Thermal control and energy balance in polymer processing

Abstract

The rubber industry is facing a lack of thermal control during rubber processing. In the process of injection molding of elastomers, improving the energy efficiency of the tools is a current challenge for industry in terms of energy consumption, productivity and product quality. Experimental measurements allow us to understand the thermal of the tool and to show the thermal heterogeneities on the surface of the mold and in the various cavities. Tests of injection molding of the rubber and a thermal balance on the energy consumption of the tool are carried out. In the rubber industry, 20% of the energy consumed by capital goods comes from heating processes; more than 50% of heat losses are linked to insufficient control and thermal insulation of Molds. The design of the tooling evolves in particular towards the reduction of the heated mass and the thermal insulation of the molds. Figure 2: rubber parts and runners used in the experimental setup. The rubber compound is based on EthylenePropylene-Diene Monomer matrix. The compound has a density of 1070 kg /m3, a thermal conductivity of 0.298 W/m /K and a constant heat mass of 1490 J/kg/K. we used a RPA (Rubber Process Analyzer) in order to measure the kinetics curves of the rubber compound vulcanization. 2.3 Mold and thermal instrumentation The mold is equipped with thermal and pressure sensors (cf. Figure 3). Figure 3: view of the mold cavities equipped with sensors. The thermal device is able to measure the rubber temperature evolution in the channels and in the various cavities (Fekiri, et al., 2017). 3 THERMO-KINETIC MODEL OF MOLDING The model geometry used for the numerical curing simulation is represented in Figure 4. Figure 4: Schematic diagram of the model geometry. Mould temperature regulation is imposed on the boundaries Γ1 and Γ5. Ωm represents the metal boundaries of the mould, Ωis represents the insulating guarding element and Ωc represents the rubber part. T+ represents the mould temperature that is to be prescribed for the optimized curing cycle. During the phase (1) in Figure 2, heat transfer in the rubber part is described by equations (1),(2) and (3) with a source term related to the enthalpy of the vulcanization reaction.   c c c c c c T Cp T T H t t                   (1) The boundary conditions of phase II are described by equations (8) and (9).     T t t T t t       (2)