Shank adaptor flushing hole design

Abstract

A rock drilling shank adaptor wherein comprising a flush hole extending radially through the body to the internal bore, the hole defined at an external side by an edge having an axially forwardmost region positioned closer to the second end than an axially rearwardmost region positioned closer to the first end; and side sections extending axially between the forwardmost region and the axially rearwardmost region to complete the edge (202) to form a closed loop wherein the axially forwardmost region and the axially rearwardmost region of the flush hole are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: xan+ybn=1 and the side sections (405) are curved having a curvature defined by a single radius (r).

Description

Field of invention

[0001] The present invention relates to a flushing hole design for a rock drilling shank adaptor which has been configured to minimise stress concentrations in the region of the flushing hole.Background art

[0002] Percussion drilling is a well-established technique that breaks rock by hammering impacts transferred from the rock drill bit, mounted at one end of a drill string, to the rock at the bottom of the borehole. The energy needed to break the rock is generated by a hydraulically driven piston that contacts a shank adaptor positioned at the opposite end of the drill string to the drill tool. The piston strike on the adaptor creates a stress (or shock) wave that propagates through the drill string and ultimately to the borehole rock bottom.

[0003] Shank adaptors typically comprise an internal bore to allow transfer of a flushing fluid to the region of the drill tool. The flushing fluid acts to both cool the tool and to expel drill cuttings and fines from the bore hole. Conventionally, the fluid is introduced into the shank adaptor via a flushing hole. A common problem with existing shank adaptors is the susceptibility for the adaptor wall to fracture with a crack originating and propagating from the flush hole due, in part, to the compressive and tensile stresses generated by the percussive piston and in particular the shock wave that is transmitted through the adaptor to the drill string and ultimately the drill tool. In underground applications, crack initiation is assisted by cavitation damage that exacerbates the problem. Shank adaptor failure is a particular problem for users as it often destroys the rubber seals at the fluid housing surrounding the adaptor. Time consuming replacement to repair of components is required resulting in very undesirable machine downtime. Therefore, it is desirable to reduce the likelihood of fractures occurring in the shank adaptor in response to both compressive and tensile forces imparted and transmitted through the adaptor. In known designs the point of highest stress around the flushing hole is at the transition corners located between one of side sections and the forwardmost region or between one of the side sections and the rearwardmost region of the flushing hole. The problem with the highest stress being located at the transition corners is the issues with cavitation are also worse in these sections and the combination of the high stress point and the cavitation is more likely to lead to cracking and therefore failure of the part. Therefore, the problem to solve is how to avoid high stress points at the transition corners of the flushing hole.Summary of the Invention

[0004] It is an objective of the present invention to provide a rock drilling shank adaptor comprising: an elongate body having a first end to be positioned towards a piston and a second end to be positioned towards a drill string; the body comprising an axially extending internal bore to allow passage of a flushing fluid to the drill string via the second end; a flush hole extending radially through the body to the internal bore, the hole defined at an external side by an edge having an axially forwardmost region positioned closer to the second end than an axially rearwardmost region positioned closer to the first end; and side sections extending axially between the forwardmost region and the axially rearwardmost region to complete the edge to form a closed loop; wherein the axially forwardmost region and the axially rearwardmost region of the flush hole are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: x a n + y b n = 1 and the side sections are curved having a curvature defined by a single radius (r).

[0005] Advantageously, this configuration minimises stress concentrations as the stress wave, which could be compressive or tensile, are transmitted axially through the shank adaptor wall past the flushing hole. Furthermore, this flushing hole geometry is advantageous as the highest point of stress is at the centre of the side sections rather than at the transition corners between the side section and the forwardmost region or rearwardmost region. The centre of the middle section is not as prone to cavitation issues and therefore the overall level of cracking and failure around the flushing holes is reduced. The present configuration therefore is advantageous to significantly increase the service life of the shank adaptor.

[0006] In some embodiments, n is ≥4. Advantageously, this is easier to manufacture.

