Monitoring of shear heating effects during injection molding of rubber to improve the process control

This work aims to get new insights into the “process monitoring tool” proposed by the authors for the online monitoring of the shear heating phenomenon during injection molding of technical rubber parts. The online monitoring is based on direct measurement of the surface rubber temperature (shear heating temperature, T SH ) by an infrared thermal camera of the rubber as it leaves the extruder barrel of the injection molding machine. The measured rubber temperature is a process indicator giving the thermal history of the rubber compound injection and process safety. Therefore, this fast process control is applied to industrial applications to investigate the processing behavior of ethylene acrylate (AEM) rubber compounds. In particular, the relationships between T SH vs injection pressure, vs injection speed, vs screw speed rotation and vs screw length over diameter ratio ( L/D ratio) and vs AEM rubber compound properties variation due to exceeding the shelf life are investigated. The results show that T SH is manly influenced by the screw L/D ratio, followed by injection pressure and screw speed rotation (especially if are set to higher levels), whereas the injection speed is the least effective parameter to reduce T SH . Furthermore, a previously found robust correlation between the shear heating parameter ( η SH ) and the minimum torque measured in rheometric laboratory tests ( M L ) is used to show the noteworthy deviation from the proportional trend when the AEM rubber compound exceeded it shelf life. Therefore, the coefficient of determination of logη_SH vs M L curves provides a good indication of process stability, while it is running.