EP1399640A1

EP1399640A1 - Rock drilling tool, a ring drill bit and an adapter for percussive drilling

Info

Publication number: EP1399640A1
Application number: EP02741584A
Authority: EP
Inventors: Per-Ola Hadin; Kenneth Larsson
Original assignee: Sandvik AB
Current assignee: Sandvik AB
Priority date: 2001-06-26
Filing date: 2002-06-20
Publication date: 2004-03-24
Also published as: SE519312C2; SE0102292L; SE0102292D0; WO2003001022A1

Abstract

The present invention relates to a rock drilling tool, a ring drill bit and an adapter for percussive drilling. The rock drilling tool (10) is intended to be connected to a casing tube (46) and a drill rod (62) in order to form a borehole. The casing tube is intended to be used as a channel for drill dust. The rock drilling tool comprises: - a drill adapter (20), including a flush duct for a flush medium, first drivers in order to transfer rotation, - a central pilot drill bit (12) provided with rock cutting members (14) and detachably connected to the first fastening means (21, 22) of the drill adapter, - a ring drill bit (17), provided with rock cutting members (41), and arranged to surround parts of the drill adapter during drilling, whereby the ring drill bit comprises second drivers intended to co-operate with the first driver of the drill adapter in order to rotate the ring drill bit with the drill adapter, and a casing shoe (18), intended to be secured to the casing tube as well as the ring drill bit, at least in connection with drilling, which casing shoe is arranged to push the casing tube only in the axial direction of the tool, whereby the casing tube (46) and the ring drill bit may be left in the borehole after finished drilling.

Description

ROCK DRILLING TOOL, A RING DRILL BIT AND AN ADAPTER FOR PERCUSSIVE DRILLING

Technical Field of the Invention

The present invention relates to a rock drilling tool, a ring drill bit and an adapter for percussive drilling according to the respective preambles of the independent claims.

Prior Art

This invention relates to a drilling tool suitable to be used for consolidation of rock at subterranean drilling, preferably by means of a so-called umbrella technique of the type that is described in e.g. US-A-5, 152,638 and US-A-4,666,336. The technique for consolidation at subterranean drilling, especially in unstable rock, means providing a protective umbrella, which consists of inserting rows of casing tubes of steel in the rock, as well as injection of rock stabilising mixtures, essentially concrete. The formed structure, known as protective umbrella, intends to carry and hold the rock together above the umbrella while the rock below the umbrella is removed.

A rock drilling tool described in US-A-3,227,230 has a so-called pilot drill bit, which is intended to operate a ring drill bit both axially by means of percussion and in the direction of the rotation by means of shoulders or the like. An advantage of prior art is that a casing tube is driven by the ring drill bit without having to be rotated, which of course would entail greater energy consumption. Furthermore, the pilot drill bit may be retracted and thereby leave the ring drill bit and casing tube in the drilled hole for e.g. filling of cement and thereby stabilising the rock. A problem in the known tools is that drill dust risk to be wedged up between the casing tube and the drilled hole so that the release of dust outside the casing tube is restrained. Furthermore, the motion of the casing tube is restrained by wedged drill dust. Other rock drilling tools of the above-mentioned type are previously known by US-A-5,590,726 and US-A-5,839,519. In each one of the known tools, connection to and release of the pilot drill bit in relation to the ring drill bit is a complicated procedure.

Objects and Features of the Invention

A primary object of the present invention is to provide a rock drilling tool of the above-mentioned type, which comprises the advantages of prior art.

Another object of the present invention is to provide a rock drilling tool where deformation of form locking parts is minimised.

Another object of the present invention is to provide a rock drilling tool where the release of dust is not restrained.

An additional object of the present invention is to provide a rock drilling tool where good driving of the ring drill bit in the direction of rotation is ensured. An additional object of the present invention is to provide a rock drilling tool where the pilot drill bit easily may be retracted from the ring drill bit.

The objects of the invention are realised by means of a rock drilling tool, an adapter and a ring drill bit having the features given in the appended claims.

Brief Description of the Drawings

Below, embodiment examples of the invention will be described, reference being made to the accompanying drawings.

