Shoulder protection for elongate drill component

Abstract

A drill rod 12 for percussive drilling comprising: a hollow elongate main length section 14, defining a longitudinal axis 5 of the drill rod 12, extending axially between a leading male end 16, for connecting the drill rod 12 to a drill bit 2, and a trailing female end 18, a through-going flushing channel 7, the female end 18 comprising a female thread, the male end 16 comprising a male thread 17 and a radially projecting shoulder 20 between the male thread 17 and the main length section 14, the main length section 14 having a circular cross-section perpendicular to the longitudinal axis of the drill rod 12, the shoulder 20 comprising a peripheral surface having a greater outer diameter than the outer diameter of the main length section, and wherein a crushing element 30,40, 50 is positioned adjacent a trailing end of the shoulder 17 and in that a radially peripheral surface of the crushing element 30, 40, 50 has a non-constant distance to the longitudinal axis 5 of the drill rod 12 around the circumference of the radially peripheral surface of the crushing element 30, 40, 50.

Description

TECHNICAL FIELD

[0001] The present invention relates to percussive drilling, and, in particular, to a drill rod for use in such drilling.BACKGROUND

[0002] Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, drill strings are typically used in which a plurality of drill rods are interconnected to advance the drill bit and increase the depth of the hole. In 'top hammer drilling' a terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes.

[0003] Drill rods used for this application usually have a male threaded end and a female threaded end and are commonly called MF-rods. The drill rods can also have a shoulder formed as a radially flared extension of the main length section of the drill close to the male threaded end. The shoulder provides increased efficiency in energy transfer between the drill rod and the drill bit. The shoulder on the first drill string rod that joins to the drill bit is exposed to high levels of wear as the hole collapses and rock cuttings gather behind the drill bit. The problem with this is that as the shoulder wears the strength of the coupling will weaken and the contact area between drill rod and drill bit will decreases which leads to a decreased transfer of energy between drill rod and drill bit. Most of these cuttings will be transported away by flushing that is transported with pressure through a hollow passage in the drill rod and then through the drill bit. The high pressure of the flushing will then transport cuttings away from the borehole but there is still a problem with wear on the shoulder as the cuttings will pass and contact the shoulder on their route away from the borehole.

[0004] WO202169657 discloses a drilling assembly for percussion drilling where the shoulder is encased in both radial and axial direction inside the mounting sleeve of the drill bit. WO2020234259 discloses a drill string rod with a shoulder that is protected by a hard layer.

[0005] In some types of rock, the cuttings formed during drilling will be too big to be transported away from the borehole by the flushing. If this is the case large pieces of rock will be collected, due to gravity, on the side of the shoulder that is away from the drill bit. In these cases, extensive wear on the shoulder may be the result.

[0006] Therefore, there is a need for improvements in drill rods such that the large pieces of rock can be removed from the borehole and thus decrease the wear on the shoulder.

[0007] It is therefore an object of the present invention to present an improved drill rod suitable for removing large rock pieces from the borehole, thus leading to decreased wear of the shoulder of the drill rod.SUMMARY

[0008] According to the present invention, the above mentioned object is achieved by means of a drill rod having the features defined in claim 1.

[0009] The drill rod for percussive drilling according to the present invention comprises: a hollow elongate main length section, defining a longitudinal axis of the drill rod, extending axially between a leading male end, for connecting the drill rod to a drill bit, and a trailing female end. A through-going flushing channel. The female end comprises a female thread and the male end comprises a male thread and a radially projecting shoulder between the male thread and the main length section. The main length section has a circular cross-section perpendicular to the longitudinal axis of the drill rod. The shoulder comprises a peripheral surface with a greater outer diameter than the outer diameter of the main length section. A crushing element is positioned adjacent a trailing end of the shoulder and a cross-section and a radially peripheral surface of the crushing element has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.

[0010] When drilling a hole using a percussive drill component a flushing channel that passes through the drill rod and exits at the front of the drill bit is used for directing a flushing agent such as air, or a fluid such as water, to the bottom of the drilled hole. The flushing agent will arrive at the bottom of the hole at a high pressure to flush the cuttings, produced during the drilling operation, to the exit of the drilled hole. The cuttings will pass between the wall of the drilled hole and the outside surface of the drill rods on its way to the exit of the drilled hole. Some cuttings, however, are too large to be effectively flushed out of the hole. Due to gravity, these large cuttings will accumulate at the trailing side of the shoulder of the drill rod that is attached to the drill bit. This accumulation of large cuttings will lead to wear on the shoulder. Heavy wear on the shoulder will decrease the efficiency of transmitting percussive energy from the drill rod, through the shoulder, to the drill bit. The drilling will thus be less effective.

[0011] The present inventors have realized that having a crushing element at the trailing end of the shoulder solves this problem. The crushing element has a radially peripheral surface that has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.

