N o v e m b e r 2 0 0 1 A S H R A E J o u r n a l 3 3

ASHRAE Journal Alignment

A

Management GuideTo Alignment

About the Author

By Victor Wowk, P.E.

Victor Wowk, P.E., is president ofMachine Dynamics, Albuquerque,N.M.

s a young plant engineer in 1983, I remember a 230F (110C)

hot water pump that repeatedly wore out mechanical seals ev-

ery 10 to15 days. Each shutdown cost the company about

$4,000 in lost production. The mechanics told me the pump was aligned

each time they replaced the seals, but it never occurred to me that they

had no instruments to align precisely and no training. This was a failure

in management. Our solution was to replace the pump with a new one

at an installed cost of $8,000. This solved the seal wear-out problem,

and we felt good that we had saved the company from further $4,000

shutdowns to replace seals. But our ignorance was expensive. We could

have aligned the pump initially in a precise manner and saved the com-

pany about $32,000 worth of grief.

inspector can use. One is to ask simplequestions such as:

Was the alignment checked after workwas completed?

What method was used for alignment? What were the initial and final con-

ditions of the shafts?Documenting the readings is a good

way to control the process of aligningand the final outcome. All coupled ma-chines need to be precisely aligned on-site. It is foolish to trust the manu-facturers alignment. At the factory, wherethe machines are mounted on the base,they are typically spaced up with a roughalignment. The evidence of this is thesame shim pack under all four feet. I rou-tinely align new machines on-site priorto start-up and usually find that the fac-tory alignment does not meet industrystandards. Therefore, all machines needto be checked for proper alignment priorto startup, especially if the shims arepainted over. Other indicators of the needfor alignment are:

A repair history of failures of cou-plings, bearings, and seals;

Binding, when turned by hand; Fluid leakage; Shredded elastomeric coupling ma-

terial in the vicinity; Loose bolts; Cracks; Abnormal noise; and Excessive temperature at the cou-

pling.The only real definitive indicator of

proper alignment is to swing a set of read-ings and compare the shaft positions toacceptable industry standards. In lieu ofdial indicator or laser readings, vibrations

This type of shaft-to-shaft coaxialitycomes to mind whenever the word align-ment is mentioned. Figure 1 shows twomachines on a base coupled togetherwith a semi-flexible coupling.

However, alignment of machines in-cludes more general orientations to runsmoothly and minimize wear. There arebearing alignments, i.e., bearings mountedto be perpendicular to shafts, gear align-ments, pulley alignments, and the properorientation of mounting surfaces.

Straightness is a significant parameterfor shafts and rotors. Flatness is a signifi-cant parameter for bases and foundations.There are also dynamic and thermalmovement effects that need to be com-pensated for on some machines.

The alignment technician needs tohave more general knowledge and skillthan simply swinging readings and shim-ming machine feet, but aligning shaftsto be coaxial is a good place to start. Thisarticle provides an overview of the tech-nology of shaft alignment so that people

responsible for expensive machines andprocesses can make informed decisionsabout the need for alignment and how torecognize when it is done correctly.

The consequences of inadequate align-ment are premature deterioration of cou-plings, bearings, and seals. Misalignmentcreates dynamic stresses on bearings andcouplings, distorts the shafts, and wearsclearances in close running seals.

The time to failure can be very short(a few minutes for an elastomeric cou-pling to unravel for gross misalignment)to several years, until accumulated fa-tigue damage fails a bearing at 50% ofits expected 20-year life. Misalignmentusually creates some abnormal noiseand vibration, which is detectable im-mediately at start-up.

How to Recognize MisalignmentVibration analysis can be used to di-

agnose misalignment along with othermechanical defects, but there are somesimple and obvious symptoms that an

3 4 A S H R A E J o u r n a l w w w. a s h r a e j o u r n a l . o r g N o v e m b e r 2 0 0 1

ASHRAE Journal

can be used as acceptance criteria, but not rejection. That is,low vibration is evidence of a good alignment, but high vibra-tion does not mean poor alignment, because other defects cancause the same or confounding vibration.

