WO2001042615A2

WO2001042615A2 - Drill rod

Info

Publication number: WO2001042615A2
Application number: PCT/US2000/042723
Authority: WO
Inventors: Stuart A. Connell
Original assignee: Ingersoll-Rand Company
Priority date: 1999-12-10
Filing date: 2000-12-08
Publication date: 2001-06-14
Also published as: AU4522501A; WO2001042615A3

Abstract

The drill rod (10) includes a first rod section (14) and a second rod section (16) that are welded together along their mating ends (14b and 16b respectively). The mating ends are heat treated to reduce the elevated hardness that is caused by the welding. Both, the first rod section and the second rod section, each include an interior passage (15 and 17 respectively) that extends between the free end (14a and 16a respectively) to the mating end. A hardened externally threaded portion (18) on the first rod section can be threaded into the separately hardened internally threaded portion in the interior passage of a second rod section of another drill rod. The first drill rod is threaded into the other drill rod so that the surface of an annular face on the free end of the first drill rod abuts against a mating shoulder of the second drill rod.

Description

DRILL ROD HAVING SELECTIVELY HARDENED SECTIONS

FIELD OF THE INVENTION The present invention relates to rock drilling equipment, and more particularly to drill rod used for rock drilling operations.

BACKGROUND In drilling construction mining holes in formations using percussive rotary techniques, it is sometimes required to add and remove drill rods to the drill string to achieve various drilling depth requirements. Presently, several different types of rod connections are possible and have certain advantages and disadvantages both in cost and ease of use.

One type of drill rod used in such applications is commonly referred to as "male/female" rod or "speed" rod 1, as shown in Fig. 1. Speed rods 1 typically include a first section 2 having an externally-threaded rod portion 3 located at a first outer end 4 of the rod 1, referred to as the "male" end 4, and a second section 5 connected to the first section 2 and having a threaded hole 6 extending into a second, opposing outer end 7, referred to as the "female" end 7. The female end 7 has an outside diameter d_f that is larger than the outside diameter d_m of the male end, and is preferably sufficiently larger such that the threaded hole 6 is configured to threadably engage with the threaded portion 3 of the male end 4 of another speed rod 1 (only one shown). A drill string (not depicted) having a desired number of speed rods 1 may be easily constructed by threadably connecting the male end 4 of each rod 1 with the female end 7 of an adjacent rod 1. Further, each speed rod 1 has a through bore hole or interior passage 8 extending along a central longitudinal axis 9 of the rod 1 between the opposing ends 4 and 7 and is used for flushing media through the drill rod 1.

Speed drill rods 1, as discussed above, are typically fabricated by one of two known manufacturing techniques. The first method is to "upset forge" one end of a material rod that initially has a constant outside diameter and a longitudinal through bore. The material at the end being forged is displaced toward the other end and simultaneously displaced outwardly, such that the forged end increases in both outside and inside diameter, while the overall length of the rod decreases. The inside surface of the forged end is then finish machined and threaded to form a female end 7, and the other end is provided with external threads 3 on the outer surface to form a male end 4. Speed rods 1 formed by hot forging processes have several inherent problems or limitations resulting from the hot forging process. One problem is that the interior bore or passage 8 of the drill rod 1 has a tendency to become reduced or close in during the forging process. The reduction in the interior passage 8 restricts the capability of flushing media through the rod 1. Another problem is that the inner surface of the drill rod 1, particularly at the forged (i.e., the female) end 7, has surface imperfections such as folded/lapped material or smeared material which act as stress concentrators. These stress concentrators cause the service life of the rods 1 to be greatly reduced. Further, the forging process also creates sub-surface intergranular imperfections, such as discontinuous grain flow lines, in the material of the forged female end 7, particularly below the inner surface of the forged end 7. These intergranular imperfections result in a weak grain structure that is incapable of supporting the normal drilling forces required.

