The present invention relates to a mining machine and is particularly, although not exclusively, concerned with excavating hard rock.
Traditionally, excavation of hard rock in the mining and construction industries, has taken one of either two forms, namely explosive excavation, or rolling edge disc cutter excavation. Explosive mining entails drilling a pattern of holes of relatively small diameter into the rock being excavated, and loading those holes with explosives. The explosives are then detonated in a sequence designed to fragment the required volume of rock for subsequent removal by suitable loading and transport equipment. The explosives are detonated once all personnel are evacuated from the excavation site and the explosive process is repeated cyclically, until the required excavation is complete.
The cyclical nature of the process and the violent nature of the rock fragmentation have to date prevented automation of the explosive process, so that the modern requirement for continuous operation and increased production efficiency has not been met. Moreover, the relatively unpredictable size distribution of the rock product formed complicates downstream processing.
Mechanical fragmentation of rock eliminates the use of explosives, has already been achieved and is well known through the use of rolling edge-type disc cutter technology. This technology has facilitated automation of the excavation process including the benefit of remotely controlled excavation machinery. However, rolling edge cutters require the application of very large forces to crush and fragment the rock under excavation. For example, the average force required per cutter is about 50 tones and typically, peak forces experienced by each cutter are more than twice than this. It is common for multiple cutters to be arranged to traverse the rock in closely spaced parallel paths, and 50 cutters per cutting array is common. Cutting machinery of this kind can weigh upwards of 800 tones, thereby requiring electrical power in the order of thousands of kilowatts for operation. As such, the machinery can only be economically employed on large projects, such as water and power supply tunnels. Additionally, the excavation carried out by such machinery is generally limited to a cross-section that is commonly circular.
Sugden U.S. Pat. No. 6,561,590 issued May 13, 2003, describes a cutting device that alleviates one or more of the disadvantages associated with prior art cutting devices. It is such a device (called the Sugden device) that is utilized in the herein later described invention. The Sugden device is a cutting device of a rotary (disc) undercutting type, that provides improved rock removal from a rock face and which is relatively economical to manufacture and operate.
The Sugden device employs a reaction mass of sufficient magnitude to absorb the forces applied to the rock by the disc cutter during each cycle of oscillation, with minimum or minor displacement of the device, or the structure supporting the device. Because the device usually applies a load at an angle to the rock face, it causes tensile fracture of the rock, instead of crushing the rock. This tensile fracture force applied to the rock is substantially less than that needed with crushing forces, such that a corresponding reduction in the required reaction mass compared to known rock excavation machinery can also be adopted. The Sugden device disc cutter when mounted to a support structure is preferably arranged so that the reaction mass can absorb the cyclic and peak forces experienced by the disc cutter, while the support structure provides a restoring force compared to the average force experienced by the disc cutter.
The Sugden device typically requires substantially reduced applied forces relative to known rock excavating machinery. A reduction at least in respect of normal forces, an order of magnitude or some other significant fraction, is envisaged. Such low forces facilitate the use of a support structure in the form of an arm or boom, which can force the edge of the disc cutter into contact with the rock at any required angle and to manipulate the position of the disc cutter in any direction. In particular, in relation to longwall mining, the disc cutter, or array of disc cutters, may be mounted to traverse the length of the long wall face and to be advanced in the main mining direction at each pass. Advantageously, the Sugden device provides for entry of the disc cutter into the rock face from either a previously excavated drive in a longwall excavation, or from pre-bored access holes, or by attacking the rock at a shallow angle to the face until the required depth for the pass is achieved. With the disc cutter mounted on a movable boom, the disc cutter can be moved about the rock face to excavate that face at any desired geometry.
The Sugden U.S. Pat. No. 6,561,590 also discloses that its cutting device is not restricted to a single disc cutter, but can include more than one. For example, the cutting device may include three disc cutters arranged along the same plane, but angled at approximately 45 degree to each other. Such an arrangement can produce a cut face of a particular shape, while the speed at which rock is removed is greatly increased. In this arrangement, each of the three disc cutters is driven by separate drive means. The use of multiple disc cutters is particularly useful for longwall operations.
The Sugden U.S. Pat. No. 6,561,590 also discloses that the cutting device is suitable for a range of cutting and mining operations and machinery, such as longwall mining, mobile mining machines, tunneling machines, raise borers, shaft sinkers and hard rock excavation generally.