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What Are The Common Classifications Of Gears?

Dec 06, 2018

The gears can be classified into a tooth shape, a gear shape, a tooth line shape, a surface on which the teeth are located, and a manufacturing method.


The tooth profile of the gear includes a profile curve, a pressure angle, a tooth height and a displacement. Involute gears are easier to manufacture, so in modern gears, involute gears are the majority, while cycloidal gears and arc gears are less used.


In terms of the pressure angle, the load capacity of the small pressure angle gear is small; while the large pressure angle gear has a higher load carrying capacity, the load of the bearing increases under the same transmission torque, and therefore is used only for special cases. The gear height of the gear has been standardized, and the standard tooth height is generally used. The advantages of the displacement gear are numerous and have been used in various types of machinery and equipment.


In addition, the gear can also be divided into cylindrical gear, bevel gear, non-circular gear, rack, worm gear according to its shape; according to the shape of the tooth line, it is divided into spur gear, helical gear, herringbone gear, curved gear; The surface is divided into an external gear and an internal gear; according to the manufacturing method, it can be divided into a cast gear, a cut gear, a rolling gear, a sintered gear, and the like.


The manufacturing materials and heat treatment process of the gear have a great influence on the bearing capacity and dimensional weight of the gear. Before the 1950s, gears used carbon steel, and in the 1960s, alloy steel was used. In the 1970s, case hardened steel was used. According to the hardness, the tooth surface can be divided into two types: soft tooth surface and hard tooth surface.


The soft tooth surface has a lower bearing capacity, but it is easier to manufacture and has better running performance. It is often used in general machinery where the size and weight of the transmission are not strictly limited, and in small quantities. Because the paired gears have a heavier burden on the small wheels, the hardness of the small gear teeth is generally higher than that of the large wheels in order to make the working life of the large and small gears substantially equal.


Hard-toothed gears have a high load carrying capacity. After the gears are finished, they are quenched, surface hardened or carburized and quenched to increase the hardness. However, in the heat treatment, the gear is inevitably deformed, so it is necessary to grind, grind or finish after the heat treatment to eliminate the error caused by the deformation and improve the accuracy of the gear.