Patent ID: 6948573
Filing Date: 2005-09-27
Classification: E21C

Abstract:
1. A device for breaking rocks comprising: a hollow cylindrical chamber having a closed lower end, a closed upper end, an access aperture in said closed upper end and an outer circumferential surface; a cylindrical plunger longitudinally-reciprocally disposed within the interior of said cylindrical chamber, said plunger being biased to a retracted position, the upper end of said plunger having an upper face and a converging portion below said upper face; at least two spools disposed equally around the circumference of said cylindrical plunger, each said spool including a converging upper end which is configured to be in slidable contact with said converging portion of said cylindrical plunger; at least two hardened inserts, each said hardened insert being secured to an outer face of an associated spool, each said hardened insert having a partial circumferential outer surface, which is coextensive with said outer circumferential surface of said cylindrical chamber, each said spool and its connected insert being biased to an inner retracted position; and means for applying a hydraulic pressure to said upper face of said cylindrical plunger; whereby said converging portion of said cylindrical plunger is urged to move downwardly, thereby urging said spools, together with said secured hardened inserts, radially-outwardly, so that said hardened inserts project radially outwardly from said outer surface of said hollow cylindrical chamber, and said cylindrical plunger including an upper threaded cylindrical portion, an adjacent, integral, cylindrical portion of greater diameter than said upper threaded cylindrical portion, an adjacent, integral frusto-conical portion, an adjacent, integral, depending cylindrical portion whose diameter is less than the diameter of said upper cylindrical portion, and a lowest integral adjacent conical point.