Fig. 1 A shows an exploded view obliquely from behind of a first embodiment of a rock drilling tool according to the present invention;

Fig. 1B shows an exploded view from the side of the rock drilling tool according to

Fig. 1A;

Fig. 1C shows a side view of the rock drilling tool according to Fig. 1A in a mounted state; Fig. 1 D shows a top view of the rock drilling tool in driving mode;

Fig. 1 E shows a cross-section of the rock drilling tool according to Fig. 1C along the line E-E in Fig. 1 D;

Fig. 1 F shows a bottom view of the rock drilling tool in driving mode; Fig. 2A shows an exploded view obliquely from behind of an alternative embodiment of a rock drilling tool according to the present invention;

Fig. 2B shows an exploded view from the side of the rock drilling tool according to

Fig. 2A;

Fig. 2C shows a side view of the rock drilling tool according to Fig. 2A in a mounted state;

Fig. 2D shows a top view of the rock drilling tool in driving mode;

Fig. 2E shows a top view of the rock drilling tool in a lifting mode, and

Fig. 2F shows a bottom view of the rock drilling tool in driving mode.

Detailed Description of the Invention

The rock drilling tool 10, illustrated in Figs. 1A-1F, is intended to comprise a conventional pilot bit for percussive rock drilling, viz. either a button bit 11 or a chisel bit 12. The rock drilling tool is intended to be driven in a direction of rotation R, see Fig. 1 D, usually anti-clockwise. The pilot drill bit in the illustrated embodiment is at one end thereof provided with rock cutting members in the form of buttons 13 or chisels 14. At the opposite end thereof, each pilot bit has a threaded boring, which has a female thread 15, 16, preferably a rope thread or a trapezoidal thread.

The rock drilling tool 10 for percussive rock drilling according to the present invention also comprises a ring drill bit 17, a tube shoe or casing shoe 18, an O-ring 19 and a drill adapter 20.

The female thread 15 of the pilot bit 12, see foremost Figs. 1C and 1E, is connected to a projection 21 at one end of the drill adapter 20, which carries a male thread 22, preferably a rope thread or a trapezoidal thread. The projection 21 and the male thread 22 can be called first fastening means. An end surface 23 of the projection is intended to transfer shock waves to the pilot bit via a bottom surface 24 of the boring, a so-called bottom abutment. The projection 21 is, preferably fixedly, secured in an adapter body 25. The adapter body 25 has a substantially cylindrical basic shape with a front drive part 26 and a rear percussive part 27. The maximum diameter of the front drive part 26 is defined in Fig. 1 D by the designation D1. The expressions "rear", "rearwardly", "front", "forwardly", "in front of, etc., are related to the feeding direction F of the drill tool during drilling. The drive part 26 has a plurality of, preferably four or five, longitudinal outer dust grooves 28, which between them form a plurality of convexly rounded longitudinal bars, ridges 29 or first drivers. The radially outermost parts of the ridges 29 coincide with a circle C1 having said diameter D1. The front ends of the ridges each comprises a button 30, which form an angle of about 35° in relation to a centre line CL of the drill tool 10. If drilling is to be effected in softer rock types, the buttons 30 in an alternative adapter may be exchanged for other crushing members such as chisel bits or hard coatings such as Stellite® or the like. Common for the different crushing members is that they have a better wearability than the steel that the adapter is manufactured from. The crushing members are intended to crush material radially outside of the pilot drill bit as well as to protect the ridges from wear and deformation. The front ends of the ridges comprise plane surfaces 58 intended to facilitate the entrance of the drill adapter into the ring drill bit. The rear ends of the ridges 29 in the drive part transform in one step via a percussive surface 31 into rear ridges 32 in the percussive part. The percussive surface 31 is angled outwardly and rearwardly in relation to the centre line CL, but may alternatively be perpendicular to the centre line. The rear ends of the grooves 28 extend continuously without steps into rear dust grooves 33. The grooves 28 and 33 are suitably produced by means of a ball nose end mill during substantially one machining operation. The radially outermost surfaces of the ridges 32 coincide with a cylinder the diameter of which is larger than the diameter D1. The radially outermost surfaces of the ridges 32 have a larger extension in the circumferential direction than the ridges 29. The rear end of the percussive part comprises a substantially plane surface 34 which is perpendicular to the centre line CL. The surface 34 surrounds the outer end of a boring 35, which comprises a female thread 36, preferably a trapezoidal thread or a rope thread. The boring 35 and the female thread 36 can be called second fastening means. The female thread 36 is intended to receive an end of a drill rod 62 that carries a male thread and furthermore an end surface for transfer of shock waves to a bottom 57 of the recess 35. The adapter body 25 comprises a central through-going duct 37 in order to permit transportation of flush medium such as air or water to ducts 38, 39 in the pilot drill bit 12. The ring drill bit 17 has a cylindrical basic shape and comprises a front conical surface 40, which carries a plurality of buttons 41. The buttons 41 are pressed into oblique borings in the ring drill bit 17. The conical surface 40 connects forwardly to a front surface 42, which is preferably perpendicular to the centre line CL. The conical surface 40 connects rearwardly to a cylinder surface 43, which is substantially parallel to the centre line. The cylinder surface defines a diameter that is somewhat smaller than the diameter that the buttons 41 ream at drilling. The cylinder surface 43 connects in turn to a circumferential recess 44, the axial extension of which is limited by radially directed shoulders 44A, 44B. The recess has a cylindrical bottom surface 44C arranged between the shoulders 44A, 44B. The axial length of the recess 44 is at least 50 % of the axial length of the ring drill bit 17. The front end of the ring drill bit has a generally greater thickness of material than the rear end 45 thereof. This in order to be able to house the obliquely positioned buttons 41. The centre line CL2 of each button 41 forms an acute angle α with the centre line CL. The radially inner parts of the buttons 41 define a circle C2 having a diameter D2.

