NO158031B - BEARING BELT CONSISTING OF AN EXTRADED MIDDLE LAYER WITH TWO PALIMATE SURFACES. - Google Patents

Description

The present invention relates to a load-bearing beam consisting of an extruded middle layer of divided vegetable material which is mixed with a binder, to which middle layer at least two outer layers with a covering layer of natural wood are glued.

Such beams, which however consist exclusively of small pieces of wood, are known from US patent no. 2,717,420. The beams have a square cross-section, in the center of which there is a continuous cavity, circular in cross-section. At the side surfaces, the beam is glued with metal strips which are obviously intended to create a laminate effect together with the extruded body and thus achieve higher strength.

From DE-OS no. 24 07 642, a wooden beam is also known which is likewise pressed from small pieces, where the essential thing is that the beam has at least three layers arranged on top of each other and extending over the entire beam, of which the two upper layers for a predominant part consists of shavings with fibers that are oriented substantially in the longitudinal direction of the beam, and where the middle layer for a predominant part exhibits shavings that are oriented in the cross-sectional plane of the beam. Such a beam with the mentioned structure can in practice only be produced by placing shavings in a mold together with glue and heating and subjecting it to a pressing pressure. Thus, the beam can only have a length corresponding to the shape, which in practice is not long enough.

Experience has shown that neither the first-mentioned nor the last-mentioned of the known beams have gained any importance in practice and have been replaced by ordinary wooden beams. In the case of beams of the above-mentioned type that are covered with metal plates, there is a risk that the adhesive connection may loosen due to various thermal stresses. In the case of large heat differences, the metal layer is led to a change in the shape of the beam, as metal has a significantly greater heat capacity and thus a greater coefficient of expansion. Furthermore, this can lead to the destruction of the adhesive connection. From what appears from DE-OS

24 07 642, sufficient load-bearing capacity cannot be achieved, except that the manufacturing method does not allow any industrial production and any advantage over ordinary wooden beams.

In practice, the problem has so far been unsolved by producing beams from small pieces of wood materials or other similar natural materials, in such a way that they are advantageous compared to ordinary wooden beams in terms of price or aging resistance, or in terms of swelling or tendency to knock themselves.

The present invention aims to solve this problem.

The invention is based on the aforementioned US patent no. 2,717,420 and consists in the fact that the middle layer occupies a significant part of the beam's volume and that the middle layer consists of an extruded body of coarse and fine chippings (German Stiftspane), which chips show an orientation predominantly in the beam's longitudinal direction, and that the cover layers consist of sawn and possibly planed wooden boards.

The beam according to the invention exhibits a surprisingly good bending strength and buckling strength, which is completely unexpected compared to previous experience. The state of the art (TJS patent 2.717.420) gives the impression that beams with an extruded middle layer must obtain their necessary stiffness from glued-on metal layers, from which one must draw the conclusion that you can only use the cover layer with great strength to obtain beams with sufficient stiffness . DE-OS no. 24 07 642 does not give any information whatsoever about the strength of the beam. It is all the more surprising that by gluing wooden boards onto the extruded central core, a significantly higher load-bearing capacity is achieved than could be expected from knowledge of the state of the art. This advantage is obviously due to the extrusion of coarser and finer cutter chips with a certain specific weight, the orientation of the chips being important. Fine shavings have a long-fibre structure of approx. 3-12 mm. Coarse chips have a length of approx. 30 mm, without deviating from the long-fibre structure. Deliberate use of flat chips will destroy the invention. The beam according to the invention is, in contrast to previously known beams or chipboard throughout homogeneous with respect to the middle layer. This means that, despite the desired orientation, a uniform chain formation of the various long chips is obtained over the entire cross-section. Examples of load capacities achieved in practice can be seen in the description below.

In addition, the invention has the advantage that similar materials are glued together, and the extruded body as a middle layer conveys significantly higher load-bearing capacity when it is glued together with sawn or planed wooden material. Also, the dimensional stability with respect to weather and wind is significantly higher than with ordinary wooden beams, as the beam according to the invention shows neither deformation nor cracking under the influence of weather and wind, and rotting can also be avoided by suitable treatment of the small pieces before extrusion. The beam according to the invention can be used both for intermediate walls and load-bearing walls. They are suitable as support beams, binders and construction elements and the like.

