EP1402146B1

EP1402146B1 - Earth drilling device

Info

Publication number: EP1402146B1
Application number: EP02744049A
Authority: EP
Inventors: Uno LÖF
Original assignee: TICC HB
Current assignee: TICC HB
Priority date: 2001-07-02
Filing date: 2002-06-27
Publication date: 2007-05-23
Anticipated expiration: 2022-06-27
Also published as: SE0102373D0; DE60220277D1; SE522135C2; EP1402146A1; WO2003004824A1; CN1599832A; SE0102373L; ATE363015T1

Abstract

The invention relates to a drilling tool and a method for down-the-hole drilling, the drilling tool being intended to drill a hole ahead of a following casing tube (13). The drilling tool comprises a central pilot drill bit (20), a reamer (33) and a guide body (12) for steering the drilling tool and casing tube relative to one another. To avoid problems with threaded connections, the guide body (12), reamer (33) and pilot drill bit (20) are mutually formed so that the rotational power is transferred from the guide body (12) to the reamer (33) and from the reamer (33) to the pilot drill bit (20), but without either of the two transfers of rotational power comprising any threaded connection, and so that an essentially radial displacement exists between the guide body (12) and the reamer (33). The construction also facilitates retraction of the reamer (33) without the pilot drill bit also needing to rotate.

Description

TECHNICAL FIELD

The present invention relates to a drilling tool for down-the-hole drilling of the type that is used for drilling in earth and covered rock, the drilling tool bemg intended to drill a hole ahead of a following casing tube.

PRIOR ART

Drilling tools are previously known that comprise a central pilot drill bit, a reamer and a guide body for steering the drilling tool and the casing tube relative to one another, said guide body having an axially fixed position on a drilling tool shaft during all working phases of the drilling tool. Said guide body is located inside the casing tube and transfers rotation and percussion energy to the reamer and the pilot drill bit. The reamer can take up both a position concentric with the guide body and the pilot drill bit, in which position the pilot drill bit and the reamer can be guided through the casing tube, and an operational, radially projecting position for drilling a hole larger than the casing tube. Reference may be made to EP-A-36 847 and SE-B-411 139 for an example of such a drilling tool.
In the case of such drilling tools, it can sometimes occur when drilling in stony ground or fissured rock, for example, that the reamer becomes wedged fast, so that there is a risk of losing the tool. The difficulty here is that the guide body with the pilot drill bit is prevented from rotating around the eccentric shaft hole of the reamer that is sticking. On reversed rotation, the threads can loosen and separate the drill string, without it being possible to bring the reamer into the retracted position in order to be taken up through the casing tube.
Furthermore, the threaded connection as such, for example between the guide body and the part that carries the reamer, is the weak point on known drilling tools. A known construction comprises a guide body, the shaft of which is integrated with said guide body and is intended to be connected to a down-the-hole hammer. A pilot drill bit is connected to the guide body by means of an externally threaded tap, which is taken up in an internally threaded hole in the guide body, and a reamer is supported rotatably by an intermediate part on the pilot drill bit. The most frequent damage that occurs in this case is a thread break on the upper part of the threaded tap.
Attempts have been made to avoid threaded connections on drilling tools in down-the-hole drilling. Thus EP-A-515 538 describes a down-the-hole drilling tool on which the threaded connection between the guide body and the shaft of the pilot drill bit is dispensed with. According to this known construction, the drilling tool comprises a central pilot drill bit, a reamer and a guide body for steering the drilling tool and the casing tube relative to one another, and a shaft that is intended to be connected to a down-the-hole hammer, said shaft and pilot drill bit forming a unit in one piece, and the guide body being attached to the shaft so that it can be dismantled, for example to exchange the reamer. However, the shaft of the guide body is provided according to this construction also with an external thread for fastening in an internal thread of a down-the-hole hammer, it again being possible for the problem of thread loosening to occur, in particular if the reamer gets stuck fast. The reamer is driven by the shaft of the pilot drill bit.
One main reason that threads can sometimes loosen in known constructions (including said EP-A-515 538) is that retraction of a wedged reamer cannot be achieved unless the pilot drill bit is rotated in a direction opposite to the direction of rotation on drilling. It is therefore easily perceived that threads can easily loosen if the reamer and/or pilot drill bit have stuck fast or are otherwise prevented from rotating freely on reversing and subsequent pulling out of the tool.
US-A-5 787 999 describes a construction of a down-the-hole drilling tool that comprises a guide body, a drill bit and reamer arms attached between these two elements, which arms can be extended into an operational position and retracted for lifting, for example, through a casing tube. However, these reamer arms are fragile and prone to damage. Furthermore, cuttings, earth etc. can easily get behind and between these reamer arms, preventing a return to the resting position, which again can lead to loss of the tool. In addition, the percussion power is transferred according to this US specification from the reamer arms to the pilot drill bit (shoulder rebate), which is undoubtedly a disadvantage in connection with large forces.

