DEVICE, INSTALLATION AND METHOD FOR PRODUCING AN ARTIFICIAL STONE SLAB HAVING COLOURED VEINS, AND ARTIFICIAL STONE SLAB SO OBTAINED

Abstract

 The invention relates to a machining device for machining a base mixture layer (20) deposited over a support surface (30), the base mixture layer comprising inorganic particles and unhardened binder; the machining device comprising:
- a machining element (11);
wherein the machining device further comprises:
- damper means (12) for dampening at least a portion of a force of the machining element (11) over the support surface (30) during machining of the base mixture layer (20), such that the machining element is configured to machine the base mixture layer (20) to produce grooves (21) from an upper surface thereof until the support surface (30).
The invention also relates to an installation and a method for producing artificial stone slabs or panels having fine coloured veins. The invention further also relates to the improved artificial stone slab so obtained.

Description

TECHNICAL FIELD

[0001] The present invention generally relates the production of artificial stone slabs, boards or panels, particularly those made of agglomerates of inorganic particles and binder, having decoration that simulates veins or streaks - which might be fine veins - of a different colour from that of the matrix, the (fine) veins extending in some depth through the thickness of the respective artificial stone slab, board or panel.

STATE OF THE ART

[0002] In the present invention "artificial stone" is understood to include composites comprising grounded stone and a binder (organic or inorganic), as well as stoneware, fine stoneware or ceramics, preferably composites. One common type of artificial stones, in which the invention is focused, are the so called agglomerated stones. Typically, manufacturing these artificial agglomerate stone composites (e.g. tiles, slabs, boards) comprises crushing filler materials (e.g. ground stone) to obtain particles with different granulometries, followed by mixing with a binder (e.g. organic resin or hydraulic inorganic cement). The mixture thus obtained is coloured, homogenized, conformed to the desired shape, compacted and cured (polymerization/crosslinking of resin or hydration of cement). The curing results in the hardening of the binder in a process that may or may not require heat, depending on the selected binder. Once the binder has been hardened, and thus also the material, it is submitted to cutting to size, gauging and polishing. Different binders are used in the industry, for example, unsaturated polyester resins or thermosetting resins such as methacrylate resins, epoxy resins, unsaturated polyester resins, or vinyl resins. The materials used as fillers vary as well, and usually are of inorganic stony origin. Just to mention a few examples, the filler can be one or more selected from the group consisting of quartz, feldspars, porphyries, granites, syenites, bentonites, basalts, nephelines, carbonates, clays, silicates, boron salts, sands, kaolins, talcs, alumina, glass materials, recycled glass, recycled porcelains, recycled stoneware, and mixtures thereof. Many of the properties of the artificial stone aggregates depend on the nature and the characteristics of the fillers. The type of binder and the filler/binder ratio also strongly influence the final properties of the articles manufactured, and where hard stone-like materials are desired, it is common to use from 80 - 95 wt.% of filler content. The granulometry of the inorganic particles can also be chosen by the skilled person and, for example, the average particle diameter can be less than 9 mm and can include a mixture of granulometries to produce specific aesthetic effects or obtain the mechanical properties required for a given application. The mixture of the filler and the binder typically includes further additives, such as a curing catalyst, colouring agents (e.g. inks, pigments), or anti-UV agents.

[0003] Since agglomerate artificial stone is intended to be an engineered imitation of natural rocks, in the production of artificial stone slabs, it is also known to create decorative effects that simulate coloured veins, particularly veins having small width, which attempt to simulate the fine veins that can be found in some types of natural stone, such as marble. With the currently known techniques, there are different types of thin veins that can be simulated. One type of thin veins that can be simulated are veins of small length randomly distributed in the body of the manufactured artificial stone, resembling randomly located thin 'capillaries'. This type of effect is obtained for example by the process described in patent document WO-2006/134179-A2.

[0004] A second type of thin veins are those extending along lengthy extensions of the stone material, following continuous random trajectories which may run from one edge of the article to another edge, for instance, along the full extension of the product (long-range veins). For the purpose of simulating these long-range thin veins in artificial agglomerate stones, the following general known process can be followed: a base mixture resulting from the mixture of inorganic particles (such as stone particles) and an unhardened binder are distributed over a production surface; this production surface is normally provided with some sort of protective sheet of paper or elastomer. A base mixture layer over the surface is formed, which has a shape corresponding to the article to be produced, i.e. a slab or a board. The layer of base mixture and binder deposited on the surface is then machined so that grooves are created at some depth through the thickness of the layer following previously defined groove paths and extending across the width and/or length of the layer.

[0005] Once the grooves have been created, a colouring mixture, of a different colour or shade to that of the initial mixture, is projected onto the grooves in such a way that the colouring mixture penetrates sufficiently into the grooves. This mixture, in addition to the dyes, may also contain binder and/or inorganic particles.

