GB2468133A

GB2468133A - Directional gas pressure device

Info

Publication number: GB2468133A
Application number: GB0903223A
Authority: GB
Inventors: Phil Routledge
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-02-26
Filing date: 2009-02-26
Publication date: 2010-09-01
Anticipated expiration: 2029-02-26
Also published as: GB2468133B; GB0903223D0

Abstract

A directional gas pressure device 1 comprises a body having openings at each end thereof, a closure member 7, 7' for each end thereof and a tie member 5 extending through the body. The closure members 7, 7' are attached to the tie member 5. The closure members 7, 7' are adapted to increase their size upon evolution of gas from a pyrotechnic charge material 4 contained within the body.

Description

Directional Gas Pressure Device

Field of the Invention

The present invention relates to directional gas pressure devices, typically for use in the breaking of rock or concrete, and in particular to a directional gas pressure device that does not require backfilling with sand or other sealants. The present invention also relates to a method of breaking rock from a face (a mine face or a quarry face) using a directional gas pressure device of the invention.

Background of the Invention

High explosives are widely used for breaking rock during quarrying and mining, and in demolition. Whilst explosives are effective, they are not particularly efficient in terms of their energy use, they are dangerous and hence are subject to specific regulation relating to their use, storage and transport. Where explosives are used for demolition, it is necessary to clear a large area around the site because of the distance both large and small particles are dispersed by explosive material. Where explosives are used in underground mines the whole mine must be cleared of personnel during blasting. Further, it is necessary to allow a certain period of time to elapse following blasting because of the possibility of rockfalls, and where blasting takes place underground, the existence of dangerous gases.

High explosives have detonation speeds in the order of 6000 to 9000 metres per second which induces a shock wave in rock, thereby breaking it. In certain circumstances high explosives may limit the depth of rock which may be removed during one blasting episode. This is because if the charge is placed too deeply beyond the surface of the rock back fractures may occur, making the mine or quarry unsafe. In such applications it is generally considered that high explosive charges should not be placed more than 1.2m beyond the rock face.

An alternative to splitting rock with explosive is the directional gas pressure system. In this system a hole is bored in a rock and a directional gas pressure device is inserted therein. The bore is backfiJled with sand or another suitable sealant. When the device is fired, rather than exploding, a chemical reaction is started which evolves a large volume of gas. The pressure within the bore builds up and is relieved by the rock splitting. The detonation speed of the pyrotechnic charges used in directional gas pressure devices is in the order of 40 to 60 metres per second. These devices do not create a shock wave. Therefore, it is possible to locate such devices further from the rock surface, thereby allowing a greater quantity of material to be removed from the face during one blasting episode.

The directional gas pressure system is more efficient than explosive charges in terms of the amount of energy released to split a rock or demolish a building. For example, when using the directional gas pressure system compared to an explosive charge, significantly less dust is produced.

This has two benefits. First, it is possible to work in closer proximity to rock being broken using the directional gas pressure system than it is where explosive charges are used. In the case of an underground mine, generally the whole mine would be cleared whilst blasting is taking place, whereas where the directional gas pressure system is used work can continue much closer to the area where rock is being broken. Another benefit of the directional gas pressure system is that the charges are intrinsically much safer than explosives. Their classification and rules relating to their use reflect this.

A further benefit of this system is that they create much less noise than high explosives and do not cause problematic emissions of toxic gases.

As mentioned above, the directional gas pressure device is inserted into a bore and the bore backfilled with sand or another suitable sealant material. Back filling with sand is inexpensive in terms of materials, but requires labour and a supply of sand where the rock is being broken. Further, sand may only be used where the direction of the bore is inclined above the horizontal, otherwise the sand may run out of the bore, in which case the rock would not be broken and the directional gas

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pressure device would not be safe. Also, the consistency of the sand used in stemming is critical.

For example, if the sand is too dry or too wet a blow out' may occur. A blow out may also occur if the sand grains are too big or of inconsistent shape.

Other back filling materials may be used, but these may be expensive. For example, resin based fillers may be used, but even with such filler materials there remains the problem that where the bore lies below the horizontal it is difficult to be certain that the bore is filled adequately without pockets of air for example. When using resins sometimes residual oil or water from the drilling machine can have an adverse effect on the resin and subsequently cause blow outs'.

