EP2548707A1

EP2548707A1 - Isostatic mold, particularly for ceramic tiles

Info

Publication number: EP2548707A1
Application number: EP12176559A
Authority: EP
Inventors: Stefano Gatti; Paolo Zobbi; Andrea Guidetti
Original assignee: Gape Due SpA
Current assignee: Gape Due SpA
Priority date: 2011-07-18
Filing date: 2012-07-16
Publication date: 2013-01-23
Also published as: ITMO20110174A1

Abstract

An isostatic mold (1), particularly for ceramic tiles, comprising at least one forming receptacle (2) which is delimited in an upper region by a first mold part (3) and in a lower region by a respective second mold part (4), at least one of the mold parts comprising a closed compression chamber (5) which accommodates a working liquid. The compression chamber (5) has a volume delimited by a first face (6) of a punch (8) and by a corresponding sliding seat (9). The punch (8) is associated slidingly and hermetically with the sliding seat (9) for its transition from an inactive position to a pressing position and vice versa; in particular in the pressing position the compression chamber (5) defines a smaller volume than the volume it defines in the inactive position. An external hydraulic circuit (10) being functionally connected to the compression chamber (5) to control the pressure of the working liquid.

Description

The present invention relates to an isostatic mold, particularly for ceramic tiles.
As is known, tiles, or other ceramic plate-like articles, are obtained by means of an industrial process for pressing ceramic powders introduced in a corresponding mold and a subsequent firing process in order to obtain the final tile.
The quality of the final product that can be obtained is linked tightly to the two production processes and in particular, as regards the pressing step, particular attention is given to the regularity and uniformity of the pressure applied to the ceramic tesserae. In fact, a non-uniform pressing step gives rise to an apparently flat ceramic tessera which, during the firing step, is subjected to different thermal deformations caused by differential shrinkages to which the different compacted regions are subjected, making the tile lose both the planarity of the flat body and the linearity of the perimetric edges.
These deformations require, therefore, a step of selecting and discarding the final product in order to offer a high-quality product to the end user.
The molds used to form the ceramic tesserae generally comprise a pressing receptacle, which is formed by an upper mold part and a lower mold part and in which the ceramic powders are pressed by means of a press of a known type.
At least one of the two mold parts comprises a punch which is associated slidingly with a suitable sliding seat for its movement from an inactive position to a pressing position along a direction substantially at right angles to the pressing plane of the ceramic tessera.
In particular, some molds of the known type comprise a mechanical balancing system which is interposed between the punch and the sliding seat provided with elastic elements, which ensure a uniform leveling of the punch during the pressing step, ensuring a constant pressure applied to each point of the mold part.
As a consequence of countless production cycles, the mechanical balancing system gradually loses its elastic characteristics, causing the punch to tilt slightly with respect to the surface to be pressed, giving an uneven pressure distribution to the ceramic tessera.
In order to obviate this drawback during the pressing step, a gasket of the hydraulic type is interposed between the punch and the sliding seat in order to define a compression chamber which accommodates an incompressible liquid, such as for example oil. Such chamber ensures a self leveling of the punch when the punch is in the pressing step in contact with the ceramic powders, defining a uniform distribution of pressure and consequently a uniform compaction of the powders..
The return of the punch to the inactive position after the pressing step is ensured again by elastic elements which, as previously defined, can lose their elasticity due to various working cycles and, by not returning the punch back into the inactive position, substantially parallel to the pressing surface, they have an inclined surface of the punch which is adapted to accommodate the ceramic powders, already during laying, in a non-uniform manner.
In addition to this, isostatic molds of the known type are not free from drawbacks, including the fact that the punch, in passing from the inactive position to the pressing position, applies substantial pressure hammers to the mold part.
These mechanical stresses affect completely the mechanical gasket, making it wear prematurely. In turn, the worn gasket allows a slight seepage of the liquid, which, by remaining in a smaller quantity in the compression chamber, does not ensure the planarity of the punch on the powders during the pressing step, giving a different pressing step with respect to the previous production cycle, forming ceramic tesserae which are mutually different and therefore of poor quality. The maintenance of these molds after a limited number of working cycles requires the halting of the production line in order to allow the replacement of the gaskets.
Another drawback of isostatic molds of the known type resides in that it is possible to produce only tiles of a preset height, requiring the replacement of at least one of the two mold parts for the production of tiles that require different pressing steps with different isostatic effects. In fact, these molds do not make it possible to modify the stroke of the punch from the inactive position to the pressing position; the constant stroke makes it possible to obtain only tiles with equal heights.
The aim of the present invention is to provide an isostatic mold, particularly for ceramic tiles, which obviates the drawbacks and overcomes the limitations of the background art, allowing a uniform distribution of pressure during the pressing step without the use of mechanical balancing systems.
Within the scope of this aim, an object of the present invention is to provide an isostatic mold which reduces the mechanical stresses to which the gasket of the hydraulic type that defines the compression chamber is subj ected.
Another object of the invention is to provide a mold which reduces maintenance times, avoiding a prolonged production stop, greatly reducing production costs.
A further object of the invention is to provide an isostatic mold that allows continuous control of the pressure of the liquid in the compression chamber, ensuring a uniform compression step during the various production cycles.
Another object of the invention is to provide an isostatic mold that makes it possible to restore the quantity of desired working liquid in the compression chamber without any machine downtime.
A further object of the invention is to provide an isostatic mold that makes it possible to vary the extent of the isostatic effect during the pressing step.
Another object of the invention is to provide an isostatic mold that is easy to provide and economically competitive if compared with the background art.
This aim and these and other objects which will become better apparent hereinafter are achieved by an isostatic mold, particularly for ceramic tiles, comprising at least one forming receptacle which is delimited in an upper region by a first mold part and in a lower region by a respective second mold part, at least one between said first mold part and said second mold part comprising a closed compression chamber which accommodates a working liquid, said compression chamber being delimited by a first face of a punch, which is opposite with respect to a second face of said punch which is adapted to form said tile, and by a corresponding sliding seat, said punch being associated slidingly and hermetically with said sliding seat for the transition from an inactive position to a pressing position and vice versa, in said pressing position said compression chamber having a smaller volume than the volume it defines in said inactive position, characterized in that it comprises an external hydraulic circuit, which is functionally connected to said compression chamber to control the pressure of said working liquid.
Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of an isostatic mold, particularly for ceramic tiles, illustrated by way of non-limiting example with the aid of the accompanying drawings, wherein:

