Note: Descriptions are shown in the official language in which they were submitted.
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Drill String Rod with Guidance Shoulder
15
Field of invention
The present invention relates to a drill string rod and a rod assembly to form
part of a drill
string having male and female ends separated by a main length section and in
particular,
although not exclusively, to a rod having an axially elongate shoulder
configured to
facilitate straight drilling and extraction of the bit end of the drill
string.
Background art
Percussion drilling is used to create a long borehole via a plurality of
elongate drill string
rods coupled together end-to-end by interconnected male and female threaded
ends. The
well-established technique breaks rock by hammering impacts transferred from
the rock
drill bit, mounted at one end of the drill string, to the rock at the bottom
of the borehole.
Typically, the energy required to break the rock is generated by a
hydraulically driven
piston that contacts the end of the drill string (via a shank adaptor) to
create a stress (or
shock) wave that propagates through the drill string and ultimately to the
base rock level.
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Conventional male and female threaded couplings are described in US 4,332,502;
US
4,398,756; US 1,926,925; US 5,169,183; EP 1705415; GB 2321073; US 4,076,436;
US
6,030,004; CA 2634557 and US 4,687,368.
When the male and female threaded ends of neighbouring rods are coupled to
create the
drill string, the joint is typically subjected to bending forces during
drilling. These bending
moments fatigue the coupling and lead to breakage within the threaded portion
of the joint.
Additionally, there is a further risk that the drill bit, attached to the
lowermost drill rod is
subject to lateral deviation when drilling and becoming jammed in the borehole
when the
drill string is extracted. Drill bit deviation during initial boring
(typically referred to as
collaring) is also problematic with conventional arrangements. Attempts have
been made
to address such problems via the interconnection of a 'coupler' located
between the drill
bit and the lowermost rod. Such couplers are typically stiffer than the rods
and are
intended to be resistant to bending so that the drill bit travels faster and
straighter during
drilling. Example additional guidance couplers are described in WO 00/65192;
US
4,874,045; EP 0192622; CA 2550801 and US 2002/0050362. However, conventional
and
additional intermediate couplers are disadvantageous for a number of reasons.
In
particular, it is not uncommon for these additional pieces to be misplaced
during use.
Additionally, due to the inclusion of additional threaded connections, the
efficiency of the
shockwave transmission to the drill bit is reduced whilst stress in the entire
drill string as a
whole is increased. There is therefore a need for a drill rod and a drill rod
assembly that
addresses these problems.
Summary of the Invention
It is an objective of the present invention to provide a drill rod connectable
to neighbouring
drill rods and a drill bit that exhibits improved guidance via a shoulder
driven percussion
drilling system. In particular, it is an objective to provide a rod provided
with a male and a
female end in which the male end is configured to form an extension of the
drill bit to
achieve straighter and faster drilling and in particular improved collaring.
It is a further
specific objective to prevent or reduce the likelihood of the drill bit
becoming jammed in
the bore hole when the drill string is extracted.
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The objectives are achieved by a drill rod having a main length section
provided with male
and female ends in which the male end is provided with an axially extended
guidance
collar or shoulder. The elongate shoulder is formed as a radially flared
extension of the
main length section to provide a stiffer threaded joint section suitable for
coupling to
female ends of adjacent rods and in particular a female threaded sleeve of a
drill bit. The
present dill rod is also particularly suitable for drilling relative small
bore holes typically of
a size approximately 54mm and less.
The guidance shoulder of the male end of the present drill rod comprises an
axial length
that is greater than an outside diameter of the shoulder. That is, the
guidance shoulder is
flared radially outward relative to the main length section but also extends
axially over a
greater distance relative to conventional shoulder driven rods so as to form
an elongate
axial extension of the drill bit. In particular, the outside diameter of the
shoulder is equal
to or approximately equal to the outside diameter of an axially rearward
mounting sleeve
of the drill bit such that the shoulder of the rod and the rearward portion of
the drill bit are
interconnected to provide a single elongate cylindrical section having an
outside diameter
that is greater than the main length section of the rod. Such a configuration
is effective to
provide both the shoulder driven characteristic for percussion drilling and a
system that is
stiffer and comprises a potential deviation angle that is less than existing
assemblies.
