An improved device for forming ceramic products, including slabs, tiles and the like, by powder pressing

Abstract: The improved device of the invention comprises a lower element (2) for supporting powder (20) to be pressed and an upper element (4) between which two elements (2 and 4) the powder (20) will be pressed. The invention is characterised by the fact that it comprises means for surrounding and sealingly isolating at least a part of the powder (20) from an outside environment when the two elements (2 and 4) are reciprocally neared. Air is aspirated from the isolated part of the powder, creating a depressed environment.

Description: The prior art in the field of forming ceramic tiles is based on the use of dies inserted into presses. The dies are, schematically speaking, constituted by a cavity into which powders are deposited, and by at least one punch having the task of pressing the deposited powders. Also known is the use of dies in which the cavity is not made in the bottom die; this is instead used for depositing a layer of powders which is then pressed by the top die or punch. Delimitation and lateral containment of the material to be pressed to form the tile or slab is performed by a forming frame associated to the punch or top die, which is mobile and projects from the top die so that it can remain in contact with the bottom plane (bearing the powders to be pressed) during the pressing operation. In prior-art devices, the forming is performed in a substantially two-stage pressing operation: a first stage, characterised by a considerable reduction in the volume of the blank tile, during which stage there is also an expulsion of air trapped in the material; a second stage, in which the by-now air-free material is further compressed, with a consequent further but smaller reduction in volume thereof. The forming is thus completed. Such a device is known from WO-A-96/15888. The two-stage pressing operation requires specific press predisposition and management which are necessarily time-consuming and result in considerably longer production times than in those processes which require only one pressing stage. On the other hand, single-stage pressing using traditional methods cannot be used because they cannot produce a blank free of serious defects, such as flaking and the like. Such a press is known from US-A-5 779 957. The main aim of the present invention is to provide an improved device for forming ceramic products, such as slabs, tiles and the like, by powder pressing, which device enables pressing to be performed in a single stage but without those limitations and drawbacks which characterise the prior art. The invention is constructionally simple and functional. A further advantage of the invention is that it enables a considerable reduction in cycle times to be achieved, with an evident and immediate improvement in productivity. These aims and advantages and more besides are all attained by the object of the invention, as it is characterised in the appended claims. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows of a preferred but non-exclusive embodiment of the invention, illustrated purely by way of a nonlimiting example in the accompanying figures of the drawings, in which: figure 1 is a schematic longitudinal section made according to a vertical plane which is parallel to an advancement direction of the materials; figure 2 is an enlarged-scale view of a detail of figure 1; figure 3 shows the same detail as in figure 2, in a different operational configuration. With reference to the figures of the drawings, 1 denotes in its entirety a device for forming ceramic products, such as slabs, tiles and the like, by powder pressing, which device 1 is schematically constituted by a press 11 having a central aperture crossed by a lower element 2, constituted by a lower continuous belt 12 exhibiting a lower rest plane 3 for bearing the powders to be pressed 20, and by an upper element 4, constituted by a horizontal branch of a continuous belt 15, ring-wound and stretched between two horizontal-axis drums 16 positioned externally, which belt 15 is moved in synchrony with the lower continuous belt 12 constituting the lower element 2. The lower element 2 lies and slides along an upper surface of the piston 10 of the press 11 and is commanded by the piston 10 to displace upwards in order to exert the pressing action. The upper element 4 is provided with a plurality of active surfaces 5, located and distributed in a predetermined order along the upper continuous belt 15. At each pressing event the active surfaces 5 are brought into contact with the rest plane 3 of the lower continuous belt 12. Each active surface 5 is characterised in that it is provided with a forming frame 6 which projects inferiorly (when the active surface 5 is in contact with the rest plane 3) and is predisposed in such a way as to delimit at its perimeter a closed pressing zone. The forming frame 6 exhibits an internal part 7 which carries out the pressing of the edge of the final pressed product. This internal part 7 is externally delimited by an edge 8 having a depth, measuring in the pressing direction, which is not less than or is equal to that of the central body of the final pressed product. In particular, the internal part 7 inferiorly projects with respect to the active surface 5 and presents a depth which gradually decreases as it distances from the edge 8. The whole forming frame 6 is constituted by a material having considerable elastic deformability (rubber or another elastomer). The upper branch of the lower continuous belt 12 is moved in synchrony with the lower branch of the upper continuous belt 15. In the described structure, the lower rest plane 3 also functions as the bottom die of the forming device. During the pressing phase, the piston 10 rises, raising the part of the lower element 2 on which the powder to be pressed has been deposited, thus pressing the powder against the active surface 5 delimited by the forming frame 6 of the upper continuous belt 15. The whole pressing operation is completed in a single phase (i.e. in a single continuous upwards stroke by the piston 10) and in a depressed environment, as will be explained herein below. Means are provided for sealingly isolating and closing off at least a part of the powders 20 comprised between the lower element 2 and the upper element 4, confining that part of the powders 20 in an isolated environment 17. The means for isolating comprise lateral walls 9 which describe a closed perimeter. The walls 9 are of constant depth and project in the direction of relative motion between elements 2 and 4 during the pressing cycle. The walls 9 are made of a very elastically-deformable material, such as rubber or another elastomer, and are of a size such as to realise an isolated environment 17 just before the powder pressing 20 begins. Also provided are means for evacuating, which evacuates the air from the isolated environment 17 in order to create a depression. The means for evacuating comprise evacuation ducts 13 located peripherally of the lateral walls 9 and internally of the perimeter the walls 9 define. The evacuation ducts 13 lead into evacuation conduits 14 afforded in the upper body (fixed punch) of the press 11, i.e. the evacuation ducts 13 are in fact through-holes made in the upper continuous belt 15, which is, as mentioned herein above, ring-wound and stretched between two parallel-axis drums 16 positioned externally of the press 11. The lower branch of the upper continuous belt 15 constitutes the upper element 4 which is provided with at least one active surface 5 which faces the lower rest plane 3 and is provided with a forming frame 6 which projects inferiorly and is located such as to delimit a perimeter of a closed pressing zone. The forming frame 6 is not only designed to create a closed pressing zone which will generate a final pressed product, but also generates, following the pressing operation, an edge zone of the final pressed product which is characterised by a greater density than that of the internal zones of the final pressed product, though a smaller depth. For this purpose the forming frame 6 exhibits an internal part 7 especially formed and designed to press the edge zone; the internal part 7 being externally delimited by an edge 8 which is of a depth (measuring in the pressing direction) that is equal or not inferior to the central body of the final pressed product. The evacuation ducts 13 are afforded in the upper continuous belt 15 in the zone comprised between the walls 9 and the edge 8, and are therefore in direct communication with the annular zone comprised between the walls 9 and the edge 8. By effect of a positioning of the lower branch of the upper continuous belt 15, the evacuation ducts 13 are positioned so as to coincide with the evacuation conduits 14. This happens at each pressing cycle when the upper continuous belt 15, ring-wound and housing a plurality of active surfaces 5 delimited by an equal number of forming frames 6, is positioned such that an active surface 5 is facing the lower element 2 bearing the lower rest plane 3 on which the powders to be pressed have been deposited. The lower element 2 is constituted by an upper branch of the lower continuous belt 12, which upper branch moves in synchrony with the lower branch of the upper continuous belt 15. Starting from the beginning of the pressing cycle, in particular from the moment when the walls 9 make contact with the rest plane 3, an isolated environment 17 is created, which isolates a space from the outside environment, which space contains a layer of powders to be pressed. By effect of the evacuation by the ducts 13, the air freed by the compacting of the powders is extracted simply and effectively. At the beginning of the pressing process, the powders are in a depressed environment, which greatly favours expelling of air from the powders, thus eliminating defects deriving from bad aspiration conditions and rendering the pressing cycle very rapid. A further advantage of the present invention is that formation operations of large-format but relatively slim slabs and tiles are completed much more quickly.

