Roymech engineering encyclopedia

Belt Drives

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Belt Drives


A belt drive is a method of transferring rotary motion between two shafts.    A belt drive includes one pulley on each shaft and one or more continuous belts over the two pulleys.   The motion of the driving pulley is, generally, transferred to the driven pulley via the friction between the belt and the pulley.  Synchronous/timing belts have teeth and therefore do not depend on friction.   Belt drives and gear transmissions have a much greater life expectancy than belt drives.  Belt drives also have relatively high inspection and maintenance demands

Belt Drive advantages

  • Easy, flexible equipment design, as tolerances are not important.
  • Isolation from shock and vibration between driver and driven system.
  • Driven shaft speed conveniently changed by changing pulley sizes.
  • Belt drives require no lubrication.
  • Maintenance is relatively convenient
  • Very quiet compared to chain drives, and direct spur gear drives

For belt drives, other than synchronous drives, the belts will slip in a high overload event providing a certain measure of safety.

The belts transferring torque by surface friction need to be in tension.   This results in the need for adjustable shaft centres or using tensioning pulleys

Types of Belt Drives

Note: More details and pictures of all belt types below are to be found at the links below table

Belt Type Description Notes
Flat Belt transfers torque by friction of the belt over a pulley. Needs tensioner. Traction related to angle of contact of belt on pulley. Is susceptible to slip. Belt made from leather, woven cotton, rubber, balata. Flat Belts
Vee Better torque transfer possible compared to flat belt. Generally arranged with a number of matched vee belts to transmit power. Smooth and reliable. Made from hi-text woven textiles, polyurethane, etc. Vee Belts
Poly-Vee Belt is flat on outside and Vee Grooved along the inside. Combines advantages of high traction of the Vee belt and the use of only one belt.  
Belt toothed on the inside driving via grooved pulleys. This enables positive drive. Limited power capacity compared to chain and Vee belt derivatives. Does not require lubrication. Extensively used in low power applications Timing Belts
Vee Link Belts Linked belts that can be used in place of vee belts. Advantage that the length can be adjusted and the belt can be easily installed with removing pulleys. Expensive and limited load capacity.  

Links to Belt Design
  1. Fenner .urethane Vee Belts etc
  2. Lathes . co. ..Notes on Flat Belting and Vee link belting
  3. Gates Industrial Drives.. .. Gates catalogue with info on timing belts, vee belts etc