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V-Belt Construction (Polyester vs Kevlar)

Standard v-drive belts are usually made from rubber with polyester tensile cords. Although this combination may vary depending upon manufacturer and belt type. Reinforcing cords can be cotton, steel or aramid.


Kevlar is a branded name of an aramid synthetic fibre with a tensile strength to weight ratio many times greater than standard steel.


Using aramid tensile reinforcement cords will improve the shock resistance capability of the belt as well permit the transmission of additional drive power.


A standard wrapped v-belt shown with trapezoidal rubber section and polyester tensile cords.

A heavy duty wrapped v-belt shown with trapezoidal rubber section and aramid tensile cords.


The aramid reinforcements offer high strength and durability as well limiting belt stretch.

As a general guide to the tensile strengths of individual reinforcing cord materials, the following general values were found.

  • Polyester 70 Mpa
  • Steel 300 Mpa
  • Kevlar 3000 Mpa

Obviously, for v-belt construction, the strength and power transmission capabilities of the belt will depend upon the size and quantity of reinforcing cords as well as the cross section size and material of the belt. /p>


Therefore, for correct selection of a v-belt it is recommended to study the supplier’s technical literature. This will guide you through the process and will consider the application, speeds, power transmitted and the centre distance between sheaves.


Charts like this from the manufacturer can be used to help select the correct section size of v-belt.






This chart is specific to a manufacturer’s range of aramid reinforced belts.