Electrical Apparatus magazine, June 2002 The Other Alignment Concern: Belt Pulleys

Misalignment between driving motor and driven machine shafts leads to many operating problems such as vibration, bearing damage, even shaft breakage. Misalignment between pulleys in a V-belt drive can also be troublesome, resulting in premature belt wear or breakage. Whereas coupled shafts may be misaligned in two ways (parallel or angular), belt pulley misalignment can take three forms: parallel, angular, or twist (in which no single plane contains both shafts).

Pulley alignment has traditionally been checked by placing a straight edge against one face of the pulleys so that it contacts the edges of both at four points (two on opposite sides of each pulley). A gap between pulley face and straight edge at any of those points indicates misalignment. A gap exceeding 5 millimeters per meter of center distance (or an angular discrepancy exceeding about one-half) is unacceptable.

That method has several shortcomings. First, simple measurements of that kind cannot readily evaluate twist (or some instances of angular) misalignment. Second, long center distances can require use of a taut string rather than a straight edge. Since a string is not rigid, it can bend at one of the contact points, resulting in an erroneous measurement. Two operators are needed to hold the string taut.

Laser alignment solves those problems as well as offering greater accuracy. A visible laser beam, usually spread into a fan shape, is sent from a transmitter clamped or magnetically attached on one pulley to a set of targets similarly mounted around the rim of the second pulley. Where the beam strikes the targets reveals at a glance the nature and magnitude of any of the three types of misalignment.

Some versions of this equipment add precision by centering both transmitter and a target directly in the pulley grooves, eliminating any error caused by irregularities in the side surface of either pulley. Time to complete the alignment check can be reduced at least 75% compared to the straight edge method.

Industry news...

Featured Technical Article
June 2002

On this page is a summary of the Electrical Apparatus June 2002 featured technical article, by Richard L. Nailen, P.E. , "The Other Alignment Concern: Belt Pulleys" Ein weiteres Problem der Ausrichtung: Riemenscheiben ... L'autre problème d'alignement: les poulies à courroie ... La Otra Preocupación Sobre el Alincamiento: Las Poleas para Correa...

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