Further, the hot-forged female end 7 of the rod 1 usually has hard "scale" on the outer surfaces thereof and a core material hardness that is significantly increased by the hot-forging process. These two adverse effects make finish machining of the female end 8 more difficult and sometimes necessitates tempering of the female end 8 prior to finish machining. Furthermore, at portions of the drill rod 1 which are not finish machined, scale caused by the forging process is often present at the inner surfaces, which may lead to premature corrosion fatigue at such sections of the speed rod. In addition to the above-described problems, upset-forged speed rods 1 generally require lengthy process times throughout its manufacturing cycle, such the forging lead time from an outside vendor, and have a number of difficulties that typically arise throughout the manufacturing cycle. For example, the drill rods 1 are difficult to handle during machining operations due to the fairly large overall length of the rods 1. Further, inconsistent machining tolerances are present in the finished rods 1 due to hard spots formed in the rod material during the forging process. Further, heat treatment of the rods 1 is difficult both due to the substantial overall length and weight of the rods 1, as well as the necessity of straightening rods which experience heat-induced bending, such straightening generally being performed by a vendor other than the one doing the heat treatment. Finally, it is also necessary to remove scale from the female threads 6 and inner surfaces of the rod 1. All of the process difficulties described above increase the costs of manufacturing the speed drill rods 1 by the upset-forging process.

Another method of manufacturing the speed rods 1 is to inertia or friction weld together two rod sections 2, 5 and then finish machining the male and female portions of the welded together drill rod 1. As is known, inertia welding involves rotating one section (e.g., section 5) at a high speed and then displacing or pushing the other section (i.e., section 2) into the rotating section, creating substantial friction and heat, which melts material at the interface of the two sections 2 and 5. When the melted material later hardens, the two sections 2 and 5 are thus welded together. The male and female ends 4 and 7, respectively, of the rod 1 are then threaded, as discussed above, if not already provided with threads before welding.

Speed drill rods 1 manufactured by inertia welding also typically have several problems or defects that arise from the inertia welding process. First, "flash" is typically present at the inertia welded joint at both the inner and outer surfaces of the drill rod 1. The flash is caused by rod material that flows, both inwardly and outwardly, during the inertia welding process. This flash restricts media flushing capability of the rod 1 and acts as stress concentrators at the inside and outside diameters of the rod, resulting in a greatly reduced service life of the rod. Therefore, the flash must be removed by appropriate means (e.g., grinding) in order to make the sections of the rod joint as smooth as possible in order to eliminate the stress concentrators. Also, as the rod material about the joint becomes hardened during the welding process, the joint section of the rod must be fully tempered.

Speed rods 1, regardless of which of two above-described processes are used to manufacture a particular rod, are all typically heat-treated in the same manner. Generally, a rod 1 is first completely carburized such that a hardened casing is formed on generally all surfaces, as represented by thickened line sections in Fig. 1 , and then is tempered from end to end. Such heat treatment is believed to cause the mating threads 3 and 6 to be wear resistant, the outer or exterior surfaces of the rod 1 to be resistant to wearing- away caused by abrasion from rock cuttings during use of the drill string, and to also reduce any adverse material effects in the rod 1 that may have been created by heat during either the forging or welding processes.

However, the effective depth of a carburized casing is typically fairly minimal and the casing does not adequately preserve the service life of the speed drill rods 1. During use, speed rod 1 is often subject to high bending loads caused by drilling feed pressure. Furthermore, as the walls of a drilled hole (not depicted) are generally not completely straight, but rather has deviating sections, the central body portion of the speed rod 1 often contacts and rubs against the material of a formation being drilled. Due to the increased hardness provided by the carburized casing, such bending loads and abrading contact with the material formation often causes friction cracks to appear on the outer surface of the central portion of the rod 1, which may lead to premature fracture of the speed rod 1.

Also, the above-described heat treatment typically raises the core hardness of the speed rods 1 so as to cause the rods 1 to be relatively fragile under normal drilling conditions. Further, completely carburized drill rods 1 require a relatively long processing cycle and hence tend to generally expensive to heat treat. Furthermore, as the drill rods 1 are generally relatively long, the carburization process can generally only be performed in a large furnace, increasing both the cost and processing time for treating the drill rod 1.

