Inflation Characteristics of Unvulcanized Gum and Compounded Rubber Sheets

Abstract

Abstract The inflation of rubber compound membranes to fill molds has a long history in rubber processing. There have, however, been few basic experimental studies of this topic. This free inflation of vulcanized rubber sheets was studied by Treloar and Rivlin and Saunders during the 1940's and 50's where it was used to investigate the form of the stress-strain relationship. Rivlin and Saunders sought to fit nonlinear elastic constitutive equations to data obtained at small inflation levels. In the early 1970's Denson and his coworkers utilized the inflation of unvulcanized polyisobutylene membranes to apply this as a procedure to evaluate biaxial and planar extensional viscosities. Similar studies were made by Maerker and Schowalter. These studies all involve free inflation of membranes. These studies of inflation of raw gum polyisobutylene sheets only looked at relatively small deformation levels where a hemispherical shape or less was achieved. Failure mechanisms in similarly inflated vulcanized SBR 1502 rubber sheets were described by Dickie and Smith. These authors did not describe the shapes of the inflated sheets. There seem to be no studies of inflation of rubber membranes into molds or useful equivalent studies of molten plastics such as thermoforming. It is the purpose of this paper to present a basic study of the inflation of membranes of various gum and compounded elastomers. We observe the manner in which the membranes freely inflate into air and also the manner in which they fill molds of various shapes. We begin with qualitative considerations but will also present quantitative measurements. Biaxial elongational viscosities have been estimated.