APPARATUS AND METHOD FOR FEEDING GRANULAR MATERIAL TO A PLANT FOR THE PRODUCTION OF SLABS OR TILES

The present invention relates to an apparatus for feeding granular material to a plant for the production of slabs or tiles.

The present invention therefore finds application in the field of the production of building materials, in particular in the production of planar elements such as slabs, tiles, panels or, more generally, elements for paving or covering buildings.

In the following, all these elements will be named in their entirety slabs without any limiting intent.

Furthermore, for ease of exposure and without any restrictive intent, the material to be formed will be called "granular material". This term therefore defines both the powder properly so-called, in the dry state, but also any other material suitable for forming slabs, such as for example the slip, which is a mixture or a suspension obtained from at least one powder and at least one liquid.

The slabs are produced by special known systems, described below in their basic features. The system usually comprises means for feeding the powders which draw the powders from special tanks and feed them to collection and transport means, for example to a conveyor belt. The powders deposited on the collection and transport vehicles are then subjected to compaction and sent for cooking.

With the recent technical developments, also in this field it became possible to produce slabs with a variegated appearance, thanks to the suitable mixing of a plurality of granular materials of different colours and/or granulometry.

In particular, thanks to the use of high performance printing heads it was possible to decorate prefabricated slabs on the surface in order to recreate, on the exposed face, a design similar to the appearance of natural stones by the appropriate creation of veins or similar. This method, however, does not apply to the production of "full-thickness" decorated slabs, in which the "design" is not limited to the superficial layer but is visible through the whole thickness of the piece.

In other words, thanks to the use of known print heads, it is not currently possible to recreate slabs that fully replicate the appearance of natural stones, thus limiting their use to applications that expose only the external face of the slab.

In order to overcome such a drawback, the Applicant has recently developed a solution in which the veins were generated through the use of a plurality of hollow and oscillating "fins" which, arranged along a slide, distribute a single vein of granular colouring material within the flow of the "main" material, preliminarily deposited by means of an array of hoppers and subsequently advanced.

This solution, therefore, makes it possible to manufacture slabs with "full thickness" veins, but the presence of fins arranged along an advancement stretch of the material considerably limits the obtainable patterns, which are actually limited to the presence of single veins of one or more different colours running within the slab.

In other words, even if the appearance of compacted slabs is very close to that of natural stones, the technologies today available do not allow replicating the variety of shapes and colours available in nature.

The object of the present invention is therefore to provide an apparatus and a method for feeding granular material to a plant for the production of slabs or tiles able to overcome the drawbacks of the prior art mentioned above.

In particular, it is an object of the present invention to provide an apparatus and a method for feeding granular material to a plant for the production of slabs or tiles with increased efficiency and versatility.

More precisely, the object of the present invention is to provide an apparatus and a method for feeding granular material to a plant for the production of slabs or tiles capable of allowing the manufacture of products with the appearance of natural stones.

Said objects are achieved by an apparatus for feeding granular material to a plant for producing slabs or tiles having the technical characteristics of one or more of the subsequent claims from 1 to 22, as well as a method for feeding granular material to a plant for the production of slabs or tiles having the characteristics of one or more of the claims from 23 to 26.

In particular, said objects are achieved by an apparatus for feeding granular material to a plant for the production of slabs or tiles comprising a distributing station and a compacting station.

Preferably, the distributing station comprises a deposition plane and a plurality of distributing members arranged above the deposition plane and configured to distribute a plurality of granular materials on said plane.

It should be noted that preferably the granular materials are different from each other and can differ from one another, for example by colour, by granulometry, by type or by two or more of these parameters.

Preferably, the deposition plane develops along at least one longitudinal direction and at least one transverse direction.

Preferably, moreover, the distributing members are arranged above the deposition plane to distribute a plurality of granular materials on said plane according to a preliminary distribution.

Preferably, the compacting station is operatively arranged downstream of said distributing station and is provided with at least one receiving cassette arranged to receive said preliminary distribution and shaped so that said granular materials are arranged according to a compacted final distribution corresponding to an aspect of the slab to be manufactured.

According to an aspect of the present invention, each of the distributing members comprises at least one array of dispensing nozzles or openings of the relative granular material arranged in succession along said transverse direction and drivable independently from each other.

Advantageously, the presence of a succession of arrays of dispensing nozzles or openings which can be driven independently from each other allows the operator to vary the distribution of the single granular materials on the distribution plane in a completely arbitrary manner, simply by varying the driving of the single nozzles/openings.