SUMMARY

The present invention provides an improved drill rod and a method of manufacturing an improved drill rod or drill string. The drill rod is made from two rod sections that serve to minimize the cost of manufacturing compared to the ordinarily long and inconvenient size of typical drill rod. Because of the convenient size of the two separate rod sections, they are separately heat treated and machined, thereby shortening the processing cycle and reducing the costs associated with their manufacture. The two rod sections can individually be more selectively hardened to provide hardened areas where strength is necessary and toughened sections where durability is required. This selective hardening provides a durable section that is less susceptible to cracks that eventually lead to fracture. The drill rod of the present invention provides simple manufacture, cost effectiveness, and a longer service life.

The drill rod includes a first rod section and a second rod section that are welded together along their mating ends. The mating ends are heat treated to reduce the elevated hardness that is caused by welding. Both the first rod section and the second rod section each include an interior passage that extends between the free end to the mating end. A hardened externally threaded portion on the first rod section can be threaded into the separately hardened internally threaded portion in the interior passage of a second rod section of another drill rod. The first drill rod is preferably threaded into the other drill rod until the surface of an annular face on the free end of the first drill rod abuts against a mating shoulder of the second drill rod.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the detailed description of the preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, which are diagrammatic, embodiments that are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: Fig. 1 is a side plan view of a known speed drill rod;

Fig. 2 is a side plan view of an improved speed rod in accordance with the present invention;

Fig. 3 is a side plan view of a first rod section of the improved drill rod; and Fig. 4 is an enlarged, side cross-sectional view of a second rod section of the improved drill rod.

DETAILED DESCRIPTION Referring to Figs. 2-4, the present invention is an improved drill rod 10 having selectively hardened sections 12. The drill rod 10 basically comprises a first rod section 14 attached to a second rod section 16, preferably by an inertia welding process, so as to form a joint 13 between the two sections 14 and 16. Each rod section 14 and 16 is separately processed to form the hardened sections 12 of the rod 10 prior to being attached together, as discussed in further detail below. The second rod section 16, which provides the female end 10b of the rod 10, has an outside diameter D_f that is substantially greater than an outside diameter D_m of the first section 14, which provides the male end 10a of the rod 10, as for reasons described below.

Referring to Figs. 2 and 3, the first rod section 14 has a first, free end 14a (i.e., "free" when sections 14 and 16 are attached), a second, mating end 14b and a longitudinal bore hole 15 extending between the ends 14a and 14b. An externally threaded portion 18 is formed in the outer circumferential surface 14c of the rod section 14 and is disposed proximal the rod section free end 14a. Further, a radial annular face or "rod contacting button" 20 is located at the free end 14a about one end of the bore-hole 15. The contacting button 20 provides a lead-in surface for mating with the female end 10b of another speed rod 10 (only one shown), as discussed below. The threaded portion 18 and the contacting button 20 are treated or processed to form the hardened sections 12 of the male end 10a of the drill rod 10, as represented by thickened line sections in Fig. 3. Preferably, an induction coil (not shown) is disposed about the free end 14a of the rod section 14a such that magnetic energy is transferred from the coil to the rod material at the free end 14a, causing the rod material to become heated (as is known). The heated rod section is then quenched such that a hardened case is formed about the threaded portion 18 and the button 20. Alternatively, the portions 18, 20 of the first rod section 14 may be hardened by any other appropriate means, such as by selective carburization (although not preferred), as described below. Referring now to Figs. 2 and 4, the second rod section 16 has a first, free end 16a, a second, mating end 16b, and a counter-bored hole 17 extending between the ends 16a and 16b. An internally threaded portion 22 is formed in the inner circumferential surface 16d that bounds the larger diameter section of the counter-bored hole 17 and extends axially from the free end 16a to a thread undercut or run-out groove 24. The internally threaded portion 22 is configured to threadably engage with the externally threaded portion 18 of another speed rod 10 (only one shown), to thereby connect together the two speed rods 10 (one shown). Further, a radial "rod mating" shoulder 26 is formed at the intersection of the larger and smaller diameter sections of the counter-bored hole 17. The rod mating shoulder 26 provides an abutment surface for the rod contact button 20 at the male end 10a of another drill rod 10 when the two rods 10 are connected together.

