Gears can be classified by tooth shape, gear shape, tooth line shape, surface on which the gear teeth are located, and manufacturing method.
The tooth profile of the gear includes tooth profile curve, pressure angle, tooth height and displacement. Involute gears are relatively easy to manufacture, so among the gears used in modern times, involute gears account for the absolute majority, while cycloidal gears and arc gears are used less frequently.
In terms of pressure angle, the bearing capacity of small pressure angle gear is small; while the bearing capacity of large pressure angle gear is higher, but the load of the bearing increases under the condition of the same transmission torque, so it is only used in special cases. The tooth height of the gear has been standardized, and the standard tooth height is generally used. Displacement gears have many advantages and have been used in all kinds of mechanical equipment.
In addition, gears can also be divided into cylindrical gears, bevel gears, non-circular gears, racks, and worm gears according to their shapes; spur gears, helical gears, herringbone gears, and curved gears according to the shape of the tooth line; The surface is divided into external gears and internal gears; according to the manufacturing method, it can be divided into casting gears, cutting gears, rolling gears, sintering gears, etc.
The gear's manufacturing material and heat treatment process have a great impact on the gear's load-carrying capacity and dimensional weight. Before the 1950s, carbon steel was used for gears, alloy steel was used in the 1960s, and case-hardened steel was used in the 1970s. According to the hardness, the tooth surface can be divided into two types: soft tooth surface and hard tooth surface.
Gears with soft tooth surfaces have lower bearing capacity, but are easier to manufacture and have good running-in properties. They are mostly used in general machinery with no strict restrictions on transmission size and weight, as well as small-scale production. In the paired gears, the small wheel has a heavier burden, so in order to make the working life of the large and small gears roughly equal, the hardness of the tooth surface of the small gear is generally higher than that of the large gear.
The hardened gear has a high bearing capacity. It is quenched, surface quenched or carburized and quenched after the gear is finely cut to increase the hardness. However, during heat treatment, the gear will inevitably deform, so grinding, grinding or fine cutting must be carried out after heat treatment to eliminate errors caused by deformation and improve the accuracy of the gear.
