Method for gluing wood products and glued wood products

Abstract

The invention relates to a method for producing a glued laminated wood product for use in construction, comprising the following steps: providing at least two wood workpieces, each comprising at least one joint surface; forming a groove in at least one of the joint surfaces, wherein the groove is arranged between a pair of peripheral edges; applying adhesive to at least one joint surface of at least a first of the two wood workpieces; arranging the first wood workpiece so that the joint surface comprising the applied adhesive meets the corresponding joint surface of the second wood workpiece, wherein at least one of the two joint surfaces comprises the groove; pressing the two joint surfaces towards each other so that the adhesive is pressed between the two wood workpieces, and maintaining the pressing for a time sufficient to bond the wood workpieces to each other; wherein the pressing force applied is strong enough to force the wood tissue to collapse at the contact area until the pressure is mainly transmitted by the adhesive, wherein the contact area is defined by the surface area of ​​the two joint surfaces of the wood workpieces that contact each other when pressed together.

Description

Technical Field

[0001] The present invention relates to a method for producing a glued laminated timber product for use in construction. Background Art

[0002] Joinery is a fundamental concept in all carpentry, and the ability to join two timber workpieces together in a solid manner (e.g. by gluing) is frequently practiced, for example in construction, carpentry, furniture making, manufacturing floor and ceiling elements, glued timber beams and joists as well as ribs and timber cladding.

[0003] A known way of obtaining a load-bearing structure is by gluing the edges of the boards to form a larger surface area. In general, edge gluing of solid wood is carried out in the following manner. Roundwood logs are processed into square wood pieces in a sawmill. The square wood pieces (called, for example, timber, lumber, boards, planks, sawn timber, etc.) are then typically stick-stacked and dried in a technical drying process to a wood moisture content of about 12-15%. The pieces thus dried are planed in a planer to make the surface to be subsequently glued flat.

[0004] In the accompanying drawings, Figure 1 Schematically illustrated is a conventional workpiece of a sawn board 1' having a flat elongated shape and a longitudinal direction substantially parallel to the main fiber direction of the board. The board 1' has parallel major faces 1a', 1b', wherein the length L of the major faces exceeds their width W, and parallel minor faces 1c', 1d'. Figure 2a -b schematically illustrates the conventional way of joining two panels 1', 2' by edge gluing. As seen herein, adhesive 4 is applied to the planed surfaces 1d', 2c' (also referred to herein as "joining surfaces"), after which the workpieces 1', 2' are aligned and pressed together to cure the glue line 5.

[0005] One disadvantage of this prior art is that excess glue is squeezed out of the glue line, resulting in "glue-tears" or "glue scabs" that adhere to the surface. This can be problematic because the glue scab is an obstacle to subsequent processing, requires additional cleaning steps or limits the choice of adhesive. Some adhesives, such as polyurethanes, have a more pronounced tendency to form glue scabs. However, polyurethanes are frequently used and present some significant advantages in processing.

[0006] There is therefore a need for more efficient methods of producing glued laminated timber products made from solid wood. Summary of the invention

[0007] It is an object of the present invention to provide an improved method for producing glued laminated timber products made of solid wood, in particular to improve the edge gluing and / or face gluing of solid panels.

[0008] The invention is defined by the attached independent claims. Embodiments are set out in the attached dependent claims.

[0009] According to a first aspect, the invention relates to a method for producing a glued laminated timber product for use in construction, comprising the following steps: providing at least two wooden workpieces, each comprising at least one joint surface; forming a groove in at least one of the joint surfaces, wherein the groove is arranged between a pair of peripheral edges; applying adhesive to at least one joint surface of at least a first of the two wooden workpieces; arranging the first wooden workpiece so that the joint surface comprising the applied adhesive meets a corresponding joint surface of the second wooden workpiece, wherein at least one of the two joint surfaces comprises the groove; pressing the two joint surfaces towards each other so that the adhesive is pressed between the two wooden workpieces, and maintaining the pressing for a time sufficient to bond the wooden workpieces to each other; wherein the pressing force applied is strong enough to force the wood tissue to collapse at the contact area, whereupon the pressure is mainly transmitted by the adhesive (i.e. after the wood tissue collapses, most of the pressure acts on the glue), and wherein the contact area is defined by the surface area of ​​the two joint surfaces of the wooden workpieces that are in contact with each other when pressed together.

