A gear transmission transfers power between two or more toothed wheels which engage directly with each other. The rotation of the first wheel forces the other wheel to turn through the anchoring of the teeth. The gear system is a basic principle which has been in use for centuries and optimised over time. Wheels of different diameters affect the rotational speed within the drive, and either cause acceleration or deceleration. A gear system can also be used to change the direction of a power source.
Depending on their position and function within a gear system, gears are known as cog wheels or crown wheels. Various versions are possible, e.g. straight (with or without hub), as a conical gear (spiral bevel gear) or as a rack.
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. It is also possible to manufacture gears according to customer specification or drawing.
The mass of a gear is 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. With this type of drive it is possible to move the rack or gear in a longitudinal direction, and usually this forwards and backwards movement is in order to change the speed, torque and/or direction of a power source.
Common standards for transmission ratios are DIN867 and DIN868.
