Materials for gears

As a basic rule one can assume that the elements of a gear pair can be best chosen from different materials, or rather, of materials with different hardness.

Examples: a pinion of hard or thermal treated steel with cast steel or half hard steel wheel -a pinion of synthetic resin with cast iron wheel – hardened steel worm with worm gear of cast iron or bronze.

It is only in gear pairs composed of elements of roughly the same dimensions and for the transmission of large powers that one chooses similar but hardened materials.

In this case, given the large hardness and (possibly) the grinded tooth surfaces, the friction is limited to a minimum and the wear is very small. Examples: gearboxes for machine tools, for vehicles, etc…

For the current gear construction, the following materials are normally used according to the to transfer power:

  • Pinion from soft steel or synthetic resin, nylon or PVC with cast iron wheel (small powers).
  • Pinion of half hard or hard steel with cast steel wheel (average powers).
  • Pinion of cemented and hardened steel, with a wheel of cast iron or cast steel (average powers and high speeds).
  • Pinion of heat treated steel with wheel of cast iron or forged steel (high powers).
  • Pinion of heat treated steel with wheel of cast iron or forged steel (high powers).
  • Pinion and wheels of smaller sizes gripping with each other, of hardened alloy steel, for the transfer of large powers on high rotational speeds.

The right choice of the material for pinion or wheel can be derived from the behaviour in operation of an existing gear pair or from the strength calculation of gears, depending on the selected characteristics. For economic reasons it is advisable to adhere to normal available material types.

The following tables show the denomination according to the standards NBN en DIN, the breaking strength, hardness, the permitted bending stress and wear resistance factor, used in the strength calculations.

In many cases, a change in the materials leads to the improvement of the resistance to wear and pitting, of an existing gear pair, whose physical characteristics are preserved.

A simple comparison of the permitted stresses or of the resistance factors against wear admits to find the extent to which the gear pair can be strengthened.

We recommend our customers to consult us in case of problems: we can calculate for you the gear pairs with problems and advise you about the best appropriate materials.