[0007] In some embodiments the axially forwardmost region and the axially rearwardmost region are each defined by between a 20 to 150° segment of a superellipse. Advantageously, this range offers the optimal balance between providing a shape that is suitable for flushing and a shape that gains the benefit of the stress reduction.

[0008] In some embodiments, r is between 20-70 mm. Advantageously, this range provides the best level of stress reduction.

[0009] In some embodiments, a shape profile of the edge is elongate such that an axial length (L) of the hole is greater than a width (W) of the hole in a plane perpendicular to a longitudinal axis of the adaptor.

[0010] In some embodiments, the shape profile of the edge is symmetrical in both an axial plane and a plane perpendicular to a longitudinal axis of the adaptor. A symmetrical shape profile is advantageous for both ease of manufacture and to provide a uniform distribution of stress around the region of the hole and generally throughout the adaptor.

[0011] In some embodiments, the shape profile of the edge is maintained in the radial direction through the elongate body from the external side to the internal bore. The stress characteristic at the region of the hole is therefore intended to be uniform in a radial direction through the adaptor wall and in particular both the external and internal surfaces of the elongate body around the region of the hole.

[0012] Another aspect of the present application relates to a rock drilling apparatus comprising a shank adaptor as described hereinbefore or hereinafter.

[0013] In some embodiments the apparatus further comprising: an elongate piston having a main length and an energy transmission end to contact the first end of the adaptor; and a drill string formed from a plurality of coupled elongate drill rods, wherein a rearwardmost drill rod of the string is coupled to the second end of the adaptor.Brief description of drawings

[0014] 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: Figure 1 illustrates an external view of a shank adaptor forming part of rock drilling apparatus comprising an elongate drill string and a hydraulically driven reciprocating piston according to a specific implementation of the present invention. Figure 2 illustrates a cross sectional side view through the adaptor of figure 1. Figure 3 illustrates a magnified cross-sectional view of the flush bore within the adaptor of figure 2. Figure 4 illustrates a magnified external view of the flush hole formed in the adaptor of figure 1 according to a specific implementation of the present invention. Figure 5 illustrates a magnified external view of the flush hole formed in the adaptor showing the super elliptical shape profile. Figure 6 is a stress simulation of a standard flushing hole design. Figure 7 is a stress simulation of the inventive flushing hole design disclosed in the present application. Detailed description

[0015] Figure 1 shows rock drilling shank adaptor 100 comprising a main body (or length section) 101 having a forward end 103 and a rearward end 104 relative to a longitudinal axis 109. A plurality of axially parallel elongate splines 106 project radially outward from an external surface 102 at a rearward region of elongate main body 101 towards rearward end 104. The splines 106 are configured to be engaged by corresponding splines of a rotational motor (not shown) to induce rotation of adaptor 100 about axis 109 during drilling operations. The adaptor 100 further comprises a flushing hole 105 (also known as a flushing bore or a flushing slot) positioned axially between ends 103, 104 and extending radially through the adaptor main body 101 from external surface 102 to an internal cavity or region extending axially within the adaptor 100.

[0016] The adaptor 100 is configured for coupling to an elongate drill string and to allow transmission of a stress wave to a drill tool (not shown) located at the deepest region of the drill hole to impart the percussion drilling action. In particular, the forward end 103 of the adaptor 100 may be coupled to a rearward end of a rearwardmost elongate drill rod 107 forming a part of the drill string. The rearwardmost adaptor end 104 is configured to be contacted by a hydraulically driven piston 108 that creates the stress wave within adaptor 100 and the drill string.

[0017] Figures 2 and 3 show that the adaptor 100 comprises an internal elongate bore 200 extending axially from the region of the flushing hole 105 to forwardmost end 103. In particular, the bore 200 comprises a rearwardmost end 206 and an open forwardmost end 207 positioned in fluid communication with the internal bore (not shown) extending through each drill rod 107.