This allows to significantly increase the flexibility of the apparatus, which has the possibility of quickly and easily changing the preliminary distribution.

It should be noted that hereinafter in the present text, reference will be made specifically to the presence of "nozzles", meaning with this term both nozzles in the strict sense and simple openings/dispensing mouths.

Preferably, moreover, the presence of a control unit associated with said distributing station is provided and configured to drive said distributing members to distribute the relative granular materials on the deposition plane depending on the shape of said final distribution and on a predetermined compaction ratio of said granular materials.

Thus, the preliminary distribution and the final distribution are closely related to each other.

In other words, a single quantity of A-shape material that occupies a first volume XYZ on the deposition plane will correspond, in the cassette, with a single quantity of material:

- having a B-shape attributable to A;

- which occupies a second volume n ^* CΎ'Z', wherein "n" is the compaction ratio, Z' is the thickness of the cassette and X’ Y' are the longitudinal and transverse dimensions of the quantity of A material modified depending on the thickness, the compaction ratio and the shape of the quantity of granular material previously deposited in the cassette.

In this regard, the control unit is preferably configured to acquire an image representative of said final distribution of the granular materials and to drive the distributing station depending on said image.

More precisely, the control unit is configured to correlate the colours of said image with the colours of said granular materials and to drive said distributing station depending on said correlation. It should be noted that each nozzle of an array is configured to distribute granular material over a predetermined operating area having a predetermined surface extension.

Preferably, the control unit is configured to recalibrate a definition of said image depending on the number of nozzles of each array and on the surface extension of the operating area of each nozzle.

Advantageously, in this way the definition of the imparted image corresponds to the definition which can be determined by means of the nozzles.

In particular, the control unit is configured to determine (displaying or not to an operator) a grid defining said image. Preferably the grid is formed by a plurality of single boxes of homogeneous dimension arranged on a predetermined number of rows, parallel to said transverse direction, and on a predetermined number of columns, parallel to said longitudinal direction.

Preferably, the dimension of the single boxes corresponds to said surface extension of the operating area of each nozzle.

Preferably, the predetermined number of columns is equal to or less than the number of nozzles constituting each array.

Preferably, the distributing station further comprises a movement system configured to determine a relative movement between said distributing members and said plane along said longitudinal direction.

More preferably, the movement system comprises a conveyor belt defining said deposition plane and movable along said longitudinal direction.

Preferably, the control unit is configured to calibrate an advancement speed of said movement system depending on the shape of said final distribution and on a predetermined compaction ratio of said granular materials.

Preferably the compacting station comprises a discharge device configured to release the granular material inside the cassette on a conveyor plane. Such discharge device comprises a conveyor movable parallel to said longitudinal direction, wherein said control unit is configured to calibrate a movement speed of said conveyor according to said advancement speed of said movement system.

Advantageously, in this way it is possible to precisely control the sliding of the material, preventing the cassette from clogging.

With reference to the cassette, it should be noted that the same has a parallelepipedal shape developing along a first, a second and a third dimension, orthogonal to each other, wherein the first dimension corresponds to a thickness of the slab or tile to be manufactured and has a significantly lower extension compared to the second and third dimension.

This cassette comprises a feeding mouth having an extension defined by said first and said second dimension and facing said distributing station in order to receive the granular material by gravity.

Preferably, the cassette also has a first pair of side walls orthogonal to the feeding mouth and defined by the second and third dimensions of the cassette, wherein at least one of said side walls is at least partly slidable along an advancement direction parallel to the third dimension.

More preferably, the control unit is configured to calibrate a sliding speed of said at least one side wall according to said movement speed of said movement system.

Advantageously, in this way all the advancement speeds of the apparatus are controlled and related, in order to allow a continuous advancement of the granular material and to govern directly any variations to be performed in real time.

It should be noted that the cassette also has a second pair of side walls defined by the first and third dimension of the cassette.

Preferably, the walls of said first pair and/or the walls of said second pair are mutually movable towards and away from each other in order to adjust said first and said second dimension of the cassette. Advantageously, being able to arbitrarily drive the distributing members not only relative to the flow rate but also to the definition of the active or non-active nozzles, this results into a considerable increase in production flexibility, since the same plant can provide for the manufacture of slabs of different sizes without substantial structural changes (except for the adjustment of the cassette walls).

According to a further aspect of the present invention, complementary or alternative to those described so far, the cassette comprises, at at least one side wall of the first pair, a curved end portion (distal to the access mouth).