The maximum diameter of the rear end 45 is adapted so that displacement of a casing tube 46 axially in relation to said end is made possible. The rear end comprises a percussive surface 47. The percussive surface 47 is angled outwardly and rearwardly in relation to the centre line CL, but may alternatively be perpendicular to the centre line. The percussive surface 47 is intended to co-operate with the percussive surface 31 in order to transfer shock waves from the drill adapter to the ring drill bit. The percussive surface 47 surrounds a central hole 48 which runs through the ring drill bit. The wall of the hole 48 comprises a plurality of, preferably four or five, longitudinal grooves 49 or second drivers. The grooves 49 are concavely formed in order to permit passage of the buttons 30 and the ridges 29 of the drill adapter through the ring drill bit until the percussive surfaces 31 , 47 abut each other. The casing shoe 18 is tubular and consists of two identical halves 18A, 18B intended to be welded together by means of two axially directed welds 50A, 50B. The dimensions of the casing shoe is selected so that the axial length thereof is shorter than the axial length of the recess 44 and so that the inner diameter thereof is somewhat larger than the smallest diameter of the recess, and also so that the maximum diameter thereof substantially coincides with the cylinder surface 43. The casing shoe is attached to the casing tube 46 via a circumferential weld 51. Thereby, the casing tube and the casing shoe are freely movable in the rotational direction in relation to the ring drill bit. Furthermore, the casing tube and the casing shoe are to a certain degree axially movable in relation to the ring drill bit in order to minimise the percussive load on the casing shoe.

The O-ring 19 is arranged in the recess 44 in order to seal the gap between the casing shoe and the recess in order to avoid penetration of drill dust between the inner cylindrical surface of the casing shoe and the ring drill bit.

Penetration of drill dust therebetween would lead to an impaired relative rotation of the casing shoe and the ring drill bit and would lead to wear of the same. An advantageous side effect of the O-ring 19 is that the same may be used in order to hold the halves 18A, 18B in the recess 44 at delivery of the drill tool before welding is carried out on the drilling spot. In such a case, the O-ring tightens around the halves 18A, 18B according to the dashed line in Fig. 1C.

The drill tool 10 is mounted in the following way. The front part 26 of the drill adapter 20 is first inserted with the projection 21 through the central hole 48 of the ring drill bit. Then the ridges 29 of the front part 26 are aligned with the grooves 49 in the hole 48 and then the front part may be inserted into the ring drill bit until the percussive surfaces 31 , 47 abut each other. A relative position between the ring drill bit and the drill adapter has now been attained according to for example Fig. 1C, whereby the buttons 30 in the drill adapter are arranged axially in front of the buttons 41 in the ring drill bit. By such a relative button positioning, a good guiding of these parts is obtained during drilling. Then the pilot drill bit 11 or 12 is screwed onto the projection 21 through co-operation between the female thread 15 and the male thread 22. Then the O-ring is applied in a conventional way to the recess 44 in the ring drill bit. Then the metal halves 18A, 18B are brought around the bottom surface 44C of the recess, after which these are welded together by means of the welds 50A, 50B. The drill tool 10 is now ready to be threaded to a drill rod 62 via the thread 36, and be welded to a casing tube 46 by means of the weld 51. The casing tube is intended to be used as a channel for drill dust.

