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.
Andrey Minkin, Peter Börsting, Norbert Becker
(ed. WoMaMarcel - 04/7/2016)
Determining the Maximum Possible Inclination Angle using DEM-FEM-Analysis
The maximum possible angle of incline is the angle at which a relative movement against the direction of conveyance starts for large, irregularly-shaped grains of material. The theoretical examination was performed taking two different heights of chevron cleat ribbings into consideration: 15 mm and 50 mm. To analyze the material behavior, the parameters of the feasibility study in Chapter 2 were taken and two different degrees of material filling used as the basis, i.e. in the normal operating state (belt is continuously loaded along its entire length) and during discharging so that behavior during deactivation and empty running could also be recorded. The maximum angle of incline of a conveyor belt depends on the interaction between the wall friction coefficient of the rubber cover / bulk material, inner friction angle or angle of repose of the bulk material, the stress condition in the bulk material (compression / loosening), and the grain size distribution (inner particle wedging in the bulk material body).
For the analysis, it was necessary to take the behavior of the coarse material in the flat-to-trough section into consideration in order to facilitate a realistic tension distribution in the bulk material. To examine the material’s behavior during a specified deformation of the conveyor belt, it was necessary to conduct a coupled FEM-DEM simulation. The FEM simulations were important in order to map the deformation of a belt section during the flat-to-trough procedure from flat, via a 35° trough, to the ideal circular shape (Fig. 8). With the DEM, the interaction between the bulk material behavior and the conveyor belt was simulated.
The bulk material feed (particle generation) took place with a belt trough of 35°. The bulk material particles are shown in the form of clumps or multispheres, i.e. conglomerates consisting of ball-shaped particles (Fig. 9a) thus allowing to take a realistic irregular grain size into consideration in the DEM simulation.
The bulk material properties were identified on the basis of a material sample, and verified with the DEM model of the material.
The wall friction coefficients between a copper ore sample (dK < 2.5 mm) and a natural rubber cover (rubber grade “ISO-H”) were calculated at +20°C and -30°C (after 24 hours in a cooling chamber) with the Jenike shear cell (Fig. 9b), and showed that the wall friction coefficient is almost independent of the temperature:
- μW = 0.57 or ΦW = 29.7° at a temperature of +20°C
- μW = 0.61 or ΦW = 31.4° at a temperature of -30°C
The selection of Coulomb friction μP = 0.8 and rotation friction μR = 0.5 for the particles in the DEM model of the copper ore resulted in the angle of surcharge of Φb,stat = 38.5°, which matched the real-life situation very well (Figs. 10a and 10b).