Page 202 - Machinery Component Maintenance

184 Machinery Component Maintenance and Repair

Face-Face-Distance Method

Advantages of face-face-distance:
1. It is usable on long spans, such as cooling tower drives, without
elaborate long-span brackets or consideration of bracket sag.
2. It is the basis for thermal growth measurement in the Indikon prox-
imity probe system, and again is unaffected by long axial spans.
3. It is sometimes a convenient method for use with diaphragm cou-
plings such as Bendix and Koppers, allowing mounting of indicator
holders on spacer tube, with indicator contact points on diaphragm
covers.

Limitations of face-face-distance:

1. It has no advantage over the other methods for anything except long
spans.
2. It cannot be used for installations where no coupling spacer is pres-
ent.
3. Its geometric accuracy will normally be lower than either of the
other two methods.
4. It may or may not be affected by axial shaft movement in sleeve
bearings, but this can be avoided by the same techniques as for
face-and-rim.

Laser-Optic Allgnment

In the early 1980’s, by means of earth-bound laser beams and a reflec-
tor mounted on the moon, man has determined the distance between earth
and the moon to within about 6 inches.
Such accuracy is a feature of optical measurement systems, as light
travels through space in straight lines, and a bundled laser ray with par-
ticular precision.
Thus, critical machinery alignment, where accuracy of measurement is
of paramount importance, is an ideal application for a laser-optic align-
ment system.
The inherent problems of mechanical procedure and sequence of mea-
suring have been solved by Prueftechnik Dieter Busch, of 8045 Ismaning
(West Germany), whose OPTALIGN@ system comprises a semiconduc-
tor laser emitting a beam in the infrared range (wavelength 820 mm),
along with a beamfinder incorporating an infrared detector. The laser
beam is refracted through a prism and is caught by a receiver/detector.