GB876367A - Improvements in and relating to envelope gaskets - Google Patents

Abstract

876,367. Joint-making packing. ANGUS & CO. Ltd., GEORGE, BAKIN, M., and TURNER, D. G. April 17, 1958 [April 25, 1957], No. 13187/57. Class 122 (3). A method of making a gasket envelope of plastic material, especially a fluorocarbon such as polytetrafluorethylene or polytrifluorochlroethylene, comprises winding thin tape of the material around a mandrel in layers, wound in opposite directions, until a sufficient thickness has been built up and then subjecting the taped mandrel to pressure and to heat to cause merging together of the layers into a homogeneous envelope which is then removed from the mandrel. In the example described, polytetrafluorethylene powder is mixed with a volatile liquid, such as a solvent naphtha, and compressed to a preform from which tape 1 is extruded which when dried, or whilst still moist, is wrapped toroidally around a mandrel 2, which is preferably chromium-plated, with a half width overlap of successive turns and reversal of direction of winding in successive layers 1a, 1b, 1c, 1d. The taped mandrel is placed between chromium-plated steel plates 4, 5 and pressed cold in an hydraulic press from which it is then removed with its plates and, if moist tape has been used, allowed to dry or dried by heating, before baking in an oven to fusion temperature, e.g. for one hour at 360‹ C., after which it is replaced in the cold press, subjected to pressure and allowed to cool. Finally, a peripheral edge 6 of the polytetrafluorethylene sheath is cut off, as indicated at X-X in Fig. 2, and the sheath removed from the mandrel to provide a channel section gasket envelope.