United Kingdom patent application published under number 2341917 describes a directional gas pressure device of the type described above.

International patent application number WO 2006/063369 describes a container for a pyrotechnic device. This invention relates to closing the container of a pyrotechnic device so that the device may be subject to less stringent rules when transported than is the case for other closure arrangements.

It would therefore be desirable to provide a directional gas pressure device the operation of which does not require backfllling.

A rock breaking cartridge is described in US 2008/0047455. In the device described the charge is housed in a tube which is closed at one end by a cap. The mid part of the tube is filled with stemming material (such as sand) and the other end is closed by a pair of wedges. When the device is inserted into a bore in rock to be broken one of the wedges is driven further into the tube thereby securing the device in the bore. The device may be used without the intermediary filler, in which case the device is held in the bore by the wedges which are forced further apart by the gas pressure within the device.

Whilst the above-mentioned device does not require backfiJling its use may be limited to relatively ow gas pressures. This is because the device relies on the gas pressure to be contained by the wedges. If the wedges fail, it is likely that the increased gas pressure would fire the device out of the bore.

Mining typically involves breaking up material to be extracted at a face, loading such material on to a transport means and delivering the material to a processing plant. As mentioned above, explosives may be used to break material from the face, but the use of explosives typically requires clearance of the mine. Blasting would usually be done whilst miners are not present, for example before the miners start work each morning or between shifts. However, this means that a comparatively large amount of material must be broken from the face to provide sufficient work for the miners to move during their shift. Also, there is the danger that unauthorised personnel may be present during blasting.

It would therefore be desirable to be able to mine material without using explosives.

Some mining does take place without blasting, using machines for example. Patent application no CA 2060288 describes a machine which uses multiple cutting blades to cut away material from a face. However, such machines may not be used in all situations, require the installation of rails and other infrastructure, and are very expensive.

Where blasting is used it is nevertheless possible to automate the blasting process to a certain extent. For example, patent application no W097/21068 describes a vehicle adapted to drill bores in a material face and insert explosive charges.

It would be desirable to provide an improved method of mining whereby material can be broken from the face in relatively small amounts but more regularly than is the case where blasting is used.

Summary of the Invention

According to one aspect of the invention there is provided a directional gas pressure device comprising a body having openings at each end thereof a closure member for each end thereof a tie member extending through the body, the closure members being attached to the tie member, wherein the closure members are adapted to increase in size upon detonation of a pyrotechnic charge material contained within the body.

The body preferably includes an inner tube.

Preferably, each closure member includes an end cap adapted to fit into the opening in the end of the body. The end cap may be slidably mounted on the tie rod. The end cap may include a collar which, in use, extends into the body between the outer wall of the inner tube and the inner wall of the body.

The closure members advantageously include a plurality of wedges, which are advantageously connected together. In one embodiment the closure member includes a number of wedges, for example four. Preferably, the wedges are slidably mounted on the tie rod.

The closure members preferably include a boss, the position of which may be fixed with respect to the tie rod. For example, the boss may be formed integrally with the tie rod, or the boss may be attached to the tie rod by screw threads. Advantageously, the boss has an inclined surface against which the wedges may slide. Hence, upon detonation of the device, the wedges are forced radially outward of the device thereby locking the device in position in the bore.

Advantageously, the wedges are formed from a single plastics element, with the individual wedges being defined by regions of weakness introduced into the plastics element during manufacture thereof for example, part of the plastics material may be cut away to define the individual wedges, or score lines may be made in the material between the individual wedges.

Preferably, the tie rod, the wedges and the boss are formed from a hard material, which advantageously is a plastics material having stress, strain and hardness characteristics similar to those of mild steel. One such plastics material is known as glass filled nylon.

The end caps are preferably formed of the same material as above.

The body is preferably formed of a plastics material, such as polypropylene or polyurethane.

The walls of the body are advantageously relatively thin, for example between 0.5 and 1 mm.

In one embodiment of the invention the closure members are removably attached to the tie member.

In another embodiment of the invention one of the closure members is fixed to the tie rod and the other is removably attached to the tie rod. The tie rod and the closure member fixed thereto may be formed as a single component, for example by moulding. The other closure member may be attached to the tie rod by screw threads.

