Page 254 - Machinery Component Maintenance

236 Machinery Component Maintenance and Repair

For electric motor growth, we have the following:

(Foot to shaft centerline, in.) (6 x (nameplate temp rise, OF) =
motor vertical growth, in. This is inconvenient, since motor temperature
rise is normally given in degrees centigrade. In case you have forgotten
how to convert, OF = (“C x 9/5) + 32.
Another rule says to use half of the above figure.
Then there is the rule that advises using 7 L, where L represents dis-
tance from base to shaft centerline in feet, and the answer comes out in
thousandths of an inch. Yet another source says to use 4 L. These rules all
assume uniform vertical expansion from one end to the other. However,
on motors having single end fans, the expansion will be greater at the air
outlet end. Angular misalignment caused by this difference can exceed
parallel misalignment caused by overall growth! The same can be true of
certain other machines with a steep temperature gradient from one end to
the other, such as blowers, compressors, and turbines.
The rules just cited were found in various published or filmed instruc-
tions from major pump manufacturers, oil refining companies and, in
one case, a technical magazine published for the electric power industry.
Their inconsistency, and their failure to recognize certain growth phe-
nomena, make their accuracy rather questionable. This is especially true
where piping growth can affect machine alignment.

References

1. Alignment Procedure, Revised Edition. Buffalo, N.Y. Joy Manufac-
turing Company, 1970. (This describes and illustrates a mathemati-
cal formula progressive calculation approach to determining correc-
tive movements based on reverse-indicator measurements.)
2. Baumann, Nelson P., and Tipping, William E., Jr., “Vibration Re-
duction Techniques for High-speed Rotating Equipment- ASME
Paper 65-WA/PWR-3.” New York: The American Society of Me-
chanical Engineers, 1965.
3. Dodd, V. R., Total Alignment. The Petroleum Publishing Company,
lblsa: 1975.
4. Dreymala, James, Factors Affecting and Procedures of Shaft Align-
ment. Dreyco Mechanical Services, Houston; 1974.
5. Essinger, Jack N., “Alignment of lbrbomachinery-A Review of
Techniques Employing Dial Indicators .” Paper presented at Second
Symposium on Compressor Train Reliability Improvement, Manu-
facturing Chemists Association, Houston, Texas, April 4, 1972.