Overcoming a Mines Embankment

IPCC-system with new Belt Conveying Concept for steep Opencast Minewalls

Overcoming a Mines Embankment

In order to allow for a continuous high capacity conveying system out of steep walled open pit mines Thyssenkrupp together with Contitech and Siemens developped the Chevron Megapipe conveyor with an up to 900 mm outer diameter. The pipe belt features highest tensile strength as well as a ribbed carrying side to hinder the transported bulk material from rolling back.
(ed. wgeisler - 30/11/2017)
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The tests involved two Contitech pipe belts with diameters of 800 mm, with and without 50-mm-high chevron cleat-ribbed profiling, inserted in a steel carrier pipe with clamping brackets. In order to recreate the dynamic tumbling effects that occur in real pipe belt conveyors when the belt pipe passes through the hexagonal conveyor idler stations, the test rig was fitted with eight pneumatic impact vibrators distributed along the length and circumference of the belt that applied pulsing vibrations to the belt and material bed. A truck-mounted crane slowly and smoothly raised the test rig at one end in order to simulate the slope or the slip angle, resp. In the area of the normal belt overlap in the pipe belt, video cameras with illumination were installed in the longitudinal direction in order to electronically record the start of the bulk material movements depending on the angle of elevation.

Fig. 4 shows views from the inside of the approx. 50% filled Chevron-Megapipe with four high-resolution video cameras and with the test rig at the angle of 45.6°: the pipe belt is vibrated by defined impacts at corresponding time intervals, and the first material particles begin to move (camera 4 shows the first four stones at the bottom of the test rig).

Fig. 4: View of the inside of the Chevron-Megapipe half-filled with material                                   

Fig.5 summarizes the results of the investigation for coarse bulk material in the pipe conveyors, with and without the mentioned chevron cleat ribs for the “critical” case (complete emptying of pipe). Half the test rig was filled for this reason with material to a fill factor of 50% of the cross section. This means that, as in real conveyor operation, there are no supporting and subsequent layers of material present when a pipe conveyor is emptied.

Fig. 5: Summary of maximum angles of elevation in the empty state                 

The maximum possible slope angle for a belt system without backward slipping of the material bed depends both on the system parameters (e.g. belt geometry, conveyor speed etc.) and on the properties of the bulk material. The angle is the result of the interaction between the wall friction coefficient (rubber cover plate/bulk material), inner friction angle of the bulk material (the angle of repose, to simplify), the stress condition in the bulk material (compression/loosening), and finally the grain size distribution (inner particle wedging in the bulk material body). As the bulk material properties of the primary crushed diabase are very similar to the properties of similar coarse-grained bulk material such as ore or rock overburden, the findings of the investigation can also be applied to other, similar primary crushed bulk materials in hard rock opencast mining. 

If we now compare the results from the current experiments against previously published results from DEM-FEM simulations [2], we can see that the theoretically determined slope angles are almost identical to the values determined in experiments. This close consistency of findings when determining the maximum slope angle confirms that purely theoretical investigations of the slip characteristics should suffice in the future for similar bulk materials and system parameters.

Investigating Impact- and Cleat Ribs’ Wear-Resistance 

Experimental investigations of the impact-strength, bond-strength and wear-resistance of the new chevron cleat ribs on the Contitech impact test rig and in a belt system transfer station in the Oetelshofen limestone opencast mine in Germany were used to determine the expected lifetime of chevron cleat ribs referring to a wear and a profile bond-strength to the belt surface under the extreme opencast mining conditions. The aim was to develop innovative chevron cleat ribs with an optimum profile geometry and to develop a rubber compound that will exhibit especially strong durability under the most severe impact and wear conditions.

The bond strength and impact strength of the chevron profiles were investigated under practical and laboratory conditions at the Contitech test facility, by means of impact tests.

Fig. 6: Experimental investigations of the bond- and impact-strength of the       
new chevron cleat ribs on the Contitech impact test rig.               

The required wear-resistance for these profiles was verified using sample belt sections as an impact plate in a material transfer station within the conveying flow of a limestone quarry (Fig. 7).

Fig. 7: Wear-resistance tests in a belt system   
    transfer station in the Oetelshofen  
limestone opencast mine.           

This figure shows that the newly developed chevron cleat rib exhibits longer durability than the 14-mm-thick upper rubber cover plate of the basic belt 2000 St3150 14:7 DIN-X. The 1026-m-long steep conveyor, the system parameters from [2] and the 14-mm-thick rubber cover plate were used to calculate the durability of the chevron profiles. Taking into account the measured hours of use until the profiles wear in the material transfer station, the theoretical durability of the chevron profiles was calculated as approximately five years or more. 

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