Patent Publication Number: US-2022234261-A1

Title: Mould for the production of slabs and relative forming method

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a mould for the production of slabs comprising from grits and/or sands of stone material bonded with a curing resin wherein the sheets have a substantially uniform thickness. 
     More in detail, the aforementioned slabs may comprise granulated material, stones or other substances reduced to small fragments, sands of stone material, quartz, etc., linked to a curing resin when subjected to the action of heat and/or in the presence of a catalyst. The present invention also relates to a production plant and a method for forming such slabs obtained by using the aforesaid mould. 
     BACKGROUND ART 
     The manufacturing of slabs consisting of grits and/or sands of natural stone material and of a binder such as a resin suitable for curing when subjected to the action of heat and/or in the presence of a catalyst is known. 
     Generally, the method for manufacturing these slabs provides for the production of a dough consisting precisely of a selected size granulated material and synthetic resin, which is deposited in quantities dosed on a conveyor belt which is advanced towards a forming station. 
     At this station, the dough is subjected to a vibro-compacting action which provides for the application of a vibratory motion of predetermined frequency under vacuum conditions, to remove any air trapped in the dough. Subsequently, the material compacted in this way is brought to a station for curing the resin. Before reaching the forming station, it is known to place a sheet or layer of protective material on the upper surface of the dough deposited on the conveyor belt. In this way it is prevented that the shutter of the pressing means may enter directly into contact with the dough, preserving its cleanliness and avoiding altering the characteristics of the upper portion of the dough. This method, although comprising a reduced number of steps, is not free from drawbacks such as the presence of shrinkages at the perimeter portions of the compacted material or, again, of an excessive over-thickness of the slab obtained at the end of the manufacturing process or of any flatness defects. In all the indicated above cases, subsequent mechanical processes are necessary, which inevitably have a negative impact on the production process, increasing costs. 
     Moreover, such problems derive from a non-optimal use of raw material, which in reality appears excessive in light of the formation of shrinkages or over-portions to be eliminated. Furthermore, the required mechanical processes determine a consequent consumption of tools for the operations of calibrating the slabs which involve a further increase in production costs. 
     There is a need in the sector to optimize the means available for the production of such slabs of grits bonded with resins as well as the relative production method. 
     OBJECTS OF THE INVENTION 
     The main object of the present invention is therefore to improve the state of the art relating to the manufacture of manufactured articles in slabs consisting of a granulated material or sands of stone material bonded with a resin and more specifically an improvement of the existing method and equipment. 
     Within the scope of this aim, an object of the present invention is to provide a mould for the production of slabs of grits bonded with resins suitable for overcoming the above described drawbacks of the prior art. 
     Another object of the present invention is to provide a mould for the production of slabs of grits bonded with easy-to-implement resins to optimize the productivity of preexisting systems. 
     A further object of the present invention is to provide a mould for the production of slabs of grits bonded with resins which are easy to actuate and use. 
     According to an aspect of the present invention, it is provided a mould for the production of slabs of grits bound with resins according to claim  1 . 
     The subject of the present invention is also a plant according to claim  9  and a method according to claim  14  for the production and forming of slabs obtained from grits and/or sands bound with curing resins. 
     The dependent claims refer to preferred and advantageous embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the detailed description of a preferred, non-exclusive embodiment of a mould for the production of slabs of grits bound with resins, illustrated by way of non-limiting example, in the appended drawings, wherein: 
         FIG. 1  is a detailed exploded perspective view of a general version of the mould for the production of slabs according to the present invention; 
         FIG. 1 a    is a detailed sectional view of an operative configuration assumed by the mould for the production of slabs according to the present invention; 
         FIGS. 2-12  are side views of a version of a plant for the production of slabs according to the present invention; 
         FIGS. 13-24  are side views of another version of a plant for the production of slabs according to the present invention; 
         FIGS. 25-36  are side views of a further version of a plant for the production of slabs according to the present invention; and 
         FIGS. 37-49  are side views of yet another version of a plant for the production of slabs according to the present invention. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows a general version of a mould  1  for the production of slabs of granular material and/or grits and/or sands bound with resins according to the present invention. For the sake of simplicity in the following description, the term grits means granulated material, stones or other substances reduced to small fragments, sands of stone material, quartz, etc., individually and/or in any size and combined together in various proportions. 
