ROCK DRILL BIT

Abstract: The present invention relates to a rock drill bit for percussive drilling, comprising a head (11) and a shank (12). The shank (12) has a central boring in which a thread (14) is provided. The thread (14) is provided to cooperate with a corresponding thread in a drill string driven by a top hammer. The boring is connected to at least one fluid passage (15), which emerges in or in the vicinity of a front face (16) of the head (11). The fluid passage connects to a first groove (17), which connects to a second groove (18) wherein at least three second grooves are provided and form between them axially forward lands. Each land carries a gauge insert (21). The gauge inserts (21) are asymmetrically positioned on the drill bit and the second groove (18) extends radially inwards to or beyond an imaginery circle (C) touching the radially innermost points of the inserts (21) generally in the plane of the front surface (16).

Description: ROCK DRILL BIT Background of the invention The present invention relates to a rock drill bit for percussive drilling, comprising a head and a shank. The shank has a central boring in which a thread is provided, said thread being provided to cooperate with a corresponding thread in a drill string driven by a top hammer. The boring is connected to at least one fluid passage, which emerges in or in the vicinity of a front face of the head. The fluid passage connects to a first groove, which connects to a second groove. At least three second grooves are provided and form between them axially forward lands, each of which carries a gauge insert. Previously known drill bits of the above-mentioned type have a number of disadvantages. The chipways constitute only a small part of the total front face area of the head such that the average diameter of the cuttings have to be small. This means that the hitherto known bits are not particularly suited for excavation purposes. Furthermore their gauge inserts are many in number relative to the diameter of the bit, which means that the chipways must be relatively small. Many gauge inserts also means costly and time- consuming regrinding. In addition the relatively poor flushing resulting from the narrow or small chipways makes it possible for cuttings to build up on the center of the front face. This built-up process impairs transfer of energy to the solid rock material in the bore which also impairs the threads in the drill string. Objects of the invention An object of the present invention is to provide a rock drill bit with asymmetrically positioned gauge inserts for enhancing the average diameter of the cuttings. Another object of the present invention is to provide a rock drill bit with a limited number of big gauge inserts in comparison with the rock drill bit diameter, partly to increase diametrical wear and partly to facilitate the regrinding process. Still another object of the present invention is to provide a rock drill bit which improves the transfer of energy to the solid rock material in the bore and which also spares the threads in the drill string. Brief description of the drawings Fig. 1 shows a rock drill bit according to the present invention; Fig. 2 shows the rock drill bit in a cross section along the line ll-ll in Fig. 1 ; Fig. 3 shows the rock drill bit in a bottom view; Fig. 5 shows the rock drill bit in a cross section along the line V-V in Fig. 4. Detailed description of the invention A rock drill bit 10 for percussive drilling according to the present invention is shown in Figs. 1 and 2. The rock drill bit 10 comprises a drill head 1 1 and a shank 12 and has a center axis 1 3. The shank has a central bore provided with a thread 14. The thread 14 is provided to cooperate with a corresponding thread in a drill string driven by a top hammer, not shown. The bore connects to three flushing channels 1 5 emerging in or in the vicinity of a front face 1 6 of the head 1 1 . Preferably the front face 16 is perpendicular to the center axis 1 3. Each channel 1 5 connects to a first groove 1 7 which has radially outwardly increasing width and depth and which connects to a second groove or chipway 1 8. Each chipway 18 is substantially V-shaped and has substantially constant width and depth axially rearwards. The chipway 18 intersects the front face 1 6 in a frusto- conical bevel 1 9. The number of chipways 18 is larger than the number of the first grooves 1 7. Axially forward lands 20 protrude between the chipways 18. Each land 20 carries a gauge insert 21 which is inclined about 35° relative to the center axis 1 3. The number of lands 20 is 4 to 10 pieces and preferably 4 to 6 pieces, depending on the size of the drill bit. The outer diameter of the drill bit is determined by the gauge inserts 21 . The drill bit has three symmetry lines N 1 perpendicular to the center axis 1 3. The gauge inserts are asymmetrically positioned on the drill bit but are symmetrically positioned on each land. With the line ll-ll as a reference line, see 0° in Fig. 1 , the inserts 21 are placed anti-clockwise as follows: 65°; 1 1 7.5°; 182.5°; 237.5°; 302.5° and 357.5°. This means that every other chipway 18 has an available space proportional to 65° and that each of the rest of the chipways 18 has an available space proportional to 55°. An insert 21 is positioned such that it forms a first angle a with the center axis 1 3 and a first adjacent insert 21 A. That insert 21 forms a second angle β with the center axis 1 3 and a second adjacent insert 21 B. The first angle a is always different from the second angle β. The advantage with such a geometry is the possibility to manufacture some large chipways on the drill bit. The insert 21 projects a distance P1 perpendicularly from the bevel 1 9. Furthermore three front inserts 22 are provided in the front face 16 and each front insert projects a distance P2. The distance P1 is preferably somewhat larger than the distance P2, about 1 mm. Each gauge insert 21 has a diameter d measured at the grip portion of the insert. The diameter d is as large as 10 - 30 %, preferably 14 - 30 %, of the diameter of the rock drill bit diameter D. When comparing said available space or bow length for the chipway 18 and the gauge insert 21 diameter d the space is 1 .2 to 1 .6 times the gauge insert 21 diameter. The front inserts 22 and the flushing channels 1 5 form a crown of equal spacing about the center axis 1 3. Each chipway 1 8 has a radial extension L1 from the envelope surface of the lands 20 to the bottom of the V-shape that is 10 - 30 % of the drill bit diameter D and preferably 14 - 30 %. Stated another way the chipway 18 extend radially inwards to or beyond an imaginary circle C touching the radially innermost points of the inserts 21 in the plane of the front surface. The number of gauge insert 21 can be 4 to 10 pieces. The first groove 1 7 extends radially inwardly beyond the flushing channel 1 5 towards the center axis 1 3 of the drill bit and terminates in the vicinity of a central insert 23. The drill bit is provided with 6 axially rearwards lands 24 which have equal spacing of 60°, see Fig. 3. The rearward lands 24 are provided to guide the drill bit in case of deflection. The envelope surface of the rearward lands 24 is on a diameter which is less than the diameter of the envelope surface of the forward lands 20. Figs. 4 and 5 shows an alternative embodiment of a drill bit 10' according to the present invention constructed for drilling of smaller holes. Like reference numerals define like details as disclosed in connection with Figs. 1 - 3. In this embodiment the drill bit is provided with one central insert 23' in the front face 16' and four gauge inserts 21 '. No front inserts are present. The chipway 18' is substantially V-shaped and its width increases but its depth decreases axially rearwardly. The drill bit has only one symmetry line N 1 perpendicular to the center axis 1 3'. The drill bit has no rearward lands. Also in this drill bit the gauge insert 21 ' are asymmetrically positioned but centrally on each land 20'. With the line V - V taken as a reference, see 0° in Fig. 5, the inserts 21 ' are spaced as follows in the anti clock-wise direction: 96°; 1 85° and 272° . This means that an insert 21 ' is positioned such that it forms a first angle a' with the center axis 1 3' and a first adjacent insert 21 A' and a second angle β' with the center axis 1 3' and a second adjacent insert 21 B'. The first angle a' is always different from the second angle β'. Thus a drill bit with asymmetrically positioned gauge insert 21 , 21 ' has been disclosed, having chipways occupying a relatively large part of the total area of the drill head in order to increase the average diameter of the cuttings to increase penetration rate and to facilitate geological sampling during ordinary drilling. The drill bit 10, 10' has a relatively small number of large gauge insert 21 , 21 ' compared to the diameter of the drill head to resist diametrical wear and to facilitate regrinding. The drill bit improves power transfer to the hole bottom thereby increasing penetration rate while sparing the threads in the drill string from blow reflexions.

