PACKAGING | TECHNOLOGY
Above: For demonstration purposes, Engel combined a transparent virgin skin material with a black recyclate, so the high content of recycled material could be clearly seen on a coinjected pail
chine to fill a two-cavity mould for an interior automo- tive part. With ImFlux, it now uses a 4,500 kN unit. One of the most counter-intuitive things about ImFlux is that, even though it takes longer to fill parts than regular injection moulding, cycle times are shorter – sometimes much shorter. This is because the process packs as it fills. “We don’t have a long pack and hold phase, and cooling times are shorter too,” Stiefel says. Cycle time reductions of up to 50% have been obtained, with the average probably between 15 and 20%. Injection pressure on average is 20-30% less. “This means that we have been able to do a lot of work in redesigning tools and increasing cavitation, even while reducing the size of machine the tools run on.”
Viscosity variation Just how much better ImFlux is than conventional injection moulding technologies at handling wide-spec materials is probably something that will be debated among rivals for a while to come. Certainly Arburg is making a strong case for its various technologies that can ameliorate viscosity variations: discussing a recently demonstrated cell processing post-industrial waste, it cites its aXw Control ReferencePilot assistance function, inte- grated into its Gestica control system to ensure an exact holding pressure and constant shot weights, and processing signals from a pressure sensor placed close to the sprue in the cavity of a one- cavity mould. To provide the basis for control, good parts made from virgin material are first produced and then used to generate a reference curve used when recyclate is subsequently processed. A further “smart” assistance function is the aXw Control PressurePilot, which Arburg says facilitates
22 INJECTION WORLD | July/August 2021
a “bionic” transition from the injection process to the holding pressure. “A prerequisite for both functions is the aXw Control ScrewPilot which provides precise screw movements and a constant injection profile,” it says. At its virtual E-symposium 2021, Engel intro- duced a new coinjection process, which it has developed in cooperation with Canadian company Top Grade Molds. It says the process enables high and completely encapsulated recycled material content in the production of pails, making it superior to conventional processes for sandwich injection moulding. The 5-gallon pail mould for the world premiere was provided by US pail manufac- turer M&M Industries. Very short cycle times were achieved in combi-
nation with a new Engel Duo Speed injection moulding machine. Engel developed the unit specifically to meet the requirements of producers of pails and storage and transport containers. Coinjection makes it possible to concentrate the
recycled material in the component’s core and encapsulate it by a layer of virgin skin material. The virgin and recycled material are of the same type to ensure that the sandwich-moulded parts can also be recycled at the end of their useful life. HDPE was used for the 5-gallon pails; the recycled material originated from post-consumer collection. “The greatest challenge in sandwich injection moulding is to achieve high recycled content without compromising product quality or perfor- mance,” says Engel. “One focus of the develop- ment was therefore on combining the two molten plastics in the pail mould without mixing them beforehand in the melt stream. As a result, the system switches between recycled and virgin material at the cavity injection point by way of a coinjection valve gate.” Christina Härter is Head of Application Engi- neering for the Netstal brand at KraussMaffei HighPerformance. “The trend towards using more PCR is very strong,” she says. “Customers are increasingly thinking of using chemically recycled PP. For example, Unilever now uses Trucircle chemically recycled PP from SABIC for tubs used for its Magnum ice-cream.” (In August 2020, Magnum announced the roll out of more than seven million ice cream tubs made with the polymer, which uses feedstock sourced from used, mixed plastics.) “We also see customers wanting to use more mechanically recycled PP for non-food-contact applications, and this is something we are quite used to. It is already quite common for producers of flowerpots to use scrap material in their
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IMAGE: ENGEL
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