NL2011875C2 - A method for producing a wood strand construction element, a construction element obtained therewith and a production facility therefor. - Google Patents

Description

A method for producing a wood strand construction element, a construction element obtained therewith and a production facility therefor

The present invention relates to a method for producing a wood strand construction element according to the preamble of claim 1, a construction element obtained therewith and a production facility therefor.

Such a method is known in the art, for example from the international patent application W02010/053353. A disadvantage of this known method consists among others of the fact that the method has to be performed in several subsequent steps. For, it is stated that the uncured wood strands cement mixture will collapse under the weight of a subsequently added layer of wood strands cement mixture. For that reason, W02010/053353 prescribes that a firstly added layer should be cured at least partially so as to obtain a sufficient rigidity for carrying said subsequent layer. In practice, this means that at least an hour of production time is required for hardening said mixture. More specifically, the production facility of W02010/053353 comprises a loop so as to be able to perform said method in several steps.

Said loop adds extra costs and also may lead to transport problems. Furthermore, even more important, the moisture content of wood strands of individual layers differs too much, especially the strands of a first laid layer that has cured at least partly in relation to the strands of a subsequently added layer, such that wood strands of subsequently added layers do not adhere sufficiently with the consequence that a final product is achieved that consists of layers that are subject to separation.

The invention aims at alleviating or preventing these problems .

More in particular, the invention aims at providing an improved method.

The invention especially aims at providing an improved method wherein the product obtained has a constant density through its

The invention furthermore aims at providing a method wherein the elements can be easily provided with inlays without interrupting the internal structure of the construction element and without interrupting the production, for example the production capacity or production speed.

The invention also aims at providing an improved product.

Finally, the invention aims at providing a production facility to enable the method according to the invention.

To obtain at least one of the above mentioned goals, the present invention relates to a method that comprises the steps mentioned in the independent claim 1, a construction element as identified in the independent claim 15 and a production facility as identified in the independent claim 17, which are hereby incorporated in the description by reference.

According to the method of the present invention, after distributing the first layer, an inlay is positioned on top of said layer, after which a second layer is distributed. Since positioning the inlay will only take less than a minute to maximally a few minutes, the complete mould will be filled in substantially less time than according to the method of the state of the art.

After distributing the first layer of wood strands, a mild compression is exerted on said freshly distributed layer, such that an increased density is obtained with respect to the freshly distributed material. After compressing said first layer, the inlay is positioned, after which a subsequent layer of wood strands is distributed which is subjected to compression as well. The force with which the first layer of wood strands is compressed is preferably such, that no further compression of said first layer is obtained when distributing said subsequent layer of wood strands .

After completely filling the mould according to the present invention, a lid or the like will be positioned on top of the mould, such that a final compression of the wood strands cement mixture is obtained after which said mixture will be hardened. It has shown that by performing said compression steps after distributing each layer, binding between subsequent layers of wood strands cement mixture is greatly improved. This provides an advantage over the method according to the state of the art, according to which the firstly added mixture is hardened at least partly before distributing a subsequent layer, which induces separation of firstly and subsequently added layers of wood strands cement mixture. Hence, the present invention provides the advantage that a wood strand construction element is obtained that has excellent binding of separately distributed layers of wood strands material. Furthermore, the product obtained with the present invention has a constant density throughout its thickness. As an additional advantage, the total required production time per finished element is greatly reduced with respect to the known method. Also, since distributing said subsequent layers is performed substantially contiguous, a loop is no longer required which saves production space .

The density of the layer of wood strands after compression is preferably between 1.5 and 4 times as high as the density of the freshly distributed layer of wood strands, preferably less than 3 times and more preferably less than 2.5 times, for example about 2 - 2.5 times .

Shortly after distributing and compressing the layer of wood strands, i.e. before same has been cured and dried, the density will be about 350 - 400 kg/m3. After curing and drying, the density will be about 300 - 350 kg/m3. Usually, the weight of freshly distributed wood strands mixture is about 17% higher than the weight of dried and cured wood strands mixture because of weight loss due to evaporation of water.

