance between dial indicators D2=Distance from p to first holding down bolt D3=Distance from P to second holding down bolt Before starting the alignment, an alignment Graph must be made-see attached graph 1 Install clock dial indicators as in Fig 4 2 With Marker pen mark of the positions of dial indicators on the coupling hubs. METHODS FOR VERTICAL ALIGNMET Always stand with the fixed m/c on your left hand side, and m/c to be moved on your right hand side. (1) Position the dial indicators as shown in the fig 4. with the “A” dial on the top of the Fixed m/c coupling hub, and the “B” Dial indicator at the bottom of the m/c to be moved. (2) Set the indicator to zero and turn both coupling hubs through 180°.Note the T.I.R of the “A” dial indicator and if the reading was plus or minus. (3) Set the “B” dial indicator to the top and turn both coupling hubs through 180°.The “B” dial will now be back at the bottom of the hub. Note the T.I.R of the “B” dial indicator and if the reading was plus or minus PLOTTING READINGS ONTO GRAPH A

F1

B

F2

0.2

A= + 0.4 /2 =0.2 B=— 0.28/2 =0.14 Reverse sign

0.14 0.05 0,0 Subtract shim =0.05 mm

— 0.15

Add shim = 0.15

D1 D2

D3

Example: “A” dial reading of +0.4 mm T.I.R “B” dial reading of -0.28mm T.I.R On the A line of the graph, plot half the T.I.R of the “A” dial indicator to pre-determined scale. As the reading was plus, the mark has to go above the pump center line. On the “B” line of the graph, plot half the T.I.R of the “B” dial indicator to the same scale ,but in this case you must reverse the sign. In the Example from minus to plus “This is very Important”. Plot point on graph above center line. Note:If the reading “B” dial was plus, reverse sign to minus. Plot point below center line of graph. Place a straight edge through the two points and draw a straight line passing through points F1 and F2.Te distance from the center line to the plotted line will be the amount of shims to be added or subtracted from F1 and F2 respectively. If the plotted line is above the center line, subtract shims—and below add shims. HORIZONTAL READINGS

A F1

F2

Machine to be moved

Fixed machine

F1

F2

Fig. 5

B

Horizontal readings are taken the same way as for vertical readings. Only the dial indicators are set in plan view. In the horizontal position the m/c to be moved is physically moved on the base frame, as shown in Fig 5.Placing dial indicators at the feet of the m/c to be moved, move m/c in accordance with plotted graph. Ensure that you are moving m/c in the correct direction. Make a note on the graph which way a minus or plus has to be moved in the horizontal position i.e Away or Towards you. Please note the following rules: (1) Always check that you have the correct distance between coupling ends. (2) When aligning Multistage Centrifugal pumps, fill pump casing with water push pump shaft into pump body to separate wear plate faces. This is very important as the wear plate faces can pick up if this is not done. (3) Always rotate both couplings together to eliminate coupling run out. MORE

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Relative reference displays the current body's centerline referenced to the previous body. Relative reference allows you to determine if your alignment is within the desired coupling angular tolerance at Ambient and Operating temperatures. See example below (Fig.-2,3)

Absolute reference shows the current body's position referenced to the leftmost (fixed) body. Absolute reference allows you to check for sufficient hold-down bolt clearance in all bodies in a train to effect an alignment without disturbing the fixed body. Useful for initial installations.

Thermal Movement is the vertical and horizontal shift in the centerline of a body due to the change in temperature from when it was aligned to operating temperature

Target alignment is the alignment to which all the shim change and horizontal movement calculations are referenced. It is the relative position of both bodies at the temperature at which they are being aligned, corrected for expected thermal movements. See example below ( figure-2) Fixture Sag is the measured bending of the alignment fixture due to its stiffness, weight, and gravity. Because of sag, the dial indicators will render false readings. Sag must be measured and algebraically subtracted from the dial indicator readings to determine the actual shaft relative positions.

Flexible couplings allow equipment shafts to operate with some deviation from perfect alignment by distorting the flexible elements. This deviation usually consists of a parallel offset and an angle that can be resolved into a single angle that the flexible element sees. This resolved angle is called the Angular Tolerance. A coupling Flexible Element can be a disk pack, diaphragm, gear, spider, etc. In other words, the bit that bends, or flexes.

