Take the right steps to ensure proper drive belt alignment

By Dan Parsons, Senior Project Engineer, Gates Corp., Denver, CO May 24, 2006

Misalignment is one of the most common causes of premature belt failure. Depending on its severity, misalignment can gradually reduce belt performance by increasing wear and fatigue, or it can destroy a belt in a matter of hours or days. While the forms of misalignment may be fairly well understood, accurate measurements and acceptable limits must be determined if maintenance personnel are to take corrective action.

Types of alignment

Any degree of misalignment, angular or parallel, can decrease the normal service life of a belt drive.

Angular misalignment results in accelerated belt/sheave wear and potential belt stability problems with individual V-belts. A related problem, uneven belt and cord loading, results in unequal load sharing within multiple belt drives, and can lead to premature failure. Joined V-belts can suffer tie band separation when operating under misaligned conditions. Belt application engineers caution that angular misalignment has a severe effect on the performance of synchronous belt drives.

Symptoms such as high belt tracking forces, uneven tooth/land wear, edge wear, high noise levels, and tensile failure due to uneven cord loading are typical indicators of misalignment. Also, wide synchronous belts are more sensitive to angular misalignment than narrow belts.

Parallel misalignment results in accelerated belt/sheave wear and potential belt stability problems with individual V-belts. Uneven belt and cord loading is not as significant as with angular misalignment. Parallel misalignment affects V-belts more than synchronous belts. V-belts run in fixed grooves and cannot free float between flanges as synchronous belts can, to a limited degree.

Parallel misalignment is generally not a critical concern with synchronous belt drives as long as the belt is not trapped or pinched between opposite flanges, and as long as the belt tracks completely on both sprockets.

Synchronous sprockets are designed with face widths greater than belt widths to prevent problems associated with tolerance accumulation, and to allow for a small amount (fractions of an inch) of mounting offset.

As long as the width between opposite sprocket flanges exceeds belt width, the belt will automatically align itself properly as it seeks a comfortable operating position on both sprockets.It is normal for a synchronous belt to lightly contact at least one of the sprocket flanges in the system while operating.Synchronous belts rarely run in the middle of the sprockets.

See the June issue of PLANT ENGINEERING for the complete story.

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