     The mould  1  defines a compartment  2  for a layer of a mixture  3  comprising grits bound with a curing resin to be compacted and subsequently cured in order to form a compact slab of uniform thickness. 
     Generally, the mould  1  has a bulk in a quadrangular or rectangular plan. 
     The attached figures show the mould  1  with a rectangular shaped plan, although it is understood that further conformations falling within the same concept of the invention are possible. 
     The mould  1  comprises a flat bottom  4  and a perimeter framework  5  which laterally delimits the flat bottom  4 . 
     The perimeter framework  5  is operatively connected to the flat bottom  4 . 
     The perimeter framework  5  comprises individual side walls  6 . 
     In the version shown in  FIGS. 2-12 , the mould  1  comprises fixed side walls  6  with respect to the flat bottom  4 . 
     Furthermore,  FIG. 2  illustrates the complete operative sequence which is characterized by a step of curing the slabs inside the mould itself. 
     Also in the version illustrated in  FIGS. 13-24 , the mould  1  comprises side walls  6  fixed with respect to the flat bottom  4 ,  FIG. 13  illustrates the relative complete operating sequence, which is characterized by a step of overturning the mould to extract the slabs from the mould and a step of curing the slabs without mould. 
     In the version illustrated in  FIGS. 25-36 , the mould  1  comprises fixed side walls  6  with respect to the flat bottom  4  and an extractor device for the extraction of the slabs from the mould. In the operating sequence illustrated in  FIG. 25 , it can be seen that, following the extraction of the slab from the mould  1 , the curing step takes place without a mould. 
     In the version illustrated in  FIGS. 37-49 , the mould  1  comprises side walls  6 , of which at least one wall  6  is tiltable with respect to the flat bottom  4  to allow the extraction of the slab. In the operating sequence illustrated in  FIG. 37 , it can be seen that the front wall is tilted substantially on the same plane as the bottom  4  to allow the extraction of the slab contained in the mould  1 , therefore the subsequent curing step takes place without a mould. 
     In all the versions, the mould  1  is of the rigid type, meaning that the material with which it is formed has a mechanical rigidity such as not to be subjected to deformations during use that could alter the shape, the flatness or in general the properties of the slab formed inside the mould  1  itself. 
     The walls that make up the mould  1 , i.e. the flat bottom  4  and the side walls  6 , have a controlled flatness. 
     Moreover, the flat bottom  4  and/or the side walls  6  have a controlled roughness to allow the production of slabs with specific surface characteristics. 
     The mould  1  can comprise a closing element  7  suitable for delimiting above the mould  1  itself. The closing element  7  is shaped as a flat slab. 
     More in detail, the closing element  7  has a footprint which is complementary to the area delimited between the side walls  6 . 
     Therefore, the closing element  7  can be introduced from above into the compartment  2 , delimiting it at the top. The closing element  7  can be configured to be operatively connectable to the upper punch of a vacuum vibro-compaction press of the layer of material contained in the mould  1 . 
     The mould  1  comprises a first protective sheet  8  covering the flat bottom  4  and the inner portion of the perimeter framework  5 . 
     In fact, the first sheet  8  defines a protection element interposed between the layer of the mixture  3  and the bottom  4  and the inner portion of the perimeter framework  5 . 
     Therefore, thanks to the presence of the first sheet  8 , the mixture does not come into direct contact with the lower and side walls of the mould  1 . 
     The mould  1  then comprises a second sheet  9  which can be positioned above the mixture  3 , which is introduced into the compartment  2 . 
     In use, the second sheet  9  is interposed between the uniform layer of the mixture  3  and the closing element  7 . 
     The second sheet  9 , in fact, prevents the layer of the mixture  3  from coming into direct contact with the latter. 
