| 摘要 |
1,243,733. Extruding foamed tubes. GATES RUBBER CO. 7 Jan., 1969 [29 April, 1968], No. 1009/69. Heading B5A. [Also in Division F2] A tube of foamed polymeric material is made by extruding a mixture of a polymeric composition and a blowing agent through a heated tube-extrusion die wherein the mixture is subjected to increasing pressure and allowing foaming to occur when the mixture emerges from the die under conditions of reduced temperature and pressure. According to the invention, such a process results in the tube having surfaces which are continuous and substantially smooth due to the formation of closed cells therein. The tube shown, Fig. 4, comprises an inner layer 25, made according to the above process, which is overlaid with knit fabric or braid reinforcement 23, the layer 25 and reinforcement being passed through a second extruder to form an outer layer 24, also made according to the above process. A suitable die, Fig. 6 (not shown), comprises a mandrel (17) and an annular die part (18), both of which continuously taper in the direction of extrusion, the angle of convergence of die part (18) being greater than that of the mandrel. The die shown, Fig. 7, allows the production of a laminated tube, mandrel 20 being associated with two axially spaced annular die parts 19, 21. After extrusion the extrudate may be force-cooled as at (26), Fig. 5 (not shown). Polymeric materials specifically mentioned are natural or synthetic rubber latices, polyvinyl halides, polyurethanes and polyethylene. |
