GB2340148A

GB2340148A - Tube rod

Info

Publication number: GB2340148A
Application number: GB9816494A
Authority: GB
Inventors: Nigel Roberts; James Yao
Original assignee: Boart Longyear Pty Ltd
Current assignee: Boart Longyear Pty Ltd
Priority date: 1998-07-30
Filing date: 1998-07-30
Publication date: 2000-02-16
Anticipated expiration: 2018-07-30
Also published as: GB2340148B; CA2278987A1; ATE258645T1; EP0979922B1; GB9816494D0; EP0979922A3; EP0979922A2

Abstract

A tube rod for rock drilling has a female threaded end (12) into which a male thread (either on a male connector or on the end of another tube rod) can be screwed to form part of a drill string. The female threaded end (12) is (a) of larger external diameter than the central section (10) of the rod and (b) has an annular groove (42%) with an asymmetrical profile, the flank of this groove nearest to the threaded end being steeper than the other flank. <IMAGE>

Description

2340148 Tube Rod This invention relates to a tube rod for rotary/

percussive rock drilling, and in particular to the way two tube rods are connected one to the other by threads. Tube rods are conventionally connected end to end by threads which allow rods to be screwed together (and unscrewed) to form a drill string which may consist of a large number of connected rods.

Tube rods, and drill strings made up from tube rods, operate in a harsh environment. Considerable stresses are built up in the rods, and these usually manifest themselves in cracking of the rods in the area of the threaded joints. This cracking usually leads to failure of the respective rod. It is therefore desirable to design the threaded ends of the rods in a way which will minimise stress build up at any particular point, in particular to minimise stress build up at the bottom of the female threads.

According to the invention, there is provided a tube rod having threaded ends, at least one of the ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and at least part of the or each female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, wherein between the female threaded end and the major part of the tube rod length there is an annular groove having a root diameter (the third diameter) which is less than both the first and the second diameter.

The groove preferably has an asymmetrical profile when seen in cross section parallel to the tube axis, and the SP2201.A2 29 July, '1998 flank nearest the threaded end is preferably steeper than the opposite flank.

The adoption of these features has been shown to result in a reduction in stress build up at the bottom of the female threaded end.

It is preferred for the female end to be of the second diameter from its end up to the annular groove. However it is within the scope of the invention for the female end to be of the second diameter only in a region surrounding the bottom of the threaded end which is where the major stress concentration occurs, or for the female end to be of the second diameter on both sides of the annular groove.

In most cases, the rod will have one male threaded end and one female threaded end. However rods with two female threaded ends are conceivable, to be joined end to end by a tubular connector with two male threaded ends.

The hollow bore of the rod is preferably reduced in internal diameter at the inner end of the female threaded socket to form a neck, and the bore diameter tapers outwards from the neck to the full bore diameter of the major part of the tube rod length.

The internal diameter of the rod can have a region between the female threaded end and the major part of the tube rod length where the internal diameter is less than at either side of this region. The internal diameter of the tube rod can taper from the ma3cr part of the tube rod length down to this region of lesser internal diameter. The internal diameter of the tube rod can also taper from the female 3S threaded end down to this region of lesser internal diameter.

SP2201.A2 29 July, 1998 The f emale threaded end can have an internal shoulder at right angles to the tube axis, with the internal diameter of the tube rod tapering down f rom the shoulder to the region of lesser internal diameter. The taper of the internal diameter can be a conical taper but is preferably a radiused taper.

The neck or region of lesser diameter of the internal bore preferably lies on substantially the same cross-section of the rod as the third (external) diameter of the rod. Preferably the third (external) diameter of the rod lies on a cross-section of the rod which is offset from the centre of the neck or region of lesser diameter in the direction towards the major part of the tube rod length.

The threaded ends can be initially separate from the rod and can be joined to a length of constant cross section tube by friction welded joints, the length of constant cross section forming the major part of the tube rod length. This is a particularly expedient method of manufacturing which allows standard tube stock to be used for the major part of the rod, with only the ends requiring machining.

The threaded region of the male end can extend f rom an annular shoulder, the shoulder being adapted to abut against the end of the female threaded end of another rod when the two rods are screwed together. The male threaded region is preferably shorter than the female threaded recess so that when the male threaded end is screwed into the female threaded end of another rod until the shoulder abuts the end of the other rod, the male end does not reach the bottom of the female recess. This helps to avoid tensile pre-loading of the joint.