[0006] The resulting base mix layer is then covered by another protective film and subjected to vibrocompaction or vibrocompression - in some instances under vacuum -, to compact and extract most of the air present in the base mix layer. Subsequently, the binder is hardened, before proceeding with the cutting, calibrating (or gauging) and/or polishing stages, until the desired artificial agglomerate stone board is obtained.

[0007] Patent document EP-3095768-A1 describes a method of manufacturing an artificial stone slab with veins in which an upper portion of a mouldable hardenable fluid mixture is engraved with a predefined pattern of grooves coinciding with a pattern of thin veins to be obtained; the inner faces of the grooves are impregnated with another mouldable hardenable fluid mixture of a different colour. The grooves are then caused to collapse and close, and the mixtures of the two colours are cured and hardened so that the visible pattern of thin veins is created. These grooves can be obtained by means of a punch (a stencil having a number of protrusions) which presses on the base mix layer by dislodging and/or compressing the mix in the positions where the grooves will be created, or apparently also, although not described in any detail, by means of a horizontal rotating disc, which is moved creating trajectories of grooves reproducing the pattern of thin veins to be obtained.

[0008] Also, in patent document WO-2016/113652-A1 a station and a method for producing colouring effects on a slab are disclosed. The station disclosed in this document includes a working surface intended to accommodate a temporary support with a basic mix layer for the formation of a slab; dye dispensing devices for emitting dyes towards the working surface so as to deposit the dyes on the basic mix layer on the temporary support; the dye dispensing devices are controllable to move over the working surface following specific trajectories; the station also comprises a tool, either a V-blade grooving tool or a mixer tool, which is also movable and is intended to mechanically interact with areas of the basic mix layer to achieve colouring effects.

[0009] The application of these known methods results in the generation of slabs or boards with coloured long-range fine veins of the second type described above. However, the inventors found out that in the artificial agglomerate stones, as obtained, the visual appearance of the veins achieved is not entirely satisfactory and does not achieve its main objective of aesthetically reproducing the appearance of natural stones, since the obtained veins do not cover the entire thickness of the slab (from top surface to bottom surface). This is due to the fact that if the punching or engraving tool is machined through the entire thickness of the base mix layer, the punching or engraving tool also presses and rubs the production surface and/or the protective sheet. This undesirably damages the production surface, the protective sheet or both. As a result, the service life of the production surface is reduced and the function of the protective sheet is significantly limited in the subsequent stages of the process (for example, during pressing). The undesirable pressure and friction of the machining tool also significantly reduce the service life of the punching or engraving tool. It has been found very difficult, or even impossible, to find the right installation settings to assure full-thickness machining of the base mixture layer during industrial manufacturing and to simultaneously avoid damage and premature deterioration of the production surface, the protective sheet or the machining tool. In order to avoid these problems, the punching or engraving tool are usually configured to limit their penetration into the base mix layer so as not to press or rub the production surface or the protective sheet; but then the thickness of the base mix layer is not fully machined, and the resulting veins do not cover the full thickness of the table.

[0010] This significantly reduces the quality of the intended natural stone imitation, especially when the veins are visible on the edges of the obtained slab, or the veins become visible when the slab is cut during installation at the site of use. The obtained veins lack the continuous appearance on all sides of the slab of the veins found in slabs obtained from natural stone.

[0011] To deal with this problem, it has been tried to grind the resulting slabs or boards to remove the portion of the thickness of the slab or board where the vein is not present, in order to obtain a slab of lesser thickness, but with full-depth veins. But obviously, this is highly impractical and uneconomical, since it requires creating slabs with thickness greater than the desired thickness, to account for the portion of the slab thickness which will be ground or milled. Working in this way translates into higher raw material, grinding material, and production costs, and into the generation of higher levels of waste.

[0012] Therefore, there is a need for a method of producing artificial stone slabs having decoration in the form of coloured fine veins which assure that the veins all extend through the whole thickness of the slab, which do not compromise the function of the protective layers used, which do not diminish the service life of the components used during their production, and which do not require extensive grinding of the slab thickness.

DESCRIPTION OF THE INVENTION

[0013] The present disclosure intends to solve the shortcomings of prior-art devices and methods by providing a machining device, installation and method which, in a simple manner, guarantee that long veins can be produced in the artificial stone slab extending through the whole thickness of the slab, in a reproducible and precise way, which are better suitable for industrial mass production.

[0014] A first aspect of the invention relates to a machining device for machining a base mixture layer deposited over a support surface, the base mixture layer comprising inorganic particles and unhardened binder; the machining device comprises:

• a machining element;

and further comprises:

• damper means for dampening a force of the machining element over the support surface during machining of the base mixture layer, such that the machining element is configured to machine the base mixture layer to produce grooves extending from an upper surface thereof until the support surface.

