TECHNICAL FIELD

The present invention relates to a wooden chipboard according to the preamble of claim 1 and to a manufacturing arrangement according to the preamble of claim 7. The invention has applications in the manufacturing industry for manufacturing chipboards and furniture.

BACKGROUND ART Nowadays lightweight wooden chipboards are manufactured, for example, by injection molding adhesive-coated woodchips past molding bars standing vertically upright centrally in the injection molding tool, forming holes or channels in a homogeneous wooden chipboard. The injection molded wooden chipboard leaves the tool with circular channels.

Nowadays wooden chipboard is also manufactured from two boards adhesively bonded together, in which channels in each board are turned towards one another in order to make the wooden chipboard lightweight. Injection-molded chipboards suffer from the disadvantage, however, that they are complicated, time-consuming and costly to manufacture. Difficulties have also emerged in the form of weaknesses in screwed connections through the wooden chipboard. Known wooden chipboards adhesively bonded together from two channeled boards facing one another suffer from the disadvantage that, despite the aim of making the wooden chipboard as lightweight as possible, the channels weaken the outward-facing side of the wooden chipboard, so that the thickness of the wooden chipboard has to be increased. The desired aim of making a more lightweight chipboard can thereby not be achieved. The quantity of material consumed is likewise large. Lightweight wooden chipboards are desirable particularly in the furniture industry.

US 4 702 870, for example, shows a method of producing wooden fiberboard containing cavities.

It is furthermore desirable to produce a lightweight, high-strength wooden chipboard which is not time-consuming to manufacture.

It is also desirable to produce a lightweight wooden chipboard which is constructed so as to prevent a screw easily being pulled out. It is likewise desirable to create a wooden chipboard manufacturing arrangement, which is capable of cost-effectively manufacturing a lightweight, high-strength wooden chipboard and affords a high production capacity in short production cycles. It is furthermore desirable to develop known wooden chipboards so as to be able to use these in the furniture industry, which requires strong and lightweight wooden chipboards. The mass production of furniture likewise requires cost-effective manufacturing of wooden chipboards, which are processed into furniture.

DISCLOSURE OF INVENTION This has been achieved by the wooden chipboard defined in the introduction having the characteristics specified in the characterizing part of claim 1.

In this way the wooden chipboard can be lightweight and at the same time strong and capable of withstanding concentrated loads on the outward-facing side of the wooden chipboard. By creating a basic foundation with adhesive surface in combination with the arched shape of the groove, creating support walls of the greatest possible load-bearing capacity, it is possible to use smaller quantities of material whilst making the wooden chipboard sufficiently thin for use in the furniture industry.

The arched shape preferably has a constant radius.

This affords an optimal strength in a lightweight wooden chipboard. Alternatively the arched shape is pointed.

In this way the basic foundation can be made thinner and the support walls thicker, compensating from the strength point of view for the thinner basic foundation, without having to increase the quantity of material consumed in the wooden chipboard and still retaining the arched shape for optimum strength.

The width of the basic foundation is preferably 3-7 mm in the transverse direction to the longitudinal direction of the grooves, depending on the radius of the arch and the thickness of the wooden chipboard. The radius R of the wall surface of the arch is then suitably 5-7 mm and the thickness of the wooden chipboard is 16-22 mm.

Alternatively the grooves are formed in both of the inward- facing sides and are arranged facing one another.

The wooden chipboard can thereby be made lightweight where the basic foundations of each board and the support walls of each board interact in that the basic foundations are adhesively bonded to one another for support and the arched shape of the grooves of each board lend optimal strength for supporting the outward-facing side in the area of the channels. A bore is suitably arranged between two adjacent grooves in a board, extending from the outward-facing side through the adhesive surface in order to strengthen the grip of a fastener.

In this way the adhesive surface, which acts primarily as basic foundation, is also used to strengthen the material of the wooden chipboard for some distance into the wooden chipboard for tightening up a screw, for example. It is desirable that this reinforcement for the insertion of screws be satisfactory, since instead of being adhesively bonded together wooden chipboards are often screwed together by the user after purchase to form furniture.

Alternatively the wooden chipboard is a furniture component.

An item of furniture can thereby be made lightweight and at the same time strong and can be made cost-effective to manufacture.

