AU2002363701A1

AU2002363701A1 - Thread joint

Info

Publication number: AU2002363701A1
Application number: AU2002363701A
Authority: AU
Inventors: Per-Olof Liljebrand; Urban Olsson
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2001-10-12
Filing date: 2002-10-09
Publication date: 2003-07-24
Anticipated expiration: 2022-10-09

Description

THREAD JOINT

Technical Field of the Invention

The present invention relates to a thread joint intended for percussive rock drilling.

Prior Art

Thread joints in drill strings are exposed to large loads in percussive top hammer drilling, wherein the drill string has the object of transferring percussive energy from a top hammer to a carbide-tipped drill bit at the free end of the drill string. Usually, the individual drill rod has, at an end, a formed female thread intended to receive a male thread at an opposite end of another drill rod. In connection with drilling, for removing drill dust out of the bore hole as well as lubricating and cooling the drill bit, water is usually used as flushing medium, possibly with certain additives, e.g. for improving the lubrication. The drill steel, i.e. the material in bits, bars, tubes, sleeves and shank adapters, is during drilling exposed to abrasive and corrosive attacks. In particular, this is the case in drilling underground where water is used as flushing medium and where the environment generally is damp. The attacks are especially serious in parts having relatively small diameters, i.e. at thread ends or thread clearances 5, the latter one of which is illustrated in Fig. 3 connected to a sleeve 4 of a drill bit. The flushing medium with drill dust travels in the return direction A at a relatively high speed. Thereby, vortex vortices B are formed at marked dimension-changes.

Objects and Features of the Invention The- present invention aims at obviating the above-mentioned problems and at jroviding an improved thread joint for percussive rock drilling, which additionally improves the efficiency in modern mining.

Another object of the present invention is to provide a thread joint, which reduces the formation of vortex vortices in percussive drilling. The present invention aims at obviating the above-mentioned problems and at providing an improved thread joint for percussive rock drilling, which additionally improves the efficiency in modern mining.

Another object of the present invention is to provide a thread joint, which reduces the formation of vortex vortices in percussive drilling.

Another object of the present invention is to provide a thread joint at which blasting effects and corrosion from exterior flushing medium is reduced.

According to the invention, said objects are attained by the features given in the characterizing portion of claim 1. Preferred embodiments of the thread joint according to the invention are further defined in the dependent claims.

Brief Description of the Appended Drawings

In the drawings: Fig. 1A shows a view of a thread joint according to the present invention shown partly in longitudinal section,

Fig. 1B shows an enlarged section according to the line B-B in Fig. 1A, and

Fig. 2 shows a view corresponding to Fig. 1 A showing an alternative embodiment of the invention. Fig. 3

Detailed Description of Preferred Embodiments of the Invention The present invention relates to a thread joint 10 for percussive rock drilling between a first drill rod 1 1 and a sleeve 13, preferably integrally fastened to a drill bit 12, as is shown in Fig. 1 . Alternatively, the sleeve may be integrally fastened to a second drill rod or to a connector tube, not shown. The sleeve 13 has a cylindrical outer surface 28. The drill bit 12 comprises a front surface 29 that accommodates a plurality of front buttons 30 and peripheral buttons 31 , only two of which are shown in Fig. 1A. The peripheral buttons 31 define the diameter of the drilled hole in a conventional way. The drill rod 1 1 , and thereby the thread joint, comprises at least one conduit

