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Introduction:
Blow molding is intended for use in manufacturing hollow plastic products; a principal advantages is its ability to produce hollow shapes without having to join two or more separately molded parts.
Although there are many variations, the two basic processes are extrusion blow molding and injection blow molding. Extrusion processes are by far the more widely used, but injection blow molding and injection stretch blow molding have captured significant market segments.
Part prices are generally higher than injection molded parts, but lower than rotationally molded parts.
Process:
Identical to injection molding except that hot liquid plastic comes out of a barrel vertically, in a hollow molten tube or "parison". The two halves of the mold close on it and compressed air blows up the parison like a balloon, forcing it outward to conform to the inside shape of the mold.
Although there are considerable differences in the available processes, all have in common a parison (precursor), enclosing of the parison in a closed female mold, and inflation with air to expand the molten plastic against the surface of the mold, where it sets up into the finished product.
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