what is a gear

A gear is a mechanical element with teeth on the rim that can continuously mesh to transmit motion and power. The application of gears in transmission has appeared very early. At the end of the 19th century, the principle of generative gear cutting method and special machine tools and cutting tools using this principle appeared one after another. With the development of production, the stability of gear operation was paid more attention.

gear structure

Generally, there are gear teeth, tooth grooves, end faces, legal faces, addendum circles, dedendum circles, base circles, and index circles.

gear teeth

Tooth for short, is each protruding part on the gear used for meshing. These protruding parts are generally arranged radially, and the teeth on the mating gear are in contact with each other, so that the gears can continue to mesh.

Alveolar

It is the space between two adjacent teeth on the gear; the end face is the plane on the cylindrical gear or cylindrical worm, perpendicular to the axis of the gear or worm.

end face

are the planes at both ends of the gear.

Law face

Refers to the plane perpendicular to the gear tooth line.

Addendum circle

Refers to the circle where the tip of the tooth lies.

root circle

It refers to the circle where the bottom of the groove is located.

base circle

The line of occurrence that forms the involute is a purely rolling circle.

Pitch circle

is the reference circle for calculating the geometric dimensions of the gear in the end face.

Classification of gears

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.

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. 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.

material for making gears

The steels commonly used in the manufacture of gears are quenched and tempered steel, quenched steel, carburized and quenched steel and nitrided steel. The 

strength of cast steel is slightly lower than that of forged steel, and it is often used in larger gears; gray cast iron has poor mechanical properties and can be used in

 light-load open gear transmission; ductile iron can partially replace steel to make gears; plastic gears are often used In places where light loads and low noise are

 required, the matching gears generally use steel gears with good thermal conductivity. In the future, gears are developing in the direction of heavy load, high speed, 

high precision and high efficiency, and strive to be small in size, light in weight, long in life and economical and reliable. The development of gear theory and 

manufacturing technology will further study the mechanism of gear tooth damage, which is the basis for establishing a reliable strength calculation method, and is the

 theoretical basis for improving the bearing capacity of gears and prolonging the life of gears; the development is represented by arc tooth profiles research new gear

 materials and new processes for manufacturing gears; study the elastic deformation of gears, manufacturing and installation errors, and the distribution of temperature

 fields, and modify the gear teeth to improve the smoothness of gear operation and ensure that the gears are fully loaded When increasing the contact area of the gear

 teeth, thereby improving the load-carrying capacity of the gear. Friction, lubrication theory and lubrication technology are basic work in gear research. Studying 

elastohydrodynamic lubrication theory, popularizing the use of synthetic lubricating oil and adding extreme pressure additives in the oil can not only improve the 

bearing capacity of the tooth surface, but also It can also improve transmission efficiency.

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