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Here’s What You Need to Know About Blow Molding

From kitchenware to traffic cones to shampoo bottles and packing materials, everywhere you turn plastic is being used for something.

The U.S. plastics industry employs approximately one million workers and contributes $375 billion to the economy. In the United States, the plastics industry is the third-largest manufacturing industry and roughly 107.5 billion pounds of plastics and resins were manufactured in 2013, an increase over the previous year’s 105.9 billion pounds.

Today the world makes and consumes about 600 billion pounds of plastic yearly and the market is growing at a rate of about five percent a year. Americans alone use about 2.5 million plastic bottles every hour.

One manufacturing process used to make plastic is blow molding. This is a process in which air is used to inflate soft plastic into a mold cavity. Injection molding and plastic manufacturing facilities can be found throughout the country in all 50 states and there are nearly 16,000 in the United States.

A standard blow molding machine consists of three major parts including the extruder, accumulator die and molds from which containers with different shapes and sizes are processed. The process of blow molding is done in two parts:

  • First, a starting tube of molten plastic is made and the tube is then inflated into the needed shape.
  • The tube is then put into a mold and inflated to take on the shape of that mold.

Blow molding is often used to make small, hollow plastic bottles. Examples of blow molded containers include those containing milk, shampoo and soda pop.

The tooling needed for blow molding is inexpensive and production is quick because parts can be manufactured and some products can be recycled. But the process does have a disadvantage in that parts must be hollow.

There are three types of blow molding. As of today, manufacturing companies could choose between the extrusion blow molding, injection blow molding and stretch blow molding. Each of the three processes is explained as follows:

  • Extrusion Blow Molding (EBM): This process is often used for mass production of plastics like bottles and is combined with the end process of filling and labeling bottles as well. Plastic is melted and formed into a profile called a parison. The parison is a tube of plastic which will be formed into a mold. The parison is put into a metal mold which has been cooled and air is blown into the parison to take a certain shape. This process can be used with many types of commonly used plastics such as PVC, PET and HDPE.
  • Stretch Blow Molding (SBM): This is a common process for producing soda bottles. The process of SBM takes an injection molded perform, which is then stretched and blown into its desired shape. SBM produces a part with a biaxial alignment and pre-heated perform are stretch in the directions of these axials.
  • Injection Blow Molding (IBM): This process is used to make plastics like single-serve bottles and medical bottles and is a two-part process. To start, molten plastic is injected into a mold around a hollow blow tube and the tube is placed into a larger mold cavity. After the blow molding process, the plastic part is removed from the blow tube.

Regardless of which product is used, plastics will continue to be a part of everyday life. According to the National Association for PET Container Resources (NAPCOR), 5,764 million pounds of PET bottles and jars are available for recycling in 2013. About 85 percent of those bottles are used for food and beverages.


Additionally, bottles and containers comprise 53 percent of HDPE packaging products and 38 percent of all HDPE products. HDPE bottles and containers have been a mainstay in the plastics industry since they began displacing metal, glass and paper packaging in the 1970s.

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