*****

The present invention relates to a method and an apparatus for consolidating slabs of natural or artificial stone material.

In particular, the present invention relates to a method and an apparatus for reinforcing slabs of natural oz artificial stone material by means of impregnation with resins.

The slabs to which reference is made in the present description are slabs which are used for lining walls, floors, furnishing surfaces in general, etc.

In these slabs it is possible to define a surface which will remain visible during use and a surface which, owing to the presence of defects or more simply a less attractive appearance, will be the non-visible surface of the slab.

In the present description the term "visible surface" is understood as meaning the surface of the skb which, during use, is intended to remain visible, while "non-visible surface" is understood as: meaning the surface of the slab which, during use, is intended to remain hidden.

As is known, one of the drawbacks during the processing of slabs of stone material is the presence of fracture lines inside the slabs, cavities or porous zones which start on the surface and extend towards the inside of the slab. These irregularities are unattractive and weaken the slab and, if not suitably treated, may result in breakage of the slab during movement ox machining.

These irregularities are typical of natural stone and may be due both to the natural factors resulting in the formation of the stone and to the extraction operations; while, in composite stones these irregularities may for example be due to machining defects.

Many methods for consolidating and reinforcing the slabs which have defects of this type are known in the state of the art

The known methods comprise essentially a step during which a resin, for example an epoxy or polyester resin, is distributed on one or both the surfaces of a slab, with the addition, where necessary, of gauze or granulated stone (also be of the same type as the stone forming the slab) inside the bigger cracks.

Then, the resin is hardened, preferably inside an oven, and, once the resin has hardened, the excess resin is eliminated.

A method of this type is described for example in IT 1293153 and IT 1350875.

There also exist other methods which are performed partly in vacuum conditions, in order to prevent air from remaining trapped inside the cracks or porous zones of the skb.

The most widely used resin-coating method, which is performed partly under a vacuum, comprises the following steps:

1) inserting the skb inside an air-tight chamber, 2) extracting the air in order to create the vacuum inside the chamber;

3) distributing a thermosetting liquid resin over the surface of the slab to be consolidated.

4) restoring the atmospheric pressure inside the chamber,

5) removing the slab from the chamber;

6) hardening the slab inside an oven by means of catalysis of the resin distributed over the surface.

Once the atmospheric pressure is restored and the slab leaves the chamber, the excess resin is preferably drawn off from the surface of the slab so as to leave a layer of resin just a few tens of a millimetre thick.

With this method it is known to consolidate both the visible surface and the opposite surface, ie. non-visible surface.

Once the resin has completed the hardening step, the slab undergoes final finish-machining of at least the visible surface.

In given conditions, for example in the case of slabs with numerous fracture lines, it is known to provide a reinforcing element, for example a mesh or matting, on the non-visible surface. This method, which is performed at atmospherk pressure, involves a step where, after distributing the resin over the non-visible surface of the slab, a reinforcing element is positioned on the same surface. Reinforcing element and resin are then subjected to a pressing action performed by means of manual or automated rolling such that the resin is distributed uniformly and the remforcing element adheres to the non-visible surface.

The prior arc, although widely used and recognized, is not without drawbacks,

Λ first drawback relates to impregnation of the slab with resin. In fact, in the case of very small cracks or pores, the resin does not always manage to penetrate deeply, leaving zones without resin inside the slab. For this reason the treated slab may have a surface which is perfectly coated with resin, but the crack inside it could be without resin. In this case, the resistance of the slab to handling and machining, although greater, might not yet be satisfactory.

A second drawback relates to the recovery of the excess resin. The method is very complex and requires a device which is also complex and difficult to dean.

The object of the present invention is to overcome, at least partially, the drawbacks of the prior art.

A first task of the present invention is to provide a method and an associated apparatus in which the penetration of the resin inside the cracks, the cavities and the pores of the slabs is improved.

A second task of the present invention is to provide a method and an apparatus in which it is no longer necessary to draw off the excess resin from the slab.

The object and the tasks are achieved with a method according to claim 1 and with an apparatus according to claim 14.