[0018] The flushing hole 105 is defined by an external edge 202 having a closed loop. The hole 105 extends radially through an adaptor wall 203 from the external surface 102 to an internal surface 201 that defines an internal bore 200. Accordingly, the flushing hole 105 is further defined by an innermost or internal edge 205 having an identical shape profile to the external edge 202, with edges 202, 205 coupled by a radially extending surface 204, that defines the radial wall of bore hole 105. The surface 204 is substantially straight and non-curved in a plane perpendicular to axis 109 such that a shape profile of hole 105 is uniform in a radial direction from the external edge 202 to the internal edge 205. In use, fluid is introduced into the adaptor 100 via the flushing hole 105. The fluid is then forced through bore 200 and into the rearwardmost drill rod 107 to provide the flushing of cuttings from the region around the drill tool (not shown) and cooling of both the drill rods 107 and cutting tool (as the adaptor 100 and rods 107 are rotated about axis 109 during cutting operations).

[0019] Figure 4 shows the flushing hole 105 comprises a generally elongate shape profile in which an axial length (L) that is greater than a width (W) in a plane 406 perpendicular to axis 109. The hole 105 may be regarded as comprising an axially forward region 400 positioned closer to adaptor forward end 103 relative to an axially rearward region 410 positioned closer to adaptor rearward end 104 and side sections 405 extending axially between the forwardmost region 400 and the axially rearwardmost region 410 to complete the edge 202 to form a closed loop. The axially forwardmost region 400 and the axially rearwardmost region 410 of the flush hole 105 are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: x a n + y b n = 1 "x" represents the horizontal co-ordinate point on the ellipse. "y" represents the vertical co-ordinate point on the ellipse. "a" represents the semi-major axis, i.e., half the length of the major axis, where the major axis is the longest diameter of the ellipse passing through the centre. "b" represents the semi-minor axis, i.e., half the length of the minor axis, where the minor axis is the shortest diameter of the ellipse passing through the centre. The minor axis is perpendicular to the major axis. "n" is the exponential factor.

[0020] There is a transition corner 412 between each end of the forwardmost region 400 and each of the end sections 405 and a transition corner 412 between each rearwardmost region 410 and each of the end sections 405.

[0021] In some embodiments, the major axis (a) of the ellipse extends in a substantially longitudinal direction. In some embodiments the major axis (a) is parallel with the longitudinal axis. In some embodiments the major axis is longer than minor axis. In some embodiments a and b are the same. In other embodiments a and b are different. In some embodiments a and b are preferably between 1-20 mm, for example between 2 - 6 mm, for example between 3 - 5 mm.

[0022] In some embodiments n is ≥4. In some example embodiments, n = 4.

[0023] An axial length of side sections 405 is greater than the corresponding length of axially forwardmost region 400 and the axially rearwardmost region 410, such that hole 105 comprises a generally elongate configuration aligned axially with the main length of the adaptor 100. Accordingly, the wall surface 204 in a radial direction from external edge 202 to internal edge 205 at each side section 405 is substantially planar.

[0024] The superelliptical curvature of the axially forwardmost region 400 and the axially rearwardmost region 410 means that the shape profile in these regions is defined by a plurality of different radii of curvature.

[0025] Figure 5 shows in some embodiments the axially forwardmost region 400 and the axially rearwardmost region 410 are each defined by between a 20- 150° segment of a superellipse, this illustrated on figure 5 as angle γ. The section of the superellipse (γ) is measured between the transition corners 412. In other words, the section of the superellipse (γ) is taken in equal amounts in both direction from the major axis (a). For example, if a 140° segment of the super ellipse is selected then this means the segment extends from +70° to -70° from the major axis (a). In some example embodiments, the axially forwardmost region 400 and axially rearwardmost region 410 are each defined by between 110 - 150° segment of a superellipse. In some example embodiments, the axially forwardmost region 400 and the axially rearwardmost region 410 are each defined by between 130 - 150° segment of a superellipse.

[0026] Figure 4 additionally shows that the side sections 405 are curved having a curvature defined by a single radius (r). In some example embodiments r is between 20-70 mm. For example, r is between 30 - 40 mm. The exact dimensions of the flushing hole will be dependent on and be adaptor to suit the size of the shank adaptor.

[0027] In some embodiments a shape profile of the edge 202 is elongate such that an axial length (L) of the hole 105 is greater than a width (W) of the hole 105 in a plane 406 perpendicular to a longitudinal axis 109 of the adaptor 100.

