Two-Stage Process Converts Post-Consumer Recyclate Into New Molded Parts

During its live e-symposium, injection molding machine and automation supplier Engel (Schwertberg, Austria) introduced a new two-stage process that can accept ground post-consumer scrap as a feedstock and convert it into new molded parts, including thick-walled components, without interim pelletization of the scrap material. Eliminating that step not only saves time and money, it lowers the heat history for the reclaimed resin.

In a release, Engel said the new machine breaks down plasticizing and injection into two independent process steps, which are nonetheless closely tuned to each other. In the first step, raw material is melted using a conventional plasticizing screw. During the second stage, that melt is transferred to a second screw for injection into the cavity. Alternatively, the plasticizing screw can be paired with piston or plunger style injection unit, allowing the molding of very large shots up to 160 kg in what the company calls a comparatively low injection-pressure process.

Engel said it designed the new piston in a way that eliminates some of the typical disadvantages that style of injection units can experience when changing materials. Rheologically optimized, the piston tip supports uniform flushing around the piston body, enabling fast material and color changes. Starting with a shot weight of 20 kg, typical applications could include containers, pallets or even large fittings.

The design of the process and the machine allows molders to integrate melt filters and degassing units on the injection side of the machine, ensuring the machine is processing a devolatilized melt stream. An Engel spokesperson told Plastics Technology that the company can test its customer’s material, as well as parts, to ensure the two-stage process creates the required upcycling quality.

In terms of overall throughput, the spokesperson said that figure depends on the customer’s needs, including the required cycle time and the raw material. Based on those inputs, Engel chooses the appropriate diameter of plasticizing screw.

In terms of clamp force, the spokesperson said the machines are designed individually based on Engel’s building blocks. Typical clamping forces start from 900 tons and range up to 4000 tons, although there are smaller clamping forces available as well. The injection and plasticizing units are arranged on top of each other in order to save space. Regarding overall footprint, the spokesperson said that due to the optimized design of each machine component there is no impact to the machine length compared to standard injection units with the same capacity. In fact, the piston injection variation actually has a smaller footprint compared to standard machines with the same injection capacity and shot weight.