5. In-stope transportation
5.2 Material handling
5.2.2 Monorail systems
operating at gradients of up to· 410• The capital costs for a large friction drive unit are typically R1 million to R5 million per train. Established suppliers include Waiter Becker, DBT/Scharf and Hydro Power Engineering (HPE).
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Rope-driven monorail: The original motivation for developing this unit was to modify the electric or electriclhydraulic monorail to operate in the stope horizon. ·Due to the cost of such a unit, DBT/Scharf felt it would be more cost-effective to use a rope-driven monorail system. The capital cost for such a unit would be approximately R550 000.
Manual and powered crawl units: These are small units suitable for horizontal operation only. They can be used as crawl systems in the stope cross cut to improve material handling with monowinch systems. They may also be applied in the strike gully, as a take-over unit for palletised material that has been delivered to the centre raise by the monorail. The capital cost for such a unit would be less than R100 000.
Method of operation
From cross cut to centre of raise
In this scenario,the monorail brings material to distribution points in the centre raise, usually at the strike gully intersection. From the strike gully, the material can be transported in several manners, by hand (human trains), by scraper scoop/basket, by in-stope monowinches or by crawl units operating in the strike gully. Although this system transports the material to the end of the strike gUlly, the material still needs to be rehandledfrom the gully to the point of application.
. Further, while material is being transferred from the gully to the face, scraping operations must be stopped.
OBT rope-driven system
The OBT Rope Drive System is driven off a rope which is driven from a winch located in the cross cut. The master trolley unit is connected to the rope and operates in the raise between the winch and the return unit (Figure 5-18).
Potentially, this system could extend the delivery point from the centre of the raise to the end of the strike gully by utilising turntables at the strike gully position. At
the centre raise/strike gully intersection, the material can be redirected to the strike gully by means of the turntable. The material is then transported to the face along overhead beams, either manually, by winch or by a crawl unit.
RAISE STOPE TRANSPORT CONCEPT .
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Figure 5-18: Rope-driven monorail system (Nehrling, 2002)
Future implications
Monorail systems from the cross cut to the stope faces may be regarded as the ultimate vision for in-stope material handling. In this scenario, material would be collected at the cross cut, transported up the centre raise and switched into the strike gully, where the monorail would transport the material to the point of installation above and below the strike gully. The material would be packaged in .such a way that it could be assembled as a ready-to-install unit, and thus only limited manual labour would be required to build the pack, i.e. to block and prestress the pack. Where other materials, such as elongates and packs are required in the stope, the monorail would transport the items to a face material handling system which would then transfer the material to the point of application.
HP WATER TRACTION DRIVE
STORAGE PAD+/-300 KG.
STABIUSING PROP
Figure 5-19: In-stope face material handling system (Wilson et al., 2000)
This is a long-term scenario, which it is estimated would take at least a decade to achieve. Based on the experiences of operating monorails in a shallow incline environment «14°), where two to three years were required to make the monorail system efficient, it is envisaged that similar periods will be needed to resolve each of the remaining technical challenges. For example, it may take two to three years for a monorail to operate efficiently from the cross cut to the centre raise. A further three years may be required to achieve similar results for the monorail operating in the strike gully. The technology for transferring material from the monorail to the desired position above or below the gully would still need to be developed, as would the face handling system for moving the material on the face.
If this vision cannot be realised, the role of the monorail as a cost-effective in- stope material transport system is questionable. The matter of utilising the monorail to move only heavy equipment is debatable, as the time and cost involved in such an installation make this mode of transportation uneconomical.
In fact, it may be worthwhile in the first place to query how often these items need to be transported in a well-operated stope. Thus, the question must be asked,
"Are monorails necessary or economically feasible in the stoping horizon?" If the monorail does not take material from the cross cut to the point of usage, then effectively the monorail is only replacing the monowinch without reducing the extent of handling requirements. The benefits of receiving palletised material in
the raise are questionable, as the material would still require further handling to reach its final position.
This is not to say that monorail systems do not have a role to play in the stoping environment. Indeed, it may still be feasible to use the monorail to develop/raise and equip stopes, thus reducing the time required to establish the stope. In this case, the monorail is used primarily as a development tool, with material handling being a secondary function. In other cases, the monorail may be used to support layouts with long backlengths.