     The first sheet  8  and the second sheet  9  then define a casing in which the mixture of material to be compacted and cured is contained. 
     The first sheet  8  and the second sheet  9  can be made of paper or paper-based or of a suitable material able to withstand temperatures between 70° and 180°. 
     The first  8  and the second protective sheet  9  can be made with one or more materials selected from the group comprising: plain paper, paper with coatings having antiadherent properties, i.e. with silicone coating, polypropylene, etc., simple cardboard, cardboard with coating having anti-adherent properties, plastic films with anti-adherent properties, water-soluble films, etc. 
     With reference to  FIG. 1 , an exploded diagram of the mould  1  according to the present invention is shown, comprising a flat bottom  4  and the perimeter framework  5 , the first sheet  8 , the layer of the mixture  3 , the second sheet  9  and the closing element  7 . 
     In  FIG. 1 , the first sheet  8  and the second sheet  9  are shown shaped as tray elements to improve the intelligibility of the invention, although meaning that the first sheet  8  and the second sheet  9  can be flat and deformed as a result of the insertion in the mould  1  or provided pre-shaped according to the actual shape of the mould  1  without any limitation. 
     With reference to the detailed view illustrated in the attached  FIG. 1 a   , it can be seen that each of the side walls  6  can present a flaring  10  at the upper end. 
     More precisely, the flaring  10  can be realized at the inner surface  11 , in use, of the side wall  6 . 
     This flaring  10  defines a chute or a guiding and centring element suitable for facilitating the insertion of the first sheet  8 , of the second sheet  9  or of the closing element  7  inside the compartment  2 . 
     In particular, the flaring  10  performs its function with the side walls  6  vertically associated with the flat bottom  4 . 
     As mentioned above, in the version shown in  FIGS. 2-12 , the mould  1  comprises fixed side walls  6  with respect to the flat bottom  4 , and the operative sequence is characterized by a step of curing the slabs inside the mould itself. 
     According to the version of the present invention illustrated in  FIGS. 2-12 ,  FIG. 2  schematically illustrates a plant  12  for the production of slabs obtained from grits and/or sands in stone material bonded with resins that can be cured when subjected to heat or to a suitable catalyst according to methods known in the field. 
     The plant  12  comprises movement means  13 ,  18 ,  19  on which at least one mould  1  is arranged, suitable for supporting and moving the latter along the various stations of plant  12  itself. By way of example, the movement means  13 ,  18 ,  19  can comprise conveyor belts  13 ′ ( FIGS. 2-12 ). 
     However, further movement means  13 ,  18 ,  19  are possible, which are configured as a roller conveyor suitable for performing the same purposes, or other equivalent means suitable for supporting and transporting the mould  1  along the various stations of the plant  12  itself. In the upper line of  FIG. 2  it is possible to note the first steps of preparation of the mould  1  with the mixture  3 , preceding the vibro-compaction step, while in the lower line of  FIG. 2  it is possible to note, among other things, the step of vacuum vibro-compaction and the curing step. 
     The plant  12  has a loading station  14 , along which the at least one mould  1  is placed on the movement means  13  ( FIG. 3 ), a lower protection sheet  8  and the mixture  3  are inserted. 
     In a lower sheet insertion station  141 , a first sheet  8  is placed on the mould  1  ( FIG. 4 ), then in a die-cutting station  142  ( FIG. 5 ) it is shaped and laid above the flat bottom  4  of the mould  1  and a layer of mixture  3  is distributed on the first sheet  8  ( FIG. 6 ). 
     A further station (not shown) may also be provided for inserting additional material to the mixture  3  to obtain particular aesthetic effects. 
     The plant  12  then has a closing station  15  of the mould  1  comprising an upper sheet insertion station  151  in which the second sheet  9  is positioned above the mixture layer  3  ( FIG. 7 ) and a cover insertion station  152  in which is inserted the closing element  7  ( FIG. 8 ), in fact creating a sandwich of dough of grits and/or sands of stone material bonded with resin between two protective sheets  8 ,  9  contained in turn inside a rigid support—flat bottom  4 , perimeter framework  5  and closing element  7 . 
