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(11) | EP 0 748 923 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Drill rod |
| (57) A drill string for rock drilling has a drill rod with, at the bit end, a female threaded
socket (4). The bit has a male threaded shank which (16) screws into the socket. The
socket may additionally have an external male thread (3). |
[0002] The standard industry established method of drilling tunnel advance holes is described as follows with reference to Figures 1 and 2. This consists (see Figure 1) of a drill rod 8 with male threads at each end 9,10, the bit end thread being of small diameter 10. A standard drill bit 11 with female thread is used to drill all the required holes, profile, charge and centre relief holes across the tunnel face.
[0003] When all the holes are completed the drill bit 11 is removed and replaced by a reaming adaptor 12 and reaming bit 13. This combination of tools 8,12 & 13 are then used to counter-drill the required centre relief holes.
[0004] According to the invention, there is provided a drill rod having at one end a thread through which the rod can be connected to other drill rods and at the other end a socket with a female internal thread adapted to receive a male threaded drill bit therein.
[0005] The invention also provides a drill string comprising at least one drill rod as set forth above and a male threaded drill bit adapted to be screwed into the female threaded socket.
[0006] The drill bit is preferably constructed such that, when the bit is screwed into the socket in the rod, the peripheral skirt of the drill bit is substantially flush with the external surface of the rod.
[0007] The external surface of the socket in the rod may additionally have an external male thread thereon.
[0008] The female thread, and the male thread when present, are preferably rope threads. Particularly suitable thread forms are R28 for the internal socket thread and the external bit thread, and HM45 for the external male thread on the socket.
[0009] The drill rod is preferably hexagonal in section, with a central round bore therethrough for the passage of flushing fluid. If the across flats dimension of the rod is 40 mm, the bore diameter can be 19 mm. The rod is preferably of steel, conveniently EN 40B.
[0010] The invention will now be further described, by way of example, with reference to the accompanying drawings; in which:
Figures 1 and 2 show a drill string according to the prior art, in two different operating configurations;
Figure 3 shows a first embodiment of a drill rod and bit according to the invention;
Figure 4 shows the drill rod of Figure 3 with a different bit mounted thereon;
Figure 5 shows a tunnel face illustrating a pattern of drilled holes;
Figure 6 shows opposite ends of a drill rod in accordance with the invention;
Figure 7 is a cross-section through the rod of Figure 6 on the line VII-VII; and
Figures 8, 9 and 10 are respectively elevation, cross-section and end view of a drill bit in accordance with the invention.
[0011] The drill rod 1 shown in Figure 3 is a hollow drill steel with hexagonal exterior shape over the major part of its length. At one end is a male thread 2 typically known as R38 (or alternatively HM38) which is for connection to a rock drill, either directly or with the interposition of other extension rods. The other end forms a socket which has both a male thread 3 on the outside and a female thread 4 on the inside.
[0012] A drill bit 5 with a male threaded connector 16 can be screwed into the female thread at the bit end of the drill rod. The drill face diameter of the drill bit 5 is slightly larger than the male thread diameter 3 on the drill rod (eg. 48mm on the drill bit and 45mm on the drill rod). This drill bit 5 is used for drilling profile holes.
[0013] In a tunnelling application centre holes 20 (Figure 5) are required which will be a larger diameter than the profile holes 22 and other charge holes 24. This is for the purpose of acting as blast relief holes which are not charged with explosive and as such allow the rock to collapse during the blasting action of the explosive charges.
[0014] The centre relief holes 20 can be drilled using a female threaded drill bit 6. The thread 7 of this bit screws onto the male thread 3 at the bit end of the rod 1.
[0015] The diameter of the male thread 3 at the bit end of the rod is such that it acts as a stabiliser for the drill rod, when drilling profile holes, in order to minimise rod deflection. This feature will improve drill string rigidity and hence reduce drill hole deviation.
[0016] In relation to the tunnelling application the male thread at the bit end is of a diameter similar to the outside diameter of the drill bit used to drill the profile holes.
[0017] Figure 6 shows opposite ends of an alternative form of drill rod in accordance with the invention. The right hand end as shown in the drawings has a socket 30 with a female thread 32 on the inside. This thread will be one of those conventionally used in drill strings.
[0018] Figure 7 shows a cross-section through the centre part of the string, on the line VII-VII. The hexagonal outer shape of the rod can be clearly seen, with a centre bore 34 for flushing fluid.
[0019] Figure 8 shows a drill bit for use with the rod of Figures 6 and 7. The bit has a male threaded shaft 26 which will screw into the female thread 32 in the socket 30.
[0020] Figure 9 is a cross-section through the bit shown in Figure 9, and Figure 10 is a view of the end (cutting) face of the same bit.
[0021] The invention allows the use of spiral or straight hole drilling bits to be used for the centre holes for the purpose of improving hole directional stability.
Method of operation
[0022] The process of driving a tunnel through rock in either mining or civil engineering applications is to drill a pattern of holes to a set depth (tunnel advance distance). The pattern of holes (see figure 5) consists of an outer ring of holes 22, called profile holes, which define the tunnel shape, other charge holes 24 of diameter equal to the profile holes across the tunnel face and relief holes 20 of a larger diameter in the centre.
[0023] The drill rod 1 is used with the drill bit 5 to drill the profile and other charge holes 22, 24 and then the drill bit is changed to a larger diameter industry standard female threaded drill bit 6 to drill the centre relief holes 20 in one pass.
[0024] The outside diameter of the male thread 3 on the rod provides drill hole stabilising action to enhance drill hole straightness and stability. The male thread 3 on the rod has the additional function of coupling with a female thread 7 of a standard drill bit 6 of a diameter suitable to drill the centre relief holes required on a tunnel face.
[0025] The male threaded drill bit 5 couples to the drill rod 1. The diameter of the drill bit is such that the rod external surface can act as a stabiliser during drilling to enhance drill hole straightness.
[0026] As a result of these features
a) Drill hole straightness is improved due to the stabilising action of the male thread 3 outside diameter against the wall of the drilled hole.
b) Improved rigidity of the drill string due to the larger cross-sectional area 15 of the bit end of the drill rod 1. This rigidity will assist the drilling of a straight hole. In addition this rigidity will enhance the drill rod life and durability as it is used for the secondary operation of scaling loose rock inside the tunnel advance.
c) Improved drill rod strength and fatigue resistance in a drilling application. This is also due to the larger cross-sectional area 15 of the bit end of the drill rod, referred to above in point b) when compared to the small cross-sectional area 17 of a conventional drill rod 8.
d) Significant time saving is a feature of this invention because this drill system
removes the requirement to use dedicated reaming equipment 12,13 to counter bore the
centre relief holes of the tunnel face. Instead a standard drill bit 6 can be used.
In addition this invention, by utilising a standard drill bit instead of dedicated
reaming equipment allows the centre holes to be drilled in one pass, and not pilot
drilled and counter drilled to a larger diameter. This feature has the added advantage
of allowing full rock drill power to be used when drilling the centre holes as against
50% power used as a maximum when using dedicated reaming equipment.