To insure a good dispersion of all ingredients in the mixture, the batch is normally given a two-pass mix. In the above formulation, the zinc oxide and the stearic acid perform the same functions, viz., activation of polymer curing, as they did in the first formulation. Akron Chemical Co. Titanium dioxide is also a coloring agent. These three constituents in combination are the pigmenting agent for the mixture. Its function is to strengthen the finished product and to act as a filler in the same manner as the Hi-Sil 233 does in the preceding formulation.
Sulfur is the vulcanizing agent.
Vandex is a proprietary name for finely ground selenium. Its function is to supplement sulfur as a vulcanizing agent. As is normal in molding techniques, the curing temperature must be carefully selected in order to prevent imperfections in the finished product. Too high a molding temperature will contribute to a condition designated backrind. This condition is characterized by an indented fracture around the body of the molded product defining the point where the two halves of the mold are brought together and is due to thermal expansion in this area during and after the molding cycle.