Handbook of Shaft Alignment Part 9 pdf

with a dial indicator, feeler gauge, snap gauge, or an inside micrometer is used to take theface measurements.11.4 PROBLEMS WITH TAKING FACE READINGS When performing any method where fac

collinear relationship when off-line) on one or the other machine case It is an either–orcondition If you decide to keep the driver stationary, you solve for the moves on the drivenmachine or vice versa.

11.2 SIXTEEN-POINT METHOD

A method similar to the face–rim method called the 16-point method is frequently used onrotating machinery connected together by rigid rather than flexible couplings The generalprocedure is illustrated in Figure 11.9

This method is typically used where one shaft is supported in two bearings and the othershaft 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 onlypure 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 90

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

+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

perpendicular to the centerlines of rotation The flange bolts are loosened, the shafts ated just slightly, insuring that the flange faces are still indexed in the recess, and a series offace readings are taken at four points around the flange faces at the twelve, three, six, and nineo’clock positions No rim readings are taken.

“Front” side face reading starting “plane”

Indicator stem will get pushed in when it gets to the bottom resulting in a positive (+) reading.

with a dial indicator, feeler gauge, snap gauge, or an inside micrometer is used to take theface measurements.

11.4 PROBLEMS WITH TAKING FACE READINGS

When performing any method where face readings are taken, measurement inaccuracies andinconsistencies 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 aresupported 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 twocomplete 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 madeand you suspect that the shafts are indeed moving toward or away from each other, then youcan try one of the following three procedures to improve the accuracy of the measurements

40 20 30

+ 10

40 20 30

FIGURE 11.6 Face measurements being taken on compressor shaft.

FIGURE 11.7 Face measurement being taken on brake drum

11.4.1 PRESET THEAXIAL POSITION

After the measurement fixtures are attached to the shaft and the dial indicator (or whatevermeasurement sensor is used) is positioned at the twelve o’clock position, before you zero theindicator, either push the shafts apart or draw them together to seat them against their thrustbearings, then zero the indicator When each 908 rotation is made during the measurementprocess again, push the shafts apart (or draw them together if that is what you did initially) toseat them against their thrust bearings, then observe and record your measurement

11.4.2 COMPENSATE FORAXIAL MOVEMENT WITHSTATIONARYINDICATORS

Figure 11.11 shows an alignment fixture attached to the shafts with an indicator taking a facereading There are two more indicators attached to magnetic bases (or any stationaryreference device) observing for axial movement of each shaft As the shafts are rotatedthrough 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 FORAXIAL MOVEMENT WITHROTATINGINDICATORS

Figure 11.13 shows an alignment fixture attached to the shafts with two indicators taking facereadings 1808 apart During rotation, if the shafts float back or forth, both indicators areaffected proportionately By taking half the algebraic difference between both sets of readingsthrough 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 ofrotation with respect to the line of sight of a reference shaft The offset is measured by the rim

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)

=

= H

H

FIGURE 11.8 Face–rim mathematics for correcting moves on either machine case

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 thegraph paper centerline as a reference and then the other shaft is positioned based on the dialindicator 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 willrepresent the shaft where the dial indicators are capturing the readings The shaft thatthe bracket is clamped to is the reference shaft and therefore will be drawn onto the graphpaper 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.

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 taper, snap,Feeler or

inside mike gauges

?

?

FIGURE 11.9 Sixteen-point method and procedure

There are nine pieces of information that you need to properly construct the shaft positionsusing this technique:

1 Which shaft will the bracket be attached to and on which shaft will the dial indicators betaking readings?

2 The distance from the outboard to inboard feet (bolting planes) of the machine wherethe bracket is attached

3 The distance from the inboard bolting plane of the machine where the bracket isattached to the point on the shaft where the bracket is held in place

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 50 60 80 Q

FIGURE 11.10 Twenty-point method and procedure

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.

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.

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

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

32

movement

Axial movement

0

− 38

Axial movement

rule is not working here

4 The distance from where the bracket is held in place to the point on the other shaftwhere the dial indicators are capturing the face and rim readings.