Figure 1 is an axial sectional view of the isostatic mold according to the invention, taken along a plane that passes through a forming receptacle;
Figure 2 is an axial sectional view of the first mold part according to the invention, taken along a plane that passes through a forming receptacle with the punch in the inactive position;
Figure 3 is an axial sectional view of the first mold part according to the invention, taken along a plane that passes through a forming receptacle with the punch in the pressing position;
Figure 4 is an enlarged-scale sectional view of the pressure compensator according to the invention, taken along a plane that passes through its longitudinal axis.

With reference to the figures, the isostatic mold, particularly for ceramic tiles, generally designated by the reference numeral 1, comprises at least one forming receptacle 2, which is delimited in an upper region by a first mold part 3 and in a lower region by a respective second mold part 4, and at least one of them comprises a closed compression chamber 5 which accommodates inside it a working liquid.
The compression chamber 5 is delimited perimetrically by a first face 6 of a punch 8 and by a corresponding sliding seat 9 thereof, where the first face 6 is opposite with respect to a second face 7 of the punch 8 adapted to form the tile.
In particular, the punch 8 is associated slidingly and hermetically with the sliding seat 9 for the transition from an inactive position to a pressing position and vice versa. In the pressing position the compression chamber 5 has a smaller volume than the volume it defines in the inactive position.
According to the invention, the isostatic mold 1 comprises an external hydraulic circuit 10, which is functionally connected to the compression chamber 5 to control the pressure of the working liquid.
Conveniently, the external hydraulic circuit 10 comprises a pressure accumulator 11 and a pressure compensator 12.
In particular, the pressure compensator 12 is composed of a substantially hollow cylindrical body, which is extended along a longitudinal axis 30, delimited by a first end face 16 and a second end face 17 in order to define an internal chamber 15 in which a piston 18 can slide hermetically. The piston 18, in turn, mutually separates a first compartment 19 and a second compartment 20 whose volume is variable according to the position of the piston 18 inside the chamber 15.
Conveniently, the first compartment 19 is connected to the pressure accumulator 11 by means of a first outlet 13 formed in the first end face 16 and the second compartment 20 is connected to the compression chamber 5 by means of a second outlet 14 formed in the second end face 17.
Inside one of the two compartments 19, 20 and particularly inside the second compartment 20 a limiter 21 is provided, which is interposed between the second end face 17 and the piston 18, limiting the stroke of the piston 18 inside the chamber 15. Conveniently, the limiter 21 is shorter than the maximum stroke of the piston 18 and in this particular embodiment it comprises a bushing 22 which adheres to the perimetric walls of the chamber 15.
Advantageously, the pressure compensator 12 can be inspected internally by means of the removal of at least one between the first end face 16 and the second end face 17, which are connected to the body of the pressure compensator 12 by means of threaded elements 31 of a known type.
Parallel to the external hydraulic circuit 10, the compression chamber 5 can be connected hydraulically to a second hydraulic circuit, not shown in the accompanying figures, which is adapted to monitor and maintain the working liquid under pressure in the external circuit 10.
In addition to this, the isostatic mold 1 comprises the first mold part 3, which has a base body 25 in which the sliding seat 9 is formed for the hermetic sliding of the punch 8. The interference between the sliding seat 9 and the punch 8 is sufficient to allow a straight movement along a direction which is substantially perpendicular to the pressing surface of the ceramic powders, ensuring tightness of the compression chamber 5 by means of gaskets of the known type arranged perimetrically on the punch 8, such as for example gaskets of the hydraulic type and extrusion-preventing guiding rings, and a slight tilting of the punch 8 in the sliding seat 9.
Inside the base body 25 cavities 26 are also provided, which accommodate in abutment the stroke limiters 23, which are connected to the punch 8 to stop the sliding of said punch 8 from the pressing position to the inactive position.
Advantageously, a pad 24 adapted to press the ceramic powders in direct contact therewith can be associated with the punch 8. The pad 24 is directly connected to the second face 7 of the punch 8 by means of threaded elements of the known type or by means of magnets installed in at least one of the two elements mutually in contact.
Conveniently, the isostatic mold 1 comprises a second mold part 4, which is arranged in a mirror-symmetrical fashion with respect to the first mold part 3 in order to define the lower part of the forming receptacle 2, and in particular the second mold part 4 has the same structure described for the first mold part 3, as shown in Figure 1.
Advantageously, each mold part 3 and 4 has a plurality of punches 8 with respective compensation chambers 5 for the simultaneous production of a plurality of tiles. Each one of the plurality of compensation chambers 5 is connected hydraulically to the following one and to the external hydraulic circuit 10.
Operation of the isostatic mold, particularly for ceramic tiles, is described hereinafter.
After a preliminary step for filling the second mold part 4, which defines the lower part of the forming receptacle 2, with the ceramic powders, one proceeds with the pressing step, in which the first mold part 3 is pressed against the second mold part 4 by means of presses of a known type.
