Modelling method for studying solid conveying process in inclined plastication unit

Abstract

Owing to the higher requirements on dosage accuracy and material strength for products with microfeatures, the analysis of the solid conveying process in a microinjection moulding machine becomes more important. A discrete element modelling method discrete element modelling (DEM) for simulating polymer particles moving in an inclined narrow screw channel is developed. Adhesion and its effects on normal contact force and rolling friction are taken into account in the modelling, allowing considerations of more influencing factors on the solid conveying process, such as temperature. The straight gravity field in the real world is transformed into the twisted time dependent gravity field in an unfolded straight channel, avoiding the calculation expensiveness induced by the complex geometry of the screw channel, which is important for DEM simulations. These have not been carried out previously. Using the developed programmes, effects of screw axis inclination on the specific throughput of the solid pellets are investigated. It is found that a larger inclination angle can induce higher specific throughput, especially when the screw rotational speed is lower. However, a smaller inclination angle is beneficial for easier throughput control. The results can be used to optimise the design of the plasticating unit as well as the operation parameters of the microinjection moulding machine. In addition, experimental studies are also carried out in this approach. Results of simulations are compared with those of experiments for verifying the accuracy of the simulation model.