Thursday, February 21, 2008

Timing Belts

Timing belts solve the slip problems of flat, O ring, and V belts by using
a flexible tooth, molded to a belt that has tension members built in. The
teeth are flexible allowing the load to be spread out over all the teeth in
contact with the pulley. Timing belts are part of a larger category of
power transmission devices called synchronous drives. These belt or
cable-based drives have the distinct advantage of not slipping, hence the
name synchronous. Synchronous or positive drive also means these belts
can even be used in wet conditions, provided the pulleys are stainless
steel or plastic to resist corrosion.

Timing belts come in several types, depending on their tooth profile
and manufacturing method. The most common timing belt has a trapezoidal
shaped tooth. This shape has been the standard for many years,
but it does have drawbacks. As each tooth comes in contact with the mating
teeth on a pulley, the tooth tends to be deflected by the cantilever
force, deforming the belt’s teeth so that only the base of the tooth
remains in contact. This bending and deformation wastes energy and
also can make the teeth ride up pulley’s teeth and skip teeth. The deformation
also increases wear of the tooth material and causes the timing
belt drive to be somewhat noisy.

Trapezoidal Tooth Timing Belt

Several other shapes have been developed to improve on this design,
the best of which is the curved tooth profile. A trade name for this shape
is HTD for High Torque Design. Timing belts can be used at very low
rpm, high torque, and at power levels up to 250 horsepower. They are an
excellent method of power transfer, but for a slightly higher price than
chain or plastic-and-cable chain

HTD Timing Belt Tooth Profile