BRIEF ACCOUNT OF THE INVENTION

A first object of the present invention is thus to be able to retract the reamer of a down-the-hole drilling tool without needing to rotate the pilot drill bit.
Another object of the present invention is to avoid threaded connections.
A third object of the present invention is to attain an operationally reliable drilling tool for down-the-hole drilling that is insensitive to penetrating cuttings and other particles.
A further object of the invention is to design a drilling tool for down-the-hole drilling with as few constituent components as possible.
Yet another object of the present invention is to develop a drilling tool with improved properties to remedy getting stuck and at the same time ensure improved manageability, both in the tool's working position and in the retracted position.
Extension and retraction are positively controlled. If a shaft break should occur and the pilot bit and reamer are left in the hole on lifting, these are caught by a tool that rotates in the same direction as the working position.
These and other objects, which are obvious to the expert, have been able to be realized in a surprising manner by designing the drilling tool in accordance with the characterizing part of claim 1. Preferred embodiments of the invented drilling tool are defined in the dependent claims.
A preferred embodiment of the invention will now be described with the aim of exemplifying it, but by no means restricting it, and will be illustrated in the enclosed drawings. These are presented briefly as follows:

Fig. 1 shows in cross-section conveying of the guide body through the casing tube with the pilot drill bit shown in side view, and a cross-section of the reamer in a retracted position concentric with the guide body.
Fig. 2 shows a corresponding view, but with the pilot drill bit and the extended reamer in the working position, below the casing shoe of the casing tube orifice.
Fig. 3 shows sectional view 3-3 in Fig. 1 of the pilot drill bit and the reamer.
Fig. 4 shows sectional view 4-4 in Fig. 2 of the pilot drill bit and the reamer.
Fig. 5 shows a side view of the pilot drill bit with camshaft, cam and shaft.
Fig. 6 shows a top view of the pilot drill bit according to Fig. 5.
Fig. 7 shows a side view of the guide body in Fig. 1 and 2.
Fig. 8 shows the end view 8-8 of the guide body according to Fig. 7.
Fig. 9 shows a side view of the reamer according to Fig. 1 and 2.
Fig. 10 shows the end view 10-10 of the reamer according to Fig. 9.
Fig. 11 shows the end view 11-11 of the reamer according to Fig. 9.
Fig. 12 shows the button pattern in end view 12-12 according to Fig. 5.