It has proven advantageous if the middle layer has a square cross-section and where an elongated hole is formed in the cross-section which forms a continuous cavity in the beam, as the distance from the wall of the cavity to the outer surfaces of the middle layer is approximately as large as the width of the cavity. Depending on which function the laminate beam according to the invention is to have, the outer layers can be arranged on the narrow sides of the middle layer or also on the wider sides. It is particularly advantageous to design two opposite outer sides of the middle layer as tongue and groove and provide these with a cover layer. This is advantageously done on the narrow side surfaces of the middle layer.

If you want to supply the middle layer in the groove spring area with the cover layer, it is an advantage to use a cover layer in several parts, as in the transition area at the groove or the spring is made a distance between the edges of the tire layer parts, and the edges in this area can possibly be chamfered. In this way, the joining of the beams is simplified and a particularly good strength is retained.

A further advantage is achieved by producing the middle layer with the long sides standing vertically. If laminate beams with a square cross-section are to be produced to be used on the bottle, these are produced on a high edge. This manufacturing method has the advantage that the same thickness is achieved on the chips to be pressed over length and cross-section. If one wanted to produce such a beam lying on the bottle, the shavings would have greater friction to the stationary mandrel in the press when they came down to the lower area of the press cylinder in free fall. In addition, hollow-shaped cavities can occur in the area under the mandrel.

All outer surfaces of the middle layer can be provided with a cover layer of wooden boards. It is then an advantage if the vertical cover layers in a load condition are inserted between the horizontal cover layers. It has also proven appropriate to chamfer the corners of the middle layer. The advantage then arises that in the corner areas a good bonding can be achieved between the middle layer and the cover layer. According to an embodiment of the invention, the mixing ratio between coarse and finer chips is approx. 50:50. It is recommended that approx. 2/3 of the chips run in the longitudinal direction of the beam and the rest across. According to the invention, a maximum stiffness is then achieved on the beam and a homogeneous, perceptible as a mutual felting of the shavings structure over the entire cross-section of the middle layer.

Two or more middle layers can be connected immediately to each other, in particular by means of gluing or gluing, and the cover layers are then provided exclusively at the outer sides of the composite middle layer. In this way, beams with particularly high load-bearing capacity can be produced, simple and small and thus cheap presses.

It can also be advantageous if the cavity located in the middle layer is filled with insulating material, e.g. polyurethane. The cavity can also be advantageously used for conveying installation material.

In the following, the invention will be explained in more detail with reference to the drawing, as schematic examples of the invention.

Figures 1-5 show cross-sections through right-angled laminate beams with two facing cover layers,

Figures 6-9 show cross-sections through laminate beams with a cover layer on all sides, and

figures 10 and 11 show cross-sections through additional beams.

In the design example according to Figure 1, a laminate beam according to the invention is shown, whose middle layer 1 consists of an extruded body. How such extruded bodies can be produced with large dimensions can be seen from DT-OS no. 25 35 989. The middle layer 1 shows along the largest side surfaces cover layer 2 which consists of natural wood material, particularly in the form of sawn or planed boards. In the center of the middle layer 1 there is a longitudinal cavity 3 with an elongated cross-section. One must here ensure that the distance between the cavity walls 3 and the two side walls of the middle layer 1 is approximately the same. At the narrow ends of the middle layer 1 there is a groove 5 and spring 4 which are profiled so that the laminate beams can be built on top of each other to form a wall, in particular a dividing wall, and are thereby securely connected to each other by means of the groove-spring connection.

In an embodiment of the invention, the overall width a of the laminate beam is approximately 156 mm, the overall height b approximately 200 mm, and the wall thickness c of the cover layers 2 approximately 8 mm, and the width of the middle layer approximately 140 mm. A beam with these dimensions exhibits, at a storage length of 3000 mm, a bending breaking strength of approx. 3020 kg. These and the following values are determined by state material testing institutes.

In example 2, the ratio between the wall thickness of the cover layers and the thickness of the middle layer 1 is greater. In this case, the wall thickness of the cover layers 2 is 20 mm, while the other dimensions are the same as example 1. The load-bearing strength of this beam is correspondingly higher than the design example according to Figure 1, assuming the same dimensions of the middle layer 1 without the price being increased accordingly.