This has also been achieved by the wooden chipboard manufacturing arrangement defined in the introduction having the characteristics specified in the characterizing part of claim 7.

This affords a cost-effective manufacturing of a lightweight and strong wooden chipboard. The elongated projections are preferably designed in such a way that the arched shape has a constant radius.

The elongated projections are suitably designed in such a way that a pointed arched shape is formed.

The projections of the press pad can thereby contribute to an optimum distribution of adhesive-coated woodchips around the projection before compression molding. Alternatively the turning element comprises an adhesive bonding element for applying adhesive to the adhesive surface of the first and second compression molded boards.

In this way manufacturing can be automated with the aid of robots, which is cost-effective.

The molding surface preferably comprises a peripheral framing surface on a level with the adhesive surfaces. A board for adhesive bonding to another board has thereby been formed, which together with the adhesively bonded board forms the wooden chipboard, which can be cut to suitable dimensions from a modular system, in which the framing surface after cutting has a homogeneous end edge without groove openings. Furniture manufactured in mass production very often has certain given measurements and the modular system is suitably adapted to such mass production measurements, in which the cut ends up in the area of the framing surface.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described below on the basis of exemplary embodiments with reference to drawings attached, of which figure 1 schematically shows a cross section through a wooden chipboard according to a first exemplary embodiment;

figure 2 schematically shows a cross section through a wooden chipboard according to the first exemplary embodiment but having another arched shape; figure 3 schematically shows how thin material dimensions can be produced through the arched shape;

figures 4a-4b schematically show an arched shape in more detail;

figures 5a-5d schematically show various boards and press pad for manufacture of the wooden chipboard in a modular system;

figures 6a-6e schematically show a spreading arrangement in the wooden chipboard manufacturing arrangement;

figure 7 schematically shows multiple spreading arrangements in an intermittent loading press; figures 8a-8b schematically show an intermittent loading press in the wooden chipboard manufacturing arrangement; and

figures 9a-9b schematically show a turning element. MODE(S) FOR CARRYING OUT THE INVENTION

The invention will now be described on the basis of exemplary embodiments. For the sake of clarity parts of no significance for the invention have been omitted from the drawing.

Figure 1 shows a cross section through a wooden chipboard 1 according to a first exemplary embodiment. The wooden chipboard 1 is constructed from two boards 3 adhesively bonded together. Each board 3 comprises an outward- facing side 5 and an inward-facing side 7. The inward- facing sides 7 of each board 3 are turned towards one another. Each board 3 has grooves 9 recessed in the inward- facing side 7. The grooves 9 form parallel channels k in the wooden chipboard 1. Between the grooves 9 in the area for adhesively bonding the boards 3 together is an adhesive surface 11, that is to say between the boards 3 in the location between the grooves 9.

The adhesive surface 11 of the wooden chipboard 1 between two adjacent grooves 9 in a board 3 constitutes a basic foundation 13 for a support wall 15. The support wall 15 is formed from adhesive-coated woodchips situated between the grooves 9. Each board 3 therefore has a plurality of support walls 15, 15', 15" etc. which support each outward-facing side 5. In figure 1 the basic foundations 13 for each support wall 15 of the opposing boards 3 are adhesively bonded together and rest against one another in the wooden chipboard 1. The support walls 15 between the grooves 9 counteract the depression of the outward-facing side 5 in the area of the bottom 17 of the groove 9 when the wooden chipboard 1 is exposed to stressing. This may be stressing in the form both of bending and of concentrated loading. Forming the groove 9 with an arched shape in its cross section transversely to its longitudinal direction in the board 3 affords an optimum load-bearing capacity and strength of the support walls 15 interacting with adjoining support walls 15', 15". In figure 1 a bore 19 is shown disposed between two adjacent grooves 9 in a board 3. The bore 19 extends from the outward-facing side 5 through the adhesive surface 11 into the other board 3. When a fastener, such as a screw 21, is screwed into the wooden chipboard 1, the threads of the screw 21 get a good grip in the hardened adhesive surface 11 containing hardened adhesive. This strengthens the grip of the screw 21 in the wooden chipboard 1, which is important in furniture manufactured from wooden chipboards 1. In figure 1 the adhesive surface 11 ' in the area of the bore 19 is wider than other adhesive surfaces 11 where no fastener is needed for constructing an item of furniture (not shown).

