Title: Natural stone element having a stress absorbing layer

The invention relates to a natural stone element, comprising a natural stone plate of which a side is destined to constitute a viewing side of the natural stone element. Usually, such an element is destined to be applied as ornamental element, for example, as part of a cladding or a noise-protection dam.

It is an assignment of the invention to provide a natural stone element of which the weight remains within acceptable limits, while there is practically no chance of breakage of the natural stone plate which is part of the element. For example, when the natural stone is granite, this assignment is not easy to solve, because granite is very susceptible to breakage, and also has a relatively high specific gravity. Granite is appreciated because of a nice appearance that is associated with this kind of natural stone, but because of the said susceptibility to breakage and the relatively high specific gravity, granite is not yet applied as widely as would be desirable. For instance, a granite element of one square meter having a thickness of 20 mm easily weighs 55 to 80 kilograms. This heavy weight requires solid mechanical attachment materials and tools for attachment to a supporting surface. When the weight of a natural stone element can be reduced, it is achieved that cranes or other tools are no longer necessary in the process of putting the element in place, and that the element can be easily arranged on a supporting surface. When it is furthermore possible to reduce the susceptibility to breakage, there is no longer a reason to have reservations regarding the application of granite.

According to the invention, the assignment as mentioned is solved by providing a natural stone element having a natural stone plate, wherein a layer which is adapted to allow for bending of the plate under the influence of a load, and which is adapted to absorb stresses related to bending of the plate, is applied to a side of the plate. In this natural stone element, the natural stone plate does not need to be thicker than 10 mm in order to guarantee that breakage does not occur in normal circumstances, as a result of which a light-weight entirety can be obtained.

A major advantage of applying a layer for absorbing stresses related to bending of the plate to a side of the natural stone plate is that the plate can be loaded at a free side, i.e. the other side than the side on which the stress absorbing layer is present, without any breakage occurring. In that case, under the influence of a load, the entirety of plate and stress absorbing layer reacts like a flexible entirety, wherein stresses of the plate, in particular tensile stresses, are absorbed by the layer. It is not necessary to make use of an aluminum honeycomb structure to reinforce the plate, as is usual. Hence, a solution is offered to the problem that aluminum and natural stone do not adhere well due to the fact that the coefficients of expansion of these materials are quite different. For example, the stress absorbing layer can be a glass fibre layer. Furthermore, the invention relates to a method for manufacturing a natural stone element, wherein a plate is sawed off a block of natural stone, wherein a layer for absorbing stresses related to bending of the plate is applied to a side of the plate, and wherein up to and including this latter action of applying a stress absorbing layer to the plate, the plate is continuously held under the influence of holding forces. By continuously holding the plate, it is achieved that it remains supported after the sawing, in any case until the moment at which the stress absorbing layer is applied to the plate, and breakage of the plate under the influence of its own weight and/or external load at the free side of the plate practically can no longer occur.

During carrying out of the method according to the invention in practice, it is possible that tilting of the plate is necessary, namely when the plate is sawn off the block by moving the saw through the block in a vertical- direction, wherein, for the purpose of applying the stress absorbing layer, the saw is put in a horizontal position after sawing. Such a tilting may be well realized in practice when a device having a vacuum pump and suction cups which are each connected to the vacuum pump through a conduit is applied, wherein, for the purpose of exerting holding forces on the plate, the suction cups are placed against the free surface of the plate, and the vacuum pump is activated. In such a case, the plate may namely be put in the horizontal position by tilting a carrier of the device on which the suction cups are located.

Once the stress absorbing layer has been applied during the manufacturing process of the natural stone element, the chance of breakage of the natural stone plate which is part of this element is minimized. This offers major advantages, already during further stages of the manufacturing process. Usually, when the natural stone is granite, finishing processes such as polishing and smoothing are carried out, wherein high pressures are exerted on the plate at the side of the granite plate which is going to serve as the viewing side. By applying a stress absorbing layer to the granite plate at the other side first, breakage of the granite plate during the finishing processes is prevented.

