Handbook of Shaft Alignment Part 3 pdf

Lorenc horizontal misalignment at 90 mils IB & OB Jaw coupling Various vibration responses to misalignment Motor driven generator test D.. Lorenc horizontal misalignment at 90 mils IB &

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. 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

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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 OFMISALIGNEDFLEXIBLECOUPLINGSDespite 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

TYPEBEARINGS

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

Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 71 6.10.2006 5:21pm

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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.)

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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.)

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

Metal ribbon coupling Various vibration responses to misalignment

D Nower horizontal misalignment at 50 mils IB & OB

Motor driven centrifugal pump

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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

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Motor driven BFW pump Motor driven demonstrator

Flexible disk-type coupling Various vibration responses to misalignment

Motor driven motor experimental test

D Dewell parallel at 96 mils

D Nower horizontal and angular misalignment at 75 mils high

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Rubber tire-type coupling Various vibration responses to misalignment

D Nower horizontal and angular misalignment at 75 mils high

1 ⫻ 2 ⫻ 3 ⫻ 4 ⫻ 5 ⫻ 6 ⫻ 7 ⫻ 8 ⫻ 9 ⫻ 10 ⫻

FIGURE 2.38 Observed vibration patterns on misaligned flexible disk-type couplings (Courtesy ofDodge-Reliance Electric, Cleveland, OH With permission.)

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Motor driven pump—Motor IB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB

Motor driven pump—Pump IB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB

Motor driven pump—Motor OB Hrz vertical misalignment Motor was 100 mils high at OB, 46 mils high at IB

TB Woods-type coupling various vibration responses to misalignment

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Sliding type bearing

Force Proximity

probes

Shaft

When the signals from two proximity probes

are combined together in a two channel

oscilloscope or vibration analyzer, the orbital

motion of the shaft can be observed (called

a Lissajous pattern).

A typical shaft orbit in a sliding type bearing

with no external forces applied to the shaft

is shown to the right Even if a pure imbalance

condition existed causing an even radial force,

the orbital pattern would be elliptical due to

the different horizontal and vertical stiffnesses

of the machine case.

If a downward force from shaft misalignment

is now applied to the rotor/bearing system,

the elliptical orbit begins to “flatten out” The

static misalignment force is limiting the

amount of shaft movement in the vertical

direction.

If the force from misalignment increase the

orbit continues to flatten and distort.

As the force begins to steadily increase, the

orbit begins to take a pickle shape.

When the force is great enough, the orbit

running speed vibration component appears.

FIGURE 2.40 Observed vibration orbital patterns on rotors supported in sliding type bearings

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0 50 100 150

10 mils 20 mils 30 mils 40 mils

FIGURE 2.41 Observed temperature patterns on misaligned jaw-type coupling (a) A photograph ofthe coupling, (b) an infrared image of the coupling running under good alignment conditions, (c) aninfrared image of the coupling running with the worst misalignment condition (d) temperature ofcoupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute,Shelburne, VT.)

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FIGURE 2.42 Observed temperature patterns on misaligned rubber tire-type coupling Upper rightphoto shows infrared image of coupling running under good alignment conditions Lower right photoshows coupling running under ‘‘worst case’’ misalignment condition indicated by rightmost bar ontemperature graph (Photos and data courtesy of Infraspection Institute, Shelburne, VT.)

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100 200

FIGURE 2.43 Observed temperature patterns on misaligned rubber insert type coupling (a) A graph of the coupling, (b) an infrared image of the coupling running under good alignment conditions,(c) an infrared image of the coupling running with the worst misalignment condition (d) temperature ofcoupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute,Shelburne, VT.)

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50 100 150

FIGURE 2.44 Observed temperature patterns on misaligned rubber ‘‘gear’’ type coupling (a) A graph of the coupling, (b) an infrared image of the coupling running under good alignment conditions,(c) an infrared image of the coupling running with the worst misalignment condition (d) temperature ofcoupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute,Shelburne, VT.)

photo-Piotrowski / Shaft Alignment Handbook, Third Edition DK4322_C002 Final Proof page 83 6.10.2006 5:21pm

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FIGURE 2.45 Observed temperature patterns on misaligned metal ribbon-type coupling (a) A graph of the coupling, (b) an infrared image of the coupling running under good alignment conditions,(c) an infrared image of the coupling running with the worst misalignment condition (d) temperature ofcoupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute,Shelburne, VT.)