[0015] By providing a machining device that includes this damper means for dampening a force of the machining element over the support surface during machining of the base mixture layer, it can be ensured that the base mixture layer is machined by the machining element from the upper surface of the base mixture layer until the support surface, preventing that the machining element is pressed or rubbed excessively against the support layer, since the damper means mitigate and/or limit the force or pressure exerted by the machining element over the support surface.

[0016] In some embodiments, the machining element is configured to machine the base mixture layer by compacting the base mixture layer on the walls of the grooves it creates, without producing swarf or shavings; that is, the machine element is a machine element that does not chip away or push material of the base mixture layer out to the side of the grooves it creates while being used.

[0017] In some embodiments, the damper means for dampening a force of the machining element comprise a spring, particularly a compression spring. A spring is a very simple and cheap way of providing damper means for absorbing, by compression and elastic deformation, the force the machining element exerts against the support surface. By choosing the material and the structural features of the spring, the dampening parameters of the spring can be set or adjusted depending on the nature, or in general the resistance to mechanization (cohesiveness, coarseness, solidity or in general), of the base mixture layer and the fragility of the support surface and/or protective layer.

[0018] In some embodiments, the damper means for dampening a force of the machining element comprise a hydraulic or a pneumatic damper, or any other means for elastically compressing and decompressing a liquid (such as oil, water or others). A hydraulic or pneumatic damper provide damper means whose dampening parameters can be precisely adjusted depending on the characteristics and the nature of the base mixture layer.

[0019] In some other embodiments, the damper means for dampening a force of the machining element comprise a rubber piece, such as a block or ball, which also is a very simple and cheap way of providing damper means for absorbing, by compression and elastic deformation, the force of the machining element against the support surface. The compression strength and the elasticity response of the rubber piece can be varied by selecting its constituent rubber material (natural rubber, silicone rubber, SBS rubber, EPDM rubber, etc.) and its mechanical properties (stress-strain behaviour), these rubber parameters allowing to adjust the dampening to the characteristics and nature of the base mixture layer.

[0020] In some embodiments the machining device further comprises coupling means for its coupling to a displacement device configured to move the machining device following specific trajectories. The displacement device can be, for example, an automatic device, such as a programmable robotic arm. This way, the machining device can be made to follow the predefined specific trajectories of the automatic displacement device along the base mixture layer. The coupling means can be mechanic coupling means (such as a clip, or a snap-fit coupling), or can be magnetic coupling means, or any other suitable means for coupling the machining device to the displacement device, preferably in an automatic manner without the direct intervention of an external user (the user might control the coupling/uncoupling with a computer).

[0021] Where the coupling means are present, the damper means - for dampening a force of the machining element over the support surface during machining of the base mixture layer - are coupled to the machining element and to the coupling means. It is also possible that the damper means are integrated in or part of the machining element and/or the coupling means. In some embodiments, the machining device further comprises a piston, coupled to the damper means and the machining element. This way, the piston facilitates a vertical movement of the machining element and the damper means can have a shorter length than when there is no piston present.

[0022] In some embodiments, the piston comprises a head having a shape complementary with a housing provided in the coupling means. This configuration blocks and prevents undesired rotation/vibrations of the machining element around the central axis of the piston, which rotation may reduce the repeatability and the definition of the grooves produced by the machining element, which would ultimately result in poor aspect of the veins in the artificial stone slab produced.

[0023] The specific trajectories can be predefined to cover a partial or full extent (length and width) of the base mixture layer, and to follow any pattern or design of the desired veins, for example, an apparently random pattern to make it look more natural. The width of the obtained grooves can be adjusted by selecting the width of the machining element.

[0024] The machining element may comprise a rolling blade or a cutting tool or any other know machining tool; the machining element has a maximum width between 5 mm and 50 mm, more preferably between 10 mm and 30 mm, so that the veins produced in the artificial stone slab obtained have the appearance of the veins of natural stone. The most preferred machining element is a rolling blade with a decreasing thickness from the rotating axis towards the external diameter of the blade, with a thickness in its broadest part between 10 mm and 30 mm. The machining element can be made of a material capable of resisting a chemical attack of any of the components of the base mixture, such as stainless steel or a polymer such as polyamide.In some embodiments, the damper means for dampening a force of the machining element over the support surface during machining of the base mixture layer are configured to damp the force by their deformation, and to elastically return to their initial form or shape, once the force of the machining element over the support surface is reduced or has disappeared. So, preferred damper means are chosen, which provide an elastic deformation-recovery response, when the stress causing its deformation is increase or reduced. A preferred damper means of this type are elastic straight metal coil springs or elastic rubber pieces, which may compress under pressure, and decompress when the compression ceases. That is, the damper means preferably returns the absorbed energy (such as deformation or compression) by means of an elastic response when the action of the force of the support surface is reduced. In this realization of the dampening means, in addition to preventing deterioration of the support surface, the machining element and/or a protective sheet (where such protective sheet is present), the machining element may move in continuous contact with the support surface and/or the protective sheet, even if the distance from the end of the displacement device (robotic arm) to the support surface varies, for example, at the boundaries or in the case of other irregularities of the support surface. This ensures that the depth of the groove is maximum at every point along the specific trajectories through the base mixture layer.