5 The distance from where the dial indicators are capturing the face and rim readings tothe inboard bolting plane of that machine

1 Zero both indicators here.

3 Observe and record both indicator measurements.

2 Rotate shafts 180 °

C = Side A reading at start

D = Side B reading at start

E = Side A reading at finish

F = Side B reading at finish

(((C) + (E)) + ((D) − (F)))/2 = axial float compensated reading from Side A to Side B

Ro

ta

R o

ta

FIGURE 11.13 Compensate for axial movement with rotating indicators

6 The distance from the inboard to outboard feet (bolting planes) of the machine wherethe dial indicators are capturing the readings.

7 The diameter on which the face readings are being taken

8 Whether the face readings are being taken on the ‘‘front’’ or ‘‘back’’ side of the couplinghub or face measurement surface Refer to Figure 11.2

9 The eight dial indicator readings taken at the top, bottom, and both sides of the rim andface measurement points

Scale the distances onto a piece of graph paper and scale the diameter of the face readingonto the T bar overlay as shown in Figure 11.16 and Figure 11.17 The top part of the ‘‘T’’represents the face of the shaft you are taking readings on and the base of the ‘‘T’’ representsthe centerline of rotation of the shaft

In this method, you dual scale the graph In other words, whatever scale factor you usefrom left to right to scale the dimensions along the length of the machinery, that same scalefactor is used from top to bottom on the graph to scale the diameter the face readings weretaken on when you transfer this dimension to the top of the T on the T bar overlay Likewise,

1 Zero both indicators here.

3 Observe and record both indicator measurements.

2 Rotate shafts 180
.

C = Side A reading at start

D = Side B reading at start

E = Side A reading at finish

F = Side B reading at finish

(((C) + (F)) + ((D) − (E)))/2 = axial float compensated reading from Side A to Side B

(((0) + (+14)) + ((0) − ( − 10)))/2 = ((+14) + (+10))/2 = +24/2 = +12

Note: If the readings are taken from top to bottom, readings D and E must be compensated

for face sag.

Side A

Side B

0

0 Starting readings

Side A

Side B

− 10

+14 Finish readings

Axial movement

ta

FIGURE 11.14 Example of compensating for axial movement with rotating indicators

whatever scale factor you select to exaggerate the misalignment condition for the rim readingsfrom top to bottom on the graph, that same scale factor is used from left to right on the graphwhen pitching or rotating the T bar overlay to reflect the face reading you observed Insurethat you use the same scale factor (inches) for both the machine dimensions and face diameterand the same scale factor (mils) for the rim and face measurements.

The procedure for plotting the face–rim technique is as follows:

1 Draw the shaft where the alignment bracket is attached directly on top of the graphcenterline

2 Next, position the clear T bar overlay to reflect the readings captured on the rim orperimeter of the other shaft If the bottom (or side) rim reading was negative, slide the

T bar toward the top of the graph paper so that the base of the T is one-half of the rimreading from the graph centerline If the bottom (or side) rim reading was positive, slidethe T bar toward the bottom of the graph paper so that the base of the T is one-half ofthe rim reading from the graph centerline

3 Pivot the T bar overlay to reflect the face readings captured There are several ways toaccomplish this You could pivot or rotate the T bar from the upper point on the top ofthe T bar where the dial indicator was zeroed and move the bottom point This is

Face peripheral and right angle drive overlay line (copy to clear transparency)

Ten divisions per inch

FIGURE 11.15 The T bar overlay (50% scale)

referred to as a ‘‘top pivot.’’ You could pivot where the base and top of the T intersectand pivot half way at the top or bottom point often referred to as a ‘‘center pivot,’’ oryou could pivot from the lower point of the T bar and move the top point often referred

Figure 11.19 and Figure 11.20 show an example of both the side and top view alignmentmodels of a motor and a pump where face–rim readings were taken.

An inexpensive device that uses the T bar overlay principle has been available commerciallysince 1973 (developed earlier at an oil refinery on the Dutch Caribbean island of Aruba)

‘‘The machinery alignment plotting board,’’ shown in Figure 11.21, is an 8.5’’ 11’’ laminated

plastic graph, with reusable plastic overlay which slides and pivots in a groove for easypositioning It can be used for face–rim, reverse indicator, and other setups, with anylegitimate indicator and bracket configuration It can also be used for two element moveplots (see references)

11.6 ARTIFICIAL FACE SURFACE

In the event that you are unable to rotate one shaft and there is not a good face surface to takemeasurements on, one idea is to temporarily provide a face reading surface by fabricating asplit disk arrangement that can be clamped onto the outer diameter of a shaft and thenremoved after the alignment is complete Figure 11.22 shows an arrangement being tested forthis purpose

sag

− 8

− 2 0

− 20

− 25 +25 0

0 T

− 22

− 26 0 T

B 0

(taken on a 6 in diameter)

Zero this side

Field readings

FIGURE 11.18 Face–rim field and compensated measurements for Figure 11.19 and Figure 11.20

Motor Side view Up Pump

Scale:

Pump shaft centerline

Plot half of the sag

Motor shaft centerline

Pitch the T bar so the full face reading ( − 20 mils) is plotted here across a 6 in diameter.

