WO2008112117A1

WO2008112117A1 - Bit rebounding bumper for down-the-hole rock drilling hammer

Info

Publication number: WO2008112117A1
Application number: PCT/US2008/002959
Authority: WO
Inventors: Dongmin Niu
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2007-03-09
Filing date: 2008-03-06
Publication date: 2008-09-18
Anticipated expiration: 2009-09-09

Abstract

A bumper (16) located behind the bit (50) shoulder (56), between the bit (50) shoulder (56) and the driver sub (14), is disclosed. The bumper (16), which can be formed of disc spring or rings or other structure made of vibration absorbing materials, isolates the driver sub (14) from a direct, backward impact force of the bit (50). A hammer (10) with the bumper (16), a hammer (10) and bit (50) combination with the bumper (16) and a method of bore hole drilling of an earth formation using a hammer (10) with the bumper (16) are also disclosed.

Description

BIT REBOUNDING BUMPER FOR DOWN-THE-HOLE ROCK DRILLING HAMMER

FIELD

[0001] The present disclosure relates to bore hole drilling of an earth formation by down-the- hole (DTH) drilling or, as is also called, in-the-hole (ITH) drilling, with a hammer that is driven by pressurized air or other fluid.

BACKGROUND

[0002] In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art. [0003] Down-the-Hole (DTH) hammer drilling is used in, for example, the mining and construction industries in oil and gas exploration and retrieval operations. In general, a reciprocating piston in the hammer repeatedly contacts the rear face of the bit, causing the bit itself to reciprocate and impact rock, which is broken under the impact force of the bit. As the air pressure used to reciprocate the hammer becomes higher and higher, as well as higher working pressures in hammers operated by water and fluid means, the following problems can occur: the stronger hammer case cylinder and driver sub used to avoid premature breakages increases the cost; premature breaking of the bit shank behind the shoulder can occur and cause loss of productive, particularly if a considerable depth of cut has been achieved, which complicates recovery of any detached portions; and machine idle time increases to maintain the rotary drive units.

[0004] Conventional understanding of the impact drilling mechanism is based on wave propagation theory. It is believed that upon an impact, a stress wave transmits from the piston of the hammer to the bit and therethrough to the face of the breaking rock. There is a portion of the stress wave that is reflected back to the hammer, causing the aforementioned problems. Hence, different kinds of devices have been introduced behind the impact piston to isolate or absorb the reflected stress wave. However, the problems with the hammer case cylinder and rotation drive unit are still there. [0005] More recently, rigid impact theory has suggested a different theory on the percussion rock drilling mechanism. Under this theory, the rigid impact effect of the bit causes the rock breakage. The bit rebounds after the impact due to the mass difference with the rock. The rebounding of the bit creates a backward impact force to the driver sub, and then to the hammer case cylinder, drill tubes and the rotary drive unit. The magnitude of the force depends on the hardness of the rock formation and the working pressure of the hammer. The repeated impact drilling creates an action force by the bit shoulder to the driver sub. Correspondingly, the severe vibrating loads create problems due to fatigue.

[0006] Even in view of the above theories and attempts to improve percussion rock drilling techniques and equipment, there is still a need to reduce or avoid the deleterious effects arising during percussive down-the-hole drilling.

SUMMARY

[0007] An exemplary down-the-hole hammer comprises a hammer case cylinder including a first thread on an inner diameter at a bit-receiving end, a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread, and a bumper, wherein the bumper is located axially more forward along an axis of the hammer than the driver sub.

[0008] An exemplary combination for bore hole drilling of an earth formation comprises a down-the-hole hammer, and a bit, wherein the bit includes: a head at a first end of the bit, the head having an active face including at least one button and at least one opening for a flushing channel, a shank rearward of the head, the shank including a plurality of splines in an outer surface, and a shoulder formed at the transition between the shank and the head, wherein the shoulder includes at least a rearward surface of the head, and wherein the down-the-hole hammer includes: a hammer case cylinder including a first thread on an inner diameter at a bit-receiving end, a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface that mate with the plurality of splines of the bit, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread, and a bumper, wherein the bumper is located axially rearward of the shoulder of j of the driver sub. [0009] An exemplary method of bore hole drilling of an earth formation comprises reciprocating a piston of a down-the-hole hammer against a rear surface of a shank of a bit, contacting an active face of a head of the bit against the earth formation to remove material from the earth formation, wherein the head is at a first end of the bit and wherein the active face includes at least one button and at least one opening for a flushing channel, and absorbing at least a portion of a backward impact force with a bumper, the backward impact force resulting from a rearward motion of the bit or a reflection of a stress wave, wherein the bit includes: the head, a shank rearward of the head terminating in the rear surface, the shank including a plurality of splines in an outer surface, and a shoulder formed at the transition between the shank and the head, wherein the shoulder includes at least a rearward surface of the head, and wherein the down-the-hole hammer includes: the piston, a hammer case cylinder including a first thread on an inner diameter at a bit-receiving end, a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface that mate with the plurality of splines of the bit, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread, and a bumper, wherein the bumper is located axially rearward of the shoulder of the bit and axially forward of the driver sub. [0010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The following detailed description can be read in connection with the accompanying drawings in which like numerals designate like elements and in which:

