Handbook Of Shaft Alignment Episode 3 Part 2 pot

18.10 MEASURING THE MISALIGNMENT AT THE SHEAVESTo measure the amount of offset, pitch, and skew that exists between the shafts and theirsheaves, measurements with a straightedge need to

conditions as shown in the lower illustration in Figure 18.17 Adjustments to the machinesmay therefore require precise, controlled moves in the vertical, lateral, and axial directions.

18.9 USING A STRAIGHTEDGE TO MEASURE MISALIGNMENT

Belt and sheave driven equipment poses a slightly different type of alignment problem thanequipment directly coupled together The basic objective is to insure that the shaft centerlinesare parallel to each other

FIGURE 18.12 Rim runout check on sheave

For decades, the most widely used alignment tool is either a string or a straightedge Todaythere are far more elaborate ways to perform belt–sheave alignment as shown later in thischapter, but most often, acceptable belt alignment can be accomplished using a simplestraightedge Bear in mind that most manufacturers of belt and sheave drives suggest thatthe sheaves should be aligned to within 1=8 in per foot distance between shaft centerlines.That is about 11 mils=in., much more forgiving that direct drive systems, which are typicallyaligned to around 1 mil=in.

FIGURE 18.13 Face runout check on sheave

Straightedges work fine for distances under 4 ft but when the distance between the drivershaft and the driven shaft begin to exceed that, a string should probably be used One tooldeveloped by Max Roeder called the A-String works extremely well and produces very accurateresults shown in Figure 18.18 and Figure 18.19 The A-String has an adjustable basethat enables one to compensate for centerline offset of sheaves as shown in Figure 18.20 Toproperly align sheaves, you must compensate for any difference in the actual center of the V ineach sheave Measure the width of the groove; then measure the flange outer thickness on eachsheave to determine what the offset may have to be if the outer flange widths are not the same.

FIGURE 18.14 Rim runout check on sheave

FIGURE 18.15 Face runout check on sheave.

FIGURE 18.16 Bent sheave

18.10 MEASURING THE MISALIGNMENT AT THE SHEAVES

To measure the amount of offset, pitch, and skew that exists between the shafts and theirsheaves, measurements with a straightedge need to be taken at two different places on theouter surface of the sheaves as shown in Figure 18.21 Measure the distances across eachsheave at the upper and lower gap measurement locations Determine what type of gapcondition you have based on the four different configurations shown in Figure 18.22 Usingfeeler gauges, measure and record the amount of the gaps (in mils) between the straightedgeand the surface of the sheaves as shown in Figure 18.23 and Figure 18.24

18.11 V-BELT MACHINE MEASUREMENTS

In addition to the gap measurements taken on the sheaves as shown in Figure 18.21 throughFigure 18.24, dimensional measurements of the two machines need to be taken as shown in

Offset—the shafts are parallel to each other and in the X−Y plane but one

shaft/sheave is to the right of left of the other shaft/sheave in the Y direction

Pitch—the shafts are in the X−Y plane

but one shaft/sheave is rotated through the Z-axis

Skew—the shafts are not in the same plane and one shaft/sheave is rotated through the X-axis

X Y Z

Combination—this is the most common type of misalignment condition (and the most complex) where the shafts are not in the same plane and one shaft/sheave

is rotated through both the

X-and Z-axis

FIGURE 18.17 (See color insert following page 322.) Types of belt and sheave misalignment conditions

Figure 18.25 A recording sheet shown in Figure 18.26 can be used to record all the requiredinformation to generate an alignment model of the misalignment condition.

18.12 MODELING V-BELT ALIGNMENT PROBLEMS

Alignment models can also be used to visualize the misalignment condition on belt and sheavedrive equipment You will have to generate two different views of your drive system One viewwill be generated from above (i.e., the top view), which will show any offset and pitchconditions between the two sheaves The end view will show any offset and skew conditionsthat exist between the two sheaves You can use two T-bar overlays (see Face–Rim graphingmethod on Chapter 11) to represent each shaft=sheave

FIGURE 18.18 A-String sheave alignment tool

18.13 V-BELT ALIGNMENT MODELING SAMPLE PROBLEM

Figure 18.27 shows an electric motor driving a fan The critical dimensions needed to generate

an alignment model of this drive system are shown in Figure 18.27 Use one of the T-baroverlays to scale off the distance from the inboard-to-outboard bolts of the motor (15 in.) andthe distance from the inboard bolt of the motor to the edge of the sheave where the straight-edge measurements are taken (5 in.) On the top of the T-bar overlay, scale off the 6 in.distance to represent where the straightedge gaps or contact point were measured Similarlyfor the fan, use the other T-bar overlay to scale off the distance from the inboard-to-outboardbolts of the fan (12 in.) and the distance from the inboard bolt of the fan to the edge of thesheave where the straightedge measurements are taken (4 in.) On the top of the T-baroverlay, scale off the 8 in distance to represent where the straightedge gaps or contact pointswere measured