[0028] In some example embodiments a shape profile of the edge 202 is symmetrical in both an axial plane and a plane perpendicular to a longitudinal axis 109 of the adaptor 100.

[0029] In some example embodiments a shape profile of the edge 202 is maintained in the radial direction through the elongate body 101 from the external side 102 to the internal bore 200.

[0030] The present application further relates to a rock drilling apparatus comprising a shank adaptor 100 as described hereinbefore or hereinafter. In some embodiments the apparatus further comprises: an elongate piston 108 having a main length and an energy transmission end to contact the first end 104 of the adaptor 100; and a drill string formed from a plurality of coupled elongate drill rods 107, wherein a rearwardmost drill rod 107 of the string is coupled to the second end 103 of the adaptor 100.Examples

[0031] The finite element software LS-Dyna was used to model the stress around the flushing hole having the inventive shape disclosed in the present application compared to a standard flushing hole having a rectangular shape with single a radii curve at each of the corners. The simulations were done using a load of 200 MPa under both compression and tension. The results are shown in table 1 below: Table 1: Stress simulation resultsFlushing hole designCompressionTensionMaximum stress (MPa)Stress concentration factorMaximum stress (MPa)Stress concentration factorStandard (Comparative)3171.66533.3Inventive flushing hole design2891.45452.7

[0032] The results shown in table 1 show that there is a 9% reduction in stress under compression and a 17% reduction in stress under tension with the inventive flushing hole design compared to the standard flushing hole design. This level of stress reduction is significant as the shank adaptor 100 is subject to high cycle fatigue, due to the rapid reciprocating impact motion of piston 108. An adaptor comprising a flush hole 105 of the present invention therefore provides an enhancement in the operational lifetime of the device. The reduction in the level of stress under tension as well as under compression is also significant as this will result in reduced crack growth.

[0033] Figures 6 and 7 show simulated stress distribution images of the standard and inventive flushing hole designs respectively, higher stress is represented by a darker colour. It can be seen that the points of highest stress (darkest areas) are at the transition corners for the standard design and in the centre of the side sections for the inventive design. It is advantageous that the highest stress points are along the side section rather than at the transition corners for reducing cracking and premature failure.

Examples

examples

Examples

[0031]The finite element software LS-Dyna was used to model the stress around the flushing hole having the inventive shape disclosed in the present application compared to a standard flushing hole having a rectangular shape with single a radii curve at each of the corners. The simulations were done using a load of 200 MPa under both compression and tension. The results are shown in table 1 below:

Table 1: Stress simulation results

Flushing hole designCompressionTension

Maximum stress (MPa)Stress concentration factorMaximum stress (MPa)Stress concentration factor

Standard (Comparative)3171.66533.3

Inventive flushing hole design2891.45452.7

[0032]The results shown in table 1 show that there is a 9% reduction in stress under compression and a 17% reduction in stress under tension with the inventive flushing hole design compared to the standard flushing hole design. This level of stress reduction is significant as the shank adaptor 100 is subject to high cycle fatigue, due to...

Field of invention

[0001] The present invention relates to a flushing hole design for a rock drilling shank adaptor which has been configured to minimise stress concentrations in the region of the flushing hole.Background art

[0002] Percussion drilling is a well-established technique that breaks rock by hammering impacts transferred from the rock drill bit, mounted at one end of a drill string, to the rock at the bottom of the borehole. The energy needed to break the rock is generated by a hydraulically driven piston that contacts a shank adaptor positioned at the opposite end of the drill string to the drill tool. The piston strike on the adaptor creates a stress (or shock) wave that propagates through the drill string and ultimately to the borehole rock bottom.

