WO2004003332A1

WO2004003332A1 - Rock drill bit and method for the manufacture thereof

Info

Publication number: WO2004003332A1
Application number: PCT/SE2003/001059
Authority: WO
Inventors: Kenneth Larsson
Original assignee: Sandvik Ab
Priority date: 2002-06-26
Filing date: 2003-06-19
Publication date: 2004-01-08
Also published as: SE0201984L; SE0201984D0; AU2003239064A1; SE520036C2; US20040065482A1

Abstract

The present invention relates to a rock drill bit (1) for percussive drilling, especially top hammer drilling, wherein said rock drill bit (1) comprises a drill head (3) provided with rock removing members (11), as well as a skirt (5). The rock drill bit (1) is provided with a number of grooves for cuttings (16A, 16B) on the outside of the skirt (5) extending in the axial direction of the rock drill bit (1). Said grooves for cuttings (16A, 16B) define lands (17) between themselves, which also extend in the axial direction of the rock drill bit (1). The rock drill bit (1) has members (9) for connection of the rock drill bit (1) to a drill rod (7). At least some of the ends fo the lands (17) that are facing away from the rock removing end of the rock drill bit (1) are formed as retrac teeth (18). Each retrac tooth (18) has at least one edge (19A, 19B). At least some of the lands (17) comprise a chip surface (31) and clearance surface (30) that form an edge angle (β), which is not greater than 100°. The present invention also relates to a method for the manufacture of a rock drill bit according to the present invention.

Description

ROCK DRILL BIT AND METHOD FOR THE MANUFACTURE THEREOF

Technical Field of the Invention

The present invention relates to a rock drill bit for percussive drilling, especially top hammer drilling, according to the preambles of the independent claims.

Background After the completion of a bore hole, the rock drill bit intended for percussive drilling, with the appurtenant drilling string, consisting of drill rods, should be removed from the bore hole. In that connection, the drill bit and the drilling string are usually rotated in the opposite direction compared to when drilling of the bore hole is effected. However, in connection with the removal of the rock drill bit from the bore hole, it may occur that rock material that has come loose from the hole wall makes the withdrawal of the drilling string and the drill bit more difficult. In order to overcome this problem, it is common that the drill bit at the rear end thereof, i.e. at the end facing away from the drill front, has cutting inserts or chisels, designated retrac teeth below, which during rotation of the drilling string and the drill bit, in connection with retracting the drilling string and the drill bit from the bore hole, crushes the rock material that has come loose from the bore wall. Said retrac teeth are made by means of special milling operations, thus constituting additional operations in addition to the prevalent operations for the manufacture of a rock drill bit of the type in question. However, the design of these known teeth at the rear end of the drill bit means that sharp corners are formed adjacent to said teeth. This in turn means that cracks are generated in connection with said teeth during operation of the rock drill bit.

By US-A-5,743,345, a rock drill bit is previously known in Fig. 3, which has an appurtenant drill rod, where the rock drill bit at the rear end thereof is provided with special cemented carbide pins that work in a way that corresponds to the above- described teeth at the rear end of the drill bit. To arrange special cemented carbide pins at the rear end of the rock drill bit, involves, however, a price rise at production of a rock drill bit of the type in question.

In SE-C2-514931 , a rock drill bit of the present type is shown. The retrac teeth of the known rock drill bit have a tendency to break down. Furthermore, the retrac teeth of the known rock drill bit have turned out to be inadequate, from a cutting point of view. Objects of the Invention

The present invention has the object of providing a rock drill bit of the kind defined in the introduction, wherein the retrac teeth of said rock drill bit are so formed that the retrac teeth are reinforced. Another object of the present invention is to provide a rock drill bit that permits good rock removal.

Still another object of the present invention is that the retrac teeth of the rock drill bit permits that transfer of shock wave energy between the drill rod situated closest to the drill bit and the drill bit takes place by means of a so-called shoulder stop.

The objects of the present invention are realized by means of a rock drill bit and a method for the manufacture of a rock drill bit having the features defined in the appended claims.

