Engine Alignment

PrinciplesTo provide the necessary alignment between the diesel engine and all mechanically dri-ven components, an understanding of the types of misalignment and the methods of measurement is required.
Many crankshaft and bearing failures are the result of improper alignment of drive
systems at the time of initial engine instal-lation. Misalignment always results in
some type of vibration or stress loading.

CAUTION: BEFORE MAKING ANY ATTEMPTS TO MEASURE RUN OUT OR
ALIGNMENT, IT IS IMPORTANT THAT ALL SURFACES TO BE MEASURED OR MATED BE COMPLETELY CLEAN AND FREE FROM GREASE, PAINT, OXIDA-TION, OR RUST AND DIRT — ALL OF WHICH CAN CAUSE INACCURATE MEA-SUREMENTS.

Common mistakes include failure to detect “run out” of rotating assemblies and paral-lel or angular misalignment of the engineand driven machine.
The run out of a hub or flywheel can be measured by turning the part in question
while measuring from any stationary point to the surface being checked. This can be
done with a dial indicator. Note: Measure to the pilot surface being used, not to an
adjacent surface, because surfaces not used for pilots normally are not machined
as closely.

This check should be made first on the face of the wheel or hub, as illustrated in
Figure 1. Whenever making a face check, make sure the shaft end play does not
change as you rotate it. The crankshaft must be moved within the diesel engine to
remove all end play and that position must be maintained throughout the alignment
procedures.

Checking Face Run Out
While turning the wheel 360°, note any change in the dial indicator reading. Anychange is caused by face run out. Face run out may be caused by foreign
material between a crankshaft flange and flywheel, uneven torquing or from machining variations.

“Cocking” of the wheel being measured may cause indications of outside diameter
run out in addition to face run out. For this reason the face run out is checked first.
After the face run out has been eliminated, outside diameter run out can be checked.

This must also be done with a dial indicator.(See Figure 2.(

Checking Outside Diameter Run Out
While turning the hub through 360°of rotation, check for any change in indicator reading. The indicator is held stationary and, if the reading changes, the outside
diameter is off center.

After the flywheel or driving hub has been checked for run out, the same procedure
should be followed on the driven side of the coupling.

After the run out of both the driving and driven sides of the coupling have been found within limits, the engine and load alignment can be checked. There are two kinds of misalignment: parallel and angular (bore and face). (See Figure 3).

Checking Parallel Alignment
Parallel misalignment can be detected by attaching a dial indicator, as shown in Figure 4, and observing the dial indicator readings at several points around the out-
side diameter of the flywheel as the wheel holding the indicator is turned.

As a rule of thumb, the load shaft should indicate to be higher than the engine shaft
because:
A-Engine bearings have more clearance than most bearings on driven equipment.

B-The flywheel or front drive rotates in a“drooped” position below the center-line of rotation.

C-The vertical thermal growth of the engine is usually more than that of the driven equipment. Engine main bearing clearance should be considered when adjusting for parallel alignment.

Note: Both parts can be rotated together if desired. This would eliminate any out-of- roundness of the parts from showing up in the dial indicator reading. In most cases rubber driving elements must be removed or disconnected on one end during alignment since they can give false parallel readings.

Checking Angular Alignment
Angular misalignment can be determined by measuring between the two parts to be
joined. The measurement can be easily made with a feeler gauge, and it should be the same at four points around the hubs Figure 5.

If the coupling is installed, a dial indicator from one face to the other will indicate any angular misalignment. In either case, the readings will be influenced by how far from the center of rotation the measurement is made.

Note: the face and bore alignment affect each other. Thus, the face alignment should be rechecked after the bore alignment and vice versa.

After determining that the engine and load are in alignment, the crankshaft end play
should be checked to see that bolting and coupling together does not cause end thrust.

Torque Reaction
The tendency of the engine to twist in the opposite direction of shaft rotation and the
tendency of the driven machine to turn in the direction of shaft rotation is torque reaction. It naturally increases with load and may cause a torque vibration. This type of vibration will not be noticeable at idle but will be felt with load. This usually is caused by a change in alignment due to insufficient base strength allowing excessive base deflection under torque reaction load. This has the effect of introducing a side to side centerline offset which disappears when the engine is idled (unloaded)
or stopped.


Belt and Chain Drives
Belt and chain drives may also cause the engine or driven machine to shift or change
position when a heavy load is applied.

