ROCK DRILL BIT AND METHOD FOR ITS MANUFACTURING

Abstract: The present invention relates to a rock drill bit (1) for percussive drilling, especially top hammer drilling. The rock drill bit (1) comprises a bit head (3) provided with rock crushing means (11), and a skirt (5). The drill bit (1) is provided with a number of grooves (16) for drill cuttings on the outside of the skirt (5) which extend in the axial direction of the drill bit (1). Protruding lands (17) are defined between the grooves (16) for drill cuttings, which likewise extend in the axial direction of the drill bit (1). The drill bit (1) has means (9) for connecting the drill bit (1) to a drill rod (7). At least some of the ends of the lands (17) facing away from the rock-crushing end of the drill bit (1) are formed which retrac teeth (18). The distinguishing feature of the drill bit according to the present invention is that each retrac tooth (18) has an edge (19), which extend along the circumference of the skirt (5). The present invention also relates to a method for manufacturing of a rock drill bit according to the present invention.

Description: ROCK DRILL BIT AND METHOD FOR ITS MANUFACTURING Technical area of the invention The present invention relates to a rock drill bit for percussive drilling, especially for top hammer drilling and a method for the manufacturing of a rock drill bit in accordance with the preambles of the independent claims. Prior art The drill bit intended for percussive drilling and its associated drill string comprising drill rods shall be removed from the drilled hole after a bore is completed. Therefor the drill bit and the drill string are rotated usually in an opposite direction compared to when drilling of the drilled hole occurs. However, in connection with withdrawal of the drill bit from the drilled hole loose rock material from the bore wall impairs withdrawal of the drill string and the drill bit. To correct this problem it is customary that the drill bit at its rear end, i.e. at the end surface facing away from a drill bit front surface, has inserts or chisels, hereinafter called retrac teeth, which during rotation of the drill string and the drill bit, in connection with retraction of the drill string and the drill bit from the drilled hole, crush the rock material which has become loose from the bore wall. Said retrac teeth are made by means of special milling operations, which consequently constitutes additional operations besides the usual operations for the manufacturing of a rock drill bit of the current type. However, the shaping of these known teeth at the rear end of the drill bit means forming of sharp corners in connection with said teeth. This in turn means that cracks are generated in connection with said teeth during operation of the drill bit. US-A-5,743,345 shows in Fig. 3 a rock drill bit with an associated drill rod, where the drill bit is provided with special cemented carbide buttons at its rear end, which function in a corresponding manner as the above-described teeth at the rear end of the drill bit. To provide special cemented carbide buttons at the rear end of the drill bit makes the manufacturing of a rock drill bit of the current type more expensive. Objects of the invention One object of the present invention is to provide a rock drill bit of the above-captioned type, wherein the retrac teeth of said rock drill bit are formed such that crack formation to a high degree is avoided in connection with said retrac teeth. Another object of the present invention is to provide the retrac teeth of the drill bit to allow that transfer of impact energy between the drill rod closest to the drill bit situated and the drill bit occurs by means of so-called shoulder abutment. The objects of the present invention are realized by means of a rock drill bit and a method for manufacturing of a rock drill bit, which attained the features of the appended claims. Short description of the drawings Below follows a description of an embodiment of a drill bit according to the present invention, and reference is made to the enclosed drawings, wherein, Fig. 1 shows a perspective view of a rock drill bit according to the present invention, wherein a drill rod is connected with the drill bit; Fig. 2 shows a longitudinal cross-section through the drill bit according to Fig. 1 , wherein the cross-section runs through a retrac tooth, and an associated drill rod is shown schematically; Fig. 3 shows a perspective view of a rear part of the drill bit according to Fig. 1 ; and, Fig. 4 shows a longitudinal cross-section through the drill bit according to Figs. 1-3 according to the present invention, wherein the cross-section runs through a retrac tooth, and an alternative associated drill rod is shown schematically. Detailed description of a preferred embodiment of a rock drill bit according to the present invention The drill bit 1 shown in Figs. 1-3 comprises a bit head 3 and a shank or a skirt 5, said bit head 3 and the skirt 5 being integral with each other. A schematically shown drill rod 7 is connected with the drill bit 1 via a thread joint. A through-going flush