the other hand, solvents like HFO-1234ze, acetone and ethanol have almost no effect. Butyls are remarkably resistant to dimethyl ether, being swelled by only 8% in the pure propellant. In formulas containing no more than about 10% dimethyl ether (DME), buna gaskets are usually serviceable. Stem Gasket Compositions: Viton Viton A is the principal representative of this rather costly and exotic series of valve stem gaskets. The composition is primarily polyfluoropropylene. Most solvents have either no effect or a very minor one, with the exception of some chlorinated solvents and DME. In their pure form, they can often liquefy the Vitons. Summing up… The aerosol valve stem gasket is called upon to provide a dynamic seal, even when in contact with a vast array of formulations, pressures and temperatures. Sometimes the elastomeric barrier may be as thin as about 0.010" (0.25mm). Depending upon valve design, the gasket must swell from about 3–12% to create the required hermetic seal, yet it must maintain nearly all of its elasticity, Durometer (hardness), resistance to leaching, lack of set and other properties. The diameter and parting line flash of the plastic valve stem must be carefully controlled and the pedestal clinch of the mounting cup must be precisely replicated during valve assembly, even at high production speeds. These factors squeeze the gasket against the valve stem to just the right degree, allowing smooth, crisp valve operation without leakage or mushiness. Our valve producers can be rightfully commended for their ability to deal with all these chemical and engineering challenges and produce aerosol valves of truly remarkable diversity and quality. SPRAY December 2016 Spray 41
Spray Decemberr 2016
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