     The plant  12  comprises a compaction station  16  comprising a press  17  ( FIG. 9 ) for vacuum vibro-compaction of the mixture  3  contained in the mould  1 . The press  17  is configured to house the mould  1  inside a pressing chamber. 
     The press  17  for vacuum vibro-compaction of the mixture  3  is not the object of the present invention and therefore will not be described in detail. 
     The plant  12  comprises second movement means  18  located downstream of the compaction station  16  ( FIG. 10 ), on which the mould  1  has to be placed leaving press  17  itself and to transfer the mould  1  to other production steps. 
     The plant  12  comprises a curing station  20  comprising at least one drying/curing apparatus  21  ( FIG. 11 ), of a type known in the field, inside which the resin present in the mixture  3  is reacted to determine its curing and then obtain a slab of compact and cured material. 
     The second movement means  18  feed the mould  1  with the mixture  3  compacted towards the curing station  20  in which the mixture  3  becomes a cured slab  31 . 
     The plant  12  can therefore comprise a discharge station  22  ( FIG. 12 ) along which the moulds  1  are positioned with the cured slabs  31  leaving the curing station  20 , and therefore the moulds  1  with the slabs  31  are transferred through third movement means  19  ( FIG. 12 ) towards a station for extracting the slabs and a station for cooling to ambient temperature, in which the slabs are suitably moved and positioned vertically in a deposit rack (not shown). 
     In the versions of the present invention which will follow in the description, the components or production stations corresponding to those described for the previous version will maintain the same numbering, while the modified components or production stations will be indicated with the same reference numbers increased by one hundred. 
     In the version shown in  FIGS. 13-24 , the mould  1  comprises fixed side walls  6  with respect to the flat bottom  4  as in the previous version, while the operating sequence is characterized by a step of curing the mixture  3  without the mould. 
       FIG. 13  schematically illustrates a plant  112  for the production of slabs obtained from grits and/or sands in stone material bonded with resins that can be cured when subjected to heat or to a suitable catalyst as in the case of the above illustrated plant  12 . 
     The plant  112  comprises movement means  13 ,  18 ,  19 ,  23  on which at least one mould  1  is arranged, suitable for supporting and moving the latter along the various stations of the plant  112  itself. 
     Also in this version of plant  112 , by way of example, the movement means  13 ,  18 ,  19 ,  23  can comprise conveyor belts  13 ′ ( FIGS. 13-24 ), or roller conveyors, or even other equivalent means suitable to support and transport the mould  1  or a slab along various stations of the plant  112  itself. 
     The plant  112  comprises a loading station  14  and a closing station  15  of the mould  1 , substantially similar to the above illustrated version of the plant  12 . 
     In detail, in the loading station  14  the at least one mould  1  is placed on the movement means  13  ( FIG. 14 ); a first sheet  8  is then laid and punched above the flat bottom  4  of the mould  1  ( FIGS. 15 and 16 ) and, in turn, a layer of mixture  3  is distributed on the first sheet  8  ( FIG. 17 ). 
     As in the preceding version, a further station (not shown) may be provided for inserting additional material to the mixture  3  to obtain particular aesthetic effects. 
     In the closing station  15  of the mould  1  the second sheet  9  is positioned above the layer of mixture  3  ( FIG. 18 ) and the closing element  7  is inserted ( FIG. 19 ). 
     As in the plant of the previous version, it is obtained a sandwich of dough of grits and/or sands of stone material bonded with resin between two protective sheets  8 ,  9  contained in turn inside a rigid support—flat bottom  4 , perimeter framework  5  and closing element  7 . 
     The plant  112  further comprises a compaction station  16  comprising a press  17  ( FIG. 20 ) for vacuum vibro-compaction of the mixture  3  contained in the mould  1 . 
     Unlike the plant of the previous version illustrated in  FIGS. 2-12 , the plant  112  comprises a mould overturning station  24  provided with second movement means  18  positioned downstream of the compaction station  16  ( FIG. 21 ). 
