ROCK DRILLING TOOL, DRILL BIT AND A METHOD OF TRANSFERRING PERCUSSIVE ENERGY

Abstract: The present invention relates to a rock drilling tool for percussive drilling comprising a drill bit (11) and a drill tube (12) co-operating by means of shoulder abutment in a threaded connection. The connection comprises at least one male thread (17) and a female thread (18). The male thread (17) is provided on a shank (19) being an integral part of the drill bit (11). The drill bit is provided with a shoulder (20) at the inner end of the shank (19), said shoulder having an abutment surface (21) facing towards the free end of the shank (19). The female thread (18) is provided in the drill tube (12) and the free end of the drill tube is provided with an impact surface (23). The threads (17, 18) are cylindrical. The present invention is characterized by combining shoulder abutment with a short head and straight energy transfer at a rock drilling tool. The invention further relates to a drill bit and a method of transferring percussive energy from a rock drilling tool to a bore hole.

Description: Rock drilling tool, drill bit and a method of transferring percussive energy Technical background The present invention relates to a rock drilling tool for percussive drilling comprising a drill bit and a drill tube. The drill bit has a head having a front surface wherefrom a number of front inserts project and peripheral inserts provided in a peripheral row, said drill bit being provided with a first thread co-operating with a second thread provided on the drill tube. The invention further relates to a drill bit and a method of transferring percussive energy from a rock drilling tool to a bore hole. It is previously known through US-A-1 , 447,855 to provide a so called shoulder abutment at threaded connections between a drill rod and a rock drill bit in an equipment for percussive drilling. At loosening of the drill bit in the known equipment with a relatively heavy drill bit, there is a risk that the thread entrance on the bit shank becomes damaged due to the substantial difference in mass on opposite sides oi the shoulder abutment. Furthermore, the known drill bit is provided with chisel edges of hardened steel, which project relatively far in the radial direction. This means that the percussive energy during percussive drilling is forced to deflect towards the radially outer tip of the edge and therefore the effective coefficient of efficiency decreases, thereby resulting in impaired guiding ability and impaired drilling speed. Chisel edges give a relatively slow drilling speed. Furthermore it seems as the known tool can have abutment between the drill rod and bit, both in the radial and axial directions which during drilling create hardening of the material with subsequent crack initiation points. Objects of the invention An object of the present invention is to provide a method of transferring percussive energy from a rock drilling tool to a drill hole, such as to provide good guidance of the bit, acceptable loads and also a good energy transfer. Another object of the present invention is to provide a rock drilling tool comprising a rigid connection which does not deflect in spite of difficult angles of attack. Still another object of the present invention is to provide a rock drilling tool, which has a good coefficient of efficiency by making the drill bit as light as possible simultaneously as the entrance of the shank is spared, during loosening, due to low bit weight. Still another object of the present invention is to provide a rock drilling tool, through which connection a good length of life can be achieved simultaneously as the part most frequently changed is easy to handle. Still another object of the present invention is to provide a rock drilling tool, whose front end of the drill tube does not have a projecting portion and therefore there will be no transport damages. Still another object of the present invention is to provide an effective rock drill bit. Description of the drawings The objects and advantages of the invention are met by providing a method, a rock drilling tool and a rock drill bit according to the features in the characterizing portions of the claims. Additional advantageous characteristics according to the invention are apparent from the dependent claims. Below embodiments of the invention will be described in connection with the appended figures. Figs. 1 to 4 show a schematical, partly sectioned view of a rock drilling tool according to the invention. Fig. 5 shows the tool in a top view. Figs. 