Reference within this specification to the deviation angle encompass the angle
by which
the drill bit may rotate about its axis to the point where the cutting head
end of the bit
and/or an axially rearwardmost part of the shoulder contact the inward facing
surface of the
borehole.
According to a first aspect of the present invention there is provided a drill
string rod to
form part of a drill string, the rod comprising: a hollow elongate main length
section
extending axially between a male end and a female end; the male end comprising
a spigot
having a threaded section projecting axially from a shoulder that axially
separates the
spigot and the main length section, the shoulder having an outside diameter
that is greater
than an outside diameter of the main length section; characterised in that: an
axial length of
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the shoulder over which the greater outside diameter extends is greater than
the outside
diameter of the shoulder.
The present shoulder configuration at the male end is applied to a drill rod
in contrast to a
third component of a drill string system, typically referred to as a 'guide
tube' positioned at
the bit end of the drill string axially intermediate the drill bit and the
endmost drill rod.
The present drill rod is advantageous to avoid the need for an additional
guide tube that
may be misplaced or damaged during use thereby preventing continued drilling.
The
present arrangement, being applied to a drill rod is advantageous to provide
improved
insertion and extraction at the drill bit at the borehole by increasing the
collective stiffness
of the drill string via the multiple male end sections present at each of the
interconnected
drill rods.
Preferably, an axial length of each elongate shoulder is less than an axial
length of each
main length section of each drill rod. The term 'main length section' may be
defined as the
axial distance between one axial end of the shoulder furthest from the spigot
and one axial
end of the sleeve (at the female end) furthest from the endmost annular face
of the female
end. That is, the main length section corresponds to the axial section of the
drill rod
between the radially enlarged shoulder and the radially enlarged female end.
Preferably, the shoulder comprises an axial length that is 5 to 40, 5 to 30, 5
to 20, 5 to 15, 7
to 13, 8 to 13 or 9 to 12% of an axial length of the main length section as
defined between
the axially inner ends of the shoulder and the radially enlarged female
sleeve.
Preferably, the outside diameter of the shoulder is a maximum outside diameter
of the rod.
Preferably the outside diameter of the shoulder is slightly less than the
maximum outside
diameter of a drill bit head to assist with guiding the driven rotation during
advancement of
the drill bit into the rock.
Preferably, the maximum outside diameter of the rod at the shoulder is uniform
or
approximately uniform over the axial length of the shoulder. Such a
configuration is
configured to be consistent with an axially rearward female cylindrical
mounting sleeve
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provided at an axially rearward end of the drill bit such that the combined
shoulder and
drill bit sleeve form a single cylindrical section of uniform outside
diameter.
Preferably, the female end comprises a sleeve portion having an internal
threaded section
to cooperate with the threaded section of the spigot of a further drill rod of
the drill string,
an outside diameter of the sleeve portion being greater than the outside
diameter of the
main length section. Preferably, the outside diameter of the shoulder is equal
to or
approximately equal to the outside diameter of the sleeve portion. However,
according to
further specific implementations, an outside diameter of the female sleeve may
be less than
the outside diameter of the shoulder. However, a configuration with equal
outside
diameters facilitates rod guidance to achieve straighter holes and extraction
of the drill
string from the bore.
Preferably, the spigot extends axially from an annular end surface of the
shoulder, an axial
length of the spigot configured such that the annular end surface of the
shoulder is capable
of abutting an annular end surface of the female end of a neighbouring rod of
the drill
string. Preferably the spigot is divided axially into a threaded section that
represents an
endmost part of the spigot and a non-threaded shank that is positioned axially
intermediate
the threaded end section and the annular end surface of the shoulder.
