CONSTRUCTION ELEMENT

Technical field

The present disclosure relates to a method for producing a medium-dimension construction element, MDCE, of wood, wherein the MDCE has an arbitrary length and has a cross section with a width in the range 3-25 cm and a height in the range 0.5-4 cm. The present disclosure further relates to an MDCE and a furniture component, such as a bed slat, thus produced.

Background

Construction elements with cross sections as stated above, MDCEs, are widely used for instance in furniture and interior decoration. Such elements can be produced for instance from solid wood or plywood as well as from non-wood materials. One problem with production methods for producing MDCE is to produce such elements at a low cost with a low environmental impact and to produce an element with consistent, reliable and relatively uniform properties.

Summary

One object of the present disclosure is therefore to provide a method for producing a medium-dimension construction element at a low cost and with reliable properties. This object is achieved by a method as defined in claim 1 . Then, in a method of the initially mentioned type, a plurality of planks, preferably wood planks, are assembled into a precursor block configuration, wherein the planks have a common general wood fiber direction. A precursor block is formed by gluing the planks of the precur sor block configuration to each other. An MDCE is formed by sawing the precursor block along a first plane, substantially parallel with the general wood fiber direction, and along a second plane, substantially parallel with the general wood fiber direction, wherein the first plane is at an angle with, preferably substantially perpendicular to, the second plane, and such that said at least one MDCE comprises material originat ing from at least two planks at any cross section along its length. This means that a construction element with features from at least two planks are formed, which means that individual features, such as a knot in one of the planks, does not weaken the element to the same extent as in an element made from a single piece of solid wood. At the same time, compared for instance to plywood, much less glue is needed and as the wood fibers extend in the direction of the length of the element, the element becomes stronger in comparison to plywood where fibers in different layers extend alternatingly in perpendicular directions. Therefore, a strong and relatively uniform construction element is obtained at a low cost.

The planks may be glued together face surface to face surface and a precursor block may be assembled from at least three parallel planks, more preferably at least four parallel planks, and still more preferably at least eight parallel planks.

All planks in the plurality of planks may have face surfaces with the same width Wp across the length direction of the planks. Alternatively, or in combination with this, at least some of the planks of the precursor block may comprise a joint, such as a butt joint or a finger joint, at a location along the length of the plank. If so, the joints of adjacent layers in the precursor block are preferably out of register with each other. This ensures that potentially weak points are spread out over the MDCE.

The first plane may extend perpendicularly to glue layers formed when gluing the planks to each other.

The MDCE may comprise material from at least three parallel planks in the precursor block.

All the glue layers in an MDCE may be parallel, and all wood layers between two glue layers may consists of a single plank in a cross section along the length of the MDCE. This makes the MDCE more structurally robust when bent about an axis forming a normal to the glue layers.

The moisture content of the planks may be in the range 8-12 % when measured in accordance with the standard EN 13183-1:2002. Typically, the planks have a thick ness Tp in the range 7-25 mm, typically 7-13 mm, and a width Wp in the range 75- 200 mm.

The planks in different layers may have different thicknesses.

The planks may comprise wood selected from the group spruce, pine, aspen, beech, birch, eucalyptus, rubber wood, and mixtures thereof. Preferably at least 90% of the total weight of planks is selected from this group. A suitable glue resin for gluing the planks to each other may be selected from a group comprising polyvinyl acetate (PVAc), urea formaldehyde (UF), polyuretane (PUR), phenolic resin adhesive, and an isocyanate-based glue, such as emulsion polymer isocyanate (EPI), and mixtures of resins in this group.

The sawing of the MDCE from the precursor may typically take place after completion of the glueing.

The present disclosure also considers a medium-dimension construction element, MDCE, of wood, having an arbitrary length and having a width in the range 3-25 cm and a height in the range 0.5-4 cm. Example MDCEs are conceivable where the cross section is in the range 0.5-12 cm in both the height and width dimensions.

Along its length, the MDCE preferably comprises, in cross section, material originating from at least two planks, glued together.

Typically, the MDCE comprises in each cross section along its length material from at least three planks, preferably at least four planks.

The planes of glue layers formed when gluing the planks may be parallel to either of a flat- or an edge surface of the MDCE along the length thereof.

The MDCE may have a rectangular cross section with a width Wm and a thickness Tm, the width Wm being preferably at least 50% greater than the thickness Tm, and the glue layers between the planks preferably extend in parallel with the thickness preferably in between opposing flat surfaces of the planks.

