The Importance of Shaft AlignmentStrategies for Ensuring the Uptime of Rotating Equipment

By Mark Ely & Karl Vietsch

A major part of keeping equipment running smoothly involves regular maintenance and upkeep and ensuringthat the machinery is kept lubricated and properly aligned.

When shafts or belts on rotating equipment are misaligned, the risk of costly, unplanned machine downtimerises dramatically. Misalignment also damages seals and couplings. Lubrication problems often can be traced toseals that have been compromised by shaft or belt misalignment. Simply replacing a seal will not stop futureseal failure and associated loss of lubricant — only correcting the misalignment will solve the problem.

Failure to align the shafts or belts properly will increase the amount of stress on the units, resulting in a rangeof potential problems that ultimately can seriously impact a company’s bottom line:

Increased friction, resulting in excessive wear, excessive energy consumption, and the possibility ofpremature breakdown of equipment

Excessive wear on bearings and seals, leading to premature failure

Premature shaft and coupling failure

Excessive seal lubricant leakage

Failure of coupling and foundation bolts

Increased vibration and noise

Shaft Misalignment

Shaft misalignment is responsible for asmuch as 50 percent of all costs related torotating machinery breakdowns.Accurately aligning shafts can prevent alarge number of machinery breakdownsand reduce much of the unplanneddowntime that results in a loss ofproduction. In today’s challengingenvironment of reducing costs andoptimizing assets, the necessity ofaccurate shaft alignment has never been

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Correctly aligned shaft

Parallel misalignment (or offset (top)) and angular misalignment (bottom)

greater.

Correct AlignmentMachines need to be aligned in both the horizontal and vertical planes. Misalignment can be due to parallel orangular misalignment, or a combination of both.

Basically, there are two types of misalignment: parallel (or offset) misalignment and angular misalignment.With parallel misalignment, the center lines of both shafts run parallel to one another, but they are offset. Withangular misalignment, the shafts run at an angle to one other.

Types of Shaft MisalignmentParallel misalignment can be furthersubcategorized as either horizontal orvertical misalignment. Horizontalmisalignment refers to misalignment ofthe shafts in the horizontal plane, whilevertical misalignment refers tomisalignment of the shafts in the verticalplane. Parallel horizontal misalignmentresults when the motor shaft is movedhorizontally away from the pump shaft,but both shafts still operate in the samehorizontal plane and parallel. Parallelvertical misalignment occurs when themotor shaft is moved vertically away fromthe pump shaft, but both shafts stilloperate in the same vertical plane andparallel.

Similarly, angular misalignment can befurther subcategorized as either horizontalor vertical misalignment. Angularhorizontal misalignment occurs when themotor shaft is at an angle with the pump shaft, but both shafts still operate in the same horizontal plane.Angular vertical misalignment occurs when the motor shaft is at an angle with the pump shaft, but both shaftsstill operate in the same vertical plane. Serious instances of misalignment can occur as a result of parallelmisalignment, angular misalignment, or a combination of the two.

Correcting Shaft AlignmentTraditional alignment methods still in common use today include visual inspection combined with astraightedge or ruler. The straightedge is positioned on two bearings supporting one or more shafts, while themaintenance inspector visually assesses whether or not the components are properly aligned. While such roughalignment methods have the advantage of being quick and relatively easy, they are also highly inaccurate anddo not produce the exacting degree of accuracy required by today's precision machinery.

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Overview of shaft alignment options -- (from left to right) straightedge, dial indic

ators, and laser shaft.

Dial indicators represent another traditional method of measuring misalignment. But while dial indicators dooffer a higher degree of accuracy, they also present certain problems. Not only do they require a high level oftechnical skill to be used properly, but the effort is also generally quite time-consuming.

Furthermore, dial indicators do not provide real-time values that enable technicians to simultaneously measureand attain correct alignment. Instead, the dial indicators must be removed and then reinstalled after eachalignment adjustment is completed. As a result, the process for obtaining critical measurements, such as feetvalues and coupling values, can be lengthy. Feet values indicate whether the pedestal or footing on which themachine rests is loose or compromised in some other way. Coupling values attest to the integrity of a couplingconnecting two shafts.