[0012] The crushing element radially extends the main length section in the area closest to the trailing end of the shoulder. Its radially peripheral surface has a non-constant distance to the longitudinal axis of the drill due to it being made of at least one protrusion or protuberance that extends in a certain direction(s) away from the longitudinal axis of the drill rod. There may be more than one protrusion or protuberance, for example 2, 3 or 4, that extends in different radial directions away from the longitudinal axis of the drill rod.

[0013] The crushing element, due to it extending away from the longitudinal axis of the drill rod, on at least one position, will impact and squeeze the large cuttings against the wall of the drilled hole. The large cuttings will then break into finer cuttings which can be flushed away from the drilled hole.

[0014] If there are too many protrusions or protuberances the distance between them will be too small for large cuttings to fit between them and the impact that they receive from the crushing element will be too small to efficiently break the large cuttings into finer cuttings.

[0015] A small transition surface may be positioned in the transition between the shoulder and the crushing element. The transition surface simplifies manufacturing of the crushing element and additionally decreases the stresses in the area between the shoulder and the crushing element. The transition surface is not part of the crushing element.

[0016] The main length section of the drill rod has a circular cross-section with a radius Rm. The crushing element can be seen as the leading end part of the main length section where there is a protrusion or protuberance extending in a radial direction. The entire peripheral surface of the crushing element preferably extends further from the longitudinal axis of the drill rod than the radius Rm of the main length section.

[0017] Throughout this application the wording leading end refers to the end of the drill rod where the drill bit is attached. The leading end thus refers to the end closest to the bottom of the drilled hole. The trailing end refers to the end furthest away from the bottom of the drilled hole.

[0018] According to one embodiment, the outer surface of the cross-section of the crushing element is smooth around the whole circumference of the outer surface of the cross-section.

[0019] Smooth in this context means that there are no sudden changes in the crushing elements peripheral surface's distance to the longitudinal axis around the circumference of the radially peripheral surface of the crushing element.

[0020] This configuration ensures that large cuttings are not just pushed in front of the crushing element but will instead get squeezed between the crushing element and the wall of the drilled hole.

[0021] Preferably, the peripheral surface of the crushing element is convex around its circumference. This ensures that there are no indents in the crushing element where cuttings may get stuck.

[0022] According to an embodiment, the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is smaller than a radius Rs of the shoulder.

[0023] This configuration ensures that the shoulder will act as a barrier for cuttings to stop cuttings from travelling back down the hole to the drill bit.

[0024] The peripheral surface of the crushing element preferably has a minimum distance to the longitudinal axis that is approximately equal to the radius Rm of the main length section.

[0025] According to an embodiment, a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod to the radius Rs of the shoulder is between 0,5-1,0. More preferably the ratio is between 0,7-0,95 and most preferably between 0,75-0,9.

[0026] This configuration ensures that cuttings will be effectively squeezed and crushed between the crushing element and the wall of the borehole. This configuration further ensures that a large range of different sized cuttings will be crushed.

[0027] According to an embodiment, the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is larger than a radius Rm of the main length section.

[0028] According to an embodiment, a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod and the radius Rm of the main length section is between 1,2-2,0. The ratio is more preferably between 1,25-1,6 and most preferably between 1,3-1,4.

[0029] This configuration ensures that a large range of different sized cuttings will be crushed.

[0030] According to an embodiment, the crushing element has an axial extension that is between 5-100 mm. The axial extension is more preferably between 10-40 mm.

[0031] The drill rod is usually manufactured by friction welding a majority of the main length section to a male end and to a female end. The male end and the female end will however comprise a small part of the main length section. This manufacturing method simplifies the manufacturing of the drill rod compared to if the drill rod was manufactured in one piece.

[0032] Due to the friction welding of the male end to the main length section the crushing element should not have an axial extension from the shoulder that is too long since a certain free distance is needed to clamp the male end during the friction welding operation. Usually a free distance of 50-90 mm is needed.

[0033] The axial extension of the crushing element must additionally have a certain minimum length to effectively crush cuttings.

[0034] According to an embodiment, the crushing element is anti-symmetric with a central axis that is offset from the longitudinal axis of the drill rod.

[0035] This is an efficient solution that preferably uses a crushing element having a single protrusion or protuberance that extends in one radial direction away from the longitudinal axis of the drill rod.

[0036] According to an embodiment, the crushing element is symmetric around the longitudinal axis of the drill rod.

[0037] This is an alternative solution where the crushing element has 2, 3 or 4 protrusions or protuberances that are symmetrically positioned around the longitudinal axis of the drill rod.

[0038] According to an embodiment, the crushing element generally has a cylindrical peripheral surface and in that the central axis of the crushing element is offset from the longitudinal axis of the drill rod.