Advantageously, this allows the passage from the substantially vertical orientation of the cassette to the substantially horizontal orientation of the conveyor plane to be softened, guaranteeing maintenance in a thickness corresponding to the first dimension of the cassette.

Preferably, both walls of the first pair have respective curved end portions substantially parallel to each other (or concentric) so as to maintain the mutual distance equal to the first dimension of the cassette (i.e. the thickness of the slab).

In this embodiment, therefore, a side wall has a first curved end portion, having a smaller radius of curvature, and the other side wall has a second curved end portion, having a greater radius of curvature.

According to an optional aspect of the invention, the ratio between the smaller radius of curvature and the first dimension of the cassette is between 0.5 and 4, more preferably between 1 and 4, even more preferably between 2 and 3.

Surprisingly, in fact, although in the literature the provision of a limited curvature between the cassette and the conveyor plane is suggested, the Applicant has experimentally verified that in the presence of high thicknesses of the slab, the increase in the smaller radius of curvature (and likewise in the greater one) carries with it considerable advantages in maintaining the original distribution of the granular material. Object of the present invention is also a method for feeding granular material to a plant for the production of slabs or tiles, preferably but not necessarily obtained by means of the apparatus described above.

The method provides the distribution of the granular materials on said plane according to the preliminary distribution and to discharge said preliminary distribution inside the cassette so that the granular materials compact and are arranged according to a compacted final distribution. According to an aspect of the invention, the distribution of the granular materials is performed depending on the shape of said final distribution and on a predetermined compaction ratio of said granular materials.

Preferably, an acquisition (or generation) of an image representative of said final distribution of the granular materials is provided.

Then, one or more colours of said image are correlated with said colouring of said granular materials.

In other words, two or more colours on the image are identified, which are correlated to the colouring of said granular materials.

This correlation step is therefore performed by assigning to each colour detected in the image a predetermined combination of one or more colouring of the granular materials.

Therefore, the correlation can be direct (colour x = colouring y) or combined, wherein a colour corresponds to a predetermined mixture of two or more colouring.

The distributing station is therefore driven depending on said correlation (and on said compaction ratio) in order to define the preliminary distribution on the plane.

It should be noted that the method is preferably configured to recalibrate a definition of said acquired image depending on the number of nozzles of each array and on the surface extension of the operating area of each nozzle.

In other words, regardless of the actual definition of the loaded or acquired image, the method involves recalibrating it according to the number of nozzles and to the dimension of the operating area, so that each "pixel" of the recalibrated image corresponds to an operating area of a single nozzle.

Advantageously, this way it is possible to determine in an absolutely arbitrary and independent manner the colouring/hue of each pixel by combining the driving of the nozzles of the same row and the advancement of the deposition plane in an appropriate manner.

In fact, by distributing a different quantity of one or more materials in the same portion of the plane, it is possible to determine the hue of each point of the plane which defines the hue of the slab through the full thickness of the same, after the deposition in the cassette.

In this regard, it should be noted that also by superimposing two layers of distinct granular materials on a same point of the plane, after the discharge of these materials inside the cassette suitably angled with respect to the plane, a mixing of the powders is obtained such that a new hue resulting from mixing is recreated in the cassette. Moreover, the possibility of alternating or mixing two or more different granular materials on the deposition plane makes it advantageously possible to obtain shades or gradual colour variations more comparable to natural stones. These and other features, with the relative advantages, will become more apparent from the subsequent exemplary, therefore not limiting, description of a preferred, therefore not exclusive, embodiment of an apparatus and a method for feeding granular materials to a plant for the production of slabs and tiles according to what illustrated in the appended figures, wherein:

- figure 1 shows a schematic perspective view of an apparatus for feeding granular material to a plant for the production of slabs or tiles according to the present invention;

- figure 2 is a schematic side view of the apparatus of figure 1 ;

- figure 3 shows a schematic view of a further embodiment of an apparatus for feeding granular material to a plant for the production of slabs or tiles according to the present invention;

- figures 4, 5 and 6 show a schematic side and partial view of the apparatus for feeding granular material to a plant for the production of slabs or tiles according to the present invention in three different variants;

- figure 4a shows a detail of figure 4.

With reference to the appended figures, number 1 indicates an apparatus for feeding granular material to a plant for the production of slabs or tiles according to the present invention.

It is to be recalled that, in the present text, the term "slabs or tiles" is used to define any tile, shingle, panel or more generally an element for paving, cladding or covering buildings.

