Finite Element Evaluation of the State of Cure in a Tire

Abstract

Abstract Curing is one of the most important steps in the tire manufacturing process. During this process, a green tire is formed to the desired shape and the compound is converted to a strong, elastic material to meet tire performance needs. The process of curing, commonly called vulcanization, is usually accomplished under pressure and an elevated temperature provided by the mold. The curing process is energy-consuming and has a strong effect on material properties. To attain an optimal state of cure for different compounds of various dimensions at minimal capital and energy costs requires proper evaluation of the state of cure in a tire. Various numerical models have been proposed to determine the state of cure of rubber compounds in molds. Their applications are limited to simple geometry and boundary conditions. For a tire, which has complex shape and variable boundary conditions, the finite element method appears to be an ideal candidate because of its versatility. In this paper, a commercial finite element code, ABAQUS, is used to determine the temperature history of a tire in the curing press. In order to evaluate the state of cure throughout a tire, a user subroutine, HETVAL, is implemented. In the subroutine, the state of cure is determined based on the temperature history using a selected kinetic model, whose cure rate parameters are obtained from moving die rheometer (MDR) measurements. The heat generation due to chemical reaction is also included. The evaluation of the state of cure using the finite element method is benchmarked using a number of rubber compounds with simple geometries and boundary conditions. Both isothermal and nonisothermal conditions are tested. The predicted temperature history of a tire is then verified by the temperature history obtained from the thermocouples embedded in the tire. Parametric studies are carried out to evaluate the effect of various temperature histories on the state of cure in a tire. The results are used to shorten the curing cycle.