[0025] In some embodiments, wherein a hardened artificial stone is to be manufactured which is hard, and shows superior scratch and heat resistance, the base mixture layer might comprise more than 50 wt.%, preferably 80 - 95 wt.%, and more preferably 85-95 wt.%, content of inorganic particles as filler; also, the base mixture might comprise less than 15 wt.% content of uncured (liquid) binder, preferably between 5 - 10 wt.%; the combination of the high filler content and low liquid binder content results in the base mixture layer, before hardening, having a texture similar to that of wet sand, with a certain solid consistency and stickiness, and with a high tendency to form aggregates and to clump together. This consistency and stickiness makes particularly difficult to obtain full-thickness grooves, by mechanizing the base mixture layer with the previous mechanizing tools and methods. The current invention allows to create full thickness grooves in an industrial setting even in these more demanding situations.

[0026] In a realization of the machining element, particularly suitable for machining the base mixture layer described in the previous paragraph, the damper means for dampening a force comprise a spring, preferably a compression spring, which may be made of metal or other resilient material, for instance with the shape of a straight coil, formed by a turning thread running in a spiral course. The spring is suitably located inside a recess of the coupling means for coupling with the displacement device. The spring is preferably designed to cooperate with a piston coupled with a rolling blade.

[0027] The inorganic particles can be obtained from natural or artificial materials, for example, by grinding, mashing and/or milling to obtain inorganic particles of different grain sizes. The inorganic particles are nowadays available from specialized companies that sell them dried and fractionated according to their granulometry. Inorganic particles can be obtained from, for example, but not limited to, materials such as marble, porphyry, quartz (both opaque and clear), silica, glass, cristobalite, granite, porphyry, quartzite, silica sand, albite, basalt, ceramic, etc. In a same base mixture, inorganic particles from a single material or a mixture of particles from different sources can be used. In particularly preferred examples, the inorganic particles comprise quartz particles, or quartz particles are incorporated into the base mixture. Inorganic particles should preferably account for 70 to 95% by weight of the base mixture, more preferably 85 to 95%.

[0028] The base mixture also contains at least one unhardened binder, which is hardenable (or curable). The binder preferably accounts for 5 to 30 % by weight, preferably 5 to 15 % by weight, of binder in relation to the total base mixture. This binder once hardened, serves to achieve cohesion and adhesion between the inorganic particles in the slab or board produced. There are numerous known binders that can be used in the state of the art. Organic resins, such as unsaturated polyester resins, are especially suitable for the present invention, but other types of binders can also be applied, for example, inorganic binders such as cement (for example, Portland cement). For example, the binder used can be a thermally cured resin, that is, that it cures, hardens, by means of heat, for example by a treatment between 70 ºC and 120 ºC. Some examples of thermosetting resins are, but are not limited to, an unsaturated polyester resin, a methacrylate resin, an epoxy resin, vinyl resins, etc.

[0029] In some embodiments, a suitable catalyst and/or accelerant is added in order to achieve the curing of this type of thermosetting resin in a practicable time. This catalyst and/or accelerant may be added in a proportion between 0.1 - 5% by weight to the weight of the binder. The catalyst is preferably incorporated into the corresponding base mixture in a mixing stage, prior to the manufacturing of the slabs.

[0030] The base mixture may further include other additives such as dyes, for example, metal oxides, adhesion promoters between the inorganic particles and the binder, for example, silanes. These types of additives and their proportion thereof are widely known in the technique.

[0031] A further object of the invention relates to an installation for producing an artificial stone slab with coloured veins, the installation comprising:

• a support surface for accommodating a base mixture layer comprising inorganic particles and unhardened binder for the formation of the artificial stone slab;
• at least one machining device according to the previously defined aspect of the invention or to any of its embodiments, the movement of the machining device being controllable to machine the base mixture layer from an upper surface thereof until the support surface following specific trajectories, such that the machining device produces grooves over an entire depth of the base mixture layer; and,
• at least one dye dispensing device for dispensing dye towards the upper surface of the base mixture layer, the dye dispensing device being controllable to move following the trajectories of the grooves created by the machining device, such that the dispensed dye penetrates into the grooves to achieve the coloured veins in the produced slab.

