Gear classification


Gears can be classified according to tooth shape, gear shape, tooth line shape, surface where the teeth are located, and manufacturing methods.

The tooth shape 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 cycloid gears and arc gears are less used.

Picture:MH-D-L5018 Gear Bevel

In terms of pressure angle, gears with small pressure angles have a smaller load-carrying capacity; gears with large pressure angles have higher load-carrying capacity, but the load on the bearing increases under 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 adopted. There are many advantages of shifting gears, which have been widely used in various mechanical equipment.

Picture:MH-D-L4708 Gear

In addition, gears can also be divided into cylindrical gears, bevel gears, non-circular gears, racks, and worm gears according to their shapes; according to the shape of the tooth line, they can be divided into spur gears, helical gears, herringbone The surface is divided into external gears and internal gears; according to the manufacturing method, it can be divided into cast gears, cut gears, rolled gears, sintered gears, etc.

The manufacturing material and heat treatment process of the gear have a great influence on the load-carrying capacity and dimensional weight of the gear. Before the 1950s, carbon steel was mostly used for gears, alloy steel was used in the 1960s, and case-hardened steel was mostly used in the 1970s. According to the hardness, the tooth surface can be divided into soft tooth surface and hard tooth surface.

The gear bearing capacity of the soft tooth surface is relatively low, but it is easier 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-scale production. Because the small wheel bears the heavier burden among the paired gears, in order to make the working life of the large and small gears roughly equal, the hardness of the tooth surface of the small wheel is generally higher than that of the large wheel.

Hardened gears have a high load-carrying capacity. After the gears are cut, they are quenched, surface quenched or carburized and quenched to increase the hardness. But in the heat treatment, the gear will inevitably be deformed, so grinding, grinding or fine cutting must be carried out after the heat treatment to eliminate the error caused by the deformation and improve the precision of the gear.

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