Abstract: A hydraulic clamp unit for a molding apparatus has a pair of opposed complimentary mold halves attached accordingly to a pair of opposed platens suspended on roller guides and moving toward each other into engagement of the mold halves to form a mold cavity surrounding a molded article of a thermoplastic material. The unit is provided with main clamp cylinders of a pull type and having piston rod chambers pressurized to exert pressure on the platens during formation of the article. Rapid movement of the platens is achieved by means of kicker cylinders having piston chambers and piston rod chambers communicating with each other. The main cylinders are locked to one of the platens by means of hydraulic mechanisms.

Abstract: An extrusion die, particularly for double-walled corrugated thermoplastic pipes, including an extrusion head, a nozzle, two concentric hollow mandrels carrying die lips and an additional cooled and vacuumed mandrel. The vacuum is maintained between the latter and the inner wall of the pipe to prevent retraction of the wall from the mandrel until the wall is set.

Abstract: A plasticating extruder with a screw having a feed section, a transition section, a metering section, a first primary flight located substantially in the first two sections, a second primary flight located substantially in the last two sections and two corresponding secondary flights located in the transition section, all the flights in the latter section radially balancing each other, and the first primary flight in the feed section balancing radially the second primary flight in the metering section. In another embodiment, the screw can in addition have a mixing section and another metering section, the latter having a flight balancing radially other flights in other sections.

Abstract: An extrusion die, particularly for double-walled thermoplastic pipes, includes an extrusion head, a nozzle, two concentric hollow mandrels carrying die lips and an additional cooling mandrel. The lips have threaded adjusting members to vary the sizes of the die gaps, the lips for the inner wall being provided with electrical heaters. The concentric mandrels have a spider with members for its radial adjustment. The cooling mandrel has substantially annular channels for a coolant, comunicating with each other by means of a sharply skewed opening and combined into a number of sections to control intensity of heat exchange.

Abstract: A corrugator for molding externally ribbed and corrugated thermoplastic pipes, including two trains of moldblock halves circulating respectively in two endless paths and cooperating with each other to form a travelling mold for the thermoplastic pipes. The halves of one train are biased in relation to and overlap those of the second train along the travelling mold and are provided with intermeshing elements hooking the halves of the two trains together.