[0003] Shank adaptors typically comprise an internal bore to allow transfer of a flushing fluid to the region of the drill tool. The flushing fluid acts to both cool the tool and to expel drill cuttings and fines from the bore hole. Conventionally, the fluid is introduced into the shank adaptor via a flushing hole. A common problem with existing shank adaptors is the susceptibility for the adaptor wall to fracture with a crack originating and propagating from the flush hole due, in part, to the compressive and tensile stresses generated by the percussive piston and in particular the shock wave that is transmitted through the adaptor to the drill string and ultimately the drill tool. In underground applications, crack initiation is assisted by cavitation damage that exacerbates the problem. Shank adaptor failure is a particular problem for users as it often destroys the rubber seals at the fluid housing surrounding the adaptor. Time consuming replacement to repair of components is required resulting in very undesirable machine downtime. Therefore, it is desirable to reduce the likelihood of fractures occurring in the shank adaptor in response to both compressive and tensile forces imparted and transmitted through the adaptor. In known designs the point of highest stress around the flushing hole is at the transition corners located between one of side sections and the forwardmost region or between one of the side sections and the rearwardmost region of the flushing hole. The problem with the highest stress being located at the transition corners is the issues with cavitation are also worse in these sections and the combination of the high stress point and the cavitation is more likely to lead to cracking and therefore failure of the part. Therefore, the problem to solve is how to avoid high stress points at the transition corners of the flushing hole.Summary of the Invention

[0004] It is an objective of the present invention to provide a rock drilling shank adaptor comprising: an elongate body having a first end to be positioned towards a piston and a second end to be positioned towards a drill string; the body comprising an axially extending internal bore to allow passage of a flushing fluid to the drill string via the second end; a flush hole extending radially through the body to the internal bore, the hole defined at an external side by an edge having an axially forwardmost region positioned closer to the second end than an axially rearwardmost region positioned closer to the first end; and side sections extending axially between the forwardmost region and the axially rearwardmost region to complete the edge to form a closed loop; wherein the axially forwardmost region and the axially rearwardmost region of the flush hole are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: x a n + y b n = 1 and the side sections are curved having a curvature defined by a single radius (r).

[0005] Advantageously, this configuration minimises stress concentrations as the stress wave, which could be compressive or tensile, are transmitted axially through the shank adaptor wall past the flushing hole. Furthermore, this flushing hole geometry is advantageous as the highest point of stress is at the centre of the side sections rather than at the transition corners between the side section and the forwardmost region or rearwardmost region. The centre of the middle section is not as prone to cavitation issues and therefore the overall level of cracking and failure around the flushing holes is reduced. The present configuration therefore is advantageous to significantly increase the service life of the shank adaptor.

[0006] In some embodiments, n is ≥4. Advantageously, this is easier to manufacture.

[0007] In some embodiments the axially forwardmost region and the axially rearwardmost region are each defined by between a 20 to 150° segment of a superellipse. Advantageously, this range offers the optimal balance between providing a shape that is suitable for flushing and a shape that gains the benefit of the stress reduction.

[0008] In some embodiments, r is between 20-70 mm. Advantageously, this range provides the best level of stress reduction.

[0009] In some embodiments, a shape profile of the edge is elongate such that an axial length (L) of the hole is greater than a width (W) of the hole in a plane perpendicular to a longitudinal axis of the adaptor.

[0010] In some embodiments, the shape profile of the edge is symmetrical in both an axial plane and a plane perpendicular to a longitudinal axis of the adaptor. A symmetrical shape profile is advantageous for both ease of manufacture and to provide a uniform distribution of stress around the region of the hole and generally throughout the adaptor.

[0011] In some embodiments, the shape profile of the edge is maintained in the radial direction through the elongate body from the external side to the internal bore. The stress characteristic at the region of the hole is therefore intended to be uniform in a radial direction through the adaptor wall and in particular both the external and internal surfaces of the elongate body around the region of the hole.

[0012] Another aspect of the present application relates to a rock drilling apparatus comprising a shank adaptor as described hereinbefore or hereinafter.