In general, it can be assumed that it is advantageous that the ratio between the thickness of the cover layers 2 and the thickness of the middle layer 1 is approximately between 1:6 and 1:25. In special cases, where other loads must be taken into account, these ratios can of course be lower or higher. Preferably, for particularly heavily loaded beams, a thickness of the cover layer 2 of the order of 20 mm can be assumed.

In the design example according to figures 3 and 4, the narrow sides of the middle layer 1 are covered with cover layer 2. The beams are shown in the drawing in the load direction. In the example according to Figure 3, the cover layer 2 is relatively thin, e.g. 8 mm, while the height of the middle layer 1 is again approx. 200 mm. In the example according to Figure 4, however, the cover layers 2 are thicker, e.g. 20 mm with the same height on the middle layer 1. The beam in figure 4 shows a bending breaking load of 5200 kg at a span of 3000 mm.

Figure 5 shows a frame beam for element construction, where the cover layers 2 are glued to the wide side surfaces of the middle layer 1, and the outer layers can serve as completely flat or smooth substrates for veneering or wallpapering or the like.

In the design examples according to figures 6-9, it is assumed that all outer surfaces of the middle layer 1 are covered by the cover layer 2,7. The deck layer 2 covers the narrow areas, and the deck layer 7 the wide areas of the intermediate layer 1. The deck layers 2,7 also consist of wooden boards.

In the example according to figure 6, the wall thickness of the cover layers can be 8 mm, while the dimensions of the middle layer are, in accordance with figure 1, 140 x 200 mm. According to the example in Figure 7, the cover layers are also 20 mm. Such beams are particularly suitable as ceiling beams and the like. 1, the design example according to figures 8 and 9 is based on a square middle layer 1 in cross-section where the continuous cavity 3 has a circular profile. In the example according to Figure 8, the wall thickness is specified as 8 mm, while the side surfaces of the middle layer 1 have a width of approx. 145 mm. With the same internal dimensions, in the example according to Figure 9, the wall thickness of the cover layers 2 is chosen to be 20 mm. The beam shown in Figure 9 exhibits a bending breaking load of 7300 kg and a buckling breaking load of 32000 kg at a span of 3000 mm.

In the design examples according to Figures 6-9, the beams are shown in the position of use, so that the load acts in a vertical direction. In these design examples, the cover layers 7 on the sides are sandwiched between the upper and lower cover layers 2. Moreover, the corners 6 of the middle layer 1 in the examples according to Figures 8 and 9 are chamfered. With the help of this feature, it is achieved that the gluing of the cover layers 2,7 to the middle layer 1 can be carried out without problems and without the bearing capacity of the beam suffering from poor gluing.

The middle layer 1 in all the beams shown in the figures is composed of natural shavings that are mixed with a binder and can consist of e.g. of 50# coarse shavings and 50% fine shavings. The strength of the beam is then optimal if the chips during extrusion are oriented in the longitudinal direction of the beam in a ratio of 2:3, which can be achieved by the nature of the chip mixture, introduction into the press chamber and dimensioning of the press pressure. Emphasis must be placed on reducing the proportion of other chip shapes, e.g. flat chip to the inevitable minimum.

In the example according to Figure 10, a beam with a groove 5 and spring 4 is shown, if the cover layer 2a, 2b and 2c has a mutual distance 8 and possibly provided with chamfers 9. In this way, a wall with a very large load capacity can be achieved.

Figure 11 shows an immediate connection between two middle layers 1 whose free outer surfaces are glued to the outer layer 2. Such a multi-layer laminate beam can be produced with simpler pressing equipment to achieve particularly large bearing strengths.

It goes without saying that the dimensions of the beams can be changed as desired and according to the occurring loads. The invention is not limited to the exemplary embodiments shown in the drawing and described above, but covers all variants that a person skilled in the art will be able to arrive at with knowledge of the present invention.

Claims (1)

Load-bearing beam consisting of an extruded middle layer of divided vegetable material which is mixed with binder, to which middle layer at least two outer layers with a cover layer of natural wood are glued, characterized in that the middle layer (1) occupies a significant part of the beam's volume and that the middle layer consists of of an extruded body of coarse and fine sticking chips (German Stiftsp&ne), which chips show an orientation predominantly in the longitudinal direction of the beam, and that the cover layers (2,7) consist of sawn and possibly planed wooden boards.