Handbook Of Shaft Alignment Episode 1 Part 4 ppsx

Higher multiples of running speed occurred on the pump from 40 to 100 kcpm particularlyduring the vertical misalignment runs.. The seven times running speed peak that occurred in the hor

. The 2
, 4
, and 6
peaks prevailed in the pump bearings.

. Higher multiples of running speed occurred on the pump from 40 to 100 kcpm particularlyduring the vertical misalignment runs

. The twice, fourth, and eighth running speed frequencies are a result of the S-shapedgrid as it traverses from its maximum tilted and pivoted positions twice each revolution

on both the coupling hubs The third and sixth running speed multiples occur as the metalgrid in the coupling changes its position during each revolution of the shafts The

Test run #2 M2W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

1 ⫻ 2 ⫻ 3 ⫻ 4 ⫻ 5 ⫻ 6 ⫻ 7 ⫻ 8 ⫻ 9 ⫻ 01

.02

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.02

Frequency (orders of running speed)

FIGURE 2.23 Inboard MOTOR, vertical direction

Test run #2 M2W

Test run #3 M21W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

1 ⫻ 2 ⫻ 3 ⫻ 4 ⫻ 5 ⫻ 6 ⫻ 7 ⫻ 8 ⫻ 9 ⫻ 01

.02

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.01

.02

.01

.02

Frequency (orders of running speed)

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

Frequency (orders of running speed)

.02

FIGURE 2.24 Inboard MOTOR, axial direction

maximum amount of rotational force occurs when the grid is in the tilted position wherebending occurs across the thickness of the grid member.

. The seven times running speed peak that occurred in the horizontal direction on theinboard motor bearing during the M55L run and the five times running speed peak thatoccurred in the axial direction on the pump are, as yet, not completely understood as tothe source of the forcing mechanism involved The higher multiples appear to be caused

by overloading the antifriction bearings

Test run #2 M2W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

1 ⫻ 2 ⫻ 3 ⫻ 4 ⫻ 5 ⫻ 6 ⫻ 7 ⫻ 8 ⫻ 9 ⫻ 01

.02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

Frequency (orders of running speed)

.02

FIGURE 2.25 Inboard PUMP, horizontal direction

2.2.8 BEFORE AND AFTERVIBRATION RESULTSFOUND ON AMISALIGNED

This case history shows actual alignment and vibration data from a drive system that hadbeen operating under a misalignment condition Vibration information was collected beforeshutdown and realignment, the unit was then aligned properly, started back up, and vibration

Test run #2 M2W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

1 ⫻ 2 ⫻ 3 ⫻ 4 ⫻ 5 ⫻ 6 ⫻ 7 ⫻ 8 ⫻ 9 ⫻ 01

.02

Frequency (orders of running speed)

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

Frequency (orders of running speed)

.01

.02

FIGURE 2.26 Inboard PUMP, vertical direction

Test run #2 M2W

Test run #3 M21W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)

.01

Frequency (orders of running speed)

Frequency (orders of running speed)

Frequency (orders of running speed)

.01

.02

Frequency (orders of running speed)FIGURE 2.27 Inboard PUMP, axial direction

data taken again Figure 2.30 shows the as-found and final alignment-data Figure 2.31 showsthe before and after radial vibration spectral data on the motor Figure 2.32 shows the beforeand after radial vibration spectral data on the pump Figure 2.33 shows the before andafter axial vibration spectral data on both the motor and the pump Notice that the radialand axial vibrations on the motor increased and the vibration on the pump decreased after themisalignment was corrected.

Test run #2 M2W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)FIGURE 2.28 Outboard PUMP, horizontal direction

2.2.9 WHYVIBRATION LEVELSOFTENDECREASE WITHINCREASINGMISALIGNMENT

As illustrated in Figure 2.2, rotating machinery shafts are exposed to two types of forces.Static forces that act in one direction and dynamic forces that change their direction Staticforces are also called preloads Preloads on shafts and bearings are caused from many of thefollowing sources:

Test run #2 M2W

Test run #4 M36W

Test run #5 M65H

Test run #6 M55L

Test run #7 M6W

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

.01 02

Frequency (orders of running speed)

FIGURE 2.29 Outboard PUMP, vertical direction

Drive train dimensions

Deionized water distribution pump 2 Alignment summary

0 2 0 N

T s B N

Motor Pump

Move outboard foot

144 mils

north

Move outboard foot

78 mils north

Move outboard foot

11 mils north

Alignment tolerance guidelines Alignment tolerance guidelines

Misalignment is the deviation of relative shaft position from a colinear axis of rotation, measures at the points of power transmissin when equipment is running at normal operating conditions.

Misalignment is the deviation of relative shaft position from a colinear axis of rotation, measures at the points of power transmissin when equipment is running at normal operating conditions.

