Improvements in the bits or cutters of rotary drills for drilling in coal, soft rocks and the like

摘要

752,525. Drills. DEACON, C. O. Aug. 24, 1954, No. 24572/54. Class 83 (3). A two-pronged bit for rotary coal &c. drills comprises cutting-tips of circular or semicircular shape in cross-section with ellipticallyshaped cutting edges made by cutting the top faces at an angle to the axis of the drill bit. A detachable bit is provided with prongs 2, 3, an apertured shank 5, and half-round cutting inserts 7, 8 spaced as shown in Figs. 1 and 3 or disposed adjacent one another (Fig. 7, not shown). The inserts are inclined at 11 to provide rake and are brazed to the bit. In a modification, (Figs. 4, 5 and 6, not shown), the inserts are of cylindrical shape and fixed in holes 15 in the bit. In a second modification (Fig. 8) the inserts 18 are fixed on radial flat surfaces 19 whilst the tangential surfaces 21 are each provided with a single insert 20, or two such inserts 24 (Fig. 16, not shown). Each prong may be provided with a single half-round or arcuateshaped insert as in Figs. 9, 12 and 13 (not shown); the embodiment of Fig. 12 embodying additional inserts 29 fixed to radial faces 30. The inserts of Fig. 3 may be less than half-round or of semi-elliptical shape (Figs. 14 and 15 respectively, not shown). The prongs of the bit may be twisted, Fig. 16 to provide radial faces 37, 38 to which half-round inserts 39, 40 are fixed as in Fig. 3. The cutting-faces may be machined on the shank metal and have a hardfacing metal applied thereto electrolytically, by spraying or by oxy-acetylene or electric welding. The inserts may be of high-speed alloy steel or hard-faced metal or provided with hardmetal facings.