SP2201.A2 29 July, 1998 4 All the features set out above, either alone or in combination, increase the resistance of the tube rod to cracking, especially cracking at the last thread root at the female end. The addition of the tapered internal bore, the increased outside diameter at the thread portion and the external groove all contribute to dispersing the stresses arising at the thread root of the female threaded part so that the stress at this critical point is reduced.

According to a second aspect of the invention, there is provided a tube rod having threaded ends, at least one of the ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and the or each female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, wherein between the female threaded end and the major part of the tube rod length there is an annular groove having a root diameter (the third diameter) which is less than both the first and the second diameter, and the internal diameter of the rod having a reduced diameter neck, the narrowest part of which coincides with the location of the third diameter.

According to a third aspect of the invention, there is provided a tube rod having threaded ends, at least one of the ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and the or each 30 female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, wherein between the female threaded end and the major part of the tube rod length there is an annular groove having a root diameter (the third diameter) which is less than both the 35 first and the second diameter, and the internal diameter of the rod having a reduced diameter neck, the internal SP2201.A2 29 July, 1998 diameter of the rod tapering into the neck from both sides of the neck.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a tube rod in accordance with the invention, with the central section foreshortened; Figure 2 is a cross section through the female threaded end; and Figure 3 is a cross section through the male threaded end.

Figure 1 shows a rod which has a central section 10, a female threaded end 12 and a male threaded end 14. The central section 10 will typically be 1.5 to 2 metres in length (but can be up to 6 metres long), whilst the male and female threaded ends will typically each have a length of about 250 millimetres.

The central section 10 is a tube having a constant cross section over its length. Typically the outside diameter will be about 80 to 90 millimetres, and the inside diameter about 65 to 75 millimetres, leaving a wall thickness of about 15 millimetres.

The end sections 12 and 14, both of which have a through bore, will be welded to the centre section 10 at 16 and 18. This welding can appropriately be achieved through a friction welding process.

SP2201.A2 29 July, 1998 The female threaded end section 12 shown in Figure 2 will be machined from solid material. Suitable steels are a 3% NiCrMo grade steel or a 3% CrMo grade steel. The section 12 has a threaded end 20, and a tube end 22 which is to be welded to the centre section 10 at 18. The external and internal diameters of the section 12 at the tube end 22 will be substantially the same as those of the centre section 10.

The other end of the section has an abutment shoulder 24, a mouth 26 into which the male threaded end of another rod w'11 i be introduced, a threaded region 28 and a relieved region 30 at the inner end of the thread section.

Figure 2 does not illustrate the thread which will be formed on the inner walls of the region 28. This thread will be a double start trapezoidal thread, of the type well known in connecting tube rods for use in rotary/percussion rock drilling. The root diameter of this thread will be substantially the same as that of the relieved portion 30.

Beyond the relieved portion 30, the wall thickness of the section 12 becomes thicker and as a result the internal bore diameter becomes less. The bore has a narrow neck at 32, and a tapered transition at 34 from the relieved portion 30 to the neck, and a further conically tapered portion 36 from the neck to the tube end 22. The tapered transition 34 is shown in the form of a conical taper, but may alternatively be a radiused taper.

The external surface of the female portion has a diameter in the region 38 which can be the same as that of the central portion 10 or can be larger. The diameter at the 35 end portion 40 is slightly larger than that of the central portion, for example 2% - 3% larger, and when the diameter SP2201.A2 29 July, 1998 at the region 38 is larger than the central portion, it can also be 2 - 355 larger.

Between the first diameter and the second diameter area regions, there is an annular groove 42 which has a root diameter substantially less than either the first or the second diameters. This groove is bounded by a smooth curve, one flank of which closest to the end 24 is steeper than the other flank. Although not shown in this figure, the transition between the steep flank and the surface 24 can be radiused, rather than the sharp edge shown. it will seen from Figure 2 that the root of the flank lies generally in a cross-sectional plane which incorporates the neck 32. The radius of the base part of this groove 42 can, for example, be 12.5 millimetres. The area of the female threaded portion between the groove 42 and the neck 32 has a greater wall thickness than any other region of the female end portion.

The male threaded portion 14 has a threaded boss 44 extending from an unthreaded collar 46. The diameter of the collar 46 is the same as that of the female end (the second diameter) so that when the male end is screwed into a female end, there is no step in the external diameter at the joint. However the male end could be of the f irst diameter and/or could have a diameter ramp at the end to blend into the external diameter of the female end without a step.

The collar 46 has externally a flat at 48 on which serial numbers or other information can be stamped.

The right hand end of the portion 14 (as seen in Figure 3) has a tube end 50 which will match the tube end 22 of the female threaded portion and will match the cross section of the central section 10.

sp2201.A2 29 July, 1998 The section has a through bore 52. The threaded portion 44 will have external threads to match the internal threads 28.

