Field of the Invention

This invention relates to an overburden discharge conveyor system, for example for use in opencast mining, and to a method of handling overburden.

Background to the Invention

In mineral operations such as open-cast mining, a large volume of material, known as overburden, has to be removed and disposed of before access is gained to the minerals of interest. The overburden can be used to fill earlier spent excavations, or stacked in readiness for this at a later stage.

In one handling method, a long conveyor, known as an overland conveyor, carries the overburden from the current mining area to the dumping location, and transfer and stacking of the overburden is then carried out by a series of linked bridging conveyors carrying the material to a stacker which lifts and deposits the material on to piles. There are two main deposition patterns, a radial pattern in which the stacker is slewed through approximately 180 degrees to deposit a curved layer, and then gradually moved forward to build up the layers, and a linear pattern, in which successive mounds of material are deposited side-by-side, the mounds merging to form a "cornsheH" configuration which can then be levelled to provide the base from which the next row is then deposited.

In each case, the bridging conveyors are linked together in a pivotal manner to permit the stacker to move relative to the overland conveyor to a limited degree, but periodically the overland conveyor has to be moved nearer to the point of deposition. This is a costly exercise, and the conveyor is out of commission for some time while the move is carried out.

The linking of the bridging conveyors is also relatively complex, and the adjustment of these and the insertion of additional sections is complicated and time-consuming. An example of a system involving the radial distribution pattern may be seen in US2007/0102263A1.

To avoid the need to convey material from a fixed point at the end of the overland conveyor, use is made of a "tripper station" which is movably mounted on the conveyor and which diverts the path of the belt vertically so that the belt adopts essentially an S-shaped profile which lifts and drops the material. A transversely-extending conveyor is positioned to receive the dropping material and convey it off at right-angles to the belt direction, allowing it to be deposited on to a bridging conveyor or the like positioned at the side of the overland conveyor. The tripper station, also known as a tripper car, is mounted on rails on or adjacent to the overland conveyor, and this permits the discharge point readily to be moved along the overland conveyor without the need for it to be dismantled or otherwise changed.

DE3834771 discloses a stacker for dumping overburden, in which a long boom conveyor extends transversely from a frame supported on tracks, a feed conveyor extending from the opposite side to receive material and deposit it on to the boom conveyor for stacking. This configuration is not adapted to cooperate with a tripper station on an overland conveyor, for example.

Summary of the Invention According to the invention, an overburden discharge conveyor system comprises, in combination:

(a) an overland conveyor for overburden, the overland conveyor having a tripper station movably mounted therein, the tripper station having a tripper car conveyor for conveying material from the overland conveyor transversely to one side thereof, and

(b) an overburden dumper, comprising a supporting frame carried by a pair of endless tracks, a boom conveyor mounted on the supporting frame and extending upwardly and outwardly from the frame from a loading end within the frame to a discharge end remote therefrom, the overburden dumper being configured such that it can be positioned alongside the overland conveyor with the tripper car conveyor discharging material directly on to the loading end of the boom conveyor.

Preferably, the supporting frame carries a tower from which extends on the side opposite to the boom conveyor a support carrying a counterweight, struts from the top of the tower supporting the boom conveyor on one side and the counterweight support on the other side.

The boom conveyor suitably includes an endless belt, for example of reinforced elastomeric material, which is supported by rollers spaced along the boom. Preferably, each supporting roller is configured as a series of smaller rollers pivotally connected end-to-end and arranged to adopt a generally arcuate path so that the belt adopts a concave channel- shape, which permits a higher volume of material to be carried than would be possible with a flat conveyor. The mounting of the roller sets on the boom is suitably achieved by means of screw or other adjusters, permitting the height of the belt relative to the boom to be adjusted, and also permitting the rollers to be lowered clear of contact with the belt in the event of a bearing seizure causing overheating of the rollers, thus avoiding the risk of a belt fire when the belt is stopped.

The invention also provides a method of handling overburden in mining, by means of the use of an overburden discharge conveyor system as hereinbefore described to perform steps comprising:

(a) transporting the overburden to a dumping location by an overland conveyor;

(b) diverting the overburden by means of a tripper station associated with the overland conveyor on to an overburden dumper and creating a first pile with a pre-determined height;

(c) moving the tripper station and the overburden dumper parallel to the overland conveyor by a predetermined distance and creating another pile overlapping with the first; (d) repeating step (c) until a desired length of adjacent piles is achieved; and (e) levelling the piles to achieve a generally flat surface.

