Analysis of a melting model for an extruder with reciprocation

Recent advances in plastic material have benefited from a more optimal design of the injector for screw inline plastic injection molding. The analysis of mass flow in the injection screw is similar to that of an extruder with a reciprocating effect. However, although there is extensive use of the plastic injection molding machine in industry, most studies have been on extruders, which are simpler to model. This paper studies the melting process and derives its transient model for accurate prediction of the most important characteristics of the reciprocating extruder. Based on this transient model, factors affecting the melting speed in reciprocating extruders are identified. These include the screw rotation speed, the screw axial movement speed, the barrel thickness, the barrel heat capacity, the temperature of heater and polymer, the parameters of the polymer, etc. The model derived was used to simulate parameters measured by Donovan. Some phenomena observed by Donovan in his experiments were explained, which also established that this model gives an accurate description of the injector dynamics. Based on this model, it is shown that a lower rotation speed and a longer rotating time improves the quality of the end products. Moreover, the heat capacity of the barrel affects the transient process of melting in the way that the thinner the barrel or the lower, the better is the heat capacity. (C) 2001 Elsevier Science B.V. All rights reserved.