Drilling of rock in order to consolidate unstable rock is carried out in the following way. A tube in a row of casing tubes of steel is introduced into the rock by the fact that the drill rod 62, which is tightened to the drill tool, is rotated and at the same time transfers shock waves to the drill adapter 20. Thereby, the pilot drill bit 11 or 12 engages in the rock during simultaneous flushing via ducts 37, 39 in the direction of the arrow 52, see Fig. 1 E. The trailing casing tube 46 and the casing shoe 18 are not intended to rotate in relation to the prospective borehole. After the pilot drill bit has worked its way into the rock corresponding to the axial length of the bit, the buttons 30 of the drill adapter will get in engagement with the rock whereby, after this, substantially all drill dust will be returned in the direction according to the arrow 57 with the flush medium via the ducts 53, 54, 55 and 56 which are formed by the wall of the hole 48 and the grooves 28. The drill dust is then transported further on via the grooves 33 and rearwardly inside the casing tube 46. The buttons 41 of the ring drill bit get in engagement with the rock when the drill adapter has worked its way into the rock about 1 cm. This stage by stage engagement sequence provides a good guiding in order to achieve straight holes in the rock. The ridges 29 of the drill adapter work as drivers of the ring drill bit and these co-operate by means of form locking. By the fact that the ridges engage relatively far into the ring drill bit in the radial direction, a relatively large torque may be transferred during the drilling, depending on the fact that the common circle C1 of the ridges has a diameter D1 that is larger than the diameter D2 of the circle C2 for the radially inner parts of the buttons 41. When the drill tool 10 has worked its way down to the desired depth in the rock, the drill rod 62 may be brought to retract the drill adapter and the pilot drill bit and thereby the ring drill bit 17, which is arranged at the end of the casing tube 46, is left in the bore hole. The procedure is repeated in order to bore in additional casing tubes. Then the casing tubes are filled with concrete or the like in order to form a protective umbrella in order to carry and hold the rock together above the umbrella while the rock below the umbrella is removed. If also the casing tube 46 and the ring drill bit are to be used at additional occasions, the other end of the casing tube may be grasped in order to retract these components. Figs. 2A-2F show an alternative embodiment of a rock drilling tool 10' according to the present invention. Equal numerals define similar details as have been described above. What operationally distinguishes this embodiment from the above-described embodiment is that retraction of the ring drill bit and casing tube 46 is made possible by means of solely the drill rod 62. This has been achieved by the fact that the drill adapter 20' and ring drill bit 17' have received constructive alterations. The drive part 26' has a plurality of, preferably four or five, longitudinal outer dust grooves 28'. The ridges 29' of the drill adapter 20' has front ends, each one of which comprises a shoulder 59' spread out on the lee-side of the adherent button, that is, the shoulder 59' comes after the button in the direction of rotation R, see Fig. 2D. The shoulder has a substantially planar bottom side 60', which is substantially perpendicular to the centre line CL. The smallest distance between a plane P' of the bottom side 60' and adherent percussive surface 31 is larger than the smallest distance between the front surface 42' and the percussive surface 47', so that a gap S' may be formed between the bottom side 60' of the shoulder and the front surface 42' in the mounted state, see Fig. 2C. The hole wall 48' of the ring drill bit 17' has relatively wide grooves 49' in order to permit the shoulders 59' to pass through the ring drill bit. Drilling of rock by means of the drill tool 10' in order to consolidate not quite so unstable rock is carried out in a similar way as has been described in connection with the initially mentioned embodiment. However, if also the casing tube 46 and the ring drill bit 17' are to be used at additional occasions, the rotation direction of the drilling rod may be reversed sufficiently to bring a part of the bottom side 60' directly in front of the front surface 42', so that a mutually overlapping, contacting area 61', see Fig. 2E, is formed at retraction of the drill adapter 20' from the bore hole. Thereby, also the casing tube 46 and the ring drill bit 17' are pushed from the bore hole and may be re-used for the next hole. The boreholes are later filled with concrete or the like. Thus, the drill tool 10, 10' according to the present invention ensures that the release of dust is not restrained, that good driving of the ring drill bit in the direction of rotation is ensured, and that the pilot drill bit easily may be retracted from the ring drill bit. An additional advantage is that various conventional rock drill bits may be used as pilot drill bits. Furthermore, according to one embodiment of the drill tool 10' according to the present invention, a practical and easy freedom of choice is ensured in regards of leaving casing tubes and ring drill bit in the bore hole or not.

The ring drill bit 17, 17' according to the above-described embodiments is provided with rock cutting members in the form of rock drill buttons. Within the scope of the invention, it is feasible that the ring drill bit has other types of rock cutting members, for instance chisels of cemented carbide.

Thus the drill adapter 20, 20' comprises a flush duct 37 for flush medium, first drivers 29, 29' in order to transfer rotation, as well as first 21 , 22 and second 35, 36 fastening means, whereby the second fastening means is intended to co-operate with one end of the drill rod.

Thus, the rock drilling tool according to the present invention comprises, among other things, protection for the form locking ridges in the form of crushing members so that deformation of the ridges is minimised. Furthermore, the crushing members contribute to ream the rock in the area between the pilot drill bit and the ring drill bit.

