Numerical Simulation of a PA66 Flow Behaviour in a Hot Runner Gate Alberto Gava, Giovanni Lucchetta Department of Innovation in Mechanics and Management, University of Padova, Via Venezia 1, 35131 Padova, Italy Phone: (+39) 049 8276823; E-mail: alberto.gava@unipd.it Summary: In actual hot runner systems for the injection moulding process, the control of polymers in gate is passive, which means that the melt temperature distribution and associated flow conductance is governed by a balance of heat convection by the flowing melt with heat conduction from the hot melt to the cold mould. This paper examines the rheological and thermal behaviour of a PA66 during freeze-off and melt flow activation. Numerical simulations were carried out according to the Finite Volume Method as implemented in the Ansys CFX ® code. Rheological and thermal data were obtained from a careful material characterization conducted on a capillary rheometer and a differential scanning calorimetry (DSC). The analyses indicated that relatively small changes in melt temperature and injection pressure can substantially increase the flow conductance and dynamically control both the gate freezing and the onset of melt flow in the subsequent cycle. Therefore, simple gate thermal actuators were designed and numerically implemented to active control the plastic melt flow. This numerical approach can be used to design and optimize the active control of hot runners gate when the use of mechanical actuation (i.e. valve gates) is not suitable due to excessive cost, critical maintenance or miniaturization of the entire system. Keywords: computer modeling, differential scanning calorimetry, injection moulding, polyamides, rheology. Introduction There has been a sustained evolution towards closed loop control in injection moulding. Advances are driven largely by economic concerns since machines can typically operate at higher production rates and with high production yields under closed loop control than with open loop control. By definition, every closed loop control requires a feedback path back to the output being controlled. Most closed loop controls act on feedback regarding machine elements, which do not necessarily provide precise control of the process states that determine the quality of moulded products. As such, injection moulding is not a closed loop process with respect to the quality of moulded parts. Instead, injection moulding is an open loop process in which many closed loop processes are linked such