In use, a hole is bored in a rock or the face of a quarry or mine, and the directional gas pressure device of the invention is inserted into the hole, leaving the initiation wire(s) protruding from the hole. The device is initiated by passing a current through an electric initiator. Combustion of the pyrotechnic mix occurs as a result of the initiation of the electric initiator causing the pyrotechnic material to evolve a significant volume of gas, thereby increasing the pressure within the device and exerting a force on the closure members to move them apart from the body. However, the closure members are constrained by the tie rod. The closure members are adapted to increase in size upon evolution of gas from the pyrotechnic material in order to seal the bore.

In one embodiment of the invention charged with 20 grams of pyrotechnic material the peak pressure was 2733.2 psi.

In another embodiment of the invention of the invention charged with 30 grams of pyrotechnic material the peak pressure was 4497.9 psi.

In another embodiment of the invention of the invention charged with 40 grams of pyrotechnic material the peak pressure was 6479.5 psi.

In another embodiment of the invention of the invention charged with 50 grams of pyrotechnic material the peak pressure was 12980.8 psi.

In another embodiment of the invention of the invention charged with 30 grams of pyrotechnic material the peak pressure was 16863.0 psi.

The present invention also provides a method of mining comprising the steps of: i) boring holes in a limited area of a mining face; ii) inserting directional gas pressure devices according to the present invention into each of the holes; iii) initiating the gas pressure devices; iv) repeating steps i to iii, and during that time collecting material separated from the mining face.

Brief Description of the Drawings

In the drawings, which illustrate preferred embodiments of a directional gas pressure device according to the invention: Figure 1 is a schematic representation of a directional gas pressure device according to the invention in its pre-detonated condition; Figure 2 is a schematic representation of the directional gas pressure device illustrated in Figure 1 in its post-detonated condition; Figure 3 is a schematic cross-sectional representation of the directional gas pressure device of Figure 1; Figure 4 is a schematic representation of a mine face illustrating the method according to the invention of extracting material from a mine or quarry face; and Figure 5 is a cross-sectional representation of the directional gas pressure device according to a second embodiment of the invention in its pre-detonated condition.

Figure 6 is a plan view of the directional gas pressure device according to a third embodiment of the invention in its pre-detonated condition.

Figure 7a is a cross-sectional representation of the directional gas pressure device of Figure 6.

Figure 7b is an enlarged view of the closure members of the directional gas pressure device shown in Figure 7a.

Figure 8 is a schematic representation of the wedges of the directional gas pressure device shown in Figure 7a.

Detailed Description of the Invention

Referring now to Figures 1 and 3, the directional gas pressure device 1 of the invention comprises an outer tube 2 formed of a suitably tough material, such as polypropylene or polyurethane. An inner tube 3 is located concentrically within the outer tube 2. The void formed between the outer tube 2 and the inner tube 3 is filled with a pyrotechnic material 4 which evolves gas when initiated. The principal gases evolved are carbon dioxide and carbon monoxide. Typically, the pyrotechnic material is ignited by electrical initiation. The internal diameter of the inner tube and the external diameter of the tie rod 5 substantially correspond, the diameter of the tie rod 5 being slightly smaller than the internal diameter of the inner tube 3, so that the rod 5 may slide in the inner tube 3. The walls of the outer tube 2 and the inner tube 3 are preferably between 0.5 and 1.0 mm.

The rod 5 is threaded 6, 6' at each end thereof. When in place in the inner tube 3, the threaded ends 6, 6' protrude beyond the ends of the inner and outer tubes 3, 2 so that tube closure members 7, 7' may be attached to them.

