Discrete element modelling of a bucket elevator head pulley transition zone

Abstract

This paper presents the results of discrete element simulations applied to a bucket elevator model with particular reference to the head pulley transition zone. This is the first stage in a larger study to better understand the mechanics of bucket elevator operation with reference to the discharge of particles at the head end. At the head end two issues arise; mechanically, the buckets are bolted to the conveying media (typically a fabric reinforced belt) and at the point of belt to headpulley tangency, the tip of the bucket undergoes a theoretical step change in velocity. This theoretical step change results in a classical under-damped response in the buckets tip velocity. In undergoing this motion, there are stresses that are passed to the carcass of the conveying media; understanding the magnitude of these stresses is one longer term goal of this research allowing a quantitative basis for the existing qualitative design guidelines such as (Handbook for conveyor and elevator belting, Apex Belting Pty Ltd). The discharge of the bulk material from the bucket has been addressed Beverly et al. (Bulk Solids Handling, 1983) but this analysis is dependent on simple, but common, bucket geometry and ignores the initial transition to the headpulley. Ignoring the transition with a low speed discharge elevator is not likely to impact on the predicted discharge pattern, however with high speed discharge elevators, the destabilising effect of the transition is expected to promote premature discharge of bulk material from the bucket. Depending on the design of the elevator casing this early discharge may or may not impact on the overall conveying efficiency.