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Custom Blow Molding Basics

Plastic blow molding companies create products using several different methods.  All of the processes start with a plastic preform or parison that is placed in a hollow mold. Air is then blown into the preform or parison so that it expands and fits to the mold cavity.

 Extrusion blow molding is the most common form and accounts for about a third of the overall blow molding industry. It uses the process laid out above to create hollow products like:

  • Milk jugs
  • Shampoo bottles
  • Automotive ducting
  • Watering cans
  • Industrial drums

Advantages of extrusion blow molding include its low tool and die costs and fast production rates.

In injection blow molding, the plastic is injection molded onto a core pin and is then moved to a different station, where the injection molded form is filled with air so that the plastic expands to fit the mold cavity. It’s frequently used to make small medical and single-serve bottles.

Injection stretch blow molding can be accomplished using a single-stage or two-stage process. While there are limits on the types of bottles created using single-stage injection stretch blow molding, the two-stage method is well-suited for cylindrical, rectangular or oval bottles.

Blow molding companies use a variety of plastics to manufacture their products.

Polyethylene accounts for the largest segment of the blow molding industry. HDPE blow molding is used for shampoo bottles, household cleaning products and toys, while low-density polyethylene is used for squeeze bottles, closers and caps, among other products.

PET blow molding is predominantly used for bottles, particularly drinking water bottles, whereas polypropylene is used for products like food containers, milk jugs and ice trays.

As can be seen, custom blow molding is used for a wide range of applications, including:

  • Packaging
  • Electrical and electronics
  • Consumer products
  • Automotive and transport
  • Building and construction
  • Medical

Plastic blow molding companies contribute to a worldwide market estimated at $75.3 billion in 2018, with the U.S. accounting for around 14% of that value.

Visit the Polysort plastics and rubber industry directory for an extensive list of blow molding companies or submit your blow molding company to the directory.

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