Method and means for transfer of granular materials

Abstract: Transfer means of granular material (15) includes a permeable baffle (33) through which a fluid acts on said granular material; it further comprises a thin belt (31) on which the said granular material lies, said thin belt being unwound from a coil (39) arranged upstream the pressing station and being rewound in coil (39) downstream the said pressing station; a method to prepare a layer of powders designed to be pressed in form of ceramic tile comprises the following steps: arranging on a support surface superimposed layers (310,312) of different powders; acting with a fluid on said superimposed layers of different powders to mix them with each other along a vertical direction.

Description: The invention relates to a method and relative apparatus for transferring in a controlled manner granular material on a support; in particular, the invention can be applied to the manufacturing of ceramic tiles to add on or take from them granular material. In the context of the present description granular material means a loose product capable of flowing, constituted by powders, granules of any form and dimension, scales, small tesserae or any mixture of said pieces. IT-B-1268908 discloses a system for decorating objects with a powdery decorating product, in which the decorating product is made to pass through the meshes of a silk-screen and is deposited on predetermined areas of a surface to be decorated. PCT/EP94/04291 discloses a system in which a decorating product, in a powdery state, is incorporated in shaped cavities of a transport belt and is projected from the belt onto a surface to be decorated. These systems provide for the decorating product being incorporated in a suitable transfer means, i.e. a silk-screen or a belt, and then ejected from said transfer means; so wear of the silk-screen and changes in the granulometry of the decorating product have been found due to the sliding of the product on the transfer means; furthermore these systems are not suitable for treating granules having large dimensions. A problem occurring, when a layer of powders to be pressed is decorated, is the change of the layer thickness, which leads to a non-uniform pressing; the same problem occurs when the tile is to be shaped with a relief structured surface. Therefore there is a need to change the thickness of a layer of powders to be pressed in order to obtain a uniform pressing. A purpose of the present invention is to improve the known decorating machines, particularly to make possible to reduce the strengths on the particles of decorating product, to change and control the thickness of decorating product to be applied, and to reduce wear of the silk-screens and/or the dies used, all that causing variability of the results. An other purpose of the present invention is to make possible to decorate a support even with rough granular materials, preserving a good definition and without the need to recover the material distributed in excess. A further purpose of the present invention is to make possible to change the thickness of a granular material layer in an easy and controllable way in order to obtain decorating effects on it. Furthermore there is the problem of transferring the granular material to the mould for pressing ceramic tiles in a controllable way, i.e. by arranging in any way in the thickness and in the surface regions different granular materials even according to well defined patterns. This requirement is particularly felt mainly after the recent sales-success of the so-called products of "porcelain gres", requiring the whole aesthetic effect of the surface is obtained during pressing without the aid of a coating applied later by glazing. Therefore there is a problem in reproducing well defined and controllable decorations with granular material, complying with a high productivity, and without generating differences in the thickness of the layer to be pressed. Different technologies have been taken into account to solve the above problem but all with remarkable difficulties of application. A first technique described in IT-B-890769 was to use multiple loading carriages, but, said technique did not allow to obtain the required aesthetic effects and, in addition, extended substantially the pressing cycles. IT-B-1146358 discloses a rotating die multiple mould press; in this case, even if there is the possibility of obtaining fair aesthetic results, remarkable financial commitments are required, special presses being required to be used. Furthermore the moulds are very bulky, expensive, complicated and it is almost impossible to use multiple parallel imprints. A further system consists in the use of a double pressing: in the first pressing a semi-finished piece is obtained on which the decorating granules are to be spread and then the whole is subjected to a definitive final pressing; this technique, besides some restrictions in the aesthetic result, involves the use of a second press, that is somewhat onerous, complicated and not