Belts and chains may also cause PTO shaft or crankshaft deflection, which can cause bearing failures and shaft bending failures. The driving sprocket or pulley must always be mounted as close to the supporting bearing as possible. Side load limits must not be exceeded. Sometimes, due to heavy side load, it is necessary to provide additional support for the driving pulley or sprocket. This can be done by providing a separate shaft which is supported by a pillow block bearing on each side of the pulley or sprocket. This shaft can then be driven by the engine or clutch through an appropriate coupling.
The size of the driving and driven sprockets or pulleys is also important. A larger pulley or sprocket will give a higher chain or belt speed. This allows more horsepower to be transmitted with less chain or belt tension.

If it is suspected that the engine or the driven machine is shifting under load, it can
be checked by measuring from a fixed point with a dial indicator while loading and unloading the engine. Torque reactive vibrations or torque reactive misalignment
will always occur under load.


CouplingsA coupling must be torsionally compatible with engine and driven load so that torsional vibration amplitudes are kept within acceptable limits. A mathematical study
called a torsional vibration analysis should be done on any combination of engine drive-line-load for which successful experience doesn’t already exist. A coupling with the wrong torsional stiffness can cause serious damage to engine or driven equipment.

All couplings have certain operating ranges of misalignment, and the manufacturers
should be contacted for this information.

Some drives, such as U-joint couplings, have different operating angle limits for different speeds.

As a general rule, the angle should be the same on each end of the shaft. (See Figure6.) The yokes must be properly aligned and sliding spline connections should move freely. If there is no angle at all, the bearings will brinell due to lack of movement.

ALIGNMENT INSTRUCTIONS
General Considerations
Alignment methods will vary depending on the coupling method selected. On Caterpillar Diesel Engines either a flexible-type or rigid-type coupling is acceptable, depending on the specific installation characteristics and the results of the Torsional Analysis.

CAUTION: IT IS IMPORTANT THAT THEPACKAGE ALIGNMENT BE CARRIED OUT AND COMPLETED WITHIN THE PERMISSIBLE TOLERANCES OF THE DRIVEN EQUIPMENT MANUFACTURER.

Alignment Instructions — Single-Bearing Driven Equipment

A. Flexible-Type Couplings — Flywheel
Housing-Mounted Driven Equipment

1-Droop
Mount a dial indicator on the engine flywheel housing. Mark the engine flywheel housing. Mark the flywheel at points A, B, C, and D in 90°increments as shown in Figure 7. The indicator tip must contact the pilot diameter of the flywheel assembly.

With the dial indicator in position (A), set the reading to zero. Place a pry bar under the flywheel assembly at position (C) and, by prying against a floor mounted support, raise the flywheel until it is stopped by the main bearings. (Caution: Do not pry against the flywheel housing.) Record the reading of the dial indicator. This is the amount of droop in the crankshaft, which results from engine bearing clearances and natural droop as a result of the overhung weight of the flywheel. The flywheel should be raised several times to get a “feel” for the bearing clearance to prevent excessive lift which means reverse bending of the crankshaft.

2-Flywheel Concentricity
Remove the pry bar and check to ensure that the dial indicator has returned to zero. If not, reset. Rotate the crankshaft, in the normal direction only, and record the Total Indicator Reading (TIR) when the flywheel positions (A), (B), (C), and (D) are at the top. (Refer to Page 58 for proper tolerances).

3-Crankshaft End Play
Ensure the crankshaft-flywheel assembly is completely to the rear- most position of the engine assembly. Reset the dial indicator to zero.

Relocate the pry bar and move crankshaft-flywheel assembly forward in the engine assembly. The dial indicator reading in this position is the crankshaft end play.


4-Flywheel Face Run Out
Set the tip of the indicator on the face of the flywheel Figure 8. Position the crankshaft to the front of its end play and zero the indicator. Shift the crankshaft to the rear of its end play, and record the TIR. With the crankshaft to the rear of its end play, zero the indicator.
Rotate the crankshaft and record the TIR when the flywheel positions (A), (B), (C), and (D) are at the top. Be sure to remove the crankshaft end play before recording these readings. Remove the flywheel housing access cover and place a pry bar between the rear face of the flywheel housing and the front face of the flywheel assembly. Move the crankshaft flywheel assembly to the rear of the engine to remove all end play.

5-Flywheel Housing Concentricity
Mount the dial indicator on the flywheel assembly with the tip located on the pilot bore of the flywheel housing and set the reading to zero.

