High Angle Conveying, the Vital (missing) Link to IPCC Systems – 2017

Belt Conveyor Technology

High Angle Conveying, the Vital (missing) Link to IPCC Systems – 2017

Installations and recent studies have demonstrated the technical and economical advantages of high angle conveying for optimization of any IPCC system, yet that industry continues to struggle with the use of conventional solutions to achieve the high angle function.
(ed. WoMaMarcel - 07/4/2017)
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Fig. 5 illustrates the basics of the Loop Belt. Having a C-profile, an inner belt is supported along the carrying-elevating path by closely spaced troughing idlers along the convex curved path until discharging over the inner belt’s head pulley. The outer belt is loaded like any conventional conveyor and carried on troughing idlers up to the start of the sandwich. At the start of the sandwich and through the C-profile, the outer belt radially urges itself and the bulk material against the supported inner belt. In this manner, it imparts a radial hugging pressure onto the bulk material that develops its internal friction – the friction that resists the gravitational slide back forces. The outer belt may tangent off of the carrying path to its head pulley or it may continue over the inner belt’s head pulley in the case of a high angle discharge. Typical Loop Belt arrangements included a long approach of the bottom belt that ran the full length of the ship as the main collector conveyor. The C-profiled elevating portion could follow a tight path through the engine room thus making no imposition on the ship’s cargo carrying capacity.

Fig. 5: Basics of the loop belt.

Many Loop Belts were built throughout the 1970s and continue today including several systems by the writer. These systems utilize all conventional conveyor components and equipment including smooth surfaced rubber belts that could be continuously scraped clean. These demonstrated very high tonnage rates exceeding 10.000 t/h utilizing belt widths up to 3048 mm (120 in) running at speeds to 6 m/s. The Loop Belt was first to introduce the concept of radial hugging pressure derived from the belt tension and the curved profile. Though it was not published by Stephens Adamson, this is according to the relationship and equation of Fig. 6.

Fig. 6: Radial load due to belt tension.

Dos Santos Sandwich Belt of the 1980s

The Loop Belts were the inspiration for the Dos Santos developments of the early 1980s. They featured all of the positive characteristics of conventional troughed belt conveyors. They were well suited for the self unloading ship systems but the C-profile did not provide the most direct high angle path along a general, straight high incline. In open pit mining, this would be the typical path from the pit to the surface along the mine high wall.

In 1979, the USA Bureau of Mines awarded to Dravo Corporation a study entitled High Angle Conveyor Study. J.A. Dos Santos was a key member of the study group. The focus was to develop high angle conveying systems for open pit mines; to provide a most direct haulage path from the pit to the surface and to displace mine haul trucks in that duty. The materials to be handled would be coarse, primary crushed ores and waste rock. Haulage rates would be high at thousands of tons per hour.

That study considered the state of the art in high angle conveying including bucket elevators, pocket belts, fin belts, sandwich belts and other specialty systems. Though the least understood from a theoretical and design standpoint, for the reasons previously mentioned, the sandwich belts, particularly in the form of the Loop Belt, appeared to offer the best characteristics for the requirements if the profile limitations could be overcome. It was during this study that the writer began the in-depth investigation that resulted in formulation of the theory and standards of sandwich belt high angle conveying, rationalized in the conventional conveyor technology. The guiding principle of the development became the prophecy: “A Sandwich Belt High Angle Conveyor, rationalized in the Conventional Conveyor Technology, will have the operating characteristics of a conventional conveyor – high reliability and availability, low operating and maintenance costs”.

The complete rationalization is beyond the scope of this writing and can be found in [2]. A very important element of the rationalization is worth illustrating here. It was necessary to develop a more realistic sandwich belt model to replace the 1950s model of Fig. 4. Such a model is depicted in Fig. 7. It accurately depicts the reasonable cross-sectional filling with enough material free edge distance to allow for the normal misalignment of the belts while running. This means that, compared to the open troughed conveyor, for the same material, rate and speed a sandwich belt conveyor requires wider belts. This does not limit the possible conveying rate as very wide belts and components are available.

Fig. 7: Sandwich belt model #2 - 1980.

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