[0012] FIG. 1 is a schematic representation of the front part of a DTH hammer illustrating an exemplary embodiment of a bumper.

DETAILED DESCRIPTION

[0013] A schematic representation of the front part of a down-the-hole (DTH) hammer illustrating an exemplary embodiment of a bumper is shown in FIG. 1. In FIG. 1, features of the down-the-hole hammer are shown in cross-section and the features of the bit are shown in [0014] An exemplary embodiment of a down-the-hole hammer 10 comprises a hammer case cylinder 12, a driver sub 14 and a bumper 16. The hammer case cylinder 12 includes a first thread 18 on an inner diameter at a bit-receiving end 20. The driver sub 14 has a second thread 22 on an outer surface and a plurality of projecting features 24 on an inner surface. The driver sub 14 is coupled to the hammer case cylinder 12 by a threaded connection 26 between the first thread 18 and the second thread 22. The bumper 16 is located axially more forward along an axis 30 of the hammer 10 than the driver sub 14.

[0015] A bit can be mounted on the exemplary embodiment of the down-the-hole hammer to form a combination for bore hole drilling of an earth formation. An exemplary embodiment of a combination for bore hole drilling of an earth formation comprises a down-the-hole hammer 10 and a bit 50.

[0016] An exemplary embodiment of the bit 50 includes a head 52 at a first end of the bit 50, a shank 54 rearward of the head 52, and a shoulder 56 formed at the transition between the shank 54 and the head 52. The head 52 has an active face 58 including at least one button 60 and at least one opening 62 for a flushing channel. The at least one button has a composition including a hard material, alternatively a composition including a cemented carbide. The shank 54 rearward of the head 52 includes a plurality of splines 64 in an outer surface 66. The shoulder 56 formed at the transition between the shank 54 and the head 52 includes at least a rearward surface 68 of the head 52. Such a rearward surface can be, for example, a surface that joins the outer surface 70 of the head 52 to the outer surface 66 of the shank 54 and can be, for example, a substantially radially oriented surface joining the two noted surfaces. Alternatively, the rearward surface can be angled at other than 90 degrees to the axis 30, can be non-planar, e.g., concave or convex, can be continuous or broken, or can be a combination of these surface types as long as the rearward surface joins the outer surface 70 of the head 52 to the outer surface 66 of the shank 54. At a second end of the bit is an anvil 72, on which a piston impacts repeatedly to advance the down-the-hole hammer.

[0017] An exemplary embodiment of the down-the-hole hammer 10 includes a hammer case cylinder 12, a driver sub 14 and a bumper 16. The hammer case cylinder 12 includes a first thread 18 on an inner diameter at a bit-receiving end 20. The driver sub 14 has a second thread 22 on an outer surface and a plurality of projecting features 24 on an inner surface. The bumper 1 fi ic WatpH nvialiv rearward of the shoulder 56 of the bit 50 and axially forward of the driver [0018] In an exemplary embodiment, the bumper 16 has an axially-oriented opening through which a shank 54 of a bit 50 can be received. In an exemplary embodiment, the bumper is substantially in the form of a hollow cylinder. In an exemplary embodiment, the bumper is formed of a vibration absorbing material, alternatively, the bumper is a type of disc spring. In one example, the bumper is formed of nylon.

[0019] When assembled, the bumper 16 is located between the bit shoulder 56 and the driver sub 14. The driver sub 14 is coupled to the hammer case cylinder 12 by a threaded connection 26 between the first thread 18 and the second thread 22 and the bit is held in the hammer by an undercut 74 at an end of the bit 50. As is illustrated in FIG. 1, the inner diameter of the driver sub 14 fits the outer diameter of shank 54, and outer diameter of the driver sub 14, in the threaded region, fits the inner diameter of the hammer case cylinder and, in the region of the end surface 46, substantially matches the hammer case cylinder outer diameter. The bumper 16, when mounted, may cover forward ends of the splines 64.

