BEARING

 

Types of bearing ;

Rolling bearings, i.e ball and roller bearings, are reliable, inexpensive and easy to maintain. They are the only type of bearing used in small and medium size three phase motors. However, they have an upper size limit that is a functions of rotationsal speed. This limit depends on bearing type, size, load, method of lubrication etc. some times sleeve bearings are preferred for large motor sizes, even where rolling bearings could be used.

           

Bearing life of rolling bearing in motors is normally 25 000 to 100 000 hours L 10 to ISO R 281. Nominal life is the number of running hours at given speed for wich the bearing can rotate before signs of fatigue – scaling  - appear on the rings or rolling elements.

ISO definition L 10 means the length of life that 90 % of a large number of identifical bearings are expected to reach or exceed. Half of the bearing achieve as times the L 10 life.