Figure 2 shows a cross section through a wooden chipboard 1 according to the first exemplary embodiment, but having a different arched shape from that shown in figure 1. The arched shape in figure 2 also has a curvature, viewed in cross section transversely to the longitudinal direction of the groove 9, but a curvature with a radius that diminishes the further away from the basic foundation 13 one gets, that is to say the radius is greatest at the 'roof (or bottom 17) of the arch. It is important, however, that 'the roof is not without a curvature. In this way the quantity of material consumed in the wooden chipboard 1 can be reduced whilst retaining good strength in thin wooden chipboards 1 for furniture. The arched shape shown in figure 1 has a curvature with a radius R which is constant. Figure 3 shows in more detail the direction of the forces f in the support walls 15, 15' supporting the outward-facing side 5 around a groove 9. The two support walls 15, 15' formed with the arched shape have a groove wall surface 23, which has a curvature of radius R of 7 mm. The thickness t of the board 3 is 9 mm, which gives a wooden chipboard 1 with a total thickness T of 18 mm, which is a usual thickness for mass-produced furniture, such as cabinets and seats. The dimension between the outward-facing side 5 of the board 3 and the 'roof (the bottom 17) may therefore be as thin as 2 mm, whilst the wooden chipboard 1 can have good strength and can be low in weight. This is shown at S in figure 3.

Here the interval A between two grooves 9 or the width of the basic foundation 13/the adhesive surface 11 is 4 mm. The C/C dimension is therefore 18 mm for the wooden chipboard 1 shown in figure 3. A force F, which acts on the outward-facing side 5, is counteracted by the resistance forces f created by the arched shape.

The woodchips (not shown) that make up the wooden chipboard 1 have a chip size of less than approximately 2-3 mm. Approximately half of the woodchips in the wooden chipboard have a chip size of less than 1 mm, which is advantageous in building up the grooves 9 of arched shape. The groove wall surface 23 of arched shape benefits from being as fine as possible, in order to avoid abrupt interruptions in the arch surface. Such interruptions could affect the strength and the load-bearing capacity of the wooden chipboard 1. The smaller chip size of less than 1 mm also makes it easier, in the manufacturing process involving compression molding, to compress the woodchips in their entirety. That is to say the finer material in the wooden chipboard 1 at the same time gives a fine surface in the arched shape and affords easier compression molding for manufacturing. The greater part of the woodchips, other than those of less than 1 mm, are woodchips of between 1 and 2 mm. Figure 4a shows an enlarged section through the wooden chipboard in figure 2. Here the radius R nearest to the basic foundation 13/the adhesive surface 11 supporting each outward- facing side 5 is 5 mm. In this wooden chipboard 1 the outer layer 25 has also been produced containing woodchips 27 with a longitudinal extent (2-5 mm). These longer woodchips 27 are oriented with their longitudinal fiber direction in the main transversely to the longitudinal direction of the grooves 9. This serves to further strengthen the wooden chipboard 1 against bending.

Figure 4b shows in more detail the direction of the forces f in the support walls 15 supporting the outward-facing side 5 around a groove 9 shown in figure 2. A force F, which acts on the outward-facing side 5 in the area of the groove 9, is counteracted by the resistance forces f created by the arched shape.

Figures 5a-5b show a board 3 for manufacturing the wooden chipboard 1 in a modular system. Figure 5a in cross section shows a board 3 manufactured with grooves 9 having an arched shape which is pointed. The board 3 is manufactured in an intermittent loading press. The board is compression molded with its grooves 9 parallel to one another. In figure 5b the board 3 is divided by an intervening area 29 without grooves, a so-called area for forming a framing surface 31. After molding and adhesive bonding together with a corresponding laterally inverted board, forming the wooden chipboard 1, the latter is cut in the area of the framing surface 31 along a cutting line (dashed line). The adhesive bonding together of the boards 3 is done in such a way that adhesive is applied to the adhesive surfaces 11 of the one board between the grooves 9 and on the framing surface 31 of the board, the boards 3 subsequently being fitted and joined together with the grooves 9 facing one another. Figure 5 c shows a press tool 33 with a press pad designed to form a framing surface 31 on three sides. A wooden chipboard 1 manufactured in this way can be used in furniture in which the end surface is hidden. Figure 5d shows a formed board 3 having a framing surface 31 all round.

