Vulcanization at High Pressures

Abstract

A technique was developed for vulcanizing cylinders of rubber 0.5 inch in diameter and up to 1 inch long at pressures as high as 150,000 pounds per square inch, using a small laboratory press (8-inch square platens). The specially designed mold was made of alloy steel according to general principles from the high pressure work of Bridgman. It was prestressed at 200,000 pounds per square inch. The temperature in the mold cavity was carefully calibrated with thermocouples to determine the equivalent length of cure of the test-specimens. Cylinders of GR-S tread stock were vulcanized for a range of cures at 1000, 20,000, 50,000, and 100,000 pounds per square inch. GR-S gum stock and Hevea gum and tread stocks were vulcanized for a range of cures at 100,000 pounds per square inch. Control specimens were cured in a regular type of mold, for which the pressure was not determined. All the volume compression during vulcanization is recovered when the pressure is released. This was determined by precise density measurements of the test-specimens. The electrical resistivity, dynamic modulus, internal friction, and resilience of the test-specimens were determined and the results are discussed.

Rheological characterization of unsaturated polyester resin sheet molding compound

“…The general concept of resistance to biaxial elongation has been put forward (1,16) as an explanation of the flow behavior of "cold" SMC during squeezing. Our work suggests that this resistance arises partly from the glass fiber network, but mainly from the provisional network of bonds within the mature SMC created by the thickener agent with the carboxyl end groups of the linear polymer.…”

“…Th which characterize the rheological behavior of fiber reinforced polyester compounds has been emphasized during recent years by the increased engineering usage of these materials. Rheological measurements are needed which better describe material characteristics under flow conditions that are directly relevant to the actual molding process (1). A characteristic of the many conventional flow tests is that none provides such data directly.…”