CURING CYCLE OPTIMIZATION OF A THICK-SECTION RUBBER PART

The curing cycle optimization is a first order concern for the rubber industry both to control part quality and to reduce curing times. The curing control of thick parts is very delicate due to low thermal diffusivity of rubber compounds. We present a numerical method for the optimization of the cure cycle of molded parts. The heat equation and vulcanization kinetic equation are solved considering the induction, curing, and reversion phases. We build a conjugate gradient optimization method that estimates an optimum temperature-time couple applied as boundary conditions necessary to obtain a desired homogeneous state of cure. We describe the experimental device including a thermally controlled mold. We also describe the thermal regulation and instrumentation including an original measuring device recording temperatures directly within the molded part while minimizing thermal disturbances during measurement. Then, we present the model validation by comparing the numerical simulation results with those obtained experimentally. We propose a curing cycle optimization method based on the calculation of the sensitivity of the state of cure with boundary condition variations. It is an iterative procedure that allows converging to the boundary conditions necessary to obtain the best compromise between the state of cure homogeneity within the part thickness and the curing time. We define a productivity criterion inversely proportional to the curing time and a quality criterion proportional to the homogeneity of the state of cure. Based on these two criteria, we define a performance index that qualifies the process considering the compromise between quality and productivity.