In a first preferred embodiment of the natural stone element according to the invention, at least one recess is located in another side of the natural stone plate than the viewing side, wherein the layer for absorbing stresses related to bending of the plate is located in the recess. Besides the stress absorbing layer, other desired layers can be arranged in the recess (es) of the _, natural stone element, for example, a layer having heat insulating and/or sound insulating properties. In that case, a protecting layer may be applied to this layer, so that damage of the insulating layer is prevented.

The invention also relates to a method for manufacturing the above-described first preferred embodiment of the natural stone element, wherein a natural stone plate is provided, wherein at least one recess is arranged in a side of the plate, and wherein material for absorbing stresses related to bending of the plate is arranged in the recess.

In a second preferred embodiment of the natural stone element according to the invention, the element has a layer of hard foam, which is located at the same side of the natural stone plate as the stress absorbing layer. A type of hard foam which is suitable to be applied within the framework of the invention is polyurethane . Advantages of this material are that it is light by having a density of about 0.08 kg/dm ³ , and that it is suitable for gluing together with another material. However, the material is not well resistant to the influence of ultraviolet radiation, but problems which could occur on this basis may easily be prevented by applying a cover element such as an aluminum cover. Such a cover element can also play a part in the support of the natural stone plate.

In order to achieve that both a viewing side and a circumference of the natural stone element according to the second preferred embodiment of the invention are having the appearance of a massive natural stone element, it is advantageous when strips of natural stone are arranged along the circumference of the natural stone plate, at the side at which the glass fibre layer and the layer of hard foam are present, i.e. the non-viewing side.

As has already been indicated, the natural stone element according to the invention is suitable to be applied for cladding. In general, in view of practical applications, the natural stone element can be provided with at least one drilled hole having means received therein for attachment of the natural stone element to a carrier such as a wall and/or any suitable hanging construction, wherein these means may also serve for reinforcing the drilled hole. For example, the attachment means can comprise components which are part of a snap system, and which are adapted to engage other components which are also part of the snap system.

It is furthermore possible that the natural stone element is provided with a frame, which serves for attachment of the element to a carrier, and which is preferably manufactured from a light and strong material such as aluminum. In the second preferred embodiment, in which the natural stone element is provided with a layer of hard foam, such a frame can be embedded in the layer of hard foam. Preferably, the various parts of the natural stone element according to the invention are connected to each other by means of a gluing process. For example, a 2-component polyurethane glue may be applied. In a natural stone element having a natural stone plate, strips of natural stone, a glass fibre layer, a layer of hard foam and a cover element, it is possible, for example, that the glass fibre layer is glued to the natural stone plate, that the layer of hard foam is glued to the glass fibre layer, that the cover element is glued to the layer of hard foam, and that the strips of natural stone are glued to a standing edge of the cover element. All in all, on the basis of an application of the invention, it is possible to save on important factors such as material, manpower and transportaL'_Wli "costs . The invention achieves a large weight- saving for natural stone elements, and minimizes reject during manufacturing and further processing of natural stone elements. Apart from that, the invention is especially suitable for providing

elements of granite, which does not alter the fact that the invention is also applicable within the framework of other natural stone elements .

The invention has many possibilities for its application. Apart from the application of the natural stone elements for cladding as already mentioned, applications as table tops, kitchen tops, indoor and outdoor tiles, pillars, grave stones, etc. are feasible.

The invention will be explained in more detail on the basis of the following description. In the process, reference will be made to the drawing, in which equal reference signs indicate equal or similar components, and in which: figure 1 diagrammatically shows a sawing device and a block of natural stone of which plates are sawn off by means of the sawing device; figure 2 illustrates a sawing process, and diagrammatically shows a block of natural stone and a number of parts of a sawing device; figure 3 shows a detail A of figure 2; figure 4 diagrammatically shows a portion of a carrier having suction cups, which is part of the sawing device as shown in figure 2; figure 5 illustrates a tilting movement of the carrier having suction cups and a plate which is held with the help of the suction cups; figure 6 diagrammatically shows the plate and the carrier having the suction cups, wherein a stress absorbing layer has been applied to the plate; figures 7-17 illustrate various steps of a method for manufacturing a natural stone element according to a first preferred embodiment of the invention; figures 18 and 19 illustrate the possibility of a natural stone element according to a first preferred embodiment of the invention having more than one recess in a natural stone plate; figure 20 illustrates a structure of a natural stone element according to a second preferred embodiment of the invention; figure 21 illustrates an application of a frame at a non-viewing side of the natural stone element according to the invention; and figure 22 diagrammatically shows a wall, a hanging construction to be attached to the wall, and the natural stone element having the frame as shown in figure 21.