always possible due to space reasons. Furthermore belt loading systems are known; these ones however do not ensure a controlled distribution of the granules because the filling of the mould space takes place with a certain displacement due to uncontrolled fall of the granules themselves, or, in other cases, there is an excess of granules around the mould that need to be collected and recycled. Among the different technologies aimed to solve the said technical problem, a technology uses a decorating image under the form of decalcomania which is included directly into the tile pressing mould: this technology is described for example in the Italian patent 1287519 for industrial invention. This method allows to have a good definition of the decoration but involves a considerable increase of the costs because, first of all, the insertion of the decalcomania into the mould has to be done before or after the insertion of the powder constituting the tile body; more operations are therefore needed to load the mould which increase greatly the duration of the working cycle. On the other hand, the cost is further increased because said decalcomanias have to be previously prepared by specialised external companies with all the consequent problems for supplying, transporting, storing, etc. It is an object of the present invention to overcome and solve the problems just described, i.e. to permit the insertion of a decorating layer, for example a decalcomania, into a pressing mould at the same time as the powder constituting the tile body is inserted, with working cycles substantially equal to the cycles for a normal tile without decorations. An other object of the present invention is to allow said decalcomania to be obtained directly during the production cycle related to the pressing. A further object of the present invention is to obtain an apparatus, which may be applied to the more widely used presses for forming ceramic tiles, i.e. presses having moulds with lower die, side die and punch always in axis, said apparatus allowing, during a production cycle with single pressing, a filling of the mould space without relative displacements among the granules, i.e. allowing different granular materials to be introduced into the mould in a single filling operation, even according to patterns well defined in the stratification and at the surface, without the presence of excess of powder to be recycled and without loss of productivity. Being the decorations constituted by a number of layers of powdery decorating materials overlapping one another, a further drawback is that, due to the wear caused by the trampling on the tiles of the floor, the materials that form the upper layers are removed in a more extensive manner than the lower layers, the appearance of the decoration being so changed. This drawback is still more serious when, as a result of polishing (as it occurs often), a large quantity of the surface layers is removed, which involves an unacceptable change of the aesthetic appearance. In an attempt to resolve this last problem, the industrial patent application RE96A000004 proposes a method for transferring at the inside of the mould cavity the superimposed layers of the decorating powders, causing them to fall, by gravity, from the end of a conveyor belt and to mix with each other during the fall through sliding over some deviating baffles. This method presents a first drawback because this operation may be performed only on the layers of the decorating powders, so that the basic layer has to be previously introduced into the mould. Therefore, with usual fixed presses, two distinct mould loading phases are required, largely extending the working cycles. Furthermore, with such a method, it is not possible to introduce at the same time also the basic layer, because the decorating powders would be mixed through the full thickness of the tile, and widely spread. A second drawback consists in the fact that, however the belt roll is small and the fall distance short, a wide spread of the powders will be present in any way, not permitting an acceptable pattern definition. A further purpose of the present invention is to improve the described technology in order to overcome its drawbacks, first of all, to allow a mould to be loaded in only one loading operation, with a well defined and controlled stratigraphical and plan arrangement of different powders and then with the possibility of mutually mixing along a vertical direction the different layers of powder in a controlled and selective way, i.e. just only in a portion of the thickness or in a selected portion of the plan surface. WO 98/11996 discloses an apparatus and a method for laying down a continuous, predetermined pattern of granular material upon a substrate. A rotating drum is provided, comprising a drum wall defining a limited retention region under vacuum, and a plurality of through-apertures arranged according to a desired pattern. Granular material, collected from a hopper located along a descending portion of the drum, is kept adherent