FIGURE 18.19 A-String sheave alignment tool

Figure 18.28 shows the top view of the motor and fan shafts Notice that you want to pitcheach T-bar overlay at the midpoint between the gap you measured at the top of each sheave andthe gap you measured at the bottom of each sheave In the case of the motor sheave gaps,the upper gap was 10 mils and the lower gap was 16 mils (10þ 16 mils ¼ 26 mils; 26 mils=2 ¼

13 mils, i.e., the midpoint) In the case of the fan sheave gaps, the upper gap was 26 mils and thelower gap was 8 mils (26þ 8 mils ¼ 34 mils; 34 mils=2 ¼ 17 mils, i.e., the midpoint) Notice

that the motor shaft and fan shaft are not parallel to each other

Figure 18.29 shows the end view of the motor and fan shafts In this view, the motor istoward us and the fan is away from us Also notice that in this particular case, the distancefrom the upper to lower straightedge measurements on the motor was 6 in., the same distancethe straightedge measurements were taken from the inboard-to-outboard edge of the motor

as shown in the top view If the distance from the upper to lower straightedge measurements isnot the same as it was between the inboard and outboard edges, you must scale off whateverthe upper to lower straightedge measurements actually were when viewing the shafts andsheaves in the end view Again, notice that you want to pitch each T-bar overlay at themidpoint between the gap you measured at the top (upper edge) of each sheave and the gapyou measured at the bottom (lower edge) of each sheave In the case of the motor sheave gaps,the upper gap was 10 mils and the lower gap was 16 mils The midpoint at the upper edge ofthe motor sheave is 5 mils, and the midpoint at the lower edge of the motor sheave is 5 mils.The T-bar for the motor should be pitched to intersect the midpoint at its upper and lower

Sheave outer flange width

is different

FIGURE 18.20 Measuring centerline offset of sheaves

points In the case of the fan sheave gaps, the upper gap was 26 mils and the lower gap was

8 mils The midpoint at the upper edge of the fan sheave is 13 mils, the midpoint at the loweredge of the fan sheave is 4 mils The T-bar for the fan should be pitched to intersect themidpoint at its upper and lower points

Why do we position the T-bar overlays at the midpoints of the gaps? Because the actualcenterline of rotation is midway between the 6 in (on the motor) and 8 in (on the fan)measurement points where the straightedge was positioned on each sheave Graphically,the top of the T-bar overlay is represented as a straight line When viewing the sheavesfrom the top or end views, the sheaves would actually appear as ellipses

Straightedge

inches inches

inches

inches

Straightedge

Sheave measurement distances with straightedge in upper position

Sheave measurement distances with straightedge in lower position

Upper to lower straightedge separation distances across each sheave

FIGURE 18.21 Measure the gap conditions on the sheaves at two different locations

FIGURE 18.22 Four possible gap conditions.

Upper position gap readings

_ mils _ mils

_ mils _ mils

_ mils _ mils

_ mils _ mils

Determine where the straightedge is touching on each sheave Measure and record the gaps on each sheave in one of the four conditions below.

Touching or gap?

FIGURE 18.23 Measure the gap conditions at the top of the sheaves

Lower position gap readings

_ mils _ mils

_ mils _ mils

_ mils _ mils

_ mils _ mils

Determine where the straightedge is touching on each sheave Measure and record the gaps on each sheave in one of the four conditions below.

• Measure the distance between the shaft centerlines

Measure the dimensions of the machinery

FIGURE 18.25 Dimensional measurements of the machines

To correct the misalignment (i.e., nonparallelism) between the motor and fan shafts in thetop view, the next step would be to determine the allowable lateral movement envelope onboth machines That is, how much room is there between the foot bolts and the holes on themotor and the fan in the north to south direction? You will have to remove the foot bolts atthe inboard and outboard end of each machine, look down the hole and see how much room

Lower position gap readings Upper position gap readings

Machine name _

_ mils _ mils

_ mils _ mils

_ mils _ mils

_ mils _ mils

_ mils _ mils

V-belt /Sheave • Alignment recording sheet

Measure the distance between the

outboard and inboard bolts of both

machines

Measure the distance from the inboard

feet to where the straightedge will be

placed to capture the gap readings on

in upper position

Sheave measurement distances with straightedge

in lower position Upper to lower straightedge

is there to move each machine north to south before you get bolt bound As shown in many ofthe alignment modeling examples in Chapter 8 and Chapter 10 through Chapter 14, super-impose these boundary conditions on the alignment model at the machinery feet on themotor and fan, then position the motor T-bar and the fan T-bar to bring the top of eachT-bar into a straight line (i.e., position the centerlines so they are parallel to each other).Figure 18.30 shows one possible alignment solution in the top view Figure 18.31 shows onepossible alignment solution in the end view.

