Note: Descriptions are shown in the official language in which they were submitted.
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Drill Rod
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to single-piece drill rods, in particular
those used in the percussive drilling of rock. The present invention also
relates to a method of manufacturing such a drill rod.
2. Description of the Related Art
It is known to manufacture hollow drill rods suitable for percussive
drilling in which a collar is located between the main body and the, usually
threaded, working end. The rods are hollow to enable the supply of a
flushing medium down the centre bore of the rod, thereby facilitating debris
removal.
In use, a percussive drill bit is threaded onto the working end, and its
skirt abuts the collar. This facilitates the transmission of downward
percussive energy from the collar to the bit face and through the skirt of the
bit. Reduction of percussive energy on the threads of both the drill rod and
the drill bit is therefore achieved, and in practice also allows more rotary
drive torque to be supplied to the drill bit. Furthermore, tool life is
increased
through the reduction in failure due to thread damage. This configuration
forms the basis of the Dual Drive Bolter (RTM), which is a drill rod design
introduced by Brunner & Lay of Springdale, Arkansas, USA.
A problem with the current manufacturing process of the existing dual-
drive drill rods is that in order for the collar to work, its diameter must be
at
least the same as that of the skirt of the drill bits to be attached to the
rod. It
is also preferable that the main body of the drill rod be of a diameter which
is
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small enough to both tolerate the various stresses it will experience in use,
but also such that its inertial mass is minimised to enable the required
percussive drive to be transmitted. In practice, therefore the main body of
the
drill tends to have a smaller diameter than that of the collar.
Creating this collar could be achieved by machining away most of the
material from a billet of drill steel, but this would be seen as an incredibly
wasteful operation considering that drill rods of this type can have main
bodies with lengths ranging up to several metres. Alternatively, the collar
and
working end thread can be manufactured as a separate part by a machining
process, and then friction welded to the main body to create the finished
drill
rod. However, problems exist with the friction welding approach as flash from
the welding operation tends to fill the centre bore of the drill rod,
requiring
removal which can prove difficult or impossible.
BRIEF SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a
single-piece hollow drill rod specifically adapted for percussive drilling,
the
drill rod having a main body, a working end having a thread for receiving a
percussive drill bit, and a collar between the thread and the main body,
wherein the collar is upset forged. The upset forged collar provides increased
resilience to stress over a purely machined component when used in
percussive drilling operations.
According to a second aspect of the present invention, there is
provided a single-piece hollow drill rod having a flushing hole therethrough,
the drill rod having a main body, a working end having a thread for receiving
a drill bit, and a collar between the thread and the main body, wherein the
collar is upset forged and the flushing hole is less than 10 millimetres in
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diameter. The use of a upset forged collar means that no flash removal is
necessary from the flushing hole, unlike with collars which are friction
welded
to the main body.
According to a third aspect of the present invention, there is provided
a method of manufacturing a single-piece hollow drill rod specifically adapted
for percussive drilling, in which a bar of hollow drill steel is forged,
comprising
the steps of: heating a working end of the drill steel to forging temperature;
upset forging a collar on the working end of the drill steel; and machining a
thread on the working end of the drill steel for receiving a drill bit such
that
said collar is positioned between the thread and a main body of the drill rod.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a drilling operative involved in a roof bolting exercise
using a percussive drilling apparatus;
Figure 2 shows a drill rod according to the present invention;
Figure 3 shows the working end of the drill rod in greater detail;
Figure 4 shows the drill rod of the present invention with a percussive
drill bit threaded on it;
Figure 5 illustrates an industrial process for manufacturing the drill
rod; and
Figure 6 shows the grain structure of the steel at the working end of
the drill rod.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Figure 1
A single-piece hollow drill rod 101 according to the present invention is
illustrated in Figure 1, which shows a scene in which a drilling operative 102
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is about to begin the drilling of a bore in the roof of a mine to facilitate
the
insertion of a roof bolt.