     In the mould overturning station  24 , the mould  1  is overturned and the mixture  3 , with the two protective sheets  8 ,  9 , is extracted from the compartment  2  of the mould  1  and is sent starting from an insertion station  25  ( FIG. 22 ) of the mixture  3 , by means of third movement means  19 , towards a curing station  20  comprising at least one drying/curing apparatus  21  ( FIG. 23 ). 
     It should be noted that the mixture  3  is cured in the drying/curing apparatus  21  wrapped only between the two protective sheets  8 ,  9 , while the drying/curing apparatus  21  is completely similar to that of the previous version, but with the possibility of loading a greater number of groups formed by the mixture  3  wrapped in the sheets  8 ,  9 , due to their smaller bulk. 
     Therefore, after the extraction of the mixture  3  from the mould  1 , which took place in the mould overturning station  24 , it is possible to recover the moulds  1  and the closing elements  7  thereof which are sent, via transfer means (not shown), to the respective stations of relevance for later use. 
     Finally, the cured mixture  3 , which became a slab  31 , is sent, through fourth movement means  23  ( FIG. 24 ), to a station for cooling at ambient temperature, wherein the slab is suitably moved and positioned vertically in a storage rack (not shown). 
     Also, in the version illustrated in  FIGS. 25-36 , a mould  101  comprises fixed side walls with respect to the flat bottom  4  as in the previous version but has an extraction device which allows the mixture  3  to be extracted before the curing step. Consequently, also the operative sequence relating to this version is characterized by a step of curing the mixture  3  without the mould  101 . 
       FIG. 25  schematically illustrates a plant  212  for the production of slabs obtained from grits and/or sands in stone material bonded with resins that can be cured when subjected to heat or to a suitable catalyst as in the previously illustrated cases. 
     This version of the plant  212  comprises movement means  13 ,  118 ,  119 ,  23  on which to place at least one mould  101  or the mixture  3 , suitable for supporting and moving the latter along the various stations of the plant  212  itself, the aforementioned means may comprise conveyor belts  13 ′ ( FIGS. 25-36 ), or roller conveyors, or even other equivalent means able to support and transport the mould  101  or a slab along the various stations of the plant  212  itself. 
     The mould  101  differs from the previous versions with respect to the methods of extracting the compacted mixture  3  inside the mould  101  itself, as better described below. 
     The mould  101  also defines a compartment  2  inside which the mixture  3  is distributed and comprises a flat bottom  4  delimited by a perimeter framework  5 , which comprises vertical walls  6 . The mould  101 , see in particular  FIGS. 26 and 33 , also has an extractor device  102  comprising through openings  103  arranged on the flat bottom  4  and a support plate  104  vertically movable which can be provided with seats  105  and extractor members  126 . 
     Moreover, the plate  104  can be rested on the flat bottom  4  by means of abutments (not shown) of adjustable height which allow the plate  104  to be positioned at different height so as to obtain greater or smaller thicknesses of the mixture  3 . 
     The support plate  104  has a plan development equal to or slightly smaller than the area of the bottom  4  delimited between the perimeter framework  5 . 
     The support plate  104  has an upper surface  114  and a lower surface  115  parallel to each other. The upper surface  114  and the lower surface  115  are flat to favour the flatness of the slab to be formed inside the mould  101 . 
     As mentioned, the flat bottom  4  comprises multiple through openings  103  which are selectively engageable by the extractor members  126  to allow the lifting and removal of the support plate  104  from the compartment  2  of the mould  101 . 
     The support plate  104 , in fact, faces the through openings  103 . 
     As stated, the support plate  104  can have a plurality of seats  105 , each at a through opening  103 . 
     In particular, each seat  105  can face through a corresponding through opening  103  to be engageable by a respective extractor member  126 . 
     According to a version of the present invention, each seat  105  is made blind by way of the thickness of the support plate  104  and acts as a firm abutment for a corresponding extractor member  126 . 
     The presence of a plurality of seats  105  can favour the stable and safe extraction of the support plate  104  from the mould  101 . 