Rotate the crankshaft in the direction of normal engine rotation and record the indicator readings at positions (A),(B), (C), and (D).

Subtract the droop dimension (Step 1) from the reading indicated at position (C) and subtract one-half the droop dimension from the reading indicated at positions (B)and (D) on the flywheel housing to determine the true concentricity.

6-Engine Mounting Face Depth
With the crankshaft-flywheel assembly moved to the frontmost position, place a straight edge across the mounting face of the flywheel housing, from position (A) to (C). With a scale measure the distance from the rear face of the flywheel housing to
the coupling mounting face of the flywheel as shown in Figure 9.

Repeat the same measurement with the straight edge located on positions (B) and (D).
Steps 1 through 6 establish the engine tolerances. The following Steps, 7 and
,8determine the driven equipment tolerances or refer to manufacturers specifications.

7-Support the driven equipment
input shaft until it is centered (all droop is removed).

8- Driven Equipment Mounting FaceDepth
With the driven equipment mounting and driving flange or face centered, as described in Step 7, and the flexible coupling attached to the input shaft, the face depth can be measured. Place a straight edge across the surface of the front face of the coupling which mates to the flywheel assembly. With a scale measure the distance from the coupling mounting face to the mounting face of the driven equipment housing as shown in Figure 10.

This dimension must equal the engine mounting face depth Step 6 less one-half of the crankshaft end play as described in Step 4. If not, it must be corrected by changing the adapting parts, or by shimming if the required correction is small. Shimming is usually the less desirable approach.

With the engine and driven equipment tolerances known, proceed to mount the driven equipment to the engine.

9-Support the driven machine on a hoist and bring it into position with the engine.

10-Align the driven equipment housing mounting flange with the flywheel housing, using locating dowels if required. Install connecting bolts with sufficient torque to compress the lock washers, but not to final torque.

11-Install the bolts which secure the coupling to the flywheel and torque as recommended.

12-Check crankshaft end play to ensure that the proper relationship exists between the engine mounting face depth Step 6 and the driven equip- ment mounting face depth Step 8.

Place a pry bar between the flywheel assembly and the flywheel housing.
The crankshaft should move both for ward and backward within the engine
and, in both positions, remain fixed when pressure on the pry bar is relaxed. Any tendency of the crankshaft to move when pry bar pressure is released indicates that the driven equipment and coupling assembly are imposing a horizontal force on the crankshaft, which will result in thrust bearing failure. If this condition exists, readjust the thickness of shims used between the driven equipment input shaft and the coupling as described in Step 8.

13-Determine quantity and thickness of shims required between the driven equipment mounting pads and the base assembly; locate the shim packs and install driven equipment mounting bolts to the base assembly.

NOTE: Always use metal shims. Tighten the bolts to one-half the torque recommendation.

14-Loosen the bolts holding the driven equipment housing to the flywheel housing until the lock washers move freely. Using a feeler gauge, check the clearance between the two housings to determine if the driven equipment is properly shimmed.

Measurement should be made in four 90°increments in the vertical and horizontal planes. If the feeler gauge indicates any area where the clearance varies by more than 0.005 in (0.13mm),readjust the driven equipment housing position by changing the shims.
There must be clearance at all points when making this check.

15-With the proper number of shims installed to align the driven equipment housing parallel to the flywheel housing, tighten the bolts securing the driven equipment housing to the flywheel housing sufficiently to compress the lock washers.

16-Torque the bolts holding the driven equipment frame to the base assembly to one-half the recommended value.

17-Repeat Step 14. If the feeler gauge measurements indicate that misalign-
ment is still present, repeat operation described in Steps 14 through 17 until proper alignment is obtained.

18-Retorque all coupling and mounting bolts to the specified torque value.


B. Flexible-Type Couplings — Remote-Mounted Driven Equipment

1-DroopMount a dial indicator on the engine flywheel housing. Mark the flywheel at points A, B, C, and D in 90°increments as shown in Figure 36. The indicator tip must contact the pilot diameter of the flywheel assembly.

With the dial indicator in position (A),set the reading to zero. Place a pry bar under the flywheel assembly at position (C) and, by prying against a floor mounted support, raise the flywheel until it is stopped by the main bearings. (Caution: Do not pry against the flywheel housing.) Record the reading of the dial indicator. This is the amount of droop in the crankshaft which results from engine bearing clearances and natural droop as a result of the overhung weight of the flywheel.

