WEIMA America Inc.

Megawatt out of chips

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Courtesy of WEIMA America Inc.

König + Neurath AG, one of the leading European office furniture manufacturers, in Karben near Frankfurt/Main besides other materials process derived timber products such as chipboards and multiplex boards to produce office furniture for nearly any furnishing purpose. The resulting wood residues are not discharged but processed to become combustible by means of which the complete heating and process heat demand of the company is met. 

Up-to-date production 
Central components of this up-to-date production facility are machining centres which completely automatic produce the basic elements of the respective pieces of furniture starting from ready-made chipboards and/or multiplex boards. The wood residues resulting from this production are transported away from the machining centres to size-reduction by conveying belts.  

Treatment of wood residues - reliable and quiet  
The conveying belts of two machining centres each run into the funnel of a downstream one-shaft size reduction machine of the model series WL 6S (Photo 1) of M/s. WEIMA Maschinenbau GmbH, Ilsfeld. The lateral insertion openings at the funnel each are covered with a stripe-type plastic curtain and the remaining sides are completely closed. These measures result in a very low annoyance caused by noise and dust. Through the funnel the wood residues fall onto the bottom of the machine body. From there they are pushed against the turning rotor by a hydraulically actuated pushing device which is controlled depending on the load and which is horizontally arranged in the machine body.

The rotors of the one-shaft size reduction machine of the WL series are made from the solid and possess a particular profiling, the so-called V-rotors (Photo 2) as well as a patented knife seat. The knife carriers in this case are welded onto the circumference of the rotor. Into these carriers the cutting knives, the so-called cutting-turning crowns, are screwed from behind. This guarantees a quick knife change since with such a design and construction the screw heads are not damaged during size reduction. The rotor width is 800 mm with a rotor diameter of 368 mm.

The 42 cutting-turning crowns made of particular knife steel possess an edge length of 40 mm and are arranged in two knife ranges. Despite the highly abrasive material the knife service life for each knife edge is approx. half a year, this means a total of approx. 2 years.

The pushing device is equipped with stripping rails that prevent an undesired material infeed between pushing device and machine housing. Optionally the pushing device is equipped with a horizontal and/or a vertical toothed rails in order to feed bulky material to the machine by force. The hydraulic system of the pushing device is installed within the machine body such that it is protected from wood dust and damage. The hydraulic cylinder is suspended on gimbals which suspension avoids undesired transverse forces acting onto the piston packing leather.

The machines are driven by an electric motor which transmits the force via the hydraulic clutch, V-belt and gearbox to the rotor - with a driving power of 22 kW and a rotor speed of approx. 80 rpm. The machines are equipped with a hydrodynamic centrifugal clutch for a load-free starting up operation. They are controlled optionally by conventional contactors or by a programmable controller.

Between the cutting-turning crowns that offer four possible turning positions and a segmented counter-knife rail which is fixed or optionally adjustable the material is reduced in size.  
Homogenous chips 
The chips produced are carried off and discharged through the strainer holes of a strainer being located below the rotor and enclosing it. The objective is to produce a chip of approx. 15 mm. In order to achieve this objective a particular strainer is used which possesses a strainer hole diameter of 12 mm in the first third and of 15 mm in its further Because of this design, longer chips and/or splinters that pass the counter-knife are also reduced in size between rotor and strainer.

Upon their arrival below the strainer the chips are sucked off by a suction system through connection pieces attached laterally at the machine body or - optionally - carried off and discharged through a screw conveyor or a conveyor belt and transported with no pressure into central chip hoppers by ventilators. The air used is afterwards separated from the dusts and chips which are also transferred to the chip hoppers. Through a mixer the chips and dusts are homogenised and - depending on the respective demand - all year long fed to the downstream heating boiler plants in order to produce primary energy and burnt there. The complete energy demand of approx. 20 MW for the required process heat, the air-conditioning systems and the heating of the complete premises is covered by this. 

Size reduction of bulky wood residues  
With a one-shaft size reduction machine of model series WL 18 Jumbo (Photo 3) installed in the open and also connected to the chip hoppers, bulky wood residues such as larger chipboard residues and stored away production wastes. The size reduction machine possesses a rotor width of 1,800 mm with a feeding opening of 1,800 mm x 1,500 mm and a rotor diameter of 482 mm. The driving power is 75 kW. The machine can be started with completely filled up funnel which is equipped with a swiveling funnel cover. In this case the funnel contents will be reduced in size and afterwards the machine will automatically shut off. The uncovered metal parts such as nails, screws, clamps, etc. are transferred outward through a metal separating installation which is integrated in the suction system. The funnel volume is approx. 5.4 m³. The funnel can be designed in accordance with customer specifications. As an option, particularly bulky material can be fed to the rotor by force through a low-pressure installation which will enter the funnel from above.

Horst Zimmer, Building Services Systems Manager of König und Neurath: 'The disposal and treatment of our own production wastes to become valuable energy result in large saving potentials for us with regard to disposal and energy cost. The compact design of the WEIMA one-shaft size reduction machines and the good interface connection to our machining centres along with the competent and individual consultation and the comprehensive service which was available any time during commissioning and thereafter were convincing arguments for our purchase decision.'  

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