[0020] In an exemplary embodiment, the bumper 16 has an outer surface that is substantially the same as an outer diameter of the hammer case cylinder 12 and an inner diameter that contacts the outer surface 66 of the bit 50, e.g., contacts the outer surface along a portion of the shank 54. Optionally, the outer surface of the bumper 16 can have a diameter greater than or less than the outer diameter of the hammer case cylinder 12. In one example, the bumper 16 has a radial thickness defined by an outer surface 40 and an inner surface 42, wherein the outer surface is substantially the same as an outer diameter of the hammer case cylinder and the inner surface contacts the shank of the bit. In a further example, the bumper 16 has an axial thickness defined by a first surface 44 at a first side and a second surface at a second side, wherein the first surface contacts an end surface 46 of the driver sub 14. The second surface is not visible in the FIG. 1 view. A distance between the first surface 44 and the second surface is larger than a distance between the forward ends of the splines 64 and the rearward surface 68. The axial thickness of the bumper 16 can vary with the materials used to fit the desired strength and isolation requirements. In exemplary embodiments, the bumper 16 can be a disc spring or rings made of vibration absorbing materials with adequate strength.

[0021] In percussive drilling, percussion energy is generated by a reciprocating piston. With each impact from the piston, buttons in the drill bit contact and penetrate the rock surface. After parVi imnart the drill ςtring is rotated to turn the drill bit to a new position as the buttons strike

•rdingly, during drilling the bit is cycleable between a first retracted position, in which axial travel of the bit in a first direction is limited by the second surface of the bumper contacting the bit, and a second extended position, in which axial travel of the bit in a second direction is limited by the bit striking the earth formation. Axial motion (A) of the bit occurs by the bit sliding along internal surfaces of the drive sub 14. Rotational motion of the bit occurs by torque transmitted to the bit via the splines 64 mated to the projecting features 24 on the inner surface of the drive sub 14. At least one of a bushing 80 and retainer 82 is internally secured to the hammer case cylinder 12, axially rearward of the driver sub 14 and at an axial position coincident with a rearward portion of the shank 54 of the bit and allows the bit 50 to slide axially when contacted by the reciprocating motion of the piston of the hammer. [0022] In the exemplary embodiment, a bumper 16 is located between the bit shoulder 56 and the driver sub 14. During operation, the bumper 16 will isolate the driver sub 14 from the direct backward impact force of the bit 50 rebounding during impact drilling, significantly reducing the loads on the driver sub 14 and case cylinder 12.

[0023] An exemplary method of bore hole drilling of an earth formation comprises reciprocating a piston of a down-the-hole hammer against a rear surface of a shank of a bit, contacting an active face of a head of the bit against the earth formation to remove material from the earth formation, wherein the head is at a first end of the bit and wherein the active face includes at least one button and at least one opening for a flushing channel, and absorbing at least a portion of a backward impact force with a bumper, the backward impact force resulting from a rearward motion of the bit or a reflection of a stress wave. During the bore hole drilling of an earth formation, the bit is cycleable between a first retracted position and a second extended position, and wherein in the first retracted position the second surface of the bumper contacts the bit. The exemplary method further comprises breaking material of the earth formation under a forward impact force of the bit.

[0024] The bumper 16 also helps to control the weight-on-bit (WOB) by properly selecting the stiffness of the bumper 16 according to a specific application to prolong the service life of the bit.

[0025] The bumper will significantly reduce any impact force arising from use, prolonging the service life of the hammer case cylinder and drill tubes and reducing the maintenance requirement of the rotary drive unit. The bumper will also allow the usage of cheaper steel for tVip raw rviinHer for lower hammer COSt. [0026] Although described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without department from the spirit and scope of the invention as defined in the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A down-the-hole hammer, comprising: a hammer case cylinder including a first thread on an inner diameter at a bit- receiving end; a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread; and a bumper, wherein the bumper is located axially more forward along an axis of the hammer than the driver sub.

2. The down-the-hole hammer of claim 1, wherein the bumper has an axially-oriented opening through which a shank of a bit can be received and wherein the bumper has an outer surface that is substantially the same as an outer diameter of the hammer case cylinder and an inner diameter that contacts the shank of the bit.