The advantages and the characteristic features of the present invention will emerge more clearly from the detailed description which follows of a number of examples of embodiment, provided by way of a non-limiting explanation, with reference to the attached drawings in which:

Fig. 1 shows in schematic form a front view of a part of the apparatus according to the present invention during a first working stepj

Fig, 2 shows in schematic form a front view of the part of the apparatus according to Figure 1 during a second working step;

Fig; 3 shows in schematic form a front view of a part of the apparatus according to the present invention during which resin is distributed over a surface of a slab;

Fig. 3A shows an enlarged view of a detail of Fig.3;

Fig. 4 shows in schematic form a part of the apparatus according to the present invention; Fig. 5 shows in schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig. 5 A shows an enlarged view of a detail of Fig. 5;

Fig. 6 shows in schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig: 7 shows In schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig. 8 shows in schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig. 8A shows an enlarged view of a detail of Fig. 8;

Fig. 9 shows in schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig. 9 A shows an enlarged view of a detail of Fig. 9;

Fig. 9B shows an enlarged view of a detail of Fig. 9;

Fig. 10 shows in schematic form the part of the apparatus according to Figure 4 in a possible working configuration;

Fig. 11 shows in schematic form a part of the apparatus according to the present invention; Fig. llA shows an enlarged view of a detail of Fig. 11;

Figure 1 shows a slab of natural or artificial stone material, indicated generally by the reference number 12.

In the slab 12 the following may be identified:

- a visible surface 14;

- a non-visible surface 16;

- side edges 18, 20, 22, 24. The method for consolidating the slab 12 of natural or artificial stone material comprises the following steps:

a) sealing the non-visible surface 16 of the slab and, where necessary, the surfaces of the edges 18, 20, 22, 24;

b) positioning the slab 12 on a support surface 26, with the visible surface 14 directed upwards;

c) providing a compressible adhesive head 28 on the visible surface 14, in the vicinity of the perimetral edge of the slab 12;

d) distributing a resin 30 over the visible surface 14, in the zone bounded by the adhesive bead 28;

e) under vacuum conditions, arranging on top of the slab a sheet 32 of anti-adhesive material and then applying pressure on the bead and resin by means of a press: ram 50;

f) : restoring the atmospheric pressure;

g) hardening the resin 30; and

h) Smsh-niacbining the slab 12.

In the present description, the expression "sealing a surface" is understood as meaning sealing cracks, holes and porous zones so that the passage of fluid and in particular air across this surface is prevented.

In accordance with a possible embodiment of the present invention the step (a) of sealing the non-visible surface 16 of the slab 12 and optionally the surfaces of the edges 18, 20, 22, 24 comprises a step of preparing the non-visible surface.

The step of preparing the non-visible surface 16 of the slab 12 may comprise a step during which the slab is washed. Washing is performed preferably using a jet of water under high pressure (several tens of bars).

The washing step may be performed by means of nozzles connected to a circuit supplying pressurized water.

Then the non-visible surface 16 of the slab 12 undergoes drying, which may comprise a first drying step using fans, preferably hot-air fans, which may be positioned, so as to act on the top surface of the slab, i.e. surface not making contact, but also on the surface of the slab resting on the support surface. For this purpose, the fans may be positioned also underneath the conveying line and therefore underneath the surface.

Moreover, the drying step may comprise a second drying step performed by means of at least one infrared-ray or hot air oven.

In accordance with a possible embodiment of the present invention, in a downstream station repair of any macro defects of the non-visible surface, such as macro cracks or macro cavities, which may also affect the entire thickness of the slab 12, is performed. This repair may be performed in a manual or automated manner. Advantageously, the macro defects are sealed by means of resin (for example polyester resin) or a quick-setting viscous filler, reinforced where necessary with gauzes or granulated material. Then hardening - usually rapid - of the resin or filler must be allowed to take place. At this point sealing of any cracks or holes visible on the surface is performed by means of the application, using manual or automatic devices, of adhesive strips of sheets which are non-breathablc to liquids and the air.

Moreover non-breathable sealing of any cracks on the side edges 18, 20, 22, 24 of the slab is performed using an adhesive strip or filler,

Very often the slab may appear to be cracked and "weak"; in this case it is possible to perform sealing of the non-visible surface by subjecting this surface to a jteinfoccing step using matting after the drying step, this achieving both reinforcing of the slab and sealing of the surface.

The mat reinforcing and impregnation step comprises a first step during which a metered amount of resin is uniformly distributed over the surface which is to be reinforced with matting (non-visible surface) .

