A reinforced Seamless pipe, e.g., of Teflon.RTM., is produced by covering a preformed seamless tube of a thermoplastic polymer with a suitable adhesive, encasing the covered tube in a reinforcing sleeve or stocking, e.g., of knitfiberglass, inserting the assembly in a hollow cylinder, pressurizing the inside of the tube with compressed air or centrifugal force while heated to about the softening point of the polymer to expand it and force adhesive into the fiberglass sleeve,cooling the assembly and reducing the pressure to atmospheric. The laminated tube can be slipped within and glued to the inside of a preformed polyester-glass or metal pipe, if desired.
Seamless pipe can be formed simply by the process of this invention as illustrated in The ends of an originally seamless polymeric fluorocarbon tube of appropriate size are firmly plugged, with an air inlet in one plug, and thetube wrapped with a film of any melt-fabricable fluoropolymer selected as an adhesive. Tubular glass fabric is pulled over the tube and smoothed.
A resin coating must have pressure resistance and adhesion. In hydroforming, the surface pressure between an object material and dies may reach thousands of atmospheres. The pressure resistance of a coating is evaluated in terms of hardness. It is desirable for resin coating to have pencil hardness H or higher as specified in JIS K5400-6.14. In hydroforming, working heat and frictional heat cause the surface temperature of an object material to rise. Usually, the surface temperature of a carbon steel pipe rises to approximately 40° C. to 60° C., and that of a stainless steel pipe rises to approximately 70° C. to 90° C. As mentioned previously, an emulsion is used as a hydraulic fluid, so that water is present between the dies and the object material. Accordingly, a coating must maintain adhesion in a heated moist state.