JAHRGANG 47, AUSGABE 2/2006

For many years multi-layer solid wood panels have been manufactured in Germany. In the first years the production had shown an apparent growth. In the last few years this trend did not proceed continuously. Therefore the aim of this work was to expand the fields of application of solid wood panels by use of light-weight middle-layers to improve several properties of the panels like insulation characteristics. The production of multi-layer solid wood panels has been carried out both under lab-scale and industrial conditions with variations of the used adhesives, the type of middle-layer materials, the type of the surface layer materi- als, the intensity of pressure and the pressing time.

Medium density fibreboards (MDF) from pine wood were made using fibres generated by the conventional thermomechanical pulping (TMP) and chemo-thermomechanical pulping (CTMP). As binders alkaline curing phenolformaldehyde resin (PF-resin), tanninformaldehyde resin (TF-resin) and a binder based on polymeric diphenylmethane diisocyanate (PMDI) were used. The results reveal that boards prepared from CTMP are superior in bending strength, transverse tensile strength and transverse tensile strength after boil test (V100 value) compared to boards from TMP. However, boards prepared from CTMP are slightly higher in thickness swelling and water absorption, the degree depends on the used resin. Further, the results indicate that using the blender gluing technique leads to better physical-mechanical properties of the boards than the conventional blowline gluing technique.

The quality of sanded wood and wood based material sur- faces was measured by different procedures. The subjective rating was represented by a new classification, which creates comparability with the objective results of measurement. The timed change of the characteristic values of surface allowed direct conclusions on substantial conditions of the sanding process and the involved machines and tools. The measuring procedure can be used as basis of a process control.

It has been investigated on wood of the species ash and beech, if the colour differences between coloured and noncoloured heartwood can be equalised by heat and hydrothermal treatments. Boiling in water, a mild treatment in an autoclave (140 °C; 3 bar) and some treatments in a vacuum oven (140-200 °C) showed significant less colour changes compared to some oxygen treatments (140-200 °C). Darker colours were achieved at elevated temperatures and conditioning time in the oxygen chamber. Heat treatment with increasing intensities resulted in a lower EMC and swelling as well as in a decrement of strength and hardness. Heat treatment on lower levels improved hardness which might be caused by the lower EMC.

The prediction of cutting forces is important for tool and machine design, wear issues and via power-consumption also for the energy balance and the production cost. The most common approaches which are currently used are an empirical two parameter description of Palitzsch and Kivimaa, a one parameter theory of Koch and Ettelt. In this paper these approaches are compared with regard to precision and simplicity of the application.

Circular saw blades are used for cutting operations. Depen- dent on increasing material strength and demand for narrow kerf, the load on the tool is growing. Because of the thickness/saw-diameter ratio, saw vibration is of crucial importance. Residual tool manufacturing stresses and process stresses have a dominant influence on the natural frequencies of the saw blade. Frequency shifts to avoid resonance can be achieved in the saw blade manufacturing chain also by grinding stresses. The possible application of Cubic Boron Nitride (CBN) as grinding material is part of ongoing research.

In extrusion and injection moulding processes high pressure is used which compresses the matrix of wood-plastic compo- sites (WPC) to values above 1.0 g/cm3. The alternative, pressure free rotomoulding process is used the first time for production of WPC-bodies. The bottleneck of binding wood particles one to each other was solved by coating the wood particles with a thermoplastic resin in a milling step. These coated particles, together with particles of the same thermoplastic resin are used to for WPC-bodies of densities distinct below 1.0 g/cm3. By reducing the density and the use of wood particles interesting savings for costs of thermoplastic resin can be achieved.