Page 189 - Machinery Component Maintenance

Chapter 5

Alignment"

For most rotating machines used in the process industries, the trend is
toward higher speeds, higher horsepowers per machine, and less sparing.
The first of these factors increases the need for precise balancing and
alignment. This is necessary to minimize vibration and premature wear
of bearings, couplings, and shaft seals. The latter two factors increase the
economic importance of high machine reliability, which is directly de-
pendent on minimizing premature wear and breakdown of key compo-
nents. Balancing, deservedly, has long received attention from machin-
ery manufacturers and users as a way to minimize vibration and wear.
Many shop and field balancing machines, instruments, and methods have
become available over the years. Alignment, which is equally important,
has received proportionately less notice than its importance justifies.
Any kind of alignment, even straightedge alignment, is better than no
alignment at all. Precise, two-indicator alignment is better than rough
alignment, particularly for machines 3600 RPM and higher. It can give
greatly improved bearing and seal life, lower vibration, and better over-
all reliability. It does take longer, however, especially the first time it is
done to a particular machine, or when done by inexperienced personnel.
The process operators and mechanical supervisors must be made aware
of this time requirement. If they insist on having the job done in a hurry.
they should do so with full knowledge of the likelihood of poor alignment

* Main source: Malcolm G. Murray. Jr.. Alignment Manual for Hori:ontal. FlexiblF-
Coupled Rotating Machines-Third Edition, 1983: available from publisher. Murray
and Garig Tool Works. 220 E. Texas Avenue. Baytown. TX 77520: Tel. (713) 427-
5923. Adapted by permission. Certain portions of this chapter. e.g. laser-optic align-
ment and some of the alignment tolerance criteria. are from other sources.

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