+30

− 20

−25 +25

0

0 T

B

0 Compensated readings

FIGURE 11.19 Face–rim side view example alignment model

Scale:

Pump shaft centerline

Plot half of the south rim reading ( − 16 mils) here.

Motor shaft centerline

Pitch the T bar so

the full face reading

0

+94

+31 -63

-32

+5 +25

+30

− 20

-25 +25

0

0 T

B

0 Compensated readings

FIGURE 11.20 Face–rim top view example alignment model

FIGURE 11.21 Murray & Garig Machinery Alignment Plotting Board.

FIGURE 11.22 Artificial face split disk system (Courtesy of Murray & Garig Tool Works, Baytown, TX.)

Dodd, V.R., Total Alignment, Petroleum Publishing Company, Tulsa, OK, 1975.

Doeblin, E., Measurement Systems: Application and Design, Mc-Graw Hill Book Company, 1975.Dreymala, J., Factors Affecting and Procedures of Shaft Alignment, Technical and Vocational Depart-ment, Lee College, Baytown, TX, 1970

Durkin, T., Aligning shafts, Part I—Measuring misalignment, Plant Engineering, January 11, 1979.King, W.F and Peterman, J.E., Align shafts, not couplings, Allis Chalmers Electrical Review,2nd Quarter, 26–29, 1951

Murray, M.G., Machinery Alignment Plotting Board, U.S Patent # 3,789,507, 1973

Murray, M.G., Choosing an alignment measurement setup, Murray & Garig Tool Works, Baytown,

TX, personal correspondence, October 12, 1979

Murray, M.G., Alignment Manual for Horizontal, Flexibly Coupled Rotating Machines, 3rd ed., Murray

& Garig Tool Works, Baytown, TX, April 21, 1987

Nelson, C.A., Orderly steps simplify coupling alignment, Plant Engineering, June, 176–178, 1967.Piotrowski, J.D., Alignment Techniques, Proceedings Machinery Vibration Monitoring and AnalysisMeeting, June 26–28, 1984, New Orleans, LA, Vibration Institute, Clarendon Hills, IL.Samzelius, J.W., Check points for proper coupling alignment, Plant Engineering, June, 92–95, 1952.Yarbrough, C.T., Shaft Alignment Analysis Prevents Shaft and Bearing Failures, Westinghouse Engineer,May 1966, pp 78–81

12 Double Radial Method

This relatively unknown method has some distinct advantages compared to the othermethods discussed in chapters 10,11,13,14, and 15 The procedure is shown in Figure 12.1.This method should only be used if there is at least a 3 in or greater separation between thenear and far indicator measurement positions The accuracy of this technique increases as thedistance between reading points increases The disadvantage of this method is that there isusually not enough shaft exposed to be able to spread the indicators far enough apart to meritusing the method except for very special circumstances

. If the machinery is supported in sliding type bearings and the shafts are ‘‘floating’’ back

or forth axially when rotating the shaft to capture readings, there is virtually no effect onthe accuracy of the readings being taken

. Can be setup to measure inner circular surfaces such as the bore of a barrel

Disadvantages

. Not enough shaft surface is exposed to spread the readings far enough apart for able accuracy

accept-. Bracket sag must be measured and compensated for

Although it has not been mentioned up to this point in the book, any of the alignmentmeasurement methods shown in Chapter 10 through Chapter 15 can be used on shaftsoriented in horizontal positions but also on shafts in vertical positions Figure 12.4 andFigure 12.5 show the double radial method being used on a vertically oriented motor andpump In this particular case, the motor and pump shafts are connected together using a rigidcoupling rather than a flexible one