[0013] In some embodiments the apparatus further comprising: an elongate piston having a main length and an energy transmission end to contact the first end of the adaptor; and a drill string formed from a plurality of coupled elongate drill rods, wherein a rearwardmost drill rod of the string is coupled to the second end of the adaptor.Brief description of drawings

[0014] 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: Figure 1 illustrates an external view of a shank adaptor forming part of rock drilling apparatus comprising an elongate drill string and a hydraulically driven reciprocating piston according to a specific implementation of the present invention. Figure 2 illustrates a cross sectional side view through the adaptor of figure 1. Figure 3 illustrates a magnified cross-sectional view of the flush bore within the adaptor of figure 2. Figure 4 illustrates a magnified external view of the flush hole formed in the adaptor of figure 1 according to a specific implementation of the present invention. Figure 5 illustrates a magnified external view of the flush hole formed in the adaptor showing the super elliptical shape profile. Figure 6 is a stress simulation of a standard flushing hole design. Figure 7 is a stress simulation of the inventive flushing hole design disclosed in the present application. Detailed description

[0015] Figure 1 shows rock drilling shank adaptor 100 comprising a main body (or length section) 101 having a forward end 103 and a rearward end 104 relative to a longitudinal axis 109. A plurality of axially parallel elongate splines 106 project radially outward from an external surface 102 at a rearward region of elongate main body 101 towards rearward end 104. The splines 106 are configured to be engaged by corresponding splines of a rotational motor (not shown) to induce rotation of adaptor 100 about axis 109 during drilling operations. The adaptor 100 further comprises a flushing hole 105 (also known as a flushing bore or a flushing slot) positioned axially between ends 103, 104 and extending radially through the adaptor main body 101 from external surface 102 to an internal cavity or region extending axially within the adaptor 100.

[0016] The adaptor 100 is configured for coupling to an elongate drill string and to allow transmission of a stress wave to a drill tool (not shown) located at the deepest region of the drill hole to impart the percussion drilling action. In particular, the forward end 103 of the adaptor 100 may be coupled to a rearward end of a rearwardmost elongate drill rod 107 forming a part of the drill string. The rearwardmost adaptor end 104 is configured to be contacted by a hydraulically driven piston 108 that creates the stress wave within adaptor 100 and the drill string.

[0017] Figures 2 and 3 show that the adaptor 100 comprises an internal elongate bore 200 extending axially from the region of the flushing hole 105 to forwardmost end 103. In particular, the bore 200 comprises a rearwardmost end 206 and an open forwardmost end 207 positioned in fluid communication with the internal bore (not shown) extending through each drill rod 107.

[0018] The flushing hole 105 is defined by an external edge 202 having a closed loop. The hole 105 extends radially through an adaptor wall 203 from the external surface 102 to an internal surface 201 that defines an internal bore 200. Accordingly, the flushing hole 105 is further defined by an innermost or internal edge 205 having an identical shape profile to the external edge 202, with edges 202, 205 coupled by a radially extending surface 204, that defines the radial wall of bore hole 105. The surface 204 is substantially straight and non-curved in a plane perpendicular to axis 109 such that a shape profile of hole 105 is uniform in a radial direction from the external edge 202 to the internal edge 205. In use, fluid is introduced into the adaptor 100 via the flushing hole 105. The fluid is then forced through bore 200 and into the rearwardmost drill rod 107 to provide the flushing of cuttings from the region around the drill tool (not shown) and cooling of both the drill rods 107 and cutting tool (as the adaptor 100 and rods 107 are rotated about axis 109 during cutting operations).

[0019] Figure 4 shows the flushing hole 105 comprises a generally elongate shape profile in which an axial length (L) that is greater than a width (W) in a plane 406 perpendicular to axis 109. The hole 105 may be regarded as comprising an axially forward region 400 positioned closer to adaptor forward end 103 relative to an axially rearward region 410 positioned closer to adaptor rearward end 104 and side sections 405 extending axially between the forwardmost region 400 and the axially rearwardmost region 410 to complete the edge 202 to form a closed loop. The axially forwardmost region 400 and the axially rearwardmost region 410 of the flush hole 105 are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: x a n + y b n = 1 "x" represents the horizontal co-ordinate point on the ellipse. "y" represents the vertical co-ordinate point on the ellipse. "a" represents the semi-major axis, i.e., half the length of the major axis, where the major axis is the longest diameter of the ellipse passing through the centre. "b" represents the semi-minor axis, i.e., half the length of the minor axis, where the minor axis is the shortest diameter of the ellipse passing through the centre. The minor axis is perpendicular to the major axis. "n" is the exponential factor.

