Limit angle of the belt conveyor inclination at transporting lumpy loads

Abstract

One of the ways to reduce capital costs and shorten length of conveyor transport routes is to increase angle of the conveyor inclination. As practice shows, limit inclination angle of general-purpose belt conveyors transporting bulk loads is 18°- 22°, while angle of natural slope of ore and coal is 40° and 35°, respectively. Such a difference between the angles of bulk load slope and limit inclination angle of the belt conveyor transporting the bulk loads is explained by the belt vibration impacting on the state of the transported load during its moving along the belt conveyor idlers. When exposed to vibrations, the solid-yielding state of the granular medium passes into a free-dispersed state at which inertial forces of the particles exceed the forces of internal coulomb friction between the particles. Moreover, as experimental studies have shown, granular medium moves relative to the conveyor belt at anglesof conveyor inclination of 18°–22°, i.e. limit angle of inclination of the conveyor belt transporting bulk load does not exceed 18°–22°. Today, limit angle of inclination of the conveyor belt transporting bulk loads is not studied well. In this research, the authors tried to determine limit angle of inclination of the conveyor belt transporting bulk loads by considering different types of the idlers: with rigid line, damping idlers and suspension idler with rope line. Limit angle of the conveyor belt inclination was determined on the basis of the change in momentum theorem applied to the lump during its moving over the idler and with the assumption that a lump, while passing over the idler, began sliding along the conveyor belt. As a result, analytical dependences of limit angle of the conveyor belt inclination on the conveyor parameters (belt tension and speed), parameters of idlers (distance between them), length of the bulk load and coefficient of friction of the lump against the conveyor belt were obtained. The studies of the obtained dependences showed that belt conveyors with damping idlers featured the widest limit angle of inclination, and inclination angel of the belt conveyors with suspension idlers had the least value. In addition, it was found that with increase of the conveyor belt speed and weight of the transported lumps limit angle of the conveyor inclination decreased and increased with increase of the belt tension. Further, critical speed of the conveyor belt was determined at which piece of load began sliding along the conveyor belt at any angle of the conveyor inclination.