GB2125850A - Cutting mineral faces and the like - Google Patents

Abstract

A machine for cutting coal or the like has a cutter drum 10 on which are provided a plurality of picks 12. At least some of the picks 12 each have a nozzle 13 associated therewith which moves with the pick and which directs a high pressure jet 14 of liquid onto the coal face 15 in the vicinity of a point where the face is struck by the pick. The jets 14 thus cut slots in the coal face 15 which assist with the cutting action of the picks 12. Each jet 14 can impinge upon the coal face 15 substantially at the actual point where the face is struck by the associated pick, or can impinge ahead of such a point. Alternatively, two such jets 14 can be provided which impinge upon the face 15 ahead of and to either side of the pick 12. <IMAGE>

Description

SPECIFICATION Cutting mineral faces and the like This invention relates to the cutting of mineral faces and the like in mining.

It is known that high pressure water jets can be used effectively to cut rocks and minerals at a mining face. It is also known that the cutting heads of present generation mining machines have been developed to the limits of existing technology. Whilst improvements are still being made to the control systems of such machines, the only way forward in improving the performance of the cutting heads is to assist the cutting action with high pressure water jets. The water jets act to reduce the cutting force required for the cutting head, because, it is believed, the high pressure water enters fractures produced by the cutting head and opens these fractures up. The reduced loading on the cutting head results in a longer service life for its individual picks, and also enables the specific energy consumption per ton of mineral won to be reduced.The use of water jets further serves to reduce dust generation by wetting the rock or mineral along the places of fracture. Existing proposals making use of this concept do, however, suffer from the disadvantage that a large quantity of small particles and fines are produced, the mineral content of which is usually lost.

It is an object of the present invention to provide an improvement in such existing proposals.

According to one aspect of the present invention, a method of cutting a mineral face or the like comprises striking said face with a pick while directing a high pressure jet of liquid onto said face, the jet being moved with the pick so that it impinges upon said face in the vicinity of a point where the latter is struck by the pick.

Most preferably, the jet of liquid is directed so that it impinges upon said face substantially at the actual point where the latter is struck by the pick.

Alternatively, however, the jet can impinge upon said face directly ahead of the pick, or a pair of jets can be employed which impinge upon said face ahead of and to either side of the pick.

According to a second aspect of the present invention, apparatus for cutting a mineral face or the like comprises a cutting head having a plurality of picks which are moved so as to strike said face, at least some of the picks having associated therewith a nozzle through which a high pressure jet of liquid is directed onto said face, each nozzle being moved with its. associated pick and being oriented so that its respective jet impinges upon said face in the vicinity of the pick.

Most advantageously, each nozzle is oriented so that its respective jet of liquid impinges upon said face substantially at the actual point where the latter is struck by the associated pick. In an alternative construction, however, each nozzle is oriented such that its respective jet impinges upon said face directly ahead of the associated pick. In a further alternative, the nozzles are arranged in pairs, with the nozzles in each pair being oriented such that their respective jets impinge upon said face ahead of and to either side of the associated pick.

Where the apparatus is in the form of a shearer and the cutting head takes the form of a rotatable drum or the like on which the picks are mounted in rows, at least some of the picks in the row nearest the axial end of the drum have said nozzles associated therewith.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a first embodiment of apparatus according to the present invention; Figure 2 shows a detail of the apparatus of Figure 1; Figure 3 is a perspective view of a second embodiment of apparatus according to the present invention; and Figures 4 and 5 respectively show details of two modified constructions.

Referring first to Figure 1, there is shown therein a shearer/loader machine for use in cutting coal, for example, at a mining face. The machine has a cutting head in the form of a rotatable drum 10, which drum is composed of a number of rings 11 each having a generally circumferentiallyextending row of picks 1 2 mounted thereon. For the sake of convenience, not all of the picks are actually illustrated. In the ring 11 which is disposed closest to the mining fact (henceforth referred to as the end ring), four of the picks 1 2 have respective nozzles 1 3 associated therewith, these picks being disposed at substantially equi-angular intervals around the rotation axis of the drum 10.The nozzles 1 3 are connected by way of a swivel connection in the drum to a high pressure water supply system, so that high pressure water jets are emitted by the nozzles, as indicated by arrows 14. As can be seen to advantage in Figure 2, each nozzle 1 3 is oriented so that its respective water jet impinges upon the mining face (referenced 15) substantially at the point where the associated pick 12 cuts the latter.

As explained previously, the water jets will assist the cutting head in cutting the coal, so that the cutting force required for the individual picks 12 is reduced. This in turn prolongs the service life of the picks and reduces vibration, so that the cutting performance becomes smoother and there is less stress of the machine parts. In addition, sparking which may occur when the picks strike the mining face is virtually eliminated, so that the danger of methane explosion is greatly reduced.