18.14 LASER ALIGNMENT SYSTEMS FOR V-BELTS AND SHEAVES

Around 1998, several companies began to develop laser alignment systems for V-belt drives.There are two different approaches that these manufacturers have taken One method is toattach the laser to the outer surface of one of the sheaves and project the laser beam toward

Upper gap = 26 mils

Lower gap = 8 mils Midpoint = 17 mils

Upper gap = 10 mils

Lower gap = 16 mils Midpoint = 13 mils

East Top view

Motor end view

Looking south from motor end Up

Upper fan gap = 26 mils

Upper straightedge position measurement plane on fan

Lower straightedge position measurement plane on motor

Lower straightedge positio n measurement plane on fa n

2 in.

or 20 mils

Upper motor gap = 10 mils

Upper fan midpoint

Lower fan gap = 8 mils

Lower motor midpoint Lower motor gap = 16 mils

Lower fan midpoint

FIGURE 18.29 End view of motor and fan shafts

Bolt hole boundary conditon

visual sighting targets attached at different points on the other sheave The laser and thetarget are held in place with magnets Figure 18.32 through Figure 18.35 show systems thatuse this approach.

FIGURE 18.31 Possible alignment corrections for the motor and fan in the end view

FIGURE 18.32 Dotline laser system (Courtesy of Ludeca Inc., www.ludeca.com, Doral, FL Withpermission.)

FIGURE 18.33 SheaveMaster system (Courtesy of Ludeca Inc., www.ludeca.com, Doral, FL Withpermission.)

FIGURE 18.34 D200 BTA Digital system (Courtesy of Damalini AB, Molndal, Sweden With permission.)

The other approach is to position the laser into the grooves of one of the sheaves and aphotodiode target into the grooves of the other sheave Figure 18.36 and Figure 18.37 showsystems that use this approach.

FIGURE 18.35 D80 BTA Compact system (Courtesy of Damalini AB, Molndal, Sweden With permission.)

FIGURE 18.36 Belt Hog (Courtesy of VibrAlign Inc., Richmond, VA With permission.)

Max Roeder, A-String User Guide, Max Roeder Consulting Inc

Power Transmission Belt Drives—Installation, Maintenance & Troubleshooting Guide, Goodyear Tire &Rubber Co., publication number 575000-3=86

FIGURE 18.37 S600 system (Courtesy of Hamar Laser Instrument Co., Danbury, CT Withpermission.)

19 Bore Alignment

The alignment of rotating machinery shafts, as discussed in the previous chapters, trates on measuring the centerline of rotation of one shaft with respect to another shaft Theseshafts are usually solid cylinders of various lengths supported by a bearing at each end Theposition of the two bearings that support each shaft dictates the location of that shaft’scenterline of rotation If we are aligning two shafts, each of which is supported in twobearings, then the goal is to align the centers of all four bearings in the two shafts Therefore,shaft alignment and bearing alignment both really mean the same thing

concen-If the shafts were made out of a perfectly clear, transparent material (e.g., glass), we couldthen visually look down the centers of the transparent shafts from each end and observe if thecenters of the supporting bearings were collinear Figure 19.1 shows what you might seeassuming that your line of sight was coincident with both centerlines of rotation

But on the other hand the shafts of machinery are not made out of a transparent material and

we cannot look straight down the centers of the shafts Consequentially, to find the centerline

of rotation of these shafts, we have to observe a point at a fixed distance from the centerline—typically the outer surface of the shaft All of the tools and methods used to perform shaftalignment as shown in Chapter 10 through Chapter 15 are based on this premise

What if we want to align two hollow cylinders with each other where we could look downthe center of the cylinders? What if these hollow cylinders could not rotate? What if onecylinder could rotate but the other could not?

19.1 ALIGNING A ROTATING SHAFT WITH A STATIONARY

HOLLOW CYLINDER

Figure 19.2 shows an electric motor and a hollow cylinder The electric motor will eventuallydrive a screw that is placed inside the barrel (i.e., hollow cylinder) The screw is used to move aviscous material down through the barrel and is expelled at the discharge end of the barrelunder pressure Drive systems of this type are called extruders and are used extensively in thefood and plastics industry In some cases, the motor directly drives the screw, in other cases,the motor is flexibly coupled to the input shaft of a gearbox and the output shaft of thegearbox drives the screw It is not uncommon to have only 5–20 mils of clearance betweenthe blades of the screw and the bore of the barrel so any misalignment between the drive shaftand the screw will cause the screw to drag against the inside of the barrel wearing away boththe screw and the bore of the barrel Frequently, the screw is not supported in bearings and theviscous material, under pressure, will act to force the screw to the center of the barrel

To align the drive shaft with the barrel, the screw is removed so that one can visually sightdown the barrel to the end of the drive shaft The goal is to align the centerline of rotation ofthe motor shaft with the centerline of the bore of the barrel Understand that it is possible toalign the centerline of the bore of the barrel to the center of the end of the shaft and still have amisalignment problem as shown in Figure 19.3

619