Brief Description of the Drawings

An embodiment of the rock drill bit according to the present invention will be described below, references being made to the accompanying drawings, wherein: Fig. 1 shows a perspective view of a rock drill bit according to the present invention; Fig. 2 shows a partial cross-section through the rock drill bit according to Fig. 1 and an appurtenant drill rod; Fig. 3 shows a side view of the rock drill bit according to Fig. 1 ; and Fig. 4 shows an end view of the rock drill bit according to Fig. 1.

Detailed Description of a Preferred Embodiment of a Rock Drill Bit According to the Present Invention

The rock drill bit 1 illustrated in Figs. 1-4 comprises a drill head 3 and a shank or a skirt 5, wherein the drill head 3 and the skirt 5 are integrated with each other. A drill rod 7 is connected to the rock drill bit 1 via a thread coupling. In the drill rod 7, a through-going flush duct 8 is arranged in the conventional way. A longitudinal centre axis 2, common for the rock drill bit 1 and the drill rod 7, is drawn in Fig. 2. As is most clearly is seen in Fig. 2, the rock drill bit 1 is provided with an internal female thread 9, which receives an external male thread 10 at one end of the drill rod 7. The drill head 3 of the rock drill bit 1 according to the present invention is provided with rock removing members in the conventional way, in the illustrated embodiment in the form of cemented carbide pins 11. A number of cooling medium channels 12 extends between the internal space of the rock drill bit 1 , which is defined by the internal female thread 9, and the front of the drill head 3. In said internal space, a first stop face 13, a so-called bottom stop, is also arranged for the free end of the drill rod 7.

At the rear end of the rock drill bit 1 , as is most clearly shown in Fig. 4, a second stop face 14, a so-called shoulder stop, is arranged, which is intended to interact with a shoulder 15 of the drill rod 7. In the illustrated embodiment, a so-called shoulder-bottom stop is frequently used, which means that the drill rod 7 is manufactured with such tolerances that, at establishment of the threaded joint between the rock drill bit 1 and the drill rod 7, the free end of the drill rod 7 initially will come to abutment against the bottom stop 13. After a relatively short time of wearing-in of the threaded coupling, also the shoulder 15 of the drill rod 7 comes to abutment against the shoulder stop 14, wherein a so-called shoulder-bottom stop has been established, i.e. abutment between the rock drill bit 1 and the drill rod 7 takes place at both the bottom stop 13 and the shoulder stop 14. This means that transfer of shock wave energy from the drill rod 7 to the rock drill bit 1 will be effected via both the bot- torn stop 13 and the shoulder stop 14.