[0039] This configuration ensures that the cuttings will be effectively crushed due to the peripheral surface of the offset cylinder having a distance from the longitudinal axis of the drill bit that progressively increases. Having a crushing element that is cylindrical in shape is also simple to manufacture.

[0040] According to an embodiment, the crushing element has a peripheral surface that is generally elliptical in shape.

[0041] This configuration ensures the cuttings will be effectively crushed due to the peripheral surface of the offset cylinder having a distance from the longitudinal axis of the drill bit that progressively increases. A crushing element having a peripheral surface that is generally elliptical in shape has the advantage that it can have its central axis coinciding with the longitudinal axis of the drill rod and then the elliptical surface will extend in two radial directions, thus forming a crushing element with two symmetrically positioned protrusions or protuberances.

[0042] According to an embodiment, the crushing element has a peripheral surface that slopes towards the longitudinal axis of the drill rod in a direction towards the trailing end of the drill rod.

[0043] With this configuration the cuttings will be squeezed both in a radial and in an axial direction.

[0044] The slope can be any shape that slopes towards the longitudinal axis of the drill bit, for example a straight line, a concave or a convex shape.

[0045] If the slope is a straight line and the cross-section of the radially peripheral surface of the crushing element is circular, then the crushing element will have the form of a truncated cone.

[0046] According to an embodiment, the crushing element is integral with the main length section.

[0047] This configuration increases the strength of the drill rod and especially the strength of the crushing element.

[0048] The crushing element is in this configuration integrally formed with the main length section. The main length section may however be manufactured by friction welding a major part of the main length section with a male end and a female end, each of the male end and female end comprising a part of the main length section.

[0049] According to an embodiment, the crushing element is integral with the shoulder.

[0050] This configuration increases the strength of the drill rod. There may additionally be a transition surface between the shoulder and the peripheral surface of the crushing element.

[0051] The invention furthermore relates to a drill string comprising at least one drill rod according to the definitions above and a drill bit.

[0052] Further advantages of the present invention will appear from the description following below.LIST OF DRAWINGS

[0053] Embodiments of the invention will now be described in detail with regard to the annexed drawings, in which: Fig. 1 is a perspective view of a drill string wherein a drill rod is coupled to a drill bit. Fig. 2a is a perspective view of the male end of a drill rod according to a first embodiment of the invention. Fig. 2b is an end view of the male end of a drill rod according to a first embodiment of the invention. Fig. 2c is a side view of the male end of a drill rod according to a first embodiment of the invention. Fig. 3a is a perspective view of the male end of a drill rod according to a second embodiment of the invention. Fig. 3b is an end view of the male end of a drill rod according to a second embodiment of the invention. Fig. 3c is a side view of the male end of a drill rod according to a second embodiment of the invention. Fig. 4a is a perspective view of the male end of a drill rod according to a third embodiment of the invention. Fig. 4b is an end view of the male end of a drill rod according to a third embodiment of the invention. Fig. 4c is a side view of the male end of a drill rod according to a third embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0054] Reference is made to Fig. 1 which shows a drill rod 12 releasably coupled to a drill bit 2 of conventional design. This assembly is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod 12 to the drill bit 2. The drill rod 12 comprises an axially extending main length section 14 and at one end a male end 16 and at a second opposite end a female end 18 and having a longitudinal axis 5. The drill rod 12 is capable of being coupled end-to-end with other adjacent drill rods 12 to form a drill string (not shown). The length of the drill rod 12 is usually between 3 to 6 m.

[0055] The middle major part of the main length section 14 is usually friction welded to the male end 16 and to the female end 18.

[0056] Figs. 2a-c shows a male end 16 of a drill rod according to a first embodiment of the invention. The male end 16 has at its leading end a male thread 17 for connecting to a drill bit 2. At the trailing end of the male 16 part of the main length section 14 is located. The main length section has a radius Rm. The trailing end is usually friction welded to a longer main length section 14 which at its other end is friction welded to a female end 18 to form the entire drill rod 12. A flushing channel 7 extends along the entire axial length for providing flushing media to the front of the drill bit 2. A shoulder 20 is positioned close to the rear end of the male thread 17. The shoulder 20 transfers percussive energy from the drill rod 12 to the drill bit 2. The shoulder has a radius Rs.