.056 050 044 038 031 025 019

.013 006

.063 056 050 044 038 031 025 019 013 006

1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4

The maximum alignment devation is 7 mils/in.

at the motor in the lateral direction The maximum alignment devation is 7 mils/in.

at the motor in the lateral direction

Move inboard foor

37 mils down

Move inboard foor

5 mils up Move inboard foor

2 mils up

Unacceptable Acceptable Acceptable

Unacceptable

Excellent Excellent

2 4 6 8 10

Speed (rpm ⫻ 1000)20

FIGURE 2.30 As-found and final alignment data on motor and pump

0.5DIDstrb P2-MIV Motor Inboard Vertical

DIDstrb P2-MIH Motor Inboard Vertical DIDstrb P2-MIH Motor Inboard Vertical

DIDstrb P2-MIV Motor Inboard Vertical

0.5 DIDstrb P2-MOH Motor Outboard Horizontal

DIDstrb P2-MOH Motor Outboard Horizontal

0 0.1 0.2 0.3 0.4 0.5

0

0 6000 12000 18000 24000 30000 0.1

0.2 0.3 0.4 0.5

0 0.1 0.2 0.3 0.4 0.5

0

0 6000 12000 18000 24000 30000 0.1

0.2 0.3 0.4 0.5

6000

DIDstrb P2-MOV Motor Outboard Vertical DIDstrb P2-MOV Motor Outboard Vertical

12000 Frequency in cpm

Before alignment After alignment Deionized water distribution pump 2 ¥ pump vibration data

0.5 DIDstrb P2-PIH Pump Inboard Horizontal

DIDstrb P2-PIV Pump Inboard Vertical

DIDstrb P2-POH Pump Outboard Horizontal

DIDstrb P2-POV Pump Outboard Vertical DIDstrb P2-POV Pump Outboard Vertical

DIDstrb P2-POH Pump Outboard Horizontal

DIDstrb P2-PIH Pump Inboard Horizontal

DIDstrb P2-PIH Pump Inboard Vertical

0.3 0.2

0.1 0

0.2 0.1

0.2 0.1

0

6000 12000 18000 24000 30000

0 6000 12000 18000 24000 30000

0.5 0.4

0.3

0.2 0.1 0

0 6000 12000 18000 24000 30000

FIGURE 2.32 Before and after radial vibration data on pump

. Gravitational force

. V-belt or chain tension

. Shaft misalignment

. Some types of hydraulic or aerodynamic loads

Dynamic loads on shafts and bearings are caused by some of the following sources (not acomplete list by any means):

. Out of balance condition (i.e., the center of mass is not coincident with the centerline ofrotation)

. Eccentric rotor components or bent shafts (another form of unbalance)

. Damaged antifriction bearings

. Intermittent, period rubs

. Gear tooth contact

. Pump or compressor impeller blades passing by a stationary object

DIDstrb P2-MIA Motor Inboard Axial

Frequency in cpm

DIDstrb P2-MIA Motor Inboard Axial 0.5

0.4 0.3 0.2 0.1 0

Frequency in cpm DIDstrb P2-POA Pump Outboard Axial DIDstrb P2-POA Pump Outboard Axial 0.5

rotating, does not vibrate As soon as the imbalanced rotor begins to spin, it also begins

to vibrate This occurs because the ‘‘heavy spot’’ is changing its position, causing the(centrifugal) force to change its direction The rotor=bearing=support system, beingelastic, consequentially begins to flex or move as these alternating forces begin to act

on the machine

Another detectable vibration pattern exists in gears and is commonly referred to asgear mesh Gear mesh can be detected as forces increase or subside as each tooth comes incontact with another Other types of mechanical or electrical problems that can be detectedthrough vibration analysis can be traced back to the fact that forces are somehow changingtheir direction

On the other hand, when two or more shafts are connected together by some flexible orrigid element where the centerlines of each machine are not collinear, the forces transferredfrom shaft to shaft are acting in one direction only These forces do not change theirdirection, as an imbalance condition does If a motor shaft is higher than a pump shaft

by 50 mils, the motor shaft is trying to pull the pump shaft upward to come in line with themotor shaft position Conversely, the pump shaft is trying to pull the motor shaft downward

to come in line with the pump shaft position The misalignment forces will begin to bend theshafts, not flutter them around like the tail of a fish

Static forces caused by misalignment act in one direction only, which is quite different thanthe dynamic forces that generate vibration Under this pretense, how could misalignment evercause vibration to occur? If anything, misalignment should diminish the capacity for motion

to occur in a rotor=bearing=support system

2.2.10 KNOWNVIBRATIONSPECTRALSIGNATURES OFMISALIGNEDFLEXIBLECOUPLINGS

Despite the fact that shaft misalignment may decrease the amount of vibration in rotatingmachinery, vibration can and does occur due to this condition As previously mentioned, ithas been observed that the vibration spectral pattern of misaligned rotating machinerywill frequently be different depending on the type of flexible coupling connecting the twoshaft together

Figure 2.34 through Figure 2.39 show vibration patterns that have been observed onmisaligned rotating machinery with different types of flexible couplings Notice that thevibration peaks are occurring at running speed (1X) or multiples of running speed (2X, 3X,4X, etc.)

