METHOD FOR PRODUCTION OF SOLID WOODEN SHEETS

Abstract: The present invention refers to a method for the production of solid slabs of wood that have an even plane that is essentially independent of variations in the moisture content ratio, a block for dividing into such slabs and a slab produced by the method. The procedure achieves a change of shape of the slab due to the effect of moisture in essentially only one specified direction in the plane of the slab due to the planks (4) sawed out from the outer sections (3) of at least one trunk (1) being joined together by means of being glued to one another to form a block, that the planks are arranged with their respective elongated annual rings (5) essentially parallel with one another to form a height (h) of a block that is equivalent to or exceeds the width or length of the desired slab, and that the slabs are separated from the block along a cross-sectional cut (6) that includes the longitudinal direction of the planks and that cuts the glued joints (7) of the planks.

Description: Method for production of solid wooden sheets The present invention refers to a method for the production of solid slabs of wood that have an even plane that is essentially independent of variations in the moisture content ratio, a block for dividing into such slabs and a slab produced by the method. This is achieved by the change of shape in the wooden material of the slab due to the effect of moisture being arranged to occur only in one direction and in the plane of the slab. It is known that the shape of wood is affected by changes in the moisture content ratio of the wood. The moisture content ratio is in turn affected by changes in the humidity of the surrounding air, which explains why the effect on the shape is most evident in natural wooden materials that have not yet been provided with an outer moisture-inhibiting layer. It is also known that the changes in shape to a large extent depend on internal tensions resulting from expansion or contraction between the fibres in the areas around the annual rings, i.e., the changes in shape take place from the heart of the trunk when observed in a radial direction. The changes in shape thus take place between the layers in the tree trunk that extend in the direction of growth, where these layers in a cross-section of the trunk make visible the annual rings. These three dimensional annual rings are referred to below as elongated annual rings. According to known techniques, slabs of wood have been produced by ordinary planks being glued to one another to form a block that has then been sawn into slabs. However, the slabs produced in this way are extremely sensitive to changes in the moisture content ratio and are essentially impossible to store so that they maintain their even plane. The reason for this is that the elongated annual rings of the planks are rotated, which means that the elongated annual rings in the planks will have different directions of orientation in different positions in the slab and, at specified positions in the slabs, will vary between different slabs sawn from the same block. The problem of changing shape can be reduced by the wood being handled in a constant humidity from when the timber is bonded together to form a block, through sawing of the block to slabs and the possible sanding of the surface, to treating the outer surface of the slabs. A further way of reducing the problem is that the outer surface of the wooden slab is treated directly following the sawing to hinder the spread of moisture. Maintaining a constant humidity in the air is often impossible, especially if transport and handling are required, and an outer surface treatment is not always desirable at such an early stage. Both of the procedures named above bring about increases in the cost of producing solid slabs of wood. The following method has been suggested to achieve a specific direction for possible changes of shape in slabs of the kind mentioned above. A spiral-shaped veneer is produced by the outer surface of a tree trunk being cut out in the direction of the circumference. The spiral of veneer is then stretched out in one plane. In this way, a slab-shaped veneer where the annual rings or elongated annual rings have been straightened out to coincide with the plane of the veneer is achieved. Several of these veneer slabs are then glued together on top of one another to form a block that is then sawn across the joints and in the direction of the growth of the tree. In this way, a slab with only one direction for changes of shape is achieved. In addition, this direction for change of shape is known and is located in the plane of the slab. This requires special equipment for cutting out the veneer and a relatively high quality of the tree truck that is to be sliced at its surface, which results in the procedure being both time-consuming and expensive. The objective of the present invention is to overcome the disadvantages named above and achieve a procedure for producing a homogeneous slab of wood whose change in shape takes place in a known direction in the plane of the slab, a block for dividing into the said slab and a slab produced by the procedure. These objectives are achieved with a procedure that is first named above and that is distinguished by those characteristics defined in the enclosed independent claims. Preferred embodiments of the invention are evident from the following non- independent claims. Additional advantages and characteristics of the invention are evident from the following non-limiting description of one preferred embodiment of the invention. The description contains references to the enclosed drawings, where fig. 1 shows schematically a common means of sawing planks from a trunk, fig. 2 shows a block according to one embodiment of the present invention, and fig. 3 shows a partial view of fig. 2 at a larger scale. The procedure according to the present embodiment for producing solid slabs of wood includes the planks sawn out from the outer sections of a trunk being joined together by means of being glued to one another to form a block. Fig. 1 shows schematically a common pattern according to which a trunk 1 is sawn into planks. The inner part of the trunk, shown as a rectangular section 2 in fig. 1. comprises that traditionally used for sawn timber products. Parts lying further to the outside, known as outer sections 3, are not considered to be suitable for sawn timber products and thus fetch a very low price. The outer section is generally considered to be waste. If the outer section is nevertheless used for sawing to planks, the elongated annual rings in these planks will be essentially plane in relation to the elongated annual rings in planks sawn out from closer to the heart of the trunk. As shown schematically in figs. 2 and 3, the procedure also involves that the planks 4 sawn out from the outer section are oriented with their respective elongated annual rings 5 essentially parallel with one another so that the length of the plank (1) and the height of the block (h) agree with or exceed the desired width and the length of the slab, and that the slabs are separated from the block along a cross-sectional plane 6, The cross-sectional plane 6 includes the longitudinal direction of the planks (equivalent to the direction of growth of the tree) and cuts the glued joints of the planks, which are also essentially parallel with the elongated annual rings. Partitioning off the slabs can occur by sawing, e.g. with a band saw or blade, by a cut, e.g. plane cutting or stock cutting, or by some other suitable means. In the present embodiment, it is stated that the length of the plank 1 is equivalent to or exceeds the length of the desired slab. This is only an example. In practice, the common height h of the planks can naturally be equivalent to or exceed the length of the desired slab and the length 1 of the block can constitute the width of the slab. Which of these alternatives applies is determined by the available machinery, the available material and the desired direction of the known change of shape in the slab. Planks that are sawn from the outer sections usually have a rectangular cross- sectional shape with the elongated annual rings essentially oriented in parallel with the main surface of the plank, as is shown in fig. 2 and 3. The slab is preferably separated by means of sawing from the block and the main surface of the sawn off slab is smoothed with, for example, a sanding machine. The slab can even be sawn with a figure saw before it is smoothed. In alternative embodiments, the slab can be separated by means of cutting. Even if the elongated annual rings of the planks are essentially plane, they do display a slightly rotated surface. The planks can thus advantageously be arranged so that the elongated annual rings of adjacent planks are arranged as a mirror image in relation to one another, i.e. front-to-front and back-to-back. With this procedure, one can saw out surprisingly stable shapes of slabs with a thickness of under 20 mm from the block. Experiments have been performed and have given good results when sawing out wooden slabs with a thickness down to 4 mm. In this way, it is possible to achieve slabs with a known change of shape influenced by moisture in the plane of the slab that are neutral with regard to the even nature of the plane. The procedure even allows the production of slabs with these sought-after characteristics from an unexpected and very cheap raw material. The block that is to be divided into wooden slabs consists of planks sawn from the outer section of a trunk and bonded to one another by means of gluing. The planks are arranged with their slightly rotated elongated annual rings essentially parallel with the glued joint, and adjoining planks are arranged with their slightly rotated elongated annual rings essentially parallel with the plane of the reciprocally glued joint. The slightly rotated elongated annual rings of the adjoining planks can be arranged front-to-front and back-to-back respectively, i.e. arranged as a mirror image in relation to one another with regard to the common glued joint. The solid slab of wood produced by means of the procedure has a number of strips sawn out of planks from the outer section and joined together by means of gluing. These strips form the slab. The glued joints that hold the strips together extend between the main surfaces of the slab and as such clearly demarcate the adjoining wooden strips. In addition, knots that may be found in the planks that form the starting material will always be glued firmly to the adjoining plank, which means that the starting material does not have to be wholly free from knots. Since the knots are found pointing radially outwards on a tree trunk, i.e. a perpendicular direction to the elongated annual rings, they will always be glued to an adjoining plank. The risk that a knot will fall off at a later stage is thus eliminated. The segments of elongated annual rings that form the strips are essentially plane and essentially parallel with one another and with a plane perpendicular to the slab. Furthermore, in the present invention, this perpendicular plane is parallel with the glued joints.