Angular Tolerance is the maximum angle that the flexible elements are allowed to distort during operation. This angle, when rotated through 360 degrees, defines a cone with its apex (point) at the center of each flexible element ( Right side -Figure 1). The centerline of a shaft (or coupling spacer) that operates within this conical region is deemed to be in tolerance.

Figure 1

Flexible coupling

Since physical adjustments are in the vertical (shim changes) and horizontal (side to side), results are shown in Vertical and Horizontal plots in the Graphic Plot . The same two views of the cone appear as triangles on these plots. A centerline lying on, or near, the outer edge of both triangles may at first appear acceptable (Red lines - Left side Figure 1). In reality, the centerline will lie outside the cone when the two projections are resolved to the true position (Blue line - Right side Figure 1).

Example of Target alignment

Flexible coupling Figure-2 (centre line of all bodies during operation)

5 Take the case of a Turbine driven Compressor with Gear box as shown in the figure-2. Assumptions Ambient temperature=25 deg C

Thermal expansion = 1.2*10¯ per deg. C Compressor shaft height from base= 800 mm Compressor shaft brearing area temp. during operation = 70 deg C Gear box shaft height from base =450 mm Gear box shaft area temp. during operation =55 deg C Calculations forbrearing shaft height increase during operation Turbine shaft height from base =700 mm Turbine brearing area temp.during operation = 55deg. C Increaseshaft in height of compressor shaft during operation = [1.2*800*(70-25)] /100000 =0.432 mm Increase in height of Gear box shaft during operation =[1.2*450*(55-25)]/ 100000 =0.162 mm Increase in height of Turbine shaft during operation =[1.2*700*(55-25)]/ 100000 =0.252 mm

Based on above calculations the Relative reference of all the three bodies at ambient temperature will be as shown below. Black dotted lines indicate the shaft centre lines of Compressor, Gear box and Turbine at ambient temperature. Green dotted line indicate the shaft centre lines of Compressor ,Gear box and Turbine under operating condition .

0.162 mm COMPRESSOR 0.27 mm

GEAR BOX 0.09

TURBINE

Figure-3 (shaft height cold alignment) 0.432-0.162 =0.27

0.252-0.162 =0.09

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Alignment Check Without removing coupling BACK Many maintenance departments in smaller plants still think that alignment is only needed for large, high-speed shafts. Many have no idea how to align two shafts beyond using a straight edge to get them close. The supplier who sells the couplings says that the coupling can take up to one degree of misalignment and not hurt anything. They design couplings that will not wear out with that much misalignment. It does not speak of equipment safety. Badly aligned shafts will ruin the bearings on the equipment in short time. All shafts, even low speed ones, must be aligned to within a few thousands of an inch TIR (Total Indicator Run out) if the bearings are to last for their full life.

L

Flexible coupling

Fixed machine coupling

Coupling of machine to be moved

A

A=Fixed machine side coupling B=Movable machine side Coupling D=diameter of the coupling L=Distance between two couplings

B

Actual Relative position of the driving Machine and the Driven machine can be checked by using the coupling as installed. It is recommended to check the machine alignment when the machines are shut down for schedule shut down. The alignment of the machines may be readily checked with a dial indicator clamped to the center of the tube. Clamp or place the indicator base on the tube. Place the indicator tip on the face of the guard near the OD. Zero the indicator at 12’O clock. Rotate both machines, flexible coupling and indicator at the same time. Take reading at 3’o clock,6 o’clock,9 o’clock and 12 o’clock reading doesn’t repeat zero, re zero the indicators and retake the readings. Take the second set of readings at the other end of the couplings. Record the readings on the data sheet. Calculate total indicator run out. Remember a POSITIVE reading occurs when the tip moves towards the indicators. BE CAREFUL of your SIGNS (+,-) when adding and subtracting. The flexible diaphragm coupling can accommodate misalignment by both end diaphragms angular deflection. These diaphragm couplings are classified by allowable angular deflection. For example… For 200 Series flexible coupling (T.I.R)