Preferably an outside
diameter of the shank is flared radially outward at the junction with the
annular end surface
of the shoulder to reduce stress concentrations and any lateral bending of the
spigot relative
to the shoulder. Optionally, an axial length of the spigot is less than or
equal to the axial
length of the shoulder.
Optionally, an outside diameter of the spigot is equal to or less than the
outside diameter of
the main length section along a full axial length of the spigot. Such a
configuration
provides an annular end surface at the shoulder configured to abut an annular
end surface
of a drill bit to achieve the desired shoulder contact coupled configuration.
Preferably, the rod comprises an internal bore extending axially through the
main length
section and the spigot, the internal bore being of uniform internal diameter
along a full
axial length of the main length section and the spigot. The uniform internal
diameter
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provides the desired control of the pressure of a flushing fluid delivered
internally through
the rod to the drill bit.
Preferably, the threaded section of the spigot comprises at least one axially
extending
helical ridge and trough wherein the outside diameter along the threaded
section at radial
positions of the ridge and trough is uniform over a full axial length of the
threaded section.
Preferably, the threaded section comprises two helical turns extending axially
over the
spigot configured to mate with corresponding thread turns provided internally
within a
mounting sleeve of the drill bit and/or the internally threaded female end of
neighbouring
drill rods.
Optionally, the rod may comprise a transition section positioned axially at a
junction of the
main length section and the shoulder; wherein an outside diameter at the
transition section
changes according to at least one radius of curvature. Optionally, an outside
diameter at
the transition section decreases radially according to a first radius of
curvature from the
main length section to an intermediate section and the outside diameter
increases radially
according to a second radius of curvature from the intermediate section to the
shoulder.
According to a second aspect of the present invention there is provided a
drill rod assembly
to form part of a drill string, the assembly comprising: a drill rod as
claimed herein; a drill
bit releasably attachable to the male end of the drill rod; the drill bit
having an axially
forward cutting head and an axially rearward mounting sleeve to attach to the
male end of
the drill rod; wherein an outside diameter of the mounting sleeve is equal to
or
approximately equal to the outside diameter of the shoulder.
Preferably, the outside diameter of the mounting sleeve is uniform or
approximately
uniform over an axial length of the mounting sleeve being defined between a
rearwardmost
end of the drill bit and an axially forwardmost end of the mounting sleeve at
which region
the outside diameter of the mounting sleeve increases to form a junction with
the cutting
head. The shoulder and mounting sleeve of the drill bit collectively define a
single
cylindrical section of constant outside diameter being slightly less than a
maximum outside
diameter of the drill bit head positioned axially forward of the mounting
sleeve and the
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shoulder. Such a configuration is advantageous to achieve the desired pressure
between
the external surface of the rod and drill bit (at the region of the male end
of the rod) and the
internal facing surface of the bore to facilitate rearward flushing of
material.
Optionally, the axial length of the shoulder is approximately equal to or less
than an axial
length of the mounting sleeve. Such a configuration reduces the deviation
angle by which
the drill bit may be deflected laterally including perpendicular to the
longitudinal axis of
the drill rod to achieve straighter holes and better collaring.
Brief description of drawings
A specific implementation of the present invention will now be described, by
way of
example only, and with reference to the accompanying drawings in which:
Figure 1 is an external perspective view of a drill string rod coupled to a
percussion drill
bit according to a specific implementation of the present invention;
Figure 2 is a cross sectional view through the drill rod and bit assembly of
figure 1;
Figure 3 is a perspective view of a male end of the drill rod of figure 2;
Figure 4 is a further perspective view of the male end of the drill rod of
figure 2;
Figure 5 is a perspective view of the male of the drill rod of figure 2
coupled to the drill bit
of figure 1 and 2;
Figure 6 is a cross section through the male end and drill bit of figure 5.
