Technical Field

[0001] The present disclosure relates generally to a down-the-hole hammer driven by a motive fluid, more specifically to means for handling flow of motive fluid through a down-the-hole hammer.

Background Art

[0002] The two most common methods for drilling rock involve either quasi-static loading of rock as used in rotary drilling, or high intensity impact loading as used in down- the-hole (DTH) drilling. DTH applications include a hammer assembly having a piston or actuator that reciprocates within the drill casing and applies a cyclical impact on an anvil. The anvil is typically part of or directly connected to the drill bit so that impact forces of the piston striking the anvil are transferred through the drill bit into the rock being drilled. The piston typically reciprocates in response to motive fluid (e.g., compressed air), alternatingly raising and lowering the piston. The motive fluid is typically exhausted from the drill through the drill bit after actuating the hammer assembly, then referred to as exhaust fluid to differentiate from the motive fluid which enters the DTH hammer. The exhaust fluid exits through the drill bit to clear cuttings and other debris from around the drill bit and carry such debris up out of the hole or bore being drilled on the outside of the hammer casing. Hybrid rock drills (called percussive assist rotary drills or PARD) that utilize a DTH hammer assembly to impact a rotary drill bit are also known, and also have a flow of exhaust fluid through the drill bit.

[0003] When the exhaust fluid exits through the drill bit, it flows over an exterior surface of the drill bit (“flows over” and variations thereof meaning in this specification that the motive fluid flows across and in contact with the drill bit exterior surface) and up the bore being drilled. In known DTH hammer assemblies having reverse circulation configurations, the exhaust fluid actually exits above the drill bit, flows down over the drill bit exterior, and then flows up through the center of the drill bit, hammer, and drill pipe or drill string to the surface. In this specification, the term “through the bit” and “bit exhaust” are intended to include exhaust fluid that flows over the drill bit exterior surface, whether flowing out of the bit and up the bore or flowing in a reverse circulation direction. [0004] In the present disclosure, the terms “down-the-hole hammer”, “hammer”, and “hammer assembly” refer to a drilling arrangement using the impact forces of a reciprocating piston or other moving actuator, whether such drilling arrangement is present in a DTH application, a PARD arrangement, or another arrangement, and regardless of whether the drilling arrangement includes a standard bit, drag bit, rotary bit, or another cutting surface.

[0005] In general, a certain amount of motive fluid is needed to achieve the desired power output from the hammer and/or lifting the rock debris and ground water pouring into the created hole. However, considering the wear life of the drill bit and the outer casing of the hammer, the supply of motive fluid often exceeds what is needed to flush the rock debris from the drill bit. It would therefore be beneficial to reduce the amount of exhaust fluid passing over the drill bit.

[0006] WO 2010/093685 A2 discloses a DTH hammer wherein at least a portion of the actuator flow portion of the motive fluid is exhausted through the proximal end of the drill, above the drill bit such that it does not flow over the drill bit's exterior surface.

[0007] The disclosed DTH hammer comprises a check valve function near the inlet for motive fluid into the hammer; the check valve function preventing effects of discontinuous motive fluid supply and associated momentary pressure drops, e.g., when adding an additional drill string during the drilling operation.

[0008] During single pass drilling, the drilling rig can comprise drill strings of fixed length adapted to the desired depth. This is primarily used for drilling shorter bore holes, e.g. up to about 20 meters deep. The DTH hammer may then be operated without interruption of the motive fluid supply. Thus, a DTH hammer adapted to support exhaust flow through the proximal end of the DTH hammer during continuous motive fluid supply would be beneficial.

Summary

[0009] An objective of the present disclosure is therefore to provide an improved DTH hammer adapted for continuous motive fluid supply. The DTH hammer is described in the appended claims. [0010] According to a first aspect of the present disclosure, there is provided a down- the-hole, DTH, hammer configured for operation under the influence of motive fluid, the DTH hammer comprising: a housing extending between a first end and a second end along a longitudinal axis of the DTH hammer; a back head connected to the first end of the housing and comprising at least one supply port for motive fluid and at least one evacuation port for exhaust fluid, separate from each other; an actuator configured to be operated by motive fluid; and a distributor arranged in the back head in fluid communication with the at least one supply port and an actuator drive flow path to control supply of motive fluid to the actuator drive flow path, wherein the distributor is further arranged in fluid communication with the at least one evacuation port and an actuator exhaust flow path to control evacuation of exhaust fluid from the actuator exhaust flow path, and wherein the distributor is configured to enable simultaneous flow of motive fluid from the at least one motive fluid supply port to the actuator drive flow path and flow of exhaust fluid from the actuator exhaust flow path to the at least one exhaust fluid evacuation port, wherein the flows of motive fluid and exhaust fluid are separated from each other.