The internally threaded section 22, the thread run-out undercut 24 and the mating shoulder 26 are treated to form the selectively hardened sections 12 of the female end 10b of the rod 10, as represented by thickened line sections in Fig. 4. Preferably, the portions 22, 24 and 26 of the second rod section 16 are heat-treated by "selective carburization" to form a hardened case at each section 22, 24 and 26. By this process, any rod portion where no hardening is desired is first coated with a substance referred to as "stop-off paint" and then the entire rod section 16 is heated in carbon rich environment. A hardened case is then formed at the non-coated surfaces of the rod section 16 but not at the painted surfaces. Alternatively, any other appropriate means for forming the selectively hardened sections 12 of the female end 10b may be used, such as for example, by induction heating the portions 22, 24 and 26 of the second rod section 16.

After the two rod sections 14 and 16 are separately processed or treated to form the hardened sections 12 of the rod 10, the mating ends 14b, 16b of the two rod sections 14, 16, respectively, are joined together to form the overall drill rod 10 (Fig. 2). Preferably, the rod sections 14 and 16 are attached together using an inertia welding process, as described in the Background section of the present application, although any other appropriate process, such as for example, upset- forging (not preferred) may alternatively be used to join the rod sections 14 and 16. Referring to Fig. 2, after the rod sections 14 and 16 are attached by inertia welding, the joint 13 is preferably locally tempered by induction heating or by using a torch flame in order to reduce any elevated hardness in the material about the joint 13. Such elevated hardness typically occurs due to localized heating generated by the friction between the mating ends 14b and 16b which the inertia welding process. Preferably, the joint 13 is fully tempered (i.e., completely from the joint outer surface 13a to joint inner surface 13b) to prevent this portion of the rod 10 from being relatively fragile and susceptible to failure or fracture.

However, if the tempering process is not appropriately performed such that only the weld-hardened sections (i.e., the joint 15 and the immediately adjacent material sections) are tempered, other, non-hardened sections of the rod 10 adjacent to the joint 15 may become tempered and the material reduced to unacceptable hardness levels. Thus, induction heating or torch flaming are preferred for tempering the joint 13 as these processes are capable of being appropriately controlled to limit the tempered regions as desired.

When the manufacturing of the improved rod 10 is completed, the hardened sections 12 of the rod 10 preferably have a hardness, as measured on the well-known Rockwell "C" scale, of at least Re 50, and hardnesses within the range of about Re 55 to about Re 60 have been found to provide suitable protection to the portions 18, 20, 22, 24 and 26 of the drill rod 10. Further, the remaining portions/sections of the rod 10 preferably have a hardness within the range of about Re 30 to about Re 42. Preferably, the drill rod 10 is fabricated of the type of steel commonly referred to as "chrome-mo ly steel", although any other appropriate grade of steel or steel alloy or another type of metal/metal alloy may alternatively be used to fabricate the improved rod 10. By hardening only certain sections 12 of the drill rod 10 and leaving the remaining rod sections in a non-hardened state, the improved rod 10 is able to resist impact damage and material wearing where such damage/wear is likely to occur (and significantly affect the functionality of the rod 10, as discussed below) while maintaining the overall rod 10 in a relatively ductile state. More specifically, the threaded portions 18 and 22, which mate with the corresponding threaded portions 22, 18, respectively, of another speed rod 10

(only one shown), have an increased hardness in order to resist damage and wearing as any significant damage/wearing of the threads prevents the rod 10 from being connected into a drill string. In addition, hardening the contact button 20 on the male end 10b and the contact shoulder 26 and undercut section 24 on the female end 10b, which are likely to impact with mating surfaces on another rod 10 during assembly and disassembly of a drill string, prevents damage that may also inhibit connection of the rod 10 into a drill string.

