Two-stage process for industrial blow molding

Abstract

An improved method and apparatus for two-stage blow molding especially suitable for large plastic containers, wherein an overhead shuttle mechanism transfers a blown preform from a preform station to a final blowing station and then to a separation station where the completed article is separated from the upper tail by which it was suspended from the shuttle mechanism during each of the transfer steps. The lower tail is separated from the preform prior to removal from the preform blowing station. An alternative form uses a rotary indexing transfer mechanism, wherein the shape of an upper flash or tail-forming clamp half which is carried by the indexing mechanism creates an interlock with the flash permitting the article to be suspended from and transferred by such single clamp half throughout the operation. The method and apparatus can be utilized to provide a two-stage blow-molded container having integrally formed, threaded bungs by the use of a pair of bung-forming inserts slipped over a pair of upwardly opening blow needles whose center distance is variable by a toggle mechanism. The cylindrical parison is extruded downwardly over the pair of blow nozzles when they are at their minimum spacing, after which they are spread apart to elliptically stretch the parison just prior to closing of the preform mold and blowing. The preform, with the bung forming inserts now captured by the lower pinched portion thereof, is transferred to a final blow mold, where the blow nozzles are inserted through the inserts for final blowing.