[0010] It is to be understood that a "joining face" in this context refers to a face / surface of a wood workpiece that is intended to be joined to a joining face of another wood workpiece that meets. The joining face is preferably planar, or at least presents a planar portion.

[0011] The skilled person will also appreciate that the adhesive may be applied to one or both of the joining surfaces of the two wood workpieces. For example, it is conceivable to use a "two-component adhesive system" in which the glue and the hardener are applied separately to the two meeting surfaces (i.e., the glue on one side and the hardener on the other side). Once pressed together, the adhesive and the hardener react immediately. Two-component adhesive systems offer the possibility of having a long working time and a very short pressing time.

[0012] It is also to be understood that "groove" in this context refers to a depression or indentation arranged in the surface of the engagement surface between raised edges. A surface comprising such a groove achieves a profile with raised edges.

[0013] It should also be understood that the expression "corresponding joining surfaces" in this context means surfaces of a single wood workpiece (wherein the "wood workpiece" may be a board / plank) which are dimensionally matched so that when adjusted and pressed against each other, the corresponding peripheries of the two faces are aligned.

[0014] Thanks to the present invention, the following advantages are achieved:

[0015] - instead of planing the two surfaces to be glued together, forming said grooves on one or both of the meeting surfaces has the effect of locking the glue in place and preventing it from leaking out at the glue line;

[0016] - locking the glue in place by means of the grooves has the effect that the surface of the wood workpiece is not contaminated by glue scab and an additional processing step of cleaning the surface can be avoided, which is a cost-saving factor;

[0017] - Overall glue consumption and therefore glue costs are reduced.

[0018] Another advantage is associated with the feature that, according to the invention, when a compressive force is applied, the wood cells in the protruding edge collapse and the height is reduced to such an extent that the compressive force becomes an action on the adhesive located in the groove. Thus, the required pressure will act on the adhesive in the joint line and also cause the adhesive to penetrate into the surface of the assembly component. ("Assembly component" refers to the encountered wooden workpieces, such as encountered boards or planks.) According to the invention, the applied pressure causes the glue to penetrate into the surface of the first several rows of wood cells adjacent to the groove. When cured, the adhesive will act as a mechanical anchor and produce a durable joint by physical adsorption and chemical bonding to the porous structure / fibers of the wood tissue.

[0019] The result is a strong and durable glued connection between two wood workpieces, which is required, for example, for load-bearing purposes in wooden construction. In other words, due to the pressed wood tissue at the protrusions, lateral overflow of the adhesive is effectively prevented or significantly reduced. At the same time, the required pressure acts on the adhesive in the joint line so that a strong structure is produced once the adhesive has cured.

[0020] According to one aspect of the invention, the wooden workpiece is a board sawn from solid wood, each board presenting a flat elongated shape and having a longitudinal direction substantially parallel to the length direction of the main fiber direction of the corresponding wooden board. Each of the at least two boards comprises a main face and a secondary face, wherein the length of the main face exceeds the width of the main face. Furthermore, in this embodiment, the groove is arranged to extend in the longitudinal direction of the board, parallel to its length direction, and is formed on at least one of the faces. According to this aspect, the groove is arranged between the peripheral longitudinal edge / protrusion pairs. Also, the joining surfaces correspond to the two faces of each corresponding board arranged to meet each other when the two boards are joined by the adhesive.

[0021] According to one aspect of the invention, said groove is formed on one of said secondary faces of at least one of said panels, which corresponds to the “edge gluing” technique.

[0022] According to another aspect of the invention, the grooves are formed on one of the main faces of at least one of the panels, which corresponds to the “face gluing” technique.

[0023] According to another aspect of the invention, the adhesive is selected to be of a type suitable for gluing solid wood together, preferably one of the following: isocyanate, polyvinyl acetate, urethane and polyurethane-based glues, or a two-component system (comprising a hardener and an adhesive) such as an adhesive based on melamine-urea-formaldehyde or phenol-resorcinol-formaldehyde.

[0024] According to yet another aspect of the invention, the method comprises subjecting the wood board to a drying step before applying the adhesive such that the wood moisture content of the board after the drying step is between 6 - 15 wt%.

