| 摘要 |
1280172 Extruding fluorocarbon heat shrinkable tubing PENNSYLVANIA FLUOROCARBON CO Inc 25 Aug 1969 42281/69 Heading B5A [Also in Divisions C3 and F2] Fluorocarbon heat shrinkable and heat sealable tubing, wherein the fluorocarbon is a copolymer of from 50-95% by weight of tetrafluoroethylene and from 5 to 50% by weight of hexafluoropropylene having a tensile strength of at least 4000 p.s.i., is made by melt extruding the copolymer as a tube at a controlled temperature and rate (see below), heating the tube to a temperature in the range 200-480‹ F. whilst expanding it against a surrounding mandrel by internal pressure and cooling the tube whilst expanding or when expanded. The polymer is extruded by means of a screw extruder in which the upstream barrel temperature is between 580‹ and 600‹ F., the downstream barrel temperature is between 560-580‹ F. and the rate of extrusion is related to the diameter of the screw as follows:- The heat shrinkable tubing so formed has ratios of expanded diameter to recovered diameter between 2À02-2À50, wall thicknesses in the range 0À015-0À060 inch and is preferably made transparent. The post-extrusion heating may be infra-red, hot air or hot liquid heating or as shown in Fig. 3, an electrical resistance heater 27. Mandrel 28 is preferably of glass and end 31 is closed by heat-sealing, pinching or alternatively by means of a plug. The internal pressure may be applied by gas, e.g. compressed air, nitrogen or carbon dioxide, by liquid, e.g oil or liquid metal, or mechanically by means of an expandable mandrel. The tubing is particularly intended for use as electrical insulation and because of the relatively high contraction on heating may be used on tapered objects, see Fig. 5 (not reproduced). |
