Hardening Slewing Bearings, Starter Rings and Gears

Induction heating is frequently used for hardening industrial gears, rings and bearings. The speed, consistency, flexibility and accuracy that induction heating offers helps manufacturers optimize capital expenditures, increase production options, improve hardening quality, and maximize energy efficiency.

Slewing Bearings
A "slewing" bearing is a rotational rolling-element bearing that supports a heavy , slow-turning or slow-oscillating load. Slewing bearings are critical components of wind turbines, solar trackers, heavy construction equipment, and tower cranes. The bearing teeth and raceways are hardened to increase their strength and resist wear.

Special Gears
Induction heating is also well suited to hardening large gears with special toothed parts that are used in to manufacture other machinery. Most induction solutions for special gears are based on proven scanner designs; GH IA develops customized machines for each part, based on individual customer specifications and requirements.

Starter Rings
A starter ring is a medium carbon steel ring with teeth that is fitted on the outside edge of a flexplate or flywheel of an internal combustion engine, mostly for automotive applications. The teeth of the starter ring are hardened to increase their strength and resist wear. After hardening, the rings are tempered to reduce the remaining stress.

The Hardening Process
Hardening is accomplished by controlling the power applied, the frequency of the inductor current and the heating and cooling times. The treatment can be achieved by one of two methods: a static process the part is placed in front of the inductor and neither moves; or a scanning process in which either the part or the inductor moves in a controlled, continuous operation.

A single Model GTV induction heating machine can be used to harden both the gear raceways (inner and outer) and the gear teeth (inner and outer). Different ring sizes (up to 1500 mm diameter) can be accommodated by machines that incorporate a clamping and rotating system. The gears can be hardened in horizontal, vertical or inclined position.

For effective hardening of slewing bearings, large gears and starter rings, induction heating machines with 150kW to 300kW of output power and operating frequencies in the range of 5kHz to 10kHz are normally used.

To achieve consistent results, this operation requires a consistent gap between the inductor (coil) and part surface. However, the parts undergo progressive metallurgical transformation as they are heated and slight geometric distortions are not uncommon. Since the size and weight of the parts make them difficult to move, the position of the inductor must be adjusted to compensate for the distortion of the parts as they are heated.

GH Group has developed a Coil Position Dynamic Correction System which detects the level of geometric distortion in the part and adjusts the position of the inductor (coil) to achieve the required gap consistency.

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