Abstract: The life of drilling bit is directly determined by three roller bit bearing′s service life.In order to find out failure form,the failure causes and mechanism of three roller bit,and further improve the life of three roller bit,Macroscopic and microscopic analysis of failed three roller bit bearing are done in this article.The results show that failure of sealing system is one of the main reasons of the failure.Overload and unbalanced distributing loads and high temperature deteriorates wear resistance and strength of metal,big radial clearance between bearing and cutter,vibration in rotating are also the primary reason of three roller bit bearing failure.

Key words: roller bit, sliding bearing, high speed, failure analysis