METHOD AND PLANT FOR PREPARING POWDERS TO FORM TILES OR CERAMIC PLATES
TECHNICAL FIELD
The present invention relates to a prearrangement method and a plant for forming tiles and plates, ceramics.
BACKGROUND OF THE TECHNIQUE Research in the ceramic sector currently aims to obtain products that imitate natural stone, such as marble and granite. These products are characterized by the presence of continuous veining or a random pattern that extends across the entire thickness of the plate. Such tiles or ceramic plates are produced by compaction, by hydraulic presses, by semi-dry atomization, ground or regranulated powders mixed in various ways together in a rearranged or random manner. Specifically, the powder mixtures are deposited by suitable means into the information cavities of rigid steel molds with which the presses are provided and then pressed to obtain the product. The same applicant has already conceived a method of tile formation which is described in the Italian patent application RE2001A000129. This method consists of depositing in the hopper, in a prearranged and / or random manner, a mixture of powders of different characteristics in such a way that a mass of powders having a veining deposited differently from the whole mass is generated in the hopper, the hopper has a discharge mouth of dimensions equal to the dimensions of the mold cavity in the forming press, both in the translational direction of the support and in the direction perpendicular thereto. Extract, in succession from the powder mass, portions that have, in the direction of translation of the support, a dimension equal to a fraction of the size of the mouth of the hopper, and in the direction perpendicular to it the same dimensions as the mouth of the hopper, so that a complete layer of powders is extracted from the dough; depositing the layer in an orderly manner in the interior of at least one cavity by means of the support and pressing the powders. The method described is implemented by a plant comprising a fixed hopper to contain a mixture of powders having marbled in imitation of a natural stone. With the lower mouth of the hopper, which has the same dimensions in plane as the cavity of the forming press, there is associated a movable means, such as a usual loading support, distributed to deposit in the cavity a succession of portions of dust extracted from the hopper, until the cavity is completely filled. EP 1110689 discloses a pressed tile press comprising a press mold within which a loading device (14,114) pours powder to be pressed. The loading device (14,114) comprises in turn a loading box (18,118) having a lower part (37,137) that opens on the basis of instructions and that runs between a loading position outside the press and a pouring position inside the mold, inside the press. The box in its loaded position is close to a medium (15,16,17,115,116,117) of entry into it of powder to be pressed and the lower part of the box, in its pouring position, is opened to pour the powder inside the mold. In one embodiment, the lower part of the box is made with a plurality of parallel plates (37) that change based on instructions, between a uniform closed position and an inclined pouring position. In another embodiment, the lower part of the opening is made with a sliding gate (137). WO 9823424 describes a method for pressing pulverized material to obtain tiles, comprising distributing powders (1) on a flexible conveyor means (3) and emptying the powders along a direction of advance through a station. (13) pressing that contains the powders in the conveyor means (3) by means of containment in the pressing station (13), pressing the powders (1) in the pressing station (13), characterized in that the containment means acts on the powders to be pressed during said advance and the containment means continues to act during the pressing. The compacted layer (14) is transferred to a mold means (4) and a portion (22) of the compacted layer (14) is cut and pressed by the descent of a punch (18) to the lower portion (19) in the mold means (4). Although it works well, the method and plant described in the above are not very versatile. In this regard, if there is a requirement for tiles of varying dimensions or large surface dimensions, they have drawbacks and disadvantages. This is because the perimeter of the lower mouth of the hopper, which coincides with the surface dimension of the mold cavity, is fixed. The current technology aims increasingly to obtain plates or ceramic tiles that have variable dimensions according to market requirements. Therefore, there is a very strong need for a more versatile plant and method that allows the tile or plate format to be changed quickly while avoiding prolonged interruptions during production which are typical of the known art, within the infrastructure of a simple and reasoned solution. The object of the present invention is to provide a method for forming ceramic tiles or plates, particularly but not exclusively in a continuous type press.
