RECYCLING | INNOVATION
weight control, minimise the reject rate,” says an internationally active processor. “This makes it substantially easier to use recycled materials.” Engel adds that fluctuations in the material
properties pose a significant challenge for the processing of recyclates. Even homogeneously collected and treated plastic wastes are subject to greater fluctuations than virgin material, since the recyclate properties are also influenced by circum- stances such as how heavily the wastes are polluted and the process used to wash, shred and repelletise the wastes. In recyclate processing, such materials are generally sourced from different suppliers. Since recycling companies use different technolo- gies, the variance is particularly high when a batch is changed. At K2019, an Engel Victory 120 machine processed fully recycled ABS into elongated sample parts. The recyclate batches came from two suppliers using different treatment technologies and raw materials from different sources. Engel says that with the injection of plastic melt into the cavity, the filling quantity is influenced by a diverse range of factors, which can have a negative effect on the part quality. Besides fluctuations in the raw material batch, they also include changing ambient temperature and atmospheric humidity, fluctuations in the closing behaviour of the non- return valve and operating fluid supply, as well as a long run-in phase, for example, after production downtime. The iQ weight control assistance system from Engel analyses the pressure change in real time during injection and compares the measured values with a predetermined reference cycle. If the software detects deviations, it adapts the injection profile, the changeover point and the holding pressure profile to current process conditions in the same shot. In the case of parts that are filled in a cascade via multiple gates, iQ weight control additionally corrects the opening and closing of the individual shut-off valves according to the progress of filling. In this way, the software ensures high process constancy and maximises the produc- tion of acceptable parts.
Engel is also using its Skinmelt sandwich process
for increased use of recycled materials. The company says that process technologies for manufacturing multi-layer and multi-component products offer great potential for using reprocessed plastic wastes even for plastic parts that are subject to strict requirements for surface quality, product protection or consumer safety. The key is to place the recycled material in the interior while the surface is made of virgin material. Engel has developed a variant of sandwich injection moulding that allows high proportions of recycled material to
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be used even with complex part geometries. Multi-component injection moulding, such as Engel Skinmelt, offers the possibility of increasing the use of recycled material even in products with strict requirements for their optical appearance and surface functions. Since the skin material can be modified as required, even food applications are possible. With careful choice of process and mould design, the part surface can be made entirely of virgin material and thereby over 50% recycled material employed. Some properties of the reprocessed recycled material in the part core, such as colour or surface hardness, can be com- pletely covered by those of the skin material. At the same time, other properties of the core, such as a possibly higher stiffness or strength, have a beneficial effect on the product performance in the sandwich laminate. Engel adds that for very sophisticated purposes, with more complex load profiles, teamwork in the development organisa- tions is important for mastering the challenges that occur there, in a similar way to the suitable choice and coordination of the skin and core components.
CLICK ON THE LINKS FOR MORE INFORMATION: �
www.plasticsrecyclers.eu �
https://axiongroup.co.uk �
www.basf.com/chemcycling �
www.jaguarlandrover.com �
www.storopack.com �
www.suedpack.com �
www.se.com �
www.tisan.com.tr �
www.celanese.com �
www.lbf.fraunhofer.de �
www.brueggemann.com �
www.songwon.com �
www.milliken.com �
www.plasticsrecycling.org �
www.engelglobal.com
July/August 2020 | INJECTION WORLD 55
Above: Engel’s Skinmelt sandwich
technology can enclose recycled material beneath a virgin material surface, for example in transport boxes
IMAGE: ENGEL
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