[0057] Integral with, and at the rear end of the shoulder 20, a crushing element 30 is positioned. Between the shoulder and the peripheral surface of the crushing element 30 a transition surface 22 is positioned. The transition surface 22 smoothly connects the shoulder 20 with the crushing element 30. The crushing element 30 is cylindrical in shape and has a peripheral surface that is circular in a cross-section perpendicular to the longitudinal axis 5. The central axis of the crushing element 30 is offset from the longitudinal axis 5. The peripheral surface of the crushing element has a maximum distance Rc from the longitudinal axis 5. Due to the offset of the central axis of the crushing element 30 in relation to the longitudinal axis 5, this maximum distance Rc is located at a specific location around the circumference of the peripheral surface of the crushing element 30. At other locations the peripheral surface will be located closer to the longitudinal axis 5. At its smallest distance the peripheral surface has a distance to the longitudinal axis 5 that is approximately equal to the radius Rm of the main length section 14. The offset cylindrical crushing element 30 will, during rotation of the drill rod 12, squeeze cuttings between the crushing element 30 and the wall of the drilled borehole, thus crushing the cuttings into smaller pieces. These smaller cuttings can then be efficiently transferred to the exit of the borehole by the flushing media.

[0058] The male end 16 is typically around 290 mm long. The radius Rs of the shoulder is typically 42 mm. The radius Rm of the main length section is typically 30 mm and the maximum distance Rc of the peripheral surface of the crushing element 30 to the longitudinal axis is typically 40 mm. The given numbers are only examples of values that can be used.

[0059] Reference is now made to Figs 3a-c, which shows a male end 16 of a drill rod according to a second embodiment of the invention. Most of the features of the second embodiment are identical to the first embodiment and the same reference numerals are used for identical features. Only the differences compared to the first embodiment will be described.

[0060] The crushing element 40 has in this embodiment a radially peripheral surface that is elliptical in cross-section perpendicular to the longitudinal axis 5. The center of the elliptical cross-section is offset from the longitudinal axis 5. The elliptical shape results in that the crushing element 40 has a more sharp or pointy end compared to having a crushing element 30 with a cylindrical shape and it gets progressively sharper, or more curved, closer to the location where the peripheral surface's maximum distance Rc from the longitudinal axis 5 is located. This is highly efficient for crushing cuttings.

[0061] As an alternative (not shown), the elliptical crushing element 40 may have its center coinciding with the longitudinal axis 5. The ellipse will then form two parts that symmetrically extend radially from the longitudinal axis 5.

[0062] Reference is now made to Figs 4a-c, which shows a male end 16 of a drill rod according to a third embodiment of the invention. Most of the features of the third embodiment are identical to the first and second embodiment and the same reference numerals are used for identical features. Only the differences compared to the first and second embodiment will be described.

[0063] The crushing element 50 has a radially peripheral surface that slopes towards the longitudinal axis 5 when moving away from the shoulder 20 or moving towards the trailing end of the drill rod 12. In the shown embodiment the peripheral surface slopes in a straight line (as seen in a side view of the drill rod 12) but alternatives where the slope of the surface has a convex or concave shape in a side view is also possible. A cross-section of the peripheral surface of the crushing element 50 forms part of a circle and when the surface slopes with a straight line in a side view the crushing element 50 forms a part of a truncated cone. A cross-section of the peripheral surface of the crushing element 50 may alternatively form part of an ellipse. The crushing element 50 described forms a crushing element with a single protrusion or protuberance. The crushing element 50 may also be symmetrical (not shown) around the longitudinal axis 5. In this embodiment there is a second protrusion or protuberance with a sloping surface on the diametrically opposite side of the longitudinal axis 5.

Examples

Embodiment Construction

[0054]Reference is made to Fig. 1 which shows a drill rod 12 releasably coupled to a drill bit 2 of conventional design. This assembly is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod 12 to the drill bit 2. The drill rod 12 comprises an axially extending main length section 14 and at one end a male end 16 and at a second opposite end a female end 18 and having a longitudinal axis 5. The drill rod 12 is capable of being coupled end-to-end with other adjacent drill rods 12 to form a drill string (not shown). The length of the drill rod 12 is usually between 3 to 6 m.

[0055]The middle major part of the main length section 14 is usually friction welded to the male end 16 and to the female end 18.

[0056]Figs. 2a-c shows a male end 16 of a drill rod according to a first embodiment of the invention. The male end 16 has at its leading end a male thread 17 for connecting to a drill bit ...

TECHNICAL FIELD

[0001] The present invention relates to percussive drilling, and, in particular, to a drill rod for use in such drilling.BACKGROUND

[0002] Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, drill strings are typically used in which a plurality of drill rods are interconnected to advance the drill bit and increase the depth of the hole. In 'top hammer drilling' a terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes.

[0003] Drill rods used for this application usually have a male threaded end and a female threaded end and are commonly called MF-rods. The drill rods can also have a shoulder formed as a radially flared extension of the main length section of the drill close to the male threaded end. The shoulder provides increased efficiency in energy transfer between the drill rod and the drill bit. The shoulder on the first drill string rod that joins to the drill bit is exposed to high levels of wear as the hole collapses and rock cuttings gather behind the drill bit. The problem with this is that as the shoulder wears the strength of the coupling will weaken and the contact area between drill rod and drill bit will decreases which leads to a decreased transfer of energy between drill rod and drill bit. Most of these cuttings will be transported away by flushing that is transported with pressure through a hollow passage in the drill rod and then through the drill bit. The high pressure of the flushing will then transport cuttings away from the borehole but there is still a problem with wear on the shoulder as the cuttings will pass and contact the shoulder on their route away from the borehole.