DESCRIPTION OF THE INVENTION This object is obtained by a method according to claim 1. According to a further aspect, the present invention provides a plant for forming ceramic tiles or plates having structural and functional characteristics in such a way as to satisfy the requirements mentioned above but at the same time eliminate the drawbacks set forth in the prior art, according to claim 3. The dependent claims define preferred and particularly advantageous embodiments of the method and plant of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS The additional features and advantages of the invention will be apparent upon reading the following description which is provided by way of a non-limiting example, with the help of the figures shown in the accompanying drawings, in which: Figure 1 is a schematic side view of a first embodiment of the plant according to the invention; Figure 2 is a front view of the plant of Figure 1 with the hopper shown in section; Figure 3 shows a second embodiment of the present invention; Figure 4 shows a method of using the plant of figure 1; Figures 5 and 6 show two applications of an alternative method of using the plant of Figure 1; Figure 7 shows a third embodiment of the present invention; Figure 8 shows a fourth embodiment of the present invention; Figures 9A-9E show alternative configurations of the discharge opening of the hopper of the present invention; Figure 10 shows a further embodiment of the plant of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION With reference to the figures, the reference number 1 indicates the totality of a plant for forming ceramic tiles or plates in accordance with the present invention. According to one embodiment of the present invention, the plant 1 comprises a receiving surface, which in the example is a conveyor belt 2, on which is placed a medium, indicated generally with the number 3, to feed a mixture of powders 33 to create a strip 100 of continuous or discontinuous powder on the web 2, a suction scraping system 4, a continuous pressing station 5 and a cutting station 6. The means for feeding a mixture of powders 33 comprises, in the example of Figure 1, three conduits 32 for feeding powders 33 of different characteristics or colors, a collection surface 31 for the powders and an impeller 30. The three conduits 32 are fed with powders 33 atomized by a feeding system, not shown, each duct 32 is fed with a powder 33 of a different color from the remaining ducts. Alternatively, several ducts 32 can be fed with powder of the same color or can be fed with a preformed mixture of powders of different color, with the proviso that the total ducts contain powders of at least two different colors. Although three feeding lines 32 are shown in the illustrated example, there may be a greater or lesser number if desired. The conduits 32 are individually slidably supported on guides 320 perpendicular to the axis of the conveyor belt 2. The powders 33 are deposited by the supply ducts 32 in a prearranged or random manner on the collection surface 31. The manner in which the powders 33 are distributed over the collection surface 31 can be controlled by modifying the timing and opening time of the various distribution conduits 32, which are provided with shut-off gate valves, not shown. For example, the typical veins of a natural stone plate can be reproduced by suitable horizontal trajectories which elaborate the conduits 32 to traverse above the collecting surface 31. However, it is possible to use fixed powder feed lines, although the use of movable ducts is preferable. The collecting surface 31 is placed substantially horizontally and preferably provided with opposed vertical side walls 36 for retaining the powders 33. The impeller 30, shown in section in the figures, is positioned transverse to the two side walls 36, above of the collection surface 31. The lower part of the impeller 30 is in contact with the powder receiving surface of the collecting surface 31 and can be moved between an extraction position and an advanced position operated by a means which is known and therefore not shown. The impeller 30 moves along the direction of movement of the underlying band 2. The impeller 30 can be replaced by a movable tray 301 (Figure 7) which pushes the powders 33 that are on the collection surface 31. At the free edge of the collection surface 31, that is, on the edge opposite that occupied by the impeller 30 when in the extraction position, there is a hopper 34 which receives the powders 33 driven by the impeller 30 when moving from its extraction position to its advanced position.
