Woodworking – Process – Mechanical cutting or shaping
Patent
1982-06-28
1984-01-31
Bray, W. D.
Woodworking
Process
Mechanical cutting or shaping
B27M 102
Patent
active
044284101
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for compressing board-shaped or otherwise flat wooden elements in order to produce a remaining compression of the wood and thereby permanently increase the hardness thereof. In particular the invention is applicable to comparatively soft wood such as pinewood and whitewood.
DESCRIPTION OF THE PRIOR ART
German patent specification No. 601162 and U.S. Pat. Nos. 1,403,722 and 2,666,463 disclose that it has been previously known to compress wooden elements to increase the hardness and the mechanical strength thereof. This is done quite simply by introducing the elements in question one by one between two mutually moveable press plates and subjecting them to an appropriate pressure.
The prior art technique such as represented not only by the above-mentioned patent specifications but also by Swedish patent application No. 7805483-0 is however limited to the use of uniform knotless wood; a material which on one hand fetches a high price and on the other is not desirable on the whole within many fields of application, since knots usually lend a characteristic, vivid and aesthetically attractive appearance to the wood. This limitation to the expensive, aesthetically not very striking wood qualities that are knotless has led to the fact that the technique in question has been carried into effect to an extremely small extent in practice.
Swedish patent specification No. 104506 discloses a method of compressing wooden elements at high pressures between reciprocating press plates. These elements are however not board-shaped or flat but consist of irregularly split logs which are charged to the press device at random without any specific knot-receiving layer between each element and the adjacent press plate. The logs treated in accordance with this method are moreover intended for the production of pulp, while the board elements treated in accordance with the present invention are intended to be used e.g. in floors, as furniture components, etc.
German patent specification No. 1075821 discloses how a plurality of flat wooden elements or boards are pressed together between two reciprocating press plates. The pressure used in this process is, however, extremely mediocre and not at all sufficient to produce a permanent compression completely throughout the wood material while reducing the thickness thereof by 30 to 50% or even to bring about the slightest tendency of any knots to come out of the surface of the board.
U.S. Pat. No. 2,974,697 and German Offenlegungsschrift No. 2112618 disclose how wooden elements are treated by being fed between rollers. None of these publications deals with the problem of keeping the knots of the wood intact during pressing. Quite to the contrary the Offenlegungsschrift No. 2112618 aims at eliminating the knots by crushing them during the pressing between the rollers.
SUMMARY OF THE INVENTION
An object of the present invention is to make it possible to compress even wood which is full of knots and thereby provide wooden elements having good impact and scratch resistance properties. According to the invention this is achieved by means of a method which is characterized by the steps of subjecting the individual wooden element to a pressure in the region of 20 to 60 MPa (Mega Pascal) during pressing between two press plates which are moveable relative to each other in a manner known per se and keeping it therebetween together with at least one layer of material, the hardness of which is less than the hardness of the knots existing in the element in question and which layer is thick enough to allow portions of the knots to be forced out of said element and into said layer without breaking to shivers by the pressure exerted.
By using a pressure in the region of 20 to 60 MPa, preferably 30 to 40 MPa, a substantially homogeneous compression throughout the wood material is achieved, leading to a permanent decrease in the thickness of ordinary wood amounting to 30 to 50%. At the same time the knots remain perfectly undestroyed due to t
REFERENCES:
patent: 1403722 (1922-01-01), Turnbull
patent: 1644801 (1927-10-01), Van Der Werff
patent: 1952664 (1934-03-01), Esselen
patent: 2136730 (1938-11-01), Sweetland
patent: 2666463 (1954-01-01), Heritage
patent: 2974697 (1961-03-01), Elmendorf et al.
AB Nils Darje
Bray W. D.
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