As a matter of fact, a lower or even higher density may be obtained, if required. For example, the density of a compressed, cured and dried element may be at least 250 kg/m3, preferably at least 300 kg/m3, and maximally 500 kg/m3, preferably maximally 450 kg/m3, more preferably maximally 425 kg/m3, most preferably maximally 400 kg/m3.

Preferred embodiments are identified in the dependent claims, which are hereby incorporated in the description by reference.

Wood strands that can be used advantageously in the present invention have a length that depends on the machine producing the wood strands. Usually, wood strands have a length of approximately 25 cm or approximately double these dimensions.

The width of the wood strands is preferably at least 1.0 mm and maximally 5.0 mm. A wood strand having a width of between 2 and 4 mm is especially preferred.

The thickness of the wood strands is at least 0.2 mm, preferably at least 0.3 mm and maximally 0.5 mm, preferably maximally 0.4 mm.

Generally, wood particles with dimensions of less than approximately 2 cm long are removed from the mixture preceding adding the hydraulic binder to the wood strands mixture, since these do pollute the machinery and moulds and reduce thermal insulating performance of the wood strand construction element obtained with the method.

It is preferred that after the first layer has been distributed, adding a subsequent layer of wood strands cement mixture is commenced within 1 hour, preferably within 30 minutes, more preferably within 20 minutes. During this period, compression of said first layer and placing the inlay is performed. This ensures that said firstly added layer of wood strands cement mixture has not hardened, which yields optimum binding results with the second added layer.

It is preferred to use wood strands that is curved or even curled in a spiral form. This means that the length of the wood strands used is approximately 25 cm when stretching same in a straight line. However, when they are curved or curled the distance from one end to the other end is less than 25 cm, preferably substantially less than 25 cm, for example less than 20 cm, more preferably less than 10 cm, like less than 5 cm. When distributing such wood strands in a mould, an open structure is obtained, providing a product that has good thermal insulating properties and a low density, for example less than 450 kg/m3, preferably less than 400 kg/m3, more preferably less than 350 kg/m3 (based on a dry, cured wood strand construction element).

The wood strand that is used in the method according to the present invention is wetted, so as to provide a good binding capacity with the hydraulic binder. The amount of water is suffi- cient for obtaining a complete setting of the hydraulic binder.

The hydraulic binder may be cement, like Portland cement or the like, or another hydraulic binder that is capable of binding to wood. The international patent application WO 2006/016844 mentions on page 3, line 25 - page 4, line 34 and further ("Method of production") among others values of ratios of water to hydraulic binder and matching amounts of wood strands that can be adequately used in the present invention as well. These values, as well as the further details mentioned there regarding filling and emptying the moulds, are herewith incorporated by reference in the present description.

The elements according to the present invention can be stuccoed or the like after having been fully hardened, for example after they have been used as wall elements for erecting a building.

When incorporating a pillar into the elements, the same must be incorporated such that the pillar is positioned vertically when positioning the construction element in its position of use. Then, the construction element can be advantageously used as a wall element for erecting a building, for the pillar will bear vertical loads that originate from one or more floors and walls above and the roof construction. The pillar can be used for connecting thereto the floor, wall or roof element above it. Then, the wood strands part of the construction element will not have to bear any external loads and hence can be made of a low density so as to have high thermal insulating properties.

In this respect, it is to be noted that a construction element according to the present invention is most preferably used as a wall element, with a vertical height, a horizontal width and a horizontal thickness. The construction element is produced in a mould such that its height and width are outlined in a horizontal direction of the mould and that the horizontal thickness of the construction element is outlined in a vertical direction of the mould.

When producing construction elements in a preferred embodiment wherein at least two moulds are positioned substantially contiguous, the side walls of the moulds provide the upper and lower sides of the construction elements, respectively of the walls pro- duced therewith. A multiplicity of pillars can be incorporated in a construction element, for example at mutual distances of from 0.5 to 3 m, depending on the required load bearing capacity.