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The hopper 34 is located vertically on the movable receiving surface, which, in the example, is the band 2, with the loading opening 37 positioned adjacent the free edge of the collection surface 31 and the discharge opening 38 placed above of the band 2 in proximity to it, however avoiding direct contact with the surface of the band 2. Advantageously, the hopper 34 has a prismatic shape having two opposite faces substantially perpendicular to the direction of advance of the band 2, the faces are placed at a spacing nB "apart, substantially equal to the thickness" S "of the powder strip 100 to be compacted Preferably, as shown, the hopper 34 has the shape of a rectangular parallelepiped having 2 faces larger, that is, the front face 34a and the rear face 34B, normal to the direction of advance of the band 2 and placed at a distance B "equal to the thickness of the strip 100 of continuous powder which is get and then compact. The height of the hopper 34, (figure 1), which is just less than the distance between the collection surface 31 and the advance plane of the strip 2, is selected based on the dimensions of the floor 1 so that make sure that the powder 33 is present along the full width "L" of the discharge opening 38 (Figure 2). The distance "L" between the hopper faces parallel to the feed direction is equal to the width of the continuous powder strip 100 required, the height dimensions H are generally selected based on the width L of the hopper, and then they vary from 0.2L to 2L, preferably from 0.5L to 1.5L. According to a preferred alternative embodiment of the present invention, the lower end of the rear face 34b of the hopper 34 can be placed at a distance "hl" from the surface of the belt 2 between 0 and S (generally between 0 and 3 mm), where S is the required thickness of the powder strip 100 to be compacted, the front face 34a is placed at a distance equal to the thickness S of the powder strip 100 to be compacted (figure 7) . To obtain with the same plant 1 any thickness S 'of the powder strip 100 to be compacted, the front face 34a can be made movable along the powder advance direction to allow the distance B between the face 34a front and rear face 34b vary. Alternatively and equivalently, the rear face 34b of both faces can be made movable. In a further embodiment, the front face 34a or the rear face 34b are tilted away from a position perpendicular to the receiving surface to obtain a smaller discharge opening 38, wider than the upper loading opening 37 (Figures 9A-9D) . In this way, the distance between the front face 34a and the rear face 34b of the hopper 34, measured in the discharge opening 38 (equal to "B + d") is greater than that measured in the loading opening 37 (like a "B"), however, the distance wB + d "in the discharge opening 38 must be less than twice the distance between the discharge opening 38 and the receiving surface, preferably the difference" d "between the distance between the two faces 34a and 34b in the discharge opening 38 and that of the loading opening 37 should be between 0 and 5 mm, more preferably between 1 and 3 mm, as an alternative to the use of the hopper 34. having its vertical front face 34a and its rear face 34b completely flat, their faces may have their lower ends, which define the discharge opening 38, formed with radii of curvature Ri, Re (FIG. 9A) so as to be the exit of the powders 33 from the hopper 34 in the forward direction and in this way is avoided any The difference in flow velocity can be found with a hopper 34 with flat faces. Indicatively, the radius of curvature Ri of the front face 34a can vary from 0 to 2 times the thickness - of the strip 100 of powder to be compacted, and the radius of curvature Re of the rear face 34b, two to four times the thickness of the strip 100 of powder to be compacted. Other configurations are possible, such as that shown in Figures 9B, 9C in which the curvatures of the inner radii of curvature Ri and the outer radii of curvature Re are "backward" from those shown in Figure 9A, imposing a braking of the flow of the front face 34a of the hopper 34 and favoring the rotation, without excessive distortion, of the powders 33 leaving the hopper 34. In a further alternative, improved with respect to the previously described solution which ends of the front face 34a and the rear face 34b are both shaped with radii of curvature, the curved portion of the face 34a is replaced by a roller. 41 which rotates in the same direction as the outflow of the powders 33 and which has a radius Ri (FIG. 9F). The rotary roller 41 extends axially along the entire width L of the front face 34a, joining the discharge opening 38, and is positioned such that the revolving surface is tangential to the inner surface of the front face 34a and is separated from the surface of the strip 2 by a distance equal to the thickness S of the strip 100 of powder required. The distance "B" in the discharge opening 38 must be substantially equal to the thickness "S" of the powder strip 100 so that, by virtue of the roller 41, the powders 33 can be transferred advantageously over the web 2 while maintaining substantially unaltered the arrangement which is inside the hopper 34; this advantage is particularly useful when the arrangement is able to provide the powder strip 100 with a predetermined desired graphic appearance, for example typical natural stone grain. The rotary roller 41 can be freely mounted so that its rotation is induced by friction with the powders 33 as they pass from the hopper 34 to the belt 2. Alternatively, the roller 41 can be motorized and rotated in a manner that its