Laser-guided tools, generally speaking, are quick, accurate, easy-to-use, and require only a singleinstallation. In addition, they deliver consistently better accuracy than dial indicators and they do not requirespecial skills to obtain accurate results virtually every time. Shaft alignment laser-guided tools typically consistof two units, each capable of emitting a precise laser beam and detecting a laser beam from its mate, plus ahandheld control device.

The units securely mount to shafts via magnetic brackets and/or a magnetic chain. To run them, the operatoractivates the instrument via the handheld control device and each unit emits a precise laser line projected ontothe other unit’s detector. A display on the handheld device provides real-time coupling and feet values duringthe alignment process, avoiding the need to remove and reinstall the measuring units after each alignmentadjustment. In addition, the laser system tool documents the values, which can be downloaded to a computerand used as a benchmark for future alignment inspections.More advanced laser-alignment systems come with a built-in step-by-step alignment process, from preparation,inspection and evaluation through correction, reporting and analysis. Some models also offer a unique databaseto store data regarding visual inspections on oil leakage, oil level, foundation bolt status, and wear indications.

Laser-alignment methods represent a marked improvement over traditional methods. A laser-driven shaftalignment device allows one to adjust alignment with far more speed and accuracy than either the straightedgeor dial method. There are many devices available on the market, with different degrees of sophistication andprice ranges.

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Correct belt alignment

Types of misalignment

Belt or Pulley AlignmentBelt alignment or pulley alignment is alsoan important maintenance task and, whencarried out correctly, can preventunplanned shutdowns and achieveconsiderable cost savings. Because beltalignment depends on the correctalignment of the pulleys on which the beltoperates, belt and pulley alignment aregenerally considered one process. Beltalignment involves aligning the belts in a manner that results in the least wear on the belts and lowest energyloss for the machine or driver unit. In practice this means the grooves of the pulleys are in line with oneanother.

Consequences of Belt MisalignmentLike shaft misalignment, belt misalignment can result in a wide range of detrimental and sometimes dangerousconsequences, including:

Reduced efficiency of the machine

Increased wear on pulleys and belts

Increased friction

Excessive energy consumption

Increased noise and vibration and

Premature bearing and belt failure

Unless the misalignment is corrected,a new replacement belt will likelywear out quickly. Continuousoperation in a misaligned state alsowill increase wear on the pulleysthemselves, as well as their axles,shafts and bearings. Maintaining belts in proper alignmentis just as important as aligning shafts.For that reason, laser-guided beltaligning devices are an essential partof an up-to-date maintenanceoperator’s tool kit.

Belt alignment laser-guided toolsconsist of two components, a laseremitting unit and a 3-D receiver. Thetool uses V-guides along withpowerful magnets that quickly attachin the pulley groove to facilitate

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Measuring prallel and angular misalignment using a straightedge or a piece of

string.

alignment of pulleys even if they haveunequal widths or dissimilar faces.

Nature of MisalignmentAs with shaft misalignment, there arevarious types of belt misalignment. Inpractice, a combination of differentmisalignments is often encounteredsimultaneously. For this reason, it isimportant that an alignmentinstrument both diagnoses and detailsthe nature of the machine'smisalignment. The followingillustrations depict the three differenttypes of belt misalignment.

Vertical angle or twistedmisalignment occurs when one ofthe pulleys has an angular error fromthe vertical angle plane. This isusually caused by incorrectpositioning of the machine and can becorrected by lifting either the front or rear feet of the motor to which the pulley is attached, depending on thedirection of the vertical angle error. This differs from shaft alignment in that one never moves both feet in avertical direction to reach the desired result. Horizontal angle misalignment occurs when the driver and the driven unit are not positioned parallel toeach other. Incorrect positioning of applications, such as the motor, typically can cause this type ofmisalignment. Horizontal angle misalignment generally can be corrected by moving the front or rear feetforward or backward on their guides, depending on the direction of the horizontal angle error, in order to twistthe motor around its center.

Parallel misalignment is the least complex form of misalignment. It is often caused by the incorrectpositioning of the motor along its shaft axis, positioned either too far forward or backward compared to theother shaft. Or it can be caused by incorrect positioning of the pulleys on their respective shaft, where one ofthe pulleys needs to be adjusted on the shaft.