[0011] By means of the distributor, the DTH hammer according to the present disclosure provides a simple and robust solution to optimize fluid flow through the back head such that motive fluid and exhaust fluid are separated from each other. The solution reduces the number of moving parts in the DTH hammer to increase service life due to reduced wear. The solution is less complex to manufacture and requires less space in the back head. The DTH hammer is especially suited for single pass drilling in that it obviates the need for a check valve.

[0012] In one embodiment, the distributor comprises at least two separate flow paths, for the motive fluid and the exhaust fluid, respectively. The two separate flow paths ensure separation of the flows of motive and exhaust fluid.

[0013] In one embodiment, at least one first flow path for the motive fluid is defined by a first internal passage in the distributor arranged in fluid communication with the at least one supply port. The first internal passage allows controlling the flow of motive fluid through the distributor in an effective manner. [0014] In one embodiment, at least one second flow path for the exhaust fluid is defined by a second internal passage in the distributor arranged in fluid communication with the at least one evacuation port. The second internal passage allows controlling the flow of exhaust fluid through the distributor in an effective manner.

[0015] In one embodiment, the at least one evacuation port is oriented in a substantially radial direction of the DTH hammer, a substantially axial direction of the DTH hammer, and/or a combination thereof. The orientation of the evacuation port may thus be adapted to available space and material thickness in the back head.

[0016] In one embodiment, the at least one evacuation port comprises one or more axially oriented channels formed in the back head. The channels may be molded during manufacture or formed by milling at a subsequent stage.

[0017] In one embodiment, the distributor comprises: a cylindrical body having at least one substantially axial conduit therein extending in a distal direction from a first end of the cylindrical body; and a tubular stem having a central distributor bore and extending in a distal direction from the cylindrical body, wherein the cylindrical body comprises at least one substantially radial conduit in fluid communication with the distributor bore, and wherein the at least one axial conduit is separated from the distributor bore and the at least one radial conduit. The structure of the distributor provides a robust and compact solution for enabling simultaneous and separate flow of motive fluid and exhaust fluid therethrough.

[0018] In one embodiment, the at least one axial conduit terminates in an annular groove formed in an outer surface of the cylindrical body. The annular groove allows distribution of the motive fluid along the circumference of the cylindrical body to facilitate fluid communication with the actuator drive flow path.

[0019] In one embodiment, the distributor comprises a plurality of axial conduits distributed about the circumference of the cylindrical body. The plurality of axial conduits allows distribution of the motive fluid through the cylindrical body to increase flow. [0020] In one embodiment, the distributor comprises two radial conduits arranged diametrically opposite to each other. The diametrically opposed radial conduits allow distribution of the exhaust fluid through the cylindrical body to increase flow.

Brief Description of Drawings

[0021] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:

Fig. l is a perspective view of a down-the-hole (DTH) hammer according to one embodiment of the present disclosure.

Fig. 2 is an exploded view of the DTH hammer shown in Fig. 1.

Fig. 3 is a cross-sectional view of the DTH hammer shown in Figs. 1 and 2.

Fig. 4 is a perspective view of a distributor according to one embodiment of the present disclosure.

Figs. 5a and 5b are cross-sectional views of the proximal end of the DTH hammer shown in Fig. 3 rotated 90 degrees with respect to each other.

Description of Embodiments

[0022] In the following, a detailed description of a DTH hammer according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, '‘supported’, and '‘coupled’ and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0023] In the present disclosure, the terms “down-the-hole hammer”, “hammer”, and “hammer assembly” refer to a drilling arrangement using the impact forces of a reciprocating piston or other moving actuator, whether such drilling arrangement is present in a DTH application, a PARD arrangement, or another arrangement, and regardless of whether the drilling arrangement includes a standard bit, drag bit, rotary bit, or another cutting surface.

[0024] For the sake of simplicity and consistency in this specification, the term ‘axial’ refers to a direction parallel to a central longitudinal axis of a DTH hammer as illustrated in the drawings. The term ‘radial’ refers to a direction perpendicular to the axis of the DTH hammer. All the main elements of the hammer discussed below are generally ring-shaped or cylindrical and therefore all have inner and outer surfaces. The term ‘inner surface’ refers to the surface facing toward the central axis or generally toward the inside of the hammer and the term ‘outer surface’ refers to the surface facing away from the central axis or generally away from the inside of the hammer. All elements also have first and second ends which, using the convention of the illustrated embodiment, may be referred to as ‘proximal’ and ‘distal’ ends with respect to the typical operating orientation of the hammer in relation to the operator.