Detailed description of preferred embodiment of the invention
Referring to figures 1 and 2, a percussion drill rod 100 comprises an axially
extending
main length section 101 that is terminated at a first end by a male end
indicated generally
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by reference 103 and at a second opposite end by a female end indicated
generally by
reference 102. Rod 100 is capable of being coupled end-to-end with adjacent
rods to form
a drill string. Male end 103 comprises a shoulder 110 that projects radially
outward
relative to main length section 101 and is formed as a cylindrical section
extending over an
axial distance being a fraction of the length of main length section 101.
Similarly, female
end 102 comprises a cylindrical sleeve section 111 having a length
approximately equal to
the axial length of shoulder 110. According to the specific implementation, an
outside
diameter of shoulder 110 and female sleeve 111 are approximately equal. A
respective
transition section 107 extends axially between main length section 101 and the
respective
shoulder 110 and female sleeve 111. Each transition section 107 comprises an
axial length
being slightly less than the axial length of shoulder 110 and female sleeve
111.
Additionally, an outside diameter of each transition section 107 is less than
the outside
diameter of main length section 101 as described in further detail referring
to figure 4.
Figure 1 illustrates drill rod 100 releasably coupled to a drill bit indicated
generally by
reference 112 of conventional configuration. Drill bit 112 comprises an
axially
forwardmost drill head 105 that mounts a plurality of wear resistant cutting
buttons 106
projecting axially forward from head 105. A mounting sleeve 104 extends
axially
rearward from head 105 and comprises an internal threaded cavity to receive a
male part of
male end 103. In particular, and referring to figure 2, male end 103 comprises
a spigot 204
that projects axially forward from shoulder 110 and in particular an annular
abutment
surface 108 that represents a forwardmost end of shoulder 110. Abutment
surface 108 is
positioned in contact with an annular endmost contact surface 109 of drill bit
sleeve 104.
According to the specific configuration, an axial length of spigot 204 is less
than a
corresponding axial length or depth of a cavity within bit sleeve 104 such
that the present
drill rod 100 is configured as a shoulder contact or shoulder driven rod.
Accordingly, the
shockwave generated by the surface piston is translated through mated surfaces
108, 109
from rod 101 into drill bit 112. In particular and referring to figures 3 and
6, an annular
endmost surface 303 of spigot 204 is separated axially from the innermost end
600 of the
internal cavity within bit sleeve 104 to provide the shoulder contact
configuration. As
detailed in figure 6, releasable mating of rod 100 and bit 112 is achieved by
cooperating
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screw threads 301, 302 projecting radially at spigot 204 and threads 601
projecting radially
within the internal facing surface of the bit sleeve cavity.
Referring to figure 2, the female end 102 of rod 100 comprises an internal
cavity 200
extending axially within sleeve 111 from an axially rearward end surface 202.
End surface
202 of a first rod is configured to contact the shoulder abutment surface 108
of the male
end 103 of a second rod when multiple drill rods 100 are coupled together end-
to-end to
form the drill string. Screw threads 201 are provided at the internal facing
surface of
sleeve cavity 200 and are configured to cooperate with the spigot threads 301,
302 of a
neighbouring rod 100. An internal bore 203 extends axially through rod 100 and
in
particular axially from female cavity 200 to the annular end surface 303 of
spigot 204.
According to the specific implementation, bore 203 comprises an internal
diameter that is
substantially uniform over its entire axial length between the male 103 and
female 102
ends.
Referring to figure 3 spigot 204 projects axially from the annular abutment
surface 108 that
extends substantially perpendicular to the cylindrical external surface at
shoulder 110.
Spigot 204 may be considered to be divided axially into threaded section 301,
302 and a
non-threaded shank 300 that is positioned axially intermediate threaded
section 301, 302
and shoulder 110. Shank 300 is flared radially outward relative to a
longitudinal axis 305
of rod 100 at the junction 304 with annular abutment surface 108 such that the
external
surface of the shank 300 at the shoulder junction 304 increases according to a
radius of
curvature.