[0004] WO202169657 discloses a drilling assembly for percussion drilling where the shoulder is encased in both radial and axial direction inside the mounting sleeve of the drill bit. WO2020234259 discloses a drill string rod with a shoulder that is protected by a hard layer.

[0005] In some types of rock, the cuttings formed during drilling will be too big to be transported away from the borehole by the flushing. If this is the case large pieces of rock will be collected, due to gravity, on the side of the shoulder that is away from the drill bit. In these cases, extensive wear on the shoulder may be the result.

[0006] Therefore, there is a need for improvements in drill rods such that the large pieces of rock can be removed from the borehole and thus decrease the wear on the shoulder.

[0007] It is therefore an object of the present invention to present an improved drill rod suitable for removing large rock pieces from the borehole, thus leading to decreased wear of the shoulder of the drill rod.SUMMARY

[0008] According to the present invention, the above mentioned object is achieved by means of a drill rod having the features defined in claim 1.

[0009] The drill rod for percussive drilling according to the present invention comprises: a hollow elongate main length section, defining a longitudinal axis of the drill rod, extending axially between a leading male end, for connecting the drill rod to a drill bit, and a trailing female end. A through-going flushing channel. The female end comprises a female thread and the male end comprises a male thread and a radially projecting shoulder between the male thread and the main length section. The main length section has a circular cross-section perpendicular to the longitudinal axis of the drill rod. The shoulder comprises a peripheral surface with a greater outer diameter than the outer diameter of the main length section. A crushing element is positioned adjacent a trailing end of the shoulder and a cross-section and a radially peripheral surface of the crushing element has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.

[0010] When drilling a hole using a percussive drill component a flushing channel that passes through the drill rod and exits at the front of the drill bit is used for directing a flushing agent such as air, or a fluid such as water, to the bottom of the drilled hole. The flushing agent will arrive at the bottom of the hole at a high pressure to flush the cuttings, produced during the drilling operation, to the exit of the drilled hole. The cuttings will pass between the wall of the drilled hole and the outside surface of the drill rods on its way to the exit of the drilled hole. Some cuttings, however, are too large to be effectively flushed out of the hole. Due to gravity, these large cuttings will accumulate at the trailing side of the shoulder of the drill rod that is attached to the drill bit. This accumulation of large cuttings will lead to wear on the shoulder. Heavy wear on the shoulder will decrease the efficiency of transmitting percussive energy from the drill rod, through the shoulder, to the drill bit. The drilling will thus be less effective.

[0011] The present inventors have realized that having a crushing element at the trailing end of the shoulder solves this problem. The crushing element has a radially peripheral surface that has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.

[0012] The crushing element radially extends the main length section in the area closest to the trailing end of the shoulder. Its radially peripheral surface has a non-constant distance to the longitudinal axis of the drill due to it being made of at least one protrusion or protuberance that extends in a certain direction(s) away from the longitudinal axis of the drill rod. There may be more than one protrusion or protuberance, for example 2, 3 or 4, that extends in different radial directions away from the longitudinal axis of the drill rod.

[0013] The crushing element, due to it extending away from the longitudinal axis of the drill rod, on at least one position, will impact and squeeze the large cuttings against the wall of the drilled hole. The large cuttings will then break into finer cuttings which can be flushed away from the drilled hole.

[0014] If there are too many protrusions or protuberances the distance between them will be too small for large cuttings to fit between them and the impact that they receive from the crushing element will be too small to efficiently break the large cuttings into finer cuttings.

[0015] A small transition surface may be positioned in the transition between the shoulder and the crushing element. The transition surface simplifies manufacturing of the crushing element and additionally decreases the stresses in the area between the shoulder and the crushing element. The transition surface is not part of the crushing element.

[0016] The main length section of the drill rod has a circular cross-section with a radius Rm. The crushing element can be seen as the leading end part of the main length section where there is a protrusion or protuberance extending in a radial direction. The entire peripheral surface of the crushing element preferably extends further from the longitudinal axis of the drill rod than the radius Rm of the main length section.

[0017] Throughout this application the wording leading end refers to the end of the drill rod where the drill bit is attached. The leading end thus refers to the end closest to the bottom of the drilled hole. The trailing end refers to the end furthest away from the bottom of the drilled hole.

[0018] According to one embodiment, the outer surface of the cross-section of the crushing element is smooth around the whole circumference of the outer surface of the cross-section.

[0019] Smooth in this context means that there are no sudden changes in the crushing elements peripheral surface's distance to the longitudinal axis around the circumference of the radially peripheral surface of the crushing element.