Claims: Claims 1 . A rock drill bit for percussive drilling, comprising a head (1 1 ) and a shank (12), said shank (12) having a central boring in which a thread (14; 14') is provided, said thread (14; 14') being provided to cooperate with a corresponding thread in a drill string driven by a top hammer, said boring being connected to at least one fluid passage (1 5;1 5'), which emerges in or in the vicinity of a front face (16;16') of the head (1 1 ), said fluid passage connecting to a first groove (1 7;1 7'), which connects to a second groove (18; 18') wherein at least three second grooves are provided and form between them axially forward lands, each of which carries a gauge insert (21 ;2T), wherein the gauge inserts (21 ;2V) are asymmetrically positioned on the drill bit and wherein the second groove (18;1 8') extends radially inwards to or beyond an imaginary circle (C) touching the radially innermost points of the inserts 21 generally in the plane of the front surface (16;1 6'). 2. A rock drill bit according to claim 1 , wherein a gauge insert (21 ;2V) forms a first angle (σ;σ') with the center axis (1 3;1 3') and a first adjacent gauge insert (21 ;21 A') and a second angle (β;β') with the center axis (1 3;1 3') and a second adjacent gauge insert (21 B;21 B') and wherein the first angle (a;a') is different from the second angle β' and wherein each gauge insert (21 ;2V) has a diameter (d) which is 10 - 30 %, preferably 14 - 30 %, of the diameter of the rock drill bit diameter (D) and wherein the second groove (18;18') is substantially V-shaped and has a substantially constant width and depth axially rearwardly. 3. A rock drill bit according to claim 1 or 2, wherein each second groove (18; 1 8') has a radial extension (L1 ) from the envelope surface of the lands (20;20') to the bottom of the V-shape that is 10 - 30 %, preferably 14 - 30 % of the drill bit diameter (D) and wherein the bow length of the second groove (18;18') is 1 .2 to 1 .6 times the gauge insert (21 ;2V) diameter (d). 4. A rock drill bit according to any of the preceding claims, wherein the number of second grooves (18) is larger than the number of first grooves (1 7) and wherein said second grooves form 4 to 10 axially forward lands (20) and wherein the number of gauge inserts (21 ) is 4 to 10 pieces. 5. A rock drill bit according to any of the preceding claims, wherein the first groove (1 7;1 7') extends radially inwardly towards the center axis (1 3; 1 3'and terminates in the vicinity of a centrally positioned insert (23;23') and wherein the gauge inserts (21 ;2V) are inclined about 35° relative to the center line (1 3;1 3').

Inventors: PALMBERG GOERAN, PALMBERG, GOERAN
Applicants: SANDVIK AB, SANDVIK AB (PUBL)
Application year: 1996
Main classification: E21B10
IPC codes: E21B10