Claims

1. A rock drilling tool for percussive drilling, whereby the rock drilling tool (10;10') is intended to be connected to a casing tube (46) and a drill rod (62) in order to form a bore hole, said casing tube is intended to be used as a channel for drill dust, said rock drilling tool comprises:

- a drill adapter (20;20') including a flush duct (37) for flush medium, first drivers (29;29') in order to transfer rotation, as well as first (21 ,22) and second (35,36) fastening means, whereby the second fastening means is intended to co-operate with one end of the drill rod,

- a central pilot drill bit (11 ,12) provided with rock cutting members (13,14) and detachably connected to the first fastening means (21 ,22) of the drill adapter,

- a ring drill bit (17; 17') provided with rock cutting members (41) and arranged to surround parts of the drill adapter during drilling, whereby the ring drill bit comprises second drivers (49;49') intended to co-operate with the first driver (29;29') of the drill adapter in order to rotate the ring drill bit with the drill adapter, and

- a casing shoe (18) intended to be secured to the casing tube as well as to the ring drill bit at least in connection with drilling, which casing shoe is arranged to push the casing tube in solely the axial direction of the tool, whereby the casing tube (46) and the ring drill bit may be left in the borehole after finished drilling, c h a r a c t e r i z e d in that an axially front end of the first driver (28,28') of the drill adapter (20;20') comprises crushing members (30) such as buttons, chisel bits, hard coatings or the like.

2. Drill tool according to claim 1 , wherein the first driver (29;29') of the drill adapter and the second driver (49;49') of the ring drill bit co-operate by means of form locking.

3. Drill tool according to claim 1 or 2, wherein the drill adapter (20;20') comprises a percussive surface (31 ) for transfer of shock waves to a percussive surface (47) at one end of the ring drill bit (17;17'), facing away from the rock cutting members (41 ) of the ring drill bit.

4. Drill tool according to any one of the preceding claims, wherein the first driver (29;29') of the drill adapter defines a circle (C1), which has a diameter (D1 ) larger than the diameter (D2) of a circle (C2) of radially inner parts of the rock cutting members (41 ) of the ring drill bit.

5. Drill tool according to any one of the preceding claims, wherein the first driver (29') of the drill adapter comprises a shoulder (59'), intended to engage with a front surface (42') of the ring drill bit in order to enable retraction of the drill tool and the casing tube (46).

6. Ring drill bit intended to be included in a rock drilling tool (10; 10') for percussive drilling, whereby the rock drilling tool (10;10') is intended to be connected to a casing tube and a drill rod (62) in order to form a bore hole, said ring drill bit (17;17') is provided with rock cutting members (41) and is arranged to surround parts of a drill adapter during drilling, whereby the ring drill bit comprises second drivers (49;49') intended to co-operate with the first driver of the drill adapter in order to rotate the ring drill bit with the drill adapter, c h a r a c t e r i z e d in that a central hole (48;48') runs through the ring drill bit, whereby the wall of the hole comprises second drivers in the form of a plurality of longitudinal grooves (49;49'), whereby the grooves are formed in order to permit passage of the first driver of the drill adapter.

7. Ring drill bit according to claim 6, wherein the second driver (49;49') of the ring drill bit is arranged to co-operate with the drill adapter by means of form locking.

8. Ring drill bit according to any one of the preceding claims 6 and 7, wherein the second drivers (49;49') of the ring drill bit define a circle (C1), which has a larger diameter (D1 ) than the diameter (D2) of a circle (C2) of radially inner parts of the rock cutting members (41 ) of the ring drill bit.

9. Drill adapter intended to be included in a rock drilling tool (10;10') for percussive drilling, whereby the rock drilling tool (10;10') is intended to be connected to a casing tube and a drill rod (62) in order to form a bore hole, whereby the drill adapter (20;20') comprises a flush duct (37) for a flush medium, first drivers (29;29') in order to transfer rotation, as well as first (21 ,22) and second (35,36) fastening means, whereby the second fastening means is intended to co-operate with one end of the drill rod, while the first fastening means (21 ,22) of the drill adapter is intended to be detachably connected to a central pilot drill bit, c h a r a c t e r i z e d in that an axially front end of the first driver (28,28') of the drill adapter (20;20') comprises crushing members (30) such as buttons, chisel bits or hard coatings or the like.

10. Drill adapter according to claim 9, wherein the first driver (29') of the drill adapter connects to a shoulder (59'), intended to engage with a front surface of the ring drill bit in order to enable retraction of the drill tool and casing tube from a bore hole.