[0020] This configuration ensures that large cuttings are not just pushed in front of the crushing element but will instead get squeezed between the crushing element and the wall of the drilled hole.

[0021] Preferably, the peripheral surface of the crushing element is convex around its circumference. This ensures that there are no indents in the crushing element where cuttings may get stuck.

[0022] According to an embodiment, the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is smaller than a radius Rs of the shoulder.

[0023] This configuration ensures that the shoulder will act as a barrier for cuttings to stop cuttings from travelling back down the hole to the drill bit.

[0024] The peripheral surface of the crushing element preferably has a minimum distance to the longitudinal axis that is approximately equal to the radius Rm of the main length section.

[0025] According to an embodiment, a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod to the radius Rs of the shoulder is between 0,5-1,0. More preferably the ratio is between 0,7-0,95 and most preferably between 0,75-0,9.

[0026] This configuration ensures that cuttings will be effectively squeezed and crushed between the crushing element and the wall of the borehole. This configuration further ensures that a large range of different sized cuttings will be crushed.

[0027] According to an embodiment, the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is larger than a radius Rm of the main length section.

[0028] According to an embodiment, a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod and the radius Rm of the main length section is between 1,2-2,0. The ratio is more preferably between 1,25-1,6 and most preferably between 1,3-1,4.

[0029] This configuration ensures that a large range of different sized cuttings will be crushed.

[0030] According to an embodiment, the crushing element has an axial extension that is between 5-100 mm. The axial extension is more preferably between 10-40 mm.

[0031] The drill rod is usually manufactured by friction welding a majority of the main length section to a male end and to a female end. The male end and the female end will however comprise a small part of the main length section. This manufacturing method simplifies the manufacturing of the drill rod compared to if the drill rod was manufactured in one piece.

[0032] Due to the friction welding of the male end to the main length section the crushing element should not have an axial extension from the shoulder that is too long since a certain free distance is needed to clamp the male end during the friction welding operation. Usually a free distance of 50-90 mm is needed.

[0033] The axial extension of the crushing element must additionally have a certain minimum length to effectively crush cuttings.

[0034] According to an embodiment, the crushing element is anti-symmetric with a central axis that is offset from the longitudinal axis of the drill rod.

[0035] This is an efficient solution that preferably uses a crushing element having a single protrusion or protuberance that extends in one radial direction away from the longitudinal axis of the drill rod.

[0036] According to an embodiment, the crushing element is symmetric around the longitudinal axis of the drill rod.

[0037] This is an alternative solution where the crushing element has 2, 3 or 4 protrusions or protuberances that are symmetrically positioned around the longitudinal axis of the drill rod.

[0038] According to an embodiment, the crushing element generally has a cylindrical peripheral surface and in that the central axis of the crushing element is offset from the longitudinal axis of the drill rod.

[0039] This configuration ensures that the cuttings will be effectively crushed due to the peripheral surface of the offset cylinder having a distance from the longitudinal axis of the drill bit that progressively increases. Having a crushing element that is cylindrical in shape is also simple to manufacture.

[0040] According to an embodiment, the crushing element has a peripheral surface that is generally elliptical in shape.

[0041] This configuration ensures the cuttings will be effectively crushed due to the peripheral surface of the offset cylinder having a distance from the longitudinal axis of the drill bit that progressively increases. A crushing element having a peripheral surface that is generally elliptical in shape has the advantage that it can have its central axis coinciding with the longitudinal axis of the drill rod and then the elliptical surface will extend in two radial directions, thus forming a crushing element with two symmetrically positioned protrusions or protuberances.

[0042] According to an embodiment, the crushing element has a peripheral surface that slopes towards the longitudinal axis of the drill rod in a direction towards the trailing end of the drill rod.

[0043] With this configuration the cuttings will be squeezed both in a radial and in an axial direction.

[0044] The slope can be any shape that slopes towards the longitudinal axis of the drill bit, for example a straight line, a concave or a convex shape.

[0045] If the slope is a straight line and the cross-section of the radially peripheral surface of the crushing element is circular, then the crushing element will have the form of a truncated cone.

[0046] According to an embodiment, the crushing element is integral with the main length section.

[0047] This configuration increases the strength of the drill rod and especially the strength of the crushing element.

[0048] The crushing element is in this configuration integrally formed with the main length section. The main length section may however be manufactured by friction welding a major part of the main length section with a male end and a female end, each of the male end and female end comprising a part of the main length section.

[0049] According to an embodiment, the crushing element is integral with the shoulder.

[0050] This configuration increases the strength of the drill rod. There may additionally be a transition surface between the shoulder and the peripheral surface of the crushing element.

[0051] The invention furthermore relates to a drill string comprising at least one drill rod according to the definitions above and a drill bit.