As is most clearly seen in Figs. 1 and 3, the rock drill bit 1 is on the outside thereof provided with a number of straight, front 16A and rear 16B grooves for cuttings extending in the axial direction of the rock drill bit 1. Each front groove for cuttings 16A is symmetrically arranged in relation to a line parallel with the centre axis 2. Each rear groove for cuttings 16B is asymmetrically arranged in relation to a line parallel with the centre axis. Each rear groove for cuttings 16B consists of a first chip surface 31 and a second chip surface 32, which are substantially perpendicular to each other. The first chip surface 31 has a radial extension that runs substantially perpendicularly to the centre axis 2. The cutting surfaces 31 and 32 meet in a rounded portion 33 that approaches the centre axis 2 in the direction axially rearwards. Between themselves, the rear grooves for cuttings 16B define a number of substantially straight lands 17 that also extend in the axial direction of the rock drill bit 1. A substantially cylindrical countersunk portion 17A is arranged between the front and the rear grooves for cuttings 16A and 16B, respectively. Among other things, the cylindrical portion 17A has the purpose of securing that guiding of the rock drill bit 1 in the bore hole is carried out by means of the portions that are located in connection with the ends of the rock drill bit 1 , and decreasing the resistance against the release of cutting dust. The grooves for cuttings 16A, 16B are in the conventional manner intended to transport away the drill dust produced at the front of the rock drill bit 1. The lands 17 are formed with retrac teeth 18, having the function of crushing the material that has come loose from the hole wall during withdrawal of the rock drill bit 1 from a drilled hole. Each retrac tooth 18 is provided with a first edge 19A, a second edge 19B and a third edge 19C. The first edge 19A is situated farthest forward in the direction of rotation R of the drill bit at each retrac tooth 18. The edge 19A is substantially parallel to the centre axis 2. The edges 19A coincide with an imaginary cylinder that intersects the peripheral buttons 11 of the rock drill bit 1. The edge 19A is formed at the intersection between a chip surface 31 and a clearance surface 30. The chip surface 31 and the flank surface 30 form an edge angle β, which is not greater than 100°, preferably not greater than 90°. The second edge 19B is positioned at the intersecting line between the chip surface and a substantially partially conical end surface 20. The second edge 19B is situated farthest back in the feeding direction of the drill bit on each land 17. The end surface 20 is arranged axi- ally inside and radially outside of the second stop face 14. The end surface 20 forms an outer angle α with a plane 21 perpendicular to a longitudinal centre axis 2 for the rock drill bit 1 or the second stop face 14. The angle α is greater than 180°. Thus, the angle between the first 19A and the second edge 19B becomes obtuse, i.e. greater than 90°. The third edge 19C is situated farthest forward in the feeding direction of the drill bit, on each land 17. The edge 19C forms an acute angle with the centre axis 2 and an obtuse angle with the first edge 19A.

The retrac teeth 18 according to the present invention may be brought about in a simple and efficient way in connection with the manufacture of the rock drill bit 1 according to the present invention. During said manufacture, the end where the retrac teeth are to be formed is turned, wherein the second stop face 14 is provided, as well as a concentric, outer surface, which forms an angle α with the second stop face 14 that is greater than 180°. In a subsequent step in the manufacture of the rock drill bit 1 according to the present invention, the grooves for cuttings 16B are provided on the outside of the rock drill bit 1 , preferably through milling. In that connection, the lands 17 situated between the grooves for cuttings 16B are automatically formed. In connection with the automatic forming of the lands 17, retrac teeth 18 are also automatically formed, see Figs. 2 and 3, at the ends of the lands 17 that are facing away from the rock removing end of the rock drill bit 1. By the geometry of the concentric, outer surface, the retrac teeth 18 will be formed with edges 19A, 19B, 19C, said edges being positioned at the maximum diameter of the skirts 5, as well as inside of the same. Thereby, each retrac tooth 18 will also have a surface 20, generally facing away from the rock removing end of the rock drill bit 1 , which surface is formed from the above-mentioned concentric, outer surface, i.e. the surface 20 also forms an angle α that is greater than 180° with the second stop face 14. The surfaces 20 are included in a cone, the imaginary cone tip of which is directed towards the threaded end of the bit 1. A substantial advantage of the retrac teeth 18 formed in this way is that there are substantially no sharp corners in connection with said teeth 18. Thereby, the risk of crack formations in connection with said retrac teeth 18 is to a large extent reduced. In the above-described embodiment of the rock drill bit 1 , the grooves for cuttings 16 and the lands 17 are straight, with an extension in the axial direction of the rock drill bit 1. However, within the scope of the present invention it is also feasible that the grooves for cuttings and the appurtenant lands run, for instance, helically at the outside of the rock drill bit. The phrase "... extends in the axial direction of the rock drill bit ...", used in the claims, should be regarded as comprising also those cases when the grooves for cuttings and the lands are not parallel to the centre axis 2.

According to the above-described embodiment of the rock drill bit 1 , retrac teeth 18 are formed between each adjacent pair of grooves for cuttings 16B. Within the scope of the present invention, it may however be conceived that for instance every second retrac tooth 18 is removed, wherein this conveniently is carried out by the fact that the end of a land 17 that is facing away from the rock removing end of the rock drill bit 1 is removed, conveniently by means of milling. The amount of retrac teeth 18 that a rock drill bit 1 according to the present invention should have is determined by a range of different parameters, wherein for exemplifying and not limiting purposes, the diameter of the drill bit, the type of rock in which the drilling takes place, as well as the drilling rig that is used, may be mentioned.

