Analysis of a melting model for an extruder with reciprocation

Recent advances in plastic material have benefited from a more optimal desi gn 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 pl astic injection molding machine in industry, most studies have been on extr uders, which are simpler to model. This paper studies the melting process a nd derives its transient model for accurate prediction of the most importan t characteristics of the reciprocating extruder. Based on this transient mo del, factors affecting the melting speed in reciprocating extruders are ide ntified. These include the screw rotation speed, the screw axial movement s peed, the barrel thickness, the barrel heat capacity, the temperature of he ater 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 als o 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 i n 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.