Comparison of Mechanical Properties of Rubber Products Molded by Transfer and Compression Methods**

Abstract

Abstract This paper compares the differences developed in rubber properties between compression and transfer molding methods for various types of polymers. It has been shown that the two molding methods produce distinctly different rubber properties for the same elastomer. Acrylonitrile butadiene rubber (NBR) shows little difference in durability between molding methods. Transfer molding (TM) reduces modulus and hardness of NBR, but improves compression set. The crosslink density of rubbers made with TM is higher than those made with compression molding (CM). Highly saturated acrylonitrile butadiene rubber (HNBR) properties are significantly different between the two molding methods. As for NBR rubbers, the TM method reduces modulus and hardness, but improves compression set. The crosslink density of rubbers made by TM is higher that those made with CM. Silicone rubber (VMQ) that does not require post cure shows the same rubber properties change as NBR. Transfer molding yields low tensile and modulus but better compression set. Polyacrylic rubber (ACM) molded with the TM method shows reduced tensile, elongation, modulus and hardness; but after post cure, modulus and hardness did not show substantial differences. The compression set was lower with TM both before and after post cure. Crosslink density is significantly higher with TM, but the difference diminishes after post cure. Ethylene acrylic rubber (EAM) and fluoroelastomer rubber (FKM) exhibit property changes similar to acrylic rubber when molded either with compression or transfer molding methods. Rubbers molded with TM methods showed a higher degree of anisotropy in rubber properties than with CM. With enlarged extension ratio, the coefficient of anisotropy increased, with the exception of ACM.