[0025] According to still another aspect of the present invention, the wood moisture content of the board is between 15-24% by weight.

[0026] According to yet another aspect of the invention, the pressing force is between 0.6-1.5 N / mm2. For coniferous wood species, the specific pressing force is typically in the range of 0.6-1.0 N / mm2 and for hardwood species, it is typically significantly higher to ensure that the adhesive penetrates into the surface of the assembled component.

[0027] According to yet another aspect of the invention, the groove has a maximum depth of between 0.1 - 0.3 mm. According to current standards, the final glue line in a wooden structure should not exceed 0.3 mm in order to be within the range of the adhesive to be used.

[0028] According to still another aspect of the present invention, the pair of peripheral edges serving as flanges of the groove presents a contact area corresponding to the surfaces of two faces of the sheet material that are in contact and abut each other when squeezed together, wherein the contact area corresponds to between 5-20% of the total horizontal area of ​​the corresponding faces containing the groove.

[0029] The invention also relates to the use of the glued laminated wood product as a wooden building element, a load-bearing timber structure or a non-load-bearing timber structure.

[0030] The invention also relates to the use of a glued laminated wood product obtainable by the method according to the invention as a building element for the construction and / or manufacture of wall, roof, floor and / or ceiling elements. For example, the wood product obtained by the method according to the invention can be used as a building element, such as a layer in a multi-layer panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A wooden beam according to the prior art is schematically illustrated.

[0032] Figure 2a -b schematically illustrates the principle of edge gluing two beams according to the prior art.

[0033] Figure 3a An end portion of a wood workpiece according to an exemplary embodiment of the invention is schematically illustrated.

[0034] Figure 3b Based on Figure 3a Detailed view of IIIb.

[0035] Figure 4a -c schematically illustrates the successive steps of an example of a method according to the invention.

[0036] Figure 5a -f schematically illustrates the successive steps of yet another example of the method according to the present invention.

[0037] Figure 6a -b shows an enlarged cross-sectional view of the glue line of a glulam product.

[0038] Figure 7a -d schematically shows a detailed view of the profile of the peripheral edge according to four different embodiments according to the present invention.

[0039] Figure 8a -b shows a photograph of the edge-glued panels. DETAILED DESCRIPTION

[0040] It should be understood that the foregoing general description and the following detailed description are exemplary only and do not limit any claimed subject matter. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0041] As explained earlier, Figure 1 A conventional wooden board or plank 1' is schematically illustrated, which has been sawn from a roundwood log. As a result, the length L of the board is substantially parallel to the main fiber direction of the wooden board. The flat elongated board 1' comprises two parallel main faces 1a', 1b' and two parallel secondary faces 1c', 1d', wherein the length L of the main faces exceeds the width W of the main faces. The board 1' further has a thickness T, which in turn is smaller than the width W.

[0042] Figure 2a - b schematically illustrates an edge gluing procedure according to the prior art, as already described in the background section of the present application.

[0043] As can be seen in the drawings, the wooden workpiece is represented here by a wooden board 2. However, the skilled person understands that the invention is not limited to "boards" but other shapes made of solid wood that meet the requirements of the claims described herein are also included within the scope of the invention.

[0044] In addition, for simplicity, Figure 3a - The plate shown in b, and Figure 4a The plates 1 and 2 shown in -c are basically the same as those used in the description Figure 1 In other words, the skilled person understands that when describing the inventive concept, the described boards 1, 2 include a major face and a minor face, and have a length L exceeding a width W, etc.

[0045] Now first turn to Figure 3a -b, the outline of the wooden workpiece according to the invention will be further described. The wooden workpiece is described herein as a board 2 made of solid wood. FIG. 3 shows the end portion of the board and Figure 3b Based on Figure 3a Detailed view of IIIb in FIG. One of the secondary faces 2c of the sheet 2 comprises a longitudinal groove 3 arranged between the pair of protruding edges 6a, 6b. This secondary face 2c represents a joint surface which is intended to be joined to another dimensionally matching joint surface of another sheet by a gluing procedure which is schematically illustrated in FIG. Figure 4a -c. In this article, Figure 3a -b) is aligned with a meeting sheet 1 having substantially the same dimensions. Adhesive 4 is applied to at least one of the two joining surfaces 1d, 2c. In the present example, the adhesive is applied to the sheet 2 containing the groove 3 and at the location of the groove, i.e. between the edges. The sheets 1, 2 are arranged so that the joining surface 1d of the first sheet 1 meets the corresponding joining surface 2c of the second sheet 2. Figure 4b As can be seen in FIG. 5 , two sheets 1, 2 are pressed toward each other with a predetermined pressing force F so that the adhesive 4 is pressed between the two joint surfaces 1d; 2c at the glue line 5. The peripheral protruding edges 6a, 6b prevent the adhesive from leaking. The pressure F is maintained for a long enough time to solidly connect / join the sheets 1, 2 to each other. In addition, the applied pressing force F is strong enough to force the wood tissue to collapse at the protruding edges 6a, 6b, resulting in the pressure acting on the adhesive in the joint line and also causing the adhesive to penetrate into the surface of the assembled component.