Figure 1 diagrammatically shows a sawing device 10 and a block 20 of natural stone of which plates 30 are sawn off by means of the sawing device 10. To this end, the sawing device 10 comprises a circular saw 11, which is rotated during operation of the sawing device 10, so that it is possible for the saw 11 to subject the block 20 of natural stone to a stone-removing process in a manner known per se, with the help of, for example, a diamond layer (not shown) which is located at the circumference of the saw 11. In the following, as an example, the natural stone is referred to as granite, wherein the block 20 of natural stone is a granite block, and wherein the plates 30 are granite plates, which does not alter the fact that the invention is also applicable with other types of natural stone.

In particular, during a sawing process, the granite block 20 and the saw 11 are moved with respect to each other, wherein the saw 11 penetrates through the granite block 20 on the basis of the stone-removing process, and wherein the position of the saw 11 is chosen such that at one side, a relatively thin plate 30 remains, whereas at the other side, the rest of the block 20 remains. In the example as shown in figure 1, during a sawing process, the granite block 20 and the saw 11 are moved with respect to each other in a horizontal direction, wherein the mutual movement is realized by displacing the granite block 20 on guiding rails 12 of the sawing device 10, as is indicated in the figure by means of an arrow. That does not alter the fact that more possibilities exist to establish the necessary relative movement of the granite block 20 and the saw 11. In this context, it is not absolutely necessary that sawing takes place in the vertical direction.

Figure 2 illustrates the actual sawing process, and shows parts of a sawing device 10 which is suitable to be applied for the purpose of performing this sawing process. The sawing device 10 comprises a carrier 13 having suction cups 14, and also has a vacuum pump 15, wherein the suction cups 14 are connected to the vacuum pump 15 through conduits 16. For example, a suitable material for the suction cups 14 is rubber. In figure 4, it is illustrated that the suction cups 14 may be positioned in the carrier 13 in a regular fashion, at a suitable mutual distance. For the purpose of the sawing process, the suction cups 14 are placed against a surface 21 of the granite block 20, at the side of the granite block 20 where a plate 30 is going to be sawn off. During the sawing process, the

vacuum pump 15 is in an activated condition, wherein light vacuum forces are exerted on the surface 21 of the granite block 20 through the suction cups 14.

The sawing process which is carried out by applying the sawing device 10 having the suction cups 14 and the vacuum pump 15 is particularly suitable to saw relatively thin plates 30 off the granite block 20, for example, plates 30 having a thickness of only 5 mm. During the sawing process, the saw 11 penetrates further and further in the granite block 20, so that a larger and larger portion 31 of the plate 30 is separated from the rest of the block 20, until the plate 30 is completely loose. Under the influence of vacuum forces which are exerted on the surface 21 of the granite block 20 at the position of the suction cups 14, it is realized that the sawn-off portion 31 of the plate 30 is supported, and is furthermore held at a distance from the saw 11, so that there can not be any contact between the saw 11 and the portion 31 that has been sawn loose, and vibrations of the saw 11 can not act on the portion 31 that has been sawn loose. For the purpose of clearly illustrating that the portion 31 that has been sawn loose is pulled away from the saw 11 to some extent, and is held by the suction cups 14 in that position, a detail A of figure 2 is shown in figure 3.

By holding the granite plate 30 to be sawn during the sawing process, wherein the weight of the plate 30 is resting on the suction cups 14, and furthermore taking care that there can not be any contact between the saw 11 and the plate 30 as soon as the plate 30 is separated from the rest of the granite block 20, it is possible to protect the plate 30 from influences of its own weight and of vibrations of the saw 11. On the basis thereof, the plate 30 can be relatively thin, because factors which could cause breakage of the plate 30 are expelled, as it were. It is not necessary that the plate 30 is held under the influence of vacuum forces. Although this is a practical option, variants are feasible.

