Spline alignment for DTH hammer assembly

Abstract

A hammer drill assembly (2) for coupling to a drill string having a drill bit (12) positioned at the forward end (8) having a drill head (16) and a bit shaft (14); wherein a plurality of axially extending bit splines (28) project radially outwards from a radially outward facing surface of the bit shaft; wherein each of the bit splines comprises a bit spline tip (30) at its axially rearward end having a rearward axially outer edge (48) and a central bit spline longitudinal axis (32); and a driver sub (26) provided axially rearward of the drill bit comprising a plurality of axially extending driver sub splines (34) projecting radially inwards from an inward facing surface of the driver sub; characterised in that : the rearward axially outer edge on at least of one of bit spline tips is non-perpendicular to the bit spline longitudinal axis along at least 25% of the width of the bit spline tip.

Description

[0001] Spline alignment for DTH hammer assembly

[0002] Field of invention

[0003] The present disclosure generally relates automatised spline alignment for a DTH hammer assembly.

[0004] Background art

[0005] The technique of down-the-hole (DTH) percussive hammer drilling involves the supply of a pressurised fluid via a drill string to a drill bit located at the bottom of a bore hole. The fluid acts to both drive the hammer drilling action and to flush rearwardly dust and fines resultant from the cutting action, rearwardly through the bore hole so as to optimise forward cutting.

[0006] The known method of attaching the drill bit the rest of the assembly involves the step of rotating the drill bit or assembly until alignment between the splines on the drill bit and the splines on the driver sub is achieved. This is currently a manual operation; however, it would be desirable to be able to have an automized system for spline alignment.

[0007] Therefore, the problem to be solved is how to provide a simple and reliable assembly and method for automatised alignment of the splines on the drill bit with the splines on the driver sub when attaching the drill bit to the rest of the DTH assembly.

[0008] Summary of the Invention

[0009] It is an objective of the present invention to provide a hammer drill assembly for coupling to a drill string having an axially forward end; an axially rearward end; and an assembly longitudinal axis, the assembly comprising: a drill bit positioned at the forward end having a drill head and a bit shaft; wherein a plurality of axially extending bit splines project radially outwards from a radially outward facing surface of the bit shaft; wherein each of the bit splines comprises a bit spline tip at its axially rearward end having a rearward axially outer edge and a central bit spline longitudinal axis; and a driver sub provided axially rearward of the drill bit comprising a plurality of axially extending driver sub splines projecting radially inwards from an inward facing surface of the driver sub; characterised in that: the rearward axially outer edge on at least of one of bit spline tips is non-perpendicular to the bit spline longitudinal axis along at least 25% of the width of the bit spline tip.

[0010] Advantageously, this enables the automation of the alignment of the splines on the drill bit with the splines on the driver sub, therefore enabling automation of the exchange of drill bits for DTH drilling assemblies. The splines can be reliably aligned in a simple way. A mechanized system can be employed so that the splines will self-align using a cheap and convenient system with only translational input movement required. The assembly is easy to manufacture using standard processes and the alignment method does not require the use of any sensors or additional actuators.

[0011] In some example embodiments the rearward axially outer edge on at least of one of bit spline tips is curved. Advantageously, this offers a smooth transition and enables the contacting surfaces to easily slide over each other. Furthermore, surface pressure and frictional forces are reduced and therefore the possibility of deformation or damage to the splines is minimised during the insertion of the bit into the driver sub. There is also the benefit that limited rotational movement occurs during the insertion of the bit into the driver sub.

[0012] In some example embodiments the rearward axial outer edge on at least of one of bit spline tips is chamfered. Advantageously, this geometry is easy and cheap to manufacture.

[0013] In some example embodiments the rearward axially outer edge on at least of one of bit spline tips has an arrowhead shape. Advantageously, this design helps to reduce the rotational movement required when the bit is being inserted into the driver sub.