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50 100 150

FIGURE 2.46 Observed temperature patterns on misaligned chain type coupling (a) A photograph ofthe coupling, (b) an infrared image of the coupling running under good alignment conditions, (c) aninfrared image of the coupling running with the worst misalignment condition (d) temperature ofcoupling at each 10 mil misalignment condition (Photos and data courtesy of Infraspection Institute,Shelburne, VT.)

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Bertin, C.D and Buehler, M.W., Typical vibration signatures—case studies, Turbomachinery national, October 1983, pp 15–21.

Inter-Bond, T., Application Update—Deltaflex Coupling—Vibration Analysis: Motor to Centrifugal Pump,Lovejoy Inc., October 1992, personal correspondence

Daintith, E and Glatt, P., Reduce costs with laser shaft alignment, Hydrocarbon Processing, August1996

Dewell, D.L and Mitchell, L.D., Detection of a misaligned disk coupling using spectrum analysis,Journal of Vibration, Acoustics, Stress, and Reliability in Design (1984), 106, 9–16

Eshleman, R.L., Torsional Vibration of Machine Systems, Proceedings of the Sixth TurbomachinerySymposium, December 1977, Gas Turbine Labs, Texas A&M University, College Station, TX.Eshleman, R.L., Effects of Misalignment on Machinery Vibrations, Proceedings of the Balancing=Align-Alignment of Rotating Machinery, February 23–26, 1982, Galveston, TX, Vibration Institute,Clarendon Hills, IL

Eshleman, R.L., The Role of Couplings in the Vibration of Machine Systems, Vibration InstituteMeeting, Cincinnati Chapter, November 3, 1983

Ganeriwala, S., Patel, S., and Hartung, H.A., The Truth Behind Misalignment Vibration Spectra ofRotating Machinery, SpectraQuest Inc., Richmond, VA, 2003

Jackson, C., The Practical Vibration Primer, Gulf Publishing Company, Houston, TX, 1979

Kueck, J.D., Casada, D.A., and Otaduy, P.J., A comparison of two energy efficient motors, P=PMTechnology, April 1996

Ludeca Inc., Maintenance Study, Evaluating Energy Consumption on Misaligned Machines, Doral, FL,1994

Mannasmith, J and Piotrowski, J.D., Machinery Alignment Methods and Applications, VibrationInstitute Meeting, Cincinnati Chapter, September 8, 1983

Nower, D., Misalignment: challenging the rules, Reliability Magazine (1994), 38–43

Nower, D., Alignment Tolerances—Why Use Them? 1996 Vibration Institute Meeting Proceedings,

pp 179–184

Piotrowski, J.D., How Varying Degrees of Misalignment Affect Rotating Machinery—A Case Study,Proceedings of the Machinery Vibration Monitoring and Analysis Meeting, June 26–28, 1984,New Orleans, LA, Vibration Institute, Clarendon Hills, IL

Piotrowski, J.D., Aligning Cooling Tower Drive Systems, Proceedings of the Machinery VibrationMonitoring and Analysis, Ninth Annual Meeting, May 20–24, 1985, New Orleans, LA, VibrationInstitute, Clarendon Hills, IL

Schultz, J and Friebel, D., The business case for reliability, Reliability (2002), 8(6)

Sohre, J.S., Turbomachinery Analysis and Protection, Proceedings of the First Turbomachinery sium, Gas Turbine Labs, Texas A&M University, College Station, TX, 1972

Sympo-Weiss, W., Laser alignment saves amps, dollars, Plant Services, April 1991

Wesley J.H., Edmondson, A., Carley, J., Nower, D., Kueck, J., Jesse, S., and Kuropatwinski, J.J.,Motor Shaft Misalignment and Detection—Phase 1, July 20, 1997, Maintenance and ReliabilityCenter, College of Engineering, University of Tennessee, Knoxville, TN

Xu, M and Marangoni, R.D., Vibration analysis of a motor—flexible coupling—rotor system subject

to misalignment and unbalance, Part I: Theoretical model and analysis, Journal of Sound andVibration (1994a), 176(5), 663–679

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Xu, M and Marangoni, R.D., Vibration analysis of a motor—flexible coupling—rotor system subject

to misalignment and unbalance, Part II: Experimental validation, Journal of Sound and tion (1994b), 176(5), 681–691

Vibra-Xu, M., Zatezalo, J.M., and Marangoni, R.D., Reducing power loss through shaft alignment, P=PMTechnology, October 1993