to the. drum surface by vacuum. After removal of excess granular material, the vacuum is discontinued causing the granular material to disengage from the drum surface and pass, by force of gravity, onto the surface of the substrate moving relative to the drum according to the desired pattern. In a first aspect of the invention, transfer means is provided arranged for transferring a granular decorating material, including screen means so configured as to move said granular decorating material from a collecting region to a discharging region along a path partially surrounding suction chamber means containing an operating fluid which acts on said granular decorating material through said screen means, said path comprising an ascending portion and a descending portion, said suction chamber means facing said screen means along a substantial portion of said ascending portion adjacent to said collecting region, so as to allow said granular decorating material to be raised adherent to said screen means from said collecting region. In a second aspect of the invention, a method for transferring granular decorating material from a collecting region to a discharging region is provided, comprising acting with an operating fluid on said granular decorating material causing said operating fluid to pass through permeable regions of screen means, said acting comprising lifting said granular decorating material from said collecting region along an ascending portion of said screen means adjacent to said collecting region. The invention would be better understood and carried into effect with reference to the enclosed drawings, which illustrate embodiments of the invention that are exemplifying but not limiting, where: Figure 1 is a vertical section of a decorating apparatus; Figure 2 is a vertical schematic section of an apparatus for transferring granular material; Figure 3 is an enlargement of the detail highlighted in the frame A of Figure 2; Figure 4 is a vertical schematic section as in Figure 2, but concerning a different embodiment. Figure 5 is a schematic side view of an apparatus according to the invention in an application to mutually mix different layers of superimposed powders. With reference to Figure 1, a hopper 1 containing. a flowable decorating product 2, for example a granular or powdery product, is provided with a lower opening 3 kept adherent to a side of a selective screen 10, arranged above a support 4, movable along a direction F. The screen 10 is provided with barrier regions, that is regions through which the transport fluid can not pass, and regions 12 permeable to the transport fluid, through which the transport fluid can easily pass and act on the product 2. The screen 10 is flexible, so that it can be wound on roller means. The screen 10, for example, can consists of a usual silk-screen with any pattern defined by the permeable regions 12. At the side of the screen 10 opposite to the side which is kept adherent to the opening 3, suction means maintain, in a chamber 19, an enough pressure drop p- to assure the adherence between the particles of the product 2 and the screen 10 at the permeable regions 12 thereof. The screen 10 is wound on a pair of rollers 20, through which the air can be sucked, and on a roller 21, external to the chamber 19, defining, together with one of the rollers 2, a horizontal path stroke for the screen 10. When moving along the direction Q, the screen 10 passes under a wall 22, surrounding the chamber 19 under pressure drop, and beyond which the product 2 is no more kept adherent to the screen 10 by the pressure drop p- and falls on the support 4, decorating it. With reference to the Figures 2 and 3 a screen 31, constituted by a weft of wires 32 forming a endless belt, leans, in a portion of its route, against a permeable wall 33, consisting of a wall provided with a number of through holes 34; the screen 31 having permeable regions 36 and non-permeable regions 37. The permeable wall 33, together with other non-permeable walls 35, surrounds a chamber 38 into which a pressure drop P- is kept by known means, not shown. In the portion of the route not in contact with the permeable wall 33, the screen 31 is wound on rollers 39 capable of moving the screen 31 sliding on the permeable wall 33, in a controlled and synchronised manner with an underlying support 40, In the upper side there is a container 41 having inside the granular material 42; at the bottom, said container is provided with an opening leading near to the screen 31 in the route portion where the chamber 38 is present: in this portion therefore, the granular material will be attracted by the permeable regions 36 of the screen 31 and here will stay adherent for a certain thickness S. In order to avoid an undesired dragging of granules 42 over the not permeable regions 37 of the screen, it is advantageously provided that, near the collecting region 43 from the container 41, the active side of the screen 31, designed to adhere to the granular material 42, is turned downwards. The collected granular