Handbook of Shaft Alignment Part 9 pdf

collinear relationship when off-line) on one or the other machine case. It is an either–or condition. If you decide to keep the driver stationary, you solve for the moves on the driven machine or vice versa. 11.2 SIXTEEN-POINT METHOD A method similar to the face–rim method called the 16-point method is frequently used on rotating machinery connected together by rigid rather than flexible couplings. The general procedure is illustrated in Figure 11.9. This method is typically used where one shaft is supported in two bearings and the other shaft is supported in one bearing on the outboard end. The coupling flanges have a recessed (rabbeted) fit. The assumption made when performing this technique is that there is only pure angular alignment present (i.e., no centerline offset) and that the flange faces are • PROCEDURE • 1. Attach the alignment bracket firmly to one shaft and position the indicators on the face and diametral surface of the other shaft (or coupling hub). 2. Zero the indicators at the twelve o'clock position. 3. Slowly rotate the shaft and bracket arrangement through 90Њ intervals stopping at the three, six, and nine o'clock positions. Record each reading (plus or minus). 4. Return to the twelve o'clock position to see if the indicator(s) re-zero. 5. Repeat steps 2 through 4 to verify the first set of readings. Rim dial indicator Face dial indicator 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 +45 +72 +27 –31 S –18 0 T B N+13 0 Indicator readings log Rim or peripheral readings Face readings FIGURE 11.1 Face and rim method and procedure. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 370 6.10.2006 12:16am 370 Shaft Alignment Handbook, Third Edition perpendicular to the centerlines of rotation. The flange bolts are loosened, the shafts separ- ated just slightly, insuring that the flange faces are still indexed in the recess, and a series of face readings are taken at four points around the flange faces at the twelve, three, six, and nine o’clock positions. No rim readings are taken. 11.3 TWENTY-POINT METHOD The 20-point method is also frequently used on rotating machinery connected together by rigid rather than flexible couplings. The general procedure is illustrated in Figure 11.10. It is typically used where both shafts are supported in two bearings. The flange bolts are loosened, the shafts separated slightly, and a series of face readings are taken at four points around the flange faces at the twelve, three, six, and nine o’clock positions along with a rim (circumferential) reading typically taken with a dial indicator. For all practical purposes this is the face and rim technique explained earlier. Rather than measure the face readings “Front” side face reading starting “plane” 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 Indicator stem will move outward when it gets to the bottom resulting in a negative (−) reading. 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 “Back” side face reading starting “plane” Indicator zeroed here Indicator stem will get pushed in when it gets to the bottom resulting in a positive (+) reading. r o t a t e FIGURE 11.2 Face readings can be taken on the front or back sides. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 371 6.10.2006 12:16am Face and Rim Methods 371 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 FIGURE 11.3 Taking face readings on different diameters will result in different readings even though the shafts are in the same angular position. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 372 6.10.2006 12:16am 372 Shaft Alignment Handbook, Third Edition 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 R o t a t e R o t a t e R o t a t e R o t a t e FIGURE 11.4 Face readings can be captured on any surface or device rigidly attached to a shaft (assuming the shafts are rotated together). Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 373 6.10.2006 12:16am Face and Rim Methods 373 with a dial indicator, feeler gauge, snap gauge, or an inside micrometer is used to take the face measurements. 11.4 PROBLEMS WITH TAKING FACE READINGS When performing any method where face readings are taken, measurement inaccuracies and inconsistencies can occur if the shafts that are rotated, move toward or away from each other, during the process of capturing the measurements. This can occur very easily if the shafts are supported in sliding or journal-type bearings. The first indication that this is occurring is if the dial indicator (or any measurement sensor) does not return to zero after a 3608 sweep is made. It is therefore suggested that at least two complete sets of readings are taken to see if there is repeatability in the measurements at each 908 location. If the measurements do not repeat within 1–2 mils after two sweeps are made and you suspect that the shafts are indeed moving toward or away from each other, then you can try one of the following three procedures to improve the accuracy of the measurements. 