Further, as the majority of the drill rod 10 remains in a non-hardened state, the ductility of the rod 10 is sufficiently high to make the rod 10 less prone to failure due to bending, shear or torsional stresses compared with a fully carburized rod 1. Furthermore, with the exposed outer or exterior surfaces 14c, 16c (i.e., when connected in a drill string) of the drill rod 10 being non-hardened (Fig. 2), these surfaces are less likely to fail due to cracks caused by friction generated by abrasive contact with the cut-out walls of a drilling formation or with drill centralizers. Also, in the event that a friction crack does initiate, the crack is likely to "rub off' due to rod material around the crack abrading away by the rubbing contact with the formation surfaces. If the cracked rod material was at higher hardness level, such as with a fully hardened drill rod 1 described in the Background section, the crack(s) would then be likely to propagate through the material of the rod 10 and could lead to fracturing of the speed rod 10. The improved rod 10 of the present invention has a number of advantages over previously known speed drill rod 1. As discussed above, selective hardening of certain sections 12 provides the benefits of hardening where needed while preserving the ductility of remainder of the rod 10. Also, by hardening portions of the individual rod sections 14, 16 in separate processes prior to attachment, it is much easier to handle the individual sections 14, 16 as compared to the entire drill rod 10. Further, as only the threaded section 18 of the first rod section 14 is hardened, it is possible to use an induction hardening process on the one end 14a, which would be much more difficult to perform if the entire length of the first rod section 14 were to be hardened. Furthermore, selective carburization of the relatively short second rod section 16 is much quicker to perform and requires significantly less furnace space than carburizing an entire drill rod 1.

By facilitating the processing required to heat treat the selected sections 12 as discussed above, the improved speed rod 10 is less time-consuming and more cost effective to produce than the previously known, fully carburized drill rod 1.

Claims

1. A steel drill rod comprising: a first rod section including a free end, a mating end, an interior passage, and an externally threaded portion adjacent the free end, wherein the externally threaded portion is hardened by heat treatment; a second rod section including a free end, a mating end, an interior passage, and an internally threaded portion within the interior passage of the second rod section adjacent the free end thereof, wherein the internally threaded portion is hardened by heat treatment; and wherein the mating ends of the rod sections are welded together to define a joint section adjacent the mating ends, and wherein the joint section is heat treated to reduce elevated hardness caused by the welding.

2. The drill rod of claim 1, wherein the mating ends of the rod sections are welded together by friction welding.

3. The drill rod of claim 1 , wherein the externally threaded portion and the internally threaded portion are hardened to at least Rς 50.

4. The drill rod of claim 3, wherein the externally threaded portion and the internally threaded portion are hardened to within Re 55 and R_e 60.

5. The drill rod of claim 1, wherein the joint section is heat treated to obtain a hardness within R_e 30 and R_e 42.

6. The drill rod of claim 1 , wherein the externally threaded portion is hardened by induction hardening.

7. The drill rod of claim 1, wherein the internally threaded portion is hardened by selective carburization.

8. The drill rod of claim 1, wherein the free end of the first rod section includes an annular face, and wherein the interior passage of the second rod section includes a mating shoulder adjacent the internally threaded portion, wherein the mating shoulder provides an abutment surface for an annular face of another drill rod when the internally threaded portion is threaded to an externally threaded portion of the other drill rod.

9. The drill rod of claim 8, wherein the interior passage of the second rod section includes an undercut adjacent the mating shoulder to provide clearance for the annular face to fully contact the abutment surface.

10. The drill rod of claim 8, wherein the annular face and the mating shoulder are hardened by heat treatment.

11. The drill rod of claim 10, wherein the annular face is hardened by induction hardening, and wherein the mating shoulder is hardened by selective carburization.

12. The drill rod of claim 1 , wherein the joint section is heat treated by an induction heating tempering process.

13. A steel drill rod made by: providing a first rod section including a free end and a mating end, an interior passage, and an externally threaded portion adjacent the free end; heat treating the externally threaded portion to increase hardness; providing a second rod section including a free end and a mating end, an interior passage, and an internally threaded portion within the interior passage of the second rod section adjacent the free end thereof; heat treating the internally threaded portion to increase hardness; welding the mating ends of the rod sections thereby defining a joint section; and heat treating the joint section to reduce elevated hardness caused by the welding.

14. The drill rod of claim 13, wherein the heat treatment of the externally threaded portion and the heat treatment of the internally threaded portion occur separately prior to the welding of the mating ends.

15. The drill rod of claim 13 , wherein the weld of the mating ends is a friction weld.

16. The drill rod of claim 13 , wherein the heat treatment hardens the externally threaded portion and the internally threaded portion to at least R_e 50.

17. The drill rod of claim 16, wherein the heat treatment hardens the externally threaded portion and the internally threaded portion within R_e 55 and R_e 60.

18. The drill rod of claim 13, wherein the heat treatment reduces the hardness of the joint section within Rς 30 and R_e 42.