The threaded section of spigot 204 comprises a pair of helical ridges 302 that
define axially
intermediate troughs 301 extending between shank 300 and the annular spigot
end surface
303. Referring to figure 4, an axial length LB of spigot 204 including shank
300 and
threaded section 301, 302 is less than an axial length LA of shoulder 110.
Shoulder length
LA is defined axially between annular abutment surface 108 (aligned
perpendicular to axis
305) and an axially rearwardmost part of shoulder 110 at which the outside
diameter of rod
100 decreases and is no longer uniform in the axially rearward direction from
annular
abutment surface 108. In particular, the rearward end of shoulder 110 is
terminated by
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transition section 107. According to specific implementations, the axial
length LB may be
in the range 60 to 100% or 75 to 85% of the axial length LA.
Section 107 may be considered to be divided into three axial regions including
a first
region 401 bordering main length section 101, a second region 402 bordering
the rearward
end of shoulder 110 and an intermediate region 400 positioned axially
intermediate the
first and second regions 401, 402. An outside diameter of rod 100 at the first
transition
region 401 decreases radially according to a first radius of curvature
(relative to main
length section 101). The outside diameter of rod 100 is substantially uniform
over
intermediate region 400 and then increases radially according to a second
radius of
curvature at second region 402. Accordingly, the outside diameter of rod 100
at transition
section 107 is formed as an axially broad groove or slight depression
positioned axially
between main length section 101 and shoulder 110. The radially curved
transition 304
minimises stress concentrations at the junction of spigot 204 and shoulder
110.
Additionally, the radius of curvature at second transition region 402
minimises stress
concentrations at the axially rearward end of the shoulder 110 and the
junction with main
length section 101.
Shoulder 110 comprises an outside or external diameter DA being approximately
equal to
the outside diameter of female sleeve 111 at female end 102. Outside diameter
DA
represents the largest outside diameter section of rod 100 along its entire
axial length. A
corresponding outside diameter of spigot 204 at the threaded section
corresponding to a
radial position at the peak of each helical ridge 302 is represented by Dc
when Dc is less
than DA. In particular, and according to specific implementations, Dc may be
in the range
60 to 100% or 75 to 85% of DA. Additionally, an external diameter DB of main
length
section 101 is less than the outside diameter DA of shoulder 110 and according
to specific
implementations DB is 70 to 100% or 85 to 99% of DA
The enhanced drilling guidance and the capability of drilling straighter holes
at increased
rate is provided by the axial length of shoulder LA being greater than the
outside diameter
of shoulder DA. When rod 100 is coupled to the drill bit 112 as illustrated in
figures 1 and
2, shoulder 110 effectively provides an axial extension of bit sleeve 104. In
particular, and
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referring to figure 5, an outside diameter DE of bit sleeve 104 is
substantially equal to the
outside diameter DA of shoulder 110 such that the two cylindrical sections
104, 110
collectively define a single cylinder extending between bit head 105 and
transition section
107 having a uniform diameter DA, DE over its entire axial length being the
combination of
LA and the axial length of the bit sleeve Lc. It follows therefore that the
shoulder axial
length LA is greater than the outside diameter DE of bit sleeve 104.
Shoulder 110 effectively provides a linear extension of bit sleeve 104 that
reduces the
possible deviation angle of the bit 112 and male end 103 of rod 100 as it is
both inserted
and extracted from the hole. That is, any bending or lateral deviation,
perpendicular to axis
305 within the bore at the region of bit 112 is reduced and is effectively
restricted by the
axial length LA of shoulder 110 and in particular the axially rearward end of
shoulder 110
contacting the internal surface of the bore. According to the specific
implementation, an
axial length Lc of bit sleeve 104 is defined between the annular contact
surface 109 (at the
axially rearward end of bit 112) and the axially forwardmost sleeve end 500 at
which the
outside diameter DE increases to form the radially enlarged drill head 105.
According to
specific implementations, bit sleeve axial length Lc may be in the range 60 to
100% or 75
to 95% of the shoulder axial length LA.