DETAILED DESCRIPTION

Fig. 1 shows the drill bit in a retracted (non-operational) position with the reamer 33. The guide body 12 (see also Fig. 7) is coupled in the usual way to a continuous drill string in a casing tube 13, by means of which string it rotates clockwise in the embodiment illustrated and can be assigned percussion energy from a down-the-hole hammer or a left-rotating top-hammer coupled in a torsionally rigid manner between the drill string and the guide body 12. The drill string and its parts are of a conventional type and are not shown in the figures. The guide body 12 has a circular-cylindrical guide part 47, which with a centring fit is guided by the orifice of the casing tube 13 for rotation coaxially with the drill axis 16. According to the embodiment shown, driven by a down-the-hole hammer, the orifice of the casing tube consists of a welded-on casing shoe 14, which forms a circular collar 15 in the inside of the casing tube 13, and a guide opening 19 for the guide part 47 of the guide body 12. Furthermore, the guide body 12 has rear shoulders 17 that during operation rest against the collar 15, so that a part of the percussion energy of the down-the-hole hammer can be transferred to the casing tube 13 to drive this down.
The pilot drill bit 20 (see also Figs. 5 and 6) comprises a shaft 21 and a cam 22 in one piece with a camshaft 42 and an operational drill bit 48. The linear measurement L (with the camshaft 42) of the shaft 21 from the plane 23 of the drill bit to its top surface 24 is greater than the diameter D of the shaft 21. The shaft 21 is terminated by an end surface 24 at right angles to the longitudinal axis 16 to take up the percussion energy and is of such a length that a gap 59 is formed between the lower surface of the guide body and the opposed, upper surface of the reamer. The shaft 21 also has a radial groove 26 intended for a flexible sliding pin 30 (cf. Fig. 8). The shaft 21 is supported rotatably in the centric hole 28 of the guide body. The shaft 21 is terminated at the top by a recess 25, which encloses the shaft 180 degrees parallel to the cam 22. Furthermore, the guide body 12 has a shoulder 27 with two parallel planes 27A, 27B at its lower end, the position of which is shown in Fig. 8.
These planes interact with two parallel planes 36A, 36B of two shoulders 36', 36" of the reamer (see Figs. 9 and 10) close to the bottom orifice of the hole 28. One advantage of a coupling formed in this way between the guide body 12 and the reamer 33 is that the least expensive and most easily exchangeable part, the reamer 33, will be worn most during operation.
The reamer 33 is shown in Fig. 2 in its extended operational position and its single-piecc design in Fig. 9, 10 and 11. In Fig. 10, the recess 34 is seen positioned for right-hand rotation (seen from above) intended for the cam 22, and the plane 35, which forms the underside that shall lie adjacent to the plane 23 of the pilot drill bit. In the case of a drilling tool with left-hand rotation, the recess 34 shall be positioned in a mirror-image position compared with Fig. 10, which can thus be done when using one and the same pilot 20. Fig. 11 shows the top side of the reamer with the two parallel shoulders 36, the longitudinal surfaces of which are parallel to the longitudinal extension of the oval recess 37. When the reamer 33 is extended, the surfaces 36A, 36B slide on the two planes 27A, 27B of the guide body, the movement of the reamer being radial, through a displacement in relation to the longitudinal axis 16, while the cam 22 is moved in the recess 34, from the retracted to the extended position.
In Fig. 1, the pilot drill bit 20 hangs freely in the guide body 12, connected via a transverse hole 38 (see Fig. 8), which passes over into a circular radial groove on the inner surface of the hole 28, the flexible sliding pin 30 being inserted into said radial groove and holding the rotatable shaft 21 together with the guide body. In a smaller hole, which is essentially perpendicular to the borehole 38, a tubular pin 31 is inserted that locks the sliding pin 30 for holding. The locking pin/plug 31 is best made of a material with a lower density than the material used in the actual fastener 12. The locking plug 31 is expediently made of an elastomer material, e.g. urethane rubber or plastic polymer (PAG). Thanks to the use of lower density in the material of the locking plug 31, the risk of the locking plug 31 being damaged / coming off can be drastically reduced. Thus this solution principle can contribute substantially to the operating reliability of the tool. It is perceived that this last-named solution is in no way restricted to just this type of drill bit, but the principle can also be used for locking interacting components in other types of drill bits.