Along a side of the construction element a girder may be incorporated, for example of wood or concrete. This girder may be connected to the pillars for obtaining a structure with improved strength. Normally, the girder is provided at a top side of the construction element when in use. For example, this girder may be provisionally connected to a side wall of the mould so as to immediately have the right position thereof. After distributing and hardening the mixture of wood strands and hydraulic binder, the provisional connection of the girder with the side wall of the mould may be removed. Naturally, the girder should have such a surface or surface finish that a good binding with the hydraulic binder is obtained. If in the erect positioned construction elements a ring beam of, optionally reinforced, concrete is preferred, a girder may be provided that is removed after hardening the mixture of wood strands and hydraulic binder. Then, after erecting the construction elements as a wall of a building, a reinforcement may be provided in the slot the girder has been removed from and concrete may be distributed therein. This has the advantage that part of the concrete will fill the cavities between the wood strands so as to provide an intense connection of the concrete ring beam and the construction elements. This is also valid if in the vertical ends of the erect elements vertical slots are provided such that two adjacently positioned elements are lined out with those slots positioned against each other. Then, this slot can be filled with, optionally reinforced, concrete and/or a separate reinforcement for producing a pillar that at the same time holds the adjacent elements firmly together. If at the same time a ring beam is provided, the pillar can be connected to the ring beam so as to provide a further increased strength.

As mentioned above, a mould may comprise four side walls, hence producing a rectangular, or equivalent, construction element. Each mould will then produce a construction element, wherein cutting is not required.

According to a further embodiment, when using the embodiment of substantially contiguous moulds, such moulds will have oppositely positioned side walls only, that extend in a longitudinal direction.

Although there is mention of mixture of wood strands and hydraulic binder in the above description, it should be clear to a person skilled in the art that said mixture comprises an amount of water as well, sufficient to provide an adequate binding capacity and setting of the hydraulic binder fully.

Hereafter, a description of the invention with reference to the accompanying figures is given.

Fig. 1 shows a first embodiment of a mould for producing a construction element according to the invention.

Fig. 2 shows a second embodiment of a mould for producing a construction element according to the invention.

Fig. 3 shows a simplified scheme of a production facility according to the invention for transporting moulds.

Fig. 4 shows a schematic perspective ghost view of a construction element according to the invention.

In the figures, the same or equivalent parts are identified by the same reference numerals. Not all parts necessary for practising the invention are identified in the figures or the description thereof, only the parts that need to be described to provide a sufficient understanding of the invention are specifically identified and described.

Fig. 1 shows a cross-section of a mould according to a first embodiment of the invention, wherein a mould 1 is comprised of a bottom 2 and two opposing side walls 3, 4, as well as two opposing end walls 5 (only one is shown). The bottom 2 is made of a construction such that it provides sufficient rigidity and strength to the mould 1. A first layer 6 of a mixture of wood strands and hydraulic binder is distributed in mould 1. The first layer 6 fills the mould 1 only partially. A pillar 7 is placed on top of this first layer 6. Along one side wall 4, a beam 8 (optionally more than one beam) is placed, such that it is substantially surrounded at three sides by said mixture. The fourth side of said beam 8 lies against the side wall 4. The pillar 7 is positioned adjacent a side of said beam 8. A plurality of pillars 7 may be provided, as can be seen in Fig. 4, where said plurality of pillars 7 is distributed along the length of beam 8.

Although not shown in Figure 1, a further layer of mixture is positioned on top of said first layer 6, pillar 7 and beam 8, to a height exceeding the top of the side walls. Then a second mould 1, generally identical to the mould 1 shown in the figure, or a lid (not shown) can be placed on top of the mould 1 as shown, so as to compress the mixture in this mould 1 to a height identical to the height of the walls 3, 4, 5.

