A PROCESS AND PLANT FOR FORMING CERAMIC TILES AND THE LIKE

Abstract: The process for forming ceramic tiles comprises depositing a layer of multi-coloured powdery material on a moving transport plane, in order to achieve a predetermined pattern, and subsequently transferring said layer internally of a moulding cavity, due to a movement of the transport plane and a contemporary displacement of the transport plane with respect to the cavity. The forming plant comprises a conveyor belt (2) able on command to perform displacements with repect to the forming cavity. A plurality of silk-screening devices (9) is predisposed to deposit a layer of powdery material bearing a predetermined design on the transport plane. The invention can be especially useful in the production of decorated vitrified stoneware tiles.

Description: Description A Process and Plant for Forming Ceramic Tiles and the Like- Technical Field The invention relates to a process and a plant for shaping ceramic tiles and the like. The invention is usefully employed in the field of decorated vitrified stoneware tile production and the like. Background Art A main aim of the invention is to provide a process for forming ceramic tiles which economically and simply enables decorations to be made on tiles which are completely contained within the breadth of the tile itself. An advantage of the invention is that it enables complex but well-defined multicoloured patterns to be made. A fVjrther advantage is that decorations are obtained on the tiles which reproduce the exterior aspect of stone slabs. A further aim of the invention is to provide a plant for realising the above process. These aims and advantages and more besides are achieved by the invention, as it is characterised in the appended claims. The process of the invention comprises a first phase, wherein a layer of powdery material is deposited on a running conveyor surface. The layer of powdery material is multicoloured so as to give the layer a predetermined pattern or decoration. This is followed by a second phase wherein the deposited powder is transferred into a shaping cavity of a mould, by effect of a movement of the conveyor, which tips the powder from an edge of the conveyor itself; the powder being caused to fall into the cavity, maintaining however the pattern of before. There then follows a third phase in which the powder is pressed in the shaping cavity, before which, if so desired, the powder can be screeded in the cavity. The layer of powdery material formed on the conveyor surface and bearing the decoration is preferably screeded, using means of known type, even before being transferred into the shaping cavity. In a preferred embodiment of the invention, the first abovementioned phase, in which a decoration in the powder itself is achieved, is preceded by a number of operations in sequence, as follows: filling one or more shaped cavities distributed on a surface according to a predetermined design or decoration; compacting the powder material internally of said cavities; transferring the compacted material on to the moving conveyor, so that the surface of the conveyor is covered with a decorated layer of compacted material, on which more powder material is deposited, preferably not compacted, and either of one colour or several, which second layer covers the decorative compacted material, all of which is then deposited in the shaping cavity. The non-compacted material can be deposited on the conveyor before the compacted layer, if so desired, the whole then being deposited in the forming cavity. The distribution of the powder on the conveyor can be done so that the more aesthetically appealing face, i.e. the one bearing the decoration, is the lower face, but the opposite can also be achieved. The tile can be achieved with the more attractive surface facing either downwards or upwards. In the above-described process the decoration is included in the powder material before pressing and can be realised, at least partially, using pre-compacted material, which determines very special decorative results in the finished tile, reproducing the natural look of stone materials, such as marble, for example. In another embodiment of the above-described process, a fraction of the compacted material foraiing the decoration arranged on the conveyor surface can be broken. Said fraction of the material, due to the effect of the breaking, is detached from the part of the material which remains compacted and is arranged haphazardly at the edge of the compacted material. This technique gives the finished tiles an ornamental effect which is very similar to the irregularities normally found in stone materials. The material used for making the tiles is preferably constituted by a mixture or granules or powders, which, after firing, results in a product having the characteristics of vitrified stoneware. If so desired, a part of the tile breadth can be made using less aesthetically attractive powder; obviously the lower part, including the bottom surface, would normally be the one made with this less attractive material. After firing, the more attractive of the two faces can be further processed by sanding and buffing. The invention provides a decoration contained within the tile itself, as it exits from the mould and without any need to add material on the surface of the tile. Very detailed and well-defined patterns and colours can be obtained on vitrified stoneware tiles using the above-described process, without especially complicating the production cycle. The process also offers the possibility of obtaining patterns which very greatly imitate the natural appearance of marble and granites. The invention also enables production of tiles having the type of decoration known as "textured", i.e. with parts of the surface in relief, which can then be sanded away or left, as so desired. