Wind-turbine gearboxes subject bearings to fluctuating loads, wide speed ranges, frequent starts and 20-year life expectations with costly high-altitude maintenance. Key requirements include through-hardened or carburised vacuum-degassed steels for cleanliness, deep and uniform case hardening, logarithmically profiled rollers to reduce edge stress, solid brass cages for shock duty, and measures against electrical erosion. Hengtuo's large spherical and tapered roller bearings serve wind gearbox and main-shaft positions with custom clearance and roller profiling options.