In addition, the term "granular material" defines both the powder properly called, in the dry state, but also any other material suitable for the forming slabs, such as for example the slip, that is a mixture or a suspension obtained from at least one powder and at least one liquid.

Given the above, the apparatus 1 for the feeding described below is a system for the distribution and compaction of granular material arranged to determine the appearance, in terms of distribution of material, of a slab. The apparatus 1 comprises a distributing station 2 and a compacting station 3.

The distributing station 2 is preferably provided with a deposition plane 4, a plurality of distributing members 5 and a control unit 10 associated therewith.

The deposition plane 4 extends along at least one longitudinal direction X and at least one transverse direction Y. Preferably, this plane 4 is substantially horizontal.

The distributing members 5 are arranged above the deposition plane 4 to distribute on said plane a plurality of granular materials P1 , P2, P3, P4 of different colours according to a preliminary distribution PP.

The term "colouring" means that the two or more granular materials present in the machine have different colours or hues, so that the combination/distribution of the same leads to the reproduction of a variegated and veined pattern, similar to that of natural stones.

The compacting station 3, instead, is operatively arranged downstream of the distributing station 2 and is provided with at least one receiving cassette 1 1 arranged to receive said preliminary distribution PP and shaped so that said granular materials P1 , P2, P3, P4 are arranged according to a compacted final distribution FD, corresponding to an aspect of the slab to be manufactured.

Preferably, the distributing members 5 are arranged in succession along the longitudinal direction X of the deposition plane 4, in order to allow each one to release the respective granular material along the plane 4.

In this regard, it is also preferably provided the presence of a movement system 16 configured to determine a relative movement between the distributing members 5 and the plane 4 along said longitudinal direction X. In the preferred embodiment, the movement system 16 comprises a conveyor belt 17 defining the deposition plane 4 and movable along said longitudinal direction X between a first end 17a and a second end 17b.

The second end 17b faces the compacting station 3 to discharge the preliminary distribution PP inside said cassette 1 1.

Alternatively, however, the movement system 16 could provide a movement of the distributing members along the longitudinal direction X.

In order to favour a homogeneous distribution of the granular material from the distributing station 2 to the cassette 1 1 , in a preferred embodiment the presence of a deflector bulkhead 19 arranged to intercept the granular material released by the distributing station 2 distributing it in the cassette. More precisely, the bulkhead 19 is located along a falling path of the granular material from the distributing station 2 towards a relative feeding mouth 1 1 a facing it.

In this way, it is advantageously possible to intercept the material falling, avoiding the localized accumulation of the same in a single area of the cassette 11 (typically at a distal wall to the distributing station 2). In the embodiment schematically shown in figure 6, the bulkhead 19 is defined by a diaphragm orthogonally oriented to the longitudinal direction X and inclined both with respect to the conveyor belt 17 and to the cassette 1 1. This diaphragm is positioned so that an impact point of the granular material is located along a vertical projection of a median plane of the cassette 1 1.

It should be noted that, preferably, each distributing member 5 comprises at least one array 6 of dispensing nozzles or openings 7 of the relative granular material P1 , P2, P3, P4 arranged in succession along said transverse direction Y and drivable independently from each other.

In other words, each distributing members 5 is defined by a transversal bar or crosspiece to the deposition plane 4 and provided with a plurality of nozzles or openings, in order to distribute the granular material over a whole "useful width" of the plane 4.

Moreover, since the nozzles (or the openings) can be driven each independently from each other, it is advantageously possible to differentiate along the all plane 4 the distribution of the single granular materials P1 , P2, P3, P4 thus allowing maximum discretion and freedom in the definition of the preliminary distribution PP.

It should be noted that hereinafter in the present text, reference will be made specifically to the presence of "nozzles 7", meaning with this term both nozzles in the strict sense and simple openings/dispensing mouths. The distributing members 5 are each associated with a tank 9 of a predetermined granular material P1 , P2, P3, P4, in order to allow a continuous feeding to each nozzle 7.

It should be noted that, in the preferred embodiment, each nozzle 7 of each array 6 is selectively switchable between a stop condition and a dispensing condition and comprises a dispensing valve 8.

This valve 8 can be driven in an open position or in a closed position.

Preferably, the valve 8 comprises a conduit developing along its own main direction up to an outlet mouth, corresponding to the nozzle or opening 7. In the preferred embodiment, this conduit comprises at least one deformable wall movable between an operating position, wherein it determines the creation of a restriction in the conduit that prevents the flow of the granular material towards the outlet mouth (closed position), and a rest position, wherein it allows the flow of the printing material towards the outlet mouth (open position).

