Blow molded plastics are any type of hollow plastic created through the process of blow molding. Even if they don't seem to be immediately familiar, blow molded plastics are actually quite common in our everyday lives. Juice, milk, and water bottles are all examples of blow molded plastics that most of us use on a daily basis.
Extrusion, the simplest method used to manufacture blow molded plastics, involves dropping the parison from the extruder and placing it in a mold where it is frozen into shape. The process begins with an extruder that is set to run without stopping. A die head is attached to the extruder, resulting in a parison that is clamped down into a hollow mold. Air pressure is then applied to the inside of parison using a blow pin. The unformed plastic is shaped into the mold’s structure, and then cooled. Beside the extrusion process, the two other basic techniques in manufacturing blow molded plastics are stretch blow molding and injection. Stretch blow molding involves injecting the mold, blowing it, and then ejecting it. The third technique, injection blow molding, is used to create smaller containers. Hot plastic is injected into the cavity of a mold, the “neck” of the product is attached, and then it is finished through the conventional extrusion process.
The process of making blow molded plastics continues to be widely used despite the popularity of other plastic manufacturing processes, such as conventional injection molding. Blow molding is perhaps the most simple and efficient method currently available to create hollow parts. Blow molding is also generally faster than other plastic manufacturing processes. The costs of producing the molds used in blow molding are also lower than those used in injection molding. Blow molding, however, is susceptible to excessive mold thickness as the polymer melts.
