The term “flash" in extrusion blow molding refers to the excess plastic material that remains on the body of a new container after the container has been formed. Though flash is a side-product of the extrusion blow molding process, it can have negative effects to blow molding efficiency as well as to the plastic part or container if not properly controlled.

Extrusion blow molding is the manufacturing process whereby plastic is melted and “extruded" into a hollow form. The melted plastic, called a “parison," is cooled in the sealed mold. Air is then blown into the parison, which presses the material into the shape of the mold. Extrusion blow molding is a significant means of manufacturing hollow parts and forms such as plastic juice and water bottles, though the full numbers of applications are extensive.

Flash is essentially the rejected waste of the process – and the problem with flash is that it can impose restrictions on the overall efficiency of the blow molding process while leading to an increased reject rate of product. The primary problem with flash is that it can attach itself to the molded part, thereby causing that part to be rejected. This poses problems associated with an increased reject rate of formed parts; leading to a slower manufacturing time with lost time and efficiency. Some of the associated problems can occur include:

  • The flash pocket isn’t large enough to hold the flash material; thereby resulting in too much plastic material;

  • The flash pocket doesn’t fill properly, which can happen if the pressure is inadequate. This will force plastic back to the container;

  • If there are any shortcomings with the process geometrics or effectiveness, this will in turn lead to pinch-off problems.

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