When it comes to plastics shredding, a crucial step in recycling, there is no such thing as one size fits all, as Candi Plastic Recycling in Sollenau, Lower Austria well knows.
Modern plastics come in all shapes and sizes, and have many different properties tailored to their application. At the end of life, these differences continue to count.
Because of the different mechanical properties of plastics, shredder cutting systems are often specifically designed to shred a particular material. The cutting geometry of pointed knives works well on tough materials such as used in big bags, ropes or nets. By contrast, flat knives are far more effective for processing rigid plastics, such as polypropylene, while relatively thick-walled items are more easily broken down over a parallel cutting edge.
The choice of cutting system, or rather the interaction of rotor and stator knives and speed, strongly affect particle quality. It is particularly important to avoid fines in the material flow as these negatively affect downstream processes and can lead to blockages in cleaning components or the fine screens of the extruder.
Using a separate shredder for each material stream tends not to be an economically viable solution.
Lindner has developed a solution based on its established Mono-Fix technology that enables knives and knife holders to be changed using just one screw. More modules have now been added to the existing system. Different pointed and flat knives are available, as well as cover plates and special counter knives that can be fixed to the same rotor body. This extended range now makes it possible not only to replace the cutting system completely in the event of wear and tear, but also to use different or mixed rotor configurations.
Mixed cutting systems can avoid common problems caused especially by difficult materials. Combining the two systems produces particles that are precisely cut by the pointed knives, with the flat knives cutting loose any milled-in material. Using special filler plates, the aggressiveness of the cutting unit can also be adjusted so that it is possible to shred heavy materials at corresponding throughputs even at low drive power. In addition to the flexible rotor configurations, customised software set-ups make it possible to tailor relevant machine control and frequency converter parameters to the application.
Lindner created the flexible cutting system in cooperation with Candi Plastic Recycling GmbH. The system is already being used by the company, which processes about 3,000 metric tons of thermoplastics such as PE, PP, PS and ABS into homogenous regranulate every year. The materials mainly come directly from international big players in packaging and brand product manufacturing.
“We process thermoplastics in almost every shape, from films to hollow bodies to lumps. Since more and more producers want to avoid waste as much as possible, the required purchase quantities are constantly increasing and with them the variety of different materials,” said Andreas Campan, Head of Production and Chief Technician at Candi Plastic Recycling. “To meet our customers’ demands, and also to ensure our facilities are as productive as possible, we rely on technologies that enable us to cover the broadest possible material spectrum.”