GB632876A - Improvements in or relating to an impact drill - Google Patents

Abstract

632,876. Earth-boring apparatus. BODINE, A. G. Sept. 12, 1947, No. 25040. Convention date, Sept. 16, 1946. [Class 85] In earth boring by percussion, the bit assembly, which may be suspended from a stand of drill pipe 14 or a cable, comprises a bit 18 rigidly attached to a heavy elastic column 17 of substantial cross-section, and a wave generator 16 which sets up in this column longitudinal vibrations. In the wave generator a small mass is caused to oscillate at high velocity, setting up in the ends of the column longitudinal oscillatory movement which is small in magnitude, but in consequence able to exert large forces which are communicated to the bit that pulverises the bottom 12 of the bore. This oscillating mass may be a piston 54 moving within the column under the action of the drill fluid pumped down the drill stem, its movement being controlled by a valve assembly 65-67 incorporated in the piston, and springs 55, 56. In an alternative form, the longitudinal oscillatory forces may be due to the drill mud rotating out-of-balance rotors mounted in chambers within the column. A third alternative is an electric motor driving a crank-shaft from which is pivotally suspended a mass, whilst a fourth alternative consists of a toothed sleeve mounted on the drill stem and arranged so that its teeth engage the wall of the borehole, with the result that, as the stem is rotated, the sleeve is caused to oscillate vertically due to coacting cam surfaces formed on the stem and the sleeve. The magnitude of the vibrations of the lower end of the column, and in consequence the pressure exerted on the bottom, may be varied by altering the crosssection of the column by tapering it or by increasing the mass of the lower end. The wave generator may be mounted at any position within the column, and the latter may be secured by an elastic coupling to a stem of drill pipe. In case of fracture of the elastic column by fatigue, a loose cable is connected between the top and bottom of the column to facilitate withdrawal of the fractured portions, whilst the column may have secured beneath it a bit suitable for boring curved holes. The Specification as open to inspection under Sect. 91 describes also how transverse vibrations are set up in the elastic column. This subject-matter does not appear in the Specification as accepted.