Blow molding, processing condition

Extrusion blow molding process (a) single-screw extruder, (b) die with a gas supplier, and (c) mold. The blow molding condition of high-density polyethylene (HOPE) was set as typically used in industry. The maximum extrusion temperature of a single-screw extruder was set at 220°C for HDPE and 250°C for HDPE/polyethylene terephthalate (PET) blend. 

Most PET botdes are produced by injection blow molding (71) the resin over a steel-core rod. The neck of the botde is formed with the proper shape to receive closures and resin is provided around the temperature-conditioned rod for the blowing step. The rod with the resin is indexed to the mold, and the resin is blown away from the rod against the mold walls, where it cools to form the transparent botde. The finished botde is ejected and the rod is moved again to the injection-molding station. This process is favored for single cylindrical botdes, but cannot be used for more complex shapes such as botdes with handles. 

The two molds needed for this process, an injection mold and a blow mold, may be located in the same molding machine or in different molding machines. In the first case, known as a one-stage process, there are multiple stations in the machine through which the material travels. For example, in a four-station machine the polymer would be injected into the preform, shuttled to a conditioning (profiled heating) station, shuttled to a blow station, and then shuttled to ejection. 

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