[0032] In some embodiments the support surface further comprises a protective sheet, and the machining element is configured to machine the base mixture layer from an upper surface thereof until the protective sheet.

[0033] In embodiments, the installation for producing an artificial stone slab further comprises a vibro-compression station, preferably with application of vacuum (this is, with air-pressure reduction) and a curing station for compacting and hardening the base mixture layer comprising the grooves filled with dye.

[0034] A further aspect of the invention refers to a method for producing an artificial stone slab with coloured veins, the method comprising:

• pouring a base mixture over a support surface to form a base mixture layer, the base mixture comprising inorganic particles and unhardened binder for the formation of the artificial stone slab;
• machining the base mixture layer from an upper surface thereof until the support surface following predefined specific trajectories, to produce grooves over an entire depth of the base mixture layer; and,
• dispensing dye towards the exposed upper surface of the base mixture layer following such specific trajectories, so that the dispensed dye penetrates into the grooves to achieve the coloured veins in the produced slab.

[0035] In some embodiments, the step of machining the base mixture layer is carried out with at least one machining device according to the previously defined aspect of the invention or to any of its embodiments.

[0036] The step of machining the base mixture layer can be carried out with a machining device including damper means for dampening a counterforce of the support surface against the machining device during machining of the base mixture layer, such that the base mixture layer is machined from an upper surface thereof until the support surface.

[0037] According to the method, the grooves are produced following predefined specific trajectories. This means that these trajectories are designed in forehand and can be repeated and reproduced accurately for an unlimited number of slabs. The design of the trajectories is intended to imitate the random trajectories normally found in natural stone slabs.

[0038] In some embodiments, after the step of dispensing dye towards the exposed upper surface of the base mixture layer following such predefined specific trajectories of the grooves created, the method further comprises subsequent steps of compacting and/or of curing the base mixture layer including the grooves penetrated with dye.

[0039] The present invention further refers to the artificial stone slab with coloured veins produced with the previously defined method or any of its embodiments, or using the previously defined installation or any of its embodiments, or using the previously defined machining device or any of its embodiments. The resulting artificial stone slab presents an improved appearance, even before calibrating/gauging, which resembles more closely the appearance of a natural stone slab, particularly because of the appearance of the veins being exposed at the edges of the slab or after cutting the slab. Since there is no need of grinding a large portion of the thickness of the slab portion where the vein is not present, the slab can be produced without modifying the employed industrial processes with a larger range of slab thicknesses, which for instance might reach up to 3 cm or more.

[0040] The different aspects and embodiments of the invention defined in the foregoing can be combined with one another, as long as they are compatible with each other.

[0041] Additional advantages and features of the invention will become apparent from the detailed description that follows and will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out. The drawings comprise the following figures:

Figure 1 shows an installation for producing an artificial stone slab with coloured veins according to a possible embodiment of the invention.

Figure 2 shows the installation for producing an artificial stone slab of Figure 1 in a different position, the machining device being at the border of the support surface.

Figure 3 is an enlarged view of the machining device shown in Figure 1, detached from the robotic arm.

Figure 4 shows a section view of the machining device, showing the damper means of the machining device located in a recess of its coupling means.

Figures 5 shows a perspective 3D view of a receiving element of the machining device, isolated from the rest, where the piston is allocated.

Figure 6 shows a perspective 3D view of the piston element, isolated from the rest, of the machining device showed in Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the invention. Next embodiments of the invention will be described by way of example, with reference to the above-mentioned drawings.

[0044] The present invention and the embodiments shown in the Figures are particularly suitable for the production of artificial stone slabs or boards having coloured veins, especially long-range fine veins.

[0045] Figure 1 shows the main components of an installation 100 for producing an artificial stone slab with coloured veins, and more precisely, an installation 100 for producing an artificial agglomerated stone slab comprising inorganic particles and a binder, with coloured long-range veins.

[0046] The installation 100 comprises a support surface 30, wherein a base mixture is homogenously deposited in a predetermined amount, forming a base mixture layer 20 of regular thickness. The support surface 30 might be formed by a levelled metal upper horizontal part of the production line, located in the discharge zone under a distribution device (not shown) for the base mixture. Alternatively, the support surface 30 might be formed by the upper horizontal surface of a movable conveyor belt made of any suitable material, which supports the base mixture layer and transports it to the next manufacturing stations where the subsequent production steps are conducted. In the installation 100 shown, the support surface 30 is covered by a protective sheet (not shown) on the part that comes into contact with the base mixture. In this embodiment, the protective sheet is a laminated sheet of Kraft paper, which may be laminated with a non-stick polymer, or it might be made of an elastomer such as a silicone rubber optionally treated with a non-adherent coating. The protective sheet serves as a temporary support for the base mixture layer 20 deposited on top of it, facilitating its transport to subsequent stages of the production process, and protecting the support surface 30 and other machine components from being in contact with the base mixture during compaction and curing. Once the slab has cured and hardened, the protective sheet may be simply detached from the slab or it may be removed by calibrating/gauging and polishing.