The carrier 13 having the suction cups 14 is not only suitable to be applied during a sawing process to support the plate 30 which is sawn off the granite block 20, but may also be useful during further processing of the plate 30. When the granite plate 30 is obtained in a vertical orientation, as is the case in the example shown in the figures, it may be advantageous to put the plate 30 in a horizontal orientation. This may easily be realized when the carrier 13 is tiltably arranged. Figure 5 serves to illustrate how a

tilting movement can be carried out with a tiltably arranged carrier 13, wherein the tilting movement is indicated by means of an arrow. Figure 6 illustrates a possible finishing of the granite plate 30, wherein the supporting carrier 13 having suction cups 14 is also shown. The finishing involves applying a layer 40 to a surface 32 of the granite plate 30, which layer 40 is suitable to absorb stresses which are occurring when the granite plate 30 is loaded at the side of the other surface 21. An example of a suitable layer 40 in this respect is a glass fibre layer. By applying the layer 40, the susceptibility to breakage of the thin granite plate 30 is reduced to a large extent, as a result of which it is achieved that the entirety 33 of the plate 30 and the layer 40 is suitable for practical applications without any problems.

Figures 7-17 illustrate various steps of a method for manufacturing a natural stone element 1 according to a first preferred embodiment of the invention. For example, the natural stone element 1 is destined to be applied as table top having the appearance of a table top of massive natural stone. A first step of the method for manufacturing the natural stone element 1 comprises providing a natural stone plate 30 as diagrammaticalIy shown in figure 7. For sake of completeness, it is noted that within the framework of the invention, various shapes and dimensions of the natural stone plate 30 are possible. A second step of the method for manufacturing the natural stone element 1 involves arranging saw cuts 34 in another side 35 of the natural stone plate 30 than a side 36 which is destined to constitute a viewing side of the natural stone element 1. This viewing side 36 may be finished in any desired way. In figure 8, -the natural stone plate 30 and a saw 17 for arranging the saw cuts 34 are diagrammatically shown. In figure 9, a back view of the natural stone plate 30 having the saw cuts 34 is shown. In this example, a rectangular circumference is defined with the saw cuts 34.

A third step of the method for manufacturing the natural stone element 1 involves removing material of the natural stone plate 30 which is located inside the circumference defined by the saw cuts 34. In the process, a milling cutter 18 may be used, for example, as diagrammatically depicted in figure 10. The natural stone waste that is obtained during milling can be collected and used in a suitable application. Taking into account an exemplary thickness of 20 mm of

the natural stone plate 30, a recess 37 having a depth of 15 mm can be formed. Consequently, the natural stone plate 30 has a thickness of 5 mm at the position of the recess 37. It is practical when the thickness is no more than 6 mm, because the chance of breakage is otherwise so high that further processing of the natural stone plate 30 is very difficult.

A fourth step of the method for manufacturing the natural stone element 1 involves applying a glue layer 41 to the natural stone plate 30, in the recess 37, as diagrammatically shown in figure 11. Subsequently, in a fifth step of the method, a next layer 40 is applied to the glue layer 41, as diagrammatically shown in figure 12. This next layer 40 is destined to absorb stresses which are related to bending of the natural stone plate 30, so that breakage of the plate 30 is prevented as a consequence of the presence of this layer 40. In this case, it is also true that the stress absorbing layer 40 may for example be a glass fibre layer.

When it is intended to adapt the natural stone element 1 for attachment to a suitable carrier construction, the element 1 can be provided with drilled holes 51, as diagrammatically indicated in figures 13 and 14. This is the case, for example, when the element 1 is applied as cladding element or noise-protection dam element. In that case, the drilled holes 51 can be used for receiving inserts 52, as illustrated by figure 15. Within the framework of the invention, the natural stone element 1 can be provided with any suitable attachment means, and the carrier construction can also be freely chosen. In many practical cases, a mechanical anchorage of the natural stone element 1 will be chosen, contrary to, for example, an anchorage by means of gluing.

