Patent Application
20180100356
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.
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®, which is a drill rod design introduced by Brunner & Lay of Springdale, Ark., 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 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.
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 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.
A single-piece hollow drill rod 101 according to the present invention is illustrated in
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
Drill rod 101 is shown isometrically and in isolation in
Referring to
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 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
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.
Working end 204 is shown in greater detail in
Drill rod 101 is illustrated in
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 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.
A high-level overview of an industrial process for manufacturing the drill rod 101 is shown in
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 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® 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.
The grain structure of the working end 202 of drill rod 101 is shown in
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.