[0025] In the context of the present disclosure, the term ‘flow path’ should be understood as the way or course followed by a fluid through the DTH hammer. A flow path does not necessarily constitute a physical structure of the DTH hammer, the term instead being used as a general description of how the fluid flows through the DTH hammer. A flow path may be defined by an internal passage in the DTH hammer or any component thereof which delimits the boundaries of the flow path and thereby constitutes a physical structure of the DTH hammer. An internal passage may in turn be subdivided into one or more sections, thus comprising conduits, channels, bores and/or openings which together form the internal passage. [0026] In the context of the present disclosure, motive fluid is a fluid that is supplied to the DTH hammer to actuate a piston of the hammer, whereas exhaust fluid is a fluid that is evacuated from the DTH hammer after having acted on the piston.

[0027] Fig. 1 shows a down-the-hole (DTH) hammer 1 according to one embodiment of the present disclosure in a perspective view. Figs. 2 and 3 are exploded and cross- sectional views of the DTH hammer 1 and illustrate the following basic components: a back head 10, a distributor 20, a cylinder 30, a piston or actuator 40, a retaining ring 50, an exhaust tube 60, a shank adapter 70, an outer sleeve or housing 80, a chuck 90, and a drill bit 100. Operation of the DTH hammer 1 will now be briefly explained with reference to Figs. 2 and 3.

[0028] Referring now to Fig. 2, the housing 80 extends between a first end 81 and a second end 82 and is arranged to accommodate the other components of the DTH hammer 1 therein. To this end, the back head 10 is fixedly arranged to the first end 81, and the chuck 90 is fixedly arranged to the second end 82. The shank adapter 70 extends between a first end 71 and a second end 72 which is attached to the drill bit 100. In other embodiments, the shank adapter 70 and drill bit 100 may be integrally formed in one piece. When mounted, the shank adapter 70 passes through the chuck 90. A washer or retaining ring 50 is provided between the chuck 90 and the housing 80 to retain the shank adapter 70 and drill bit 100. The washer 50 engages a first splined portion 73 adjacent the first end 71 and restricts distal movement of the shank adapter 70 in a flush position of the DTH hammer 1, i.e., when the drill bit 100 is not in contact with rock to be drilled.

[0029] The inner cylinder 30 extends between a first end 31 and a second end 32 and is fixedly arranged inside the housing 80 such that an intermediate space 35 (cf. Figs. 5a and 5b) is formed between the housing 80 and the inner cylinder 30. Further, the inner cylinder 30 comprises at least one first through-going hole 33 adjacent the first end 31 and at least one second through-going hole 34 adjacent the second end 32.

[0030] Referring now to Fig. 4, there is shown a perspective view of a distributor 20 according to one embodiment of the present disclosure. The distributor 20 comprises a cylindrical body 21 having at least one through-going longitudinal or axial conduit 22 therein extending in a distal direction from a first end 23 of the cylindrical body, substantially parallel to a longitudinal axis of the distributor 20. The distributor 20 may comprise a plurality of axial conduits 22 distributed about the circumference and terminating in an annular groove 28 formed in the outer surface of the cylindrical body 21. Together, the axial conduits 22 and the annular groove 28 form a first internal passage in the distributor 20, defining a first flow path for the motive fluid through the distributor 20.

[0031] The distributor 20 is fixedly arranged between the back head 10 and the first end 31 of the inner cylinder 30 and extends partially into the first end 31 of the inner cylinder 30 such that the annular groove 28 is aligned with the first holes 33 in the inner cylinder 30, as shown in Figs. 5a and 5b. Thus, the axial conduits 22 and annular groove 28 are in fluid communication with the intermediate space 35 through the first holes 33 in the inner cylinder 30.

[0032] Further, the distributor 20 comprises a tubular stem 24 extending in a distal direction from the cylindrical body 21 and having a central distributor bore 26. The distributor bore 26 is separate from the axial conduit 22 and terminates near the first end 23 of the cylindrical body 21, i.e., the distributor bore 26 is open at a distal end and closed at a proximal end. Additionally, the distributor body 21 comprises one or more substantially radial conduits 27 in fluid communication with the distributor bore 26, optionally through a wider cavity 29 adjacent the first end 23 of the distributor 20, and separate from the axial conduits 22. The radial conduits 27 extend laterally in a substantially radial direction from the distributor bore 26, substantially perpendicular to the longitudinal axis of the distributor 20, and terminate in orifices in the outer surface of the cylindrical body 21. In one embodiment, the distributor comprises two radial conduits 27 arranged diametrically opposite to each other. The radial conduits 27 are arranged in fluid communication with evacuation ports 14 in the back head 10 formed e.g., by one or more axially oriented channels 15 milled in the back head 10. Together, the distributor bore 26 and the radial conduits 27 form a second internal passage in the distributor 20, defining a second flow path for the exhaust fluid through the distributor 20, the second flow path being separate from the first flow path.