In the stop condition, the control unit 10 drives the valve 8 of the nozzle 7 so as to keep it in said closed position.

On the contrary, in the dispensing condition the control unit 10 drives each nozzle 7 with a succession of duty cycles wherein the valve can be selectively opened or closed and the flow rate of granular material P1 , P2, P3, P4 from the single nozzle is proportional to the length of the opening intervals within each duty cycle.

More precisely, each duty cycle consists of an opening interval, wherein the valve 8 is driven in said open position, and of a closing interval, wherein the valve 8 is driven in said closed position.

The length of the opening interval with respect to the closing interval within each duty cycle determines the flow rate of granular material P1 , P2, P3, P4 dispensed by the single nozzle.

Therefore, it is advantageously possible to determine the flow rate of the dispensed material and, consequently, the quantity of each material deposited in a predetermined area of the plane 4 with a simple calibration of the length of these intervals.

Moreover, the control unit 10 is preferably associated with the movement system 16 and is configured to also calibrate an advancement speed of said movement system 16 depending on the shape of said final distribution FP and on the predetermined compaction ratio of said granular materials P1 , P2, P3, P4.

Therefore, the control unit 10 is configured to drive the distributing members 5 and the movement system 16 in a coordinated manner.

According to an aspect of the present invention, the control unit 10 is configured to drive said distributing members 5 to distribute the relative granular materials P1 , P2, P3, P4 on the deposition plane 4 according to the shape of said final distribution FP and to a predetermined compaction ratio of said granular materials P1 , P2, P3, P4.

In other words, given the final distribution FP, the control unit 10 is programmed to calculate the geometry of the preliminary distribution PP and configured to drive the distributing station accordingly.

In particular, the control unit 10 is configured to:

- singularly drive the nozzles 7 of each array 6;

- calibrate an advancement speed of said movement system 16 depending on the shape of said final distribution FP and on the compaction ratio of said granular materials P1 , P2, P3, P4.

The compaction ratio is defined as the ratio between the volume occupied by a predetermined quantity of granular material on the plane 4 and the volume occupied by the same quantity of granular material in the cassette 1 1 .

Preferably, this compaction ratio is calculated empirically, according to one or more of the following parameters:

- type of granular material,

- granulometry of the granular material,

- nozzles dimension;

- nozzles distribution;

- environmental conditions.

Preferably, the control unit 10 is further configured to acquire an image IM representative of the final distribution FP of the granular materials P1 , P2, P3, P4 in order to process it and drive the stations.

This image IM is preferably a drawing or a photo representative of the final appearance of the slab or tile to be produced.

In other words, the IM image is a representation of the slab as it is desired to be manufactured.

Moreover, the control unit 1 is configured to correlate the colours of said image IM with the colouring of the granular materials P1 , P2, P3, P4 available in the distributing members 5 and to pilot the distributing station 2 depending on said correlation.

This correlation is preferably performed by assigning to each colour detected in the image a predetermined combination of one or more colouring of the granular materials.

Therefore, the correlation can be direct (colour x = colouring y) or combined, wherein a colour corresponds to a predetermined mixture of two or more colouring.

Advantageously, since it is not always possible a perfect correspondence between the type and number of hues of the image and the type and number of hues available, this allows to recreate the best possible approximation of the desired hues based on the available colouring.

The control unit 10 preferably comprises a user interface 10a configured to allow a user to realize and/or load said image IM.

In this way the user/operator has the possibility of advantageously using images at his disposal, for example photographs of natural stones with particular veins, or he can recreate a distribution of the veins and colours in accordance with the requests of the customers.

This user interface 10a is further configured to allow the operator to determine (manually or automatically) the correlation between the colours of said image IM and the colours of said granular materials P1 , P2, P3, P4. By way of example, in embodiments wherein the image has colouring ranging from white to red, passing through at least a light pink hue and a dark pink hue, via the user interface 10a the operator has the possibility of defining that:

- the white colour corresponds to the granular material of a first distributing member;

- the red colour corresponds to the granular material of a second distributing member;

- the light pink hue corresponds to a combination of the two granular materials of the two distributing members with opening intervals of 70% and 30% of the duty cycle respectively;

- the dark pink hue corresponds to a combination of the two granular materials of the two distributing members with opening intervals of 30% and 70% of the duty cycle respectively.

According to a further (and optional) aspect of the invention, the control unit 10 is further configured to recalibrate a definition of said image depending on the number of nozzles 7 of each array and on the surface extension of an operating area of each nozzle 7. By "definition" we mean here to define the number of points (pixels) that make up the image, that is its "cyberdimension".

