Rock bit with extended centre jet

摘要

A rotary cone bit for drilling bore holes in earth formations whose body has a thread pin end and a dome end 18 from which extend three legs 14. A cutter cone 20 rotatably mounted to each leg 14 and is radially orientated about the bits central axis 36. Each cutter cone 20 has a gage row 28 of cutting elements 26 extending from the cone surface nearest the mouth 24 and a nose row 30 extending nearest the cones apex. A centre jet 32 for emitting fluid or mud is located on the dome 18. The jet 32 has a converging nozzle 34 with an exit orifice 57 which extends above a predefined horizontal plane intersected by the nose row cutting elements 30. The exit orifice 57 has a constant diameter for a length at least equal to its diameter for reducing the diffusion of the fluid or mud flow emitted. Fluid or mud emitted from the centre jet travels substantially uninterrupted within a cylindrical space 40 between the cones which is not invaded by any cutting element. This reduced diffusion substantially uninterrupted fluid flow strikes the bore hole bottom with maximum impact energy for enhanced removal of earth formation cuttings.