Thermal stabilization equipment for dimensional heat treatment of bearing rings

Abstract

1. Heat treatment of bearing components, particularly rings, leads to distortion of the shape (ovality, conicity) and to a change in dimensions (size variation) as a result of development of elastoplastic strains. 2. Use of methods for hardening rings in salts, hot oil (120–180°C), ring rotation on shafts, or straightening reduces ring shape distortion, but it does not overcome their size variation. 3. An effective way of reducing both ovality and size variation for rings is use of special thermal stabilizing methods. 4. The optimum method of dimensional heat treatment is hardening of rings in a stepped go-die or go-gage. In contrast to a cylindrical die in a stepped die with the minimum pressing forces during heat treatment the prescribed interference is created between rings and a die (gage) over the whole martensitic transformation range. 5. In order to increase the efficiency of using a stepped die or gage it is necessary in selecting their entry diameters to introduce a correction for the original ring size after turning and die (gage) heating during operation, and in slecting their length the cooling rate should be considered in the region of the martensitic temperature range. 6. With the use of short dies (gages) it is desirable to use additional ring cooling in thermal stabilizing equipment which makes it possible to vary the rate of martensitic transformation providing the required interference over the whole martensitic transformation range.