DETAILED OBSERVATION ON A REAL-TIME BASIS OF THE MOLD FILLING PROCESSOF RUBBER COMPOUND, USING AN INSTRUMENTED INJECTION-MOLDING MACHINE

A technique has been developed to measure the sigma = f(gamma) flow cu rve of accelerated rubber compounds in the very conditions of the inje ction moulding process. By using an instrumented injection moulding ma chine and a spiral mould equipped with pressure transducers, pressure traces are recorded on a real time basis with a fast data acquisition equipment The recorded data are analyzed and processed using the appro priate algorithms. By performing a detailed study with a silica filled EPDM compound, it has been observed that, even with a cavity of relat ively simple design, the injection moulding process is quite complex. Significant compressibility effects, combined with the warming-up of t he flowing material, occur in the earlier period of the injection; suc h effects arise over a few seconds. In selected conditions, a speed co ntrolled injection process is indeed obtained, as long as the mould sa fety pressure is not attained. In those conditions, the instrumented s piral mould allows the flow curve of the material at the mould tempera ture to be assessed, an impossible measurement with other rheological techniques such as capillary rheometry. The actual flow curves obtaine d suggest that there are slippage effects during the spiral channel fi lling.