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Characterisation of wood fibres for MDF - off-line and on-line measurements for production monitoring

: Benker, B.; Erbreich, M.; Plinke, B.; Wollmann, A.

BioComposites Centre, Bangor:
Seventh Panel Products Symposium 2003. Proceedings : Llandudno, Wales, 8th, 9th, and 10th October 2003
Bangor: The BioComposites Centre, 2003
ISBN: 1-8422-0057-7
European Panel Products Symposium (EPPS) <7, 2003, Llandudno>
Conference Paper
Fraunhofer WKI ()

In the manufacture of MDF there is a need for direct measurement methods for the size parameters of the fibres, helping particularly with the control of the disintegration process. In a joint project new methods were tested. The main focus of the investigations were two optical methods, laser scanner and diffraction spectrometry. Both methods are able to measure the particles in an air-borne state (aerosol) or stirred in water (suspension) and both were successfully used for the measurement of particle size on a laboratory scale as well as on-line devics monitoring the refining process. Due to their measuring principle they are not able to analyse completely the complex structure of the fibres but they provide data useful as "fingerprint" in the laboratory and the production. At first, mixtures of different sieve fractions were dispersed in a fluid of which portions were analysed off-line showing that the mixture ratio could be determined quantitatively with both methode.
For the on-line measurement the instruments were installed in the duct from the blow line dryer to the cyclone of a laboratory refiner plant. Under different conditons fibre material was produced from chips of pine, spruce and beech wood as well as from used wood. The temperature and the retention period in the pre-evaporator were varied as well as the gap width in the refiner. The distribution of the particle size reflected the alterations in the disintegration parameters and in the characteristics of the wood species. Both measuring devices indicated, under on-line conditons, changes in the gap width of the refiner. Furthermore, it turned out that long fibres play an important role in the correlation of the properties of the fibre material and the board properties.