channel 8 is in a usual manner provided in the drill rod 7. A longitudinal center axis 2 common for the drill bit 1 and the drill rod 7 is drawn into Fig. 2. Such as is most visible in Fig. 2 the drill bit 1 is provided with an internal female thread 9, which receives an external male thread 10 at one end surface of the drill rod 7. The bit head 3 of the drill bit 1 according to the present invention is in a usual manner provided with rock crushing means, in the shape of cemented carbide buttons in the shown embodiment, of which several annulariy positioned peripheral buttons 1 1 are shown. Several flushing channels 12 extend between the internal space of the drill bit 1 defined by the internal female thread 9, and the front of the bit head 3. There is also provided a first abutment surface 13 in said internal space, a so-called bottom abutment, for the free end of the drill rod 7. There is provided a second abutment surface 14, a so-called shoulder abutment, at the rear end of the drill bit 1 , which is best visible in Fig. 3, which is intended to cooperate with a shoulder 15 on the drill rod 7. In the embodiment shown in Figs. 1-3 is normally used a so-called shoulder-bottom abutment, which means that the drill rod 7 is made with such tolerances that at forming of the threaded connection between the drill bit 1 and the drill rod 7 the free end of the drill rod 7 initially gets into engagement against the bottom abutment surface 13. After a relatively short time of wear of the threaded connection also the shoulder 15 of the drill rod 7 gets into engagement against the shoulder abutment surface 14, whereby a so-called shoulder-bottom abutment has been formed, i.e. abutments between the drill bit 1 and the drill rod 7 occur at both the bottom abutment surface 13 and the shoulder abutment surface 14. This means that transfer of the impact energy from the drill rod 7 to the drill bit 1 will occur at both the bottom abutment 13 and the shoulder abutment 14. Such as is best seen in Figs. 1 and 3 the drill bit 1 is provided with a number of straight grooves 16 for drill cuttings on its external surface, which extend in the axial direction of the drill bit 1 and therebetween define a number of straight protruding lands 17, which likewise extend in the axial direction of the drill bit 1. Such as is seen in Figs. 1-3 the protruding lands 17 have a reduced height along an intermediate part of its length. This reduction of material at the protruding lands 17 inter alia objects to ensure that guiding of the drill bit 1 in the drilled hole occurs by means of the parts of the protruding lands 17 which are situated in connection to the ends of the drill bit 1. The grooves 16 for drill cuttings are in usual manner intended to transport away the drill dust generated at the front of the drill bit 1. Such as can be seen in Figs. 1-3 the protruding lands 17 are formed with retrac teeth 18 at their rear ends, i.e. the ends facing away from the rock crushing end of the drill bit 1 , which teeth are intended to crush the material which has loosened from the bore wall during retraction of the drill bit 1 from a drilled hole. Each retrac tooth 18 is provided with an edge 19, which is situated at the part of the connecting protruding land 17 situated furthest away from the central axis 2. The cutting edges 19 coincide with an imaginary cylinder that intersects the peripheral buttons 11 of the drill bit 1. The retrac teeth 18 according to the present invention can be achieved in a simple and rational manner in connection with the manufacture of the drill bit 1 according to the present invention. The end where the retrac teeth shall be formed is turned in a lathe during said manufacturing, whereby the second abutment surface 14 and a concentrical outer surface, which forms an angle α with the inner second abutment surface 14 which is less than 180°. In a subsequent step during manufacturing of the drill bit 1 according to the present invention the grooves 16 for drill cuttings are made on the outside of the drill bit 1 , preferably through milling. Thereby the protruding lands 17 situated between the grooves 16 for drill cuttings are formed automatically. Reduction of the height of the lands 17 is suitably made by means of milling. In connection with the automatic formation of the protruding lands 17 also retrac teeth 18 are automatically formed, see Figs. 2 and 3, at the ends of the protruding lands 17 which are facing away from the rock crushing end of the drill bit 1. The retrac teeth 18 will be formed with edges 19, said edges 19 are situated on the diameter of the skirt 5 since the concentric, outer surface forms an angle, that is less than 180°, with the inner second abutment surface 14. Thus also each retrac tooth 18 will exhibit a surface 20 facing generally away from the rock crushing end of the drill bit 1 , which is formed from the above-captioned concentric outer surface, i.e. the surface 20 likewise forms an angle with the second abutment surface 14 which is less than 180°. The surfaces 20 coincide with a cone, which imaginary cone apex is directed towards the rock-crushing end