Claims: An improved device for forming ceramic products, including slabs, tiles and the like, by powder pressing, comprising a lower element (2) for supporting powders (20) to be pressed, and an upper element (4), between which lower element (2) and upper element (4) the powders (20) will be pressed, characterised in that it comprises means for surrounding and sealingly isolating at least a part of the powders (20) about to be pressed between the lower element (2) and the upper element (4) from an outside environment and creating an isolated environment (17) for the powders (20); also comprising means for evacuating air, which create a lower pressure in the isolated environment (17) by evacuating air there-from. The device of claim 1, characterised in that the means for surrounding and sealingly isolating comprise lateral isolating walls (9) which describe a closed perimeter. The device of claim 2, characterised in that the lateral walls (9) exhibit a constant size in a direction corresponding to reciprocal movements of the lower element (2) and the upper element (4) during a pressing cycle, and in that the lateral walls (9) are made of a very elastically-deformable material. The device of claim 2, characterised in that the means for evacuating air comprise evacuation ducts (13) predisposed peripherally and close to the lateral walls (9) and internally of the perimeter described by the lateral walls (9). The device of claim 3 or 4, characterised in that the lower element (2) bears a lower rest plane (3) for supporting the powders (20) to be pressed, and in that the upper element (4) exhibits at least one active surface (5) facing the lower rest plane (3), which at least one active surface (5) exhibits a forming frame (6) which projects inferiorly thereof and which is destined to delimit a perimeter of a closed pressing zone; the forming frame (6) also and as a consequence being destined to delimit a final pressed product obtained by a forming operation; the forming frame (6) also generating, during the forming operation, an edge of the final pressed product which edge has a greater density than a density of an internal zone of the final pressed product, and which edge has also a smaller depth than a depth of the internal zone of the final pressed product. The device of claim 5, characterised in that the forming frame (6) exhibits an internal part (7) which performs a pressing operation on the edge of the final pressed product, and which is externally delimited by a delimiting edge (8) having a depth which, measured in a direction in which a pressing operation is performed, is not less than or is equal to a depth of a central body of the final pressed product (21). The device of claim 5 or 6, characterised in that the upper element (4) exhibiting the at least one active surface (5), delimited by the forming frame (6), is constituted by a lower surface of an upper continuous belt (15) which is ring-wound and stretched between two parallel-axis drums (16) located externally of the device; the evacuation ducts (13) being constituted by through-holes afforded in the upper continuous belt (15) in a zone comprised between the lateral isolating walls (9) and the delimiting edge (8). The device of claim 7, characterised in that the evacuation ducts (13) are predisposed to be brought into a coincidental position with corresponding evacuation conduits (14) made in an upper body of the press (11). The device of claim 7, characterised in that the ring-wound upper continuous belt (15) houses a plurality of the active surfaces (5) delimited by an equal plurality of forming frames (6) distributed along the upper continuous belt (15). The device of claim 9, characterised in that at least the forming frame (6) is made of a material having considerable elastic deformability and in that the lower element (2) bearing the lower rest plane (3) for supporting the powders (20) to be pressed, as well as the final pressed product, is constituted by an upper branch of a lower continuous belt (12) which is moved in synchrony with the lower branch of the upper continuous belt (15).

Inventors: STEFANI FRANCO, STEFANI, FRANCO
Applicants: SYSTEM SPA
Application year: 2000
Main classification: B28B3
IPC codes: B28B7, B28B3, B28B5