material that rises adherent to the screen 31 will be automatically and continuously replaced' by natural sliding fall from the container 41. Over the collecting region 43, can be advantageously placed a scraping blade 44 in order to level the layer of granular material 42. Along the whole downward route of the screen the granular material 42 is kept adherent due to the presence of the chamber 38 in pressure drop, while, downwards, near the support 40, the granular material remains on the support 40 due to lack of pressure drop and gravity effect; the transfer can be aided through the action of other means as for example a body 45, having a suitable vibration and in contact to the screen 31. Before the rollers 39 a cleaning system of the screen 31 can be advantageously placed, for example a sucking mouth 46. The screen 31 can work away from the support 40 but may also work in contact with it. This second possibility is very advantageous when said support 40 is constituted by a layer of another granular material in this case the granular material 42 will penetrate into the support 40, keeping it levelled and furthermore the pattern will result better defined due to the absence of falling and sliding of said granular material 42. Said penetration can be achieved by forcing said material 42 into the levelled support 40, in such a case the granular material 42, displacing automatically the other granular material of the support 40, replaces it and keeps it levelled, or said penetration can be achieved introducing said granular material 42 into cavities 49 already provided in the support 40. As represented in Figure 4, the invention is used to take in a selective manner granular material from an underlying support 40; in such a case the taken granular material 47 can be easily recycled causing it to fall into an upstream distributing device 48; this use is particularly useful to modify in a controlled manner the thickness of a layer of granular material, or to obtain said cavities 49, in which a different material may be introduced. It is pointed out that the invention allows an effective control of the dosing of the granular material simply regulating the pressure drop level in the chamber 38; for example, using: a screen 31 with 1296 meshes per cm2 consisting of wires having a diameter of 0.12 mm; a granular material 42 having a specific weight of 1.8 g/cm 3 and a dimension of the granules between 0.6 and 1 mm; a pressure drop of 500 Pa (about 51 mm H2O) in the chamber 38; a layer of granular material 42 having thickness S of about 1.5 mm may be transferred; the thickness S may be reduced or increased by increasing or reducing the pressure drop. The invention can be carried out in different forms, for example: with movable or stationary planar screens, with drum-shaped screens, for applications on the movable support 40 (as in the explained examples) or stationary. In this last event, since the support 40 is stationary, the apparatus will be caused to translate. The invention is also suitable for transferring material in form of great scales or tesserae without real limits of dimension, particularly valuable aesthetic effects being obtainable using these materials, as for example mosaic surfaces or imitations of natural stones. Figure 5 shows a different embodiment of the invention, in which elements already disclosed with reference to previous figures have been designated with the same reference numerals, preceded by the number "3". With reference to the Figure 5 the invention can be used as mixing apparatus 313 of layerd powders 310, 312 such an apparatus, placed closely above the layer to be modified, during the motion of relative translation, raises the surface layers, initially arranged on a base powder layer 305, and leaves them fall subsequently in a downstream position. A layer 316 of mixed powders is therefore obtained. The particular substantially vertical orientation of the layers when they detach from the screen 331, sliding on a wall 352, favours an optimal mixing of the layers during the fall; furthermore, since the fall may be very limited, the plan disposition of the decoration will be thrown into disorder only to a minimum extent. By using the screen 331 with both permeable regions and non-permeable, the mixing may be obtained only on a selected portion of the layers and/or at different depths; so obtaining special aesthetic effects. The mixing devices 313 can be used also in conditions different from those up to now described, for example they can be used for applications on an already pressed or fired material or to form decalcomanias or again a layers of powders already loaded in a mould can be mixed. Furthermore, the layer to be mixed can be kept stationary while the mixing device 313 translates. The apparatus according to the invention makes possible therefore to apply an unlimited number of different decorating layers with well defined patterns and to mix them with each other in a controllable and selective manner, which is particularly productive and advantageous.