After hardening out sufficiently, the top mould or lid can be removed after which the construction element can be removed from the mould 1. A further embodiment of the invention is shown in Fig. 2, showing a mould having oppositely positioned longitudinal side walls 3, 4 only. One side wall 4 can be connected hingedly to the bottom 2 of the mould 1. After the construction element is hardened out sufficiently, the side wall 4 can be hinged away from the construction element, after which the construction element can be removed easily from the mould 1. The distance over which the side wall 4 is moved, should preferably be such that the element can be hoisted out of the mould 1. As a further embodiment, the side wall 4 is hinged over at least 90°, after which the element can be pulled out of the mould (in the Figure, to the right; i.e. in the same direction as the straps in the element).

According to a further embodiment, the distance of opposite side walls increases from the bottom of said mould, for example by attaching the walls at an angle of at least 90 degrees, preferably approximately 91 degrees, with respect to the mould bottom. This enhances releasing the element from the mould when turning the mould upside down.

So as to be able to easily pull out the element from the mould, an elongate element 9, for example a beam, which can be a short piece of wood, is positioned in the mould 1 on top of a layer 6 of mixture of wood strands and hydraulic binder (perpendicular in the plane of Figure 2). It can be positioned in the same plane as the pillar 7, shown in Fig. 1, for example between two substantially parallelly placed pillars 7. A hoist strap 10 is placed around the beam 9 and is directed to the side of the side wall 4, preferably guided through a girder (top beam) 8 and then guided out of mould 1 over top 11 of side wall 4. Alternatively, strap 10 may be positioned in a recess of beam 8, positioned against side wall 4, and may be clamped against said beam 8. For lifting stability, at least two straps per element are provided. The girder 8 preferably extends over the entire length of the side wall 4. The girder 8 spreads out forces that are exerted thereon when pulling the strap 10 at an angle, over the entire length of the construction element.

The strap 10 can also be used for handling the construction element after is has been taken out of the mould 1, for hoisting and loading and when using same for erecting the walls of a building or the like.

Fig. 3 shows a diagrammatical flow chart of a production line according to the invention. It is comprised of a wood strands production facility 12, for example an Eltomatic™ machine, well known in the art. A mixture of wood strands 19, water 20 (optionally with some additions as commonly known in the art) and hydraulic binder 21 is provided to a distributor 13, for distributing the mixture over a width substantially equal to the width of a mould 14. Here, a row of adjacently positioned moulds 14 is transported through the distributor so as to continuously distribute said mixture in adjacently and successively transported moulds. Then, mould 14 is further transported to a filling station 16, provided so as to be able to optionally add an inlay 23. This inlay may be as described above. Adding the inlay may be performed by hand or automatically. Then, the moulds are in a still continuous fashion forwarded to a second distributor to add a further layer of mixture on top of the previously added layer of mixture and the optionally added inlay. Thereafter, the moulds 14 are in a continuous fashion transported to a saw 22, cutting the mixture that was added into the mould by the distributors in step c) and step e), at both ends of said moulds so as to be able to transport the individual filled moulds to the curing area.

Both distributors 13, 13a may have a common source of mixture of wood strands 19, water 20 and hydraulic binder 21, or may each have their own source of mixture of wood strands 19, water 20 and hydraulic binder 21. When each distributor 13, 13a has its own source of mixture, the production facility's capacity could be doubled.

As a matter of fact, the diagrammatical flow chart in Fig. 3, may roughly be a good representation of a real production facility.

Fig. 4 shows an outline of a construction element obtained according to the invention. The mixture of wood strands and hydraulic binder is omitted for clarity. A girder 8 and pillars 7 are clearly visible, as well as one of the straps 10 and one of the beams 9. The girder can be connected to the pillars by means of connecting elements 18 (only one is shown). This connection can be made when positioning the said items in the mould or after the elements have been taken out of the mould. Furthermore, it is clear from the embodiment in this Figure, that the strap is guided through a hole in the girder. The ends 19 of the pillars are flush with the bottom wall of the construction element.

In this respect, it is clear that the bottom side of the construction element according to the invention, on which it rests when in use, should be perpendicular with respect to its sides.