[0014] In some example embodiments at least one of the bit splines extends axially further rearward compared to the rest of the bit splines. Advantageously, this enables the ease of the spline alignment and avoids the need to add an additional part such as an alignment pin, thereby avoiding any weakening of the structure of the shank.

[0015] In some example embodiments there is an alignment pin positioned on the forward end of at least one of the driver sub splines. Advantageously, this is a cheap and simple feature that can be added to aid automized spline alignment.

[0016] In some example embodiments the at least one alignment pin has a higher surface hardness than the bit splines. Advantageously, the means the surface of the alignment pin will not deform under pressure, instead the bit spline tip(s) may locally deform and will slide over the surface of the alignment pin thus inducing rotational movement between the bit and the rest of the assembly so that the splines will align.

[0017] In some example embodiments the surface hardness of the alignment pin is at least 1 HRC higher than the surface hardness of the bit splines. Advantageously, this hardness difference means that the alignment pin will not plastically deform when pressed against the bit spline tips, thus enabling the rotational alignment.

[0018] In some example embodiments the at least one alignment pin is made of carburized steel. Advantageously, this material is sufficiently hard, but also cheap and easy to manufacture.

[0019] In some example embodiments the at least one alignment pin has a circular geometry. Advantageously, this is easy to manufacture.

[0020] In some example embodiments the width of the at least one alignment pin is less than the width of the drive sub spline it is aligned with. Advantageously, this prevents contact between the alignment pin and the drive side of the spline during operation. Following the installation of the drill bit into the driver sub and during the drilling operation it is beneficial that there is no contact between the bit splines and the alignment pin, there should only be contact between the bit splines and the driver sub splines so that the alignment pin does not carry any torque or load during the alignment or drilling operations in order to avoid creating an unnecessary high stress point. In some example embodiments at least one of the driver sub splines extends axially further forward than the rest of the driver sub splines. Advantageously, this aids the automatization of the spline alignment and avoids the need for additional parts to be fixed to the driver sub, for example there is no need to add an alignment pin.

[0021] Another aspect of the present application relates to a method for aligning the bit splines with the driver sub splines in the assembly disclosed hereinbefore and hereinafter wherein the drill bit and driver sub are pushed together using only axial movement.

[0022] Advantageously, this provides a simplified and cheap method of spline engagement that is possible to be automated. The drill bit can be attached to the assembly using only axial movement, the rotational movement is created from the design of the splines and the torque transmitted elements will self-align.

[0023] Brief description of drawings

[0024] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0025] Figure l is a cross section of a DTH assembly.

[0026] Figure 2 is a side view of a drill bit having chamfered bit spline tips.

[0027] Figure 3 is a side view of a driver sub comprising an alignment pin.

[0028] Figure 4 is a side view of a drill bit having curved bit spline tips.

[0029] Figure 5 is a side view of a drill bit having bit spline tips with an arrowhead geometry.

[0030] Figure 6 is a side view of a drill bit having one elongated bit spline. Figure 7 is a side view of driver sub having one elongated driver sub spline.

[0031] Figure 8 is a perspective view of the drill bit being inserted into the driver sub for spline alignment.

[0032] Detailed description

[0033] Figure 1 shows a cross section of a down the hole (DTH) hammer assembly 2 comprising a substantially hollow cylindrical casing 4 having an axially rearward end 6 (attachment end) and an axially forward end 8 (cutting end). A top sub 10 is at least partially accommodated within the rearward of casing 4 whilst a drill bit 12 (cutting head) is at least partially accommodated within the forward end of the casing 4. The drill bit 12 comprises a bit shaft (shank) 14 and a drill head 16 having a plurality of wear resistant cutting buttons (inserts) 18.

[0034] A distributor cylinder 20 extends axially within casing 4 and an elongate substantially cylindrical piston 22 extends axially within cylinder 20 and casing 4, the piston 22 is capable of shuttling back and forth along a central longitudinal axis 24 extending through the assembly 2. Pressurised fluid is delivered to assembly 2 via a drill string (not shown) that is coupled to the top sub 10. Fluid passages are arranged inside the hammer assembly 2 to drive the piston’s 22 motion. Fluid is alternatively pressurized and vented into and out of the drive chambers. Exhaust of the pressurized fluid from the assembly 2 is used to remove cutting from the drilled hole.

