Gear is a kind of mechanical element with continuous meshing on the rim to transmit motion and power. The application of the tropical mould gear in transmission has appeared for a long time. At the end of the 19th century, the principle of generating gear cutting method and the emergence of special machine tools and cutting tools using this principle have attracted more and more attention with the development of production.

The commonly used steels for gear manufacturing 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, which is commonly used for gears with larger size; the mechanical property of gray cast iron is poor, which can be used in the open gear drive with light load; nodular cast iron can partially replace steel to make gears; plastic gears are mostly used in places with light load and low noise requirements, and the gears matched with them are generally steel gears with good thermal conductivity.

In the future, gears will be developed in the direction of heavy load, high speed, high precision and high efficiency, and strive for small size, light weight, long service life and economic reliability.

The development of gear theory and manufacturing process will further study the mechanism of gear tooth damage, which is the basis of establishing reliable strength calculation method, improving gear bearing capacity and prolonging gear life; developing new tooth profile represented by arc tooth profile; researching new gear material and manufacturing process; researching elastic deformation, manufacturing and installation of gear In order to improve the running stability of the gear, the distribution of the error and temperature field should be modified, and the contact area of the gear should be increased when the gear is fully loaded, so as to improve the bearing capacity of the gear.

Friction, lubrication theory and lubrication technology are the basic work in gear research. Studying the theory of elastohydrodynamic lubrication, popularizing the use of synthetic lubricating oil and properly adding extreme pressure additives to the oil can not only improve the bearing capacity of the tooth surface, but also improve the transmission efficiency.