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of some preferred but non-exclusive embodiments of plants for realising the above-described process, illustrated purely by way of non-limiting examples in the accompanying figures of the drawings, in which: figure 1 shows a schematic side view in vertical elevation of a part of the plant in a first embodiment thereof; figure 2 is an enlarged-scale detail of figure 1 ; figure 3 shows a roller of figure 1, in a frontal view; figure 4 shows a second embodiment of a part of the plant; figure 5 shows a detail of a third embodiment of the plant; figure 6 shows a detail of a further embodiment of the plant in a vertical-elevation side view; figure 7 is a plan view from above of figure 6; figure 8 is a detail of figure 6 in enlarged scale. Disclosure of Invention With reference to the above-mentioned figures from 1 to 3, 1 denotes in its entirety a loading device for loading a ceramic tile mould with powder material. The mould, of known type and not illustrated, can be actuated by a press and is provided with a shaping cavity destined to be filled with powder material for pressing. The loading device 1 comprises a conveyor 2 having a closed belt 3 ring-wound about pulleys 4 and provided superiorly with a flat and horizontal transport surface 5. The conveyor belt 2 can on command perform movements relative to the mould forming cavity. In particular the conveyor 2 can be translated in a horizontal direction, indicated by the arrow 6 in figure 1, in both directions. At least one silk-screening device 7 is predisposed above the mobile transport plane 5, which silk-screening device 7 can deposit on the plane a layer of powdery material bearing a predetermined design or decoration. In the present example two rotary silk-screening devices 7 are shown, operating one after the other on the transport surface 5. A different number of silk-screening devices, of another type too, could be used instead. In the example shown in figure 1, each silk-screening device 7 comprises a cylindrical rotary screen 8 internally of which is situated a hopper 9 for feeding the powder material. One or more sections 10 of the screen 8 are preferably closed, letting no powder pass through. The length of the sections 10 depends mainly on the shape of the tile to be made. The layer of dust bearing the decoration can be deposited by moving the belt 3 under the silk screening devices 7, while the devices 7 themselves deposit the dust in such a way that the dust laid by a screen 8 is superposed on the dust laid by a previous screen 8. Means for regulating the advancement speed of the belt 3 are provided, so that the thickness of the material deposited on the belt through the screens 8 can be controlled. The silk-screening devices 7 can move transversally with respect to the advancement of the belt 3. In use, therefore, the dust can be deposited while the screens 8 themselves are moved transversally, which enables special decorations to be achieved. A hollow drum 11 is predisposed above the conveyor belt 2, upstream of the silk- screening devices; the drum 11 is rotatable in the direction indicated by the arrow 12, has a horizontal axis, and exhibits cavities 13 on its external surface, distributed according to a predetermined design. A hopper 14 discharging powdery material operates on the external surface 11a of the hopper 11, filling the cavities 13. A scraper 15 can be provided to remove excess powder from the surface 1 la of the drum 11, leaving only the powder contained in the cavities 13. A part of the external surface 1 la of the drum 11 is wound about by a belt 16 which is ring-wound or slidable on rollers or pulleys 17. The belt 16 holds the material inside the cavities 13, preventing exit therefrom. A first roller 18 with a tamping function operates on the external surface 1 la of the drum 11 so as to compress the powder in the cavities 13. The belt 16 is forced to pass between the drum and the tamper roller 18. When a cavity 13, full of powder, passes below the tamper roller 18, the material therein is compacted (see figure 2). A second roller 19, having an expelling function, operates internally of the drum 11 to press the surface of the drum outwards, favouring the release of the powder contained in the cavities 13 above the belt 16. During the rotation of the drum 11, when a full cavity passes in proximity of the expeller roller 19, the compacted material inside is deposited on the belt 16. Thus a shaped decorated or patterned compacted material is deposited on the belt 16. Both the tamper 18 and the expeller 19 are preferably convex is shape, as shown in figure 3. The belt 16, which moves continuously, deposits the design on the upper transport surface 5 of the conveyor belt 2. The compacted material, by effect of the transport surface 5 advancement, passes below the silk-screening devices 