[0046] Figure 5a -f also describes the method according to the invention, in which two joining surfaces are glued together in successive steps. First, two joining surfaces are provided, which are Figure 5a, one of the two joining surfaces comprises a groove 3. Glue 4 is applied to at least one of the joining surfaces, preferably at the location of the groove 3. The two joining surfaces are aligned and brought close to each other, initially causing the applied adhesive to be displaced and distributed within the groove 3 ( Figure 5d -e). Then, the two joint surfaces will come into contact, as can be seen in FIG5. The surface area of ​​the two joint surfaces 1d; 2c that come into contact with each other when pressed together is defined as the "contact area" 7. At the moment when the two boards come into contact with each other, the pressing force F will act only on the contact area. However, the magnitude of the pressing force is adjusted to be strong enough to cause the wood tissue to give in and collapse at the protruding edge, as shown in FIG5. Figure 5f As described in FIG. This collapse results in the compression force F being transmitted mainly through the adhesive 4 located in the glue line. Since the compressed wood tissue at the periphery of the glue line prevents the adhesive from escaping / leaking out, the pressure forces the adhesive to penetrate into the tissue surrounding the glue line instead.

[0047] Figure 6a -b shows a microscopic cross-section of a glue line 4 between two panels 1 , 2 which have been joined by the method described herein. Figure 6b The detailed view of shows that the wood tissue 5 at the contact surface 7 has collapsed due to the level of compression force applied during the gluing step.

[0048] Figure 7a –d illustrates various conceivable contours of the joint surface including the groove 3. For example, Figure 7b and 7d The profile presents a variation of the inclined surface s, while Figure 7c The contour has a radius r.

[0049] As will be appreciated by those skilled in the art, the profile of the groove 3 and the surrounding protruding edges 6a, 6b may vary without hindering the technical function of the invention. Preferably, however, the maximum depth d of the groove is between 0.1-0.3 mm. This ensures that the final glue line does not exceed a width of 0.3 mm after extrusion and curing, which is the maximum allowed for load-bearing glued wood structures.

[0050] Example

[0051] Test Setup

[0052] Use a thickness of 30 mm (thickness refers to the attached Figure 1 The edge gluing of spruce wood panels (with the "T" in the figure) was carried out using a one-component polyurethane adhesive.

[0053] A reference test was performed in which wood panels with flat joint surfaces were edge glued. The panels were pressed together long enough to allow the adhesive to cure and stabilize.

[0054] Sample tests were also carried out in which wood panels were edge glued using the method according to claim 1. In the sample tests, one of the two joint surfaces contained a Figure 7a The profile of the profile shown in , where the groove depth d is 0.25 mm and the width w of the protruding edge is 2.0 mm. During edge gluing of the samples, the sheets were pressed together under conditions corresponding to the reference, i.e. the pressure level and curing time were the same for the reference and the samples.

[0055] result

[0056] The reference edge gluing results in noticeable glue overflow where the glue has been squeezed out of the glue line, leaving adhesive droplets on the surface of the glued sheets. This is seen in Figure 8a In the photo, there is a line of glue overflow along the glue line.

[0057] However, the samples containing contoured edges showed no adhesive overflow along their corresponding glue lines, as seen in Figure 8b The tests also showed that the shear strength and delamination tendency were similar for the reference and the samples, respectively.