2.2.11 VIBRATIONCHARACTERISTICS OFMISALIGNEDMACHINERYSUPPORTED INSLIDING

The vibration spectral patterns in Figure 2.34 through Figure 2.39 were seen on rotatingmachinery supported in rolling element type bearings Frequently a different pattern emerges

on machinery supported in sliding type bearings as shown in Figure 2.40

2.2.12 USINGINFRAREDTHERMOGRAPHY TODETECTMISALIGNMENT

A very interesting study was performed by two maintenance technicians from a bottlingcompany in 1991 The test was conducted by coupling a 10 hp motor to a 7200 W electricgenerator A specific flexible coupling was installed between the motor and the generator; theunit was then accurately aligned and then started up Vibration, ultrasound, and thermal

imaging data was then collected after 10 min run time The unit was then shutdown, 10 mils ofshims were placed under all 4 ft of the motor, the drive system started back up and the datawas collected again This was repeated several times with an additional 10 mils of shimsinstalled under the motor feet each time After the motor and generator drive was misaligned

Motor driven ANSI pump

J Lorenc horizontal misalignment at 90 mils IB & OB

Jaw coupling Various vibration responses to misalignment

Motor driven generator test

D Nower horizontal and angular misalignment at 15 mils/in.

FIGURE 2.34 Observed vibration patterns on misaligned jaw-type couplings (Courtesy of Lovejoy,Downers Grove, IL With permission.)

Motor driven ANSI pump

J Lorenc horizontal misalignment at 30 mils IB & OB

Gear coupling Various vibration responses to misalignment

Gas/power turbine driven compressor

J Piotrowski horizontal misalignment at 65 mils IB & OB

FIGURE 2.35 Observed vibration patterns on misaligned gear type couplings (Courtesy of RexmordCoupling Group, Milwaukee, WI With permission.)

Motor driven ANSI pump

S Chancey vertical misalignment 50 mils at IB & 75 mils at OB

J Lorenc horizontal misalignment at 90 mils IB & OB

Metal ribbon coupling Various vibration responses to misalignment

Motor driven generator test

D Nower horizontal misalignment at 50 mils IB & OB

Motor driven centrifugal pump

J Piotrowski horizontal misalignment at 36 mils IB & OB

30–40 mils, the flexible coupling being tested was removed, a different flexible coupling designwas then installed, the shims were removed from the motor to get back to near perfectalignment, and the process was repeated.

Figure 2.41 through Figure 2.46 show the results of the six different flexible couplingsthat were tested Notice that as the misalignment increased, so too did the temperature

of the coupling or of the flexing element The increase in temperature is somewhatlinear as illustrated in the temperature graphs with each coupling tested Disappoint-ingly, however, the vibration and ultrasound data was never published with theinfrared data

In addition, there must be a word of caution here because it is very tempting tomake generalizations from this data Not every flexible or rigid coupling will increase

in temperature when subjected to misalignment conditions The flexible couplings used inthis test were mechanically flexible couplings (the chain and metal ribbon types) or elasto-meric types

In mechanically flexible couplings the heat is generated as the metal grid slides back andforth across the tooth slots in the coupling hubs or as the chain rollers slide across thesprocket teeth as the coupling elements attempt to accept the misalignment condition Inthe elastomeric couplings, the elastomer is heated through some sliding friction but pri-marily by shear and compression forces as these coupling elements attempt to accept theirmisalignment conditions

What would have happened if a flexible disk or diaphragm type coupling was alsotested? Flexible disk or diaphragm couplings accept misalignment conditions by elasticallybending the two disk packs or diaphragms and virtually no heat will be generated bythe flexure of metal disks as these types of couplings attempt to accommodate anymisalignment conditions

2.2.13 POWERLOSS DUE TOSHAFTMISALIGNMENT

It has been widely publicized that shaft misalignment will cause the driver to work harder andtherefore take more energy or power to run the drive system However, a study conducted bythe University of Tennessee in 1997 where both 50 and 60 hp motors were purposely misaligned

to dynamometers using four different types of couplings and subjecting each coupling to 15misalignment conditions came to the following conclusions: ‘‘The results of these tests show

no significant correlation between misalignment and changes in efficiency when the testedcouplings were operated within the manufacturer’s recommended range Power consumptionand power output remained constant regardless of the alignment condition.’’

2.2.14 THEMOSTEFFECTIVEWAY TODETERMINE IF MISALIGNMENTEXISTS

After years of study, one invariable conclusion can be made Misalignment disguises itselfvery well on the operating rotating machinery There are no easy or inexpensive ways

to determine if rotating machinery is misaligned while it is running The most effective way

to determine if a misalignment condition exists is to shut the drive system down, safety tagand lock out the machinery, remove the coupling guard, and employ one of the alignmentmeasurement methods described in Chapter 7 to see if a misalignment condition is present.Even if the alignment looks good when you do an off-line check, running misalignment mayoccur So it is suggested that you also review Chapter 9, which discusses off-line to runningmachinery movement