It is also clear from Fig. 1 that arranged centrally inside the drill bit is a flushing channel 43, 44, the diameter of which is adapted to the desired flushing medium and/or flow quantity. The flushing channel 43 in the guide body 12 passes over into a flushing channel 44 in the pilot drill bit 20. Cylindrical recesses 43A and 44A respectively are located in the area of the transition of the flushing channel 43, 44 between the guide body 12 and the pilot drill bit 20. These recesses are essentially of the same external diameter, to be able to accommodate a sealing sleeve 50 of suitable material, preferably plastic. A groove 44B is arranged roughly in the middle in the recess 44A of the pilot drill bit, which groove is intended to cooperate with a correspondingly formed annular bulge 51 of the sealing sleeve 50. Due to this, the sealing sleeve 50 can be snapped firmly into the recess 44A in the pilot drill bit 20, so that it is fixed. The task of the sealing sleeve 50 is to seal the upper joint that occurs between the pilot drill bit 20 and the guide body 12. This thus prevents flushing medium from leaking out into the joint.
As indicated in Fig. 5, the sealing sleeve 50 can be used advantageously to regulate the flow of the flushing medium by choosing a sleeve 50 with the desired inner diameter R₅₀. The driller thus has access to many sleeves of varying inner diameter, so that the optimum flow can be obtained quickly and easily.
According to Fig. 2, the pilot drill bit 20 and reamer 33 are in the working position. The casing shoe 14 with the rebate 15 transfers the percussion energy from the shoulders 17 lying at the rear to the collar 15 (does not apply when driving using a top-hammer, as the casing shoe is absent and the guide body 12 is guided against the inside of the actual casing tube) in the axial direction of the drill string in the casing tube, in which case such a projection of the guide body 12 ahead of the front edge of the casing shoe 14 or casing tube 13 should be achieved that the distance from this to the plane 39 of the upper side of the reamer is approximately equal to or slightly less than the length of the shoulders 17. When the periphery-cutting reamer buttons 49 rest against a hard base, the plane 39 is pressed against the underside of the guide body and the percussion energy is transferred to the reamer buttons 49, the reamer being fixedly bound in the extended position by the cam 22 according to Fig. 4, and being supported to the rear by the shaft 21 in the hole 28 and the opposing closer pattern of carbide buttons 46 of the pilot drill bit (cf. Fig. 4 and 12), which provides a counter-pressure from the drilled hole wall. It is evident from Fig. 6 that the pilot drill bit 20 is advantageously equipped in a known manner with a number of peripheral buttons 58.
The reamer processes a radius from the centre axis 16 and on rotation provides a circular hole that is larger than the outer envelope diameter of the casing tube 13. The pilot drill bit gets its rotation from the camshaft 42 with cam 22 (Fig. 5) and its position in the reamer's recess 34, as well as the shaft's recess 25 (Fig. 5 and 6) and the carrier shoulder 18 (Fig. 8).
The guide body 12 has axial, preferably straight flushing grooves 40, which are terminated to the rear between the shoulders 17 and there have ejector openings 41 acting to the rear and connected to the inner bottom plane, which consist of the hole 28. The flushing grooves 40 are terminated blindly ahead before they reach the front edge of the guide body 12 and a part of the groove opens in the plane 27.
