Thursday, May 31, 2012

Minimum Belt Wrap and Tooth Engagement

Synchronous belt horsepower ratings listed in our catalogs are based on a minimum of six teeth in mesh between the belt and the sprocket. The ratings must be corrected for excessive tooth loading if there are less than six teeth in mesh. The number of teeth in mesh can either be calculated using Design IQ or the simple formula below

Where:                   D = pitch diameter, large sprocket, inches
d = pitch diameter, small sprocket, inches
C = center distance between shafts, inches
Ng = number of grooves in small sprocket

In cases where fewer than six teeth are in full contact, 20% of the horsepower rating must be subtracted for each tooth less than six not in full contact.
In addition to the number of teeth in mesh, some drives with more than two shafts may have a greater potential for the belts to ratchet where loaded sprockets have six teeth in mesh, but a small arc of contact. In order to minimize this condition, each loaded sprocket in the drive system should have an arc of contact, or belt wrap angle, of at least 60 degrees. Non-loaded idler sprockets do not have tooth meshing or wrap angle requirements.

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