The floating gear in the transmission is usually helical gear. Wherein, the normal force Fn is the comprehensive force of the gear; Tangential force Ft makes the gear transmit torque; The radial force Fr makes the inner hole of the gear exert pressure on the needle roller; Due to the existence of the axial and radial clearance of the gear, the axial force Fn causes the gear to tilt along the axial direction and swing during operation. During the swing of the gear, the inner hole of the gear produces small displacement axial reciprocating motion under the radial pressure with respect to the roller needle. This motion is called "fretting", and the resulting wear is called "fretting wear".
Fretting wear is a molecular wear process, that is, the two contact surfaces move back and forth with small displacement under vertical load, so that the contact surface is close enough to the extent that van der Waals force acts, resulting in material separation from the parent body and then being oxidized. It can be seen that the material loss caused by fretting wear is the result of the combined action of chemistry (oxidation) and machinery (loaded movement). The mechanical action scrapes off the oxide layer and adsorption layer, exposing the clean and active fresh metal surface. The fresh surface quickly absorbs the surrounding gas and oxidizes, which is a chemical action. Material loss is caused by alternating mechanical and chemical actions.
