A new Technology for Steep Incline High Capacity Open Pit Conveying
A new conveyor design is set to help reduce conventional heavy-duty truck traffic and the resulting high operating costs in open pit mines. This article presents the design and the initial findings of the feasibility study on the Chevron-Megapipe conveyor for a 350 m-deep open pit mine and a mass flow of 5000 t/h.
A research and development consortium founded by Contitech, Siemens, and Thyssenkrupp will be marketing the jointly develop Chevron-Megapipe conveyor. The high-strength ribbed steel cable conveyor with its nominal strength of up to 9500 N/mm and an outer diameter of up to 900 mm facilitates the cost-effective conveyance of ore and overburden with lump sizes up to 350 mm over mine slopes with angles of inclination of 30° to approx. 45°.
Steep-angle Conveyors — Overview and Comparison
Open pit mines worldwide are frequently operated in shovel/truck mode at present, i.e. the material recovered by the hydraulic excavator is loaded onto heavy-duty trucks, and transported by these out of the open pit mine across unpaved roads winding up along the pit slope with maximum inclinations of up to 9%. As an open pit mine’s size, depth, and production capacity grow, so too does the truck fleet required for material transportation. Despite truck sizes of 106 to 260 t dead weight and transport capacities with payloads of 240 to 400 t, a truck fleet in larger mines can be made up of 100 single vehicles or more.
The operating cost of truck transport accumulate from tire wear and tear, diesel consumption (keeping in mind that a trucks dead weight always has to be transported additionally to the payload), personnel cost for truck drivers, maintenance, road refurbishment, etc. Furthermore, operating a larger truck fleet safely requires a high level of coordination effort to control its immanent safety risks.
In flat open pit mines with overall slope angles of less than 30°, truck traffic can be reduced or replaced through the use of commercially-available, troughed conveyor belts or even smooth closed-trough belts, e.g. pipe belts (Fig.2, left).
Although troughed belt systems can also be used in hard rock open pit mines with steeper overall slope angles >30°, they require relatively long conveying routes out of the open pit mine.
The ever decreasing ore content in many of the world’s deposits means that more and more overburden has to be carried away in order to recover a certain quantity of minerals. The Thyssenkrupp integrated skip conveying and crushing system allows uncrushed run-of-mine to be lifted along the shortest route out of the pit with overall slope angles of 45° to 90°  (Fig. 2, bottom right). If the material has been crushed in advance, the Flexowell or Pocketlift systems from Contitech are also suitable here (Fig. 2, top right).
The Chevron-Megapipe conveyor is now a pipe belt conveyor with performance data that has never been achieved before for gradability and conveying capacity. It is fed by a primary crushing stage located in the area around the feeding station, and is equipped with a pipe belt with an outer diameter of (DA = 780…900 mm) with a ribbed carrying side cover. In the area around the belt width where the Chevron ribbing has been applied, chevron cleats continuously cover the belt’s entire area lengthwise (except the overlapping area and the areas adjacent to the overlapping area, as shown in Fig. 1).
The ribbing of the carrying side cover can feature both a different pattern (fishbone, chevron cleat, etc.) as well as different cleat heights and thicknesses. In general, the cleat height has an interval of 10 to 50 mm, but can also be larger if necessary. The chevron cleats are arranged continuously lengthwise, and this ensures a better grip between the conveyor belt and the material.
When the Megapipe is rolled up out of the troughed state and into the tube state in the material feeding area, the material in the enclosed belt is compacted. This causes the material’s internal friction to rise. In turn, the increased internal friction and the high wall friction coefficient of the bulk material in a Chevron-Megapipe positively interact with each other and, consequently, the friction-locked material transportation with a significantly higher inclination comparing to standard belts takes place.