Abstract: In a process for the production of corrugated plastic tubes an extrusion device passes plastic material into a perpendicularly arranged injection head for injecting the plastic material into a perpendicularly arranged mold section comprising at least two pairs of movable mold jaws arranged in axially mutually superposed relationship. A drive device is associated with each pair of mold jaws for displacement thereof in the radial and axial directions.

Abstract: An apparatus for making smooth walled tube (20) in a travelling mold tunnel (26) includes corrugations (32) for traction of tube being molded. An extrusion nozzle (16) having an exit angle of 45.degree. or more may provide additional advantage.

Abstract: A method of adjusting gap of a plastic flow channel is provided in a plastic forming device having a first body part adjacent one side of and adjustable relative to the channel and a second body part on which the first body part is mounted by a tight fitting between the first and second body parts. When the device is not in operation one of the body parts is subjected to a first temperature change producing a temporary temperature differential and a loosening of the fitting between the body parts. Positioning of the first body part on the second body part is adjusted while the fitting is loosened and then the one body part is subjected to a second temperature change opposite to the first temperature change to offset the temperature differential and restore the tight fitting between the body parts.

Abstract: Annularly or helically ribbed or corrugated semi-rigid thermoplastic pipe is modified to have a smooth outer wall. The ribbed or corrugated pipe is passed through a heated sleeve to squash and smooth the outer profile of corrugated pipe or bend over ribs of ribbed pipe and mold a smooth outer skin of the pipe. Apparatus for forming the modified pipe includes a travelling mold tunnel for the production of ribbed or corrugated pipe and a smoothing sleeve downstream thereof. The smoothing sleeve has a heater to heat it sufficiently to mold the smoother outer skin.

Abstract: Annularly or helically ribbed or corrugated semi-rigid thermoplastic pipe is modified to have a smooth outer wall. The ribbed or corrugated pipe is passed through a heated sleeve to squash and smooth the outer profile of corrugated pipe or bend over ribs of ribbed pipe and mold a smooth outer skin of the pipe. Apparatus for forming the modified pipe includes a travelling mold tunnel for the production of ribbed or corrugated pipe and a smoothing sleeve downstream thereof. The smoothing sleeve has a heater to heat it sufficiently to mold the smoother outer skin.

Abstract: The invention concerns an apparatus and process particularly for molding profile thermoplastic tubing and process. The apparatus includes the travelling mold type for molding profile tubing, e.g. corrugated or ribbed, including double walled tubing of various types. A sizing plug for the internal diameter of the pipe is provided with suction applying device which applies suction of diminishing strength in the upstream direction of the plug to the inside diameter of the pipe to provide a smooth inside wall of the pipe and allowing faster pipe formation. Suitably, the plug is a cooling plug and provision may be made for communicating the suction to cooling liquid to draw it to the surface of the plug to provide lubrication for a faster pipe forming process.