Surface Strengthening Technologies: Key To Enhancing Gear Service Life

Core Surface Strengthening Technologies

• Laser Quenching Technology: A surface heat treatment process based on high-energy-density laser beams. It forms an extremely thin, high-hardness martensitic strengthened layer on the tooth surface through precise control of heating area and cooling rate. It features a minimal heat-affected zone (gear deformation is only 1/3 of traditional induction quenching), uniform and controllable hardened layer depth (usually 0.3–1.0 mm), and can achieve "targeted strengthening" for specific high-stress areas like tooth roots and meshing zones. Typical applications include high-speed EMU gears, aviation planetary gears and industrial robot reducer gears.

• Ion Nitriding Technology: Through glow discharge under vacuum conditions, nitrogen atoms penetrate the tooth surface to form a nitride compound layer and a diffusion layer. The compound layer consists of ε-Fe₂₋₃N and γ'-Fe₄N, while the diffusion layer serves as a tough transition zone. Operating at a low temperature (480–560°C) with minimal deformation, it is suitable for precision gears (grade 6 and above), achieving a surface hardness of HV 950–1200. Compared with non-nitrided gears, it improves contact fatigue life by 2–3 times and extends the pitting initiation period by approximately 60%.

• Shot Peening Technology: A mechanical surface strengthening process that bombards the tooth surface with high-speed metal or ceramic microspheres to introduce a residual compressive stress layer. This "cold plastic deformation" effectively offsets tensile stress peaks under operating loads and delays crack initiation. Key parameters include shot media (steel shots, ceramic shots, glass beads), intensity (Almen A value controlled at 0.2–0.4 mm) and coverage (≥ 100%). Experiments show it can improve gear bending fatigue life by 40%–70%.

• Composite Surface Strengthening Technology: Single strengthening methods are gradually replaced by composite processes in high-end rail transit gears. Examples include the "carburizing + shot peening + laser re-strengthening" combination (balancing hardness gradient and crack resistance) and the "ion nitriding + micro-polishing" scheme (enhancing surface finish and oil film formation). These processes perform exceptionally well under complex load conditions such as torque impact and variable-speed meshing, and have been applied in multiple subway gearboxes and wind power main transmission systems.

Future Development Trends

• Digital Control: Utilizing infrared temperature control feedback to regulate strengthening depth and uniformity.

• Green Manufacturing: Developing low-energy-consumption and nitrogen oxide emission-free environmentally friendly nitriding processes.

• Remanufacturing Application: Advancing re-strengthening technologies for gear repair and service life extension.