[0035] A driver sub 26 (alternatively termed a drive chuck) is positioned surrounding the bit shaft 14. The axially forward end of the driver sub 26 is positioned towards bit head 16 and an axially rearward end of the driver sub 26 is accommodated within an axially forward region of casing 4.

[0036] Figure 2 shows a side view of the drill bit wherein a plurality of axially extending bit splines 28 (also known as ridges or teeth) project radially outwards from a radially outward facing surface of the bit shaft 14; wherein each of the bit splines 28 comprises a bit spline tip 30 at its axially rearward end having a rearward axially outer edge 48 and a central bit spline longitudinal axis 32. The central bit longitudinal axis 32 is parallel with, but not necessarily co-linear with, the assembly longitudinal axis 24. The rearward axially outer edge 48 on at least of one of bit spline tips 30 is non-perpendicular to the bit spline longitudinal axis 32 along at least 25% of the width of the bit spline tip 30, for example along at least 50% of the width of the bit spline tip, for example along at least 75% of the width of the bit spline tip, for example along at least 90% of the width of the bit spline tip. In some embodiments all the bits spline tips 30 have a rearward axially outer edge 48 that is non-perpendicular to the bit spline longitudinal axis 32. In some embodiments only some of the bits spline tips 30 have a rearward axially outer edge 48 that is non-perpendicular to the bit spline longitudinal axis 32 along at least 25% of the width of the bit spline tip 30. In other words, the width of the bit spline tips 30 varies when measured at different points along the bit spline longitudinal axis 32.

[0037] In should be understood that the bit spline tips 30 are the section of the bits splines 28 that engage with the driver sub spline tips 38, an elongated driver sub spline tip 46 or the alignment pin 36 during the alignment process during the alignment process. The bit spline tips 30 are the sections of the bit spline 28 that have a varied width when measured at different points along the bit spline longitudinal axis 32. The rearward axial outer edge 48 of the bit spline tip 30 is located at the rearward most end of the bit spline tip 30, this is the edge that will make contact with the driver sub spline tips 38, the elongated driver sub spline tip 46 or the alignment pin 36 during the alignment process. The bit splines 28 may also have a further axially outward edge that is positioned forward of the bit spline tip 30 that may be perpendicular or non-perpendicular with the bit spline longitudinal axis 32.

[0038] Figure 3 shows a driver sub 26 comprising a plurality of axially extending driver sub splines 34 projecting radially inwards from an inward facing surface of the driver sub 26.

[0039] The driver sub 26 is positioned axially rearward of the drill bit 12 and during assembly the drill bit 12 is inserted into the driver sub 26 so that the bit splines 28 and the driver sub splines 34 engage. Rotational drive to the bit head 16 is transmitted from the drill string (not shown) through casing 4 and driver sub 26 to drill bit 12. Each driver sub spline 34 has a driver sub spline tip 38 on its axially forward end. The driver sub spline tips 38 may have a geometry that is perpendicular or non-perpendicular to a driver sub spline longitudinal axis 40. The driver sub spline longitudinal axes 40 are parallel to the assembly longitudinal axis 24. The driver sub spline tips 38 are the sections of the driver sub splines 34 that engage with the bit spline tips 30 during the alignment process.

[0040] In some embodiments, as shown in figure 2, at least one of the bit spline tips 30 has a chamfered geometry. In other words, the bit spline tips 30 are inclined relative to the bit spline longitudinal axis 32. In this embodiment, the rearward axial outer edge 48 of the bit spline(s) tips 30 is / are chamfered.

[0041] Figure 4 shows that in some embodiments the at least one of the bit spline tips 30 has a curved geometry. In this embodiment, the rearward axial outer edge 48 of the bit spline tip(s) 30 is / are curved.

