What Are The Categories Of Gears?

Gears can be classified according to tooth shape, gear shape, tooth line shape, surface where the gear teeth are located, and manufacturing method.
The tooth shape of a gear includes tooth profile curve, pressure angle, tooth height, and displacement. Involute gears are relatively easy to manufacture, so involute gears account for the absolute majority of modern gears, while cycloidal gears and circular arc gears are less used.
In terms of pressure angle, small pressure angle gears have a smaller load-bearing capacity; while large pressure angle gears, although they have a higher load-bearing capacity, increase the load on the bearing when the torque is the same, so they are only used in special cases. The tooth height of gears has been standardized, and standard tooth height is generally used. Displacement gears have many advantages and have been used in various types 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 shape; they can be divided into spur gears, helical gears, herringbone gears, and curved gears according to the shape of the tooth line; they can be divided into external gears and internal gears according to the surface where the gear teeth are located; they can be divided into cast gears, cut gears, rolled gears, sintered gears, etc. according to the manufacturing method.
The manufacturing material and heat treatment process of gears have a great influence on the load-bearing capacity, size and weight of gears. Before the 1950s, gears were mostly made of 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 two types: soft tooth surface and hard tooth surface.
Gears with soft tooth surface have lower load-bearing capacity, but are easier to manufacture and have good running-in performance. They are mostly used in general machinery with no strict restrictions on transmission size and weight, and small-scale production. Because the small wheel has a heavier load in the paired gears, in order to make the working life of large and small gears roughly equal, the hardness of the small wheel tooth surface is generally higher than that of the large wheel.
Gears with hard tooth surface have high load-bearing capacity. They are quenched, surface hardened or carburized and quenched after the gear is fine-cut to increase the hardness. However, during heat treatment, the gear will inevitably deform, so grinding, grinding or fine cutting must be performed after heat treatment to eliminate the error caused by deformation and improve the accuracy of the gear.