The flywheel should be raised several times to get a “feel” for the bearing clearance to prevent excessive lift which means reverse bending of the crankshaft.

2-Flywheel Concentricity
Remove the pry bar and check to ensure that the dial indicator has re- turned to zero; if it is not, reset. Rotate the crankshaft, in the normal direction only, and record the TIR when the flywheel positions (A), (B), (C),and (D) are at the top.

3-Crankshaft End Play
Ensure the crankshaft-flywheel assembly is completely to the rearmost position of the engine assembly. Reset the dial indicator to zero. Relocate the pry bar and move crankshaft-flywheel assembly forward in the engine assembly. The dial indicator reading in this position is the crankshaft end play.

4-Flywheel Face Run out
Set the tip of the indicator on the face of the flywheel Figure 36. Position the crankshaft to the front of its end play and zero the indicator. Shift the crankshaft to the rear of its end play and record the TIR. With the crankshaft at the rear of its end play, zero the indicator. Rotate the crankshaft and record the TIR when the flywheel positions (A), (B), (C), and (D) are at the top. Remove all end play before recording each reading. Remove the flywheel housing access cover. Then place a pry bar between the rear face of the flywheel housing and the front of the flywheel assembly.

Move the crankshaft-flywheel assembly to the rear of the engine, removing all end play.


5- Mounting
The engine and the driven equipment should be mounted so that any necessary shimming is applied to the driven equipment. The centerline of the engine crankshaft should be lower than the centerline of the driven equipment by approximately 0.0065 in (0.165mm) to allow for thermal expansion of the engine. The value 0.0065 in(0.165mm)allowed for thermal expansion is for the engine only. If it is anticipated that thermal expansion will also affect the driven equipment centerline to mounting plane distance, that value must be subtracted from the engine thermal expansion value in order to establish the total engine centerline to driven equipment centerline distance. When measuring this value, the TIR will be 0.013in plus the droop as estab lished in Step 1.

Shim packs under all equipment should be 0.200 in (5 mm) minimum thickness to provide for later correc- tions which might require the removal of shims.

6-Coupling
Attach the driven member of the coupling to the flywheel and tighten all bolts to the specified torque value.

Gear-type couplings, double sets of plate-type rubber block drives, and Cat viscous-damped couplings are the only ones that can be installed prior to making the alignment check. Most couplings are stiff enough to affect the bore alignment and give a false reading.

7-Angular Alignment
Mount a dial indicator to read between the driven equipment input flange and the flywheel face and measure angular misalignment. Adjust position of driven equipment until TIR is within 0.008 in.

8-Linear Relationship
Mount dial indicator to the driven equipment side of the flexible coupling and indicate on the outside diameter of the flywheel side of the coupling. Zero the indicator at 12 o’clock and rotate the engine in its normal direction of rotation and check the total indicator reading at every 90°. Subtract the full“droop” from the bottom reading to give the corrected alignment reading.

The value of the top-to-bottom reading should be 0.008 in (0.20 mm) or less
under operating temperature conditions, with the engine indicating low.

Adjust all shims under the feet of the driven equipment the same amount
to obtain this limit.

The final value of the top-to-bottom alignment should include a factor for
vertical thermal growth.

Subtract one-half the “droop” from the 3 o’clock and 9 o’clock reading. This
should be 0.008 in (0.20 mm) or less.

Shift the driven equipment on the mounts until this limit is obtained.

Note: the sum of the side “raw” reading should equal the bottom reading within
0.002 in (0.051 mm). Otherwise the mounting of the dial indicator is too weak to support the indicator weight.

9-The combined difference or readings
at points B and D should not exceed a total of 0.008 in (0.20 mm). (SeeFigure 12).

10-Crankshaft End Play
The crankshaft end play must be rechecked to ensure that the driven equipment is not positioned in a manner which imposes a preload on the crankshaft thrust washers. (Refer to Step 4.) Place a pry bar between the flywheel assembly and the flywheel housing. The crankshaft should move both forward and backward within the engine and, in both positions, remain fixed when pressure on the pry bar is relaxed. Any tendency of the crankshaft to move when pry bar pressure is released indicates that the driven equipment assembly must be moved rearward on the base assembly or, if
used, the number of shims between the input flange and the flexible coupling must be reduced.

Tolerances and Torque Values
Permissible alignment tolerances and torque values for Caterpillar standard mounting hardware are available from your Caterpillar.