peripheral speed is equal to, and in the same direction as, the forward speed of the band 2; this can be obtained by connecting the roller 41 to an independent meshing motor, or connecting it via a suitable transmission system to the driving members for the band 2. Finally, the rotary roller 41 can be braked, that is, it can be associated with a braking device for braking in relation to the flow-out speed of the powder 33 inside the hopper 34 and therefore in relation to the speed of the strip 2. Finally, in a further embodiment of the invention, it can be tilting the central plane of the hopper 34 with a predefined inclination "a" to the forward direction of the powder strip 100 to be compacted (Figure 9D). Particularly advantageous is the method in which the central plane is inclined for the conveyor belt 2 from the upper part downwards in the direction of advancement of the powder strip 100, ie with a "negative inclination ua" (FIG. 9E) In this case, the actual weight of the powders 33 in the hopper 34 acts substantially only on the rear face 34b, to advantageously reduce the mixing of the powder layers on the front face 34a, which are those that define the upper visible part of the strip 100 of dust coming out, accordingly, when the powder layers are placed in a prearranged distribution within the hopper 34 to provide the strip 100 with a required graphic appearance (eg natural stone veining) ), this mode allows them to transfer over band 2 and at the same time avoids excessive distortion In operation, with reference to figure 1, the supply conduits suitably polished for the powders 33 deposit by gravity the powders 33 contained therein on the collection surface 31, to reproduce the desired streaking. When the powders 33 have been deposited on the surface 31, the impeller 30 is driven from its extraction position to its advanced position to drive the mass of the powders 33 towards the hopper 34, placed vertically between the band 2, and then return to its extraction position and allow a new loading cycle for the powders 33. The mass of powders 33, when arriving at the hopper 34 by gravity, gradually sediments from the bottom thereof upwards, towards the discharge opening 38 . Since the distance between the discharge opening 38 and the surface of the conveyor belt 2 is equal to the thickness "S" of the powder strip 100 to be deposited, that portion of the powder mass 33 which initially descends, it is deposited directly on the band 2, which, in this case, represents the receiving surface for the powders 33. When the hopper 34 is full, the band 2 is advanced along the direction of advance, indicated by the arrow in the figures, so as to empty the hopper 34. The operations described in the above can be carried out either discontinuously (figures 4, 6) or continuously (figures 1, 5 and 7), this latter mode increases the productivity of the plant 1. In other words, the mass of the powders 33 deposited continuously in the hopper 34 reproduces, through its volume, a natural stone plate, which is vertically in a direction perpendicular to the strip 2. This plate, represented In practice, strip 100 of continuous powder is deposited on band 2 by gravity during the advance of the band., while maintaining the previously obtained distribution of the powders 33 within the hopper 34. Preferably, in a process part subsequent to the hopper 34 in the direction of advance of the web, the scraping system 4 is placed by suction comprising a device 40 customary for scraping the upper surface of the powder strip 100. Said suction system 4, schematically illustrated but not described in detail given that it is of the known type, allows a thin powder surface layer to be removed from the strip 100 in such a way as to clear the arrangement and contrast of the powders with colors different present in strip 100 of powder. The dust strip 100, guided by the
- band 2, then reach station 5 of continuous pressing, also of known type. The press station 5 comprises a compactor strip positioned above the conveyor belt 2 for compacting the powder strip 100 and obtaining a continuous compacted article.
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Essentially, compaction is carried out between the surface of the conveyor belt 2 and the surface of the super exposed parallel compactor belt 50. The dust strip 100 is retained laterally on the strip 2 by providing laterally, parallel to the direction of advance of the strip 2, a containment means which, in the example, are two side containment walls 35, only one of the which is visible in the figures. The containment walls 35 preferably extend until the completion of the compaction. The compaction carried out with the compactor strip 50 is sufficient to obtain a compacted article which does not require additional compaction, however, in certain cases the compaction forms a pre-compacted manipulable article designed for subsequent final compaction. At the end of the compaction the article is divided into plates of predefined dimensions in the cutting station 6 by usual cutting devices. In the illustrated example, the cutting station 6 comprises two rotating blades 60 for cutting in the perpendicular direction in. the direction of advance of band 2, and by. at least two additional rotating blades 61, only one of which is visible in the figures, for cutting the compacted article in the advance direction of the strip 2. Preferably, the described plant 1 is administered by a processor, not shown, the which controls its operation. According to an alternative embodiment, the plant 1 may have a double system for feeding the hopper 34 (figure 3). Essentially, towards the side of the hopper opening 