Professor Bill McBride

The OLDS elevator is a variation of a vertical screw elevator where instead of the screw flight rotating inside a fixed tube, the tube rotates around a fixed screw flight. This difference may seem superficial but the mechanics of operation are significantly different and the resulting device, the OLDS elevator, has the potential to replace and improve upon numerous existing elements of many plants. As part of the TUNRA bulk solids general research program, investigations were carried out into the OLDS elevators performance. The results of these investigations are summarised in this overview document. Further information can be located in the references.

In recent years there has been a steady increase in the number of self unloading ships involved in the world shipping trade. This paper focuses on unloading difficulties encountered on board the M.V. River Yarra, a vessel converted to self-unloading configuration in late 1991 which is now working around the Australian coastline. These difficulties arose when discharging cohesive materials such as gypsum, salt and slag. Due to the design of the reclaimer units a portion of the cargo within each hold was not positively reclaimed. This resulted in large unstable sections of cargo which caused damage to the reclaimer unit when they collapsed. The investigation involved the development of computer based solid models of each hold, the determination of strength and frictional characteristics of the various cargoes and a review of the slope stability of the cargo within the hold. From the solids model, the amount of cargo positively reclaimed and the capacity lost due to alterations to the holds were calculated. Measurement of the frictional and bulk strength characteristics allowed an analysis of the product stability within the hold during reclaim.

The design of screw feeders requires detailed consideration of the geometry at the interface of the screw and the feeder. This paper focuses on the determination of the required screw geometry and variable volumetric efficiency along the screw in order to predict the required parameters of pitch, screw diameter, and core or shaft diameter to meet the stated objectives. Experimental results are presented which corroborate the theoretical predictions. Specific examples are highlighted and the optimization of screw geometry to achieve a required objective such as uniform draw-down is outlined.

The design of screw feeders requires detailed consideration of the geometry at the interface of the screw and the feeder. This paper focuses on the determination of the required screw geometry to achieve specified draw-down performance objectives. A theory is presented which takes into account the screw geometry and variable volumetric efficiency along the screw in order to predict the required parameters of pitch, screw diameter, and core or shaft diameter to meet the stated objectives. Experimental results are presented which corroborate the theoretical predictions. Specific examples are highlighted and the optimization of screw geometry to achieve a required objective such as uniform draw-down is outlined.