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3 Foundations, Baseplates, Installation, and Piping Strain

Every rotating machinery drive system requires some kind of supporting structure to hold it

in position Imagine for a moment, the design concerns for machinery that is located near ariver or a lake, on top of an underground aquifer, near a busy highway, in the middle of aswamp, operating on seagoing vessels, offshore oil and gas platforms, or on the 18th floor of

an office complex The foundations and support structures not only have to bear the weight

of the machinery but also have to be designed to maintain a stable position if the machinerybegins to vibrate Frequently alignment problems can be traced back to design, installation,

or deterioration problems with the foundation, base or soleplate, or the machine housingsthemselves It is going to be not only difficult to obtain accurate alignment initially but alsoequally difficult to maintain satisfactory alignment over long periods of time if the machinery

is sitting on unstable or improperly designed foundations and frames

Not all, but a large percentage of rotating machinery sits on or is somehow attached to theground When selecting a site for rotating machinery, civil engineers must be concerned with thesoil conditions and stability of the ground where the machinery is to be located To a greatextent, the Earth will act as a giant shock absorber for any motion that occurs in the machineryand also act as the main support for the equipment What is the earthbound rotating machinerysitting on—bedrock or sand? It is also common to find rotating machinery in the upper floors of

a building or on the roof Is the frame attached to beams or columns and what isolates the framefrom the building?

All types of rotating machinery will exhibit some level of vibration during its operation

so design engineers need to be concerned about how much vibration (or noise) can or will

be transmitted through the structure to the surrounding environment Foundations, tures, and machine casings can be rigorously designed and checked utilizing computer-aideddesign and engineering techniques before fabrication ever begins The field of structuraldynamics and finite element analysis has provided the means to calculate structural modeshapes and system resonances of complex structures to insure that frequencies from theattached or adjacent machinery do not match the natural frequency of the structure itself.However this technology cannot easily remedy all the equipment installed before theseanalysis tools were available and many of us are saddled with equipment sitting on poorlydesigned or constructed bases that are cracked or warped or static piping strain that was notcorrected during the installation or that has increased from the foundation settling over aperiod of time or from movement of the piping supports

struc-Over moderate to long periods of time soils, foundations, and structures will gradually shiftdue to a wide variety of factors Temperature changes from season to season, compaction ofsoils underneath foundations, swelling of base soils from water or freezing are some of themore common causes of shifting to occur It is unreasonable to assume that alignmentconditions will not change over time and periodic alignment checks should be performed

89

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It is important for the personnel who maintain rotating machinery to have a basic standing of how machinery should be supported and what problems to look for intheir foundations, baseplates, and frames to insure long-term alignment stability in theirmachinery.

under-In addition to the machinery to ground or structure interface, attention must also bedirected to any physical attachments to the machinery such as piping, conduit, or ductwork

It is desirable to insure that these attachments produce the minimum amount of force on themachinery to also insure good stability This chapter will hopefully provide the reader withthe basic foundation design principles and some techniques to check equipment in the field todetermine if problems exist with the foundation and frame, or the interface between themachinery and the foundation, or piping and conduit attached to the machine itself

3.1 VARYING COMPOSITION OF EARTH’S SURFACE LAYER

The best place to start this discussion is at the bottom of things All of us realize that there is amajor difference in stability as we walk along a sandy beach and then step onto a large rockoutcropping Different soil conditions produce different amounts of firmness Since rotatingmachinery could potentially be placed anywhere on the planet, the soil conditions at thatlocation need to be examined to determine the stability of the ground For new installations

or where foundations have shifted radically, it may be a good idea to have boring testsconducted on soils where rotating machinery foundations will be installed Table 3.1 showssafe bearing load ranges of typical soils The recommended maximum soil load from acombination of both static and dynamic forces from the foundation and attached machineryshould not exceed 75% of the allowable soil bearing capacity as shown in Table 3.1

3.2 HOW DO WE HOLD THIS EQUIPMENT IN PLACE?

I suppose someone has attempted to sit a motor and a pump on the ground, connected by theshafts together with a coupling, and started the drive system up without bolting anythingdown My guess is that they quickly discovered that the machines started moving around alittle bit after start up, then began moving around a lot, and finally disengaged from each otherhopefully without sustaining any damage to either of the machines Maybe they tried it againand quite likely had the same results I am sure they finally came to the conclusion that this

TABLE 3.1

Soil Composition

Bearing Capacities of Soils: Safe Bearing Capacity

Shale and other medium rock (blasting for removal) 10–15 0.96–1.43 Hardpan, cemented sand and gravel, soft rock (difficult to chisel or pick) 5–10 0.48–0.96 Compact sand and gravel, hard clay (chiseling required for removal) 4–5 0.38–0.58 Loose medium and coarse sand medium clay (removal by shovel) 2–4 0.20–0.38

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was not going to work for long periods of time and decided to ‘‘hold the machines’’ in theirstarting position somehow How are we going to do this exactly? What should we attach themto? How about some wood? No, better yet, something like metal or rock, something that isstrong.