It should be noted, in fact, that each nozzle 7 of an array 6 is configured to distribute a granular material P1 , P2, P3, P4 over a predetermined operating area having a predetermined surface extension.

In this way the control unit advantageously adjusts the image definition on the basis of the definition obtainable thanks to the distribution of the nozzles 7. In fact, a greater definition will correspond to a greater number of nozzles 7 arranged on the array 6 per unit of length.

The control unit 10 is preferably configured to determine a defining grid G for said image formed by a plurality of single boxes P of homogeneous dimension and arranged on:

- a predetermined number of rows R, parallel to said transverse direction

Y,

- a predetermined number of columns C) parallel to said longitudinal direction X.

The dimension of the single boxes substantially corresponds to the surface extension of the operating area of each nozzle 7.

The predetermined number of columns C is instead equal to or less than the number of nozzles 7 constituting each array 6. For slabs with maximum width, the number of columns C will be equal to the number of nozzles. To manufacture smaller slabs, it will be possible to use fewer nozzles, reducing the number of grid columns.

With reference to the compacting station 3, the cassette 1 1 has a parallelepipedal shape developing along a first, a second and a third dimension, orthogonal to each other.

The first dimension corresponds to a thickness of the slab or tile to be manufactured and is significantly smaller than the second and third dimensions.

In particular, the second dimension corresponds to the width of the slab or tile to be manufactured, that is the dimension transverse to the advancement direction of the granular material.

The cassette 11 comprises the feeding mouth 1 1 a and has a first and a second pair of side walls orthogonal to the feeding mouth 1 1 a.

The feeding mouth 11 a has an extension defining said first and said second dimension.

The first pair of side walls 14 defines the second and third dimension of the cassette 1 1.

The second pair of side walls 15 defines the first and third dimension of the cassette 1 1.

Preferably, the feeding mouth 1 1 a faces said distributing station 2 to receive the granular material by gravity.

Therefore, at least in a condition of receiving the material, the feeding mouth 1 1 a is located at a lower level with respect to the second end 17b of the conveyor belt 17 (or more generally of the plane 4).

Preferably, the distance between the second end 17b of the conveyor belt 17 and the feeding mouth 1 1 a is less than 30 cm.

More preferably, this distance is between 5 cm and 30 cm; it should be noted in this regard that it is desirable to have a certain "gap" between the second end 17b of the conveyor belt 17 and the feeding mouth 1 1 a in order to favour mixing between the superimposed granular materials during distribution. Preferably, the third dimension of the cassette 11 is coplanar to the longitudinal direction X of the plane 4 (if evaluated along the centre line thereof) and develops transversely, preferably orthogonally, to said longitudinal direction X.

In the illustrated and preferred embodiment, this third dimension is substantially vertical.

Preferably, the walls 14 of said first pair and/or the walls 15 of said second pair being mutually movable towards and away from each other in order to adjust said first and said second dimension of the cassette 1 1.

In other words, the cassette 1 1 has a dimension that can be adjusted by translating the walls of at least one, preferably each, first or second pair of side walls 14, 15 towards or away from each other in order to quickly change the size of the slab to be produced.

Advantageously, being able to arbitrarily drive the distributing members not only relative to the flow rate but also to the definition of the active or non-active nozzles, this results into a considerable increase in production flexibility, since the same plant can provide for the manufacture of slabs of different sizes without substantial structural changes (except for the adjustment of the cassette walls).

Moreover, at least one of the side walls 14 of the first pair is preferably at least partly slidable along an advancement direction parallel to the third dimension.

In the preferred embodiment, such a wall 14 is at least partly defined by a belt 14a' or by a conveyor movable along the third dimension and selectively drivable by means of the control unit 10.

The control unit 10 is therefore configured to calibrate a sliding speed of said at least one side wall 14 according to said movement speed of said movement system 16.

Even more preferably, with reference to the embodiment shown in figure 5, both walls 14 of the first pair of side walls are at least partly defined by a belt 14a', 14a" or by a conveyor movable along the third dimension and selectively drivable by the control unit 10. In particular, preferably both belts 14a', 14a" or conveyors are driven with the same advancement speed so as not to affect the distribution of the granular material performed upstream.

In the preferred embodiment, the cassette 11 comprises a first belt 14a' or a conveyor movable along the third dimension and having a rectilinear stretch 20 defining a wall of the first pair 14 proximal to the distributing station 2.