[0033] In other embodiments (not shown), the exhaust fluid may pass from the radial conduits 27 via a space between the housing 80 and the back head 10, for instance through gaps in the thread profiles. [0034] Returning to Fig. 2, the actuator is in the form of a piston 40 extending between a first end 41 and a second end 42 and comprises a central piston bore 43. The piston 40 is arranged to reciprocate in an axial direction inside the housing 80 to impact on the distally arranged drill bit 100. The first end 41 of the piston 40 extends partially into the second end 32 of the inner cylinder 30, as may be seen in Fig. 3.

[0035] With continued reference to Fig. 3, an internal space of the inner cylinder 30 defines a drive chamber 36 proximal to the piston 40 and an internal space of the housing 80 defines a return chamber 85 distal to the piston 40. The tubular stem 24 of the distributor 20 extends into the drive chamber 36, placing the distributor bore 26 in fluid communication therewith.

[0036] The drill bit 100 comprises a central drill bit bore 101 which is aligned with and in fluid communication with a central bore 74 of the shank adapter 70. The exhaust tube 60 is seated in the central bore 74 of the shank adapter 70 and extends from the first end 71 in a proximal direction. The drill bit bore 101, the central bore 74 of the shank adapter 70 and the exhaust tube 60 together form a bit exhaust path for exhaust fluid to flush debris from the external face of the drill bit 100. In the context of the present disclosure, motive fluid is the fluid that is supplied to the DTH hammer 1 to actuate the piston 40, whereas exhaust fluid is the fluid that is evacuated from the DTH hammer 1 after acting on the piston 40, as will be explained further below.

[0037] As noted above, the piston 40 is arranged to reciprocate inside the housing 80 when motive fluid is supplied through a drill string (not shown) attached to the back head 10. This reciprocating motion periodically places the intermediate space 35 in fluid communication with the drive chamber 36 and the return chamber 85, respectively, through the at least one second hole 34 in the inner cylinder 32. The periodic fluid communication between the intermediate space 35 and the drive chamber 36 and the return chamber 85, respectively, causes motive fluid to be supplied from the intermediate space 35 to the drive chamber 36 and return chamber 85 in alternating fashion, to cause the piston 40 to reciprocate in a distal and a proximal direction, respectively.

[0038] At the same time, reciprocation of the piston 40 in the housing 80 periodically places the piston bore 43 in fluid communication with the return chamber 36 and the drive chamber 85, respectively. The periodic fluid communication between the piston bore 43 and the return chamber 85 and the drive chamber 36 causes exhaust fluid to be exhausted from the return chamber 85 and the drive chamber 36 in alternating fashion, distally through the exhaust tube 60, shank adapter bore 74 and drill bit bore 101, and/or proximally through the distributor bore 26.

[0039] The piston 40 comprises a first flared portion 45 adjacent the first end 41 having an outer diameter substantially corresponding to the inner diameter of the inner cylinder 30, and a second flared portion 46 adjacent the second end 42 having an outer diameter substantially corresponding to the inner diameter of the housing 80. The drive chamber 36 is defined by a section of the inner cylinder 30 having an inner diameter greater than the outer diameter of the first flared portion 45. The return chamber 85 is defined by a section of the housing 80 having an inner diameter greater than the outer diameter of the second flared portion 46.

[0040] Displacement of the piston 40 in a proximal direction at least temporarily places the drive chamber 36 in fluid communication with the intermediate space 35 when the first flared portion 45 of the piston 40 fully extends into the drive chamber 36.

Contrarily, displacement of the piston 40 in a distal direction at least temporarily places the return chamber 85 in fluid communication with the intermediate space 35 when the second flared portion 46 of the piston 40 fully extends into the return chamber 85.

[0041] Concomitantly, the displacement of the piston 40 in the proximal direction at least temporarily cuts off fluid communication between the drive chamber 36 and the piston bore 43, while placing the return chamber 85 in fluid communication with the piston bore 43. Additionally, the displacement of the piston 40 in the distal direction at least temporarily cuts off fluid communication between the return chamber 85 and the piston bore 43, while placing the drive chamber 36 in fluid communication with the piston bore 43.

