subject: Blow Molding Machine [print this page] Blow molding machine capable of relatively high production rates at relatively low cost is provided. The blow molding machine comprises a base, a reciprocating shuttle mechanism supported by the base, a single blow molding station supported by the base, and adapted to receive a parison for forming the hollow article at the blow molding station, a pair of cooling stations supported by the base on flanking sides of the blow molding station, a pair of blow pin carriages spaced from one another, each of which is connected to the shuttle mechanism and is indexable to the blow molding station and to one of the cooling stations. Each blow pin carriage can comprise one or more blow pin assemblies that are movable independent of the shuttle mechanism between a rest position and a blow position.
Two general classes of plastic products are made in this manner--packaging products and technical parts. Packaging products include such items as bottles, jars, jugs, cans, and the like. Technical parts include automotive components such as bumpers, fuel tanks, functional fluid containers, ducting, and the like.
The blow molding process can be of two general types: extrusion blow molding and injection blow molding. In extrusion blow molding, a parison is lowered between mold halves from an extruder. The mold halves then close around the parison, and the mold is transferred to a blowing station where the parison is then expanded against a mold cavity by introduction of a blowing gas, usually air. In injection molding, a thermoplastic material is first injection molded into a preform parison which is then transferred to a blow mold and expanded in the same manner as in an extrusion blow molding process. In both cases, however, the parison is transported from a parison receiving station to a blow molding station to complete the fabrication of a hollow plastic article.
In continuous extrusion, a molten parison is produced from an extruder die without interruption, and a segment thereof is severed and positioned into a mold. In many blow molding machines, the molds are moved from station to station on rotating vertical wheels, on a rotating horizontal table, or with a reciprocating action of a shuttle mechanism.
Most of the current blow molding machines utilize the reciprocating mold concept according to which the molds are shuttled back and forth from the parison receiving station to the blow molding station. A major drawback of the reciprocating mold concept, however, is a limitation on production rate because of the multiple stations in the process, namely the parison insertion station, the blow molding station, and the cooling station. Another drawback of the reciprocating mold concept is that many heavy parts must be moved during the blow molding process. For example, an entire shuttle mechanism with multiple blow molding stations and parison receiving stations may need to be moved during the process. Another concern present in many existing blow molding machines is the number of moving parts in the machines.
A further problem with most blow molding concepts is that after the parison is positioned in a mold, the mold is then taken to a separate blowing station where the air or other fluid is injected into the parison to form the hollow article. The time required to move the mold from the station where the parison is positioned to the blow molding station creates stress on the parison before inflation because of cooling that occurs with the parison, which makes the inflation process more difficult.
In view of the relatively large commercial demand for various types of plastic articles, it would be desirable to have a blow molding machine of relatively high capacity that can produce high quality articles at a relatively low cost, and which avoid the problems discussed. The present invention satisfies this desire by reducing the amount of tooling, reducing the mass of moving parts, reducing the traveling distance of moving parts, reducing the stress on the parison before inflation, minimizing in-mold time for the hollow article to improve cavity utilization, and maximizing cooling effectiveness.