Preferably, the cassette 1 1 comprises a second belt 14a" or a conveyor facing the first belt 14a' to define a wall of the first pair 14 distal to the distributing station 2.

The second belt 14a" preferably comprises a first rectilinear stretch 21 , developing along the third dimension and defining said wall 14, and a second stretch 22, preferably also rectilinear and transverse (more preferably orthogonal) to the first stretch 21 .

In the preferred embodiment, the first 21 and the second rectilinear stretch 22 are connected to each other by a curved portion 18b, preferably defined by the sliding of said belt on an idler roller interposed between the two rectilinear stretches 21 , 22.

The compacting station 3 further comprises a discharge device 12 configured to release the granular material inside the cassette on a conveyor plane 12a.

In this way it is advantageously possible to substantially operate in a continuous way, without the need for interruptions for emptying the cassette 11.

In the preferred embodiment, the discharge device 12 comprises a conveyor 13 movable parallel to said longitudinal direction X.

In other words, the conveyor plane 12a is substantially horizontal, or anyway angled/transversal to the cassette 1 1 in order to receive the granular material P1 , P2, P3, P4 distributed according to the final distribution FR and transport it in successive stations (e.g. oven). Preferably, with reference to the embodiment illustrated in figure 5, the second rectilinear stretch 22 of the second belt 14a" is parallel to said conveyor plane 12a and, more preferably, spaced from it by a quantity corresponding to the first dimension of the cassette 1 1 (i.e. thickness of the slab).

In this embodiment, the conveyor plane 12 and the second belt 14a" (as well as the first 14a') are driven at the same advancement speed.

Advantageously, such continuity of movement between the cassette 1 1 and the conveyor plane 12 facilitates a correct outflow of the granular material and facilitates the maintenance of a correct distribution thereof.

In this regard, the cassette 11 preferably comprises, at at least one side wall of the first pair 14, a curved end portion 18a (distal to the access mouth 1 1 a).

This curved end portion 18a advantageously has the purpose of softening the passage from the substantially vertical orientation of the cassette 1 1 to the substantially horizontal orientation of the conveyor plane 12a, ensuring that it is kept in a thickness corresponding to the first dimension of the cassette.

The curved end portion 18a, in fact, avoids the establishment of a section of greater thickness in the inversion area between the cassette 11 and the conveyor plane 12a.

Preferably, both walls 14 of the first pair have respective curved end portions 18a, 18b which are substantially parallel to each other (so as to maintain the mutual distance equal to the first dimension "b").

In this embodiment, therefore, a side wall 14 has a first curved end portion 18a, having a greater radius of curvature "c", and the other side wall 14 has a second curved end portion 18b, having a smaller radius of curvature "a". The greater radius of curvature "c" preferably corresponds to the sum between the smaller radius of curvature "a" and the first dimension "b" (i.e. the thickness of the cassette 1 1 ).

With reference to figures 4 and 4a, the first curved end portion 18a corresponds to the curved portion of the second belt 14a".

According to an optional aspect of the invention, the ratio between the smaller radius of curvature "a" (in the numerator) and the first dimension "b" (in the denominator) is between 0.5 and 4, preferably between 1 and 4. Even more preferably, this ratio is between 2 and 3.

In other words, the ratio between the smaller radius of curvature "a" (in the numerator) and the greater radius of curvature "c" (in the denominator) is between 0.33 and 0.8, preferably between 0.5 and 0.8.

In the preferred embodiment, the ratio between the smaller radius of curvature "a" and the greater radius of curvature "c" is between 0.65 and 0.75.

Therefore, the ratio between the first dimension "b" (in the numerator) and the greater radius of curvature "c" (in the denominator) is between 0.2 and 0.66, preferably between 0.2 and 0.5, more preferably between 0.2 and 0.33.

In the preferred embodiment, the ratio between the first dimension "b" and the greater radius of curvature "c" is between 0.25 and 0.33.

Preferably, the cassette 1 1 has a first dimension "b" lower than or equal to 40mm and the ratio between the first dimension "b" and the smaller radius of curvature "a" is between 0.5 and 4.

Alternatively, the cassette 1 1 can have a first dimension "b" greater than 40mm, wherein the ratio between the first dimension "b" and the smaller radius of curvature "a" is between 2 and 3.

Surprisingly, although in the literature the provision of a limited curvature between the cassette and the conveyor plane is suggested, the Applicant has experimentally verified that in the presence of high thicknesses of the slab, the increase in the smaller radius of curvature (and likewise in the greater one) carries with it considerable advantages in maintaining the original distribution of the granular material.

