Open-pit mining often relies on excavators and trucks for the extraction and subsequent removal and transport of the material. Diesel is the standard energy source used to run the machinery. This mining method has several disadvantages, i. e. high operating costs for fuel, personnel, accommodation, travelling and maintenance, a high safety risk caused by the effects of the weather or by the human factor or a heavy burden on the environment caused by CO2 and noise emissions.
Slope angles in open-pit mines can come up to 70°, which is why roads for trucks in open-pit mines are usually laid out in terraces. RopeCon® offers an alternative way of organising the transport of material in difficult terrain (Figure 1).
RopeCon® is a product of Doppelmayr Transport Technology GmbH, Wolfurt/Austria, and has been developed specifically to transport material of all kinds. The system is perfect for transporting material in and over difficult terrain: it can traverse obstacles such as rivers, buildings, gorges, or roads without any problem whatsoever and will easily overcome steep conveying sections of up to 70°.
RopeCon® transports the material on a flat belt with corrugated side walls. This belt design originates from vertical conveying, where it has been used for decades. The flat belt performs a haulage function and is driven by, and guided around, a drum at both ends. It is mounted on axles arranged at regular intervals to support it. Running wheels are fitted to both ends of the axles. These wheels run on track ropes with fixed anchoring and guide the belt. The track ropes are lifted off the ground on tower structures. Due to the rope support structure distances between the towers can be several hundred metres long, and RopeCon® will affect neither the terrain between the towers nor roads, trucks or other infrastructure.
Depending on the steepness of the terrain, the RopeCon® belt can be fitted with cleats in order to stabilise the material on the belt. These components, too, originate from vertical conveying and allow for a transport of the material over inclines of up to 90°.
RopeCon® can also be extended in line with the axis of the conveyor belt. As the open-pit mine grows and changes, the loading or discharge point can be adjusted flexibly along that axis to meet the new requirements. Additionally, under certain conditions, it is possible to discharge the material at several discharge points along the axis of the conveyor belt.
The greatest possible grain size along with the maximum conveying angle will determine the width of the flat belt, the height of the corrugated side walls, the height of the cleats and their spacing. Subject to certain conditions, RopeCon® can handle lump sizes of up to 1,000 mm. In this case, there is no need to crush the material prior to transporting it out of the pit.
Conveying capacity, conveying speed, possible nominal breaking strength and required nominal breaking strength of the flat belt are the factors which determine the greatest possible vertical rise. The conveying speed is usually limited by the maximum grain size. High-strength flat belts with steel cord tension members and nominal strengths of more than 7,800 N/mm are state-of-the-art. The necessary nominal strengths are determined in accordance with the provisions of German Industrial Standard DIN 22101:2011-12. Where conveying capacities are lower and grain sizes smaller, RopeCon® can overcome differences in elevation of up to 1,200 m.
Easy maintenance characterises RopeCon®: all moving parts such as i. e. the running wheels are attached to the belt and therefore keep passing through the stations, where they can be serviced without a problem. RopeCon® can also be fitted with an inspection vehicle to facilitate inspection along the line. Consequently, only a small number of personnel is required to operate and service the system.
For the following example a mine operator must transport 5,000 t/h of ore from a loading station at the bottom of an open-pit mine to a discharge station located outside the mine (Figure 2). RopeCon® spans a terraced open-pit mine over a length of 486 m and a vertical rise of 350 m in one long stretch. It does not touch the terraces so that they can be used by the mining vehicles as before. The conveying track runs in a straight line and can be chosen independent of the geological conditions between the ground contact points. RopeCon® can be loaded and emptied just like any conventional belt conveyor, e.g., via chutes. The drive unit for the RopeCon® system in the example is positioned outside the mine. Doppelmayr has assumed a transport route of approximately 5.1 km between the loading and the discharge point if the material is to be transported on trucks. With a maximum vehicle load capacity of 363 t approximately 15 trucks will be necessary to achieve the required conveying capacity. RopeCon® will achieve the same conveying capacity at just 60 % of the costs.
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