of the drill bit 1. A substantial advantage of the in this manner developed retrac teeth 18 is that there are no sharp corners in connection with said teeth 18. Thereby the danger for crack formation in connection with said retrac teeth 18 is reduced to a high degree. In other words the method for manufacturing of the rock drill bit from a cast blank, not shown, comprises the following steps: A- turning the rock crushing end surface facing away from the end surface, thereby achieving an end surface which forms an angle, less than 180°, with the plane 21 , B- forming the grooves 16 for drill cuttings on the outside of the drill bit 1 , preferably by milling, which grooves are made to extend between the rock crushing end surface and the turned end surface of the drill bit, and C- forming the intermediate protruding lands 17 through the development of the grooves, whose ends face away from the rock crushing end surface defines the retrac teeth 18, which have edges 19 extending along the circumference of the skirt 5 and are situated substantially on said circumference. In addition, the surface 20 in connection with step B is formed on the retrac teeth which surface 20 forms the angle α, less than 180°, with the plane 21. Furthermore, when the end facing away from the rock crushing end surface is turned a second abutment surface 14 is achieved, which is concentric with and situated inside the surface 20, which forms the angle α with the plane 21. Also, some of the retrac teeth may be removed by means of a subsequent machining, preferably by milling. In Fig. 4 is shown a rock drill bit 1 according to Figs. 1-3 connected to a drill rod 7', which has an alternative design when compared to the drill rod 7 according to Figs. 1-2. The principal difference between the drill rod 7 according to Figs. 1-3 and the drill rod 7' according to Fig. 4 is that the latter is designed without a shoulder. In a joint of the drill bit 1 and the drill rod 7' according to Fig. 4 transfer of shock wave energy exclusively occur through a so-called bottom abutment, i.e. the free end surface of the drill rod 7' abuts against the first abutment surface 13 of the drill bit 1. Even if the drill bit 1 according to Fig. 1 is in principle identical of the drill bit 1 according to Fig. 4 tolerances, as regards the axial distance between the first abutment surface 1 , the bottom abutment, and the second abutment surface 14, the shoulder abutment, be larger if a drill rod T according to Fig. 4 is used. The reason thereto is of course that the drill rod 7' does not have any shoulder, i.e. the second abutment surface 14 is in principle not used. Conceivable modifications of the invention At the above-described embodiment of the drill bit 1 the grooves 16 for drill cuttings and the protruding lands 17 are straight and extend in the axial direction of the drill bit 1. However, within the scope of the present invention the grooves for drill cuttings and the associated protruding lands may for example run helically on the surface of the drill bit. The claims use the expression "... extend in the axial direction of the drill bit ..." shall be considered as including also the cases when the grooves for drill cuttings and the protruding lands does not run the shortest way between the ends of the drill bit. According to the above-described embodiment of the drill bit 1 retrac teeth 18 are formed between each adjacent pair of grooves 16 for drill cuttings. Within the scope of the present invention for example every second retrac tooth 18 may be removed, and this suitably made by removing the end surface of a protruding land 17 facing away from the rock crushing end surface of the drill bit 1 , suitably by means of milling. How many retrac teeth 18 a rock drill bit 1 according to the present invention will exhibit is determined from many different parameters, wherein in exemplifying and not limiting purpose can be mentioned the diameter of the drill bit, which type of rock is drilled and which drilling-rig is used. At the above-described embodiment of a rock drill bit 1 it is provided with a second abutment surface 14, a so-called shoulder abutment, wherein the orientation of a surface 20 of the retrac teeth 18 is defined by the angle α which said surface 20 forms with the second abutment surface 14. In case the drill bit according to the present invention does not have any second abutment surface it may be appropriate to define the orientation of said surface 20 through the angle which the actual surface 20 forms with an imaginary plane 21 which extends perpendicularly to the center axis 2 of the drill bit. For the sake of clarity such plane 21 is drawn in Fig. 4, wherein also the angle α is depicted. In this connection shall be pointed out that also if the drill bit according to the present invention comprises a second abutment surface 14 the orientation of the surface 20 close to the retrac teeth 18 is defined referring to the angle α which said surface forms with the plane 21. Reference to the plane 21 is consequently general regardless of whether the drill bit comprises any second abutment surface 14 or not.