During this step, the punch 8, in the inactive position, moves toward the pressing position, sliding along the sliding seat 9 and reducing accordingly the volume of the compression chamber 5, in which the working liquid is present at an initial pressure of approximatively 2-4 bars.
The working liquid, being incompressible, tends to flow out in regions of the mold in which the pressure is lower, i.e., toward the external hydraulic circuit 10. The working liquid, by means of high-pressure piping, reaches the pressure compensator 12.
Inside the pressure compensator 12, the piston 18 that hermetically separates the first compartment 19 from the second compartment 20 starts to move toward the first end face 16 under the action of the working liquid at a higher pressure than the pressure of the fluid present in the pressure accumulator 11, increasing the volume of the second compartment 20 and reducing the volume of the first compartment 19.
When the piston 18 ends its stroke inside the pressure compensator 12, the working liquid in the compression chamber 5 and in the external hydraulic circuit 10 is unable to flow out into further regions at lower pressure and, under the action of the press, spreads uniformly in the compression chamber 5, ensuring an isostatic pressing in the underlying forming receptacle 2, reaching an operating pressure of approximately 400-500 bars.
After the pressing step, the press moves the two mold parts 3 and 4 away from each other, moving away also the punch 8 from the unfired tile just formed. The working liquid is no longer under pressure under the action of the press and accordingly the fluid inside the pressure accumulator 11 is now at a higher pressure than the working liquid.
The fluid pushes the piston 18 toward the second end face 17, increasing the volume of the first compartment 19 and reducing the volume of the second compartment 20. In turn, the working liquid returns into the compression chamber 5, increasing its volume, pushing the punch 8 toward the inactive position until the stroke limiters 23 abut against the cavities 26 formed in the base body 25.
The movement of the punch 8 from the inactive position to the pressing position is proportional to the volume of the working liquid that flows out into the pressure compensator 12 and more precisely to the variation of the volume of the second compartment 20. The insertion of the bushing 22 inside the second compartment 20 limits the stroke of the piston 18 and accordingly the movement of the punch 8, allowing the system a greater or smaller isostatic effect.
Advantageously, the second mold part 4 arranged below also has the same isostatic compensation system, which in addition to ensuring a uniform distribution of pressures during the pressing step ensures the leveling of the plane of the punch 8 on which the ceramic powders are deposited thanks to the hydraulic self-balancing system.
In this particular embodiment, two forming receptacles 2 are illustrated which are mutually connected by means of a passage channel 27, which ensures the isostaticity described previously for both of the forming receptacles 2.
Moreover, in an embodiment not shown in the accompanying figures, the isostatic mold 1 comprises a second hydraulic circuit which is functionally connected to the compression chamber 5 for the continuous monitoring of the pressure of the working liquid in the inactive position of the punch 8.
The second circuit comprises compensation means for replenishing any seepages of the working liquid and safety hydraulic limiting valves if the working liquid reaches excessively high pressures during the pressing step.
In practice it has been found that the isostatic mold, particularly for ceramic tiles, according to the present invention, fully achieves the intended aim and objects, since it makes it possible to obtain a uniform pressing step without the use of mechanical balancing systems subject to wear, allowing a hydraulic self-balancing system.
Another advantage of the isostatic mold, according to the invention, consists in that it reduces the mechanical stresses to which the mold parts are subjected, by discharging the greatest mechanical stresses in an external hydraulic circuit.
Moreover, it should be noted noted that the fluid inside the pressure accumulator achieves a shock-absorber function because its compressible nature makes it possible to dampen slightly the almost immediate movement of the movable piston inside the pressure compensator.
A further advantage of the isostatic mold, according to the invention, consists in that it reduces drastically the maintenance times because the element that is most subject to wear is the pressure compensator, which is arranged externally to the mold. Its external position facilitates and reduces machine downtime greatly in case of maintenance.
Another advantage of the isostatic mold, according to the invention, consists in that it is possible to control continuously the isostatic effect of the punch by monitoring continuously the pressure of the working liquid.
A further advantage of the isostatic mold, according to the invention, consists in the possibility to vary the extent of the isostatic effect.
The isostatic mold, particularly for ceramic tiles, thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.
Moreover, all the details may be replaced with other technically equivalent elements.
In practice, the materials used, so long as they are compatible with the specific use, as well as the contingent shapes and dimensions, may be any according to requirements and to the state of the art.
The disclosures in Italian Patent Application No. M02011A000174 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

