Abstract:

Decreasing the probability of cone-losing of rock bit by improving the cone retention technique, it should have quite significant effect on reducing cost of drilling and increasing bit utilizing efficiency. This paper summarized the development history of cone retention or cone-locking technique of rock bits.
Principles and characteristics of several typical configurations,ball retainer, snap ring retainer, threaded ring retainer, and trapped ball cone-losing indicator, were described respectively.A new cone-losing indicator design, trapped rollerindicator,which utilizes the sharp changes of both twisting moment and ROP of bit as alarm signal, was introduced and analyzed. The
simulative drilling test have proved that this new technique have an ability to inspect the bearing clearance exactly, and the trapped roller will increase the twisting moment and decrease the ROP of bit by locking the cone utomatically when the critical clearance is reached.

Key words: roller bit, cone-lock, bearing, wear, cone-losing indicator