Because each water jet impinges upon the mining face substantially at the point where the latter is struck by the associated pick, a significant reduction in cutting force is obtained even at comparatively low water jet pressures, and the generation of fines as well as dust is greatly reduced.

In the construction illustrated in Figure 1, the conventional low pressure water dust suppression system is omitted, and therefore the aforementioned swivel connection is formed by a singie passage through which the high pressure water flows. The flow rate of the water through the nozzles 13 is relatively low, and therefore the water jet system uses a smaller quantity of water than would the dust suppression system if provided: however, this quantity is quite sufficient to give effective dust suppression since the water will always be in the coal itself rather than in the air. Accordingly, the total amount of water used in the cutting operation is reduced as compared with conventional techniques wherein dust suppression is employed with mechanical cutting.It is possible, however, to use the high pressure water jets in conjunction with a conventional dust suppression system, in which case the swivel connection in the drum will be of dual passage type wherein the passages are connected to the high pressure and low pressure systems, respectively.

In the above-described construction, the diameter of the nozzles 1 3 (and hence the diameter of the water jets), the pressure of the water, the distance of the nozzles from the mining face 1 5 (the "standoff" distance) and the rate at which the jets traverse the mining face will depend very much upon the prevailing operating conditions and the type of coal to be cut, but generally these parameters will be determined as follows.

Nozzle Diameter It is the usual practice in high pressure water jet cutting systems to employ nozzles having a diameter of less than 2.5 mm: in the present invention, nozzle diameters of between 0.25 mm and 1.5 mm are preferred.

Water Pressure In general, increased water pressure will result in a deeper cut. However, the optimum working pressure will in practice be determined by the type of pumping equipment available and the type of coal or rock to be cut. It has been determined that optimum working pressure is three times the threshold pressure, i.e. the pressure at which the water jets just begin to cut the coal. Optimisation of the working pressure is also dependent upon such factors as the total power available and the spacing between the cuts. Typically, a pressure of between 50 MPa and 1 50 MPa will be used.

Standoff Distance As the standoff distance increases, the depth of cut generally decreases due to the water jet breaking up and and the impact of the resultant droplets. There will, however, be an optimum standoff distance to produce a maximum depth of cut for a given range of nozzle diameter, pressure and traverse rate. Typically, the standoff distance will between 50 mm and 75 mm.

Traverse Rate There is an optimum combination of traverse rate and number of traverses that will produce the deepest cut in a given material with the least expenditure of energy. Ultimateiy, the depth of cut that can be obtained by any such combination is limited by interaction between the water jet and the mining wall and by pressure decay. Typically, a traverse rate of between 0.5 m/s and 4.0 m/s will be employed.

The pumping equipment which supplies high pressure water to the nozzles 1 3 can include direct drive (fixed displacement) hydraulic pumps: although such pumps are capable of delivering power in an efficient manner, they are however disadvantageous in that their delivery rate can be varied only by altering their speed, and a bypass capability must be provided to prevent the system pressure increasing in the event that one or more of the nozzles should become blocked. For this reason, it is preferred to employ variable displacement intensifier pumps. Using such pumps, the water pressure and flow rate can easily be increased, for example when harder rock is encountered, simply by altering the stroke of the pump.If the nozzles 13 should become blocked as aforesaid, or when the system is operated under no-load conditions, the water pressure is maintained without the need to provide a bypass feature. Moreover, the pressure is easily stabilised by adjusting the pump, which adjustment can be performed either manually or automatically.

Hence, intensifier pumps are capable of providing an actual system efficiency which is higher than that obtainable with fixed displacement pumps.

In the above-described construction, nozzles 13 are associated with only some of the picks 12 of the end ring 11. The arrangement may be modified, however, so that such nozzles are associated with all of the picks on the end ring, or indeed all of the picks on the whole drum 10.

Figure 3 shows an arrangement suitable for use in a longwall shearer where most wear occurs at the end ring 11. In this arrangement, a nozzle 13 is associated with each pick 12 on the end ring and directs a high pressure jet of water onto the mining face at a point where the latter is struck by the respective pick, in the manner described previously with reference to Figure 2. However, no other high pressure water jets are provided on the drum. Instead, the picks on the remaining rings 11 have nozzles 1 6 associated therewith which are connected to a low pressure water supply system for dust suppression. In this case, the swivel connection in the drum 10 is of the dual passage type described previously. This arrangement requires less power for a similar improvement in performance as compared with the construction shown in Figure 1.