[0047] Preferably, the base mixture layer is deposited inside a frame 31 located on and projecting up from the support surface 30 with a shape corresponding to the article to be manufactured (rectangular in Figure 1). This frame 31 might be made of metal or any other suitable material resistant to the components of the base mixture. In embodiments, this frame 31 can be raised from the support surface 30 to advance the base mixture layer to the compaction and curing stations (not shown).

[0048] The base mixture layer 20 comprises inorganic particles and unhardened binder for the formation of the artificial stone slab. This mixture, normally coloured, is produced using one or several mixers (not shown), in a known manner.

[0049] In this particular example, the inorganic particles account for 85-95% by weight of the base mixture and primarily comprise quartz particles. The unhardened binder accounts for 5-15% by weight and comprises an unsaturated polyester liquid resin which can be cured between 80 °C and 100 °C.

[0050] The installation 100 further comprises a rolling blade 11, that can freely rotate around its axial axis 15. The material of the rolling blade 11 is preferably stainless steel or a polymer, e.g. polyamide. The outer diameter of the rolling blade 11 is chosen depending on the thickness of the base mixture layer to be machined, and can vary from 5 cm to 40 cm, preferably from 10 cm to 30 cm. The width of the rolling blade can also vary depending on the thickness of the grooves to be produced, so that wider blades produce thicker grooves, and can vary from 5 mm to 50 mm, preferably from 10 mm to 30 mm. In the installation 100 shown in Figures 1-3 the rolling blade has an outer diameter of 20 cm and a width at its broadest part of 25 mm. The rolling blade 11 is provided with a ball bearing 17 around the axis element 15.

[0051] The configuration of the machining element as a rolling blade 11, preferably with the parameters described herein, provides advantages in comparison with other alternative machining elements. Thus, as the rolling blade 11 is moved mechanizing the base mixture layer 20, the mixture is pressed on the sides of the blade, generating compacted walls of the grooves, which enhance their stability and prevent them from crumbling down before the dye is applied to the inside of the grooves. This enhances the definition of the veins obtained in the produced slab. In configurations such as wedge-shaped mechanizing devices, the groove is created by pushing the mixture out to create the grooves (in a similar way a snowplow pushes out snow from the road to the road edges). This results in accumulation of mixture on the sides of the grooves, translating into density differences in the finished slab, into more unstable groove walls, and into a poorer definition of the veins.

[0052] As better shown in Figures 3 and 4, the rolling blade 11 is coupled to a programmable automatic displacement device, in the embodiment shown being a robotic arm 50. Alternatively, in an embodiment not shown, the automatic displacement device might be as well a cartesian robot. The robotic arm 50 is programmable to move automatically over the base mixture layer 20 following pre-established trajectories or paths, which are defined to simulate the random veins found in natural stones. The rolling blade 11 is coupled to a rotatable end of the robotic arm 50 by means of mechanic coupling means. In the embodiments shown, the coupling means may be configured in the form of "fingers" (not shown) located at the end of the robotic arm 50, which grip and clamp a cylindrical part 13 of the machining device, which is connected through a piston 14 to an element 15 functioning as the rotation axis of the rolling blade 11. Thus, in addition to the coupling means 13, the rolling blade 11 is coupled to the robotic arm 50 by means of the damper means 12, which, as can be seen in Figure 4, is embodied by a metallic compression coil spring 12, which is itself coupled with the piston 14 connected to the rotation axis element 15 of the rolling blade 11. In the shown embodiment, the spring 12 is coupled with the piston 14 by resting in direct contact with it, the spring 12 and the piston 14 being housed in a housing or receptacle 16 provided in the cylindrical part of the coupling means 13, allowing axial compression of the metallic spring 12, and the axial movement of the piston 14 inside and outside the receptacle 16.

[0053] In this specific example, compression coil spring 12 is a steel compression spring with flat ends, the main parameters thereof being as follows:

K= 2,47 N/mm (elastic constant)

Total length: 90 mm

Outside diameter: 20 mm

Wire diameter 2 mm

Total number of loops: 13

Number of active loops: 11

Length at maximum compression: 28 mm

Recommended travel 56,50 mm.

Steel quality: according to EN 10270-1 SH.

