pulley alinement after belt tension is adjusted, since movement of the equipment will cause undue wear
on new belts.
After a set of V-belts has been applied, the drive should be run for at least 15 minutes, allowing
the belts to stretch, become well seated in the grooves, and equalized on both sides of the drive before
they are checked for tension and correct matching. After the belts have made this preliminary run, check
the belt deflection; it should be about 1 inch at midspan. Run the drive at top speed, checking the driven
pulley speed with a hand tachometer; if it falls within 5 percent of calculated speed, the belts are tight
enough. If, however, the driven pulley speed cannot be brought up to rating, check the wear condition of
the sheaves since sheaves that are badly worn may not deliver the proper speed.
To find the speed of the driven pulley, use the following formula:
Speed of driven pulley = diameter of driving pulley x
speed in revolutions per minute
+ diameter of driving pulley.
The same formula is used for flat belts as for V-belts.
2.6.
ALINING SHAFTS
If two or more rotating shafts are coupled, proper alinement should be provided to eliminate
vibration and bending of the shafts. The method of securing satisfactory alinement will vary with the
number of bearings on each shaft and the type of coupling used. If shafts with single bearings are alined
properly, there will be no radial displacement between the coupled ends and no angular displacement of
shafts. If each shaft to be coupled has more than one bearing, a type of coupling must be used which
will permit a small amount of radial or angular displacement since it is not always possible to achieve
absolute alinement between two shafts carried in separate housings.
a. Radial misalinement. When the centers of the two shafts do not coincide, radial
misalinement occurs. The displacement, illustrated in figure 2.2, causes excessive vibration and wear
within the coupling because of radial movement of the two halves of the coupling with respect to each
other. This displacement also causes pulsating loads on the bearings, shortening their life.
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