There are many kinds of gear materials, and there are many factors to consider when selecting them. The following points can be used for reference when selecting materials:
1) The gear material must meet the requirements of working conditions. For example, in order to meet the requirements of small mass, high power transmission and high reliability, the gear used in aircraft must be made of alloy steel with high mechanical properties; in mining machinery, the gear drive is usually made of cast steel or cast iron with large power, low working speed and high dust content in the surrounding environment; in household and office machinery, the power is very small, but It is required that the transmission is stable, low noise or no noise, and can work normally under the condition of less lubrication or no lubrication. Therefore, engineering plastics is often used as gear material. In a word, the requirement of working condition is the first factor to be considered when choosing gear material.
2) The size of gear size, blank forming method, heat treatment and manufacturing process shall be considered. Large size gears generally adopt casting blanks, and cast steel or cast iron can be selected as gear materials. The gears with medium or lower size requirements are usually made of forged blanks, which can be made of forged steel. When the size is small and the requirement is not high, the round steel can be used as the blank.
The methods of gear surface hardening are carburizing, nitriding and surface hardening. When carburizing process is adopted, low carbon steel or low carbon alloy steel shall be selected as gear material; nitriding process can be adopted for nitriding steel and quenched and tempered steel; when surface quenching is adopted, there is no special requirement for materials.
3) Normalizing carbon steel, no matter how to make the blank, can only be used to make gears working under stable or light impact, and can not bear large impact load; quenching and tempering carbon steel can be used to make gears working under medium impact load.
4) Alloy steel is often used to make gears with high speed, heavy load and working under impact load.
5) For the gear transmission of aircraft, the size of gear is required to be as small as possible, and the high-strength alloy steel with surface hardening treatment should be used.
6) The hardness difference of metal soft tooth surface gear should be 30-50 HBS or more. When the tooth surface of the small gear and the big gear has a large hardness difference (for example, the tooth surface of the small gear is hardened and ground, and the tooth surface of the big gear is normalized or tempered), and the speed is high, the harder tooth surface of the small gear will have a significant cold hardening effect on the softer tooth surface of the big gear, thus improving the fatigue limit of the tooth surface of the big gear. Therefore, when the hardness difference between the matched two tooth surfaces is large, the allowable contact fatigue stress of the large gear can be increased by about 20%, but it is necessary to pay attention to the tooth surfaces with high hardness, and the roughness value should be reduced accordingly.