Gears can be classified according to tooth shape, gear shape, tooth line shape, tooth surface and manufacturing method.
The profile of gear includes profile curve, pressure Angle, tooth height and displacement.
Involute gear is relatively easy to manufacture, so involute gear is the absolute majority of modern used gear, while cycloidal gear and circular gear are less used.
In the aspect of pressure Angle, the bearing capacity of gear with small pressure Angle is small.
But the high pressure Angle gear, although the bearing capacity is higher, but in the case of the same transfer torque bearing load increase, so only used for special cases.
And gear tooth height has been standardized, generally using standard tooth height.
The advantages of displacement gear more, has been throughout all kinds of mechanical equipment.
In addition, the gear can be divided into cylindrical gear, bevel gear, non-circular gear, rack, worm gear according to its shape;
According to the shape of tooth line, it is divided into spur gear, helical gear, herringbone gear and curved gear.
According to the surface where the gear tooth is divided into external gear, internal gear;
According to the manufacturing method can be divided into casting gear, cutting gear, rolling gear, sintering gear, etc.
The manufacturing material and heat treatment process of gear have great influence on the bearing capacity and dimension weight of gear.
Before the 1950s, gears were mostly carbon steel, alloy steel was used in the 1960s, and surface hardened steel was used in the 1970s.
According to hardness, the tooth surface can be divided into soft tooth surface and hard tooth surface.
The bearing capacity of the gear with soft tooth surface is low, but it is easy to manufacture and has good runnability. It is mainly used in the general machinery with no strict limit on the size and weight of transmission and small amount of production.
Because of the pairing gear, the small wheel burden is heavy, so in order to make the size of the gear work life roughly equal, the small gear tooth surface hardness is generally higher than the big wheel.
The bearing capacity of gear with hard tooth surface is high. It is hardened, surface hardened or carburized after the gear is cut in order to improve its hardness.
But in the heat treatment, the gear will inevitably produce deformation, so after the heat treatment must be grinding, grinding or fine cutting, in order to eliminate the error caused by deformation, improve the accuracy of the gear.
