Patent EP-1123189-A1 (EP)
Inventor: WEINMANN ROBERT
IPC: B29C45/72
Filed: 1999-10-22
Abstract: The injection molding of plastics preforms (10) uses mechanically sliding components in the final cooling zone for the injection molded products, to increase the effect at the air side. A controlled pressure or under pressure (31,32) zone is at the end of the water-cooled tube, opposite the insertion end, with sliding components between the pressure zone and the interior of the cooling tube. They are valves and preferably pistons so that, through the valve action, the injection molded product is drawn by suction and held firmly, to be ejected by an overpressure. The water-cooled tube has a curved base at the side of the pressure/under pressure zone, to increase the cooling effect of the water cooling on the injection molded product. It has a hemispherical base, to take the immersed rounded end of the cooling tube, to be drawn against the stop by the under pressure. The curved base fits round the end of the cooling tube without play. A sliding valve pin moves through an opening so that, on an under pressure, the passage opening is free to the interior of the tube and, on an overpressure, the ejection action is supported. Air jets are at the insertion end of the cooling tube, pushed in cycles into the molded preforms to blow air into them and/or suck the air out of them. The final cooling is in three stage, with an extraction unit (11), a transfer grip (12), and a final cooling unit (19). Air jets form part of the transfer grip, and a centering mandrel transfers the preforms from the grip into the final cooling stage. Their working is set by an overall control, which co-ordinates their working cycles preferably independently of each other. The transfer grip take the preforms in a horizontal lie, and swing them into the vertical, to be pushed into the water-cooled sleeves of the final cooling stage. During transfer, the preforms are hardened by an intensive air stream for several secs., especially at the inner sides of their rounded bases. The difference in pressures, between the inner and outer surfaces of the rounded bases of the preforms, is controlled and especially coordinated by a blown air stream and/or an under pressure, in a pulse in one direction or the other. The air jets are suction jet mandrels, with suction openings for the open end of the preform, with control to set the air flow either to the closed base region within the preform, or a strong vacuum action within it, or a combination of effects. The extraction and transfer grip systems are structured to take an equal number of preforms. The final cooling stage has two or more rows containing water-cooled sleeves, so that the injection molded preforms can be inserted into the cooler by rows and in cycles, to reduce the injection molding cycle time and increase the cooling time. The extraction and transfer time equals an injection molding cycle time, and the total cooling time is at least two to three times the molding cycle time. The molded preforms are given a double cooling, from outside and within, during a significant part of the molding cycle time directly after the extraction of the molded preforms. An Independent claim is included for an injection molding assembly with a water-cooled preform extraction unit and an air-cooled transfer grip, so that at least one cooling action on them is uninterrupted between the extraction from the mold to the ejection from the final cooling stage. Preferred Features: The final cooling stage has a slide action on a horizontal plane from an exact preform transfer position and an ejection position over a conveyor belt (20), in lateral and/or longitudinal sliding movements.