Gears are subjected to multiple stresses during operation. For example, when transmitting power, the root of the tooth experiences bending stress, while the tooth surface undergoes contact stress. Understanding these stress distributions allows for the selection of an appropriate quenching process. If bending stress is the primary failure factor, gears made of medium-carbon steel can undergo surface hardening treatments such as induction hardening. This process provides high hardness and excellent wear resistance to the tooth root surface while maintaining a certain level of toughness in the core, effectively resisting bending fatigue.

For heavy-duty gears that endure high contact stress, carburizing and quenching may be a more suitable choice. In this process, low-carbon alloy steel gears are heated in a carbon-rich medium, allowing carbon atoms to diffuse into the tooth surface to a certain depth. The gears are then quenched and tempered at a low temperature, forming a hardened layer with high hardness and wear resistance. This significantly improves the gear’s resistance to contact fatigue wear, thereby extending its service life.

Different forms of wear occur during gear operation, including adhesive wear and abrasive wear. If a gear operates in an environment containing impurities, it is prone to abrasive wear. In such cases, an understanding of wear mechanisms suggests the use of chemical heat treatment methods such as nitriding. Nitrided gears develop a hard, chemically stable nitrided layer on the surface, which effectively resists cutting action from abrasive particles. Additionally, nitriding is performed at relatively low temperatures, minimizing gear deformation and helping maintain precision.

For gears operating under high-speed, heavy-load conditions where lubrication may fail locally, adhesive wear is likely to occur. In such situations, surface treatment methods such as hard chrome plating can enhance the friction properties of the gear surface, reducing adhesive wear.

In fact, not only gears but all mechanical components require a precise understanding of their actual working conditions to select and optimize the appropriate heat treatment process. Below is an example of a differential.

Function of a Differential

The power from a car’s engine is transmitted through the clutch, gearbox, and driveshaft before reaching the drive axle, which then distributes power to the half-shafts, driving the wheels. In this power transmission pathway, the drive axle is the final assembly, with its main components being the reducer and the differential.

Working Principle of a Differential

1.      When the driving wheels on both sides tend to slip, the driving force acting on each wheel is no longer equal. This imbalance is transferred through the half-shafts and half-shaft gears to the planetary gears, disrupting their equilibrium. As a result, in addition to rotating together with the differential case, the planetary gears also rotate on their own axes.

2.      When the driving wheels on both sides do not tend to slip, the force acting on both wheels is equal, keeping the planetary gears balanced. In this case, the planetary gears only rotate together with the differential case without self-rotation.