     The plant  212  of  FIGS. 25-36  comprises a loading station  14  and a closing station  15  of the mould  101 , substantially similar to the above illustrated version of the plant  12 ,  112 . 
     In the loading station  14  the at least one mould  101  is placed on the movement means  13  ( FIG. 26 ); a first sheet  8  is then laid and punched above the plate  104  of the mould  101  ( FIGS. 27 and 28 ) and, in turn, a layer of mixture  3  is distributed on the first sheet  8  ( FIG. 29 ). 
     As in the preceding versions, a further station (not shown) may be provided for inserting additional material to the mixture  3  to obtain particular aesthetic effects. 
     In the closing station  15  of the mould  1  the second sheet  9  is positioned above the layer of mixture  3  ( FIG. 30 ) and the closing element  7  is inserted ( FIG. 31 ). 
     It is obtained a sandwich of dough of grits and/or sands of stone material bonded with resin between two protective sheets  8 ,  9  contained in turn inside a rigid support support plate  104  and flat bottom  4 , perimeter framework  5  and closing element  7 . 
     The plant  212  further comprises a compaction station  16  comprising a press  17  ( FIG. 32 ) for vacuum vibro-compaction of the mixture  3  contained in the mould  101 . 
       FIG. 33  shows the station  124  for extracting the mixture  3  compacted and wrapped between the two protective sheets  8 ,  9 . 
     The extraction station  124  comprises second movement means  118  located downstream of the compaction station  16 , of the extractor members  126  which pass through the through openings  103  of the mould  101  and can be inserted in the seats  105  of the support plate  104 , and of the movement means  127  to move the mixture  3  with the two protection sheets  8 ,  9  from the extraction station  124  to the insertion station  125 . 
     The mould  101  arriving at the extraction station  124  through the second movement means  118  is positioned above the extractor members  126 . 
     First the closing element  7  is lifted by means of gripping means (not shown), then the aforesaid extractor members  126  are raised, pass through the through openings  103  of the flat bottom  4  and are inserted in the seats  105  of the support plate  104 , then they raise the plate  104  to the same height as the third movement means  119  of the insertion station  125 . 
     The movement means  127  then move the mixture  3  with the two protective sheets  8 ,  9  from the bottom plate  104  onto the third movement means  119 , which in turn feed a curing station  20  comprising at least one drying/curing apparatus  21  ( FIG. 35 ). 
     After the extraction of the mixture  3  from the mould  101 , which took place in the extraction station  124 , it is possible to recover the moulds  101  which are sent, via transfer means (not shown), to the respective stations of relevance. As for the previous version, the mixture  3  is cured in the drying/curing apparatus  21  wrapped only between the two protective sheets  8 ,  9 . 
     Finally, the cured mixture  3 , which became a slab  31 , is sent, through fourth movement means  23  ( FIG. 36 ), towards a station for extracting the slabs and a station for cooling to ambient temperature, wherein the slabs are suitably moved and positioned vertically in a storage rack (not shown). 
     In the version shown in  FIGS. 37-49 , a mould  201  has at least one of the side walls  6  which can be movably connected to the flat bottom  4  to selectively free at least one passage for accessing the inside the mould  201  and favour the extraction of the mixture  3  which is compacted and cured on the inside. According to a version of the present invention, the side walls  6  are operatively connected to the flat bottom  4  through hinge connections not shown in detail in the figures. 
     At least one of the individual side walls  6  can be tilted independently of the other side walls  6 , with respect to the flat bottom  4  between a horizontal position, in which the single side wall  6  frees an access passage inside the mould  201  and a vertical position in which the single side wall  6  defines a containment side for the mixture to be retained inside the mould  201 . 
     By tilting at least one side wall  6 , in fact, a passage is freed to allow the extraction of the layer of material formed inside the mould  1  itself. 
     According to a further version of the invention, not shown in the accompanying figures, at least one of the side walls  6  can be connected to the flat bottom  4  by means of a removable connection, such as a joint or the like, for the same purposes described  20  relating with the previous version. 