Claims: Transfer means arranged for transferring a granular decorating material (2; 42; 310, 312), including screen means (10; 31; 331) so configured as to move said granular decorating material (2; 42; 310, 312) from a collecting region to a discharging region (4; 40; 48) along a path partially surrounding suction chamber means (19; 38; 338) containing an operating fluid which acts on said granular decorating material (2; 42; 310, 312) through said screen means (10; 31; 331), said path comprising an ascending portion and a descending portion, characterized in that , said suction chamber means (19; 38; 338) faces said screen means (10; 31; 331) along a substantial portion of said ascending portion adjacent to said collecting region, so as to allow said granular decorating material (2; 42; 310, 312) to be raised adherent to said screen means (10; 31; 331) from said collecting region. Transfer means according to claim 1, wherein said screen means (10; 31; 331) includes regions (37) non-permeable to said operating fluid. Transfer means according to claim 1, or 2, wherein said screen means (10; 31; 331) is arranged in the form of a drum. Transfer means according to claim 1, or 2, wherein said screen means (10; 31; 331) is arranged in the form of an endless belt. Transfer means according to any of preceding claims, wherein said suction chamber means (19; 38; 338) is provided with at least one opening (34) through which said operating fluid is drawn back into the said suction chamber means (19; 38; 338) in order to withdraw said granular decorating material (2; 42; 310, 312). Transfer means according to any of preceding claims, wherein said collecting region is arranged adjacent to an efflux opening (3; 43) of container means (1; 41) in which said granular decorating material (2; 42; 310, 312) is contained. Transfer means according to claim 6, wherein said efflux opening (3; 43) is turned towards said screen means (10; 31; 331) in a region of said screen means (10; 31; 331) having an outer face facing downwards. Transfer means according to any of claims 1 to 5, wherein said collecting region is arranged above an underlying support (40). Transfer means according to claim 8, and further comprising a recycling device (48) suitable for receiving said granular decorating material (2; 42; 310, 312) in said discharging region. Transfer means according to any of claims 1 to 8, wherein said discharging region is arranged above an underlying support (4; 40). Transfer means according to any of preceding claims and further comprising support belt means arranged to support said granular decorating material (2; 42; 310, 312). Transfer means according to claim 11, wherein at least two initially distinct layers (310, 312) of said granular decorating material (2; 42; 310, 312) are arranged on said belt means. Transfer means according to claim 11, or 12, wherein said screen means (10; 31; 331) is arranged above said granular decorating material (2; 42; 310, 312). Method for transferring granular decorating material (2; 42; 310, 312) from a collecting region to a discharging region, comprising acting with an operating fluid on said granular decorating material (2; 42; 310, 312) causing said operating fluid to pass through permeable regions (12; 36) of screen means (10; 31; 331), characterized in that , said acting comprises lifting said granular decorating material (2; 42; 310, 312) from said collecting region along an ascending portion of said screen means (10; 31; 331) adjacent to said collecting region. Method according to claim 14, wherein said lifting comprises selectively collecting said granular decorating material (2; 42; 310, 312). Method according to claim 14, or 15, wherein said acting comprises sucking said operating fluid through said screen means (10; 31; 331). Method according to any of claims 14 to 16, wherein said acting takes place near an efflux opening (3; 43) of container means (1; 41) in which said granular decorating material (2; 42; 310, 312) is contained. Method according to claim 17, wherein said acting takes place while said screen means (10; 31; 331) have one of their outer faces interacting with said granular decorating material (2; 42; 310, 312) and facing downwards. Method according to any of claims 14 to 18, wherein said. acting takes place while said screen means (10; 31; 331) lies above said granular decorating material (2; 42; 310, 312). Method according to any of claims 14 to 19, wherein said granular decorating material (2; 42; 310, 312) is distributed in at least two layers (310, 312). Method according to claim 20, wherein said granular decorating material (2; 42; 310, 312) is submitted to the action of said operating fluid in such a manner that said at least two layers (310, 312) are at least partially mixed with each other. Method according to any of claims 14 to 21, wherein said acting comprises picking up said granular decorating material (2; 42; 310, 312) from an underlying support (40). Method according to any of claims 14 to 22, and further comprising discharging said granular decorating material (2;.42; 310, 312) from said screen means (10; 31; 331). Method according to claim 23, wherein said discharging comprises causing said granular decorating material (2; 42; 310, 312) to fall on an underlying support (4; 40). Method according to claim 23, wherein said discharging comprises recycling said granular decorating material (2; 42; 310, 312).

Inventors: ALGERI MARIS, CAMORANI CARLO ANTONIO, ALGERI, MARIS, CAMORANI, CARLO ANTONIO
Applicants: ALGERI MARIS, CAMORANI CARLO ANTONIO, ALGERI, MARIS, CAMORANI, CARLO ANTONIO
Application year: 1998
Main classification: B65G15
IPC codes: B28B13, B28B1, B28B3