Mining equipments and crushers in the mining mines

Mining equipments selected

The use of semi-continuous mining technology does not dictate any particular form of excavation machine. Applicable units for feeding a mobile crushing system might include:
• hydraulic shovels,
• large front end loaders,
• medium-sized rope shovels,
• large rope shovels.

All of these styles of equipment are used to load mobile in-pit crushing systems at varying rates. Typically front end loaders are used for rates up to 2000 t/h (Caterpillar Handbook). In those instances where greater capacity than this is required either a hydraulic shovel or a rope shovel may be used.

Currently the largest mobile crushing machines in service are fed directly by large rope shovels (P&H 4100XPB). Large electric rope shovels offer significant economies of scale. A single machine, capable of a continuous capacity of up to 10 000 t/h, operating without replacement for the life of the mine, offers an attractive option for large-scale operations. At the limits of current standard machine operations, the 100 tonne rope shovels are able to mine an 18 m face (P&H 4100XPB). At 10 000 t/h, a mobile crushing machine of this size is readily able to mine up to 44 Mtpa (without a belt wagon) and possibly as much as 50 Mtpa with one.

Possibly more appropriate for operation in an iron ore operation, mid-sized electric rope shovels (approximately 60 tonnes/pass of the P&H 2800XPB variety (P&H 2800XPB)) offer some economies of scale. A single such machine is capable of up to 5000 t/h. At the limits of current machine operations, the 60 tonne rope shovels are able to mine an 18 m face, but might be more appropriately employed on a 9 or 10 m bench. Remote mining operations frequently utilise hydraulic shovels in lieu of electric rope shovels. Their selection often reflects a need for their greater mobility and, since diesel powered machines are readily available, the absence of any requirement for electrical reticulation into the mine. Diesel hydraulic units do not have the capacity to shift 100 tonnes of waste per dipper pass and as such are not directly comparable to large electric rope shovels, but they are an attractive alternative to the smaller rope shovels. The maximum extraction rate anticipated for this style of machine would be of the order of 4000 t/h.

Having considered styles of loading equipment, it is important to note that both the electric rope shovels and hydraulic shovels exhibit similar life of mine capital cost profiles. The hydraulic shovels are cheaper to purchase, but do not have the same operational life and require more frequent refurbishment or replacement.

For smaller operations, large front end loaders could load a mobile crusher hopper without difficulty. An interesting possibility would be two units operating simultaneously; although this offers possible production rate improvements over a single hydraulic shovel it does not offer any significant operational cost advantage.

Crusher

Mobile and semi-mobile crushing machines can be built around any style of crusher. Traditionally the nature of the material being crushed has dictated the style of comminution machine; jaw crushers and gyratory crushers have traditionally been used to reduce the size of hard rock lumps, although neither machine copes well with significant clay inclusions, and recent work on rolls crushers and sizers has produced units capable of breaking lumps with quite high compressive strengths. Recent trials in a copper mine in Chile have produced similar operating costs and throughputs to a large gyratory crusher when presented with ore with characteristic strength of over 200 MPa and sizes of more than 3 m. A realistic capacity for machines of this type is therefore of the order of 200 MPa. Tougher material may be presented to the machine, and it will be crushed, but only at the expense of operational throughput and operating costs. Occasional large or hard lumps shouldn’t pose significant threats to the operation of the machine, provided it is not a sustained operational requirement.

Without a doubt the greatest benefit offered by a sizer is the capacity of the larger units to handle more than 10 000 t/h. With some care in selection of blasting and closed side setting on the discharge side of the machine, a large gyratory crusher might achieve similar throughput, but the size of such a machine makes placing it inside a mobile crushing rig problematic. A gyratory machine able to handle 4000 - 5000 t/h is more readily included in a mobile rig than its larger compatriots and so ore mining might be best performed using a hydraulic excavator feeding a gyratory crusher, while waste might best be handled by a rope shovel feeding a sizer. Rock characterisation is required before that decision can be finalised.