Claims: Claims 1. Procedure for the production of solid slabs of wood that have a change of shape due to the effect of moisture in essentially only one specified direction in the plane of the slab due to the annual rings being oriented standing and essentially parallel with the said specified direction characterised in that planks (4) sawed out from the outer sections (3) of at least one trunk (1) are arranged on top of one another with their respective elongated annual rings (5) essentially parallel with one another to form a height (h) of block that is equivalent to or exceeds the width or length of the desired slab, that the planks are joined together by being glued to one another to form a block, and that the slabs are separated from the block along a cross-sectional cut (6) that includes the longitudinal direction of the planks and that cuts the glued joints (7) of the planks. 2. Procedure according to claim lcharacterised in that the slab is cut out from the block and that the main surface of the sawn-out slab is smoothed, preferably with a band sanding machine. 3. Procedure according to claim 2characterised in that the slab is figure sawn prior to smoothing. 4. Procedure according to claim lcharacterised in that the slab is separated by means of a cutting device and that the planks are arranged in an alternating front-to-front, back-to-back manner. 5. Procedure according to any of the previous claims characterised in that the slab is separated from the block with a thickness under 20 mm, preferably in the thickness range 3-15 mm. 6. Block for separating into slabs of wood according to the procedure in claim 1 characterised in that the block consists of planks (4) sawed out from the outer sections (3) of a trunk (1) and arranged on top of one another by means of gluing, that the planks are arranged with their slightly rotated elongated annual rings essentially parallel with the glued joints (7), and that adjacent planks are arranged with their slightly rotated elongated annual rings back- to-back and/or front-to-front. 7. Solid slab of wood produced according to the procedure in claim 1 characterised in that the slab has a number of strips joined together to form the slab by means of gluing, that the glued joints extend between the main surfaces of the slab and as such clearly demarcate the adjoining wooden strips, that the segments of elongated annual rings are essentially plane as well as essentially parallel with one another and with a plane perpendicular to the slab.

Inventors: LINDKVIST ULF, LINDKVIST, ULF
Applicants: DEGERBYNS TRAE AB, LINDKVIST ULF, LINDKVIST, ULF
Application year: 1998
Main classification: B27M3
IPC codes: B27M3, E04C2