The apparatus may therefore comprise a station for detecting the shape and the dimensions of the slab 12 so that the resin may be distributed, depending on the actual shape and dimensions of the slab being processed, by resin distribution means. Detection may be performed for example by means of optical devices which are connected to a processing unit The distribution means may be, for example, directable nozzles which are controlled depending on the ^formation received from the processing unit

In accordance with a possible embodiment of the present invention, the distribution means apply uniformly onto the non-visible surface 16 of the slab 12 a metered amount of resin, preferably polyurethane or epoxy resin.

By way of example, a quantity of resin equal to about 100-000 g/m ² depending on the consistency of the matting, and preferably between 130 and 400 g/m ¹ , may be distributed over the surface.

A reinforcing element in the form of a fabric or mat is then deposited on the surface 16 on which the resin has been distributed so that the resin impregnates, at least partially, the reinforcing element.

In accordance with a possible embodiment of the present invention, the remfbrcing element may have a gram weight of between 100 and 600 g/m ² and preferably between 200 and 400 g/m ² .

Advantageously, for a reinforcing element with a gram weight of about 200 g/m ² about 150- 250 g/m ² of resin may be needed.

In accordance with a possible embodiment of the present invention, joining together of the reinforcing element and slab may be performed manually. The apparatus composes a station for supplying the reinforcing element The station may comprise first means for supporting a reel of reinforcing material in the form of a continuous strip, which are positioned above the line for conveying the flat supports with the slab 12, The station may comprise means for gripping and pulling along the reinforcing element, designed to be displaced above the slab to be reinforced -with matting. The gripping; and pulling means may be for example of the pincef type.

The gripping and pulling means may be designed to be displaced above the slab and therefore pull the reinforcing element along and on top of the slab.

In the vicinity of the downstream end of the slab, automatic cutting means may be provided for cutting the strip of reinforcing material in the transverse direction. The automatic cutting means may be, for example, a cutter designed to move in the transverse direction.

In accordance with a possible embodiment of the present invention the automatic cutting means are operated depending on the shape of the slab which has been detected in the upstream detection station.

Once it has been pulled along and cut, the mnfotcing element falls and test on top of the layer of resin applied beforehand on the surface of the slab.

At this point this reinforcing element is impregnated, at least partially, preferably by means of a manual or automatic rolling action.

The slab thus reinforced with matting is then subjected to a hardening step.

Hardening of the resin by means of heating may be performed inside a hardening oven and may last about 2-80 minutes, depending on the nature of the resin used, at a temperature of between 40 and 90°C, thus achieving non-breathable sealing of any cracks or through-holes.

Advantageously, hardening of the resin may occur at a temperature of about 80-100°C by means of contact application of a heated plate for a duration of about 2-5 minutes; alternatively it may be performed at a temperature of less than 60°C, and preferably between

40°C and 50°C, for a duration of about 80 minutes by means of heating with hot air.

Downstream of the hardening station the slab is removed from the flat support and normally cooled at room temperature.

Once the step of sealing the non-visible surface 16 and the edges 18, 20, 22, 24 has been completed, the step of impregnating the visible surface 14 of the slab 12 is performed.

With reference to Figure 1, the slab is deposited on top of a support surface 26 so that the top side is the visible side 14. The support surface 26 may be tor example a roller conveyor, as shown in Figure 1.

The visible side 14 may then be sized and/or smoothed if it is not perfectly flat. After the sizing and/or smoothing operation, the slab may undergo a washing step, for example using high-pressure water jets. The slab is then dried, for example in an oven at about 45-50°C for about 80 minutes so that the moisture due to the previous washing step is eliminated. Then, if necessary, any larger cavities are consolidated by means, for example, of stone granules fixed using a quick-setting glue.

The adhesive bead 28 is then applied on the visible surface 14 in the vicinity of the perimettal edge of the slab. In accordance with a possible embodiment of the present invention, the adhesive bead 28 is applied manually by an operator using an extruder.

Alternatively, the adhesive bead 28 may be applied using automatic means, such as a robotic ^' nozzle 38 (shown in Figures 1 and 1 A).

In this connection, the apparatus may comprise a station (not shown) for detecting the shape of the slab 12, so that the adhesive bead 28 may be distributed depending on the actual shape and dimensions of the slab being processed, via the robotic nozzle 38, Detection may be performed for example by means of optical devices connected to a processing unit

The adhesive bead 28 is formed using an adhesive material, such as a paste-like, hardenable, adhesive mastic Advantageously, the height of the adhesive bead 28 is between 2 and 3 mm. The adhesive bead 28 therefore defines a sealing path (in the manner of a containing shoulder) situated close to the perimeter of the slab, so as to create a kind of tank or tray inside which the resin 30 may be deposited.

