A gear transmission transfers power between two or more toothed wheels that directly mesh with each other. Gears of different diameters affect the rotational speed within the gear system, and either cause acceleration or deceleration.
Different versions are available: for example, straight gears, gear racks and conical gears (also called bevel gears).
Gears are usually made of steel or stainless steel, but they are available in other materials such as plastic. Gears can also be supplied in hardened variants and/or with special surface treatments.
In addition to the standard range of gears, special gears based on drawings are also available. Even in the case of customised production, a suitable gear is available for each application.
The dimensions of a gear are determined by its "module" and number of teeth. The module is the ratio between the pitch circle diameter and number of teeth. The underlying formula is: m=d/z. Here, m = module, d = pitch circle diameter and z = number of teeth.
Since gears with different module values cannot mesh, gears intended to mesh within a gear system must have the same module. A gear drive with a large module can transmit greater forces than one with a small module.
A gear can also be used in combination with a non-rotating component, known as a rack. This type of drive allows the rack or gear to move in a longitudinal direction; usually to change the speed, torque and/or direction of the power source in the case of a reciprocating motion.
Common standards for transmission ratios are DIN 867 and DIN 868.