CAUTION: DURING OPERATION, SHOULD A CHANGE IN THE VIBRATION
OR SOUND LEVEL OCCUR, ALIGNMENT SHOULD BE RECONFIRMED. THIS IS PARTICULARLY TRUE FOR SEMIMOBILE INSTALLATIONS AND ON ANY FIXED INSTALLATIONS WHICH ARE SUBJECT TO INFREQUENT RELOCATION. ALIGNMENT SHOULD ALSO BE CHECKED ON A PERIODIC BASIS OR AT TIME OF MOVEMENT IF INSTAL- LATION IS ON A SUBBASE OR SKID- TYPE BASE.

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Alignment Handout

Factors Influencing Alignment procedure1- Eccentricity (runout)
Check
· This might be done by a dial gauge

2- Baseplate of machines (soft-foot)
· Machines feet must be mounted perfectly horizontal with the baseplate.
· The contact between the baseplate and the feet can be checked with a set of shims or with feeler gages.
· During a new installation,
o it is essential to use accurate straight edges and levels to make sure that all feet of the machine are on the same plane.
· The accepted tolerance level for these planes is usually 0.1 mm.
· Simple tests for soft-foot are by setting up the dial gage (at fixed place) and place a shim under one front foot and the reading noted.
· It is then removed and placed under the next front foot. The reading should be the same.
· The same procedure must be repeated for the rear feet.
3- Axial position of machines· The axial position of shaft ends is referred to as the distance between shaft ends (DBSE).
· Normally, most couplings allow a large tolerance in the axial position.
· However, for couplings like disk couplings, an error in the axial position result in;
o places the discs under stress and
o decreases their life.
o may generate axial thrusts, which ultimately add extra load to the machine’s thrust bearings.
· It is therefore necessary to take this aspect into consideration, especially when machines operate at high temperatures.

4- SAG
· For spacer couplings, a sag (deflection) check should be done on the indicator bracket to be used for the alignment.
· The DBSE in these couplings may be long, and when alignment brackets are clamped to one hub and extended to the other hub, there is a tendency for them to sag.
· This sag can alter the dial gage readings, leading to misinterpretation and errors.
· For bracket lengths larger than 25–30 cm, it is essential to provide additional stiffness to minimize sag.
· It is therefore necessary to perform a sag check of the bracket.
· A sag check is essential only for aligning horizontal machines, because the sag is caused by gravity due to the weight of the bracket.

Alignment techniques
· There are many methods to align a machine. The appropriate method is selected based on;
Ø the type of machine,
Ø rotational speed,
Ø the machine’s importance & production,
Ø the maintenance policy and
Ø alignment tolerances.

· Machines “I”
{Which are not fragile (breakable) in their construction}.
Ø rotating at less than 1500 rpm,
Ø lower horsepower range,
Use merely a straight edge to align machines.
Considering all aspects, it is acceptable to align them to the range of 0.3–0.8 mm.

Machines “II”
{Majority of machines}
Fragile (breakable) in their construction (mechanical seals and expansion bellows)
Machines operating at;
Ø speeds of 3000 rpm and higher,
Ø in the medium power range of 20 kW–1 MW
should be aligned within 0.1 mm.
· This requirement necessitates the use of comparators like dial gages, and methods with minimum residual errors.
Alignment conventions using a dial indicator
· The dial gage is the most common comparator used during alignment.
· The dial gage functions based on the rack-and-pinion principle. The conventions that are followed are shown in Figure 6.9.
· When the spring is compressed, the dial pointer is pressed inward and the clock needle moves clockwise, indicating a positive reading.
· When the pointer moves outwards, the clock needle moves counter clockwise, indicating a negative reading.
· It is recommended to jog the pointer from the top to ensure that it is not stuck.

The dial gage functions based on the rack-and-pinion principle. The conventions that are followed are shown in Figure 6.9.

Figure 6.9 Dial indicator

Another convention for alignment readings in the horizontal plane is shown in Figure 6.10.

Figure 6.10 Alignment readings in the horizontal plane

Thus, the convention maintains left and right when standing behind the driver, facing the driver.
Left and right readings on the dial gage are recorded accordingly.


Shaft setup for alignment
· The connection to the shaft must be simple and rigid.
· The clamp shown in Figure 6.11 is a good example. Magnetic clamps must be avoided, because their attachments are not reliable.

Figure 6.11 Shaft setup for alignment

· There are many types of alignment brackets available in the market, and a typical one is shown in Figure 6.12.

