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By venting all four corners of the mold, extrusion blowmolding toolmaker fhw-moulds GmbH (Bottrop, Germany) says its tooling for a 20-liter jerry can presents a special solution for removing air from extrusion molds, ultimately improving cycle time and surface appearance.

PlasticsToday Staff

February 9, 2012

1 Min Read
Need to vent? Try new blowmold tool design

By venting all four corners of the mold, extrusion blowmolding toolmaker fhw-moulds GmbH (Bottrop, Germany) says its tooling for a 20-liter jerry can presents a special solution for removing air from extrusion molds, ultimately improving cycle time and surface appearance.

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fhw-moulds extrusion blowmold

In a typical extrusion blowmolding process, as the mold closes around the parison and it is inflated and pressed into the cavity wall by the air being blown into it, existing air in the tool is trapped between the parison and the two mold halves.

This trapped air must be removed, and typically, to speed up the venting process, conventional molds utilize vents at the parting line to expel trapped air, sometimes with the help of vacuum. fhw notes that the downside of this method is the fact that air can only be removed locally and the introduction of a vacuum leaves small marks on the finished part.

In fhw's design, the vent is cut across the entire height of the mold corner to eliminate the occurrence of marks on the finished part. In this way, the company says entrapped air can be removed quickly and effectively. Since mold cooling is so important to the overall cycle time, Jean Ingenbrand, managing director of fhw-moulds notes that the additional up-front costs for this special mold reportedly have a very short payback time.  

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