Increased use of recycled materials in injection molding applications has thrown up numerous challenges for vendors of injection molding machines, in particular how to ensure process stability with a raw material feed whose properties might vary over time.

At K 2019, five exhibits at three locations will demonstrate Austrian machine builder Engel's contribution to the circular economy—the focus is on processing recycled material, improving process stability, and the trend towards design for recycling.

“The stability of the injection molding processes is key to being able to use recycled materials also for higher quality products,” as Günther Klammer, head of the Plasticizing Systems division and Circular Economy expert at Engel, emphasizes. Recycled material is naturally subject to greater batch variations than virgin material. In order to significantly reduce its influence on the process, the intelligent iQ weight control assistance system will be used on a victory 120 Tech injection press at Engel’s stand (Hall 15, Stand C58) to process recycled acrylonitrile-butadiene-styrene (ABS). The raw material feed consists of recycled ABS materials with MFIs of 31 and 21 supplied by MGG Polymers and Bage Plastics.

The software from Engel’s inject 4.0 program ensures a constant melt volume during injection by monitoring melt pressure and screw position as input parameters and adjusting parameters such as injection speed profile and switchover point to ensure that the theoretical and actual injection profile curves match. This reportedly ensures consistent product quality, even with strongly fluctuating raw material quality. “Intelligent assistance opens the door for recycled materials to a far broader range of applications,” says Klammer. “Industry 4.0 is an important enabler for the circular economy.” On the hardware side, Klammer notes that regrind and agglomerate have lower bulk densities and screw designs need to take this into account.

One further approach to using recycled materials more widely is sandwich components with a core of recycled material embedded in virgin material. The aim is, on the one hand, to design increasing numbers of products for this type of two-component production, while, on the other, increasing the proportion of recycled material in the sandwich structures.

The proportion of recycled material that can be used in the core is essentially determined by the geometry of the molded part and the flow pattern in the cavity. The polypropylene (PP) shipping boxes that Engel is producing at its stand using the Engel skinmelt process pose a particular challenge in this respect. Despite the complex component geometry, Engel still succeeded in achieving a recycled content of over 50% with the skinmelt process. What is also important is the grade purity “ensuring that the sandwich-molded products can also be easily recycled at the end of their service life”, as Klammer emphasizes. The recycled PP employed originates from post-consumer collection. Engel collaborates with Der Grüne Punkt (The green dot), Duales System Deutschland (DSD, Germany), to this end.

Designing for recycling means that the subsequent recycling process is taken into account as early as in the development of a new product and that the requirements of the circular economy and sustainability are taken into account in the product design. Further examples where this is already working well can be found in the packaging industry and in composite lightweight design. In the production of thin-walled packaging in the IML (in-mold-labeling) process, for example, there is a trend towards mono-material systems in which the label and pellets are made of the same material, such as PP.

Wherever you look in composite lightweight design, thermoplastic-based solutions point the way to the circular economy. In the Engel organomelt process, fiber-reinforced prepregs with a thermoplastic matrix such as organic sheets and tapes are overmolded with a thermoplastic from the matrix material's material group. The entire composite component consists only of thermoplastic and glass fibers and has the potential to be recycled at the end of its useful life. At its stand, Engel is demonstrating the production-ready process with an automotive door module application.

The all-PP part incorporates three organic sheets of a thickness of 2.5 mm, 1 mm, and 0.6 mm. According to Norbert Müller, Head of Center for Lightweight Composite Technologies, one of the challenges was how to process three sheets of differing thickness, particularly from a heating perspective. The 2.5-mm-thick sheet is pre-shaped in a separate cavity before transfer to the main cavity along with the other two sheets for subsequent forming and overmolding. Woven fabric and cross-ply tapes are used as reinforcing materials with glass fiber loadings of 45–50%.

At K 2019, Engel is stretching the circular economy lifeline far beyond its main stand. In the outdoor exhibition area between Halls 10 and 16, post-consumer waste is being converted into miniature waste containers on an Engel victory injection molding machine.

Erema's recycling pavilion is located in the immediate vicinity. Another victory machine is producing card boxes from recycled fishing nets there. The polyamide recycled material comes from Chile, where three American machine manufacturers have set up collection points for end-of-life nets. Previously, these nets were often disposed of in the sea due to the lack of available collection infrastructure. In Chile, the nets are recycled on an Erema system and processed into skateboards and sunglasses on Engel injection molding machines. The project proves how interdisciplinary and international interaction can also be used to close material cycles where there are no comprehensive collection systems to date.