· The guiding principle for the selection of brackets is that they should be rigid with minimal sag (see the rod diameters).

Figure 6.12 Alignment brackets

Types of misalignment
Misalignment in machines is due to;
· angularity and
· offset,
· but in almost all cases the misalignment of machines is a combination of both.

i- Angularity· is the difference between the values on the comparator (dial gage) for a half revolution”180o” (because for one complete revolution we return to the original position).
· For a given angular misalignment, angularity depends on the diameter described by the dial gage.
· It can be seen that when d1 increases to d2, p1 increases with the same ratio to p2. This value must be fixed when a certain tolerance is given (Figure 6.13).

Figure 6.13 Angularity (parallelism)

Angle of misalignment:

Where p1, p2 = dial gage reading when rotated by 180°; d1, d2 = diameters described by the dial gage.

ii- Offset (concentricity),
· The offset is the radius of rotation for the dial gage, as indicated in Figure 6.14.

Concentricity =1/2 dial gage reading

· The dial gage readings would indicate the diameter, and hence should be reduced by half to obtain the true offset reading.

Figure 6.14 Radial misalignment (concentricity)

However, as mentioned before, in practice misalignment of machines is due to a combination of both factors, as depicted in Figure 6.15.

Figure 6.15 Misalignment of shafts with angularity and offset

Two dial method of alignmentThe necessary steps to align a machine are:
1. The first step is to loosen the coupling bolts so there is no restriction during the measurement of angularity of the existing misalignment.
2. A feeler gage is then run through the coupling hubs to ensure that the hubs are not touching.
The necessary steps to align a machine are:
i- The radial test (R) to measure the OFFSET ;
· The dial gage is attached as shown in Figure 6.16.
· The test done in the vertical and horizontal planes.
· To obtain the offsets in both planes, four readings will be required.
1. Top, bottom, left and right
2. Clock positions – 12 o’clock, 3 o’clock, 6 o’clock and 9 o’clock positions.
Clamping
· The dial gage here generally placed on the top (12 o’clock) position, and the zero on the scale is turned to coincide with the needle.
· The pointer must be jogged to ensure that it is free and that the readings are repeatable.

Figure 6.16 Dial gage setup at top position. The difference in readings after 180
indicates offset in vertical or horizontal planes


· Shafts are turned manually through one complete revolution, and readings at every quadrant (quarter) are noted.
· The readings recorded at the four locations are written down in the format shown below (fig. 6.17).
· The ‘R’ in Figure 6.17 indicates that these are radial readings, meant for offset corrections.

Figure 6.17Readings in mils

ii- The Facial reading to measure the ANGULARITY;
· The clamp is re-adjusted with the dial gage pointer now set to measure the angularity, as shown in Figure 6.18.
· The pointer (as shown in the figure) is now parallel to the axes of the shafts.
· Just like the offset, the angularity must be measured in horizontal and vertical planes as well.
· The dial gage is rotated through one complete revolution and stopped at every quadrant to make a note of the readings.

Figure 6.18 Dial gage setup at top position. The difference of readings
after 180° indicates angularity in vertical or horizontal planes

· The ‘F’ in Figure 6.19 indicates that these are facial readings, meant for angularity corrections.

Figure 6.19 The ‘F’ indicates facial readings
(note the diameter described by the dial gage)

iii-Steps to fix the alignment
· The next step is to convert these values of (R) and (F) to appropriate shim thickness that should be added or removed to fix the alignment.
To proceed to the next step, additional information about the location of the front and the rear feet from the dial gage pointer is required.

*In Figure 6.20
· The pump is the fixed machine (FM) and the motor is the machine to be shimmed (MTBS).
· This implies that all the corrections will be done by adding and removing shims under the motor feet. The pump will not be disturbed from its position.
· The distance from the pointer of the dial gage to the front foot (FF) of the motor is designated as ‘A’.
· The distance of the rear foot (RF) to the dial gage pointer is designated as ‘B’.

Figure 6.20 Shimming Calculation

· Two sets of calculations are required. One set for the vertical plane and the other for the horizontal plane.

1. Calculations for the vertical plane
*Offset correction· Let us say the offset readings for the top and bottom positions are 0 and -5 mils, respectively.
· If the dial gage pointer is on the motor (MTBS) and the dial gage is rotating, hence the –ve and +ve signs are as shown in (figure 6.9).
· The negative sign indicates that the motor shaft is higher than the pump shaft.
· It is higher by half the final reading minus the initial readings. Thus:

Hence, shims of 2.5 mils should be removed from the front and rear feet of the MOTOR.