[0052] Further advantages of the present invention will appear from the description following below.LIST OF DRAWINGS

[0053] Embodiments of the invention will now be described in detail with regard to the annexed drawings, in which: Fig. 1 is a perspective view of a drill string wherein a drill rod is coupled to a drill bit. Fig. 2a is a perspective view of the male end of a drill rod according to a first embodiment of the invention. Fig. 2b is an end view of the male end of a drill rod according to a first embodiment of the invention. Fig. 2c is a side view of the male end of a drill rod according to a first embodiment of the invention. Fig. 3a is a perspective view of the male end of a drill rod according to a second embodiment of the invention. Fig. 3b is an end view of the male end of a drill rod according to a second embodiment of the invention. Fig. 3c is a side view of the male end of a drill rod according to a second embodiment of the invention. Fig. 4a is a perspective view of the male end of a drill rod according to a third embodiment of the invention. Fig. 4b is an end view of the male end of a drill rod according to a third embodiment of the invention. Fig. 4c is a side view of the male end of a drill rod according to a third embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS

[0054] Reference is made to Fig. 1 which shows a drill rod 12 releasably coupled to a drill bit 2 of conventional design. This assembly is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod 12 to the drill bit 2. The drill rod 12 comprises an axially extending main length section 14 and at one end a male end 16 and at a second opposite end a female end 18 and having a longitudinal axis 5. The drill rod 12 is capable of being coupled end-to-end with other adjacent drill rods 12 to form a drill string (not shown). The length of the drill rod 12 is usually between 3 to 6 m.

[0055] The middle major part of the main length section 14 is usually friction welded to the male end 16 and to the female end 18.

[0056] Figs. 2a-c shows a male end 16 of a drill rod according to a first embodiment of the invention. The male end 16 has at its leading end a male thread 17 for connecting to a drill bit 2. At the trailing end of the male 16 part of the main length section 14 is located. The main length section has a radius Rm. The trailing end is usually friction welded to a longer main length section 14 which at its other end is friction welded to a female end 18 to form the entire drill rod 12. A flushing channel 7 extends along the entire axial length for providing flushing media to the front of the drill bit 2. A shoulder 20 is positioned close to the rear end of the male thread 17. The shoulder 20 transfers percussive energy from the drill rod 12 to the drill bit 2. The shoulder has a radius Rs.

[0057] Integral with, and at the rear end of the shoulder 20, a crushing element 30 is positioned. Between the shoulder and the peripheral surface of the crushing element 30 a transition surface 22 is positioned. The transition surface 22 smoothly connects the shoulder 20 with the crushing element 30. The crushing element 30 is cylindrical in shape and has a peripheral surface that is circular in a cross-section perpendicular to the longitudinal axis 5. The central axis of the crushing element 30 is offset from the longitudinal axis 5. The peripheral surface of the crushing element has a maximum distance Rc from the longitudinal axis 5. Due to the offset of the central axis of the crushing element 30 in relation to the longitudinal axis 5, this maximum distance Rc is located at a specific location around the circumference of the peripheral surface of the crushing element 30. At other locations the peripheral surface will be located closer to the longitudinal axis 5. At its smallest distance the peripheral surface has a distance to the longitudinal axis 5 that is approximately equal to the radius Rm of the main length section 14. The offset cylindrical crushing element 30 will, during rotation of the drill rod 12, squeeze cuttings between the crushing element 30 and the wall of the drilled borehole, thus crushing the cuttings into smaller pieces. These smaller cuttings can then be efficiently transferred to the exit of the borehole by the flushing media.

[0058] The male end 16 is typically around 290 mm long. The radius Rs of the shoulder is typically 42 mm. The radius Rm of the main length section is typically 30 mm and the maximum distance Rc of the peripheral surface of the crushing element 30 to the longitudinal axis is typically 40 mm. The given numbers are only examples of values that can be used.

[0059] Reference is now made to Figs 3a-c, which shows a male end 16 of a drill rod according to a second embodiment of the invention. Most of the features of the second embodiment are identical to the first embodiment and the same reference numerals are used for identical features. Only the differences compared to the first embodiment will be described.

[0060] The crushing element 40 has in this embodiment a radially peripheral surface that is elliptical in cross-section perpendicular to the longitudinal axis 5. The center of the elliptical cross-section is offset from the longitudinal axis 5. The elliptical shape results in that the crushing element 40 has a more sharp or pointy end compared to having a crushing element 30 with a cylindrical shape and it gets progressively sharper, or more curved, closer to the location where the peripheral surface's maximum distance Rc from the longitudinal axis 5 is located. This is highly efficient for crushing cuttings.

[0061] As an alternative (not shown), the elliptical crushing element 40 may have its center coinciding with the longitudinal axis 5. The ellipse will then form two parts that symmetrically extend radially from the longitudinal axis 5.

