Method and apparatus for the continuous manufacture of a compound pipe with a pipe socket

A method for the continuous manufacture of a compound pipe (23) with a pipe socket (108), the compound pipe (23) consisting of a smooth internal pipe (107) and an external pipe (105) provided with transverse grooves (24) and welded together with the internal pipe (107), comprising the following steps:

• an external tube (104) is extruded into traveling molds (2, 2');
• by a partial vacuum applied from the outside of the traveling molds (2, 2'), the external tube (104) is provided with a corrugation with transverse grooves (24);
• an internal tube (106) is extruded into the external tube (104);
• gas at a first pressure (p2) above ambient pressure (p3) is blown into the space between the external tube (104) and the internal tube (106);
• the internal tube (106) is pressed against corrugation troughs (24a) of the external tube (104), where it is welded together with the external tube (104);
• at predetermined intervals the external tube (104) is widened by a partial vacuum applied from the outside of the traveling molds (2, 2') to form an essentially smooth-walled, about cylindrical pipe socket (108);
• a space between the external tube (104) and the internal tube (106) is vented by connecting said space with the atmosphere;
• the internal tube (106) is acted upon from the inside by gas at a second pressure (p4) above ambient pressure (p3) and while being widened is forced with its full surface against the external tube (104);
• and
• while the external tube (104) and the internal tube (106) are widened to form the pipe socket (108), the external tube (104) and the internal tube (106) are extruded to have thicker walls than during the manufacture of the compound pipe (23) provided with transverse grooves (24), the increasement in the wall thickness being generated by reducing the advancing speed of the traveling molds (2, 2').

An apparatus for the continuous manufacture of a compound pipe (23) with a pipe socket (108), the compound pipe (23) consisting of a smooth internal pipe (107) and an external pipe (105) provided with transverse grooves (24) and welded together with the internal pipe (107),

• wherein mold means traveling in a direction of production (4) are provided by serially arranged, traveling half shells (2, 2'), said half shells (2, 2'), which are provided with annular mold recesses (102), and of which two at a time combine as a pair on a molding path (9) to form a mold with a central longitudinal axis (29), being arranged on a machine bed (1) to be guided in a circuit and in the direction (4) of production,
• wherein the mold recesses (102) are connected to a partial vacuum source via partial vacuum channels (103) formed in the half shells (2, 2'),
• wherein an injection head (25) of an extruder is arranged upstream of the molding path (9),
• wherein the injection head (25) is provided with a first ring-shaped nozzle (93) for the extrusion of an external tube (104) into the mold formed by the half shells (2, 2') and, downstream in the direction (4) of production, with a second ring-shaped nozzle (63) for the extrusion of an internal tube (106) into the external tube (104) and, at its rear end seen in the direction (4) of production, with a temperature-regulating bell (62),
• wherein at least one first gas duct (56) is provided in the injection head (25) opening out of the injection head (25) between the first nozzle (93) and the second nozzle (63) for introducing gas under ambient and higher pressure into the space between the external and internal tube (104, 106), and
• wherein a second gas duct (100) is provided in the injection head (25) opening out of the injection head (25) between the first nozzle (63) and the temperature-regulating bell (62) for introducing gas under pressure into the internal tube (106),
• wherein
• at least one pair of half shells (2, 2') is provided with a socket recess (109) for forming the pipe socket (108),
• the at least one first gas duct (56) is connected to a valve (125a), which is switchable over between on the one hand a source of gas at a pressure (p2) above ambient pressure (p3) for pressurizing the space between the external and internal tube (104, 106) while forming the compound pipe (23) and on the other hand ambient pressure for venting said space while forming the pipe socket (108),
• the second gas duct (100) is connected to a valve (125) which is switchable over to a source of gas at a pressure (p4) above ambient pressure for pressurizing the internal tube (106) while forming the compound pipe (23) and pipe socket (108), and switches (123, 124) are provided which trigger the valves (125a, 125) in dependence on the position of the socket recess (109) relative to at least one of the second gas duct (100) and the at least one first gas duct (56).