Belt Alignment MethodsBelt alignment can be performed by either traditional visual methods or the laser method. Traditional methodsusually employ strings and/or straightedges. Laser methods utilize a laser beam, which provides for a muchhigher degree of accuracy.

The main advantage of these traditional methods is the limited length of time needed for adjustment, althoughthe use of a straightedge takes more time than visual assessment alone. The major disadvantage is the lack ofaccuracy. For example, some belt manufacturers recommend a maximum misalignment of 0.5 degrees or even0.25 degrees, which is difficult to accomplish by using visual assessment. These traditional low-tech methodsinvolve a good deal of trial and error, naked eye approximation, and rough estimates. All told, that means alarge margin for error, which is unacceptable for precision pulley alignment.

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A laser belt alignment system enables one to adjust alignment with far more speed and accuracy than withtraditional methods. Systems available on the market can be categorized according to the way the devices areattached to the pulley and the way they align. Generally, there are two groups, one that aligns the face of thepulleys and one that aligns the grooves of the pulleys.

Most products on the market use the face or side of the pulley as a reference for aligning the pulleys and belts.The advantage of this method is that it can be used for belt types other than V-belts, such as timing belts.V-belts, however, comprise the majority of belts found on the market, especially in industrial applications. Themain disadvantage is that the face of the pulley is the only reference point. This means that only the faces ofthe pulleys are aligned with each other. This method results in varying degrees of accuracy when the pulleysare of different thickness, brands or kinds (e.g. one single-belt pulley and one multiple-belt pulley) or when thefaces are not well finished.

Products that align using the grooves of the pulleys in which the belt runs tend to provide substantially higherlevels of accuracy regardless of the thickness, brand or type of pulleys.

Soft Foot“Soft foot” is a condition in which one of the feet of a machine does not sit flat on the baseplate. Soft foot isamong the most common causes of misalignment. Accordingly, one of the first steps to take in an alignmentcheck is to assess the equipment’s foundation and employ a suitable shaft alignment tool to identify and correctpotential soft foot conditions. Some laser-guided alignment tools have a soft foot operation capability thatguides the user through corrective procedures. Shim plates generally can be used to bring machines back intoboth vertical and horizontal alignment.

Bearings out of square with their housings are another common cause of misalignment. Often a condition ofwear, the out-of-square bearing and/or its housing will need to be corrected or replaced in order to bringmachines back into alignment.

Maintaining Correct AlignmentOnce misalignment is detected, analyzed and corrected, an ongoing alignment maintenance program isimportant to keep operations running smoothly. As part of this maintenance, alignment checks should beperformed to document alignment conditions before a machine is removed from service. This gives users theability to install new or rebuilt machines with the same proper alignment values. In addition, a maintenanceprogram should include periodic checks to verify conditions are still within tolerance.

Taking these simple steps to detect, correct and maintain proper shaft and belt alignment can prevent costly,unplanned downtime. Fortunately, there is a range of modern laser-alignment options available to make thisprocess easier than ever before.

Mark Ely is currently based in Holland as a product marketing manager at SKF Maintenance Pro

ducts. He is aMarine Engineer graduate and served in cruise ships for a few years, where he quickl

y learned the real world,hands-on side of engineering. With nearly 25 years of service within SKF, Mr. Ely ha

s extensive experience inmaintenance applications and shaft alignment, as well as product development and pro

duct marketing. Mr. Elycan be reached at

mark.ely@skf.com

.

Karl Vietsch has worked for the SKF Condition Monitoring Centre, Livingston, for almost three ye

ars. Duringthis time, Mr. Vietsch has served as a Business Engineer (BSc), and provided alignme

nt support service bytelephone. In his role as a project manager for gearbox repair, he called SKF to do

the alignment job for agearbox that he and his team had repaired. Karl has significant mechanical hands-on

experience and has

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strived to make the lives of the alignment engineer and management easier. The resul

t of his efforts is thedevelopment of the SKF TKSA 60 and TKSA 80 shaft alignment systems. Reach Mr. Vietsc

h atKarl.Vietsch@skf.com

.

www.skf.com

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