extrusionblow

Extrusion blow molding, commonly referred to as extrusionblow, is a plastic forming process used to produce hollow, closed-section parts. The process starts by extruding a molten thermoplastic through an annular die to form a slender, tube-shaped parison.

Next, two mold halves close around the parison. Compressed air is driven into the parison, expanding it so that it conforms to the interior surfaces of the mold cavity. After cooling, the mold opens and the finished part is ejected. The method is well suited for large or non-symmetrical containers such as bottles, jerrycans, drums, and tanks, where wall thickness control is important.

Materials commonly used include HDPE and LDPE, linear and branched polypropylenes, and, in some cases, PET for certain grades. Multi-layer or coextruded parisons allow barrier properties and color or cosmetic layers to be added, expanding application possibilities.

Extrusion blow molding competes with injection blow molding and stretch blow molding. It typically offers lower tooling costs for basic shapes and is effective for high-volume production of large hollow parts, but may have longer cycle times and looser tolerances compared with alternative methods. Variants include continuous extrusion blow molding and multi-layer extrusion blow molding.

Applications span household and industrial packaging, chemical and automotive containers, and large-volume packaging. The technique has evolved to accommodate recycled content and to produce containers with varied wall thicknesses and shapes.