Doctor of Philosophy
Department of Mechanical Engineering
Yu, Yongqin, Theoretical modelling and experimental investigation of the performance of screw feeders, Doctor of Philosophy thesis, Department of Mechanical Engineering, University of Wollongong, 1997. http://ro.uow.edu.au/theses/1601
Screw feeders are being widely used in industry to feed reliably many kinds of bulk solids because of their simplicity in structure, good metering characteristics, total enclosure for safety, great flexibility of design and wide application. However, to date, the design of this type of equipment is still not precise due to an overall shortage theoretical analyses and experimental data reported in the literature. For this reason, this thesis aims at formulating theoretical models to predict the performance of single and twin screw feeders. The models concentrate on the volumetric efficiency, draw-down performance and torque or power requirement of screw feeders.
The models are based on analyses of the relevant particulate mechanics. An element of bulk solid sliding on the helical surface of a screw flight will move in a direction related to the angle of friction between the bulk solid and the surface, and helical of the flight surface. An analytical solution to the integral equation to express the volumetric efficiency of screw feeders has been obtained. A theoretical model for the torque requirement is developed by analysing the stresses acting on the five confining surfaces surrounding the bulk solid contained within a pitch. This model allows the torque characteristics to be predicted. A criterion for uniform draw-down performance is presented based on the pitch characteristics of the screw.
To obtain detailed information on the interaction among the screw geometry, the operating conditions and properties of the bulk solid, a systematic experimental investigation is undertaken into the performance of screw feeders with different screw and trough configurations, three types of bulk material and different operating conditions. Experimental programs on the twin screw feeders are also conducted to observe the effect of operating conditions and geometric parameters. The factors affecting performance of the twin screw feeders also are analysed.
Experimental data are compared with the results obtained from the theoretical predictions. The volumetric efficiency, draw-down performance and torque requirements of screw feeders predicted by the theoretical models developed in this work are found to provide results which agree well with experimental data.
The performance prediction models are also applied in industrial practice. Some typical problems experienced by industry are analysed. New design of screw feeders are provided for four upgrade projects.