[0042] Figure 5 shows that in some embodiments the at least one of bit spline tips 30 has an arrowhead geometry. In this embodiment, the rearward axial outer edge 48 of at least one of the bit spline tips 30 has an arrowhead shape.

[0043] Figure 6 shows that in some embodiments at least one of the bit splines 28 extends axially further rearward than the rest of the bit splines 28. In other words, there is at least one elongated bit spline 42. There could be just one elongated bit spline 42 or multiple elongated bit splines 42, but preferably no more than half of the bit splines 28 are elongated. The elongated bit spline 42 could be combined with any of the bit spline tip geometries described hereinbefore and hereinafter. In some embodiments, the elongated bit spline(s) 42 is / are longer than the rest of the bit splines 28 by at least 0.5 x the width of the bit splines 28. For example, the elongated bit spline(s) 42 is / are longer than the rest of the bit splines by at least 1 x the width of the bit spline 28.

[0044] The bit splines 28 could be continuous as shown in figures 2, 5 and 6 or non-continuous as shown in figure 4. If the bit splines 28 are non-continuous the alignment is facilitated using the rearward portion of the bit splines 28 and the torque during the drilling operation is created with forward portion of the bit splines 28.

[0045] Figure 3 shows that in some embodiments there is an alignment pin 36 positioned on the forward end of at least one of the driver sub splines 34. In other words, the alignment pin 36 could be positioned on a driver sub spline tips 38, where the driver sub spline tips 38 are at the axially forward end of the driver sub splines 34. In some embodiments, there is an alignment pin 36 on just one of the drive sub spline tips 38. In other embodiments, there are alignment pins 36 on multiple of the drive sub spline tips 38.

[0046] In some example embodiments the at least one alignment pin 36 has a higher surface hardness than the surface hardness of the bit splines 28. In some embodiments the surface hardness of the alignment pin 36 is at least 1 HRC (Rockwell C Hardness) higher than the surface hardness of the bit splines. Rockwell hardness is measured according to the ISO 6508 standard.

[0047] In some example embodiments the alignment pin 36 is made of carburized steel. It could be made from cemented carbide or any other suitable hard material. Alternatively, the alignment pin 36 could be hardened for example, but not limited to, by quenching and tempering the steel.

[0048] In some example embodiments the alignment pin 36 has a circular geometry. Alternatively, the geometry could be elliptical, rectangular or any other suitable shape.

[0049] In some example embodiments the width of the at least one alignment pin 36 is less than the width of the driver sub spline 34 it is aligned with.

[0050] The alignment pin(s) 36 could be manufactured as part of the driver sub assembly 26 or added on afterwards. If the alignment pin 36 is added on afterwards, it is typically fixed into place by shrink fitting. Alternatively, the alignment pin 36 could be welded or glued in place, attached with a threaded connection or by using any other suitable means. Figure 7 shows that the in some example embodiments at least one of the driver sub splines 34 extends axially further forward than the rest of the driver sub splines 34. In other words, there is at least one elongated driver sub spline 44. There could be just one elongated driver sub spline 44 or multiple elongated driver sub splines 44, but preferably no more than half of the driver sub splines 34 are elongated. The elongated driver sub spline 44 has an elongated drive sub spline tip 46. The elongated drive sub spline tip 46 could have any suitable geometry, for example but not limited to chamfered, arrowhead or curved.

[0051] The elongated driver sub spline(s) 44 is / are longer than the rest of the driver sub splines 34 by at least 0.5 x the width of the driver sub splines 34. For example, the elongated driver sub spline(s) 44 is / are longer than the rest of the bit splines by at least 1 x the width of the driver sub spline 34.

