What are the two different types of blow molding methods?

Manufacturing process for forming and joining together hollow plastic parts

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Blow molding (or moulding) is a manufacturing process used to create hollow plastic and glass parts like bottles and containers. Typically, three main types of blow molding are utilized: extrusion blow molding, injection blow molding, and injection stretch blow molding. The procedure begins by heating plastic to soften it into a preform or parison—a tube-shaped piece of plastic open at one end for compressed air.

History

This process draws from the glassblowing technique. In 1938, Enoch Ferngren and William Kopitke developed a blow molding machine, which they sold to Hartford Empire Company, marking the commercial start of blow molding. Initially, the 1940s saw limited product variety and quantity. However, as technology advanced, more products emerged. Plastic steadily replaced glass in some products due to its durability. The first mass-produced plastic bottles appeared in America in 1939. Germany soon followed and is now a leading blow molding machine manufacturer. In the U.S. soft drink industry, plastic containers surged from zero in 1977 to ten billion pieces by 1999, with growth continuing.

Typologies

Extrusion Blow Molding

In extrusion blow molding, melted plastic is extruded into a tube or parison. This parison is enclosed in a cooled metal mold. Air inflates the parison into the desired shape, which hardens upon cooling and is then ejected from the mold. There are two main extrusion methods: continuous and intermittent. Continuous extrusion steadily feeds the parison, while intermittent extrusion collects, then expels plastic after each form cools.

Notably, continuous extrusion systems include rotary wheel and shuttle machinery, whereas intermittent systems use reciprocating screw and accumulator head machinery. Proper equipment ensures consistent wall thickness by adjusting the die gap with parison programming devices.

Spin Trimming

Excess material from the molding process can be removed by spin trimming, where a spinning blade trims the excess. Spin trimmers are effective on materials like PVC, HDPE, and PE+LDPE. Titanium nitride-coated blades enhance durability, making them preferable to standard steel blades.

Injection Blow Molding

Injection blow molding (IBM) uses a core rod to mold a preform, which then is blown into the final shape. This method is primarily for small medical and single-serve bottles and includes steps of injection, blowing, and ejection.

Injection Stretch Blow Molding

Injection stretch blow molding, either single-stage or two-stage, merges injection molding with blow molding. The single-stage method handles both preform and bottle blowing in one machine, while the two-stage method handles these steps separately, reheating the preform in the second stage.

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