pps proceeding - Abstract Preview
pps proceeding
Symposium: S11 - Elastomers and Thermoplastic Elastomers
Poster Presentation
 
 

Model for the prediction of elongational heating of rubber compounds in conical dies

Perko Leonhard (1)*, Fasching Michael (2), Friesenbichler Walter (1)

(1) Chair of Injection Moulding of Polymers, Montanuniversitaet Leoben - Styria - Austria, (2) Polymer Competence Center Leoben GmbH - Styria - Austria

The bulk temperature is a very important parameter for the processing of rubber compounds hence it is very difficult to measure and even harder to predict by means of simulation. Besides shear heating, which is a well-known phenomenon, elongational heating is neglected by most of the injection molding simulation tools. Up to now no efforts are known for calculation and measurement of this heating effect. The law of conservation of energy describes the thermodynamic changes in a fluid that flows through a circular conduit. From this equation based on models of Binding and Cogswell a new model for the prediction of temperature changes in rubber compounds flowing through conical dies and runner segments was deduced where elongational heating was described in a completely new approach. For comparison to the state-of-the-art a standard POLYFLOW simulation was carried out without taking into account the elongational component of a flow. To verify the theoretical calculations experiments on a rubber injection molding machine were made using a specially designed mold for the measurement of the bulk temperature of the purged material by means of a thermocouple. The pressure in front of the die was monitored by means of a pressure transducer. Different die geometries were used to cover the angle-dependence of the bulk temperature. The injection speed was varied to examine the influence of the volumetric flow rate. The measured bulk temperature increase showed a dependence of the flow rate and the cone angle with the flow rate being dominant. The results of the temperature measurements correlate with the calculations in quality; hence a quantitative prediction could not be achieved up to now. The computer simulation neglecting the elongational flow completely failed to predict the higher pressure loss and bulk temperature. Therefore further efforts have to be made to increase the quality of the prediction and develop a better understanding of elongational flows in polymer processing.