Process of and apparatus for making plastic tubing

Apparatus for continuous molding of thermoplastic extrudate in a travelling mold tunnel to form an elongate molding, comprising:

• a travelling tunnel mold assembly of adjacent mold blocks, each mold block being carried on a mold block carrier, and each mold block having a bore therethrough, the bores of adjacent mold blocks being aligned axially and having a circular cross-section;
• each mold block comprising a pair of pivotally connected parts where the connected parts are movable between a closed position of the block in which the bore is circumferentially enclosed and an open position in which the connected parts are located with respect to each other to release elongate molding formed between them;
• a tunnel conveyor for the tunnel mold assembly to convex it horizontally and axially in a molding run between a tunnel entrance and a tunnel exit;
• means to open each mold block as it reaches the tunnel exit;
• means to return each mold block on a return path from the tunnel exit to the tunnel entrance, upstream of the return path, and means to close the returned mold blocks to form the mold tunnel, said means for returning including:
• a removal conveyor arranged to move generally in the plane of the tunnel conveyor to receive and convey each opened mold block sequentially from the tunnel conveyor, each mold block being orientated with its bore parallel to the mold tunnel;
• a return conveyor generally in the plane of the tunnel conveyor arranged to move horizontally parallel and opposite to the tunnel conveyor to receive and convey mold blocks sequentially from the removal conveyor, each mold blocks being orientated with its bore parallel to the mold tunnel;
• and
• an approach conveyor generally in the plane of the tunnel conveyor arranged to move horizontally and parallel to the removal conveyor, to convey mold blocks sequentially from the return conveyor, each mold block being orientated with its bore parallel to the mold tunnel, the mold block being of fixed orientation with its bore parallel to the tunnel axis during travel on all of the return path to be added to the tunnel entrance.

A method for continuous molding of thermoplastic extrudate in a travelling mold tunnel to form an elongate molding, comprising the steps of;

• extruding a parison of thermoplastic extrudate into a travelling tunnel mold assembly of adjacent hinged mold blocks each mold block being pivotable between the closed mold tunnel forming position and an open position having a bore therethrough, the bore of adjacent mold blocks being aligned axially,
• conveying the tunnel mold assembly in a horizontal plane and axially in a molding run between a tunnel entrance and a tunnel exit;
• opening each mold block as it reaches the tunnel exit;
• returning each mold block along a substantially horizontal return path which is generally coplanar with the molding run from the tunnel exit to the tunnel entrance upstream of the return path, and
• closing the returned mold blocks to form the mold tunnel.

A method for continuous molding of thermoplastic extrudate in a travelling mold tunnel to form an elongate molding, comprising;

• extruding a parison of thermoplastic extrudate into a travelling tunnel mold assembly of adjacent mold blocks each mold block having a bore therethrough, the bore of adjacent mold blocks being aligned axially, each mold block comprising a pair pivotally connected parts whereby the parts are movable between a closed position of the block in which the bore is peripherally enclosed, and an open position in which the parts are located, with respect to each other, to release the elongate molding formed between them;
• conveying the tunnel mold assembly horizontally and axially in a molding run between a tunnel entrance and a tunnel exit;
• opening each mold block proximate to the tunnel exit;
• returning each mold block on a return path from the tunnel exit to the tunnel entrance upstream of the return path by removing opened mold blocks from the tunnel conveyor onto a removal conveyor generally running in the plane of the tunnel conveyor, and receiving and conveying each opened mold block sequentially from the tunnel conveyor, each mold block being orientated with its bore parallel to the mold tunnel;
• and
• transferring the opened mold blocks from the removal conveyor to a return conveyor generally in the plane of the tunnel conveyor running horizontally parallel and opposite to the tunnel conveyor, and receiving and conveying mold blocks sequentially from the removal conveyor, each mold block being orientated with its bore parallel to the mold tunnel;
• and
• transferring the mold blocks from the return conveyor to an approach conveyor generally in the plane of the tunnel conveyor running horizontally and parallel to the removal conveyor, receiving and conveying mold blocks sequentially from the return conveyor, each mold block being orientated with its bore parallel to the mold tunnel;
• maintaining the mold blocks to be added to the tunnel entrance in a fixed orientation with their bore parallel to the tunnel axis;
• and
• closing the returned mold blocks proximate to the tunnel entrance to form the mold tunnel.

Apparatus for continuous molding of thermoplastic extrudate in a travelling mold tunnel to form an elongate molding, comprising:

• a travelling tunnel mold assembly of alignable, pivotally hinged, mold blocks each having an axially alignable bore therethrough and each mold block being pivotal between a closed tunnel-forming position and an open position and each mold block being drivable connected to a motor for opening and closing the mold block;
• a generally planar conveyor for conveying the mold blocks in a pathway generally lying in a common plane where the pathway includes an axially extending molding run between a tunnel entrance and a tunnel exit, a lateral removal run to move an individual mold block away from the tunnel exit, a return run generally parallel to the axial molding run, and an approach run for guiding the mold block to the tunnel entrance;
• and
• means to close the mold block at the tunnel entrance to form the mold tunnel.

A method for continuous molding of thermoplastic extrudate in a travelling mold tunnel to form an elongate molding, comprising;

• extruding a parison of thermoplastic extrudate into a travelling tunnel mold assembly of adjacent mold blocks each mold block having a bore therethrough, the bore of adjacent mold blocks being aligned axially, each mold block comprising a pair pivotally connected mating sections which are movable between a closed position and an open position;
• conveying the tunnel mold assembly horizontally and axially in a molding run between a tunnel entrance and a tunnel exit;
• opening each mold block proximate to the tunnel exit;
• establishing a generally horizontally disposed return path co-planar with the molding run, the return path being defined by a removal run, a return run, and an approach run where the removal and approach runs are generally parallel to each other and both are generally perpendicular to the return run;
• and
• returning each mold block on the return path from the tunnel exit to the tunnel entrance upstream of the return path.