[0054] In the embodiments shown in Figures 3 and 4, the cylindrical part 13 for coupling with the robotic arm 50 is formed by two detachable parts 13' and 13", fixed together by screws 13'''. The receptacle 16 extends along both parts 13' and 13". The piston 14 may be shaped as a cylinder with a head 14', which is intended to be housed in the receptacle 16. The head 14'prevents the piston 14 from coming out of the receptacle 16 during use. The head 14' is favorably provided with a shape complementary with the shape of the receptacle 16, which blocks and avoids undesired rotation/vibrations of the rolling blade 11 around axis Z of the piston 14. Such undesired rotation would cause problems in the repeatability and the definition of the grooves 21 produced by the blade 11, and would ultimately result in poor aspect of the veins in the artificial stone slab produced.

[0055] During the machining of the base mixture layer 20, the robotic arm 50 is programmed to move so that the rolling blade 11 at its end enters into contact with the support surface 30 and/or the protective sheet, by extending from the exposed surface of the base mixture layer 20, and preferably this contact is maintained continuously while the rolling blade 11 is moved through the layer. This ensures that the grooves machined by the rolling blade 11 are complete, that is, they extend over the entire thickness of the base mixture layer 20; there is no need for limiting the extension of the grooves as in the previous art. Since the spring 12 is capable of mitigating or absorbing at least some portion of a force that the rolling blade 11 effects over the support surface 30 during machining of the base mixture layer 20, and over the protective sheet, damage or deterioration of the support surface 30 and of the protective sheet is minimized and/limited. This is achieved by the capacity of the spring 12 to absorb such force (or the counterforce of the support surface 30 and/or the protective sheet) and by means of the spring's elastic deformation and/or compression upon pushing of the piston 14. By adjusting the parameters or properties of the spring (material, length, number and dimensions of wires, resistance to compression, elasticity, etc.), it is possible to adjust and/or limit the pressure that the rolling blade 11 may exert on the support surface 30, and thus, to assure full thickness machining without important deterioration of the tools. When the force is reduced, the spring 12 is decompressed (the deformation of the spring is elastic), and the piston 14 is pushed towards its original position, for instance, to proceed to the machining of a different part of the base mixture layer 20.

[0056] Preferably, the robotic arm 50 is configured to move the rolling blade 11 so that contact with the support surface 30 and/or the protective sheet is continuous, that is, the rolling blade 11 does not separate from them while machining a vein in the base mixture layer 20, thereby improving production times and avoidance of irregularities in the depth of the produced veins.

[0057] Since the rolling blade 11, spring 12 and piston 14 are coupled to the robotic arm 50, and the end of the robotic arm 50 is rotatable, the rolling blade 11 can be moved automatically according to the predefined specific trajectories programmed for the robotic arm 50, producing continuous full-thickness and long-range grooves over the entire width and length of the base mixture layer 20, if desired.

[0058] The installation 100 further comprises one or more dye dispensing devices 40 (only one dye dispensing device 40 being shown in the Figures), which dispense dye towards the upper surface of the base mixture layer 20 into the grooves 21, after the grooves 21 have been machined in the base mixture layer 20. The dye dispensing device 40 is mounted on the same robotic arm 50 (or coupled thereto) as the machining device, and therefore can also be moved following the specific trajectories of the robotic arm 50. Alternatively, in an embodiment not shown in the Figures, the dye dispensing device might be located on a different robotic arm. The dye dispensing device 40 might be a spraying or projecting head mounted at the end of the robotic arm 50. When the dye dispensing device 40 is mounted on the same robotic arm 50 as the rolling blade 11, it is preferably done in a position that allows the dispensing of the dye just after the groove 21 has been machined. In either configuration, with one or several robotic arms 50, the dye can be dispensed specifically and exclusively into the grooves 21 after the rolling blade 11 has produced the full-depth grooves 21 in the base mixture layer 20. The dye penetrates in the grooves 21, colouring their walls, to achieve the coloured veins in the produced slab after compaction and hardening.

[0059] The dye is a colouring composition which may be solid (in powder form) or liquid, and comprises one or more pigments. The dye may also comprise solvent, resin, inorganic particles, or a mixture of at least two thereof.

[0060] In a subsequent step of the manufacturing of the slab, the base mixture layer 20 with the grooves 21 filled with the dye is covered with another layer of protective film, in this case a second layer of Kraft paper, on top before being compacted. Different forms of compaction are possible. Preferably, compaction is done through a press, and more preferably in combination with vibration, through the process known as vibro-compression. In addition or alternatively to the vibro-compression, the compaction can be done with air extraction by means of vacuum application. Vacuum vibro-compaction, is a widely known method, and frequently used for the manufacture of artificial stone articles from inorganic particle-bound agglomerates.