6 and 7 show cross-sections of alternative ends of the female thread. Detailed description of preferred embodiments of the invention The rock drilling tool 10 as shown in the figures comprises a rock drill bit 1 1 and a drill tube 12. The bit 1 1 has a head 13 provided with a front surface 14, wherefrom a number of front inserts 15 projects, and a peripheral row of peripheral inserts 16, preferably provided with spherical or ballistic working surfaces. The drill bit is provided with a male thread 1 7, which is provided to cooperate with a female thread 18 on the tube. The male thread 1 7, which is provided on a shank 19, is an integral part of the percussive drill bit 1 1 . The drill bit is provided with a shoulder at the inner end of the shank 19, which shoulder has a planar abutment surface 21 facing towards the free end of the shank 19. The abutment surface 21 extends perpendicularly relative to a longitudinal center axis 22 of the drill tool 10. The weight of the head 13 including the inserts is maximum 2.5 times, preferably less than 2 times the weight of the shank 19 when the parts are separated at the shoulder 20. The free end of the drill tube 12 has the shape of a planar, hollow end surface 23, which extends perpendicularly relative to the center axis 22. The threaded connection further comprises a female thread 18, which is made in the drill tube as an integral part thereof. The shape of the bottom of the female thread is in most cases adapted to provide optimum strength for the tube as in Fig. 6. Alternatively as in Fig. 7 for instance, the bottom of the female thread may have the shape of a planar surface 24, which extends perpendicularly relative to the center axis 22 in the case bottom abutment is beneficial. In the latter case, the distances between the shoulder abutment and the surface 24 and the end surface 26 of the shank, respectively, such that the latter are in contact with or reach contact later on as the tool is used, such that the area on the bit for straightly directed energy increases. In most cases it is advantageous to provide thread clearances 27 and 28 in connection with the shoulder abutment, to level the bending forces and to avoid abutment in that area between the parts 12 and 19. The threads 17, 18 may be cylindrical rope threads or cylindrical trapezoidal threads and have a pitch angle of about 5-15°. The rock drilling tool 10 has a central flush channel, which is divided into at least two other channels in the head. It is apparent from the figures that the abutment surface 21 of the drill bit in active position always abuts against the planar end surface 23 on the free end of the tube, which means that shoulder abutment is established. In Fig. 4 is schematically shown a rock drilling tool according to the present invention, wherein the axial length from the shoulder 20 to the free end of the shank is L1 and the height of the bit 1 1 between the shoulder 20 and the front surface 14 is L2. The axial length L2 of the head is 0.2 to 0.9 times, preferably about 0.5 times the axial length L1 of the shank. The outer diameter of the drill tube 12 and the shoulder 20 is designated D1 and the smallest outer diameter of the shank is designated D2, which is approximately the same as the smallest diameter of the female thread. The largest diameter of the head 13 is designated D3, which preferably is equal to or somewhat less than the diameter of the circle radially outwardly touching the peripheral inserts 16. The relation D3/D1 is preferably larger than 1 and preferably less than 1.5. The radially outermost part of the shoulder 20 describes according to Fig. 5, a circle having a diameter Dl and forming a cylinder 25 which intersects the peripheral inserts 16 substantially in the middle or in the vicinity of their active working surfaces. The latter forces the percussive energy to where it is most useful, i.e. the impact wave can travel straightly towards the insert without any energy consuming deflections. The drill tube 12 thus has a substantially constant outer diameter D1 and the axial length L2 of the head is provided shorter than the axial length L1 of the shank. The percussive energy transfers substantially straightly from the drill tube to points of contact with the drill hole via inserts 16 by having an imaginary cylinder 25 being an extension of the outer diameter Dl of the shoulder intersecting the peripheral inserts 16. The present invention is thus characterized by combining shoulder abutment with a short head and straight energy transfer at a rock drilling tool.

