Woodworking – Process – Mechanical cutting or shaping
Patent
1998-01-29
2000-04-25
Bray, W. Donald
Woodworking
Process
Mechanical cutting or shaping
144364, 144380, 144271, B27M 102
Patent
active
060532246
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for pressure treatment of wood. The device comprises a treatment space in the form of a pressure chamber, which during the pressure treatment accommodates one or more wood elements and a pressure medium for transferring the pressure to the wood elements, the pressure medium surrounding the wood elements on more than one side.
The device is especially suitable for hardening-treatment of elongated plane wood elements, such as boards sheets and plates.
BACKGROUND OF THE INVENTION
It is previously known to change the properties of wood products by pressure treatment. SE 446 702 describes one method for hardening and stabilizing wood. The method comprises heating the wood to a temperature of 75-160.degree. C. and compressing it by mechanical pressing at a compression pressure of 50-1000 bar for 0.1-60 seconds. For carrying out this treatment, a roller press is used. However, it has proved that this method leads to an uneven treatment result. The change in hardness of the treated wood varies markedly between various points on the treated surface. This insufficient treatment result is primarily connected with disadvantages of the roller press. During calendering, the treatment pressure is applied along a line on the surface of the treated element. The calendering means that small natural variations in the thickness and density of the untreated wood element result in different local roll pressures. Thus, also the treatment result varies locally. Furthermore, calendering results in the pressure being applied in only one direction. During the rolling, therefore, the treated element tends to float out in breadth and in length. This results, among other things, in the edges of the element becoming uneven. Still worse, however, is that the unidirectional pressure contributes to the locally varying treatment result. The material in those parts of the element which are located along the edges of the element easily floats out and only experiences the vertical compression. In those parts which are not situated at the edge, on the other hand, the internal friction of the wood prevents the material from floating out. The material in these parts therefore experiences also a certain and greatly varying internal horizontal counter-pressure, which leads to making these parts harder than at the edges of the element. It is primarily the locally varying hardness result that makes calendering unsuitable for pressure treatment of wood elements.
Swedish patent application 7805483-0 describes a method for pressing veneer. The description states that it is known to press veneer at moderate pressures of about 1-5 MPa and also that it has proved to be suitable, when pressing pine wood veneer, to work with pressures around 150-350 MPa. According to this document, the pressure should be applied by means of a hydraulic press across the whole veneer surface simultaneously. These statements would seem to be unreasonable to a person skilled in the art. Generating such high pressures over such large surfaces with prior art technique would seem to be, if not impossible, at least commercially unrealizable. It is more likely that the pressures intended throughout the description are to be given in the unit bar, that is, that the actual pressures intended are one-tenth of those given in MPa in the description.
With this interpretation, the description becomes more reasonable and then addresses a problem which is associated with pressing of veneer. It describes how pine wood veneer, which is pressure-treated in a mechanical surface press or roller press, tends to be crushed and pulverized when the surface pressure exceeds 350 bar. This phenomenon, which of course is undesired, is due to the fact that the pressure is applied in one direction only.
Also SE 432 903 relates to a method for hardening wood by compressing flat wood elements. When carrying out the method, the wood element is placed in a treatment space, between two press devices which are movable relative to each other. Between th
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Hellgren Keijo
Johannisson Tom
Asea Brown Boveri AB
Bray W. Donald
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