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VOLUME 46, ISSUE 1/2005

Changes in wood induced by thermo-mechanical pulping for making medium density fibreboards (MDF)

Language: German
Pages: 7 - 12
Authors: Edmone Roffael, Udo Hennicke, Claus Behn, Thomas Schneider

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Thermo-mechanical pulping of wood for making medium density fibreboards (MDF) induces different physical and chemical changes. These include the formation of water solu- ble wood degradation products such as low molecular weight carbohydrates and volatile organic acids. The water soluble products impact the pH-value and buffering capacity of the fibres and consequently their behaviour towards adhesives. The fibres have lower equilibrium moisture content (EMC) than the wood itself, UF-bonded boards are of even lower EMC than the fibres used for their preparation. Removal of water soluble compounds from the fibres after pulping dete- riorates the physical properties of the UF-bonded fibreboards prepared therefrom. It decreases the internal bond strength and increases the thickness swelling of the boards.

Investigations to the material behaviour during three dimensional forming of veneer

Language: German
Pages: 13 - 19
Authors: André Wagenführ, Beate Buchelt

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In order to describe the behaviour and the limits of veneer during a three dimensional deformation investigations for its evaluation have been carried out. Veneer as a thin material showed a different deformation and failure behaviour during three dimensional deformation, depending on the veneer thickness. The deformations of the whole veneer surface during the three dimensional forming were measured with an optical measuring method. With the measured deformations the strains were determined. The investigations were carried out at three wood species Beech (Fagus sylvatica L.), Maple (Acer pseudoplatanus L.) and American walnut (Juglans nigra L.) and two different veneer thicknesses (0.2 ... 0.3 mm and 0.8 0.9 mm). It was obtained that thin veneer showed a more regular deformation pattern than thick veneer due to the different bending behaviour of the different thick veneers in the different directions (longitudinal and tangential respectively radial direction).

Alternative Rye-based Binders for the Manufacture of Wood-based Panels

Language: German
Pages: 20 - 28
Authors: Detlef Krug, Andreas Weber, Rolf Schirner, Andrea Hanke

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Raw wood, and the semi-finished products made from it, have - over the past twenty years and especially in the construc- tion industry under an ecological and economic aspect - experienced a tremendous enhancement of status. Increasing environmental awareness has supported the tendency towards the use of natural binders in wood-based materials, which are derived from renewable raw materials. The IARC assessment of June 2004 regarding formaldehyde as being "cancer-indu- cing" has additionally boosted this development. The rye flours that were drychemically modified by the Ceresan Erfurt GmbH formed the starting point for the development of binding agent formulations. At the Kunststoff-Zentrum Leipzig gGmbH (KuZ), these rye flours were, by means of processing agents, further prepared in a twin screw extruder, granulated and eventually ground after cooling. The powders so obtained were used at the Institut für Holztechnologie Dresden gGmbH (ihd), proportionately substituting synthetic adhesives, in the manufacture of wood-based panels. Regarding their physical-mecha- nical properties, the manufactured boards met the normative requirements to particleboards acc. to DIN EN 312 as well as to MDF acc. to DIN EN 622-5.

Calibration of wood materials by means of face milling

Language: German
Pages: 29 - 34
Authors: Johannes Tröger, Magnus Enssle

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When calibrating wood and wood materials, it would be possible to achieve reductions in the costs of energy and tools by means of replacing the procedure section of rough grinding by face milling. The Institute for Machine Tools carried out tests with regard to the improvement in cutting edge geometries, the selection of favourable cutting materials and suitable setting parameters. Here, crowned diamond cutting edges coated with PCD showed the best results in the range of high feeds per tooth and low cutting speeds, when machining chip boards. In accordance with determined law-governed correlations, the required rough-milling quality of 100 µm core roughness height can be achieved even after a feed travel of 500 km. The rough-milling process is followed by the finish-grinding process with the aim of achieving a core roughness height of 25 µm. Today the required minimum allowance of 0.6 mm for a mill-ing calibration is partly already reached or even undercut in case of standard chip boards by means of improved pressing methods. Nevertheless a lot of material producers, particularly in the area of solid wood, still have enough leeway for rough milling. For example, in case of boards with a thickness of 50 mm, allowances of 1.2 mm cannot be undercut yet

Flat lamination by means of hot melts - a new bonding technology

Language: German
Pages: 35 - 39
Authors: Horst Hoffmann, Andrew Nixon

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The lamination of panels with a wide range of substrates including wood, wood-derived materials, metals and plastics, using a hot melt is commomly known as Flat Lamination. In this application a heated roller coater is used to apply the hot melt to the panel. A second panel or foil is then placed onto the coated panel and passed through a roller press or static press. The applied hot melts normally have a low viscosity, and high initial tack; and long open time which allows the assembly of larger panels to be made. Common for this application is the use of reactive polyurethane hot melts ,although for certain applications a standard low viscosity EVA or pressure sensitive hot melt can be used. This relatively new application of applying hot melts via a heated roller coater provides new possibilities to rationalize production, and solve problems seen in using traditional adhesives.

Integration of a Preheating System and Cooling Zone for the MDF-Production

Language: German
Pages: 40 - 44
Authors: Marius Barbu, Karl Lerach, Franz Pölzleitner

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One of the most important concerns of the wood composite boards industry in the last decade consists of increasing the mat temperature before hot pressing, having as main goal to decrease the pressing time, thus determining a higher productivity. This applies mainly during the manufacturing of thick boards, which can be obtained either using continuous presses having an adequate length or a corresponding pressing duration. Many developments focussed on the preheating of mats, leading to several specialized techniques designed for different wood composite boards and their respective equipment. Steam injection, targeted into the core of a moving fibermat, instead of its faces, proved its efficiency. CoreHeaterTM is the steaming wing which, related to the continuous pressing techniques, provides a simple economic and technical way to preheat the fibermat. Such an integration of this equipment into a continuous press with cooling zone was successful at MDF Hallein, proving the advantages of this combination in terms of pressing time reduction without any major changes in the board properties.

Future of smoothing technology - dust-free MDF-finishing for industry

Language: German
Pages: 50 - 55
Authors: Klaus Rehm, Christoph Raatz

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While reducing sanding and coating costs for industrial produced furniture, the smoothing technologies are suitable for continuous machining (Roller-smoothing) and CNC-routing (Fix-smoothing). Both of this technologies use electrical heat and pressure for fixing fibres on the milled profile surfaces. Smoothed profiles have very low roughness and higher density. Current developments are design and testing a heatable tool magazine for industrial use.

Woodfibre Insulation Boards

Language: German
Pages: 45 - 49
Authors: Michael Hoppe

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Insulating boards made from wood fibres and binders in a dry process are used in a wide range of applications. These boards are produced using a proven and fully developed technology comparable to the MDF technology. Plant substrate boards and semi-finished products are further interesting versions with a future potential. The plant size depends primarily on the selected board programme, production costs are dominated by binder, energy and transportation as key factors. New developments offer interesting market opportunities and healthy profit margins.

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