Mould optimisation through cavity venting

Aug 12, 2023

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Knarr has introduced a novel approach to address the challenges posed by mould venting. To this end, the company has created a high-precision helical geometry that allows for efficient and reliable venting of excess air.

Often, air or gases are produced during the injection moulding process that must not be trapped in the cavity under any circumstances. Otherwise, cavities are created which are detrimental to the moulded part. To avoid quality deficits in the plastic part, the excess air must be released from the closed system.

Sufficient venting has always been considered one of the demanding tasks in plastic injection moulding. Traditionally, this requirement has been met with ground surfaces on the ejector pin, for example. This undoubtedly achieves satisfactory results with regard to venting - but other risks such as burr formation or poorer guiding behaviour and thus significantly more wear have to be accepted.

Knarr meets the challenge with a high-precision helical geometry that ensures reliable venting. “Even in our own mould making, we are repeatedly confronted with the difficulties of venting. The solutions available to date have all been less than ideal,” says Florian Schneider from Knarr’s technical sales department, explaining the reasons for the new approach.

The ejectors for venting are not only available in all common diameters between two and twelve millimetres, but also in intermediate sizes and up to a standard length of 450 mm. In special solutions, the ejectors are also manufactured up to a length of 750 mm including the helical geometry. As an additional standard to the hardened version (300133), the company also offers the vent ejector pin with a DLC coating (300133DLC). The robust DLC coating does not require any further lubrication and is particularly suitable in this application to prevent clogging of the helical geometry.

Thanks to the helical geometry and the resulting unequal arrangement of the surfaces, we achieve significantly improved guidance of the ejector in the fitting bore and thus significantly lower wear, reports Florian Schneider. In addition to the convenient interchangeability with standard pins, he sees another major benefit: “Thanks to the high-precision manufacturing, we can guarantee the depth of the helical geometry of 0.02 mm over the entire length of the ejector pin. Cutting to finished size without creating a burr or even further outline machining is thus possible without any problem.”

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