[0042] In one embodiment, the piston bore 43 comprises a first narrow section 47 adjacent the first end 41 of the piston 40 having a diameter substantially corresponding to the diameter of the tubular stem 24 of the distributor 20, and a second narrow section 48 adjacent the second end 42 of the piston 40 having a diameter substantially corresponding to the diameter of the exhaust tube 60. The reciprocating motion of the piston 40 in the proximal direction at least temporarily cuts off fluid communication between the drive chamber 36 and the piston bore 43 when the tubular stem 24 of the distributor 20 extends into the first narrow section 47. Contrarily, the reciprocating motion of the piston 40 in the distal direction at least temporarily cuts off fluid communication between the return chamber 85 and the piston bore 43 when the exhaust tube 60 extends into the second narrow section 48 (as shown in Fig. 3).

[0043] By means of the reciprocating motion of the piston 40, the actuator drive flow path of the motive fluid to actuate the piston 40 in the drive stroke and return stroke is kept separated from the actuator exhaust flow path of the exhaust fluid for evacuation.

[0044] In one embodiment (not shown), the piston bore 43 comprises a first section extending from the first end 41 of the piston 40 and a second section extending from the second end 42, wherein the first and second sections are not in fluid communication with each other. In other words, the piston bore 43 is not through-going. As a result, the exhaust fluid from the return chamber 85 will only be evacuated in the distal direction through the exhaust tube 60, shank adapter bore 74 and drill bit bore 101, whereas the exhaust fluid from the drive chamber 36 will only be evacuated in the proximal direction through the distributor bore 26. By varying the length of the first and second sections, it is possible to control the amount of exhaust fluid being evacuated in the respective directions.

Alternatively, other aspects such as the dimensions of the drive chamber 36 and the return chamber 85 may be varied to achieve the same purpose.

[0045] The distributor 20 is configured to control simultaneous flow of motive fluid and exhaust fluid, respectively, into and out of the housing 80 in such a way that the flow of motive fluid is separated from the flow of exhaust fluid. To this end, the distributor 20 comprises a cylindrical body 21 extending between a first, proximal end 22 and a second, distal end 23.

[0046] Referring now to Figs. 5a and 5b, there is shown close-up views of the proximal end of the DTH hammer 1, illustrating the flow of motive fluid and exhaust fluid through the distributor 20 according to one embodiment of the present disclosure. The distributor 20 is arranged in an internal space of the back head 10 proximal to the inner cylinder 30. The back head 10 comprises a threaded conical portion 11 for connection with drill pipes of a drill string (not shown) and supply of motive fluid through a proximal opening called the supply port 12. Further, the back head 10 comprises a flat recess 13, known as a key grip, as well as one or more evacuation ports 14 for an exhaust fluid, as will be further explained below.

[0047] When motive fluid is supplied through the supply port 12 into the interior of the back head 10, the motive fluid flows through the axial conduits 22 of the distributor 20 and further into the intermediate space 35 via the groove 28 aligned with the first holes 33 of the inner cylinder 30, as indicated by the downwardly oriented arrows. From the intermediate space 35, the motive fluid continues flowing in a distal direction and out through the second holes 34 of the inner cylinder into the drive chamber 36 and the return chamber 85, as explained above. In this way, the actuator drive flow path is defined.

[0048] At the same time, the exhaust fluid is evacuated from the drive chamber 36 and the return chamber 85, respectively, and flows through the distributor bore 26, via the radial conduits 27 and out through the evacuation ports 14, as indicated by the upwardly oriented arrows.

[0049] The distributor 20 allows simultaneous but separate supply of motive fluid and evacuation of exhaust fluid through the back head 10 by means of a single component. This solution greatly reduces the space required inside the back head 10 for accommodating the distributor 20, thereby facilitating manufacture, in addition to increasing service life due to elimination of moving parts and reduced wear.

[0050] Due to the structure of the distributor 20, the first and second flow paths are separated from each other such that motive fluid and exhaust fluid may flow simultaneously through the distributor 20 in substantially opposite directions to achieve a simple and robust solution for optimizing fluid flow through the back head 10 during operation of the DTH hammer 1. The DTH hammer according to the present disclosure is especially suited for single pass drilling wherein fluid pressure is substantially maintained throughout the drilling operation, obviating the need for a check valve to prevent ingress of fluid and rock debris into the interior of the DTH hammer. [0051] Embodiments of a DTH hammer according to the present disclosure has been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0052] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.