| 摘要 |
<p>An earth-boring bit (11) has a cutter (15) provided with hard gage inserts (61; 71) that protrude from the gage surface (23) of the cutter (15) to engage the side of the borehole for holding gage. The gage insert (61; 61) has a substantially flat, polygonal face (63; 73), the sides of the polygonal face (63,;73) defining at least a pair of sharp cutting edges (65; 75) and at least a pair of cutting surfaces (67; 77) that define a negative rake angle with respect to the sidewall (51) of the borehole that is being sheared by the gage insert (61; 71). The face (63; 73), cutting edge (65; 75), and cutting surface (67; 77) of the gage insert (61; 71) are formed of a super-hard and abrasion-resistant material such as polycrystalline diamond or cubic boron nitride. The body (33) of the insert (61; 71) is formed of a hard, fracture-tough material such as cemented tungsten carbide. The improved gage inserts (61; 71) are secured into sockets in the gage surface (23) of the rolling cone cutter (15) by interference fit. The improved gage inserts (61; 71) provide an actively cutting gage surface that engages the sidewall (51) of the borehole to promote shearing removal of the sidewall material. Such an improved gage insert (61; 71) provides an earth-boring bit (11) with improved gage-holding ability, and improved steerability in directional drilling operations. <IMAGE></p> |