The MDCE has a rectangular cross section with a width Wm and a thickness Tm, the glue layers between the planks extend in parallel with the thickness, and in a cross section, the wood in between two glue layers consists of a single plank.

The present disclosure further considers a furniture component, such as a bed slat, comprising an MDCE as configured and/or produced as indicated above.

Brief description of the drawings

Fig 1 illustrates the assembling of a precursor block configuration.

Fig 2 shows the finished precursor block.

Figs 3 and 4 illustrate the sawing of a precursor block into construction elements.

Fig 5A and 5B show a construction element sawn from a precursor block, and fig 6 illustrates an example of a product built with such construction elements. The present disclosure relates to a method for producing a medium-dimension con struction element, MDCE, of wood. By an MDCE is meant an elongated construction element with a cross section width in the range 3-25 cm and a cross section height in the range 0.5-4 cm. The length of the MDCE may be arbitrary but is usually a few meters or less, typically the length is 3.0 meters or less and longer than 0.2 m. Such elements may be useful for instance in furniture and interior decoration, with MDCEs used as bed slats being one typical example.

In the present disclosure, an MDCE is produced by assembling a plurality of planks into a precursor block configuration, forming a precursor block by gluing the planks of the precursor block configuration to each other, and sawing the precursor block into a plurality of MDCE elements. This process is illustrated in figs 1-4.

In a first step, illustrated in fig 1, a plurality of planks 1 are assembled into a pre cursor block configuration 3. By a plank 1 is here meant a thick, more or less parallelepiped-shaped wood board piece. The plank 1 has a length or longitudinal direction, in the direction the wood fibers generally extend, which length Lp usually is several times its width Wp and thickness Tp across that length direction. The cross section of the plank 1 may be quadratic, but more likely approximately rectangular, having narrower sides defining two edge surfaces 5 of the plank, and wider sides defining two face surfaces 7 of the plank. At each end of the plank there are end surfaces 9. Other terms than plank, such as a wood board or a beam may be used. With reference to the above-mentioned general extension of the wood fibers, it may be noted that exceptions to that direction may exist, for example locally where knots are formed in the plank 1. In principle, a non-rectangular cross section of the plank would be possible within the present disclosure, such as a rhomboidal one. Typically, a precursor block 3 is assembled from at least four parallel planks and more likely more than ten such planks.

One suitable example of a plank dimension would be 10 mm thick (Tp), meaning a width of the edge surface 5 of 10 mm, and 150 mm wide (Wp), meaning a width of the face surface 7 of 150 mm, and having a length (Lp) of a few meters. Plank pieces of shorter length, e.g. of a length of 20 to 100 cm, may be used to fill spaces in a precursor block in an efficient manner in some cases. More generally, planks with a thickness Tp in the range 7-25 mm, and widths Wp in the range 75-200, such as 100- 150, mm are considered. As will be discussed, it may be advantageous to vary the thickness of the planks over the precursor block, typically to use thinner planks at the inner and outer layers of the stack of planks forming the precursor block.

Suitable wood materials include relatively soft wood selected in the group comprising spruce, pine, aspen, beech, birch, and eucalyptus, rubber wood, and mixtures thereof, although other wood species can be considered as well.

The planks may be dried to a relatively low moisture content, such as in the range between 8-12 % when measured in accordance with the standard EN 13183-1:2002, this being slightly lower than the moisture content at which wooden planks are usually traded in the tempered zone. The planks may be planed before being assembled.

When assembled into a precursor block configuration, as illustrated in fig 1 , the planks 1 may be placed face surface 7 to face surface 7, and it is in this interface between face surfaces 7 of adjacent planks 1 that glue is applied. The application of glue usually takes place simultaneously with the assembling.

Although it is possible and, in many cases, preferred to only use planks having the length of the desired final product, less wood material may be wasted if planks can be joined in their length directions, as illustrated in fig 1. This can be done by as sembling and gluing together planks, end surface 9 to end surface 9, in the assemb ling phase, as illustrated in fig 1. Such joining of a straight end face to another straight end face is referred to as a butt joint 8, which has the advantage of requiring minimal preparation work. Alternatively, the planks can be joined beforehand to the desired length, in which case e.g. finger joints can also be used in combination with gluing.