14 for transportation of flushing medium, such as water. Said conduit 14 connects to at least one conduit 15 in the drill bit 12. The drill rod 1 1 has a hexagonal radial cross-section and comprises a first outer surface 16. The drill rod may alternatively have a circular cross-section. The first outer surface 16 has a first outer diameter D1 , first end 17 comprises a first end surface 21. The first drill rod 11 comprises a second outer surface 22 having an outer second diameter D2. The second outer surface 22 is turned or ground to an accurately defined diameter D2 and has an axial extension from 1 mm to 50 mm. The second outer surface 22 is axially arranged between the first outer surface 16 and the thread end 20. The sleeve 13 comprises a recess 23 that comprises a female thread 24 and an inner stop face 25. The recess 23 connects to a second end surface 26 of the sleeve. The second end surface 26 is substantially ring-shaped. A substantially cylindrical inner surface 27 is arranged between the second end surface 26 and the female thread 24. The inner surface 27 has an inner diameter D3. The thread joint 10 becomes mounted when the spigot 17 has been threaded into the recess 23 until the first end surface 21 abuts against the inner stop face 25. At a mounted thread joint, the dimensions of the parts are arranged in such a way that the second end surface 26 of the sleeve is arranged axially beyond the thread end 20 of the male thread 18 or a thread clearance 33' (see Fig. 2), so that at least a part of the inner surface 27 conceals the weakest cross-section of the first drill rod. The weakest cross-section of the drill rod is the part of the drill rod that has the smallest cross-sectional area, such as at the thread end 20 of the male thread 18 or at the thread clearance 33'. The second end surface 26 of the sleeve is then arranged in a plane P, which intersects the second outer surface 22 axially beyond the thread end 20 of the male thread 18. The distance X between the thread end 20 and the plane P is at least 1 mm. Thus, the second end surface of the sleeve is arranged at least 1 mm axially beyond the thread end of the male thread.

The inner diameter D3 of the inner surface 27 is at least equally large as, maximum 1 mm larger than, the outer second diameter D2 of the second outer surface 22 but smaller than the first outer diameter D1 of the first outer surface 16. The chosen dimensions give relatively small geometrical transitions between the parts 11 and 12 for decreasing the extent of vortex vortices, so that the effect on the extension joint from drill dust and aggressive water decreases. The flushing medium may alternatively consist of an admixture of air and water.

The relatively small geometrical transitions may also be described by defining a first imaginary cylinder C1 , which constitutes an axial extension of the inner surface 27 and a second imaginary cylinder C2, which constitutes an axial extension of the outer surface 28 of the sleeve 13, see Fig. 1 B. The first imaginary cylinder C1 intersects the drill rod 11 while the second imaginary cylinder C2 extends outside of the drill rod. Thereby, vortex vortices in the transitions or the joints are minimised at the same time as the control of the drill string in the borehole is improved. Both the imaginary cylinders C1 and C2 intersect the peripheral buttons 31.

The outer surface 28 of the sleeve 13 has a third outer diameter D4, which is larger than the first outer diameter D1 of the first outer surface 16.

It should be noted that the thread end of the male thread may be arranged within the axial area that the female thread defines and that the cylindrical surface then surrounds a thread clearance and at least a part of the turned or ground second outer surface.

Fig. 2 shows an alternative embodiment of a thread joint 10' according to the present invention. Equal parts have been designated with the same reference designations as in Figs. 1A and 1 B. The thread joint 10' has a drill rod 1 1' and a rock drill bit 12' for percussive drilling. The drill bit 12' has a sleeve 13' having a recess 23' wherein a relatively long, turned or ground inner surface 27' and the female thread 24 are arranged. The outer surface of the sleeve is denominated 28'. The drill rod 1 1' has a threaded spigot or end 17' and a relatively long, turned or ground second outer surface 22'. What foremost makes this embodiment different from the one above- described is that the second outer surface 22' and the inner surface 27' have been made axially longer, whereby abutment between the same may be attained along the distance X', so that also an improved control of the rock drill bit 12' is obtained. Furthermore, it is outlined in Fig. 2 that a sealing ring 32, i.e. an O-ring or the like, may be arranged in the inner surface 27' of the sleeve 13' for further decreasing the vortex vortices and the circulation close to the end surface 26 of the sleeve 13'. Furthermore, the embodiment according to Fig. 2 comprises a thread clearance 33". The thread clearance 33' consists of a circumferential concave recess, which enables clearance for thread tools in chasing of threads of the male thread. The distance X' is in this case measured between the plane P and the thread clearance 33' and is at least 1 mm. Thus, the second end surface of the sleeve is arranged at least 1 mm axially beyond the thread clearance 33'.

