On the basis of definition analysis of limit speed of famous foreign bearing companies, and tests of same bearings in machines with different heat transfer condition, different support method and different themral capacity, and other tests on different structural grease-lubricated bearings, it should be pointed out that the difinitions about limit speed in most companies are not strict enough. Proven by the test results, if is clear that the heat transfer condition is one of the key factors for limit speed. How to decide the limit speed on sealed bearings and the detailed datas are given in this paper.
