Patent GB-783240-A (GB)
Title: Improvements in or relating to reinforced polytetrafluoroethylene pipe and method ofmaking it
IPC: F16L9/12
Filed: 1956-01-12
Abstract: 783,240. Reinforced polytetrafluoroethylene pipes. RESISTOFLEX CORPORATION. Jan. 12, 1956 [Jan. 14, 1955], No. 1142/56. Class' 99(2). A pipe comprises a lining of polytetrafluoroethylene, i.e., material sold under the Registered Trade Mark " Teflon " at least one layer of reinforcing glass fabric impregnated with polytetrafluoroethylene the lining being sintered and fused to the reinforcing layer after being laminated therewith into pipe form. Fig. 3 shows a mandrel 10 of suitable smooth-surfaced metal such as polished steel, chromium plated steel or stainless steel. This mandrel may first be lubricated generously with silicone oil such as mold release oil and prebaked at 750‹F. for about an hour to facilitate removal of the finished pipe. Optionally after baking it may be given a second coating of silicone oil. A layer of unfused paste extruded tape 11 of Teflon (Registered Trade Mark) made as described below is then helically wrapped thereon to form a continuous impervious lining for the pipe. Over this lining one or more reinforcing layers of Teflon (Registered Trade Mark) impregnated glass fabric 14 are then wrapped helically in the opposite direction the amount of overlap and the number of layers depending on the thickness and strength of the pipe wall desired. Only one such layer has been shown as illustrative. As a final outside layer unfused paste extruded Teflon (Registered Trade Mark) tape 16 may be helically wrapped over the last layer of impregnated glass fabric thus forming an impervious outer covering. Such covering is, however, not usually required. Upon the pipe thus built up may then finally be wrapped one or more layers of plain glass fabric tape which applies pressure to the pipe when heated because the Teflon (Registered Trade Mark) has greater thermal expansion than the glass. When all the wrappings are in place the mandrel is placed in or passed through an oven for sintering the unfused Teflon (Registered Trade Mark) and for bonding the several layers together under conditions which will raise its temperature above about 620‹F. which is the fusion temperature of the material. Upon cooling the outer wrapping of glass tape is removed and the finished pipe removed from the mandrel. The pipe may have an inner lining of Teflon (Registered Trade Mark) and three superposed layers of Teflon (Registered Trade Mark) impregnated glass fabric. In another embodiment the pipe has two intermediate layers of Teflon (Registered Trade Mark) impregnated glass fabric and an outer covering of Teflon (Registered Trade Mark). The wall thickness may be built up by increasing the number of reinforcing layers 14. The pipe ends may be sealed as shown in Fig. 7 by sealing the outermost layer 16 of Teflon (Registered Trade Mark) to the innermost layer 11 of Teflon (Registered Trade Mark). In another method of sealing the end, Fig. 6, a number of layers of unfused paste extruded Teflon (Registered Trade Mark) tape 19 are wrapped around the lining. In making a sheet of Teflon (Registered Trade Mark) by paste extrusion, Teflon (Registered Trade Mark) powder is admixed with an extrusion aid. A lubricant, preferably naphtha thickened with a small amount of polyisobutylene and extruded to the desired shape passing then through a heated zone at a temperature which causes evaporation of the lubricant and then through an oven at a higher temperature which sinters or fuses the Teflon (Registered Trade Mark) particles into a very tough homogeneous body. The material which is used according to the invention is not the final sintered product but the intermediate product from which the volatiles have been removed. This material may be in the form of tubing which can be slipped on a mandrel or tape which can be spirally wrapped on the mandrel with an overlap or long sheets which can be longitudinally wrapped on the mandrel. Spiral wrapping of the tape is generally most satisfactory.