They require tension to maintain the right amount of friction. Positive drive or synchronous belts rely on the engagement of teeth on the belt with grooves on the pulley.įlat belts are the purest form of friction drive while V-belts have a friction multiplying effect because of wedging action on the pulley. There is no slip with this belt except for ratcheting or tooth jumping. Modern flat belts are made with reinforced, rubberized fabric that provides strength and high friction levels with the pulley (Fig. This eliminates the need for high tension, lowering shaft and bearing loads. Flat belts have thin cross-sections and wrap around pulleys easilyĪ significant advantage of flat belts is efficiency of nearly 99%, about 2.5-3% better than V-belts. Good efficiency is due to lower bending losses from a thin cross-section, low creep because of friction covers and high modulus of elasticity traction layers, and no wedging action into pulleys. Pulley alignment is important to flat belts. Belt tracking is improved by crowning at least one pulley, usually the larger one.
Flat belts are forgiving of misalignment however, proper alignment improves belt life.ĭifferent flat belt surface patterns serve various transmission requirements. In high-horsepower applications and outdoor installations, longitudinal grooves in the belt surface reduce the air cushion flat belts generate. The air cushion reduces friction between the pulley and belt. The grooves nearly eliminate the effects of dirt, dust, oil, and grease and help reduce the noise level.įlat belts operate most efficiently on drives with speeds above 3000 fpm. Continuous, smooth-running applications are preferred. Speed ratios usually should not exceed 6:1. At higher ratios, longer center distances or idlers placed on the slack side of the belt create more wrap around the smaller pulley to transmit the required load. V-belts are commonly used in industrial applications because of their relative low cost, ease of installation, and wide range of sizes (Fig. The V-shape makes it easier to keep fast-moving belts in sheave grooves than it is to keep a flat belt on a pulley.
The biggest operational advantage of a V-belt is the wedging action into the sheave groove. This geometry multiplies the low tensioning force to increase friction force on the pulley sidewalls (Fig.
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