The tube closure members 7, 7' comprise seals 8, 8' and 9, 9', wedges 10, 10' and bosses 11, 11'. The bosses 11, 11' include internally threaded bores. The seals 8, 8' and 9, 9' include centrally aligned holes whose diameters correspond to the external diameter of the inner tube 3 in the case of seals 8, 8' and the external diameter of the tie rod 5 in the case of the seals 9, 9'. When assembled, the seals 8, 8' fit in the ends of the body so that collars 12, 12' depending thereof fit between the inner and outer tubes 2, 3. The seals 9, 9' lie on the surfaces of collars 12, 12' respectively. A collar comprising a plurality of wedges 10, 10' lies between the bosses 11, 11' and the seals 9, 9'. The inner surfaces 15, 15' of the wedges 10, 10' are inclined to the longitudinal axis of the device. The surfaces 14, 14' of the bosses 11, 11' are inclined at substantially the same angle as the surfaces 15, 15' of the wedges 10, 10'. Hence, with the surfaces 14, 14' in engagement with surfaces 15, 15' any movement of the wedges 10, 10' towards the bosses 11, 11' causes the said wedges to move outwards.

Figure 5 illustrates an alternative embodiment of the invention in which the boss 11 of the closure member 7 is formed integrally with the tie rod 5, for example by moulding a suitable plastics material. The closure member 7' is as described with reference to Figures 1 to 3.

Figures 6 and 7 illustrate another embodiment of the invention in which the closure members 7, 7' comprise seals 8, 8', wedges 10, 10' and bosses 11, 11', but exclude the seals 9, 9' of the previous embodiments. Figure 6 shows a plan view of the new embodiment, Figure 7a shows a cross-section of the new embodiment through line A-A in Figure 6, and Figure 7b shows an enlarged view of the closure members 7, 7'. Tn this embodiment there is no inner tube 3, and the wedges 10, 10' have a different structure than they did in the previous embodiments. Cross-section and perspective views of the new wedges 10, 10' are shown in Figure 7b and Figure 8, respectively. As can be seen, the wedges 10, 10' are frusto-conically shaped to complement tapered bosses 11, 11' and contain slots 27 along part of their length to provide points of weakness. These points help to ensure that the ends of the wedges 10, 10' are driven into the wall of the bore 23 upon detonation.

The depth of the slots 27 at the outer surface 28 of the wedges 10, 10' is smaller than the depth of the slots 27 at the inner surface 29 of the wedges 10, 10'. Tn the example illustrated in these Figures 6 and 7 the wedges 10, 10', the closure members 7, 7', the tie rod 5 and the bosses 11, 11' are all formed of plastics materials having substantially similar hardnesses.

Referring now to Figure 4, a mine face 20 is illustrated. To break rock from the face 20 using a directional gas pressure device of the invention, a plurality of bores 23 are drilled in the rock.

Devices 1 are then inserted into the bores 23. Before detonation, however, angled slots 24, 25 have to be cut into the mine face directly adjacent to the roof 21 and floor 22 of the mine to ensure a clean, even break. The bosses 11, 11' are suitably tightened prior to insertion of the devices 1 into the bores 23. The devices 1 are then initiated, causing the face 20 to fracture resulting in pieces of rock 24 being freed from the face. The broken rock is then transported from the mine face via a strike gully 26.

There is no requirement to backfill the bore with a stemming agent. Upon initiation of the device 1, the pyrotechnic material 4 begins to evolve gas, thereby increasing the pressure within the device 1. This increase in pressure causes the seals 8, 8' to move axially along the tie rod 5 towards the seals 9, 9' and hence wedges 10, 10', thereby causing the wedges 10, 10' to move in the same axial direction. The effect of the corresponding inclined surfaces 14, 14' and 15, 15' is to cause the wedges 10, 10' to move outwards into engagement with the wall of the bore in which the device 1 is situated, and hence to seal the bore, thereby confining pressurised gas to that part of the bore where the device is situated. The bores 23 are drilled to have a nominal diameter 1 mm greater than the diameter of the devices 1. The shape and dimension of the wedges 10 and bosses 11 are such that the ends of the wedges may move outward by up to 5 mm, thereby ensuring that the wedges engage with the walls of the bores 23, even where there may be a surface irregularity in the bore wall. The device 1 is thereby secured in the bore at both ends thereof Further, the gas pressure is restrained by the tie rod 5. The force generated by the increase in gas pressure is often sufficient to drive the ends of the wedges into the wall of the bore 23.