Claims: Claims 1. A rock drill bit (1 ) for percussive drilling, especially top hammer drilling, said rock drill bit (1 ) comprising a bit head (3) provided with rock crushing means (11 ), and a skirt (5), wherein the outside surface of the skirt (5) of said drill bit (1 ) is provided with a number of grooves (16) for drill cuttings which extend in the axial direction of the drill bit (1 ), said grooves (16) for drill cuttings defining protruding lands (17) therebetween, which likewise extend in the axial direction of the drill bit (1 ), said drill bit (1 ) having means (9) for connecting the drill bit (1 ) to a drill rod (7; 7'), wherein at least some of the ends of the lands (17) facing away from the rock crushing end of the drill bit (1) are formed which retrac teeth (18), characterized in that each retrac tooth (18) has an edge (19), which extend along the circumference of the skirt (5) and is situated substantially on said circumference. 2. The rock drill bit (1 ) according to claim 1 , characterized in that each retrac tooth (18) comprises a surface (20) situated inside the associated cutting edge (19), which forms an angle (α) with an imaginary plane (21 ), which is perpendicular to a longitudinal center axis (3) of the drill bit (1), said angle (α) being less than 180°. 3. The rock drill bit (1 ) according to anyone of the claims 1 and 2, characterized in that the for connecting the drill bit (1 ) to a drill rod (7; 7') consists of an internal female thread (9) at the drill bit (1 ), and that a first abutment surface (13) is provided in connection with a bottom of the female thread (9). 4. The rock drill bit (1) according to anyone of the claims 1-3, characterized in that the cutting edges (19) coincide with an imaginary cylinder which is concentric with the longitudinal center axis (2) of the drill bit (1 ), and that said imaginary cylinder intersects a number of peripheral buttons (11 ) at a front of the bit head (3). 5. The rock drill bit (1) according to anyone of the claims 1-4, characterized in that it has a second abutment surface (14), which is situated separate from but in connection with the retrac teeth (18). 6. A method for manufacturing of a rock drill bit (1) for percussive drilling, especially top hammer drilling, wherein a rock crushing end of the drill bit (1), an internal female thread (9) and cooling channels (12) are made from a cast blank through suitable machining, said cooling channels extending between the internal female thread (9) and the rock crushing end surface, characterized in that the method comprises the following steps: A) turning the rock crushing end surface facing away from the end surface, thereby achieving an end surface which forms an angle (α), less than 180°, with a plane (21 ) perpendicularly to a longitudinal center axis (2) of the drill bit (1 ), B) forming grooves (16) for drill cuttings on the outside of the drill bit (1 ), preferably by milling, which grooves (16) for drill cuttings are made to extend between the rock crushing end surface and the turned end surface of the drill bit (1). C) forming intermediate protruding lands (17) through the development of the grooves (16) for drill cuttings, whose ends facing away from the rock crushing end surface defines retrac teeth (18), which have edges (19), which extend along the circumference of the skirt (5) and are situated substantially on said circumference. 7. The method according to claim 6, characterized in that a surface (20) in connection with step B is formed on the retrac teeth (18) which forms a certain angle (α), less than 180°, with the plane (21). 8. The method according to claim 7, characterized in that when the end facing away from the rock crushing end surface is turned is achieved a second abutment surface (14), which is concentric with and situated inside the surface (20) which forms a certain angle (α) with a plane (21) perpendicularly to the longitudinal center axis (2) of the drill bit (1 ). 9. The method according to anyone of the claims 6-8, characterized in that some of the retrac teeth (18) are removed by means of a subsequent machining, preferably by milling.

Inventors: AASBERG BENGT, EDERYD BERTIL, LARSSON KENNETH, AASBERG, BENGT, EDERYD, BERTIL, LARSSON, KENNETH
Applicants: SANDVIK AB
Application year: 2001
Main classification: E21B10
IPC codes: E21B10, E21B17