MOULD MAKING PETplanet Insider Vol. 24 No. 12/23 www.petpla.net 29 Very long, thin cores tend to bend due to the injection pressure so that they are no longer perfectly centred in the cavity, resulting in uneven wall thicknesses. In tests, MHT and GR8 achieved extreme concentricity with a preform weighing 43 g and 135mm long. AFM can be used in existing PET injection moulding machines with an external power unit. A further colPeter Clarke from the R&D company GR8 Engineering about the project Having seen an interesting post on the subject of material savings in preform production, we contacted the post creator Peter “Plastic Pete” Clarke from the R&D company GR8 Engineering Ltd. and exchanged ideas, first in writing, then by telephone. It quickly became clear that there was an interesting story and an issue to be addressed here, namely a fundamental question for all material processors: in an age of bottle necks with minimal heights and thin-walled bodies, how can the use of PET materials in bottle production be reduced even further without significantly compromising the consumer and user experience? laboration with machine manufacturer Sacmi led to the result that AFM can be used in their machines without additional equipment. As stretch blow moulding and filling processes always take place after preform production, it is important to incorporate these into a new process. MHT has been part of the Krones Group since 2018 and therefore has the relevant expertise on its doorstep. Customers have the option of mapping preform production with this technology at MHT in a prototyping process or, if required, carrying out all laboratory and stretch blow moulding tests at Krones. Initial tests on the stretch blow moulding machine have already been carried out and have shown improved basic stretching. The joint development team is planning further trials - and then nothing will stand in the way of introducing AFM to the preform market. www.mht-ag.de Peter, the Head of Creative Engineering at GR8 and the source of the idea, had the topic on his radar long before the utilisation of lightweight and material savings reached the current level. “We had a mould with a single cavity built back in 2007 to test the process,” he explained. “As explained by MHT, the method is that the core moves back slightly during injection and then moves forward to complete the filling and packing, making the preform base thinner and allowing the resulting material to flow into the preform wall. We have experimented with hydraulic control, springs and a combination of both, all of which actually work. The best method, however, is a mechanical spring behind the core that resists the flow of material through the pusher and a hydraulic control that moves the core forward towards the end of the filling process.” GR8 produced the 135mm preforms mentioned by MHT with a wall cross-section of 1.5mm and an L/T of 90:1. The process was also used in the production of equal-length preforms with a wall cross-section of 3.3mm within a cycle time of 12s, with the material being processed at 255°C using secondary cooling in the robot removal. “We then developed the aforementioned Antiflex method, where the geometry of the base of the preform is configured to self-centre when the core is pushed forward towards the end of the filling process,” Peter Clarke continued. Another improvement was the introduction of Back Flow Assist to eliminate the crystallinity of the gate, particularly in the gate opening area. The geometry of the gate area is designed in such a way that excess material flows back through the gate when the core is pushed forwards. The reheating of the long, thinner-walled preforms would also allow energy savings of around 40%, as PTI’s experience has shown, says Peter. The partnership with MHT began in 2016, when the mould manufacturer built a 4-cavity mould and modified one of its injection moulding machines so that AFM technology could be used. Since then, thousands of preforms have been produced with AFM. “Our main customer was Pepsi, with preform tests carried out by PTI in Geneva,” said Peter. Further testing took place in Moscow and around 20,000 preforms were produced for shipping, but since Russia’s war of aggression, AFM technology has lost momentum, Peter continued, and is now on the lookout for other potential customers. https://shorturl.at/bkuER Peter Clarke, Head of Creative Engineering at GR8 Engineering Ltd.
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