For, if the edges of the bottom side are not perpendicular, the construction element may fall over. Hence, referring to Fig. 1 and 2, the side wall 3 of the mould 1 should be at a substantially right angle with respect to the bottom wall 17 of the mould 1.

The other side wall 4 and the optional end wall 5 may be positioned at an obtuse angle with respect to the bottom wall 17 so as to facilitate the removal of the construction element from the mould 1.

The wood strands is preferably obtained by using an Eltomat-ic™ Rotating Wood Strands Machine, as known in the art. This machine, including the mixer for obtaining the mixture of wood strands, binder and water is known to skilled men in the art throughout the world.

The production facility for producing the construction element according to the present invention and for performing the method according to the present invention, comprises: means for providing and distributing the mixture, at least one mould with four sides or a series of consecutive moulds with only two longitudinal sides each, optionally means for supplying stucco and positioning girders, pillars, barriers, boards, beams or straps and the like. Additionally, it may comprise transporting means for transporting said moulds to and from said distribution means, for at least twice distributing a mixture of wood strands and cement into said mould.

Preferably, if an inlay consisting of a board or another relatively heavy material is placed on a layer of mixture, spacers may be provided for carrying said inlay, so as to prevent an unwanted compression of the layer of mixture.

Some overfilling of the mould with mixture may be required to slightly compress the mixture by placing a lid or another mould thereon. The mould should be filled completely, however, compressing the mixture in the mould should be as little as possible. Overfilling may comprise a height of mixture above the mould of maximally 10 cm, preferably maximally 5 cm, more preferably maximally 4 cm, most preferably maximally 2 cm. Hence, if the side walls of the mould have a height of 50 cm, the total height of the layer of mixture in the mould, before placing the lid or another mould thereon, is maximally 60 cm, preferably maximally 55 cm, or more preferably maximally 54 cm, most preferably maximally 52 cm.

It may be preferred to compress a firstly added layer in the mould so as to obtain a first layer with an increased density and rigidity.

According to a further embodiment, the thickness of the element obtained after compressing said mixture in said mould may be determined by applying a lid or a top mould that at least partly extends between the side walls of the mould. This ensures that the element obtained has a thickness that is less than the height of the side walls of said mould.

An alternative embodiment comprises the step of placing an inlay on the bottom of said mould after which the layers of wood strands are distributed in said mould and same are compressed. Said inlay may remain in the mould after removing the element from said mould or may be detached from the wood strands, such that an element is obtained having a thickness that is reduced with respect to an element comprised without applying such inlay.

According to a still further embodiment, it may be preferred to add an inlay in the mould before adding a first layer of mixture that is adhered to the wood strands. Such an inlay may be comprised of stucco or a board, for example an Eltoboard™ or the like so as to at least partly, optionally completely or substantially completely, cover the outer wall of a construction element. As a matter of fact, a gap between boards can be provided, if wanted or required. Optionally, both walls or one or the other wall of a construction element may be covered by adding a board at any of the down side and/or top side of the mould.

Hence, the method according to the invention may comprise any of the steps: - placing an inlay in the mould before step c); -placing an inlay in the mould after step e); and - placing an inlay in the mould before step c) and after step e). The inlay may be comprised of at least one of a damp proof course, a reinforcing layer, an insulating layer, a girder, a pillar and a hoisting means, each optionally provided with cement binding properties; for example chosen from at least one of a wood strand cement board, an asphalt paper, a foamed polymer and a wooden pole.

Claims (19)