As illustrated in the Figure, a percussive drill bit 103 has been
threaded onto the drill rod 101 at a working end, and the drill rod 101 itself
is
inserted into a stoper drill 104 at a machine. The stoper drill 104 is a
pneumatic hammer drill typically used in overhead drilling applications which
require percussive action, such as when roof bolting.
In rock drilling applications as illustrated in Figure 1, along with other
applications such as scaling in which loose rocks are cleared from tunnels,
the level of deflection, strain and stress the components such as drill rod
101
are exposed to in use can be sufficient to cause component failure. Thus,
measures must be taken to optimise the design and manufacture of these
components within constraints such as price, dimensions and material.
Figure 2
Drill rod 101 is shown isometrically and in isolation in Figure 2. The
drill rod 101 shown is manufactured by processing hexagonal bars of hollow
drill (or tool) steel; the process of manufacture will be described with
reference to Figure 5.
Referring to Figure 2, the drill rod 101 has a machine end 201 which
includes a thread 202 for facilitating location in either a shank adapter or a
coupling to another drill rod. Shank adapters allow the drill rod 101 to be
connected to the chuck of a drilling machine such as stoper drill 104, and
couplings allow the drill rod 101 to form part of a drill string. Thread 202
is, in
this embodiment, a standard R25 rope thread, but it will be appreciated that
the thread could be altered so as to optimise the performance of machine
end 201 depending upon the required characteristics. The shank 201 could
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alternatively have a geometric profile, such as a hexagonal profile to allow
direction connection to the chuck of a drilling machine.
The drill rod 101 further comprises a main body 203 which is in the
present embodiment hexagonal in cross section. The main body 203 has a
5 length
L203, which in this embodiment is 1 metre, but can vary depending on
the requirements of drill rod 101. In addition, the main body 203 has a
dimension of 25 millimetres across the hexagon flats. In an alternative
embodiment the main body 203 is of round cross section, with a diameter of
25 millimetres. Other cross sectional shapes could be used in addition to
hexagonal or circular, such as square or octagonal. The selection of the
cross-sectional dimensions of main body 203 is variable, and standard sizes
such as 32 millimetres and 39 millimetres can be adopted depending upon
design requirements.
The drill rod 101 also has a working end 204, which in a similar way to
machine end 201 has a thread 205 to facilitate the threading thereon of a
drill bit, such as percussive drill bit 103. Again, thread 205 is in this
embodiment rope thread standard R25 to allow the use of standardised
components. Alternatively, the thread form could be standard conical or
cylindrical types.
Between main body 203 and working end 204 is located a collar 206,
which is upset forged. Forged collar 206 will be described further with
reference to Figure 4, and the forging process will be described further with
reference to Figure 5.
Recalling that drill rod 101 is hollow, and as can be seen in the Figure,
drill rod 101 includes a flushing hole 207 of 9 millimetres in diameter.
Flushing hole 207 extends all the way through drill rod 101, to allow, in use,
a
flushing medium to be provided to the drill bit located at the working end
204.
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Figure 3
Working end 204 is shown in greater detail in Figure 3, along with the
forged collar 206 and a portion of main body 203. The forged collar 206 is in
the embodiment comprised of a shoulder feature, having an annular surface
301 substantially perpendicular to the rotation axis of the drill rod 101.
Forged collar 206 is in the present embodiment a half-ball collar, which is
formed by machining the drill rod 101 following the forging process described
with reference to Figure 5.
Figure 4
Drill rod 101 is illustrated in Figure 4 with percussive drill bit 103
threaded thereon. When the percussive drill bit 103 is fitted, its flushing
flutes
401 align to be in fluid communication with flushing hole 207 in drill rod
101.
Forged collar 206 is positioned in relation to thread 205 such that
percussive drill bit 103, when fitted, engages with both the thread and the
forged collar to facilitate dual-drive percussive drilling. Deflection of the
percussive drill bit 103 during drilling operations would, without forged
collar
206, tend to cause a high degree of bending stress at the point of contact
between the percussive drill bit 103 and the thread 205, illustrated at point
403 for a deflection in the direction 404.