For a moment, refer to Figure 1.3 and Figure 6.41, which show how under moderate tosevere misalignment conditions, the shafts will start elastically bending As discussed inChapter 6, elastic bending occurs on both rigid and flexible couplings On rigid couplingsthe elastic bending will begin with just small amounts of misalignment Therefore, shaftalignment measurements should never be taken across an engaged rigid coupling On thevertical pump shown in Figure 12.4 and Figure 12.5, the rigid coupling between the motorand pump shafts must be disengaged to relieve any bending stresses due to a misalignment

389

condition The pump shaft, which is supported by the thrust bearing on top of the motor, dropsdown and is physically centered in its upper bushing using feeler gauges or wedges Once this

is done, the pump shaft should not be rotated to prevent damaging the impeller from dragging

2 Zero the indicator(s) at the twelve o’clock position.

3 Slowly rotate the shaft and bracket arrangement

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 step 2 through step 4 to verify the first set

FIGURE 12.1 Double radial method and procedure

FIGURE 12.2 Double radial method used between an output shaft of a gear, which could be rotatedwith an indicator measuring the ‘‘near’’ position on a gear input shaft that could not be rotated

on the pump housing As the motor shaft can still be rotated and there is a significant distance

of pump shaft exposed, the double radial method is a good choice for this alignment situation

12.1 BASIC MATHEMATICAL EQUATIONS FOR THE DOUBLE

RADIAL METHOD

Figure 12.6 shows the mathematical relationship between the machinery dimensions and thedial indicator readings captured using the double radial method The equations will solve forthe moves that need to be made to correct the misalignment condition (i.e., bring the shaftsinto a collinear relationship when off-line) on one or the other machine case

FIGURE 12.3 Double radial method used between an output shaft of a gear, which could be rotatedwith an indicator measuring the ‘‘far’’ position on a gear input shaft which could not be rotated

FIGURE 12.4 Double radial method used on vertical motor and pump, with indicator measuring thenear position with a dial indicator

FIGURE 12.5 Double radial method used on vertical motor and pump, with indicator measuring the farposition with a dial indicator.

side to side in mils)

side to side in mils)

Note: Readings N and F must be sag compensated readings.

12.2 MODELING THE DOUBLE RADIAL METHOD

The basic measurement principle of the double radial technique is to capture two (or more ifdesired) circumferential readings at different points along the length of a shaft

There are six pieces of information that you need to properly construct the shaft positionsusing this technique:

1 The distance from the outboard-to-inboard feet (bolting planes) of the first machine

2 The distance from the inboard bolting plane of the first machine to the point on the shaftwhere the bracket is located on the first machine

3 The distance from where the near dial indicator is capturing the rim readings on thesecond machine to the point where the far dial indicator is capturing the rim readings onthe second machine

4 The distance from where the far dial indicator is capturing the rim readings on thesecond machine to the inboard bolting plane of the second machine

5 The distance from the inboard-to-outboard feet (bolting planes) of the second machine

6 The eight dial indicator readings taken at the top, bottom, and both sides on both shaftsafter compensating for sag (i.e., what a perfect, ‘‘no sag’’ bracket system would havemeasured) Be aware of the fact that there will probably be two different sag amounts ateach of the dial indicator locations

Accurately scale the distances along the length of the drive train onto the graph centerline

FIGURE 12.7 Dimensional information needed for plotting double radial measurements

The procedure for plotting the double radial technique is as follows:

1 Draw the shaft where the bracket is clamped on top of the graph centerline

2 Start with the top to bottom or side-to-side dial indicator readings on the other shaft(i.e., the one you did not draw on the graph centerline)

3 Plot the other shaft centerline position by starting at the intersection of the graphcenterline and the point where the near dial indicator was capturing the readings

on the other shaft If the bottom (or side) reading was negative, place a point half ofthe bottom (or side) readings from the graph centerline toward the top of the graph

If the bottom (or side) reading was positive, place a point half of the bottom (or side)readings from the graph centerline toward the bottom of the graph (the same as in thepoint-to-point modeling techniques) Do not draw any lines yet

4 Next, start at the intersection of the graph centerline and the point where the far dialindicator was capturing the readings on the shaft If the bottom (or side) reading wasnegative, place a point half of the bottom (or side) readings from the graph centerlinetoward the bottom of the graph If the bottom (or side) reading was positive, place apoint half of the bottom (or side) readings from the graph centerline toward the top ofthe graph (opposite of the point-to-point modeling technique)

Up Side view

+10

− 36 +16

Sag compensated readings