Claims

1. A method for producing a glued laminated timber product for use in construction, comprising the following steps: i. Providing at least two wooden workpieces (1, 2), each workpiece comprising at least one joining surface (1a, 1b, 1c, 1d; 2a, 2b, 2c, 2d); ii. forming a groove (3) in at least one of the engagement surfaces (1a, 1b, 1c, 1d; 2a, 2b, 2c, 2d), wherein the groove (3) is arranged between the peripheral edge pair (6a, 6b); iii. applying an adhesive (4) to at least one joining surface (1a, 1b, 1c, 1d) of at least the first workpiece (1) of the two wooden workpieces; iv. arranging the first wooden workpiece (1) so that the joint surface (1a, 1b, 1c, 1d) containing the applied adhesive (4) meets the corresponding joint surface (2b, 2a, 2d, 2c) of the second wooden workpiece (2), wherein at least one of the two joint surfaces contains the groove (3); v. pressing the two joining surfaces (1a, 1b, 1c, 1d; 2b, 2a, 2d, 2c) toward each other so that the adhesive (4) is pressed between the two wooden workpieces (1, 2), and maintaining the pressing for a time sufficient to bond the wooden workpieces to each other; vi. wherein the applied compressive force (F) is strong enough to force the wood tissue at the peripheral edge at the contact area (7) to collapse until the pressure is mainly transmitted through the adhesive, wherein the contact area (7) is formed by the two joining surfaces (1a, 1b, 1c, 1d; 2b, 2a, 2d, 2c) The surface areas that contact each other when pressed together are defined, and wherein the peripheral protruding edges (6a, 6b) prevent leakage of adhesive.

2. The method according to claim 1, wherein: a. The wooden workpiece is a board (1, 2) made of solid wood, each of which has a flat and elongated shape and has a longitudinal direction parallel to the main fiber direction of the corresponding wooden board, b. Each of the at least two sheets (1, 2) comprises a main face (1a, 1b; 2a, 2b) and a secondary face (1c, 1d; 2c, 2d), wherein the length (L) of the main face exceeds the width (W) of the main face, c. the groove (3) is a longitudinal groove (3) extending in the length direction formed on at least one of the surfaces (1a, 1b, 1c, 1d; 2a, 2b, 2c, 2d), wherein the groove (3) is arranged between the peripheral longitudinal edge pair (6a, 6b), d. The joining surfaces (1a, 1b, 1c, 1d; 2b, 2a, 2d, 2c) correspond to the two surfaces of each of the corresponding sheets (1, 2) arranged to meet each other in step iv of claim 1.

3. The method according to claim 2, wherein the groove (3) is formed on one of the secondary faces (1c, 1d; 2c, 2d) of at least one of the sheets (1, 2).

4. The method according to claim 2, wherein the groove (3) is formed on one of the main faces (1a, 1b; 2a, 2b) of at least one of the sheets (1, 2).

5. The method according to any one of the preceding claims, wherein the adhesive is an isocyanate, polyvinyl acetate, urethane, a polyurethane-based glue, an adhesive based on melamine-urea-formaldehyde or phenol-resorcinol-formaldehyde.

6. The method according to any one of claims 1 to 4, further comprising subjecting the wood board to a drying step before applying the adhesive such that the wood moisture content of the board after the drying step is between 6 - 15 wt. %.

7. A method according to any one of claims 1 to 4, wherein the wood moisture content of the board is between 15 and 24% by weight.

8. The method according to any one of claims 1 to 4, wherein the extrusion force is between 0.6 and 1.5 N / mm2.

9. The method according to any one of claims 1 to 4, wherein the depth of the groove (3) is between 0.1 and 0.3 mm.

10. A method according to any one of claims 1 to 4, wherein the pair of peripheral longitudinal edges (6a, 6b) serving as flanges of the groove (3) presents a contact area (7) corresponding to the surfaces of two faces (1a, 1b, 1c, 1d; 2a, 2b, 2c, 2d) of the sheets (1, 2) that are in contact with each other when they are squeezed together, wherein the contact area corresponds to between 5-20% of the total horizontal area of ​​the corresponding faces (1a, 1b, 1c, 1d; 2a, 2b, 2c, 2d) containing the groove (3).

11. Glued laminated wood product for use as a construction element obtainable by the method according to any one of claims 1 to 10.

12. Use of a glued laminated timber product as claimed in claim 11 as a wall, roof, floor or ceiling element.

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