Our rotating equipment needs to be attached to something that will hopefully hold it in astable position for long periods of time I have seen just about every possible configurationyou can imagine Even the scenario mentioned above The most successful installationsrequire that the machinery be attached to a stable platform that enables us to detach one

or more of the machines from its platform in the event that we want to work on it at anotherlocation Classically we attach and detach our equipment with threaded joints (i.e., bolts andnuts) You could, I suppose, glue or weld the machines to their platform, and it would just be

a little more difficult to detach them later on

The devices that we have successfully attached our machinery to are baseplates, soleplates,

or frames There are advantages and disadvantages to each choice The baseplates, plates, or frames are then attached to a larger structure, like a building, ship, aircraft andautomotive chassis, or Earth There are many inventive ways of attaching rotating machinery

sole-to transportation mechanisms (e.g., boats, mosole-torcycles, airplanes), and design engineers arestill coming up with better solutions for these types of machinery-to-structure interfacesystems Our discussion here will concentrate on industrial machinery

The vast majority of rotating machinery is either held in position by a rigid foundation(monolithic), attached to a concrete floor, installed on an inertia block, or held in position on

a frame There are advantages and disadvantages to each design There are also good waysand poor ways to design and install each of these methods to keep our machinery aligned andprevent them from bouncing all over the place when they are running In summary, machinesare attached to intermediary supports (i.e., baseplates, soleplates, and frames) that are thenattached to structures (i.e., buildings, floors, foundations) Figure 3.1 shows a typical rigid

FIGURE 3.1 Rigid foundation for induced draft fan

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foundation design, Figure 3.2 shows a typica inertial block (aka floating) design, andFigure 3.3 shows a typical frame design.

3.2.1 BASEPLATES

Baseplates are typically either cast or fabricated as shown in Figure 3.4 and Figure 3.5

A fabricated baseplate is made using structural steel such as I-beams, channel iron, angle,structural tubing, or plate, cutting it into sections, and then welding the sections together It isnot uncommon to replace structural steel with solid plate to increase the stiffness of the basesimilar to Figure 3.6

3.2.1.1 Advantages

1 Most commonly used design for industrial rotating machinery

2 Provides excellent attachment to concrete foundations and inertia blocks assuming theanchor bolts were installed properly and that the grout provides good bonding

3 Can be flipped upside down and grout poured into the cavity before final installationFIGURE 3.2 Spring isolated inertia block with motor and pump

FIGURE 3.3 Frame supporting a belt drive fan

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FIGURE 3.4 Cast baseplate.

FIGURE 3.5 Fabricated baseplate

FIGURE 3.6 Weak structural steel was replaced with solid plate on this baseplate

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4 Machinery can be placed onto the baseplate prior to installation and roughly aligned inthe lateral and axial directions to insure that the foot bolt locations are drilled andtapped accurately to hopefully prevent a bolt bound condition or incorrect shaft end toshaft end spacing

5 Equipment mounting surfaces can be machined flat, parallel, and coplanar prior toinstallation

6 Some designs include permanent or removable jackscrews for positioning the machinery

in the lateral and axial directions

3.2.1.2 Disadvantages

1 Usually more expensive than using soleplates or frames

2 Equipment mounting surfaces are frequently found not to be flat, parallel, and coplanarprior to installation

3 Difficult to pour grout so it bonds to at least 80% of the underside of the baseplate

4 Possibility of thermally distorting baseplate using epoxy grouts if pour is thickerthan 4 in

5 Frequently installed with no grout

3.2.2 SOLEPLATES

Soleplates are effective machinery-mounting surfaces that are not physically connectedtogether Figure 3.7 shows a soleplate being prepared for grouting on a medium-sized fanhousing They are typically fabricated from carbon steel and there are usually two or moresoleplates required per concrete foundation or inertia block Correct installation is more

FIGURE 3.7 Soleplate being prepared for grouting

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