Patent ID: 8178034

Claim:
A method for the continuous production of a plastic compound pipe ( 10 ) comprising a pipe socket ( 41 ), the plastic compound pipe ( 10 ) consisting of a smooth internal pipe and an external pipe which is welded together therewith and is provided with transverse grooves ( 38 ), wherein half shells ( 12 , 12 ′) are guided in circulation and in a direction of conveyance ( 4 ), which half shells ( 12 , 12 ′) are provided with annular mold recesses ( 32 ) and combine in pairs on a molding path ( 16 ) to form a mold with a central longitudinal axis ( 18 ); wherein at least one pair of half shells ( 12 , 12 ′) is provided with a socket recess ( 42 ), the socket recess ( 42 ) having a substantially cylindrical wall ( 43 ); wherein a relative overpressure is generated which acts from an inside to an outside; wherein a die head ( 8 ) of a first extruder ( 1 ) comprising a drive motor ( 3 ) is disposed upstream of the molding path ( 16 ); wherein the die head ( 8 ) is provided with an outer die ( 22 ) and with an inner die ( 21 ) arranged downstream in the direction of conveyance ( 4 ) and with a calibrating mandrel ( 25 ) at its downstream end when seen in the direction of conveyance ( 4 ); wherein the inner die ( 21 ) is connected to the first extruder ( 1 ); wherein a second extruder ( 2 ) comprising a drive motor ( 3 ′) is provided which is connected to the outer die ( 22 ); wherein an internal tube ( 39 ) of plastic melt is extruded from the inner die ( 21 ), wherein an external tube ( 37 ) of plastic melt is extruded from the outer die ( 22 ); wherein the drive motors ( 3 , 3 ′) are actuated in such a way that an extruder speed n1 of the first extruder ( 1 ) is increased from a speed n1, 1 during the production of the compound pipe consisting of a smooth internal pipe and an external pipe with transverse grooves ( 38 ) to a speed n1,2 while an expanding transition portion ( 44 ) of the socket recess ( 42 ) is moving across the inner die ( 21 ); and that the extruder speed of the first extruder ( 1 ) is then reduced to a speed n1,3 while the substantially cylindrical wall ( 43 ) of the socket recess ( 42 ) is being moved across the inner die ( 21 ), wherein n1,2>n1,3>n1,1 applies.