[0020] There is a transition corner 412 between each end of the forwardmost region 400 and each of the end sections 405 and a transition corner 412 between each rearwardmost region 410 and each of the end sections 405.

[0021] In some embodiments, the major axis (a) of the ellipse extends in a substantially longitudinal direction. In some embodiments the major axis (a) is parallel with the longitudinal axis. In some embodiments the major axis is longer than minor axis. In some embodiments a and b are the same. In other embodiments a and b are different. In some embodiments a and b are preferably between 1-20 mm, for example between 2 - 6 mm, for example between 3 - 5 mm.

[0022] In some embodiments n is ≥4. In some example embodiments, n = 4.

[0023] An axial length of side sections 405 is greater than the corresponding length of axially forwardmost region 400 and the axially rearwardmost region 410, such that hole 105 comprises a generally elongate configuration aligned axially with the main length of the adaptor 100. Accordingly, the wall surface 204 in a radial direction from external edge 202 to internal edge 205 at each side section 405 is substantially planar.

[0024] The superelliptical curvature of the axially forwardmost region 400 and the axially rearwardmost region 410 means that the shape profile in these regions is defined by a plurality of different radii of curvature.

[0025] Figure 5 shows in some embodiments the axially forwardmost region 400 and the axially rearwardmost region 410 are each defined by between a 20- 150° segment of a superellipse, this illustrated on figure 5 as angle γ. The section of the superellipse (γ) is measured between the transition corners 412. In other words, the section of the superellipse (γ) is taken in equal amounts in both direction from the major axis (a). For example, if a 140° segment of the super ellipse is selected then this means the segment extends from +70° to -70° from the major axis (a). In some example embodiments, the axially forwardmost region 400 and axially rearwardmost region 410 are each defined by between 110 - 150° segment of a superellipse. In some example embodiments, the axially forwardmost region 400 and the axially rearwardmost region 410 are each defined by between 130 - 150° segment of a superellipse.

[0026] Figure 4 additionally shows that the side sections 405 are curved having a curvature defined by a single radius (r). In some example embodiments r is between 20-70 mm. For example, r is between 30 - 40 mm. The exact dimensions of the flushing hole will be dependent on and be adaptor to suit the size of the shank adaptor.

[0027] In some embodiments a shape profile of the edge 202 is elongate such that an axial length (L) of the hole 105 is greater than a width (W) of the hole 105 in a plane 406 perpendicular to a longitudinal axis 109 of the adaptor 100.

[0028] In some example embodiments a shape profile of the edge 202 is symmetrical in both an axial plane and a plane perpendicular to a longitudinal axis 109 of the adaptor 100.

[0029] In some example embodiments a shape profile of the edge 202 is maintained in the radial direction through the elongate body 101 from the external side 102 to the internal bore 200.

[0030] The present application further relates to a rock drilling apparatus comprising a shank adaptor 100 as described hereinbefore or hereinafter. In some embodiments the apparatus further comprises: an elongate piston 108 having a main length and an energy transmission end to contact the first end 104 of the adaptor 100; and a drill string formed from a plurality of coupled elongate drill rods 107, wherein a rearwardmost drill rod 107 of the string is coupled to the second end 103 of the adaptor 100.Examples

[0031] The finite element software LS-Dyna was used to model the stress around the flushing hole having the inventive shape disclosed in the present application compared to a standard flushing hole having a rectangular shape with single a radii curve at each of the corners. The simulations were done using a load of 200 MPa under both compression and tension. The results are shown in table 1 below: Table 1: Stress simulation resultsFlushing hole designCompressionTensionMaximum stress (MPa)Stress concentration factorMaximum stress (MPa)Stress concentration factorStandard (Comparative)3171.66533.3Inventive flushing hole design2891.45452.7

[0032] The results shown in table 1 show that there is a 9% reduction in stress under compression and a 17% reduction in stress under tension with the inventive flushing hole design compared to the standard flushing hole design. This level of stress reduction is significant as the shank adaptor 100 is subject to high cycle fatigue, due to the rapid reciprocating impact motion of piston 108. An adaptor comprising a flush hole 105 of the present invention therefore provides an enhancement in the operational lifetime of the device. The reduction in the level of stress under tension as well as under compression is also significant as this will result in reduced crack growth.

