German extrusion blow mold maker fhw-moulds GmbH has developed a venting system for removing air from the molds at the corners, not the parting line.
As the mold closes around the parison and it is inflated, air gets trapped between the parison and the mold halves. Conventional molds often are equipped with vents at the parting line, sometimes with the help of vacuum. But fhw-moulds said the problem is that air can only be removed locally, and the vacuum can leave small marks on the finished part.
The fhw-moulds solution: the extrusion blow molding of a jerry can is now vented on all four corners of the mold, and vacuum can be used to increase the venting. The vent is cut across the entire height of the corner, eliminating any marks on the part.
The corner-venting design also reduces cycle time, according to the company in Bottrop, Germany. The firm formerly was known as Friedrich H. Weischede Formenbau GmbH.
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