Conventional hexagonal and round rock drill rods are rolled and the accuracy in the circumferential direction becomes relatively poor why it is chosen in the thread joint according to the present invention to turn or grind the inner surface 27, 27' for enabling a good abutment between the surfaces 22, 22' and 27, 27'.

Thus, the present invention relates to a thread joint intended only for percussive rock drilling, preferably by means of top hammer drilling. The thread joint 10 is formed in order to reduce the formation of vortex vortices in percussive drilling by minimising dimension differences between parts included in the joint. The dimensions of the joints are chosen such that blasting effects and corrosion from exterior flush water are reduced and are directed towards greater dimensions of the joint.

Claims

1. Thread joint for percussive rock drilling between a first drill rod and a sleeve fastened to a drill bit (12; 12'), to a second drill rod or to a connector tube, wherein the thread joint (10; 10') comprises at least one conduit (14) for transportation of flushing medium, such as water, wherein the first drill rod (11 ;11') has a first outer surface (16) having a substantially axially constant, largest first outer diameter (D1 ) as well as a first end (17; 17') provided with a male thread (18), such as a rope thread or trapezoidal thread, for per- cussive drilling, wherein said male thread (18) comprises a thread start (19) and a thread end (20), wherein the first end comprises a first end surface (21), wherein the first drill rod (11 ;11') comprises a second outer surface (22;22') having an outer second diameter (D2), wherein the second outer surface (22;22') is arranged axially between the first outer surface (16) and the thread end (20), wherein the sleeve (13; 13') comprises a recess (23;23') comprising a female thread (24) and an inner stop face (25), wherein the recess connects to a second end surface (26) of the sleeve, wherein the second end surface (26) is substantially ring- shaped, wherein a substantially cylindrical inner surface (27;27') is arranged between the second end surface and the female thread, wherein the inner surface has an inner diameter (D3), c h a r a c t e r i z e d in that, in a mounted thread joint (10; 10'), the second end surface (26) of the sleeve is arranged axially beyond the thread end (20) of the male thread (18) or a thread clearance (33') so that at least a part of the inner surface conceals the weakest cross-section of the first drill rod, such as the thread end of the male thread (18) or the thread clearance (33') and in that the inner diameter (D3) of the inner surface is at least equally large as the outer second diameter (D2) of the second outer surface (22;22') and smaller than the first outer diameter (D1 ) of the first outer surface (16) and in that a first imaginary cylinder (C1 ) constitutes an axial extension of the inner surface (27;27') and a second imaginary cylinder (C2), which constitutes an axial extension of an outer surface (28;28') of the sleeve (13;13') and in that the first imaginary cylinder (C1 ) intersects the drill rod (11 ;11 ') while the second imaginary cylinder (C2) extends outside of the drill rod.

2. The thread joint according to claim ^characterized in that the second end surface (26) ofthe sleeve is arranged at least 1 mm axially beyond the thread end (20) ofthe male thread (18) or the thread clearance (33').

3. The thread joint according to claim 1 or 2, characterized in that the sleeve (13; 13') has a third outer diameter (D4), which is larger than the first outer diameter (D1 ) of the first outer surface (16).

4. The thread joint according to any one of claims 1-3, characterized in that the inner diameter (D3) of the inner surface is maximum 1 mm larger than the outer second diameter (D2) ofthe second outer surface (22;22').

5. The thread joint according to any one of claims 1-4, characterized in that the second outer surface (22;22') is machined to a cylindrical shape, such as by means of turning or grinding.

6. The thread joint according to claim 6, characterized in that both imaginary cylinders (C1,C2) intersect peripheral buttons (31) of the rock drill bit (12;12').