What is the difference between V-belts and Flat belts?

1. Flat-belt

In comparison to V-belts, flat belts require significantly higher pretensioning in order to transmit a certain torque without slippage. This especially applies to large transmission ratios and thereby low angles of contact. Tension pulleys with defined contact pressure are recommended in cases of this kind to reduce the transverse force.

Flat belts are not advisable for high outputs at high speeds.

Angle of contact increased by tension pulley for reducing transverse force.

2. V-belt

V-belts are characterized by their trapezium shaped (v-shaped) cross-section. They consist of a tensioning section of multiple layers of endlessly wound polyester fiber cord threads, the core which is made of a high-quality rubber mixture and the enclosure which is made of rubberized cotton or synthetic fabric. Depending on the intended use, different designs are used.

V-belt designs

  • a) Standard V-belt
  • b) Narrow V-belt
  • c) Narrow V-belt – open-edged, toothed
  • d) Wide V-belt (toothed)
  • e) Double V-belt
  • f) Joined V-belt
  • g) Poly V-belt

To increase the flexibility of the belt, multiple toothed V-belts are used, enabling smaller diameters. When loaded, the V-belt pulls itself into the trapezium shaped groove of the pulley and generates the friction contact required for torque transmission through the V-effect on both edges. The V-belt itself may not touch the bottom of the groove.

The fact that high standard forces between pulleys and belts occur at low pretension (thereby offering a good friction connection) offers advantages for the V-belt. These advantages include low bearing load and reliable operation even in the case of small angles of contact. The V-belt is less efficient in comparison with the flat belt, as it is restricted by the high amount of flexing required and the associated significant temperature increase of the belt.

With few exceptions, V-belts are manufactured as endless and supplied in standard lengths. Shaft spacing can therefore not be freely selected for the design of the V-belt gearbox. For installation reasons, certain constructive precautions are also to be taken.


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