Welding method for joining thermoplastic polymer sheets

摘要

A method and apparatus is provided for welding in edge to edge formation, thermoplastic polymer sheets, especially sheets of PTFE or other fluoropolymenrs for use in lining process vessels. The sheets are edge butted and a heating element is applied over substantially the whole of the join and is subjected to a pressure equal to atmospheric, so that an even pressure is applied over the whole join whilst the heating element is heated so as to melt weld the edges together. In the embodiment the join and the heating element are enveloped by a flexible member 22, adhered by a removable adhesive 31 either side of the join [and across its ends]. The member is then evacuated via means 51 to create a vacuum so that atmospheric pressure is acting upon the heating element along the whole length of the join. The welded joins produced by this method have an efficiency of at least 50% of virgin elongation and at least 80% of tensile strength.