[0062] Reference is now made to Figs 4a-c, which shows a male end 16 of a drill rod according to a third embodiment of the invention. Most of the features of the third embodiment are identical to the first and second embodiment and the same reference numerals are used for identical features. Only the differences compared to the first and second embodiment will be described.

[0063] The crushing element 50 has a radially peripheral surface that slopes towards the longitudinal axis 5 when moving away from the shoulder 20 or moving towards the trailing end of the drill rod 12. In the shown embodiment the peripheral surface slopes in a straight line (as seen in a side view of the drill rod 12) but alternatives where the slope of the surface has a convex or concave shape in a side view is also possible. A cross-section of the peripheral surface of the crushing element 50 forms part of a circle and when the surface slopes with a straight line in a side view the crushing element 50 forms a part of a truncated cone. A cross-section of the peripheral surface of the crushing element 50 may alternatively form part of an ellipse. The crushing element 50 described forms a crushing element with a single protrusion or protuberance. The crushing element 50 may also be symmetrical (not shown) around the longitudinal axis 5. In this embodiment there is a second protrusion or protuberance with a sloping surface on the diametrically opposite side of the longitudinal axis 5.

Examples

Embodiment Construction

[0054]Reference is made to Fig. 1 which shows a drill rod 12 releasably coupled to a drill bit 2 of conventional design. This assembly is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod 12 to the drill bit 2. The drill rod 12 comprises an axially extending main length section 14 and at one end a male end 16 and at a second opposite end a female end 18 and having a longitudinal axis 5. The drill rod 12 is capable of being coupled end-to-end with other adjacent drill rods 12 to form a drill string (not shown). The length of the drill rod 12 is usually between 3 to 6 m.

[0055]The middle major part of the main length section 14 is usually friction welded to the male end 16 and to the female end 18.

[0056]Figs. 2a-c shows a male end 16 of a drill rod according to a first embodiment of the invention. The male end 16 has at its leading end a male thread 17 for connecting to a drill bit ...

Claims

1. A drill rod (12) for percussive drilling comprising: a hollow elongate main length section (14), defining a longitudinal axis (5) of the drill rod (12), extending axially between a leading male end (16), for connecting the drill rod (12) to a drill bit (2), and a trailing female end (18); a through-going flushing channel (7); the female end (18) comprising a female thread; the male end (16) comprising a male thread (17) and a radially projecting shoulder (20) between the male thread (17) and the main length section (14); the main length section (14) having a circular cross-section perpendicular to the longitudinal axis of the drill rod (12); the shoulder (20) comprising a peripheral surface having a greater outer diameter than the outer diameter of the main length section; characterized in that a crushing element (30,40, 50) is positioned adjacent a trailing end of the shoulder (17) and in that a radially peripheral surface of the crushing element (30, 40, 50) has a non-constant distance to the longitudinal axis (5) around the circumference of the radially peripheral surface of the crushing element (30, 40, 50).

2. A drill rod according to claim 1, characterized in that a peripheral surface of the cross-section of the crushing element (30, 40, 50) is smooth around the whole circumference of the peripheral surface of the cross-section.

3. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) has a maximum distance Rc from the longitudinal axis (5) that is smaller than a radius Rs of the shoulder (17).

4. A drill rod according to claim 3, characterized in that a ratio, Rc / Rs, of the maximum distance Rc from the crushing element (30, 40, 50) to the longitudinal axis (5) to the radius Rs of the shoulder is between 0,5-1,0.

5. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) has a maximum distance Rc from the longitudinal axis (5) that is larger than a radius Rm of the main length section (14).

6. A drill according to claim 5, characterized in that a ratio, Rc / Rm, of the maximum distance Rc from the crushing element (30, 40, 50) to the longitudinal axis (5) and the radius Rm of the main length section (14) is between 1,2-2,0.

7. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) has an axial extension that is between 5-100 mm.

8. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) is anti-symmetric with a central axis that is offset from the longitudinal axis (5).

9. A drill rod according to any of claims 1 to 7, characterized in that the crushing element is symmetric around the longitudinal axis (5).

10. A drill rod according to any of claims 1 to 8, characterized in that the crushing element (30) generally has a cylindrical peripheral surface and in that the central axis of the crushing element (30) is offset from the longitudinal axis (5).

11. A drill rod according to any of claims 1 to 9, characterized in that the crushing element (40) has a peripheral surface that is generally elliptical in shape.

12. A drill rod according to any of the previous claims, characterized in that the crushing element (50) has a peripheral surface that slopes towards the longitudinal axis (5) in a direction towards the female end (18).

13. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) is integral with the main length section (14).

14. A drill rod according to any of the previous claims, characterized in that the crushing element (30, 40, 50) is integral with the shoulder (17).

15. A drill string comprising at least one drill rod (12) according to any of the previous claims and a drill bit (2).

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