Gear classification

Gears can be classified according to tooth shape, gear shape, tooth line shape, tooth surface and manufacturing method.

The tooth profile of the gear includes tooth profile curve, pressure angle, tooth height and displacement. Involute gear is easy to manufacture, so involute gear is the majority of modern gears, while cycloid gear and circular arc gear are seldom used.

In the aspect of pressure angle, the bearing capacity of small pressure angle gear is smaller, while that of large pressure angle gear is higher, but the bearing load increases under the same transmission torque, so it is only used in special cases. And the tooth height of the gear has been standardized, and the standard tooth height is generally used. There are many advantages of modified gears, which have been used in all kinds of mechanical equipment.

In addition, the gear can be divided into cylindrical gear, bevel gear, non-circular gear, rack, worm and worm gear according to its shape; spur gear, helical gear, herringbone gear and curve gear according to the shape of the tooth line; external gear and internal gear according to the surface of the tooth; casting gear, cutting gear, rolling gear and sintering gear according to the manufacturing method.

The manufacturing materials and heat treatment process of gears have a great influence on the bearing capacity and size and weight of gears. Before 1950s, carbon steel was used for gears, alloy steel was used in 1960s, and surface hardening steel was used in 1970s. According to the hardness, the tooth surface can be divided into soft tooth surface and hard tooth surface.

The gear with soft tooth surface has low bearing capacity, but it is easy to manufacture and has good running in performance. It is mostly used in general machinery with no strict restrictions on transmission size and weight and small production. Because of the heavy burden of the small gear in the matched gear, the hardness of the small gear surface is generally higher than that of the large gear in order to make the working life of the large and small gears approximately equal.

The bearing capacity of hard gear is high, it is after gear finishing cutting, then quenching, surface quenching or carburizing quenching treatment, in order to improve the hardness. But in the heat treatment, the gear will inevitably deform, so after the heat treatment, it must be grinded, grinded or finely cut to eliminate the error caused by the deformation and improve the accuracy of the gear