Changeover bit for extended life, varied formations and steady wear.

摘要

A roller cone bit may (10) be used as a rotating drag bit by treating the roller cones as carriers (12) for a plurality of distinguishable types of drag cutters (14,16). The roller cones (12) are each coupled to a mechanism (32,46,56) which selectively allows rotation of the roller cones (12). The roller cones (12) are otherwise fixed and as the bit (10) is rotated, the drag cutters (14) are brought into operative engagement with the rock formation. However, where the roller cones are selectively allowed to rotate, rotation of the drag bit (10) rotates the roller cones (12) to thereby bring a second set of drag cutters (16) into an operative configuration for cutting the rock formation. A mechanism (58,64) then selectively locks the roller cones (12), to prevent further rotation, thereby keeping the second set of drag cutters (16) fixed in place. By selectively permitting rotation and preventing rotation of the roller cones (12), a plurality of sets of drag cutters (14,16) can be brought into an operative configuration for cutting the rock formation. Therefore, such a drag bit (10) may be employed to bring drag cutters (14,16) selectively into play to cut different types of rock formation, or to present renewed cutters (16) after an initial set of cutters (14) have been worn by a predetermined degree. Furthermore, rotation of the roller connes (12) may be slowed from that normally expected by application of a drag to each roller cone (12). The drag cutters (14,16) on each roller cone (12) will thereby be sequentially brought into an operative cutting configuration with respect to the rock formation and where will be evenly distributed among all the drag cutters (14,16) diposed on each roller cone (12).