[0052] Alternatively, the driver sub 26 may comprise at least one driver sub spline tip 38 having a geometry that is non-perpendicular to a driver sub spline longitudinal axis 40, for example but not limited to curved, chamfered or arrowhead. In other words, the width of the driver sub spline tips 38 varies when measured at different points along the driver sub spline longitudinal axis 40. This could be combined with positioning an alignment pin 36 on at least one of the bit spline tips 30 and / or with the drill bit having at least one elongate bit spline 42. For this alternative assembly, it would not be essential that at least one of the bit spline tips 30 to have a geometry that is non-perpendicular to the bit spline longitudinal axis 32, for example in the case when an alignment pin is used. The bit spline tip 30 could have a geometry that is perpendicular or non-perpendicular with the bit spline longitudinal axis 32.

[0053] Figure 8 shows the drill bit 12 inserted in the driver sub 26. A further aspect of the present invention relates to a method of aligning the bit splines 28 with the driver sub splines 34 in the assembly as disclosed hereinbefore or hereinafter wherein the drill bit 12 and the driver sub 26 are pushed together using only axial movement. In other words, the rotational movement is created from spline alignment features that have been added to the assembly 2 and so no rotational movement is required to be inputted. The requirement to only use axial movement makes automized bit changing possible and also makes the process cheaper and more reliable, there is no need for extra sensors and actuators to be employed. References in the description to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature or a particular combination of features (e.g., component(s), element(s), integer(s), structure(s), operation(s), and / or step(s)), but every embodiment may not necessarily include the particular feature or the particular combination of features. Such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, or a particular combination of features, is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, or combination of features, in connection with other embodiments whether or not explicitly described.

Claims

Claims1. A hammer drill assembly (2) for coupling to a drill string having an axially forward end (8); an axially rearward (6) end; and an assembly longitudinal axis (24), the assembly (2) comprising: a drill bit (12) positioned at the forward end (8) having a drill head (16) and a bit shaft (14); wherein a plurality of axially extending bit splines (28) project radially outwards from a radially outward facing surface of the bit shaft (14); wherein each of the bit splines (28) comprises a bit spline tip (30) at its axially rearward end having a rearward axially outer edge (48) and a central bit spline longitudinal axis (32); and a driver sub (26) provided axially rearward of the drill bit (12) comprising a plurality of axially extending driver sub splines (34) projecting radially inwards from an inward facing surface of the driver sub (26); characterised in that: the rearward axially outer edge (48) on at least of one of bit spline tips (30) is nonperpendicular to the bit spline longitudinal axis (32) along at least 25% of the width of the bit spline tip (30).

2. The assembly (2) according to claim 1 wherein the rearward axially outer edge (48) of at least one of the bit spline tips (30) is curved.

3. The assembly (2) according to claim 1 wherein the rearward axially outer edge (48) of at least one of the bit spline tips (30) is chamfered.

4. The assembly (2) according to claim 1 wherein the rearward axially outer edge (48) of at least one of the bit spline tips (30) has an arrowhead shape.

5. The assembly (2) according to any of the previous claims wherein at least one of the bit splines (28) extends axially further rearward than the rest of the bit splines (28).

6. The assembly (2) according to any of the previous claims wherein an alignment pin (36) is positioned on the forward end of at least one of the driver sub splines (34).

7. The assembly (2) according to claim 6 wherein the at least one alignment pin (36) has a higher surface hardness than the bit splines (28).

8. The assembly (2) according to claim 7 wherein the hardness of the alignment pin (36) has a hardness that is at least 1 HRC higher than the hardness of the bit splines (28).

9. The assembly (2) according to any of claims 6 - 8 wherein the at least one alignment pin (36) is made of carburized steel.

10. The assembly (2) according to any of claims 6 - 9 wherein the at least one alignment pin (36) has a circular geometry.

11. The assembly (2) according to any of claims 6 - 10 wherein the width of the at least one alignment pin (36) is less than the width of the drive sub spline (34) it is aligned with.

12. The assembly (2) according to any of the previous claims wherein at least one of the driver sub splines (34) extends axially further forward than the rest of the driver sub splines (34).

13. A method of aligning the bit splines (28) with the driver sub splines (34) in the assembly disclosed in any of claim 1 - 12 wherein the drill bit (12) and the driver sub (26) are pushed together using only axial movement.

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