Whilst the open wedges present gaps through which gas may escape, this does not significantly compromise the effectiveness of the device. There are a number of reasons for this. In the example including seals 8, 8', which may be formed from a plastics material which is softer than the seals 9, 9' and wedges 10, 10', the increase in gas pressure within the device causes these seals 8, 8' to deform, the deformation comprising the thickness of the seals 8, 8' being reduced and the diameter increased. Hence, the peripheral wall of the seal 8, 8' comes into engagement with the wall of bore 22. Further, the release of gases by the pyrotechnic material 4 is accompanied by a significant release of heat, which is sufficient to cause the hard plastics materials to become malleable and thereby expand to seal against the wall of the bore 22. Also, the conduits presented by the opened wedges 10, 10' are relatively small and do not allow gas to escape with sufficient speed to prevent a significant build up of pressure within the bore in the region around the device. As mentioned above, the seals 8, 8' are not essential to the invention. The pyrotechnic charge would cause deformation of the seal 9, 9' to seal the device.

The resulting effect is the same as with other directional gas pressure devices, i.e. the rock is broken. However, no stemming agent is required. This means that the directional gas pressure device 1 can be used in applications where existing gas pressure devices may not be used. Further, in all applications, the method of using such devices is simplified because there is no need for the blaster to carry stemming agent, to backfill the bore with stemming agent, or to carry the necessary tools for backfilling stemming agent.

The invention also provides an improved method of mining where three teams of personnel work in conjunction with one another. Again referring to Figure 4, a first team drills the bores into which the devices of the invention are inserted. The second team breaks down rock using directional gas pressure devices of the invention, while the third team works behind the second clearing broken rock. This has the advantage that mining becomes almost a continuous process, where a little rock is broken away from a seam, and such rock is substantially cleared away before the next rock is broken away from the seam. It is generally more efficient to make the mining process as continuous as possible. Having to blast sufficient material to occupy a workforce for a whole shift may present its own logistical difficulties.

Claims

Claims 1. A directional gas pressure device comprising a body having openings at each end thereof a closure member for each end thereof, a tie member extending through the body, the closure members being attached to the tie member, wherein the closure members are adapted to increase their size upon evolution of gas from a pyrotechnic charge material contained within the body.
2. A device according to Claim 1, wherein the body includes an inner tube.
3. A device according to Claim 1 or 2, wherein each closure member includes an end cap adapted to fit into the opening in the end of the body.
4. A device according to any preceding claim, wherein the end cap is slidably mounted on the tie rod.
5. A device according to any preceding claim, wherein the end cap includes a collar adapted to extend into the body between the outer wall of the inner tube and the inner wall of the body.
6. A device according to any preceding claim wherein closure members include a plurality of wedges.
7. A device according to Claim 6, wherein the at least two of the wedges are connected together.
8. A device according to Claim 6 or 7, wherein the wedges are slidably mounted on the tie rod.
9. A device according to any preceding claim, wherein the closure members include a boss, the position of the boss being fixed with respect to the tie rod.
10. A device according to Claim 9, wherein the boss is formed integrally with the tie rod, or attached to the tie rod by screw threads.
11. A device according to Claim 9 or 10, the boss has an inclined surface against which the wedges may slide.
12. A device according to any of Claims 9 to 11, wherein the wedges are formed from a single element, with the individual wedges being defined by lines of weakness introduced into the element during manufacture thereof.
13. A device according to any of Claims 9 to 12, wherein the tie rod, the wedges and the boss are formed from a hard material.
14. A device according to any of Claims 9 to 13, wherein the end caps are formed of a hard material
15. A device according to any preceding claim, wherein at least one of the closure members is removably attached to the tie member.
16. A device according to any preceding claim, wherein the tie rod and one of the closure members are formed as a single component.
17. A device according to any preceding claims, further comprising an initiator, and wherein gas is caused to evolve from the pyrotechnic charge material upon initiation of the said initiator.
18. A method of mining comprising the steps of: i) boring holes in a limited area of a mining face; ii) inserting directional gas pressure devices as claimed in any of Claims 1 to 16 into each of the holes; iii) causing pyrotechnic charge material contained in the devices to evolve gas; and iv) repeating steps i to iii, and during that time collecting material separated from the mining face.
19. A method of mining according to Claim 17, wherein the holes are bored in a direction substantially normal to the plane of the mining face.
20. A directional gas pressure device substantially as shown in, and as described with reference to, the drawings.