*Angularity correction· Let us say the angularity readings for the top and bottom readings were 0 and - 2 mils, respectively.
· If the dial gage pointer is touching the rear face of the motor coupling hub see (figure 6.9).
· The negative sign indicates that the coupling has a narrower gap at the bottom than at the top.
The dial measures at (scribes) a circle of 5 in.

The angle

Because the angle is very small, the tan inverse function can be neglected:
Hence, P1=.002 in.

(The formula would reverse if the pointer is touching the front face of the coupling hub, which is normally the case when there is a long spacer between the couplings.)
= 0.0004 radian
=0.4 milli-radians = 0.0004´ (180/p) = (0.023o)

· This angle “θ” is also the angle of inclination of the motor axis w.r.t. the pump axis.

· Line AB is the existing axis inclination of the motor (Figure 6.21).
· It must be lifted by amount x at the FF (front foot) location and by y at the RF (rear foot) location.

Figure 6.21 Calculating X and Y values

· The x and y values are calculated as follows;
x and y are approximated as arcs and the following formula can be used:
S = r × θ

Where;
S = arc length;
r = radius;
θ = included angle in milli-radians.

Final- Vertical

The final results should include corrections for both the offset and the angular corrections.
At point A{Front Foot FF}:Offset results – remove shims of 2.5 mils
Angularity results – add shims of 3.2 mils
Thus, insert shims of 0.7 mils under the front foot of the motor.

At point B{Rear Foot RF}:
Offset results – remove shims of 2.5 mils
Angularity results – add shims of 7.2 mils
Thus, insert shims of 4.7 mils under the rear feet of the motor.

Calculations for the horizontal planeThe dial gauge is: from behind the motor, left is the initial reading and right is the final reading.
*Offset calculations:
Left reading: +1 mils
Right reading: - 6 mils
Pointer on left;
+1 means the measured point on motor shaft is to the left by “1”
Pointer on the right;
- 6 means the measured point on motor shaft is to the left by “6”
{To imagine this, just draw the dial gage and its direction}
· Because the dial pointer is on the motor shaft, a negative reading indicates that the motor shaft axis is to the left of the pump shaft axis.

Offset = (Final reading – Initial reading) /2

Move points A and B of the motor to the right by 3.5 mils.

*Angular calculations:
Left reading: + 4 mils
Right reading: - 6 mils
+ 4 means that the left point of the motor hub is away to the pump hub by “4”.
- 6 means that the right point of the motor hub is close from the pump hub by “6”.
{To imagine this, just draw the dial gage and its direction}

As the dial pointer touches the rear face of the motor coupling hub, the shaft axis resembles what is shown in Figure 6.22.
In this case:mils = 0.01 inch.
Thus:


= 0.002 radians (0.114o)
= 2 milli-radians

Hence:
x = 2 ´ 8 = 16 mils – move to the left;
y = 2 ´18 = 36 mils – move to the left.

Figure 6.22

Final- Horizontal

At point A{Front Foot FF}:
Offset results – move 3.5 mils to the right
Angularity results – move 16 mils to the left
Thus, move to the left by 12.5 mils.

At point B {Rear Foot RF}:
Offset results – move 3.5 mils to the right
Angularity results – move 36 mils to the left
Thus, move to the left by 32.5 mils.


The procedure would be;
· The vertical shim corrections should always be done prior to the horizontal shifts.

· Once the vertical shims are adjusted, the bolts should be tightened and a quick test of the vertical plane reading should be made to confirm the accuracy.

· If the accuracy is satisfactory, the bolts can be loosened and the horizontal alignment should be done with jack bolts (if provided).

The limitations of this method are:
· Calculations are necessary, which may be difficult to do in the field.
· It is beneficial to be able to visualize the shaft orientation from the dial gage readings but this requires practice.
· Inexperienced technicians can find this confusing.
· Errors in calculations may occur if there is bracket sag and/or error in the dial gage readings.
· If the shaft of one or both the machines has substantial axial floats, the angular readings can be erroneous.


Laser alignmentAlignment with comparators such as dial gages characterized by;
· a fair degree of precision,
· demand skill,
· demand training and
· Require experience.
Consequently, these methods are;
· tend to provide errors and
· can take a considerable amount of time.

