Analysis of Gear Heat Treatment Defects

The gears installed in the transmission, reducer and differential undertake the tasks of changing speed, output torque and driving the vehicle. When the gear works, all the torque acts on the meshing teeth to make them bear great bending stress and contact stress, and periodically acts on each tooth to make it bear the effect of repeated alternating stress. In the process of meshing and transmitting torque or relative rolling, gears will also slide relatively and produce friction. The vehicle often shifts gears, causing the gear end to be hit many times.

In addition, due to different road conditions, environment and vehicle speed, the gear sometimes works under overload and strong impact conditions, resulting in a variety of different failure forms of the gear. Under the action of various stresses, the damage of vehicle gears can be divided into root damage and tooth surface damage. The former mainly includes fatigue fracture and impact fracture of tooth root; The latter is mainly characterized by spalling, excessive wear and gluing of the tooth surface. Therefore, the gear is required to have the following main properties: high bending fatigue strength and high contact fatigue strength, high hardness and good wear resistance on the tooth surface, and sufficient strength and toughness at the heart. However, gear damage is the result of many factors, such as improper processing, assembly, lubrication and use. Nevertheless, the strength of gear steel is still the focus of attention. Due to various reasons of gear heat treatment process and gear materials, various heat treatment defects have accelerated the local damage or even complete failure of the gear.

Based on the analysis of the stress state of vehicle gears, the defects easy to appear in the process of gear heat treatment and their influence on service performance are put forward. Under the required dimensional surface accuracy, normal bearing and good lubrication conditions, the main factors affecting the failure of vehicle gears are not only the defects of gear heat treatment, but also the chemical composition and metallurgical quality of the materials used to manufacture gears. Therefore, the R & D and application of gear materials and heat treatment technology can be strengthened, so as to gradually achieve the goal of strength, toughness, lightweight and high efficiency in the vehicle industry.

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