Preferably, the method includes the further steps of: (f) locating between the tripper station and the overburden dumper an intermediate conveyor carried by a pair of endless tracks extending transversely thereof and respectively located adjacent to the two ends of the conveyor, one end being below the discharge point of the tripper station and the other end discharging on to the overburden dumper; and then

(g) repeating steps (b) to (e).

Further intermediate conveyors may be used to extend further the range at which material can be dumped without the need to move the overland conveyor. The overburden dumper may be self-powered, for example by means of one or more internal combustion engines mounted on the frame, but is preferably electrically powered via a power cable which is suitably run along the overland conveyor, serving to power it and the tripper station as well, from a central electrical power supply for the mine. The intermediate conveyors, where used, may also be electrically-powered, an extension cable extending along the or each intermediate conveyor to provide electrical power for the dumper and any successive intermediate conveyor.

The new system avoids the need for a complicated slewing bridge conveyor. During the first pass, the dumper is able to deposit the overburden material at a significant distance from the long overland conveyor. Typically, a discharge distance of around 68m can be achieved, and when the first pass is complete, the additional intermediate conveyors can increase the distance, permitting at least a second pass at a greater range from the overland conveyor. The dumper uses a single pair of racks, and occupies a relatively small footprint. The tracks are parallel to each other and can be fixed in the vertical plane for simplicity, or can be pivotally mounted to accommodate undulating ground conditions. Each intermediate conveyor is movable on its own pair of tracks independently of the overburden dumper and of any other conveyor, simplifying operations, since there is no requirement to move a number of interlinked bridging conveyors simultaneously.

The entire system can be operated from a single control cabin located on the overburden dumper. In a preferred embodiment, the tripper station is arranged to carry its conveyor on transverse rails, permitting the position of the tripper conveyor to be adjusted to ensure that the material is discharged directly and accurately on to the boom conveyor of the overburden dumper, or an intermediate conveyor, reducing the precision required in placing these components alongside the overland conveyor. A drive means can be provided on the tripper station to move the conveyor transversely to its correct position, at which it can be pinned in position. The tripper car conveyor is also preferably height adjustable to assist positioning over the next conveyor. Because the material transfer point between the tripper car conveyor and the overburden dumper is a free transfer point, no mechanical forces are transferred between the two structures, and the absence of transfer points within the dumper reduces or avoids the problems associated with spillage and its effect on operational availability.

Brief Description of the Drawings

In the drawings, which illustrate exemplary embodiments of the invention:

Figure 1 is a diagrammatic side elevation of the overburden dumper; Figure 2 is an enlarged end elevation of the dumper;

Figure 3 is a perspective view of the dumper;

Figure 4 is an enlarged perspective view of the rear portion of the dumper, on an enlarged scale;

Figure 5 is an enlarged side elevation of the transfer point between the tripper station and the overburden dumper;

Figure 6 is an enlarged sectional view through the conveyor boom of the dumper, showing the conveyor belt supports;

Figure 7 is a diagram illustrating the path of the belt at the topmost part of the boom conveyor; Figure 8 is a perspective view of an intermediate conveyor according to one aspect of the invention;

Figure 9 is a diagram illustrating a single stage, single level method of stacking overburden according to the invention; Figure 10 is a diagram illustrating a single stage, three level method of stacking overburden according to the invention; Figure 11 is a plan view of the method illustrated in Figure 10; and Figure 12 is a diagram illustrating the use of an intermediate conveyor in the method shown in Figure 10.

Detailed Description of the Illustrated Embodiment

Referring first to Figures 1 to 4, the overburden dumper comprises a supporting frame 1 mounted on a pair of endless crawler tracks 2. A boom conveyor 3 extends obliquely upwardly from the frame in a direction transverse to the alignment of the tracks 2 to discharge from the elevated end 4 thereof remote from the frame 1. A tower frame 5 extends upwardly from the supporting frame 1 and is braced at its lower part by diagonal braces 6 mounted above the tracks 2 on each side of the frames. A platform 7 extends from the tower frame 5 on the opposite side thereof from the boom 3 and carries counterweights or ballast 8 at its free end together with the operator's cabin 9 and electrical and maintenance cabin 10. Supporting struts 11 and 12 extend from the top of the tower frame 5 to support the boom 3 and the platform 7 respectively, so that the ballast counterbalances the load on the boom.