Forged collar 206, being shaped as a shoulder feature and thus
providing the annular face 301, therefore reinforces the skirt 401, and
results
in bending stress caused by deflections applied to the bit to be spread along
the whole of main body 203. Percussive action is also transmitted to skirt 401
directly by forged collar 206 via the annular face 301, rather than solely
through thread 205.
As described previously, the annular face 301 is substantially
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perpendicular to the axis of rotation of the drill rod 101. Angles of between
80
and 110 degrees between the annular face 301 and the drill rod's rotational
axis have been found to provide suitable levels of performance.
Figure 5
A high-level overview of an industrial process for manufacturing the
drill rod 101 is shown in Figure 5. The process involves upset forging a bar
of
drill steel to form forged collar 206.
At step 501, a bar of drill steel 511 is received. For the manufacture of
drill rod 101, the bar of drill steel 511 is a hollow, hexagonal bar of drill
steel,
but alternatively hollow, round drill steel billet can be used if the intended
purpose of the drill rod requires its use.
At step 502, the bar of drill steel 511 is heated to forging temperature
by use of a furnace heat source, or by use of a high-frequency induction coil,
focussed on the location at which the forged collar is to be formed.
At step 503, the heated bar of drill steel 511 is placed in forging dies
512 and 513. Die 513 has a shape corresponding to the profile of the bar of
drill steel 511, whilst die 513 is shaped so as to form generally the half-
ball
shape.
At step 504, the dies 512 and 513 are closed by pressing them
together in a forging machine, which in the present embodiment is an upset
forging machine.
At step 505, the now forged bar of drill steel 511 is removed from the
press and from the dies, and includes an un-machined forged collar 514,
which includes external flash 515.
At step 506, further treatment of the forged bar of drill steel is
undertaken to produce the final finished drill rod 101, for example removal of
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flash 515 by machining, turning to add thread 206 and heat treatment etc.
The forging process employed by the present invention is
advantageous because no flash is formed in the flushing hole 207, and thus
no machining of the flushing hole 207 is required. Friction welding techniques
tend to create a volume of flash in the centre bore which can only be
removed through use of a thermic (oxygen) lance, due to the flash of course
being itself composed of hardened drill (or tool) steel. Alternatively,
Stellite
(RTM) or carbide drill bits can be used to remove the flash, but there are
practicality issues in terms of locating the rod in a suitable drill press to
create the required pressure between the bit and the flash to facilitate this
removal technique.
In any event, with drill rods that have small flushing hole diameters,
particularly those which have a flushing hole with a bore of less than 10
millimetres, the thermic lance or drill option is simply not available, as the
tools required to effectively remove the flash in a bore of this size do not
exist. Thus, the present invention facilitates the inclusion of a forged
collar
onto single-piece hollow drill rod having a flushing hole therethrough by way
of upset forging, the flushing hole being of less than 10 millimetres in
diameter.
When compared to other forging methods, upset forging usually
requires less draft than drop forging and gives better dimensional accuracy.
In addition, the forging can often be done in one closing of the dies,
allowing
for automation of the manufacturing process.
Figure 6
The grain structure of the working end 202 of drill rod 101 is shown in
Figure 6.
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As shown in the Figure, the upset forging process creates a
favourable grain structure in the upset forged collar 206, which follows
generally the shape of the half-ball collar. This greatly increases the
ability of
drill rod 101 to tolerate the stress experienced during bit deflection.
Bending
stresses are spread over the entire length of the drill rod 101 during use,
allowing high deflection without failure whilst still returning to a straight
condition when the stress is removed. This is a particularly important
property to have during drilling operations such as roof bolting and scaling
in
mine tunnels, which are particularly harsh applications and create high levels
of bending stress and necessarily require percussive action. Thus the
present invention also provides an improved drill rod specifically adapted for
percussive drilling by including an upset forged collar between the main body
and the machine end, which provides advantages over collars which are
simply turned using a lathe from untreated bar stock. This is a particularly
important property when considering the stresses that arise during
percussive drilling.
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