In both of the embodiments described above, each high pressure water jet 14 pressure water jet 14 impinges upon the mining face substantially at the exact point where the latter is struck by the respective pick 12. As stated previously, this particular arrangement enables a significant reduction in the cutting force to be obtained even at relatively low pressures.As an alternative, however, the nozzles 13 can be oriented such that each high pressure water jet 14 impinges upon the mining face 1 5 directly ahead of the point where the latter is struck by the respective pick 12, as indicated in Figure 4, or the nozzles 13 can be provided in pairs with the nozzles in each pair being oriented so that the respective water jets 14 impinge upon the mining face 1 5 ahead of and to either side of the point where the latter is struck by the associated pick 12, as depicted in Figure 5.

In Figures 4 and 5, reference numeral 17 denotes slots which are cut in the mining face by the water jets. Unless the depth of these slots is a significant fraction of the pick cut depth, the fracture caused by the pick will be below the slot 17 and will thus negate its effectiveness in assisting the pick.

Accordingly, very high power water jets will be required for normal speeds of rotation of the drum 10. The water pressure could however be reduced where lower traverse rates are possible, for example at the end ring 11.

Claims (21)

1. A method of cutting a mineral face or the like, comprising striking said face with a pick whilst simultaneously directing a high pressure jet of liquid onto said face, the jet being moved with the pick so that it impinges upon said face in the vicinity of a point where the face is struck by the pick.

2. A method as claimed in claim 1 , wherein the jet of liquid is directed so that it impinges upon said face substantially at the actual point where the face is struck by the pick.

3. A method as claimed in claim 1, wherein the jet of liquid is directed so that it impinges upon said face directly ahead of the pick.

4. A method as claimed in claim 1 , wherein a pair of such jets of liquid are employed, which impinge upon said face ahead of and to either side of the pick.

5. A method as claimed in any preceding claim, wherein the or each jet of liquid issues from a nozzle whose diameter is between 0.25 mm and 1.5 mm.

6. A method as claimed in any preceding claim, wherein the or each jet of liquid has a pressure at its source of between 50 MPa and 1 50 MPa.

7. A method as claimed in any preceding claim, wherein the or each jet of liquid issues from a nozzle which, at the time when the pick strikes said face, is spaced between 50 mm and 75 mm from said face.

8. A method as claimed in any preceding claim wherein the pick is traversed across said face at a rate of between 0.5 m/s and 4.0 m/s.

9. A method as claimed in any preceding claim, wherein the or each jet is produced by pumping said liquid through a nozzle using a variable displacement intensifier pump.

10. Apparatus for cutting a mineral face or the like, comprising a cutting head having a plurality of picks which are moved so as to strike said face, each of at least some of the picks having associated therewith a nozzle through which a high pressure jet of liquid is directed onto said face in use, each nozzle being moved with its associated pick and being oriented so that in use its respective jet impinges upon said face in the vicinity of the pick.

11. Apparatus as claimed in claim 10, wherein each nozzle is oriented so that in use its respective jet of liquid impinges upon said face substantially at the actual point where the face is struck by the associated pick.

12. Apparatus as claimed in claim 10, wherein each nozzle is oriented so that in use its respective jet of liquid impinges upon said face directly ahead of the associated pick.

13. Apparatus as claimed in claim 10, wherein at least some of the nozzles are arranged in pairs, with the nozzles in each pair being oriented so that in use their jets impinge upon said face ahead of and to either side of a respective one of the picks.

14. Apparatus as claimed in any one of claims 10 to 13, wherein the cutting head takes the form of a rotatable drum or the like on which the picks are mounted in rows extending around the drum, at least some of the picks in the row nearest the axial end of the drum having said nozzles associated therewith.

1 5. Apparatus as claimed in any one of claims 10 to 14, wherein each nozzle has a diameter of between 0.25 mm and 1.5 mm.

16. Apparatus as claimed in any one of claims 10 to 15, wherein the liquid is forced through each nozzle at a pressure of between 50 MPa and 150 MPa.

17. Apparatus as claimed in any one of claims 10 to 16, wherein each nozzle is spaced between 50 mm and 75 mm from a point on the associated pick where the latter strikes said face in use.

1 8. Apparatus as claimed in any one of claims 10 to 17, further comprising means for moving the cutting head such that the picks thereof traverse said face at a rate of between 0.5 m/s and 4.0 m/s in use.

19. Apparatus as claimed in any one of claims 10 to 18, wherein the liquid is forced through the nozzles by a variable displacement intensifier pump.

20. A method of cutting a mineral face or the like, substantially as hereinbefore described with reference to any one of Figures 2,4 and 5 of the accompanying drawings.

21. Apparatus for cutting a mineral face or the like, substantially as hereinbefore described with reference to Figures 1 and 2, or Figures 1 and 2 as modified by either of Figures 4 and 5, or Figure 3, or Figure 3 as modified by either of Figures 4 and 5 of the accompanying drawings.