When planks 1 are joined in their length directions, it is advantageous to avoid having such joints 8 close to each other, to increase the mechanical strength of the finished product. Typically, joints at laterally adjacent planks could be offset, for instance by at least 10 mm. The joints of adjacent planks in the precursor block may thus be out of register with each other

As illustrated in fig 1 , the assembling can be made manually, but of course the as sembling task lends itself well to automation. When the assembling configuration has been completed, or simultaneously with the assembling, glue is applied at the face surfaces 7 of the adjacent planks 1 where they are to be in contact with each other. The planks are then glued by applying some pressure to form the precursor block 11 illustrated in fig 2. The glue application may be carried out with a procedure well known in the art, for instance by rolling or spraying glue onto those surfaces.

Different glues may be used for this purpose, but glue resins in a group comprising polyvinyl acetate (PVAc), urea formaldehyde (UF), polyuretane (PUR), phenolic resin adhesive, and an isocyanate-based glue, such as emulsion polymer isocyanate (EPI), and mixtures of resins in this group, are considered suitable.

Depending on the chosen glue resin, a temperature, typically in the range 15-70 degrees Celsius, is suitable for curing the glue, typically using a cold press, heated press plates or by a high-frequency press. The precursor block 11 may be pressed, during curing, in a direction perpendicular to the planes in which the glue extends, such that adjacent face surfaces 7 are pressed against each other, and for instance with a pressure of 5-20 kg/cm ² .

In this way, a precursor block 11 as illustrated in fig 2 is formed. This precursor block 11 has the shape of a parallelepiped with rectangular cross section and may now be sawn into a number of construction elements. It is possible to form a plurality of precursor blocks 11 at the same time in a press, glue need not be applied between all layers of wood.

It is advantageous to separate gluing and sawing in two distinctly separate stages, such that sawing takes place once the gluing process is completed. This allows separating the gluing process, which requires a relatively clean environment from the sawing which generates airborne dust to some extent.

The precursor block 11 is sawn into a plurality of MDCEs as illustrated in figs 3 and 4. As shown, a band saw 17 or a frame saw may typically be used for this purpose.

With reference to fig 2, to form MDCEs, the precursor block 11 is sawn at several locations and along first and second planes 10, 12. Those planes may be substantial ly parallel with the general wood fiber direction, and, typically, the first and second planes are substantially perpendicular to each other, although this is not necessary. For instance, a rhomboid cross section can be formed when sawing the precursor. The precursor block 11 is further sawn in such a way that a resulting MDCE comprises material originating from at least two parallel planks along most of its length, or more preferably along its entire length. As shown in fig 2, the first planes 10 along which the precursor is sawn are parallel with the flat surfaces 7 (cf. fig 1 ) of the included planks and typically with such a spacing along the short end 13 of the precursor block that each piece comprise material from at least 3-4 planks. An individual plank may be locally weak, for instance at a knot in that plank. However, as that plank is joined usually with two or more other planks at each weak location this is compensated for to a large extent.

The second planes 12 along which the precursor is sawn, may be parallel with the flat side of the precursor block 11 , coinciding with the edge surfaces 5 of the planks (cf. fig 1).

Preferably thus, one of the planes 12 along which the precursor is sawn extends perpendicularly to glue layers formed when gluing the planks to each other.

Advantageously, the MDCE comprises material from at least three or four parallel planks in the precursor block. This means that a knot, for instance, in one of the planks will locally decrease the strength of the MDCE to an even lesser extent.

Fig 5A illustrates an MDCE 15 having a rectangular cross section with a width Wm and a thickness Tm. In many cases it may be preferable that the width W is at least 50% greater than the thickness Tm, and the glue layers extend in parallel with the thickness, although many other embodiments are possible.

When used as a furniture component, the MDCE is preferably oriented such that the glue layers extend vertically as illustrated in the cross section of fig 5B. It is preferred that in the cross section each layer of wood in between the layers of glue comprise material from one plank only along the thickness Tm, as illustrated in fig 5B. Thus in each cross section, the glue layers extend only in one direction. As shown in the cross section of fig 5B, if the beam is bent about an axis extending horizontally, no significant shear forces will be applied across the glue layers which improve the structural strength.

Furniture components produced in this way may include for instance beams for double beds, typically Wm=60 mm Tm=60 mm, beams for couches, typically Wm=65 mm Tm=25 mm, and bed slats, typically Wm=60-80 mm Tm=8-15 mm. Fig 6 illustrates one example of use of an MDCE 15 produced as described earlier in the framework of a bed 19 where such an MDCE is used as a furniture component in the form of a bed slat.

It may be preferred to provide planks with varied thicknesses in the precursor block. For instance, the planks in the end of the stacks may be thinner to produce MDCEs with uniform thickness being built from a uniform number of planks.

The present disclosure is not limited to the above-described examples and may be varied and altered in different ways within the scope of the appended claims.