Cure Simulation; A Comparison of Compression and Extrusion Molding In Thick Products

Curing of rubber is a complex process which involves the insertion of crosslinks to convert the rubber into a useful functional material. The estimation of the cure time needed for product manufacture of small or thin walled products is often arrived at by means of a rheometer trace. Though, this has been recognised as adequate for thin walled products, the production of large rubber articles requires a more rigorous analysis of cure kinetics for an essentially non-isothermal process. Often finite element analysis is used to generate non-isothermal temperature histories in a thick component and then an appropriate cure kinetic equation is solved to predict the state of cure.

 In addition to generating the capability for cure time prediction, there is a need in the industry to minimise cycle time and therefore cost involved in product manufacture. For large products, the viability of the use of extrusion molding, whereby the rubber is extruded to a heated mold at the same temperature as the mold has been demonstrated in previous reported work in this laboratory.

 In the present work, the cure simulation module of Autodesk Moldflow has been used to compare the state of cure of a large molding manufactured by conventional compression molding and extrusion molding. The product thickness at which, extrusion molding becomes preferable has been investigated and the influence of material properties used to manufacture the part on the transition thickness has also been assessed. Available experimental data on the temperature histories on a large laminated bearing manufactured using compression molding is compared using Moldflow Autodesk and Abaqus predictions.

 The usefulness of extrusion molding for very large components is demonstrated and the advantages of using of simulation codes to assist in shortening cycle times in product manufacture are illustrated.