A DRAG BIT FOR ROTARY ROCK DRILLING

Abstract: A drill bit of the drag bit type for rotary drilling has three cylindrical cutting inserts (13) that are clamped against the bit body by means of wedges that are pre-stressed by means of one or more threaded connections that have axes that are substantially longitudinal with respect to the bit. A single threaded connection can be common to all the wedges and it can be subject to the reaction torque in the tightening direction during drilling.

Description: A DRAG BIT FOR ROTARY ROCK DRILLING The most common way of securing cutters or inserts for a bit body of a rock drill bit is to braze them to the bit body. A disadvantage is that the inserts cannot be replaced. Several other ways of securing cutters or inserts are also known. In US patent 829 634 a drill bit is shown in which blade formed "cut¬ ters" have shanks which are clamped by wedging action to the bit body. This way of securing the cutters is " suitable only for drill bits adapt¬ ed to loose formations only. In British patent specification 1 377 280 a drill bit. is shown in which cutters or inserts are screwed to holders which are then affixed to the bit body. The inserts are backed up poorly and the screws that hold the inserts are likely to be destroyed, so that the inserts cannot be easi- ly released. It is an object of the invention to provide a rugged, rigid drag bit for rock drilling in which the inserts are both reliably secured and easy to release. To this end the inserts are clamped as defined in the claims. Fig 1 is a longitudinal section through a drag bit according to the in¬ vention. Fig 2 is a transverse section taken along line 2-2 in Fig 1. Fig 3 is a view of the drag bit shown in Fig 1. Fig 4 is an end view seen as indicated by the arrows 4-4 in Fig 3. Fig 5 is a longitudinal section through a drag bit according to the in¬ vention. Fig 6 is an end view seen as indicated by the arrows 6-6 in Fig 5. Fig 7 shows a detail of the drag bit shown in Figs 5 and 6. Fig 8 is a view seen as indicated by the arrows 8-8 in Fig 7. Fig 9 is a longitudinal section through a drag bit according to the in¬ vention. Fig 10 corresponds to Fig 9 but shows some details in view. Fig 11 is an end view as indicated by the arrows 11-11 in Fig 10. Fig 12 is a longitudinal section through a drag bit according to the in¬ vention. Fig 13 is a transverse section taken along line 13-13 in Fig 12. Fig 14 is a longitudinal view corresponding to Fig 12. Fig 15 is an end view seen as indicated by the arrows 15-15 in Fig 14. Fig 16 is a longitudinal section through a drag bit according to the invention. Fig 17 is a transverse section taken along line 17-17 in Fig 16. Fig 18 is a longitudinal view corresponding to Fig 16. Fig 19 is an end view seen as indicated by the arrows 19-19 in Fig 18. Fig 20 is a longitudinal view through a drag bit according to the in¬ vention. "" **' Fig 21 is a transverse section taken along line 21-21 in Fig 20. Fig 22 is a longitudinal view corresponding to Fig 20. Fig 23 is an end view seen as indicated by the arrows 23-23 in Fig 22. The drill bit shown in Figs 1-4 comprises a steel body 12 that is screwed to a drill stem 11. Three circular cylindrical inserts or cutter plates 13 are clamped substantially transversely in their back¬ ing sockets in the body by means of wedges 16. The wedges are pre- clamped by means of three screws 17 that are screwed into the wedges and are parallel with the rotation axis 1 of the bit. The wedges en- gage the flat circular cutting surfaces of the inserts. Cylindrical pins 18 extend into corresponding cylindrical blind bores in the body 12 and in the inserts 13 in order to lock the discs in their positions. The pins 18 can be loose and they can have a slide fit in the bores or they can be secured either to the bit body or to the inserts, preferably to the cutter discs. The use of pins 18 for locking is not quite necessary but it is advantageous. The drill bit has a central flushing channel 19 that is branched into three branches, one leading to each insert. The flushing channel 19 is supplied with flushing fluid through a central flushing channel in the drill stem 11. The pins 18 are perpendicular to the cutting surfaces of the inserts. In the embodiments that are described below some details that corre¬ spond to details in the embodiment according to Figs 1-4 have been given the same reference numerals as in these figures. The drill bit shown in Figs 5-7 has a body 12 and a removable central body 20 that forms three wedges 21-23. The central body has a thread inserts 13 can simultaneously be clamped by means of the nut 25. Pins 18 are suitably used as in the embodiment according to Figs 1-4 al ¬ though they are not shown. ■ The drill bit shown in Figs 9-11 has a body 11 that comprises a base 30, three separate top pieces 31-33, a central body 34 and a sleeve 35. The central body 34 has a flange 36 that cooperates with shoulders 36 on each of the three top pieces, and it has a thread 38 that cooperates with the base 30. The sleeve 35 forms a conical wedge 39 together with the three top pieces 31-33. When assembling the bit, one may screw it together by hand only. The reaction .torque during drilling tends to tighten the bit. During the tightening, the wedge surfaces 39 will stick and turning will occur in the annular support 40 between the • sleeve and the base 30. It is of course necessary that there is clear- ance 41 between the three top pieces 31-33 in order for the three in ¬ serts to be clamped. Trie drill bit shown in the Figs 12-15 comprises a base 42, a sleeve 43 and a top piece 44.. The top piece has three slots 45 so that its upper portion is divided into three parts. The sleeve has a conical surface 46 by which it forms a conical wedge arrangement together with the three upper portions of the top piece, and the reaction torque during drilling tightens a thread 48 in the same way as it does with the drill bit according to the Figs 9-11. The drill bit according to the figures 12-15 has the advantage that the top piece and the inserts are held to¬ gether as a unit also when the bit is disassembled. The pins 18 are shown inserted in through bores 47 instead of in blind bores since they must be inserted from the outside. Suitably, they are fastened with "Lock Tite" or the like in the bores of the top piece. They can alter- natively be in the form of screws that are screwed into threaded bores in the top piece. Another alternative is to use screws with heads and screw the screws into threaded blind holes in the inserts. The drill bit shown in the Figs 16-19 comprises a base 50, a sleeve 51, a top piece 52 and three separate wedges 53 for clamping the inserts 13. The wedges 53 are put in place from below before the top piece is mounted in the base 50 and they are prevented from falling out by the sleeve 51. The sleeve 51 can be screwed on from below until its thread be limitedly axially movable but it cannot fall out. The top piece 52 can then be screwed into the base 50 and the reaction torque during drilling tightens the thread 54 between the base 50 and the top piece so that the top piece 52 is screwed down into the base 50, that is, the sleeve 51 forces the wedges forwardly (upwardly) relative to the top piece to clamp the inserts 13. The sleeve 51 acts upon shoulders 55 on the wedges 30. The base 50 is not necessary but the top piece 52 can be screwed di- rectly on a drill stem that has an end similar to the end of the illu¬ strated base. The Figs 20-23 show a drill bit that is rather like the one show in the Figs 16-19. It distinguishes from the latter in two ways. The wedges have a larger angle of wedge action and the contact surface 58 between the base and the sleeve is spherical. These two differences reduce the demand on the tolerances. The larger angle re¬ sults in that the wedges need be forced forwardly a shorter distance and that differences in size have a smaller effect on the position of the wedges. The spherical surface makes the sleeve 51 take up oblique positions when necessary so that the same force is applied to all the wedges. The spherical surface 58 has its radial center 59 in the plane through an annular contact surface 60 of the sleeve against shoulders 55 of the wedges. This annular contact surface 60 is suitably rounded in its transverse section as can be seen in Fig 20. The inserts 13 can suitably be General Electric Stratapax (TM) cutter plates that ' comprise a tungsten carbide cylinder with a thin very hard diamond containing layer on the one of its flat end faces that form the cutting surface. If the cutting portion of the circular cutter plates has been worn, the wedges can be released and the cutter plates turned so that an unworn part of the cutting surface can be used. If any part of the body would be worn out before the cutter plates are worn out, the cutter plates can be moved to another bit body.