The method of alignment using LASERS (Figure 6.34);
· overcomes the disadvantages listed above and
· it is gradually becoming the preferred method of alignment for most machines.
· Data collection and calculations have become;
o fast and
o accurate
· Some laser systems need less than a quarter turn of the shaft to produce very good shim correction data.
· They have built-in alignment tolerances, and hence there is no need for an expert to judge on the quality of the residual misalignment.
· Laser beams can travel over long distances, and alignment can be done very accurately with relative ease (comfort).
· Laser beams do not bend over great distances and for this reason the sag effect is entirely eliminated.

Figure 6.34 Laser alignment

· The laser alignment system (Figure 6.35) comprises;
Ø an analyzer and
Ø two laser heads.
· The laser heads are attached to the two shafts
· The laser heads must face each other, and each head has a laser emitter and receiver.
· When the shafts are turned, the receivers trace the movement of the laser beams.
· These values are communicated to the analyzer.
· Machinery data and the required distances are initially entered into the analyzer.
· The data from;
o the laser heads and
o the given machinery data
are used to accurately determine the shim corrections for the machine.
· Once the laser head and the reflector are installed, the shafts must be rotated.

Figure 6.35 Laser alignment system comprising of laser head,
reflector and analyzer (Prueftechnik – Optalign Plus system)

One emitter and one receiver system;
· Some entry-level laser alignment systems only have one laser emitter head and a reflecting prism on the other.
· These systems are ideal for general purpose machines.
· They eliminate the dial gages and provide an alignment calculator.
· The methodology with these systems is same as the previous one.
· At every quarter revolution, the analyzer must be activated to acquire the reading.
· After this, the analyzer provides the alignment correction information.

Some advanced LASER systems
Some systems include additional features that make alignment of machines an easy task.
These features are:
· Complex trains comprising of as many as five machines can be handled.
· Communications that eliminate cables between the laser heads and the analyzer.
· Errors due to vibrations from other machines can also be eliminated through averaging.
· Uncoupled and non-rotating machines can also be aligned.
· Less than a quarter rotation may be sufficient to obtain misalignment data.
· It is possible to do live horizontal alignment. This means that there is no need to take a reading and transfer it to the analyzer for calculation. The instant communication of the heads and analyzer accomplishes this automatically.
· One or two soft foot conditions can be identified.
· Once a machine is aligned, its history and data can be stored.
· They provide built-in misalignment tolerances.


Alignment tolerances
In practice, it is almost impossible to obtain;
· a zero offset
· and zero angularity,
and thus machines have to be left with a certain residual misalignment.
This residual misalignment has little or no detrimental effect on the operation of machines.

· The above values are assumed to be pure offset or pure angle.
· In practice, a combination of the two is more common and tolerances should account for this combination.
For example, a machine is running at 3000 rpm and the residual misalignment data is:
· offset: 2.6 mils
· angularity: 0.25 mil/in.
In pure terms, these values would be acceptable.
Nonetheless, let us see if the combination of the two is acceptable. To achieve this, a XY graph is made as shown in Figure 6.36.
If an offset of 2.6 with an angularity of 0.25 mils/in. is plotted, it could be beyond the acceptable range.

Figure 6.36 Alignment tolerances

ROTALIGN PRO
(Laser shaft alignment system)

1. Lock-out the machine.
2. Mount the chain brackets to the shafts.
3. Mount the emitter [waterproof, dust proof] on one bracket.
4. Mount the receiver [waterproof, dust proof] on the other bracket.
5. Turn on the emitter.
6. You have only one laser to adjust.
7. Only one cable is needed to connect the laser head to the hand-held computer.
8. Three short steps and you have your alignment data;
§ Dimension
§ Measure
§ Results
9. DIM
§ Press the DIM key your screen displays to you some data to put in.
§ Then determine the dimension of your machine and put them into the computer.
10. Measure (M)
§ Press measure key then you are ready to begin.
§ Turn the shafts for 1/4 (quarter) turn or less and forget about the clock position
11. Results
§ Press the result key, the screen displays as found to scale the alignment conditions AND the corrections needed.
12. Do physically the corrections required for the machine and repeat your job UNTIL the computer tells you that you have a good alignment.
(This is appeared with the sign on the screen).
13. Some benefits of this laser system are;
§ Determine the soft foot condition and analyze it and give the suggestions.
§ It can provide alignment for non-rotating shafts.
§ It can automatically the thermal expansion and gives the corrections.
§ It is capable of aligning the vertical machines.
§ The software can be updated from the website.

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