Large granulators with high drive powers have so far been used for single-stage size reduction of big and heavy pipes or large-volume plastic products. This results, among other things, in a high investment volume, high noise emissions, frequent blade changes, high energy and personnel costs, and much more. The two-stage system with universal shredder and secondary granulator from WEIMA is used in plastics processing plants for the economical processing of start-up lumps, sprues, scrap parts, foils, cables, pipes, etc. The two-stage shredding system can be used for a wide range of applications.
WEIMA delivers over 1,000 machines per year. Many of them are used for inhouse recycling, post-consumer and post-industrial plastic waste recycling. You can find an excerpt of current reference projects here:
Based on the advantages and disadvantages of both machine types, shredders and granulators, plastic processing industries prefer a combination of both machine types: the two-stage system. With this concept companies can use the advantages of both machine types while eliminating the disadvantages of both machine types:
- Lower wear and tear
- Lower energy consumption
- Constant High output
- Minimum intervention required
Two-stage shredding is the ideal basis for economical processing of many plastic residues. Pre-shredding to a particle size of up to approx. 40-60 mm is carried out on a single-shaft universal shredder which can be used for almost any material shape from film to solid blocks of material.
Subsequently, in a secondary shredder of the WNZ or WSM series, the regrind is reduced to a particle size of approx. 3-15 mm suitable for re-granulation. The two size reduction units can be arranged either one behind the other or one above the other.
The shredder rotor is turning relatively slow (approx. 100 rpm) and knives are not, in comparison to granulators, blades but concave knives. This strongly reduces the wear and tear on this machine. In addition, big solid pieces like lumps can be processed without any problems. Small foreign objects like standard nails are not a problem for the shredder. No continuous feeding required – the shredder has a big hopper which can be filled by a forklift truck. Due to the hydraulic pusher, which is part of the single shaft shredder, the machine operates without any intervention. Material discharge can be by conveyor belt, screw auger or by air extraction. Low rotor speed = high torque!
Due to the fact that the rotor of the granulator turns very fast (approx. 500 rpm), the capacity of the granulator is quite good and it produces very small flakes sizes <20mm. This is also possible because of the blade knives.
Due to the fact that the rotor of the granulator turns very fast, the wear on the machine is increased. Especially the wear is increased if the material is not 100% clean production waste or if the material itself is abrasive. Another disadvantage of a granulator is the continuous infeed which is required in order to reach a constant output of the machine. A granulator in general HAS to be connected to an air extraction system for material discharge. Due to the knife configuration (blades) and due to the rotor speed it is very difficult to process big solid pieces like plastic lumps. Wear and energy consumption will be very high. High rotor speed = low torque!
Because of its knife configuration (concave knives) and because of its low rotor speed, the shredder can process materials down to a MINIMUM flake size of approx. 15 or 20mm. It will not be effective to use a shredder with 8mm screen - the capacity would be very low!
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The WEIMA showroom is equipped with shredding and compacting machines of all sizes and technologies. This allows us to simulate your application as realistically as possible. You have the possibility to send us your material or to visit us directly in Ilsfeld. From our gallery you have the best view directly into the cutting room. This allows you to observe the shredding process live.
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Alternatively, you can send us material for testing. Click here for the form.
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