The commonly used steels for manufacturing gears include 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 is often used for larger gears; gray cast iron has poor mechanical properties and can be used in light-load open gear transmissions; ductile iron can partially replace steel in making gears; plastic gears are mostly used in places with light loads and low noise requirements, and the gears paired with them are generally steel gears with good thermal conductivity.
       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.
  Study the elastic deformation, manufacturing and installation errors and temperature field distribution of the gear, modify the gear teeth to improve the smoothness of the gear operation, and increase the contact area of the gear teeth at full load, thereby improving the load-bearing capacity of the gear.
       Friction, lubrication theory and lubrication technology are basic work in gear research. Studying the elastohydrodynamic lubrication theory, promoting the use of synthetic lubricating oil and appropriately adding extreme pressure additives to the oil can not only improve the load-bearing capacity of the tooth surface, but also improve the transmission efficiency.