19. The drill rod of claim 13, wherein the heat treatment of the externally threaded portion is induction hardening.

20. The drill rod of claim 13, wherein the heat treatment of the internally threaded portion is selective carburization.

21. The drill rod of claim 13, wherein the free end of the first rod section includes an annular face, and wherein the interior passage of the second rod section includes a mating shoulder adjacent the internally threaded portion, wherein the mating shoulder provides an abutment surface for an annular face of another drill rod when the internally threaded portion is threaded to an externally threaded portion of the other drill rod.

22. The drill rod of claim 21 , wherein the interior passage of the second rod section includes an undercut adjacent the mating shoulder to provide clearance for the annular face to fully contact the mating shoulder.

23. The drill rod of claim 21 , wherein the process further comprises heat treating the annular face to increase hardness prior to the welding of the mating ends and heat treating the mating shoulder to increase hardness prior to the welding of the mating ends.

24. The drill rod of claim 23, wherein the heat treatment of the annular face is induction hardening, and wherein the heat treatment of the mating shoulder is selective carburization.

25. The drill rod of claim 13 , wherein the heat treatment of the j oint section is an induction heating tempering process.

26. A method of manufacturing a drill string comprising: providing a first rod section having a free end, a mating end, an interior passage, and an externally threaded portion adjacent the free end; providing a second rod section having a mating end; heat treating the externally threaded portion of the first rod section to increase hardness; welding the mating ends of the first and second rod sections to provide a first drill rod having a joint section adjacent the mating ends; heat treating the joint section of the first drill rod to reduce elevated hardness caused by the welding; providing a third rod section including a mating end; providing a fourth rod section including a free end, a mating end, an interior passage, and an internally threaded portion within the interior passage of the fourth rod section adjacent the free end thereof; heat treating the internally threaded portion of the fourth rod section to increase hardness; welding the mating ends of the third and fourth rod sections to provide a second drill rod having a joint section adjacent the mating ends; heat treating the joint section of the second drill rod to reduce elevated hardness caused by the welding; and connecting the first drill rod to the second drill rod by threading the externally threaded portion of the first drill rod into the internally threaded portion of the second drill rod.

27. The method of claim 26, wherein the heat treatment of the externally threaded portion of the first rod section occurs prior to the welding of the mating ends of the first and second rod sections and the heat treatment of the internally threaded portion of the fourth rod section occurs prior to the welding of the mating ends of the third and fourth rod sections.

28. The method of claim 26, wherein the weld of the mating ends of the first drill rod and the weld of the mating ends of the second drill rod are friction welds.

29. The method of claim 26, wherein the free end of the first rod section of the first drill rod includes an annular face, and wherein the interior passage of the second rod section of the second drill rod includes a mating shoulder adjacent the internally threaded portion, wherein connecting the drill rods includes threading the first drill rod into the second drill rod until the surface of the annular face of the first drill rod abuts against the mating shoulder of the second drill rod.

30. The method of claim 29, wherein the interior passage of the second rod section of the second drill rod includes an undercut adjacent to the mating shoulder to provide clearance for the annular face to fully contact the mating shoulder.

31. The method of claim 29, further comprising heat treating the annular face to increase hardness prior to the welding of the mating ends of the first and second rod sections and heat treating the mating shoulder to increase hardness prior to the welding of the mating ends of the third and fourth rod sections.

32. The method of claim 31, wherein the heat treatment of the annular face is induction hardening, and wherein the heat treatment of the mating shoulder is selective carburization.

33. The method of claim 26, wherein the heat treatment hardens the externally threaded portion and the internally threaded portion to at least R_e 50.

34. The method of claim 33, wherein the heat treatment hardens the externally threaded portion and the internally threaded portion to within R_e 55 and R_e 60.

35. The method of claim 26, wherein the heat treatment reduces the hardness of the joint sections within Rς 30 and R_e 42.

36. The method of claim 26, wherein the heat treatment of the externally threaded portion is induction hardening.

37. The method of claim 26, wherein the heat treatment of the internally threaded portion is selective carburization.

38. The method of claim 26, wherein the heat treatments of the joint sections of the drill rods are induction heating tempering processes.