If so desired, a layer 42 having insulating properties can be applied to the stress absorbing layer 40. In that case, this insulating layer 42 is also located in the recess 37 of the natural stone plate 30. For example, the insulating layer 42 may be a heat insulating or a sound insulating layer, and may comprise cellular glass, for example. Furthermore, a glue layer 43 and a protecting layer 44 may be applied on the insulating layer 42. Like the stress absorbing layer 40, the protecting layer 44 may be a glass fibre layer, for example, which does not alter the fact that various other suitable possibilities exist within the framework of the invention. For example, it is also possible to apply a layer of fibre- reinforced polyester for protection of underlying layers.-

Figures 16 and 17 illustrate the structure of a natural stone element 1 according to the invention, which comprises a natural stone plate 30 having a recess 37 arranged therein, in which a glue layer 41, a stress absorbing layer 40, an insulating layer 42, a glue layer 43, and a protecting layer 44 are successively arranged. As a result, an element 1 is obtained, which has the appearance of natural stone, while being light, practically insusceptible to breakage, and while having insulating properties. The recess 37 can be completely filled with the various layers 40, 41, 42, 43, 44, as shown in figure 16.

In the shown example, the natural stone element 1 is provided with a number of drilled holes 51 in which inserts 52 are arranged. The drilled holes 51 and inserts 52 are arranged on the natural stone element 1 at strategic positions, so that the inserts 52 can do duty in a desired way in hanging the natural stone element 1 on a suitable hanging construction.

Figures 18 and 19 show an alternative embodiment of the natural stone element 1 according to the invention, wherein it is a particular of this embodiment that it is provided with two recesses 37. In respect of recesses 37 having a rectangular circumference as shown, it is true that in view of the strength of the natural stone element 1, it may be advantageous when corners of these recesses 37 are beveled, as can be seen in figure 18.

Within the framework of the invention, it is a possibility to provide the natural stone plate 30 with a temporary carrier having a stress absorbing layer such as a glass fibre layer thereon at the viewing side 36 during the manufacturing process of the natural stone element 1, preferably prior to arranging the saw cuts 34. As a result, the chance of breakage of the natural stone plate 30 is considerably reduced, as the stress absorbing layer is capable of absorbing pressure loads to which the plate 30 is exerted at the non-viewing side 35, and of supporting the plate 30 when bending occurs. An example of a temporary carrier is any suitable adhesive foil, which may be removed from the viewing side 36 of the natural stone plate 30 at a desired moment without leaving permanent traces thereon. For example, the tension absorbing layer may temporarily be arranged at the viewing side 36 of the natural stone plate 30, between two layers of adhesive foil.

Figure 20 illustrates a structure of a natural stone element 2 according to a second preferred embodiment of the invention. This natural stone element 2 comprises a natural stone plate 30, natural stone strips 38 which are arranged along the circumference of the plate 30, a glass fibre layer 40, a layer 45 of polyurethane hard foam and a cover element 46. In the shown example, the glass fibre layer 40 is applied to both the natural stone plate 30 and the natural stone strips 38, wherein it is noted that it is important that at least the natural stone plate 30 is provided with the glass fibre layer 40. The cover element 46 serves for preventing influence of harmful ultraviolet radiation on the polyurethane hard foam, and is preferably manufactured from a light and strong material such as aluminum.

In this second embodiment of the natural stone element 2 according to the invention, the natural stone components 30, 38 may also be at least as thin as 5 mm, even when the natural stone is granite. On the basis of the application of the glass fibre layer 40, flexibility is obtained to such an extent that breakage of the natural stone plate 30 practically can not occur for a large range of loads, including loads which are related to normal use of the natural stone element 2.

Furthermore, in respect of this second embodiment of the natural stone element 2 according to the invention, it is also true that the various components thereof may be connected to each other by means of glue. During the manufacture of the natural stone element 2, the natural stone plate 30 is provided first. Subsequently, the glass fibre layer 40 is applied to a side of this plate 30, which is destined to constitute a non-viewing side of the plate 30. The layer 45 of polyurethane hard foam is glued to this layer 40. Thereafter, the cover element 46 is placed over the layer 45 of polyurethane hard foam, and is glued to this layer 45. Finally, the natural stone strips 38 are glued to a standing circumferential edge 47 of the cover element 46.

