High volume blow molding

The process is used for high volume BM of very small containers such as pharmaceutical vials and whiskey bottles. A multi-cavity mold is used with an extruded parison whose circumference approaches twice the total width of the closely spaced cavities. Before the mold closes, the parison is stretched and semi-flattened laterally so that it extends across the full width of the cavities. The process is usually combined with blow/fill/seal techniques. 

This type of extrusion blow molding machine uses something called a shuttle machine to get all the parts in place. Alternatively, a rotary machine, illustrated in Figure 14-61, can be used. Rotary extrusion blow molders are used in high volume applications, as in the production of laundry detergent bottles. 

Blow molding. With few exceptions, plastic bottles produced in volume are blow molded. Less well known are the other blow-molded hollow shapes such as children s toys, storage sheds, etc. Typically, these are double-walled. For high-volume molding of hollow shapes, blow molding is the only option if the shape and material requirements are suitable. 

In the early 1950s, high density polyethylene (HDPE) was developed and today blow molding is the largest user of HDPE, which is the largest volume thermoplastic produced in the world, with over a billion pounds produced worldwide. 

Generally, injection blow molding is used for small bottles and parts less than 500 mL in volume. The process is scrap-free, with extremely accurate control of weight and neck finish. However, part proportions are limited and the method is impractical for containers with handles and tooling costs are relatively high. 

Injection blow molding No scrap excellent thickness control accurate neck finishes outstanding surfaces, can produce low volume of products High tooling costs larger objects not possible... 

Poly(ethylene terephthalate) is used to produce fibers or is processed as a thermoplastic material by injectionmolding or blow-molding. Sorption of pyrrole in films of this polymer followed by immersion of the film in an aqueous FeCls solution produced blends of polypyrrole and poly(ethylene tere late). The 30 /zm thick film obtained presented high optical transmittance at 633 nm and a conductivity in the range of 0.03-0.1 S cm [65]. Authors suggest that polypyrrole is distributed uniformly in the free volume of the poly(ethylene tereftalate) host, forming a conducting network at low concentrations (5%). 

Blow mold and extrusion tooling required only—cost is 30-40% of injection tooling cost. Superior for very low volume requirements under 500,000 per year. Must have three core rods for each cavity and an injection mold. Tooling is precise and expensive. However, high price is justified by higher efficiency and is some times indicated by preference for this method. 

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