In use, the male end 14 of one rod is screwed into the female end 12 of another rod. The two are screwed together until the shoulder S4 of one male end comes into contact with the shoulder 24 of the female end. There is no contact between the extreme end 56 of the male end and the internal shoulder 58 of the female end.

It has surprisingly been found that the formation of the annular groove 42 helps to reduce stress concentrations in the female threaded end, these concentrations otherwise arising in the area of the last thread root of the threaded region 28.

This resistance to failure is enhanced by the increased 20 diameter of the region 40 and by the internal tapered surfaces at 34 and 36.

These measures cause a dispersion of the overall stress so that the stress of the critical point is reduced.

SP2201.A2 29 July, 1998 9

Claims

Claims

A tube rod having threaded ends, at least one of the ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and at least part of the or each female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, and an annular groove between the female threaded end and the major part of the tube rod length, the annular groove having a root diameter (the third diameter) which is less than both the first and the second diameter.
2. A tube rod as claimed in Claim 1, wherein the groove has an asymmetrical profile when seen in cross section parallel to the tube axis.
3. A tube rod as claimed in Claim 2, wherein the flank of the groove nearest to the threaded end is steeper than the opposite flank.
4. A tube rod as claimed in any preceding claim, wherein one of the ends has a f emale thread and the other end has a male thread.
5. A tube rod as claimed in any, wherein the hollow bore of the rod is reduced in internal diameter at the inner end of the f emale thread to form a neck, and the bore diameter tapers outwards from the neck to the full bore diameter of the major part of the tube rod length.
6. A tube rod as claimed in any one of Claims 1 to 5, wherein the internal diameter of the rod has a region between the female threaded end and the major part of the tube rod length where the internal diameter is less than at either side of this region.

SP2201.A2 29 July, 1998 -
7. A tube rod as claimed in Claim 6, wherein the internal diameter of the tube rod tapers from the major part of the tube rod length down to the region of lesser internal diameter.
8. A tube rod as claimed in Claim 6 or Claim 7, wherein the internal diameter of the tube rod tapers from the female threaded end down to the region of lesser internal diameter.
9. A tube rod as claimed in any one of Claims 5 to 7, wherein the female threaded end has a shoulder at right angles to the tube axis, and the internal tube bore tapers from the shoulder down to the region of lesser internal diameter.
10. A tube rod as claimed in any one of Claims 7 to 9, wherein the taper of the internal diameter is a conical taper.
11. A tube rod as claimed in any one of Claims 5 to 10, wherein the neck or region of lesser diameter of the internal bore lies on substantially the same cross-section of the rod as the third (external) diameter of the rod.
12. A tube rod as claimed in Claim 11, wherein the third (external) diameter of the rod lies on a cross-section of the rod which is of f set f rom the centre of the neck or region of lesser diameter in the direction towards the major part of the tube rod length.
13. A tube rod as claimed in any preceding claim, wherein the threaded ends are initially separate from the rod and are joined to a length of constant cross section tube by SP2201.A2 29 July, 1998 friction welded joints, the length of constant cross section forming the major part of the tube rod length.
14. A tube rod as claimed in any preceding claim, wherein the male threaded end has a threaded region extending from an annular shoulder, the shoulder being adapted to abut against the end of the female threaded end of another rod when the two rods are screwed together, the male threaded region being shorter than the female threaded recess so that when the male threaded end is screwed into the female threaded end of another rod until the shoulder abuts the end of the other rod, the male end does not reach the bottom of the female recess.
15. A tube rod having threaded ends, at least one of the ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and the or each female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, wherein between the female threaded end and the major part of the tube rod length there is an annular groove having a root diameter (the third diameter) which is less than both the first and the second diameter, and the internal diameter of the rod having a reduced diameter neck, the narrowest part of which coincides with the location of the third diameter.
16. A tube rod having threaded ends, at least one of the 30 ends having a female thread, the major part of the tube rod length between the threaded ends having an outside diameter (the first diameter) and the or each female threaded end having an outside diameter (the second diameter) which is larger than the first diameter, wherein 35 between the female threaded end and the major part of the tube rod length there is an annular groove having a root SP2201.A2 29 July, 1998 12 - diameter (the third diameter) which is less than both the first and the second diameter, and the internal diameter of the rod having a reduced diameter neck, the internal diameter of the rod tapering into the neck from both sides 5 of the neck.
17. A tube rod substantially as herein described with reference to the accompanying drawings.

SP2201.A2 29 Julv, 1998