The overland conveyor 13 incorporates a tripper station 14 movable along the conveyor and causing the upper surface of the conveyor belt to be elevated and then formed into a generally S-shaped bend to drop material from the belt on to a tripper conveyor 15 mounted transversely in the tripper station by means of rails (not shown) and provided with driving means, for example electric motors, (also not shown) to move the conveyor 15 transversely on the mounting rails, and vertically relative to the tripper station car, which is either mounted on rails located on the ground on opposed sides of the overland conveyor, or on rails carried by the overland conveyor itself. The tripper station is further described hereinafter with reference to Figure 5.

As may be seen from Figure 2, and more particularly from Figure 6, the conveyor belt 16 within the boom is concave on its upper path, being carried by strings 17 each of five short rollers (for example) pivotally connected together to form a flexible chain adopting a downwardly curved supporting surface for the belt. The chain may be held in place by means of hooks 18 at each end engaging anchorage points on the boom and permitting quick release, or screw adjusters permitting adjustment of the height of the belt relative to the boom framework and enabling the string 17 to be quickly lowered clear of the belt 16 in the event of seizure of the roller bearings resulting in overheating. While the belt continues to move, the risk of the overheated rollers causing damage to the belt is smaller, but there would be a risk of fire if the belt were stopped in contact with overheated rollers. This arrangement for support of the belt also permits easy inspection of the supports in use. The return run of the belt 16 is on a similar arrangement, but with just two rollers in each lower string 19.

Figure 5 shows the tripper station and the associated part of the overburden dumper in more detail. The overland conveyor has a belt 20 similarly supported on curved strings 21 of rollers to form the belt into a concave shape. The tripper station 13 elevates a portion of the belt over the tripper conveyor 15 in which the belt is again supported on curved strings 22 of pivoted rollers to give the upper surface a concave profile. Material is discharged from the tripper conveyor 15 on to the lower end of the boom conveyor 3, which is provided with surrounding hopper guides 23 to direct any stray material on to the belt. It will be seen that, in order to ensure that the material is discharged from the tripper conveyor correctly on to the boom conveyor of the overburden dumper, it may be necessary to move the tripper conveyor transversely and/or vertically relatively to the tripper station. The speed of the boom conveyor is set to be higher than that of the tripper conveyor to ensure efficient transfer between the two, reducing the risk of spillage or build up of material. In addition, the high speed of the boom conveyor in the dumper (for example around 6.3m/s) reduces the loading per metre on the conveyor belt and the conveyor structure generally.

Figure 7 illustrates the profile of the boom conveyor belt 16 at the upper end 4 of the boom conveyor. The head-end conveyor drum 24 is displaced upwardly from the plane of the remainder of the belt, with the belt supports 17 also being displaced progressively towards it for the last portion of the conveyor to give a parabolic profile upwards which achieves an extra amount of horizontal displacement of the dumped material.

Figure 8 illustrates an intermediate conveyor unit 25 which consists of a frame 26 mounted on two endless tracks 27, one adjacent each end of the 25 frame, which also carries an electric drive motor 28 for the conveyor belt 29. It will be seen that the unit is self-contained and operable separately of the overburden dumper, but co-operating with it to extend the range of deposition of material from the overland conveyor, thereby avoiding the need to move it. The belt has a lowered end 30 which can be positioned beneath the tripper conveyor 30 on the tripper station, as described hereinafter with reference to Figure 12. Figure 9 illustrates one method of deposition of overburden in accordance with the invention. Overburden from the overland conveyor 13 is fed by the tripper station 14 to the dumper, whose boom conveyor 3 lifts and deposits the material to form a conical pile 31. Levelling of the conical pile 31 on completion forms a bench 32 from which further deposition can take place, as illustrated in Figure 12.

Figure 9 illustrates a single bench operation, while Figures 10 and 11 illustrate a triple bench operation, with the lowermost bench 33 being progressively buried beneath the middle bench 34, formed in the same way, while this in turn is progressively buried under the uppermost bench 35, this method permitting very large and deep excavations to be refilled progressively by overburden excavated from elsewhere in the opencast mine, for example.

While Figures 9 to 11 illustrate a single-pass method, it is possible to extend the range of deposition without moving the overland conveyor by the use of the intermediate conveyor 25, as described with reference to Figure 8. Material from the tripper station 14 is discharged on to the intermediate conveyor 25, which in turn discharges the material on to the lower end of the boom conveyor in the overburden dumper so that the next pass extends the bench further outwardly of the overland conveyor. The range can be further extended by the use of another intermediate conveyor between the first intermediate conveyor and the dumper.