| 摘要 |
844,895. Lining and covering tubes. RESISTOFLEX CORPORATION. Jan. 22, 1958 [Jan. 30, 1957], No. 2192/58. Class 99(2). A process of preparing a tube of prestressed, sintered polytetrafluoroethylene resin which is substantially dimensionally stable indefinitely at room temperature but adapted due to its prestressing to alter its girth substantially uniformly throughout its length upon being heated to a temperature below the gel point of the resin and thereafter cooled, comprises the steps of taking a tube of sintered polytetrafluoroethylene resin which is at a preselected elevated temperature below the gel point of the resin, applying a deforming force to the tube while at that temperature so as to alter its girth, cooling the tube while maintaining the application of the force, and subsequently removing the force. As shown, a length of P.T.F.E. tubing 10 is mounted within a steel tube 12 provided with flanges 14, 16, the ends of the tubing being secured by clamps 22 to plugs 18, 26 ; the plug 18 is provided with a vent passage 20, and the plug 26 has an inlet needle valve 30 fitted in a bore 28 thereof. To safeguard against the blowout of the plugs retaining plates 32, 34 are secured to the flanges 14, 16. The assembly is placed in an oven, heated to a temperature of 600‹F, and then removed from the oven, and air pressure is supplied through the valve 30 to build up the pressure inside the tubing to 200 pounds per square inch whereby the tubing is expanded against the wall of the tube 12 ; the plugs 18, 26 are drawn inwardly as the result of radial expansion of the tubing. The air pressure is maintained until the tubing has cooled to about 100‹F when the air supply is disconnected and the tubing removed from the tube 12. In the preparation of a pre-stressed length of tubing for use as a liner, an apertured plug 40, Fig. 3, is fitted to each end of the tubing and the latter after being heated in an oven is subjected to a tensile force and stretched to become reduced in girth, the tension being maintained when the tubing cools. The plugs are removed and a quench bath may be employed. In an alternative method, after heating in an oven, the tubing is pulled through one or more reducing dies. |
