Approximately one-third of the electric motors in the industrial and commercial sectors use drive belts. Drive belts provide flexibility in the positioning of the motor relative to the load. Pulleys (sheaves) of varying diameters allow the speed of the driven equipment to be increased or decreased relative to the motor speed.
A properly designed belt power-transmission system offers high efficiency and low noise, requires no lubrication, and presents low maintenance requirements. However, certain types of belts are more efficient than others, offering potential energy cost savings. The majority of drive belts use V-belts, which use a trapezoidal cross section to create a wedging action on the pulleys to increase friction and improve the belt’s power transfer capability. Joined or multiple belts are specified for heavy loads. Drive belts can have a peak efficiency of 95% or more at the time of installation. Efficiency is dependent on pulley size, pulley wear, V-belt alignment, transmitted torque, under or oversizing belts for load requirements. Efficiency can deteriorate by as much as 5% over time if slippage occurs because the belt is not periodically retensioned.
The most important operational and maintenance issue in a drive belt is its tension. If belts are too loose, they tend to vibrate, wear rapidly, and waste energy through slippage. If belts are overtightened, they will show excessive wear. An increased belt load may shorten bearing life through excessive lateral loading and could possibly result in shaft failure. The proper tension of a V-belt is the lowest tension at which the belt will not slip at peak-load conditions. After the break-in period, belt tension should be checked every 3 to 6 months.
A notched belt has grooves or notches that run perpendicular to the belt’s length, which reduces the bending resistance of the belt. Notched belts can use the same pulleys as cross-section standard V-belts. They run cooler, last longer, and are about 2% more efficient than standard V-belts.
Synchronous belts (also called cogged, timing, positive-drive, or high-torque drive belts) are toothed and require the installation of mating grooved sprockets. These belts operate with a consistent efficiency of 98% and maintain their efficiency over a wide load range. In contrast, V-belts have a sharp reduction in efficiency at high torque due to increased slippage. Synchronous belts require minimal maintenance and retensioning, operate in wet and oily environments, and run slip-free. However, synchronous belts are noisier than V-belts, less suited for use on shock-loaded applications, and transfer more vibration due to their stiffness.
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