Process for producing a reinforced tube

A process for producing a reinforced tube which has a thin-walled inner tube and an outer sheath made of thermoplastic or elastomeric material as well as thin strips which extend in an axial direction on the outside of the inner tube and are reinforced with textile threads and which consist of plastic connectable to the material of the inner tube, the strips appearing as a closed layer, including the steps of:

• a. extruding the thermoplastic or elastomeric material from an annular nozzle to form the inner tube 2,
• b. encircling the extruded inner tube with a closed layer of the strips (6), which are at least coated with heat-activatable adhesive material and which extend in the axial direction of the inner tube,
• c. subjecting the inner tube (2) to a relatively low internal pressure (3) while passing the inner tube and the closed layer of thin strips through a sizing guide 5, while supplying heat at the entrance of the guide, thereby expanding the tube against the strips and the strips against the guide, the heat at the guide entrance being effective to activate the adhesive and bond the tube to the layer of strips, the guide being long enough to cool the tube and strips sufficiently so that they set as an integral structure,
• d. winding a second layer of strips (10) of heat activatable adhesive material spirally over the first layer bonded to the inner tube and bonding the second layer to the first layer by heating,
• e. passing the tube with the connected layers of strips through pinching rolls to close the tube and thereby maintain the tube upstream from the rolls at said relatively low internal pressure, said rolls being also effective to drive the tube and the layers of strips bonded thereto, and
• f. finally subjecting the reinforced inner tube (14) to a relatively high internal pressure (13) and applying to it the outer sheath (20).