Figures 21 and 22 are related to a cladding 50 according to the invention, which, as an example, comprises the above-described natural stone element 2 according to the second preferred embodiment of the invention, and a carrier frame 53, wherein the carrier frame 53 is destined to be attached to a wall 60, and is adapted to carry the natural stone element 2. Besides the glass fibre layer 40 and

the layer 45 of polyurethane hard foam, the natural stone element 2 furthermore comprises an aluminum interior frame 54 which is connected to the glass fibre layer 40, and which is embedded in the layer 45 of polyurethane hard foam. In figure 21, a depiction of the natural stone element 2 having the interior frame 54 is given, wherein the glass fibre layer 40, the layer 45 of polyurethane hard foam and the cover element 46 are omitted for the sake of clarity. Figure 22 shows the complete cladding 50 and a portion of a wall 60, wherein the natural stone element 2 having the interior frame 54 is depicted in a sectional view.

The carrier frame 53 may be manufactured from an aluminum section, and may be attached to a wall 60 by means of screws 55, for example, preferably from non-corrosive steel or another durable material . For the purpose of the attachment of the natural stone element 2 having the interior frame 54 to the carrier frame 53, the cladding 50 may be provided with a snap system. Figure 22 serves for illustrating this possibility. In the shown example, the snap system comprises a number of pins 57 which are located on the carrier frame 53, and a number of components 58 having recesses for receiving the pins 57, which will hereinafter be referred to as inserts 58, and which are located in the natural stone element 2. The inserts 58 may be arranged both in the element frame 54 and to the cover element 46. Naturally, at the position of the inserts 58, the cover element 46 needs to be provided with holes for allowing the pins 57 which are located on the carrier frame 53 to pass.

On the basis of the above-described construction, applying the cladding 50 to a wall 60 is very simple. The only action that is needed is screwing the carrier frame 53 to the wall 60, and establishing a snap connection between the natural stone element 2 having the interior frame 54 and the carrier frame 53 by pushing the natural stone element 2 against the carrier frame 53 at a suitable position. Because of the fact that the natural stone element 2 has a structure according to the invention, it may be light, which considerably facilitates handling and positioning of this element 2. By applying the cladding 50, a wall 60 can be provided with a nice appearance with natural stone plates 30. Usually, this is not often done with conventional natural stone elements, especially granite elements, due to the weight of such elements. This possibility is now available, thanks to the invention.

It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed above, but that various amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the appended claims .

The invention may be summarized as follows. A natural stone element 1, 2 comprises a natural stone plate 30 and a stress absorbing layer 40 which is applied to a non-viewing side 35 of the plate 30.

In a first preferred embodiment of the natural stone element 1, the natural stone plate 30 is provided with at least one recess 37, wherein the stress absorbing layer 40 is located in this recess 37. If so desired, one or more other layers may also be arranged in the recess 37, for example, a layer 42 having insulating properties. As an advantageous consequence of the presence of the recess 37, weight is saved, while breakage of the natural stone plate 30 at the position of the recess 37 is prevented on the basis of the presence of the stress absorbing layer 40, since this allows for bending of the plate 30 without breakage. A portion of the natural stone plate 30 where the recess 37 is not present is suitable to be provided with drilled holes 51, in which inserts 52 or other suitable means for attachment of the natural stone element 1 to a suitable hanging construction may be fixed. In a second preferred embodiment of the natural stone element 2, a layer 45 of hard foam is applied to the stress absorbing layer 40, a cover element 46 for covering the layer 45 of hard foam is provided, and natural stone strips 38 are arranged along a circumference of the natural stone plate 30, which consequently also cover a standing edge 47 of the cover element 46.

Especially on the basis of an application of a thin natural stone plate 30, the natural stone element 1, 2 can be. very light, which is an important advantage and allows for many applications of the natural stone element 1, 2, such as for cladding 50, among other things. It is the stress absorbing layer 40 which provides for a construction having the proper flexibility, as a result of which breakage of the natural stone plate 30 is prevented, so that this plate 30 may be thin, indeed.