Figure 2 shows the slab 12 where the step of preparing the adhesive bead 28 has been completed.

With reference to Figures 3 and 3A, step d), relating to distribution of the resin 30 over the visible surface 14 within the zone bounded by the adhesive bead 28, will be described below. According to a first embodiment: of the present invention, a uniform layer of resin, which has been deaerated previously, is distributed inside the tray formed in the previous step and consisting of slab 12 and bead 28, said layer having a thickness of about 0.3 - 0.5 mm and therefore being in an amount equal to about 300-500 g/m ¹ .

Advantageous^ the resin may be an epoxy or polyester resin.

Distribution of the resin may be performed by means of at leas t one dispensing nozzle 40. In accordance with an alternative embodiment of the present invention, the resin 30 is distributed on the visible surface 14 of the slab 12 inside an environment where a vacuum having a given residual pressure value is formed.

According to a possible embodiment of the present invention, the sheet 32 of anti-adhesive material to be positioned above the slab is prepared. The sheet 32 of anti-adhesive, preferably transparent, material is positioned inside an impregnation station 42 (see Fig. 5).

The sheet 32 may be made of polyethylene, polypropylene or PET, etc. The sheet 32 may have a gram weight of between 80 and 200 g/m ² .

The impregnation station 42 may comprise:

- a bell member 44, movable between a raised position which allows the passage of fluid between an internal zone thereof and the outside, as well as passage of the slabs 12 and the sheet 3¾ and a lowered position, in contact with the conveying surface 36, for example belt conveyor, where fluid is unable to pass between an internal zone thereof and the outside, and vice versa;

- a vacuum plant, comprising suction ducts 46, 48 which connect the plant to the inside of the bell member 44; and

- a press ram 50 movable vertically with respect to the bell member, the pressing surface thereof being provided with a conformable element 52.

The conformable element 52 is made of soft and/or elastic material, such as foam rubber (preferably with a smooth surface),

Advantageously, the ram 50 extends so as to cover the surface of the slab.

Among other functions, the conformable element is also able to compensate for any small differences in evenness and parallel alignment of the ram and the surface of the slab. In fact, the dimensions of the slabs may also be considerable, of the order of 220x360 cm, so that the ram, since it must have larger dimensions, is of a notable size. Moreover, it is evident that, during the lowering operation, there may be points of the ram, in particular where greatly spaced from each other, which are not at the same height so that the conformable element also has the function of compensating for these height differences.

In accordance with a possible embodiment of the present invention, the press ram 50 is designed to engage with the sheet 32.

According to the embodiment shown in Figure 4, the sheet 32 is moved by the conveying surface 36 inside the impregnation station and in particular inside the bell member 44.

Then, the ram is lowered so that the conformable element or mattress 52 comes into contact with the sheet 32 for engagement therewith. In accordance with a possible embodiment of the present invention, the ram and the conformable element 52 may be provided with air flow vents 54 connected to a vaojvnn-generating plant. Advantageously, the conformable element 52 may be porous and therefore the negative pressure produced for engagement with the sheet 32 may be obtained directly by means of the porous surface.

In this way the sheet 32, owing to the negative pressure created, is retained by the ram, as shown in Figure 5.

Alternatively, the ram may be provided with mechanical engaging means, such as pincers, suitable for gripping the sheet 32 along its contour.

According to further embodiments of the present invention, the sheet 32 may be electrostatically charged or provided with a thin layer of adhesive so as to adhere autonomously to the smooth bottom surface of the conformable element 52.

Thereafter, as shown in Figure 6, the ram 50 is raised together with the sheet 32 which adheres to the pressing surface of the conformable element 52, and the slab 12 together with the resin layer 30 enters into the impregnation station 42, With reference to Figure 7, once the slab 12 reaches the position inside the impregnation station, the bell member is lowered and the means designed to generate the vacuum with a given residual pressure inside the bell member 44 are activated. Advantageously, the residual pressure may be less than or equal to about 35 mbar. The air present inside the cavities and cracks of the slab 12, which is at atmospheric pressure, increases its volume, perforating the thin layer of resin and, Sowing out of the cavities, is. sucked out by the vacuum plant.