[0061] After compaction, the binder in the compacted base mixture layer is hardened. For this purpose, when the binder is an organic resin, the compacted base mixture layer is placed in an oven at a sufficiently high temperature to cure within reasonable time. For unsaturated polyester catalysed organic resins, preferably used, the temperature should be in the range 80 - 110 ºC and the residence time in the oven should be between 15 - 60 minutes. For inorganic binders of the hydraulic cement type, curing can be carried out at room temperature over a period of one to several days.

[0062] The slabs, boards or plates obtained can be cut and/or calibrated to the desired final dimensions and can be polished on one or both larger faces, depending on the foreseen application.

[0063] In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0064] On the other hand, the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

Claims

1. Machining device for machining a base mixture layer (20) deposited over a support surface (30), the base mixture layer comprising inorganic particles and unhardened binder; the machining device comprising:

- a machining element (11);

wherein the machining device further comprises:

- damper means (12) for dampening at least a portion of a force of the machining element (11) over the support surface (30) during machining of the base mixture layer (20), such that the machining element is configured to machine the base mixture layer (20) to produce grooves (21) from an upper surface thereof until the support surface (30).

2. Machining device according to claim 1, wherein the damper means for dampening a force of the machining element (11) comprises a spring (12).

3. Machining device according to claim 1, wherein the damper means for dampening a force of the machining element (11) comprises any of a hydraulic or pneumatic damper, or a rubber piece.

4. Machining device according to any of claims 1-3, wherein the machining device further comprises coupling means (13) for coupling the machining element (11) to a displacement device (50) configured to move the machining device following predefined specific trajectories.

5. Machining device according to claim 4, wherein the damper means are coupled to the machining element (11) and the coupling means (13).

6. Machining device according to any of claims 1-4, wherein the machining device further comprises a piston (14) coupled to the damper means (12) and to the machining element (11).

7. Machining device according to any of claims 1-6, wherein the machining element comprises a rolling blade (11), preferably with a width between 5 mm and 50 mm, and preferably between 10 mm and 30 mm.

8. Machining device according to any of claims 1-7, wherein the damper means (12) for dampening a force of the machining element (11) over the support surface (30) during machining of the base mixture layer are configured to damp the force by their elastic deformation, and to elastically return to their initial form, once the force of the machining element (11) over the support surface (30) is reduced or has disappeared.

9. An installation (100) for producing an artificial stone slab with coloured veins, the installation comprising:

- a support surface (30) for accommodating a base mixture layer (20) comprising inorganic particles and unhardened binder for the formation of the artificial stone slab;

- at least a machining device according to any of claims 1-8, the movement of the machining device being controllable to machine the base mixture layer (20) from an upper surface thereof until the support surface (30) following specific trajectories, such that the machining device produces grooves (21) over an entire depth of the base mixture layer; and,

- at least one dye dispensing device (40) for dispensing dye towards the upper surface of the base mixture layer 20, the dye dispensing device (40) being controllable to move following the trajectories of the grooves (21) created by the machining device, such that the dispensed dye penetrates into the grooves (21) to achieve the coloured veins in the artificial stone slab.

10. Installation according to claim 9, wherein the support surface (30) further comprises a protective sheet, the machining element being configured to machine the base mixture layer (20) from an upper surface thereof until the protective sheet.

11. Method for producing an artificial stone slab with coloured veins, the method comprising:

- pouring a base mixture over a support surface (30) to form a base mixture layer (20), the base mixture layer (20) comprising inorganic particles and unhardened binder for the formation of the artificial stone slab;

- machining the base mixture layer (20) from an upper surface thereof until the support surface (30) following predefined specific trajectories, to produce grooves (21) over an entire depth of the base mixture layer (20); and,

- dispensing dye towards the exposed upper surface of the base mixture layer (20) following such trajectories of grooves (21), so that the dispensed dye penetrates into the grooves (21) to achieve the coloured veins in the artificial stone slab.

12. Method according to claim 11, wherein the step of machining the base mixture layer (20) is carried out with at least one machining device according to any of claims 1-8.

13. Method according to any of claims 11-12, wherein after the step of dispensing dye towards the exposed upper surface the base mixture layer (20) following the trajectories of grooves (21), the method further comprises subsequent steps of compacting and/or of curing the base mixture layer including the grooves (21) penetrated with dye.

14. Method according to any of claims 11-13, wherein the step of machining the base mixture layer (20) is carried out with a machining device including damper means (12) for dampening a counterforce of the support surface (30) against the machining device during machining of the base mixture layer (20), such that the base mixture layer (20) is machined from an upper surface thereof until the support surface (30).

15. An artificial stone slab with coloured veins produced with the method of any of claims 11-14, or with the installation of any of claims 9-10 or with the machining device of any of claims 1-8.

Drawing