TECHNOLOGY | SIZE REDUCTION
Right: Lindner says mixed rotor configu- rations ensure trouble-free shredding of difficult materials, such as large lumps
application, the force provided by the drive unit focuses on a very small area, with the cutting system shredding highly tear-resistant materials as if it were a knife or scissors. However, flat knives are ideal for processing rigid plastics like polypropyl- ene. Materials such as plates, crates, or plastics manufacturing residues from extrusion and injection moulding, for example, which are rela- tively thick-walled compared to fibres, can be broken down more easily over a parallel cutting edge. The knives operate over a large area and aggressively draw in material, and this, in turn, has a positive effect on throughput. The choice of the right cutting system, or rather
the interaction of rotor and stator knives and speed, also decisively influences particle quality. It is particularly important to avoid fines in the material flow because they negatively affect downstream processes and can lead to blockages in cleaning components or the fine screens of extruders, for example.
Economics also play an important role. It is often the case that contract recyclers have to accept other materials, such as lumps from production processes, along with the main material, which may be a film. Furthermore, several different types of waste plastics often have to be processed to fully utilise production capabilities. If a separate shredder is used for each material stream – de- pending on the company’s size and volumes being shredded – it is difficult to demonstrate economic viability. For this reason, smaller batches are often sold on, which in turn reduces overall productivity. In order to address this problem, Lindner has turned its established Mono-Fix technology into a smart system. The company says that with the Mono-Fix – originally developed to minimise downtimes during maintenance – knives and knife holders can be changed easily through using just one screw. More modules have now also been
Right: Weima has supplied a WLK 1500 single-shaft shredder to UK-based Devon Contract Waste for recycling a wide range of hard plastics
added to the existing system. Different pointed and flat knives are available, as well as 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 prob- lems caused by difficult materials, such as large lumps and purgings, because pointed knives would otherwise mill into the plastic, causing throughput to drop sharply. Combining the two systems produces particles that are precisely cut by the pointed knives, and the flat knives cut 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. Turnkey packages can be ordered as material-spe- cific options are perfectly suited to the relevant application and shredder. Weima has supplied a WLK 1500 single-shaft
shredder to UK-based Devon Contract Waste for recycling a wide range of hard plastics. Following the acquisition of the plastics recycler Polymer Industries, Devon Contract Waste expanded its recycling portfolio to include post-consumer and post-industrial plastics waste. The facility processes all types of plastic waste, including kayaks, floating platforms, laboratory crates, toys, safety helmets and fuel tanks into granulate. The plastic flakes are sold to UK and EU manufacturing companies and used as a secondary raw material in the manufac- turing of plastic products. The existing processing machines were increas- ingly limiting the capacities. For this reason it was decided to invest in a new plant. The target was to process more than 1,000 kg of plastic waste per
38 PLASTICS RECYCLING WORLD | May/June 2021
www.plasticsrecyclingworld.com
IMAGE: WIEMA
IMAGE: LINDNER
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