During drilling, a predominant part of the drilling work is borne by wear of the pilot drill bit, since this drills an area slightly smaller than the inner diameter of the casing shoe 14 or the inner diameter of the casing tube 13. Radial extension of the reamer 33 is executed when the orifice of the casing tube or casing shoe is located behind the end plane of the guide body 12, the plane of the pilot drill bit fitted with buttons is pressed against the ground and its grip and friction are considerably greater than the friction force at the opposite end plane of the shaft 24, the pilot drill bit remaining stationary when the guide body and the reamer turn relative to the shaft 21 and the camshaft 42. The radius end of the cam 22 fits in the end position into the hole 37 and recess 34, which coincide. The back of the cam 22 forms a camshaft 42, which bears on the opposite end position of the hole 37, which prevents the reamer from executing an oscillating movement during operation. On retraction of the reamer 33, the direction of rotation is reversed and the above radial movement is repeated by the reamer, the shoulders 36', 36" of which slide, with the sliding planes 36A, 36B, against the parallel planes 27A, 27B of the guide body, ensuring retraction and retention of the reamer in the position according to Fig. 3.
The flushing medium, which can consist of venting from the down-the-hole hammer, is supplied via the drill string to the channel 43 (Fig. 7) in the guide body and routed onwards to the channel 44 in the pilot drill bit, which opens via channel arms on the one hand into openings 45 on the camshaft 42 and cam 22 respectively and on the other hand onto the front surface of the pilot drill bit fitted with buttons. The guide body has venting holes 41 close to the bottom plane of the hole 28. As stated above, there is a number of flushing holes 45 in the pilot drill bit with channels 44, which holes are taken up radially in the camshaft 42 and cam 22, these providing an excess pressure in the recess 34, which in turn prevents drill cuttings and other particles from entering. The flushing medium flows out partly by the end plane 35 of the reamer.
As is clear from the above description, a design of a drilling tool for down-the-hole drilling has thus been developed in which threaded connections can be entirely dispensed with. This gives a level of operating reliability unattained hitherto. Furthermore, the consecutive transfer of power from the guide body to the reamer, and from the reamer to the pilot drill bit, means that the reamer may be rotated half a turn on retraction without the pilot drill bit rotating. This facilitates secure retraction of the reamer in tight working positions, which was hitherto impossible, since according to the prior art it is the pilot drill bit that drives the reamer.
It is perceived that what has been described above is only one preferred embodiment and that for the expert there is room for a number of modifications that fall within the scope of the claims. According to the embodiment described above, it is indicated that the shaft 21 and the operational drill bit 48 are an integrated unit. However, it is also possible within the framework of the invention to have an arrangement in which the shaft and drill bit are separate parts, but are connected in a torsionally rigid manner to one another, for example by means of molecular connection. Furthermore, it is perceived that the coupling 27, 36 between the guide body and the reamer 33 can be executed in the reverse manner, so that the reamer 33 instead of the guide body 12 is provided with a central shoulder, and the guide body 12 is provided with two laterally arranged shoulders. It is also perceived that the sealing sleeve 50 does not necessarily have to be arranged in recesses in the flushing channel. It can be desirable in certain cases to e.g. only provide one recess in the pilot 20, or even to exclude recesses and then only use a groove in the pilot 20 or another suitable means for keeping the sleeve positioned in the joint. In addition, it is perceived that other sliding connections 30.can be used, for example balls with a diameter adapted to the radius of the grooves 26, 38. It is also perceived that the flushing holes 41 can be positioned in many other planes than those described above, in certain cases advantageously above the sleeve 50.
It is also perceived that the displacement of the reamer does not necessarily have to take place along a straight sliding plane, but can take place via a sliding plane that is curved to a certain extent, a certain rotation of the reamer 33 in relation to the guide body 12 occurring, the displacement however continuing to be regarded as essentially radial in relation to the guide body 12. Furthermore, it is perceived that the basic principle according to the invention can also be used if threaded connections are used in the power transfer.
The abstract is also an integral part of this description.