     According to a further version of the invention, not shown in the attached figures, the mould  1  can comprise at least one mechanism for opening and/or tilting at least one of the side walls  6 . By way of example, such a mechanism can be of the automatic, mechanical and/or electromechanical and/or servo-hydraulic and/or servo-pneumatic type. 
     The plant  312  of  FIGS. 37-49  comprises a loading station  14  and a closing station  15  of the mould  201 . 
     The at least one mould  201  is arranged on the movement means  13  with at least one side wall  6  open and resting on the movement means  13  ( FIG. 38 ); a first sheet  8  is then laid and punched at the top on the bottom  4  of the mould  201  ( FIG. 39 ) and, in turn, a layer of mixture  3  is distributed on the first sheet  8  ( FIG. 40 ). 
     As in the preceding versions, a further station ( FIG. 41 ) may be provided for inserting additional material  3 ′ to the mixture  3  to obtain particular aesthetic effects. 
     In the closing station  15 , the side walls  6  are closed arranging them in vertical position ( FIG. 42 ) and the second sheet  9  is positioned above the layer of mixture  3 ,  3 ′ ( FIG. 43 ) and the closing element  7  is inserted ( FIG. 44 ). 
     It is obtained a sandwich of dough of grits and/or sands of stone material bonded with resin between two protective sheets  8 ,  9  contained in turn inside a rigid support—flat bottom  4 , perimeter framework  5  and closing element  7 . 
     The plant  312  further comprises a compaction station  16  comprising a press  17  ( FIG. 45 ) for vacuum vibro-compaction of the mixture  3  contained in the mould  201 . 
       FIGS. 46, 47  show the station  224  for extracting the mixture  3  compacted and wrapped between the two protective sheets  8 ,  9 . 
     The extraction station  224  comprises second movement means  18  located downstream of the compaction station  16 , of the extraction means (not shown) of the mixture  3 ,  3 ′ wrapped between the two protective sheets  8 ,  9  and the third movement means  19 . 
     In the extraction station  224 , the closing element  7  is lifted by means of lifting means of the closing element  7 , and at least one side wall  6  is tilted by means of tilting means of the side walls  6  of the mould  201 , in the specific case the front wall  6  is tilted according to the advancement direction A of the mould  201  on the second movement means  18  ( FIG. 46 ). 
     The extraction means extract the mixture  3 ,  3 ′, wrapped between the two protective sheets  8 ,  9 , according to the advancement direction A of the mould  201  and position it on the third movement means  19 , which in turn send the mixture  3 ,  3 ′ towards the drying/curing apparatus  21  ( FIG. 47 ). 
     After the extraction of the mixture  3 ,  3 ′ from the mould  201 , which took place in the extraction station  224 , it is possible to recover the moulds  201  which are sent, via transfer means (not shown), to the respective stations of relevance. 
     As for the previous version, the mixture  3  is cured in the drying/curing apparatus  21  wrapped only between the two protective sheets  8 ,  9 . 
     Finally, the cured mixture  3 ,  3 ′ which became a slab  31  is sent, through fourth movement means  23  ( FIG. 49 ), towards a station for extracting the slabs and a station for cooling to ambient temperature, wherein the slabs are suitably moved and positioned vertically in a storage rack (not shown). 
     Among the advantages of the present invention it is possible to mention that, at the time of leaving the press, all the surfaces of the mixture  3  compacted inside the mould  1 ,  101 ,  201  are flat and smooth, without burrs. 
     As said, the rigidity of the mould  1 ,  101 ,  201  allows to obtain a compacted layer of mixture  3  which has perimeter surfaces, upper and lower geometrically free from defects of flatness or burrs. 
     In practice, by means of the mould  1 ,  101 ,  201  it is possible to obtain slabs of compacted material without surface shrinkages, in the context of a solution capable of optimizing production costs with respect to conventional compact sheet forming plants which, after the forming step, provide numerous and costly processes to recover the surface characteristics of the slab itself. 
     The above described mould  1 ,  101 ,  201  and the respective plants  12 ,  112 ,  212 ,  312  are susceptible to several modifications and variations within the scope of protection of the following claims.