Page 249 - Machinery Component Maintenance

Machinery Alignment 231

1 1. Make machine and/or piping adjustments while running, using vi-
bration as the primary reference.
12. Laser measurement represents another possibility. The OPTA-
LIGN@ method described on pages 184 and 185 has recently been
extended to cover hot alignment checks and is further explained on
pages 233 and 234.

Let us now examine the listed techniques individually.

Guesswork. Guesswork is rarely reliable. Guesswork based on experi-
ence, however, may be quite all right-although perhaps in such cases it
isn’t really guesswork. If a certain thermal growth correction has been
found satisfactory for a given machine, often the same correction will
work for a similar machine in similar service.

Trial-and-error. Highly satisfactory, if you have plenty of time to experi-
ment and don’t damage anything while doing so. Otherwise, to be
avoided.

Manufacturers’ Recommendations. Variable. Some will work well, others
will not. Climatic, piping, and process service differences can, at times,
change the growth considerably from manufacturers’ predictions based
on their earlier average experience.

Calculations Based on Measured or Assumed Metal Temperatures, Machine
Dimensions, and Handbook Coefficients of Thermal Expansion. Again, re-
sults are variable. An infrared thermometer is a useful tool here, for
scanning a machine for temperature. This method ignores effects due to
hydraulic forces, torque reactions, and piping forces.

Calculations Based on Rules of Thumb. Same comment as previous para-
graph.

Shut Down, Break Coupling, and Measure before Machines Cool Down.
About all this can be expected to do is give an indication of the credulity
of the person who orders it done. In the time required to get a set of mea-
surements by this method, most of the thermal growth and all of the
torque and hydraulic effect will have vanished.

Same as Previous Paragraph Except use CiampOn Jigs to Get Faster Mea-
surements Without Having to Break the Coupling. This method, used in
combination with backward graphing, should give better results than 6,
but how much better is questionable. Even with “quick” jigs, a major
part of the growth will be lost. Furthermore, shrinkage will be occurring