MUD SHAFT FOR THE DRILL STRING OF A ROTARY PERCUSSIVE DRILLING RIG, IMPACT STACK FOR A MUD SHAFT AND ROTARY PERCUSSIVE DRILLING RIG

摘要

A mud shaft for fitting into an outer drill string (5) of a rotary percussive drilling rig (1) having an overburden percussion mechanism is described. In this case, the rotary percussive drilling rig (1) has a central chisel bit (3), which is rotationally driven and is subjected to axial blows by a down-the-hole hammer (4), and a rotationally driven drill bit (6) subjected to axial blows by an external hammer (7). The mud shaft (8) has a cylindrical body, on the axial end regions of which standardized connecting threads (81, 82) are provided for connecting to the outer drill string (5) and to the external hammer (7), and which, at its end region facing the down-the-hole hammer (4) in the fitted state, has a blind-hole-like receptacle (83) which is connected to a supply bore (94) for the down-the-hole hammer (4). Arranged in the receptacle (83) is an impact stack (9) which comprises a number of annular steel discs (91) and, preferably vulcanized, elastomer discs (92). In this case, an elastomer disc (92) is always arranged between each two steel discs (91).