[0033] Figures 6 and 7 show simulated stress distribution images of the standard and inventive flushing hole designs respectively, higher stress is represented by a darker colour. It can be seen that the points of highest stress (darkest areas) are at the transition corners for the standard design and in the centre of the side sections for the inventive design. It is advantageous that the highest stress points are along the side section rather than at the transition corners for reducing cracking and premature failure.

Examples

examples

Examples

[0031]The finite element software LS-Dyna was used to model the stress around the flushing hole having the inventive shape disclosed in the present application compared to a standard flushing hole having a rectangular shape with single a radii curve at each of the corners. The simulations were done using a load of 200 MPa under both compression and tension. The results are shown in table 1 below:

Table 1: Stress simulation results

Flushing hole designCompressionTension

Maximum stress (MPa)Stress concentration factorMaximum stress (MPa)Stress concentration factor

Standard (Comparative)3171.66533.3

Inventive flushing hole design2891.45452.7

[0032]The results shown in table 1 show that there is a 9% reduction in stress under compression and a 17% reduction in stress under tension with the inventive flushing hole design compared to the standard flushing hole design. This level of stress reduction is significant as the shank adaptor 100 is subject to high cycle fatigue, due to...

Claims

1. A rock drilling shank adaptor (100) comprising: an elongate body (101) having a first end (104) to be positioned towards a piston and a second end (103) to be positioned towards a drill string; the body (101) comprising an axially extending internal bore (200) to allow passage of a flushing fluid to the drill string via the second end (103); a flush hole (105) extending radially through the body (101) to the internal bore (200), the hole (105) defined at an external side (102) by an edge (202) having an axially forwardmost region (400) positioned closer to the second end (103) than an axially rearwardmost region (410) positioned closer to the first end (104); and side sections (405) extending axially between the forwardmost region (400) and the axially rearwardmost region (410) to complete the edge (202) to form a closed loop; characterized in that: the axially forwardmost region (400) and the axially rearwardmost region (410) of the flush hole (105) are curved having a curvature defined by a segment of a superellipse having a semi-major axis (a); a semi-minor axis (b) and an exponential factor (n) according to the equation: x a n + y b n = 1 and the side sections (405) are curved having a curvature defined by a single radius (r).

2. The shank adaptor (100) according to claim 1 wherein n is ≥4.

3. The shank adaptor (100) according to claim 1 or claim 2 wherein the axially forwardmost region (400) and the axially rearwardmost region (410) are each defined by between 20- 150° of a segment of superellipse.

4. The shank adaptor (100) according to any of the previous claims wherein the r is between 20-70 mm.

5. The shank adaptor (100) according to any of the previous claims wherein a shape profile of the edge (202) is elongate such that an axial length (L) of the hole (105) is greater than a width (W) of the hole (105) in a plane (406) perpendicular to a longitudinal axis (109) of the adaptor (100).

6. The shank adaptor (100) according to any of the previous claims wherein a shape profile of the edge (202) is symmetrical in both an axial plane and a plane perpendicular to a longitudinal axis (109) of the adaptor (100).

7. The shank adaptor (100) according to any of the previous claims wherein a shape profile of the edge (202) is maintained in the radial direction through the elongate body (101) from the external side (102) to the internal bore (200).

8. A rock drilling apparatus comprising a shank adaptor (100) as claimed in any preceding claims.

9. The apparatus as claimed in claim 8 further comprising: an elongate piston (108) having a main length and an energy transmission end to contact the first end (104) of the adaptor (100); and a drill string formed from a plurality of coupled elongate drill rods (107), wherein a rearwardmost drill rod (107) of the string is coupled to the second end (103) of the adaptor (100).

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