3. The down-the-hole hammer according to claims 1 or 2, wherein the bumper is formed of a vibration absorbing material.

4. The down-the-hole hammer according to claims 1 or 2, wherein the bumper is a type of disc spring.

5. A combination for bore hole drilling of an earth formation, the combination comprising: a down-the-hole hammer; and a bit, wherein the bit includes: a head at a first end of the bit, the head having an active face including at least one button and at least one opening for a flushing channel, a shank rearward of the head, the shank including a plurality of splines in an outer a shoulder formed at the transition between the shank and the head, wherein the shoulder includes at least a rearward surface of the head, and wherein the down-the-hole hammer includes: a hammer case cylinder including a first thread on an inner diameter at a bit- receiving end, a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface that mate with the plurality of splines of the bit, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread, and a bumper, wherein the bumper is located axially rearward of the shoulder of the bit and axially forward of the driver sub.

6. The combination of claim 5, wherein the bumper is substantially in the form of a hollow cylinder and has an axially-oriented opening through which the shank of the bit is received.

7. The combination of claim 5, wherein the bumper has a radial thickness defined by an outer surface and an inner surface, wherein the outer surface is substantially the same as an outer diameter of the hammer case cylinder and the inner surface contacts the shank of the bit.

8. The combination of claim 7, wherein the bumper has an axial thickness defined by a first surface at a first side and a second surface at a second side, and wherein the first surface contacts an end surface of the driver sub.

9. The combination of claim 8, wherein the bit is cycleable between a first retracted position and a second extended position, and wherein in the first retracted position the second surface of the bumper contacts the bit.

10. The combination of claim 5, wherein the bumper has an axial thickness defined by a first surface at a first side and a second surface at a second side, and wherein a distance between the first surface and the second surface is larger than a distance between a forward end of the splines and the rearward surface the head.

1 1. The combination of claim 5, wherein the bumper is formed of a vibration absorbing material.

12. The combination of claim 5, wherein the bumper is a type of disc spring.

13. The combination of claim 5, wherein the down-the-hole hammer includes at least one of a bit retainer and a bit bushing, wherein the at least one of a bit retainer and a bit bushing is internal to the hammer case cylinder, axially rearward of the driver sub and at an axial position coincident with a rearward portion of the shank of the bit.

14. The combination of claim 5, wherein the at least one button has a composition including cemented carbide.

15. A method of bore hole drilling of an earth formation, the method comprising: reciprocating a piston of a down-the-hole hammer against a rear surface of a shank of a bit; contacting an active face of a head of the bit against the earth formation to remove material from the earth formation, wherein the head is at a first end of the bit and wherein the active face includes at least one button and at least one opening for a flushing channel; and absorbing at least a portion of a backward impact force with a bumper, the backward impact force resulting from a rearward motion of the bit or a reflection of a stress wave, wherein the bit includes: the head, a shank rearward of the head terminating in the rear surface, the shank including a plurality of splines in an outer surface, and a shoulder formed at the transition between the shank and the head, wherein the shoulder includes at least a rearward surface of the head, and wherein the down-the-hole hammer includes: the piston, a hammer case cylinder including a first thread on an inner diameter at a bit- a driver sub having a second thread on an outer surface and a plurality of projecting features on an inner surface that mate with the plurality of splines of the bit, wherein the driver sub is coupled to the hammer case cylinder by a threaded connection between the first thread and the second thread; and a bumper, wherein the bumper is located axially rearward of the shoulder of the bit and axially forward of the driver sub.

16. The method of claim 15, comprising breaking material of the earth formation under a forward impact force of the bit.

17. The method of claim 15, wherein the bumper is substantially in the form of a hollow cylinder and has an axially-oriented opening through which the shank of the bit is received.

18. The method of claim 15, wherein the bumper has a radial thickness defined by an outer surface and an inner surface, wherein the outer surface is substantially the same as an outer diameter of the hammer case cylinder and the inner surface contacts the shank of the bit.

19. The method of claim 18, wherein the bumper has an axial thickness defined by a first surface at a first side and a second surface at a second side, wherein the first surface contacts an end surface of the driver sub.

20. The method of claim 19, wherein the bit is cycleable between a first retracted position and a second extended position, and wherein in the first retracted position the second surface of the bumper contacts the bit.

21. The method of claim 15, wherein the bumper is formed of a vibration absorbing material.

22. The method of claim 15, wherein the bumper is a type of disc spring.

23. The method of claim 15, wherein the down-the-hole hammer includes at least one of a bit retainer and a bit bushing, wherein the at least one of a bit retainer and a bit bushing is internal to the hammer case cylinder, axially rearward of the driver sub and at an axial position coincident with a rearward portion of the shank of the bit.

24. The method of claim 15, wherein the at least one button has a composition including cemented carbide.