Two-stage granulation with the CentriCut granulator
Dipl.-Ing. Gunter Schippers, NUGA AG Kunststoffschneidmühlen, Balgach/Schwitzerland
Morein Plastics GmbH (www.morein.nl), a plastics recycler founded around 20 years ago, has recently moved its production from Denekamp in The Netherlands to Nordhorn in the German state of Lower Saxony. The move was necessary because the old production location had become to small due to strong expansion. At the same time as the start of production at the new location, the company has also started up a two-stage shredding plant (Photo 1), the core element of which consists of a CentriCut 44sl granulator from Nuga AG, Balgach/Switzerland.
Proximity to customers and fast collection and supply important for efficiency
Morein Plastics processes residual production material consisting mainly of PE, PP and PS, but also PET, into ground materials. The suppliers of the residual production materials are above all plastics processing companies in Germany. The customers for the ground materials are located mainly in The Netherlands however. The new location guarantees optimum and flexible logistics, as much as in one direction as in the other. The company's own transport fleet enables here fast removal at the point of where the surplus materials arise, as well as fast supply of customers with ground material.
The highly modern Morein Plastics operation is located on a production area of approx. 25,000 m² with a roofed-over hall of 4,500 m² and 500 m² office space. The new production location offers the company a corresponding large amount of storage capacity, so that large lots can also be collected from customers and stored. So a practically round-the-clock guarantee of collection and supply is possible. The processing capacity is currently approx. 6,000 t/a with two-shift operation.
Two-stage granulation - flexible and cost-effective processing
In contrast to the previous single-stage processing with only one large granulator, two-stage processing offers Morein Plastics more flexible handling of the material fractions to be processed. Material tasks involving, for example, large and heavy plastics parts such as start-up cakes or large hollow items, takes place via the hopper of a single-shaft shredder, that preconditions the material fractions to be processed further to a size of approx. 50mm. The pre-granulated material is then transported to the CentriCut granulator via a conveyor belt with an integrated metal detector and granulated down to the desired particle size. There is flexibility allowing smaller plastics waste to be conveyed directly to the CentriCut and thereby processed in a single-stage process.
Jan Reinink, founder and managing director of Morein Plastics says: "Overall, we require less drive power when using two granulation stages, compared with single-stage processing with a conventional granulator. We observe here much less power peaks, even at high throughput. The processing window of the materials to be worked has been significantly increased with two-stage processing. Large volume parts can, for example, only be granulated in a conventional granulator with sharp blades. Processing with pre- and post-granulation is however still also quite possible with less sharp blades".
CentriCut - best results in quality, energy consumption and throughput
Material feeding takes place in the CentriCut via a horizontally arranged screw, whereby the material flow ensures axial dosing to the CentriCut rotor. The material is flung by centrifugal force produced by the rotation of the open rotor against the grinding chamber wall formed between the sieve and stator blades and that extends over 360° to complete enclose the grinding chamber. The material is granulated cleanly and free of dust there between the rotor and stator blades and delivered through a sieve in particle size of approx. 6mm. The ground material is suitable for immediate further processing and 90% of it is processed by Morein's customers into flower pots, buckets for the building industry, film, sheet, etc.
The ground material is rapidly delivered by means of an integrated, powerful extraction system through two hard-wearing perforated sieves with large surface area that are arranged around the grinding chamber. The resulting very short residence time of the ground material in the machine leads to very low specific energy consumption, to low blade wear and finally to extremely high throughput. The rotor (Photo 2) is open, this design meaning that low mass has to be moved, of equally of benefit to the energy consumption.
An electronic control system applied to the rotor and screw shafts, and that operates irrespective of the load, prevents over-filling of the grinding chamber, as well as build-up of material on the sieve. The control of the entire equipment takes place via the CentriCut, whereby power peaks at the granulator are prevented and an even throughput achieved, specific to the task involved. The flexible harmonisation of the grinding equipment with the rate of feeding by the conveying screw, irrespective of the load, as well as the integrated material extraction, enables reliable processing, even for plastics with high sensitivity to elevated temperatures.
The throughput of the CentriCut 44sl lies in a range of up to 3,000 kg/h, depending on the type of plastic. The corresponding power rating amounts to just 75 kW. The diameter of the rotor blade is 440 mm and its width 480 mm.
High efficiency from top blade quality and super fast blade changing
The rotor and stator blades consist of identical design, precision tempered metal plates in special steel, that are mounted on special blade carriers. There are five rows of blades around the circumference of the rotor of the CentriCut 44sl and there is an arrangement of four stator blades in the grinding chamber wall. In order to enable fast blade changing, all of the blades are exchanged together with the cutting plates. This way, a complete change of blades is possible within just 60 minutes, which is a significant time advantage over conventional granulators. Blade adjustment is not required, as the cutting gap has been designed so that it retains its dimensions during the entire life of the blade strips. Faults due to settings are therefore excluded. Cutting blades that have been damaged by contaminating materials can be changed individually and within a short time. The integrated material extraction with optional inclusion of compressed air connection enables, on one hand, fastest possible extraction of the ground material, on the other hand, very fast cleaning of the machine, that is of particular advantage when changing colour or material. The grinding chamber may be opened without tools via a swivelling sieve enclosure mounted on the side, so that fast exchange of sieves is also possible - for example, when changing the required particle size. The machine is fitted with a completely integrated safety and sound protection housing.
Morein Plastics GmbH has been active for more than 20 years in plastics recycling. Apart from processing of residual plastics into ground materials - also on a contract basis - the company operates a regranulation service for recycling films. The overall investment in the new land, buildings and technical equipment at the new location in Nordhorn amounted to approx. two million Euro. A changeover to three-shift operation, bringing with it a significant increase in capacity is presently at the planning stage. The company employs a staff of 10 employees.
NUGA AG has been constructing granulators and associated accessories for granulation of plastics for customers throughout the world for more than more than 15 years. The granulators have been built with horizontal feeding screws right from the beginning. The machines are used mainly as central granulation mills within two-stage granulation plants and for special applications, such as granulation of bottles (in PP, PET etc.). The company employs a staff of approx. 30 employees.
Nuga Systems AG
9436 Balgach, Switzerland
Phone: +41 (0) 71 720 00 40
Fax: +41 (0) 71 720 00 45