Claims: Claims 1. Method of transferring percussive energy from a percussive drilling tool to a bore hole, wherein said tool comprises a drill tube and a drill bit co¬ operating by means of at least shoulder abutment in a threaded connection, said connection comprising at least one cylindrical male thread (1 7) and a cylindrical female thread (18), said male thread (1 7) being provided on a shank (19) being an integral part of the drill bit (1 1 ), said drill bit being provided with an abutment surface (21 ) facing towards the free end of the shank (19), said female thread (18) being provided in the drill tube (12) and the free end of said drill tube being provided with an impact surface (23), c h a r a c t e r i z e d i n that the drill tube (12) is given a substantially constant outer diameter (D1 ) and that the axial length (L2) of the head is shorter than the axial length (L1 ) of the shank and that the percussive energy is transferred substantially straightly from the drill tube to points of contact with a bore hole by means of inserts (16) by having an imaginary cylinder (25) being an extension of the outer diameter (D1 ) of the shoulder intersecting the peripheral inserts (16) provided on the head. 2. Rock drilling tool for percussive drilling comprising a drill bit (1 1 ) and a drill tube (12) co-operating by means of at least shoulder abutment in a threaded connection, said connection comprising at least one male thread (17) and a female thread (18), said male thread (1 7) being provided on a shank (19) being an integral part of the drill bit (1 1 ), said drill bit being provided with a shoulder (20) at the inner end of the shank (19), said shoulder having an abutment surface (21 ) facing towards the free end of the shank (19), said female thread (18) being provided in the drill tube (12) and the free end of said drill tube being provided with an impact surface (23), said threads (17,18) being cylindrical, characterized in that the drill bit (11) has a head (13) having a front surface wherefrom a number of front inserts (15) project and that peripheral inserts (16) are arranged in a peripheral row and that the drill tube (12) has a substantially constant outer diameter (D1) and that the axial length (L2) of the head is shorter than the axial length (LI) of the shank and that an imaginary cylinder (25) being an extension of the outer diameter (D1 ) of the shoulder intersects the peripheral inserts (16). 3. Rock drilling tool according to claim 2, characterized in that the cylinder (25) intersects each insert (16) in or in the vicinity of its axially outermost part and that the weight of the head (13) is maximum 2.5 times, preferably less than 2 times the weight of the shank (19). 4. Rock drilling tool according to claim 2 or 3, characterized in that the axial length (L2) of the head is 0.2 to 0.9 times the axial length (L1) of the shank, preferably about 0.5 times the axial length of the shank. 5. Rock drilling tool according to claim 2, 3 or 4, characterized in that the drill bit (11) is provided with a shoulder (20) at the inner end of the shank (19), said shoulder having a planar abutment surface (21 ) facing towards the free end of the shank (19) and that the abutment surface (21) extends perpendicularly relative to a longitudinal center axis (22) of the drill tool (10). 6. Drill bit for percussive drilling comprising a head (13) and a shank (19) having a cylindrical male thread (17), said shank (19) being an integral part of the drill bit (11), said drill bit being provided with a shoulder (20) at the inner end of the shank (19), said shoulder having an abutment surface (21) facing towards the free end of the shank (19), characterized in that a number of front inserts (15) project a front surface (T4) of the head (13) and that peripheral inserts (16) are provided in a peripheral row and that the axial length (L2) of the head is shorter than the axial length (L1) of the shank and that an imaginary cylinder (25) being an extension of the outer diameter (D1) of the shoulder intersects the peripheral inserts (16). 7. Drill bit according to claim 6, characterized in that the cylinder (25) intersects each insert (16) in or in the vicinity of its axially outermost part. 8. Drill bit according to claim 6 or 7, characterized in that the axial length (L2) of the head is 0.2 to 0.9 times the axial length (LI) of the shank, preferably about 0.5 times the axial length of the shank. 9. Drill bit according to claim 6, 7 or 8, characterized in that the weight of the head (13) is maximum 2.5 times, preferably less than 2 times the weight of the shank (19). 10. Drill bit according to anyone of claims 6 - 9, characterized in that a thread clearance (28) is provided between the head and the male thread.

Inventors: BECCU RAINER, LARSSON KENNETH, BECCU, RAINER, LARSSON, KENNETH
Applicants: BECCU RAINER, LARSSON KENNETH, SANDVIK AB, BECCU, RAINER, LARSSON, KENNETH
Application year: 1996
Main classification: E21B10
IPC codes: E21B10, E21B17