An isostatic mold (1), particularly for ceramic tiles, comprising at least one forming receptacle (2) which is delimited in an upper region by a first mold part (3) and in a lower region by a respective second mold part (4), at least one between said first mold part (3) and said second mold part (4) comprising a closed compression chamber (5) which accommodates a working liquid, said compression chamber (5) being delimited by a first face (6) of a punch (8), which is opposite with respect to a second face (7) of said punch (8) which is adapted to form the tile, and by a corresponding sliding seat (9), said punch (8) being associated slidingly and hermetically with said sliding seat (9) for transition from an inactive position to a pressing position and vice versa, in said pressing position said compression chamber (5) having a smaller volume than the volume it defines in said inactive position, characterized in that it comprises an external hydraulic circuit (10), which is functionally connected to said compression chamber (5) to control the pressure of said working liquid.
The isostatic mold (1) according to claim 1, characterized in that said external hydraulic circuit (10) comprises a pressure accumulator (11) and a pressure compensator (12), said pressure compensator (12) comprising a first outlet (13), which is functionally connected to said compression chamber (5), and a second outlet (14), which is functionally connected to said pressure accumulator (11).
The isostatic mold (1) according to one or more of the preceding claims, characterized in that said pressure compensator (12) comprises a substantially cylindrical internal chamber (15), with a first end face (16) and a second end face (17) which are mutually opposite and are connected respectively to said first outlet (13) and to said second outlet (14), said internal chamber (15) accommodating slidingly and hermetically inside it a piston (18) for forming a first compartment (19) and a second compartment (20) which are mutually separated by said piston (18) and are connected respectively to said first outlet (13) and said second outlet (14).
The isostatic mold (1) according to one or more of the preceding claims, characterized in that it comprises a limiter (21), which is insertable in said second compartment (20) to limit the stroke of said piston (18) in said internal chamber (15).
The isostatic mold (1) according to one or more of the preceding claims, characterized in that said limiter (21) comprises a bushing (22).
The isostatic mold (1) according to one or more of the preceding claims, characterized in that it comprises stroke limiters (23) to limit the sliding of said punch (8) from said pressing position to said inactive position.
The isostatic mold (1) according to one or more of the preceding claims, characterized in that it comprises at least one pad (24) which is designed to adhere to the tile to be formed, said pad (24) being connected mechanically or magnetically to said punch (8).
The isostatic mold (1) according to one or more of the preceding claims, characterized in that it comprises compensation means, which are connected functionally to said external hydraulic circuit (10) to restore said working liquid.
The isostatic mold (1) according to one or more of the preceding claims, characterized in that said first mold part (3) and said second mold part (4) comprise respective punches (8), which are associated slidingly with respective compression chambers (5) for the transition of said punches (8) from said inactive position to said pressing position and vice versa, said compression chambers (5) being functionally connected to respective external hydraulic circuits (10) for controlling the pressure of said working liquid.
The isostatic mold (1) according to one or more of the preceding claims, characterized in that it comprises a plurality of forming receptacles (2), which comprise respectively at least one compression chamber (5), said compression chambers (5) being connected to each other and connected to said external hydraulic circuit (10).