Abstract: A core unit is moved into position within the mold halves of an injection mold and a casting is molded therein. The outer wall zones of the casting are cooled sufficiently to enable the casting to maintain its shape. At the beginning of the shrinking of the casting and while the inner wall zones of the casting are still in the plastic state but before any stresses are set up in the casting the divided mold is opened. The core and the casting thereon are removed from the mold to a cooling station where the casting is rapidly cooled and the core is then removed from the cooled casting. A corrugation can be formed in a tubular casting by positioning a ferromagnetic insert member upon the core and establishing a magnetic field to maintain the insert member in position during the casting process. The core can be provided with permanent magnets or electromagnets to hold the insert member in position.

Abstract: The temperature of an extruder screw having an axial bore therein is controlled by providing a closed temperature control system within the screw which is in heat transfer relationship with a second temperature control system through which is circulated a cooling medium from an outside source. The quantity of outside cooling medium may be monitored to control the closed temperature control system. The apparatus for carrying out this process comprises a cooling medium retained within the screw and a heat exchanger extending into the cooling medium. A second cooling medium from an outside source is circulated through the heat exchanger so that heat is transmitted from the closed circuit cooling medium to the open circuit cooling medium.