What is Blowmolding?

Blow molding is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow molding:

  • Extrusion blow molding: Plastic is melted and extruded into a hollow tube (a parison). The parison is then captured by closing it into a cooled metal mold. Air is then blown into the parison, inflating it into the shape of the hollow container, or part. After the plastic has cooled, the mold is opened and the part is ejected.
  • Injection blow molding: Generally used in the production of small glass/ plastic objects in large quantities, this process is divided into three steps: injection, blowing and ejection. The polymer is first injection molded onto a core pin; then the core pin is rotated to a blow molding station to be inflated and cooled.
  • Injection stretch blow molding: In the ISB process, the preforms are heated (typically using infrared heaters) above their glass transition temperature, then blown using high-pressure air into bottles using metal blow molds. The preform is always stretched with a core rod as part of the process.

The blow molding process begins with melting down the plastic and forming it into a parison or in the case of injection and injection stretch blow molding (ISB) a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.

The parison is then clamped into a mold and air is blown into it. The air pressure then pushes the plastic out to match the mold. Once the plastic has cooled and hardened the mold opens up and the part is ejected.

The Blowmolding Process

In the blowmolding process, the polyethylene is extruded in a vertical orientation at about 400 degrees.  The material descends from the accumulator, which is located at the top of the machine, down through the blow stand.

Once the extrusion is complete, the polyethylene is pinched off forming a sealed balloon at which point in time hot air is injected at about 125 psi to make the balloon form against the one that’s in the mold. 

The mold is all die cast aluminum and is fitted with water cooling to provide a rapid transition from the molten state of the polyethylene to a stable part that we can withdraw.  The entire process only take about 11 minutes so in the blow molding technology we are able to achieve high volume manufacturing of parts at about 6-8 times what you would be capable of doing in a rotational molding process. 

Benefits of Blowmolding

  • Can produce the smallest to the largest products – all shapes and sizes
  • One piece construction – no connections or seams
  • Ability to choose from a wide range of materials or resins
  • High production rates
  • Multiple wall construction choices
  • Excellent performance under pressure
  • Trim is reusable

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Contact us to learn more about Roth’s Blowmolding Capabilities and how it can transform your product development efforts.

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Roth Industries, INC. | 800.969.7684