Note: Descriptions are shown in the official language in which they were submitted.
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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
reds are conventionally connected end to end by thre$ds
which allow rods to be screwed together (and unscrewed) to
form a drill string which may consist of a large number of
connected rods.
Hackgrou d to t a Zavex~,t~.vn
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 tracking 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 paint, in
particular to minimise stress build up at the bottom of
the female threads.
Suamiar~r of the. Iaveatioa
According to a first aspect of the invention, there is
provided a tube rod for percussion rock drilling 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
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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
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 df the second diameter only in a region surrounding
the bottom of the threaded end which is where the major
ZO 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 sad sad
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 bare 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
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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 major part of the tube rod length down
to this region of leader internal diameter. The internal
diameter of the tube rod can also taper from the female
threaded end down to this region of lesser internal
diameter.
The female threaded end can have an internal shoulder at
right angles to the tube axis, with the internal diameter
of the tube rod tapering.down from 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 z~egion of lesser diameter of the internal bore
pz~efezably 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 oonstant 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 from an
annular shoulder, the shoulder being adapted to abut
against the end of the female threaded end of another rod
when the two rode are screwed together. The male threaded
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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.
The annular shoulder can be stepped and the mating end of
a female threaded end aecti.on of another rod can have a
shoulder such that when the rode are screwed together, the
shoulders interengage to prevent substantial radial
movement of one shoulder relative to the other. This
helps to prevent relative radial movement at the shoulder
which in turn helps to reduce bending of the asaemb~.ed
string of rods.
This feature can represent an independent invention, and
thus according to a second aspect of the invention, there
is provided a tube rod assembly far perCUSSion rock
drilling, the assembly including a plurality of rods
connected end to end by joints comprising interengaging
male and female Ghzeada wherein when the joints are
assembled, an end of a female threaded compozzent is in
contact with an external shoulder on the adjacent male
threaded component, the external shoulder hava.ng a
ciz~cumferentially extending stepped land, with part of the
end of the female threaded component fitting around the
land to hinder relative radial movement between the two
ends at the position of the shoulder.
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
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stresses arising at the thread and internal profile of the
female threaded part so that the stresses at these
critical regions are reduced.
According to a third aspect of the invention, there is
pro~rided 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 fourth 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 internal
diameter of the rod tapering into the neck from both aides
of the neck.
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The invention also extends to a female threaded tube rod
end for j oining to a length of tube tv contribute to the
formation of a tube rod as set forth above.
Hrief Descziptioa of the Drawings
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;
Figure 3 is a cross section through the male
threaded end;
Figure 4 is a cross-section through an alternative
male threaded end:
Figures 5 and 6 are cross-sections through two
alternative female threaded ends: and
Figure 7 shows a second embodiment of tube rod in
accordance with the invention.
Detailed Deaeri~ation of Preferred 8~nbodiments
Figure 1 shows a rod which has a central section 7.0, a
female threaded end section 12 and a male threaded end
section 14. The central section 10 will typically be 1.5
to 2 metres in length (but can be up tv 6 metres long),
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whilst the male and female threaded end sections will
typically each have a length of about 25o millimetres.
The central section l0 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 to at 16 and
18. This welding can appropriately be achieved through a
friction welding process.
The female threaded end section 12 shown in Figure 2 will
normally be machined from solid material. Suitable steels
are a 3% NiCrMo grade steel or a 3% CrMo grade steel. The
section 12 has an internally threaded end 2o, and a tube
end 22 which is to be welded to the centre section to at
1B. The external and internal diameters of the section 12
at the tube end 2z will be substantially the same as those
of the centre section lo.
The end 2o of the section has an abutment shoulder 24, a
mouth 26 into which the male threaded end of another rod
will be introduced, a threaded region 28 and a relieved
region 3o at the inner end of the thread section.
Figure 2 does not illustzate 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/pereussion rock drilling. The root diametez~ of
this thread will be substantially the same as that of the
relieved portion 30.
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Beyond the relie~red portion 30, the wall thicknesB of the
section 12 becomes thicker and as a result the internal
bore diameter becomes less. The bore has a narxow neck at
32, and a tapered transition at 34 from the relieved
portion 30 to the neck, and a further comically 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 (see Figure 6).
The external surface of the female portion has a diameter
i.n the region 38 which can be the same as that of the
central portion 10 or can be larger. The diameter at the
end portion 4o is slightly larger than that of the central
portion, for example 2% - 6~ larger, and When the diameter
at the region 38 is larger than the central portion, it
can also be 2 - 6% 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 z4
can be radiused, rather than the sharp edge shown. It
will seen from Figure 2 that the base of the groove lies
in a cross-sectional plane which incorporates the neck 32.
The radius of the base part of this groove 42 can, for
example, be 22.5 millimetres. Between the groove 42 and
the neck 32 the female threaded section 7.2 has a greater
wall thickness than at any other region of its length.
The male threaded end section 7.4 (see Figure 3) has a
threaded boss 44 extending from an unthreaded collar 46.
The diameter of the collar 46 ~.s the same as that of the
female end (the second diameter) so that when the male end
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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 first 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 he.nd end of the portion 14 (as seen in Figure: 3)
has a tube end 5o which will match the tube end 22 of the
female threaded portion and will match the cross section
of the central section 10.
The section has a through bore 52. The threaded portion
~4 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 54 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 S8 of the female end.
In Figures 4 to 7, the same reference numerals are used
where they denote parts which are directly equivalent to
parts described with reference to Figures 1 to 3.
Figure 4 shows a male threaded end section 114 which
differs from the section shown in Figure 3 by the
introduction of a land 155 which engages, when the rods
are screwed together, inside the mouth 26 of the adjacent
female threaded end section, and forms a close fit in that
mouth so as to prevent any significant radial mo~rement
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between the shoulders 24 and 54_ This minimises any
tendency to bending in the assembled drill rod string.
Figure 5 shows an embodiment where both the neck 132 and
the groove 142 are elongated as compared with the
embodiment shown in Figure 2. This assists in reducing the
stress level at the inner end of the threaded region 28,
particularly in the part of the threaded zegion closest to
the neck 132.
Figure 6 shows an embodiment similar to that of Figure 2,
but where the tapered transition 34 is replaced by a
radiused transition 234.
The relationship
between the
various parameters
can be as
follows, where:
A represents the external diameter of the central
section to
E represents the maximum extet~nal diameterof the
female threaded end section 14
C represents minimum external diameter of the
female threaded end section 7.4 (at the groove
42)
D repreaez~ts the smallest internal diameterof the
threaded section 14 (at the throat 32)
S represents the cure diameter of the female
thread 28.
The following relationships hold good for rods in
accordance with the invention:
A is less than 8
B is up to 15o~ of E
C is loo - 130 of E
D is 4S - 60~ of E.
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In addition to the features described above which reduce
the susceptibility of the rod tv stress cracking, the
external surface of the rod can be provided with external
helically fluted portions 60, 6z (Figure ~). These fluted
portions help to enhance the straightness of holes being
drilled, by maintaining some contact with the walls of the
hole while allowing flow of drilling fluid and drilling
debris past the rod up the hole. The rod is thus held
straight in the hole, so that the drill bit is always
presented to the rock ahead in the correct orientation_
There may be one (60) or two (60,62) of these fluted
portions on each rod.
It has suzprisingly 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 and internal
recess of the threaded region 28.
This resistance to failure is enhanced by the increased
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.