Claims

1. Rock drill bit (1 ) for percussive drilling, especially top hammer drilling, wherein said rock drill bit (1) comprises a drill head (3) provided with rock removing members (11), as well as a skirt (5), that the rock drill bit (1 ) is provided with a number of grooves for cuttings (16A,16B) on the outside of the skirt (5), which grooves for cuttings extend in the axial direction of the rock drill bit (1), wherein said grooves for cuttings (16A,16B) between themselves define lands (17), also extending in the axial direction of the rock drill bit (1 ), that the rock drill bit (1 ) has members (9) for connection of the rock drill bit (1 ) to a drill rod (7), wherein at least some of the ends of the lands (17) facing away from the rock removing end of the rock drill bit (1) are formed as retrac teeth (18), wherein each retrac tooth (18) has at least one edge (19A,19B), characterize d in that at least some of the lands (17) comprise a chip surface (31) and a clearance surface (30), which form an edge angle (β) that is not greater than 100°.

2. Rock drill bit (1 ) according to claim 1, characterized in that the edge angle (β) is not greater than 90°.

3. Rock drill bit (1 ) according to claim 1 or 2, characterized in that a second edge (19B) is arranged in an intersecting line between the chip surface and a substantially partially conical end surface (20), wherein the end surface (20) is arranged axially inside and radially outside of the second stop face 14, and in that the angle between the first (19A) and the second edge (19B) is obtuse.

4. Rock drill bit (1 ) according to any one of claims 1,2 or 3, characterized in that the members for connection of the rock drill bit (1) to a drill rod (7) consists of an internal female thread (9) of the rock drill bit (1), and that a first stop face (13) is arranged adjacent to the bottom of the female thread (9).

5. Rock drill bit (1 ) according to any one of claims 1-4, characterized in that each groove for cuttings (16B) is asymmetrically arranged in relation to a line parallel with the centre axis (2), wherein the groove for cuttings (16B) consists of a first chip surface (31 ) and a second chip surface (32), which are substantially perpendicular to each other.

6. Rock drill bit (1 ) according to any one of claims 1-5, characterized in that the second stop face (14) is situated spaced-apart from, but adjacent to, the retrac teeth (18).

7. Method for the manufacture of a rock drill bit (1 ) for percussive drilling, especially top hammer drilling, wherein a rock removing end of the rock drill bit is effected from a cast work piece through convenient machining, an internal female thread (9), as well as cooling medium channels (12) extending between the internal female thread (9) and the rock removing end, characterized in that the method comprises the following steps:

A that the end facing away from the rock removing end is turned, wherein an end surface is provided that forms an angle (α), greater than 180°, with a plane (21) perpendicular to a longitudinal centre axis (2) for the rock drill bit (1 ),

B that grooves for cuttings (16) are formed at the outside of the rock drill bit (1 ), preferably by means of milling, which grooves for cuttings (16) are brought to extend partly between the rock removing end and the turned end of the rock drill bit (1),

C that by forming the grooves for cuttings (16), intermediate lands (17) are defined, the ends of which facing away from the rock removing end define retrac teeth (18) that have edges (19A) extending axially along the envelope surface of the skirt (5), and are substantially situated on said envelope surface.

8. Method according to claim 7, characterized in that in connection with step B, the retrac teeth (18) are given a surface (20) that forms a certain angle (α), greater than 180°, with the plane (21).

9. Method according to claim 8, characterized in that a second stop face (14) is provided when the end facing away from the rock removing end is turned, which stop face is concentric with and positioned outside the surface (20), and which is perpendicular to a longitudinal centre axis (2) of the rock drill bit (1 ).

10. Method according to any one of claims 6-9, characterized in that some of the retrac teeth (18) are removed by a subsequent machining, preferably by means of milling.