Claims: Claims 1. Drag bit for rotary rock drilling having at least two releas- able cutting inserts (13) , which are clamped substantially transvers¬ ely in the drill bit by means of wedging elements (16,21,39,45,53), the wedging elements being pre-stressed by means of a threaded connection (17,24,38,48,54) which has an axis that is substantially longitudinal with respect to the drill bit, c h a r a c t e r ¬ i z e d b y an element 16,21,31,44,53 in engagement with a part of the cutting surface of a respective insert (13) for clamping the insert against a cutter backing surface of the bit. 2. Drag bit according to claim 1, c h a r a c t e r i z e d i n that the inserts (13) are turnable about an axis that is trans¬ verse to their cutting surfaces, the inserts (13) being claimable in various positions of turning. 3. Drag bit according to claim 2, c h a r a c t e r i z e d i n that each insert .(13) is guided by a pin (18) that is perpendicular to the cutting surface of the insert and the insert is turnable about the axis of the pin. 4. Drag bit according to any one of the preceding claims, c h a r¬ a c t e r i z e d in that said threaded connection (24,38,48,54) is common to all the inserts (13) of the bit and its axis coincides with the rotation axis of the bit. 5. Drag bit according to claim 4, c h a r a c t e r i z e d i n that said threaded connection (38,48,54) is arranged to be subjected to the reaction torque during drilling in the direction of tightening. 6. Drag bit according to any one of the preceding claims, c h a r a c t e r i z e d i n that said inserts (13) have flat cutting surfaces. 7. Drag bit according to claim 6, c h a r a c t e r i z e d i n that said inserts (13) are circular. 8. Drag bit according to claim 4 or 5, c h a r a c t e r i z e d i n that there are three inserts and three wedges and a tiltable ele¬ ment (51, Fig 20) is arranged to equalize the forces applied to the wedges. 9. Drag bit according to claim 8, c h a r a c t e r i z e d i n that said tiltable element is a sleeve (51) that rests in a spherical socket in order to be tiltable.

Inventors: ANDERSSON K, EKWALL C, LEWKOWICZ J
Applicants: ANDERSSON K, ATLAS COPCO AB, EKWALL C, LEWKOWICZ J
Application year: 1980
Main classification: E21B10
IPC codes: E21B10