37 of the hopper 34 there is an additional picking surface 31 ', which is also provided with feeding ducts 32' for the powders 33 'and a pusher 30', which are identical to those already described and which are located in a position symmetrical to it, around the axis of the hopper 34. With the means 3 and 3 'of double feeding can synchronize the operation of the two means to create a strip 2 of continuous powder on the band 2 which improves the continuity of the powder discharge from the hopper 34. According to a further preferred alternative embodiment, which is shown in figure 7, the feeding means 3 comprises, in addition to what already shown in the figure 1, a powder loading hopper 322 and a feed conveyor belt 321. In practice, both the basic colored powders of the dust-loading hopper 322 and the different color or nature powders originating from the conduits 32 fall on the conveyor belt 321 generally positioned horizontally with prearranged paths. controlled by adequate electronic control systems, not shown. The feed web 321 discharges the precharged powder in this manner onto the collection surface 31 for the powders 33. The feed web 321 can be fixed in one position or can be synchronized (or not synchronized) with the stroke of the impeller 30. Preferably, the plant 1 is provided with a second feed system 3 'totally similar to the preceding one and symmetrically placed therearound around a plane of vertical symmetry through the hopper 34 (figure 7). In addition, a head 400 loaded with multiple tubes is placed exactly above the loading opening 37 of the hopper 34, as is visible in Figure 7. This head 400 discharges directly into the hopper 34 without passing via the feed band 321 or impeller 30 (or tray 301) obtaining additional effects, in particular layers and veins which are very thin and pronounced in comparison with the powder mass. The method and the plant for forming ceramic tiles and plates of the present invention can also be used to deposit a layer 100 'of powder on the surface of a continuous monochromatic plate 200 (Figure 5) previously obtained using means known in the art., generally indicated by the numbers 7 and 8. Such known means of the art comprises, for example, a discharge duct 7, a hopper 70, a leveling roller 72 for regulating the thickness of the base plate 200 and a possible station. 80 distributed to provide light compaction to the material to avoid possible "remixing" of the base plate 200 with the powder layer 100 '. In this way, the grain effect obtainable by the method and the plant 1 of the present invention does not extend to the entire mass of the final plate but only through a part of the surface, obtaining a saving of colored powders, the which are more expensive than the base plate materials. Essentially, the mixture of powders 33 leaving the hopper discharge mouth 38 makes contact on the base plate 200 which, in this second case, represents the receiving surface for the powders 33. A further alternative is that shown in FIG. Figure 6, in which the powders present in the hopper are deposited discontinuously on a tile 201 previously formed by a first discontinuous pressing system 300. After applying the layer 100 'of surface powder, the tile 201 is transported by rollers 303 to a second pressing system, for example a discontinuous pressing system 302 (FIG. 6). In this case, as in the others of discontinuous operation, it is suitable to provide the hopper 34 with a gate valve, not shown, which can be closed when necessary to avoid the outflow of the powders 33 in the absence of a tile below the discharge opening 38. In the example shown in example 10, a loading tray 250 is used as the receiving surface, associated with a sliding support with reciprocating movement along a surface 340 for depositing a powder layer 120 within a cavity 320. extracted from the hopper 34, which will be compacted by usual means such as a die 350. The dimensions of the support 250 are such that they allow the loading of a powder layer 120 having a thickness S equal to the distance B between the faces 34a, b of the hopper 34. In this case the use of a suitable gate valve can be avoided by using, instead, a closure plate 330 extending from the rear of the holder 250 in such a way that closing the discharge opening 38 even when in its advanced position to deposit the powder layer 120 within the cavity 320. According to the invention, as shown in Figure 8, one of the faces (front 34a or rear 34b) of the hopper 34 may consist of a vertical portion of an endless movable strip 39 passing around three rollers, to accompany the material discharged therein, in a manner similar to that already described. Preferably, the peripheral speed of the web 39 is substantially equal to that of the web 2. Alternatively, the web 39 can transport agglomerated materials in the hopper 34 so that they are deposited on the surface of the powders 100 that are going to compact From the foregoing description, it will be apparent that the method and plant of the present invention allows requirements to be met while solving the drawbacks set forth in the introduction to the present disclosure with reference to the known art. In this regard, the method and plant of the present invention allows ceramic plates of a desired thickness to be formed continuously with patterns in volume reproducing the grain of the natural stone. In addition, the method and the relative plant allow the grain formed in the powder mixture present in the hopper to be transferred quickly and efficiently on the ceramic plate. In addition, the distribution of the powder mixture inside the hopper is retained to form the strip of powder to be compacted.