It should be noted that, the control unit 10 is preferably configured to calibrate a movement speed of said conveyor 13 depending on said advancement speed of said movement system 16.

In the preferred embodiment, the control unit 10 is configured to maintain the movement speed of the conveyor 13 lower than the advancement speed of the movement system 16 in order to maximize the compaction of the granular material.

Object of the present invention is also a method for feeding granular material to a plant for the production of slabs or tiles, preferably but not necessarily obtained by means of the apparatus 1 described above.

In this regard, and without thereby losing generality, in the following description of the method object of the invention, the terminology and the numerical references used so far in the apparatus description will be maintained, where possible and mutatis mutandis.

The method provides the distribution of the granular materials P1 , P2, P3, P4 on the deposition plane 4 according to the preliminary distribution PP and to discharge said preliminary distribution PP inside the cassette 1 1 so that the granular materials P1 , P2, P3, P4 compact and are arranged according to the compacted final distribution FP.

According to an aspect of the invention, the distribution of the granular materials is performed depending on the shape of said final distribution FP and on the predetermined compaction ratio of said granular materials P1 , P2, P3, P4.

Similarly to what previously described, the granular materials P1 , P2, P3, P4 are of different colouring, where the term "colouring" means that the two or more granular materials present in the machine are provided with different colours or hues, so that the combination/distribution of the same leads to the reproduction of a variegated and veined pattern, similar to that of natural stones.

Preferably, the acquisition (or generation) of an image IM representative of the final distribution FP of the granular materials based on which the preliminary distribution PP is determined.

Preferably, one or more colours of the image IM are correlated with relative colouring of said granular materials P1 , P2, P3, P4.

In other words, two or more colours on the image are identified, which are correlated to the colouring of said granular materials.

This correlation step, already described in detail previously, is therefore performed by assigning to each colour detected in the image a predetermined combination of one or more colouring of the granular materials.

This correlation therefore provides the definition of which available colouring or combination of colouring of the granular materials P1 , P2, P3, P4, a given colour of the image corresponds to.

The correlation can be direct (colour x = colouring y) or combined, wherein a colour corresponds to a predetermined mixture of two or more colouring. Following the IM image acquisition and correlation, which can be performed automatically or by an operator, the distributing station is driven depending on said correlation and on said compaction ratio in order to define the preliminary distribution on the plane.

The method is preferably configured to recalibrate a definition of said acquired image depending on the number of nozzles of each array and on the surface extension of the operating area of each nozzle.

In other words, regardless of the actual definition of the loaded or acquired image, the method involves recalibrating it according to the number of nozzles and to the dimension of the operating area, so that each "pixel" of the recalibrated image corresponds to an operating area of a single nozzle.

In this way, it is advantageously possible to parametrize the distribution of the granular material from the single nozzles in a directly proportional way to the chromatic content of a single box of the recalibration grid.

The invention achieves the intended aims and achieves important advantages.

In fact, the provision of a control unit capable of calculating the preliminary distribution of the granular materials on the plane depending on the desired appearance of the tile and of driving the distributing station accordingly, enables to control with precision and extreme flexibility the definition of the "pattern" of the slab, while maintaining a structure capable of creating full-thickness veins.

Advantageously, this way it is possible to determine in an absolutely arbitrary and independent manner the colouring/hue of each pixel by combining the driving of the nozzles of the same row and the advancement of the deposition plane in an appropriate manner.

In fact, by distributing a different quantity of one or more materials in the same portion of the plane, it is possible to determine the hue of each point of the plane which defines the hue of the slab through the full thickness of the same, after the deposition in the cassette.

In this regard, it should be noted that also by superimposing two layers of distinct granular materials on a same point of the plane, after the discharge of these materials inside the cassette suitably angled with respect to the plane, a mixing of the powders is obtained such that a new hue resulting from mixing is recreated in the cassette. Moreover, the possibility of alternating or mixing two or more different granular materials on the deposition plane makes it advantageously possible to obtain shades or gradual colour variations more comparable to natural stones. Furthermore, the provision of movement means which can be driven independently along the entire path of the granular material, from the deposition plane to the conveyor plane, allows the outflow of the material to be precisely regulated, avoiding possible clogging and guaranteeing the continuity of the process.

Furthermore, the use of transversal arrays of nozzles can be independently driven allows to vary the "useful" width of the distributing station by means of simple software commands, facilitating the rapid implementation of size changes, which involves a considerable advantage in terms of productivity and flexibility.