Figures 6a-6e show a spreading arrangement 35 in a wooden chipboard manufacturing arrangement 37. A dispenser 39 and a lower press pad 41 (or so-called support pad) move relative to one another in such a way that the dispenser 39 dispenses adhesive-coated woodchips 43 on to the lower press pad 41. The lower press pad 41 moves in relation to the dispenser 39 (see figure 6b) and a chip mat 45 is formed on the lower press pad 41. A spreading template 47 (chip distributor) provided with slits 49 is then positioned above the chip mat 45. The dispenser 39 is now moved over the spreading template 47 and dispenses adhesive-coated woodchips onto the latter, where the woodchips are distributed through the slits 49 and drop down on to the chip mat 45 forming strands 51, as is shown in figures 6c and 6e. A chip mat 45 of varying thickness has been created with strands 51, the chip mat now being ready for compression molding. The chip mat 45 applied to the lower press pad 41 is defined as a charge with the reference designation x. A plurality of charges x', x", x'" ...x ⁿ are prepared in this way by means of a plurality of spreading arrangements 35 or spreading stations and fed simultaneously into compartments 53 in a compression molding element 55 forming part of the wooden chipboard manufacturing arrangement 37. This saves time and the production becomes cost-effective . See the schematic representation in figure 7. The compression molding element 55 is a so-called intermittent loading press (see figure 8a). Figure 8a shows the intermittent loading press, in which a plurality of charges x\ x", x'" ...x"have been placed in compartments 53 of the intermittent loading press. Each compartment 53 also comprises an upper press pad 57. Heat is generated by means of a heating element (not shown) and the intermittent loading press drives an upper press tool 59, which sets the upper press pads 57 moving towards the lower press pads 41 containing respective chip mats 45. The upper press pad 57 has a molding surface 61 comprising elongated parallel projections 63 having plane surfaces 65 between them for forming adhesive surfaces 11 (see figure 9b) of the boards 3 for joining together. In its cross section transversely to its longitudinal direction each projection 63 is formed with a curvature for forming grooves 9 of arched shape in the board 3. The chip mats 45 are compressed under heat and the boards 3 are formed and begin a hardening process. The molding surface 61 also comprises a peripheral framing surface 31 on a level with the adhesive surfaces 1 1, as shown earlier in figure 5c.

The boards 3 are fed out from the compression molding element 55 after molding of the boards 3 and partially cool. The woodchips (not shown) in the boards 3 have a chip size of less than approximately 2-3 mm. Approximately half of the woodchips in the wooden chipboard have a chip size of less than 1 mm, which is advantageous in building up the grooves of arched shape. The wall 23 of arched shape benefits from being as fine as possible, in order to avoid abrupt interruptions in the arch surface. Such interruptions could affect the strength and the load-bearing capacity of the wooden chipboard 1. The smaller chip size of less than 1 mm also makes it easier during the compression molding to compress the woodchips in their entirety. That is to say the finer material in the board 3 at the same time gives a fine surface in the arched shape and affords easier compression molding for manufacturing. The greater part of the woodchips, other than those of less than 1 mm, are woodchips of between 1 and 2 mm.

Figures 9a-9b show a turning element 67 in the form of a robot 69. The robot 69 comprises a robotic arm 71, which turns the finally pressed boards 3 towards one another after applying adhesive to adhesive surfaces 11 of the boards and laying the one board 3 with its inward-facing side 7 downward against the opposing board 3, forming the wooden chipboard 1, which is shown in figure 9b. Before turning, the boards are fed out from the intermittent loading press. An output device (not shown) for feeding out each compression molded board comprises ejectors (not shown) which eject each board 3. The turning arrangement 67 comprises an adhesive bonding element 66 for applying adhesive to the adhesive surfaces 11 of the first and second compression molded boards 3. The finished lightweight and strong wooden chipboard 1 in figure 9b has a weight of approximately 400 kg/cubic meter.

The present invention must not be regarded as being limited to the exemplary embodiments described; variations and combinations of the examples shown or other examples may exist within the scope of the claims attached. Various types of adhesive, such as PVAC, UF, phenol, hot-melt adhesive or joiner's adhesive, may be used.