Claims

Drilling tool for down-the-hole drilling, which drilling tool is intended to drill a hole ahead of a following casing tube (13), the drilling tool comprising a central pilot drill bit (20), a reamer (33) and a guide body (12) for steering the drilling tool and casing tube relative to one another so that an essentially radial displacement exists between the guide body (12) and the reamer (33), characterized in that the guide body (12), reamer (33) and pilot drill bit (20) are mutually formed so that the rotation power is transferred from the guide body (12) to the reamer (33) and from the reamer (33) to the pilot drill bit (20).
Drilling tool according to claim 1, characterized in that the guide body (12) has at least one sliding plane (27A; 27B) and that the reamer has at least one shoulder (36'; 36") with a sliding surface (36A; 36B) intended at least partly to bear on and slide against said sliding plane (27A; 27B) in such a way that the rotation movement of the guide body is transferred to the reamer through the interaction between said sliding plane (27A; 27B) and sliding surface (36A; 36B) respectively and that mutual sliding is permitted between said sliding plane and sliding surface to facilitate radial extension and retraction respectively of the reamer (33).
Drilling tool according to claim 1 or 2, characterized in that the rotation movement is transferred from the reamer (33) to the pilot drill bit (20) in that the pilot drill bit has a radially projecting cam (22), which is in engagement with a recess (34) in the reamer (33) adapted to the cam (22).
Drilling tool according to claim 3, characterized in that the recess (34) in the reamer (33) is designed so that it permits a certain mutual rotation between the cam (22) and the recess (34), the reamer (33) being moved from a radially extended position to a radially retracted position when its recess (34) is rotated around the cam (22) from a first end position to a second end position.
Drilling tool according to any of the preceding claims, characterized in that the pilot drill bit (20) comprises a shaft (21) that is connected rotatably to the guide body (12) by means of a sliding connection, preferably in the form of an annular sliding pin (30), which permits the pilot drill bit to remain motionless while the guide body and reamer rotate on retraction and extension respectively of the reamer.
Drilling tool according to claim 4 and/or claim 5, characterized in that the guide body (12) and reamer (33) rotate roughly a half turn on retraction and extension respectively of the reamer.
Drilling tool according to any of the preceding claims, characterized in that the reamer (33) in addition to said recess (34) has a through hole (37) of a mainly oval shape, and that this hole (37) together with said recess (34) forms an essentially polygonal shape with three sides (Fig. 10).
Drilling tool according to any of the preceding claims, characterized in that the reamer (33) has peripheiy-cutting buttons (49) and that the pressure against these buttons during operation is compensated for to a certain extent by a closer button pattern (46) along the opposing peripheral edge of the pilot drill bit (20, 48).
Drilling tool according to any of the preceding claims, characterized in that by its orifice the casing tube (13) has a casing shoe (14), which at its upper end has a rebate (15), that the guide body (12) has shoulders (17) at its upper end which during operation bear on said rebate (15), due to which the casing tube (13) is driven downwards into the hole.
Drilling tool according to claim 2, characterized in that said sliding surfaces (36A; 36B) and sliding planes (27A; 27B) respectively have the same curve, preferably said sliding surface and sliding plane respectively being straight planes.
Drilling tool according to claim 1, characterized in that neither of the two said transfers of rotational power comprises any threaded connection.
Drilling tool according to claim 1, characterized in that a flushing channel (43, 44) is arranged centrally inside the drill bit, which flushing channel (43, 44) extends through the guide body (12) into the pilot drill bit (20), a sealing sleeve (50) being arranged in the area of the transition of the flushing channel (43, 44) between the guide body (12) and the pilot drill bit (20).
Drilling tool according to claim 12, characterized in that in the area of the transition of the flushing channel (43, 44) between the guide body (12) and the pilot drill bit (20) there is arranged at least one recess (43A, 44A), preferably two, which recess(es) (43A, 44A) has/have essentially the same diameter as the outer diameter of the sealing sleeve (50).
Drilling tool according to claim 5, characterized in that said sliding connection (30) is locked in the guide body (12) by means of a body (31), the density of which is lower than the material that is used in the fastener/guide body (12).
Method of down-the-hole drilling with a drilling tool intended to drill a hole ahead of a following casing tube (13), the drilling tool comprising a central pilot drill bit (20), a reamer (30) and a guide body (12) for steering the drilling tool and casing tube relative to one another, characterized in that the guide body (12), reamer (33) and pilot drill bit (20) are mutually formed so that the rotational power is transferred from the guide body (12) to the reamer (33) and from the reamer (33) to the pilot drill bit (20), but without either of the two said rotational power transfers comprising any threaded connection.