7, which deposit on the powder material a layer of powdery material which may exhibit another predetermined design or decoration. A screed, of known type and not illustrated, can operate on the transport surface 5, after the silk-screening devices, to level the layer of powdery material deposited on the surface. The shaping cavities of the mould will be filled by causing the abovementioned layer to fall from the edge of the transport surface by effect of the movement of the surface itself and a contemporaneous movement of the conveyor belt 2 with respect to the shaping cavities. Once the shaping cavity is filled, the powders are pressed to produce an unfired tile whose better surface, which will be the face of the tile, will be the product of a pattern that is not merely superficial but which is contained within the breadth of the tile itself. In figure 4 a second embodiment of the invention is shown, in which at least one silk screening device 27 is provided with a flat screen 28. A horizontally-mobile hopper 29 distributes the powder. The material can be deposited through the screen 28 both with the belt 23 still and the hopper 29 in movement and with both the belt 23 and the screen 28 in movement. In the example of figure 4 the blind cavities, where the tamping of at least a part of the decoration is carried out, are made on a belt 30 wound on pulleys 35 and 36 and comprising an upper horizontal tract on which a hopper 32 deposits powdery material. A scraper 33 can be provided to remove excess powder, leaving only the powder inside the cavities. In this case the tampers, which tamp the powder down in the cavities, comprise two counterposed rollers 34 between which the belt 30 is made to move. The expellers, which transfer the compacted design on to the transport surface 25, are realised using the same pulley 35 about which the belt 30 affording the cavities is wound. The pulley 35 is preferably convex, like the roller 19 of figure 3, while the other pulley 36 is preferably concave at its centre. In a third embodiment of the invention shown in figure 5, means for transferring the compacted powder from the cavities to the conveyor belt. In this case a belt 40, bearing the cavities in which the powder which will form the final pattern is tamped down, is wound on a drum 41 which is rotatable on command, and an idle roller 42 is predisposed between said belt 40 and the drum 41. The belt 40 runs on the roller 42 which is distanced from the drum 41. A further belt, denoted by 43, partially winds about the drum 41 and the belt 40. The belt 43 carries out essentially the same functions as the belt 16 of figure 1. A tamping roller 44 compresses the powder previously deposited in the cavities of the belt 40. The action of the roller 42 on the belt 40 favours the release of the compacted powder and its laying on the underlying belt 43. Figures from 6 to 8 show means for depositing powder material on a conveyor belt 50, in a further embodiment of the invention. The means comprise one or more distribution conduits 51 , arranged one after another, each having an oblong outlet mouth 52 situated above the belt 50. Each conduit 5, which extends more or less vertically, can perform on command a movement in a transversal direction 53 to the advancement direction of the belt 50, as well as a rotation movement, shown by arrow 54, about a vertical longitudinal axis x, so that the outlet mouth 52 can be oriented selectively with respect to the advancement direction of the belt. If the outlet mouth 52 is arranged with the longer part directed the same as the advancement direction of the belt, the powder which exits from the mouth will be deposited on the belt so that it occupies a fairly narrow space thereon, while if the outlet mouth 52 is arranged with the longer sides directed perpendicular to the belt advancement direction, the deposited powder will occupy a wider space thereon. Thus, simply by rotating the conduit it is possible to vary the width of the powder deposited on the belt, obtaining a varied decoration which, on the finished tiles, recalls the appearance of a natural stone slab. Each distribution conduit 51 is provided, at the outlet mouth 52, with means for intercepting the powder, by means of which the delivery rate of the powder can be controlled at the outlet. The means for intercepting can comprise a mobile obturator 57 which on command can control the section of the passage through which the powder has to pass on exit from the conduit 51. An oscillating blade 58 is arranged internally of the conduit 51 and can be commanded to move altematingly in a vertical direction, thus preventing blockage of powders in the conduit 51. The conveyor belt 50 can perform controlled movements in both directions. The control of the belt 50 serves to produce infinite combinations of patterns and decorations in the powders thanks to the equally infinite movements the belt and the conduits 51 are capable of. The means for controlling, of known type and not illustrated, synchronically govern both the belt drive and the conduit 51 movement organs. During functioning the decoration is in fact created by predetermined sequences of movement of the conduits 51 (lateral displacements either to the left or right, and rotations in both directions about respective longitudinal axes x) and the belt 50 (running forwards or backwards).