With reference to the embodiment of the present invention, in which the resin is distributed under vacuum conditions, it is evident that air under atmospheric pressure is no longer present inside the cracks and therefore, during the aforementioned step, there will be no air flow between the cracks and the vacuum plant

Once the bell member 44 has been lowered, the ram 50 is also lowered until the sheet 32 comes into contact with the adhesive bead 28 (Figures 8 and 8A). The conformable element 52 with the sheet 32 is pressed against the adhesive bead 28 which is compressed, and therefore the sheet 32 comes into contact with the resin 30 which is pressed over the whole surface and therefore made to penetrate inside the cavities and cracks (Figure 9, 9 A, 9B). Then the bead is further compressed until it reaches a thickness similar to that of the adjacent layer of resin.

Since the bead 28 is adhesive, the sheet 32 is glued along the adhesive bead 28, therefore forming a so-called hermetically sealed pocket composed of the visible surface 14 of the slab 12, the adhesive bead 28 and the sheet 32.

Thereafter the atmospheric pressure inside the bell member is gradually restored Consequently the sheet 32 exerts a thrusting force on the resin 30, which causes the resin 30 to be drawn inside all the holes and cracks present in the slab, owing to sealing of the opposite side. Adhesion of the sheet 32 against the bead 28 prevents any resin from corning out of the pocket.

As shown in Figure 10, the ram 50 is then raised, after first deactivating any vacuum systems or mechanical systems for engaging the sheet 32. In this way the sheet remains in adhering contact with die head 28 and the layer of resin 30, The bell member 44 together with the ram is then also raised.

In accordance with a possible embodiment of the present invention, after restoring atmospheric pressure inside the bell member, the pressure may be increased to a value greater than atmospheric pressure, so as to increase the pressure of the sheet 32 against the resin 30 and therefore the capacity for the resin 30 to penetrate inside the cracks of the slab.

Thereafter, once atmospheric pressure has been restored and the bell member raised, the slab is extracted from the impregnation station.

It is evident that, owing to the thrust produced by atmospheric pressure, the sheet pressed firmly against the bead 28 by the atmospheric pressure compresses the resin, forcing it increasingly inside the impregnated cracks, without die risk of any voids, the bottom side being well sealed in a non-breathable manner and the bead ensuring a perfect perimetral seal. The surface of the plastic sheet 32 which, during use, is directed towards die slab may be smooth.

According to an alternative embodiment, a dense grid of projections with a thickness of about 0.2 - 0.4 mm, directed towards the surface of the slab, may be provided. In this way it is possible to favour a minimum thickness of the resin passage over the entire surface of the slab so as to obtain a uniform distribution of the resin underneath the sheet acted on by the atmospheric pressure.

Advantageously die projections may have a diameter of about 2 mm. Moreover they may be in the form of spherical caps. In accordance with a possible embodiment of die present invention they may be arranged about eight every cm ² .

Advantageously manual rolling or rolling by means of a mechanical device may be then performed on the surface of the sheet 32. The rolling operation exerts a kind of massaging action on top of the sheet 32. Advantageously rolling may be performed by means of a mobile roller 56 (as shown in Figure 11).

In this way, the thrust exerted by the rolling massaging action on top of the sheet 32 allows the resin to be pushed from the zones with less porosity or cracks, where the resin could accumulate, to the zones with greater porosity or cracks, so as to obtain a uniform distribution thereof over the whole surface and ensure complete filling with resin of all the cavities, at the same time avoiding using an excessive amount of resin and thus lirniting the costs of the operation.

Thereafter hardening of the resin is performed. For this purpose the slab 12 may be inserted inside an oven at a temperature of 50-60 ^e C for a duration of about 80 minutes.

Once the resin has hardened, the sheet 32 is removed by means of a manual or automated peeling action, and smoothing and polishing of the visible surface is also performed. With this operation obviously the thin layer of superficial resin is removed.

The advantages compared to the methods and the apparatus of the prior art are therefore now evident.

Firsdy less resin is wasted since, owing to the formation of the lateral seal with the bead 28 and owing to the manual or automatic tolling operation, the resin may be conveyed into the zones where it is most needed.

The apparatus is therefore less complex, since complicated systems for extraction of the resin ate no longer necessary.

It is thus possible to obtain a process which is not overly complex and may be realized using an apparatus which is not too cosdy, ensuring optimum consolidation of the slabs with total vacuum impregnation of the cracks and porous zones using resin. Hie person skilled in the art, in order to satisfy specific needs, may make modifieations to the embodiments described above and/or replace the element described with equivalent elements, without thereby departing from the scope of the attached claims.