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 FIGURE 11.5 If the shafts are moving axially during the face measurement sweep, indicators can be positioned to observe the axial movement of each shaft to correct each face measurement. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 374 6.10.2006 12:16am 374 Shaft Alignment Handbook, Third Edition FIGURE 11.6 Face measurements being taken on compressor shaft. FIGURE 11.7 Face measurement being taken on brake drum. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 375 6.10.2006 12:16am Face and Rim Methods 375 11.4.1 PRESET THE AXIAL POSITION After the measurement fixtures are attached to the shaft and the dial indicator (or whatever measurement sensor is used) is positioned at the twelve o’clock position, before you zero the indicator, either push the shafts apart or draw them together to seat them against their thrust bearings, then zero the indicator. When each 908 rotation is made during the measurement process again, push the shafts apart (or draw them together if that is what you did initially) to seat them against their thrust bearings, then observe and record your measurement. 11.4.2 COMPENSATE FOR AXIAL MOVEMENT WITH STATIONARY INDICATORS Figure 11.11 shows an alignment fixture attached to the shafts with an indicator taking a face reading. There are two more indicators attached to magnetic bases (or any stationary reference device) observing for axial movement of each shaft. As the shafts are rotated through their 908 arcs, measurements are observed and recorded on all three indicators. Figure 11.12 shows an example of how to compensate for the axial movement observed. 11.4.3 COMPENSATE FOR AXIAL MOVEMENT WITH ROTATING INDICATORS Figure 11.13 shows an alignment fixture attached to the shafts with two indicators taking face readings 1808 apart. During rotation, if the shafts float back or forth, both indicators are affected proportionately. By taking half the algebraic difference between both sets of readings through a 1808 rotation, the axial float that occurred will be canceled out. Figure 11.14 shows an example of how to compensate for the axial movement observed. 11.5 MODELING THE FACE AND RIM METHOD The face and rim method measures an offset and an angle of another shaft’s centerline of rotation with respect to the line of sight of a reference shaft. The offset is measured by the rim Face–rim method mathematics where : A, B, C, D, E = distances shown (in.) H = diameter of face readings (in.) F = face reading difference (from top to bottom or side to side in mils) Y = one half of the rim reading difference (from top to bottom or side to side in mils) Driver Driven Inboard feet of driver Outboard feet of driver F (A + B + C) – (Y) F (B + C) – (Y) H = = H Inboard feet of driven Outboard feet of driven F (D + E) + (Y) FD + (Y) = = H H BC D EA F Y 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 H FIGURE 11.8 Face–rim mathematics for correcting moves on either machine case. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 376 6.10.2006 12:16am 376 Shaft Alignment Handbook, Third Edition indicator and the angle is measured by the face indicator. Similar to the reverse indicator, line to points modeling method described in Chapter 10, one of the shafts is placed directly on the graph paper centerline as a reference and then the other shaft is positioned based on the dial indicator measurements obtained. To graph the face–peripheral method you need to have a clear piece of plastic with a ‘‘T’’ inked onto the plastic similar to what is shown in Figure 11.15. The T bar overlay will represent the shaft where the dial indicators are capturing the readings. The shaft that the bracket is clamped to is the reference shaft and therefore will be drawn onto the graph paper centerline. This technique is typically used for rigid couplings with spigot (recessed) fits commonly found on machinery where one rotor is supported in two bearings and the other rotor is supported by one bearing. Motor Generator 1. Insure the coupling bolts are loose and there is a slight separation (around 20 mils) between the coupling hub faces to prevent any stress or binding force interaction from one shaft to another. 2. Place a reference mark on one (or both) of the shafts, usually at twelve o'clock. 3. Accurately mark off 90° increments on the coupling hubs from the twelve o'clock reference. 4. Use feeler, or taper gauges capable of measuring to 0.001 in. (1 mil) to measure the gaps between the coupling hub faces at these 90° intervals (i.e., both sides, top and bottom). 5. Measure the diameter of the coupling hubs where the gaps were captured. 6. Record each gap reading and rotate both shafts 90°. 7. Capture another set of readings and rotate the shafts 90° again. 8. Repeat step 7 until the reference mark has returned to its original position at twelve o'clock. Procedure Reference mark Feeler or taper, snap, inside mike gauges ? ? FIGURE 11.9 Sixteen-point method and procedure. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 377 6.10.2006 12:16am Face and Rim Methods 377 There are nine pieces of information that you need to properly construct the shaft positions using this technique: 1. Which shaft will the bracket be attached to and on which shaft will the dial indicators be taking readings? 2. The distance from the outboard to inboard feet (bolting planes) of the machine where the bracket is attached. 3. The distance from the inboard bolting plane of the machine where the bracket is attached to the point on the shaft where the bracket is held in place. This technique is typically used for rigid couplings commonly found on machinery where both rotors are supported in two bearings. Steam turbineGenerator 1. Insure the coupling bolts are loose and there is a slight separation (around 20 mils) between the coupling hub faces to prevent any stress or binding force interaction from one shaft to another. 2. Place a reference mark on one (or both) of the shafts, usually at twelve o'clock. 3. Accurately mark off 90° increments on the coupling hubs from the twelve o'clock reference. 4. Attach a bracket or fixture to one shaft and span over to the other shaft to place a dial indicator on the diametral surface or rim of the coupling. Zero the indicator at the twelve o'clock position. 5. Use feeler or taper gauges capable of measuring to 0.001 in. (1 mil) to measure the gaps between the coupling hub faces at these 90° intervals (i.e., both sides, top and bottom). 6. Measure the diameter of the coupling hubs where the gaps were captured. 7. Record each gap reading and rotate both shafts 90°. 8. Capture another set of feeler gauge readings and note the reading on the dial indicator that is now on the side of the coupling hub. Rotate the shafts 90° again. 9. Capture another set of feeler gauge readings and note the reading on the dial indicator that is now on the bottom of the coupling hub. Rotate the shafts 90° again. 10. Capture another set of feeler gauge readings and note the reading on the dial indicator that is now on the other side of the coupling hub. Rotate the shafts 90° again returning the reference mark back to twelve o'clock. Procedure Reference mark Feeler or taper, snap, inside mike gauge ? ? 0 10 20 30 40 50 60 70 80 Q FIGURE 11.10 Twenty-point method and procedure. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 378 6.10.2006 12:16am 378 Shaft Alignment Handbook, Third Edition 0 50 10 40 20 30 + _ 10 40 20 30 0 5 0 1 0 4 0 2 0 3 0 + _ 1 0 4 0 2 0 3 0 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 5 0 1 0 40 2 0 3 0 + _ 1 0 4 0 2 0 3 0 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 5 0 1 0 4 0 2 0 3 0 + _ 1 0 4 0 2 0 3 0 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 50 10 40 20 30 + _ 10 40 20 30 0 5 0 1 0 4 0 2 0 3 0 + _ 1 0 4 0 2 0 3 0 Compensating for axial shaft float when capturing face readings Why is this important? Rotating machinery that is supported in sliding type bearings is designed to move somewhat freely in the axial direction. The amount of axial travel is restrained by thrust bearings or by electromagnetic forces. The amount of axial float varies from machine to machine but can be as little as 20 mils (0.020 in.) and as much as a half inch or more such as found on medium to large (i.e., 500 hp+) electric motors. If you plan on using the face–rim alignment measurement method for shaft alignment purposes, you must compensate for any axial movement that occurs during the shaft alignment measurement process. 1. Attach the alignment bracket to either one of the shafts, place a dial indicator at the twelve o’clock position on the other shaft or coupling hub face as shown insuring the dial indicator is at mid-travel on the stem. Anchor a magnetic base (or other stationary fixture) to the machine case (or any stationary object), place a dial against the coupling hub, end of the shaft, or anything attached to the shaft where the indicator can observe any axial displacement during rotation. If both shafts can move in the axial direction, a magnetic base and indicator must be positioned on both shafts as shown. Zero all the indicators and prepare a measurement recording sheet. 2. Rotate both shafts through a 90° rotation. Carefully observe each indicator during rotation noting if the stem is being pushed in (i.e., clockwise needle rotation, aka positive readings) or if it is traveling outward (i.e., counterclockwise needle rotation, aka negative readings). Stop after the 1/4 turn has been achieved and record the measurement on every dial indicator. 3. Again, rotate both shafts through a 90° rotation carefully observe each indicator during rotation noting if the stem is being pushed in or if it is traveling outward. Stop after the 1/4 turn has been achieved and record the measurement on every dial indicator. 4. If possible, again, rotate both shafts through a 90° rotation carefully observe each indicator during rotation, stop after the 1/4 turn has been achieved and record the measurement on every dial indicator. (Also see Section 6.10.) Magnetic base Axial movement Axial movement Captures ‘face’ measurements for shaft alignment purposes Measures any axial movement that occurs during rotation 4 3 2 1 R o t a t e R o t a t e R o t a t e R o t a t e R o t a t e R o t a t e R o t a t e R o t a t e FIGURE 11.11 Compensate for axial movement with stationary indicators. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 379 6.10.2006 12:16am Face and Rim Methods 379 [...]... correct the misalignment condition (i.e., bring the shafts into a collinear relationship when off-line) on one or the other machine case 397 Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C013 Final Proof page 398 398 26 .9. 2006 8:56pm Shaft Alignment Handbook, Third Edition 01 _ + 0 01 02 10 _ 0 + 02 03 10 03 04 05 04 20 20 30 30 40 50 40 Driver Driven • Procedure • 1 Attach the alignment bracket(s)... centerline of the coupling spool (jackshaft or drive shaft) Since there is only one flex point at the end of each shaft, near FIGURE 13.2 Shaft to coupling spool method used on cooling tower fan drive with bracket attached to motor shaft and indicator taking reading on spool Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C013 Final Proof page 399 Shaft to Coupling Spool Method 26 .9. 2006 8:56pm... line of sight (i.e., the centerline of rotation) of the other shaft Draw a straight line through these two points from the coupling end to the outboard end of the other shaft Figure 12.8 and Figure 12 .9 show an example of both the side and top view alignment models of a motor and a fan where double radial readings were taken Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C012 Final Proof... 196 9 Dodd, V.R., Total Alignment, Petroleum Publishing Company, Tulsa, OK, 197 5 Doeblin, E., Measurement Systems: Application and Design, Mc-Graw Hill Book Company, 197 5 Dreymala, J., Factors Affecting and Procedures of Shaft Alignment, Technical and Vocational Department, Lee College, Baytown, TX, 197 0 Durkin, T., Aligning shafts, Part I—Measuring misalignment, Plant Engineering, January 11, 197 9 King,... amounts of misalignment Therefore, shaft alignment measurements should never be taken across an engaged rigid coupling On the vertical pump shown in Figure 12.4 and Figure 12.5, the rigid coupling between the motor and pump shafts must be disengaged to relieve any bending stresses due to a misalignment 3 89 Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C012 Final Proof page 390 390 26 .9. 2006... 8:56pm 399 FIGURE 13.3 Shaft to coupling spool method used on cooling tower fan drive with bracket attached to gear input shaft and indicator taking reading on spool FIGURE 13.4 Shaft to coupling spool method employed on gear coupling with measurements taken on the spacer (spool) Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C013 Final Proof page 400 400 26 .9. 2006 8:56pm Shaft Alignment Handbook, ... Alignment Handbook, Third Edition DK4322_C012 Final Proof page 396 26 .9. 2006 8:56pm Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C013 Final Proof page 397 13 26 .9. 2006 8:56pm Shaft to Coupling Spool Method There are situations where two pieces of rotating machinery are positioned a considerable distance apart; and trying to employ the alignment techniques shown in chapters 10, 11, or 12 would... misalignment condition (i.e., bring the shafts into a collinear relationship when off-line) on one or the other machine case FIGURE 12.4 Double radial method used on vertical motor and pump, with indicator measuring the near position with a dial indicator Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C012 Final Proof page 392 392 26 .9. 2006 8:56pm Shaft Alignment Handbook, Third Edition FIGURE... Accurately scale the distances along the length of the drive train onto the graph centerline as shown in Figure 12.7 Fan 10" 4" Side view Up 94 " Fan 20 in FIGURE 12.7 Dimensional information needed for plotting double radial measurements Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C012 Final Proof page 394 394 26 .9. 2006 8:56pm Shaft Alignment Handbook, Third Edition The procedure for plotting... input shaft that could not be rotated Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C012 Final Proof page 391 26 .9. 2006 8:56pm Double Radial Method 391 FIGURE 12.3 Double radial method used between an output shaft of a gear, which could be rotated with an indicator measuring the ‘‘far’’ position on a gear input shaft which could not be rotated on the pump housing As the motor shaft can . Procedures of Shaft Alignment, Technical and Vocational Depart- ment, Lee College, Baytown, TX, 197 0. Durkin, T., Aligning shafts, Part I—Measuring misalignment, Plant Engineering, January 11, 197 9. King,. diameter of the face readings onto the top of the T bar overlay. Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C011 Final Proof page 384 6.10.2006 12:16am 384 Shaft Alignment Handbook, . coupling alignment, Plant Engineering, June, 92 95 , 195 2. Yarbrough, C.T., Shaft Alignment Analysis Prevents Shaft and Bearing Failures, Westinghouse Engineer, May 196 6, pp. 78–81. Piotrowski / Shaft