Abstract: In at least one method for manufacturing a double-walled, thermoplastic tube with a connecting sleeve, which enables precise and complete moulding of the connecting sleeve by simple means, it is provided that a) a first tube (1) is extruded into a mould tunnel (4) comprising at least one row of moulds (5) guided on a path, b) the first tube (1) is given a corrugated shape in at least one first section and expanded into a connecting sleeve in at least one second section, c) a second tube (6) is extruded into the first tube and pressed against the corrugation troughs (8) of the first tube (1), d) while the first tube (1) is being given a corrugated shape and the second tube (6) extruded into the first, the space (A) between the two tubes (1, 6) is subjected to a pressure p1 that is above atmospheric pressure, e) the space (A) between the two tubes (1, 6) is subjected, at a specified time before or after expansion of the first tube (1) into a connecting sleeve, to an essentially constant pressure p2?p1 above atm

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 improved, endless mold tunnel, clamshell-type, thermoplastic tube molding apparatus and method using exteriorly disposed, compressive roller elements and a cooperating keyway/matching lug assembly for maintaining the alignment of the independent mold blocks and mold block half sections substantially orthogonal relative to opposed half sections and relative to the contiguous upstream and downstream mold blocks in said tunnel while allowing for the introduction of cooling fluid or vacuum.

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 a cooling plug for sizing the interior surface of thermoplastic extruded pipe. Vacuum and/or pneumatic pressure is applied at the surface of the plug. The pneumatic pressure may cause the inner wall to balloon outwardly to form bells within a mold or within an outer wall, to fit into corrugations of an outer corrugated tube, etc. The vacuum may be used to pull the inner wall back to the surface of the plug after application of pneumatic pressure.

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.

Abstract: Method and apparatus for encasing drainage pipes, using fibrous or particulate loose filler material guided onto the drainage pipe by means of a hollow screw and held there with a permeable envelope material preferably wound round with a filament. The pitch or number of threads on the screw, the height thereof and the speed at which the screw rotates determine the amount of filler material applied to the drainage pipe per unit of area. The apparatus comprises a machine consisting of a guide tube carrying an internal hollow screw, the drainage pipe being guided in the interior of the screw, the encasing envelope material being placed externally upon the said guide tube and preferably being wound around with a filament at the end of the screw.