A method for manufacturing a structural element of wood strands, comprising the steps of: a) providing a mold with a bottom and at least two side walls, preferably two opposite side walls; b) providing a curable mixture of wood strands and a hydraulic binder; c) dividing a portion of the mixture into the mold to provide a layer of the mixture, which layer has a freshly distributed height, and compressing the layer so that the layer has a compressed height that is less than the freshly distributed height; d) placing an insert on the layer of the mixture that is distributed in step c), without essentially curing the layer of the mixture that is distributed in step c); e) dividing another portion of the blend to provide another layer of the blend, the other layer having a freshly distributed height, and compressing the other layer so that that other layer has a compressed height that is less then the freshly distributed height, and then performing the step of: f) placing a cover on the mold to compress the mixture in the mold with an underside of the cover and curing the mixture. The method of claim 1, wherein the mixture of wood strands and hydraulic binder comprises an amount of water sufficient to bind the hydraulic binder to obtain a structural element of wood strands with interconnected wood strands. Method according to claims 1 and 2, wherein the height of the side walls is between 20 and 60 cm. Method according to claims 1-3, wherein the distance from the side walls is at least 120 cm, preferably at least 240 cm, more preferably at least 270 cm, and at most 350 cm, more preferably at most 325 cm, with the most preferably is about 300 cm. Method according to claims 1-4, wherein at least two molds are positioned substantially successively and are provided with mixture substantially successively in step c), and wherein longitudinal side walls of successive molds are aligned with each other. The method of claim 5, wherein the layer of the mixture divided in step c) and step e) is cut between two molds to obtain separate molds, each comprising a layer of the mixture. The method of claim 1, wherein the insert comprises at least one of a girder, a pillar and a hoisting means, for example a wooden post; each optionally with cement-binding properties. A method according to claim 1 or 7, wherein one of the following steps is performed: - an insert is placed in the mold prior to step c); - an insert is placed in the mold after step e); - an insert is placed in the mold before step c) and after step e). The method according to claim 8, wherein the insert comprises at least one of a vapor-tight layer, a reinforcing layer, an insulating layer, a beam, a pillar and hoisting means, each optionally provided with cement-binding properties; for example selected from at least one of a wood-strand cement plate, asphalt paper, a foamed polymer, and a wooden pole. 10. Method as claimed in any of the claims 7, 8 or 9, wherein the hoisting means comprise an extending element which is situated substantially parallel to and at a distance from a side wall and a hoisting belt connected to the extending element and extending to and up to outside that side wall of the mold. The method of any one of claims 7 to 10, wherein the pillar extends between two opposite side walls, or between a side wall and a beam positioned against an opposite side wall. The method of claim 1, wherein at least one side wall is pivotally connected to the bottom, and the pivotally connected side wall is pivoted outward after step f) in order to be able to remove the structural element from the mold. The method of claim 1, wherein at least 50% of the wood strands, preferably at least 70% of the wood strands, has an extended length X, wherein the distance from a first end to a second end of the wood strands located in the mold is less than 70% of the distance X, preferably is less than 50% of the distance X, more preferably is less than 30% of the distance X, most preferably is less than 10% of the distance X. A method according to claim 1, wherein the thickness of the element obtained after compression of the mixture in the mold is determined by arranging a lid or an upper mold that extends at least partially between the side walls of the mold, such that the element obtained has a thickness which is less than the height of the side walls of the mold. The method of claim 1, comprising the step of placing an inlay on the bottom of the mold and then dividing the layers of wood strands into the mold, further comprising the step of separating the inlay and the wood strand element after curing the wood-strand element, so that an element is obtained with a thickness that is less than an element obtained without applying the insert. Holding strand construction element, obtained with a method according to one of claims 1 to 15, characterized in that the element has a density of at least 250 kg / m3, preferably at least 300 kg / m3, and at most 500 kg / m3, preferably at most 450 kg / m3, more preferably at most 425 kg / m3, most preferably at most 400 kg / m3. 17. Holding strand construction element, obtained with a method according to any one of claims 1 - 15, characterized in that the element comprises a hoisting belt that extends from one side of the element and which is connected to an extending element which is substantially is included horizontally in the structural element. A production facility for carrying out the method according to any one of claims 1 to 15, comprising at least one mold with a bottom and at least two side walls, means for providing a mixture of wood strands and cement, means for distributing the mixture of wood strands and cement in the mold, characterized in that the production facility further comprises: transport means for successively transporting the molds to and from the distributing means, for distributing at least twice a mixture of wood strands and cement in the mold s. The production facility of claim 18, further comprising a station for positioning an insert in the molds.