Claims: Claims. 1). A process for forming ceramic tiles and the like, comprising: a first phase in which a layer of powdery material is deposited on a mobile transport plane (5, 50), in such a way that said powdery material exhibits a pattern; a second phase wherein said layer of powdery material is transferred internally of a foraiing cavity of a mould by effect of a movement of said transport plane (5, 50), which causes the powdery material to fall from an edge of the transport plane (5, 50), and by effect of a contemporaneous displacement of said transport plane (5, 50) with respect to the cavity, so that said powdery material is caused to fall internally of the cavity and is deposited in the form of a layer and still exhibiting said pattern; and a third phase in which the powdery material deposited in said cavity is pressed. 2). The process of claim 1, wherein said first phase comprises: filling one or more shaped cavities distributed according to a predetermined design with powdery material; tamping said powdery material internally of said cavity or cavities; fransferring said material, after tamping, on to the mobile transport plane (5), so that a compacted patterned powdery material is deposited on said transport plane (5). 3). The process of claim 2, comprising a laying of further powdery material on said compacted patterned material, said further material being preferably not compacted, in order to achieve a layer covering said pattern of said patterned material. 4) A plant for forming ceramic tiles and the like, of a type comprising a mould, functioning by means of a press, provided with a shaping cavity destined to be filled with powdery material to be pressed, and further comprising a loading device (1) of the mould, wherein said loading device (1) comprises: at least one conveyor belt (2), provided superiorly with a transport plane (5, 50), which can be commanded to move, performing displacements with respect to said forming cavity; and means for depositing on said transport plane (5, 50) a layer of powder material bearing a predetermined pattern, said forming cavity during functioning receiving said layer of material from the transport plane (5, 50) by force of gravity and by effect of a movement of the transport plane (5, 50) and a displacement of the conveyor belt (2) with respect to the foπning cavity. 5). The plant of claim 4, wherein said means for depositing comprise at least one silk-screening device (7, 27) or, preferably, a plurality of said devices (7, 27) for operating one after another on the transport plane (5) in order to deposit several layers, one laid on top of another. 6). The plant of claim 5, wherein at least one of said silk screening devices (7) comprises a tubular screen (8), which is able to rotate about a longitudinal axis thereof and inside which means for supplying powdery materials (9) are located. 7). The plant of claim 5 or 6, wherein at least one of said silk-screening devices (27) comprises a flat screen (28) on which the means for supplying powdery materials (29) are predisposed, said screen (28) and said means for supplying (29) being reciprocally mobile. 8). The plant of any one of claims from 4 to 7, comprising: an endless moving surface (1 la, 30, 40) affording one or more cavities (13); means for filling said cavities (13) with powdery material destined to form a tile; means for compacting said powdery material in said cavities (13); and means for transferring the compacted material from the surface having the cavities (11a, 30, 40) to the transport plane (5). 9). The plant of claim 8, wherein said means for compacting comprise at least one pressing roller (18, 34, 44) for pressing against said surface having cavities (11a, 30, 40). 10). The plant of claim 8 or 9, wherein said means for transferring comprise an element (19, 35, 42) which operates internally of said surface having cavities (1 la, 30, 40) and flexes said surface having cavities externalwise. 11). The plant of claim 10, wherein said element comprises a roller (19) internal of and tangential to a drum (11), an external surface (11a) of which drum (11) affords said cavities (13), the roller (11) being preferably convex at a centre portion thereof. 12). The plant of claim 10 or 11, wherein said surface having cavities (40) is at least in part wound on a rotating drum (41) and that said element (42) is arranged between said surface having cavities (40) and said drum (41). 13). The plant of any one of claims from 8 to 11, wherein said surface having cavities (30) is wound about pulleys (35, 36), said element (19, 35, 42) preferably comprising one of said pulleys (35). 14). The plant of any one of claims from 8 to 13, wherein said means for filling comprise a hopper (14, 32) for unloading the powdery material on said cavities (13) and a scraper (15, 33) for removing excess material. 15). The plant of any one of claims from 4 to 14, wherein said means for depositing comprise at least one distribution conduit (51) for the powdery material, provided with at least one outlet mouth (52) situated above the transport plane (50) and further able to perform on command movements in a transversal direction to the advancement direction of the transport plane. 16). The plant of claim 15, wherein said outlet mouth (52) is oblong and said conduit (51) is able to rotate so as to vary an orientation of the outlet mouth (52) with respect to a movement direction of the transport plane (50).

Inventors: FRANCESCHINI ALBERTO, FRANCESCHINI, ALBERTO
Applicants: FRANCESCHINI ALBERTO, FRANCESCHINI, ALBERTO
Application year: 1998
Main classification: B28B13
IPC codes: B28B13