How to Correct MisalignmentTo correct misalignment, measure the existing shaft orienta-

tion, calculate how much to move and in which direction, andthen precisely move one or both machines with small, con-trolled movements. Instruments used for measurement are:

Straight edges, feeler gages, and wires, Dial indicators, and Lasers.Prior to 1950, high-speed machines (3,600 rpm) were pre-

cisely positioned using straight edges, feeler gages, and wires,and they ran okay. A precise alignment is still possible todayusing these instruments and a conscientious aligner. The vari-able is the person doing the alignment. Because of the variableresults, many companies have moved on to more precise andquantifiable measuring instruments. However, acceptable align-ments are still achievable using straight edges and feeler gages.

Dial indicators are the most useful instruments because theyare most universal. Dial indicators can be used in the reverse-indicator setup (Figure 2) and in the face-and-rim setup (Figure3) along with all of their variations. Dial indicators can be used tomeasure shaft runouts and soft foot directly. Soft foot is a fieldterm that describes uneven bases and results in casing distortion.Dial indicators can also measure other types of distortion andgeometric features by re-fixturing the indicators. Dial indicatorsare used from the smallest spindles to aligning the largest ma-chines on the planet. They are the most universal because noother instrument, including lasers, can do all that dial indicatorscan. Typical fixture costs are $1,000 to $3,000 for a starter set.

Lasers are the most restrictive. They can only use the reverse-indicator method on machines that the clamps and heads will fiton. They have difficulty with small machines because the clampswill not fit and there is insufficient clearance to rotate the heads.Lasers cannot use the face-and-rim method without special slid-ing T-clamps. The face-and-rim method is necessary when onlyone shaft can be rotated. The face-and-rim method, which only

dial indicators can do, is the preferred method for large ma-chines and long drive shafts with significant shaft sag. Lasersdo automate the measurement and calculation parts of the taskand remove some opportunities for confusion. Lasers do notleave the machines in any better alignment condition than dialindicators are capable of achieving. They achieve equivalentresults as dial indicators, but at 10 times the initial cost. Typicallaser fixtures costs are $5,000 to $40,000.

The important observation to make when observing align-ment is that two indicators are required. A single indicatorcannot determine the four points required to plot the orienta-tion of the two shafts.

All machines are moveable; it is just that some are moreeasily moved than others. When the proper instruments andmethods are used, it is perfectly valid to move either, or all,machines to achieve coaxiality.

There are presently no ISO or ANSI standards for machinealignment, but there are some guidelines and/or specificationswithin industry and government. A good specification shoulddefine the final desired results at the machine shaft interface.It should not restrict the technician to specific instruments,like laser aligned, or specific methods like no more than0.002-in. (0.05 mm) rim-and-face runout of the coupling. Thelatter does not consider coupling runout, bar sag, thermalgrowth, or casing distortion.

The aligner is typically the last person to handle the ma-chine prior to startup. There is a window of opportunity here,with tools in place, to detect and correct some defects that

Figure 1: Alignment usually denotes coaxial shafts.

Figure 2: Reverse indicator setup.

Shaft A 0.010 in.

Dial A

Dial B

Shaft B

N o v e m b e r 2 0 0 1 A S H R A E J o u r n a l 3 5

Figure 3: Face-and-rim setup.

affect reliability. Therefore, a good specification should askthe aligner to measure for, or as least consider, the followingfactors:

Safety: Is everything tight? Timing: of the alignment when all work around the ma-

chine is done; Pipe strain; Couplings: for proper axial spacing; Bases and foundations: for rigidity and stability; Casing distortion (soft foot): caused by non-flat mount-

ing surfaces; Allowable shims: stainless steel is preferred;

Shaft A

FaceRDG

Shaft B

Rim Reading

Shaft runout: more than 1.0-mil Total Indicator Reading(T.I.R.) will cause vibration problems;

Thermal growth: when temperature rise is more than 20F(11C) (which means all motors); and

Bolt-bound conditions: how can this be handled (i.e.,what are the allowable fixes)?

A good alignment specification should also define the ac-ceptable offset and angularity of the shafts, and require docu-mentation of its final condition. Such an alignment specifica-tion was composed for Sandia National Laboratories as part ofa federally funded project. This specification is available onthe web at www.mt-online.com/current/05-00sa.html.

Advertisement in the print edition formerly in this space.