EP1106336B1

EP1106336B1 - An apparatus for removing air from soft powder material in a press-forming cycle for manufacture of ceramic products

Info

Publication number: EP1106336B1
Application number: EP19990204104
Authority: EP
Inventors: Franco Stefani
Original assignee: System SpA
Current assignee: System SpA
Priority date: 1999-12-03
Filing date: 1999-12-03
Publication date: 2006-07-19
Anticipated expiration: 2019-12-03
Also published as: EP1106336A1; ES2264577T3; CN1309014A; BR0005610A

Description

The invention relates to an apparatus for removing air from soft powder material during the press-forming cycle in the manufacture of ceramic products.
Specifically though not exclusively the invention is applicable in press-forming powders for the forming of ceramic slabs and/or tiles.
In the press-forming operation, especially of slabs or tiles, one of the main problems is removal of the air present inside the bottom die mixed with the ceramic material to be pressed.
Ceramic powder mixtures, usually composed of granules with a calibre of a few tenths of millimetres often referred-to as "soft" material, always retain a certain quantity of air when placed in the bottom die.
This air must be eliminated if the powder is to be correctly compacted. However, owing to the small degree of play present in the coupling between the bottom die and the punch, when a very rapid pressing action is carried out (rapid pressing is advantageous for technical reasons as well as for productivity levels) it is difficult to remove the air completely from the powder; it remains imprisoned and can create dangerous sacks of air which can result in a characteristic defect commonly known as flaking.
The bigger the product (tile) is, the more evident and accentuated the defect.
The prior art teaches remedies which consist of pauses in the pressing cycle, which fundamentally means that the press-formers have a punch downstroke which is not continuous but which includes one of more pauses of a predetermined duration.
During these pauses, made at pressures which are lower than the maximum punch pressure, the press hydraulic circuit is commanded to discharge the punch hydraulic cylinder at certain points during the process and for short predetermined times.
Thus, thanks to the elastic expansion of the material under compression, the punch rises by a small amount, sufficient for the partially-compressed air to escape from the material and be bled out through the space created by the small play existing between the punch and the bottom die.
With quite thick or large products, often two or even three pauses are necessary at different levels of compression in order to obtain proper air removal.
This prior art technique for resolving the problem of air removal creates other, not insignificant drawbacks.
A first of these drawbacks is the inevitable slowing down of the press-forming cycle, which negatively influences machine productivity.
A further drawback is that the management of the whole forming operation is rendered more complicated, as the operation cycle must be tailored to the single product being pressed. Air removal techniques are not the same for all products, but rather depend on many factors: the shape of the tile, its thickness, the type of "soft" material, the humidity level of the material itself, its granulometry, etc. All of these factors lead to the necessity of making an empirical search and try-out routine for each product to find out how many pauses will be needed and at what compression levels.
A still further drawback relates to the structure of the hydraulic circuit of the press-forming machines which, obviously, have to be predisposed so as to enable easy setting and carrying-out of the press-forming cycle characterised by one or more pauses.
A still further drawback can consist in a reduction in the overall quality level of the press-forming operation - with other parts of the cycle (i.e. the actual powder-pressing, loading and extraction) hurried up in the attempt to recuperate time lost due to the air-removal pauses.
EP 1 098 104 discloses a mold comprisong a pressing tool defining a pressing-chamber with the mold A pressing-wall facing the material to be pressed has narrow through holes allowing the passage of gaseous media and having at least one connection with the surrounding atmosphere
US2026940 discloses an apparatus for pressing semi-dry ceramic material under hish pressure comprisinz a mold, means for applying pressure to batch of such material in the mold, in which a face of the mold is provided with a plurality of bores. Said bores are connected to means for creating vacuum with a Plurality of interconnecting channels.
The main aim of the present invention is to provide an apparatus able to obviate the above-described drawbacks and limitations in the prior art.
The invention offers numerous advantages over traditional prior art press-forming techniques.
One of these advantages consists in the fact that a pressure-time curve can be drawn up for use during the press-forming cycle, which curve is determined solely according to the "pressability" characteristics of the material.
Another advantage is that, with similar machine performance possibilities, material characteristics and product result, press-forming cycles made according to the invention are considerably quicker and simpler.
A further advantage relates to the structure of the hydraulic circuit of the press-former used for the forming cycle, which is decidedly simpler, with all the advantages that greater simplicity brings.
These aims and advantages and more besides are all achieved by 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 not exclusive embodiment thereof, illustrated purely by way of example in the accompanying figures of the drawings, in which:

figure 1 is a schematic section made according to line I-I of following figure 2;
figure 2 is a schematic section made according to line II-II of figure 1.

With reference to the figures of the drawings, 1 and 2 respectively denote an upper and a lower element of a press 8, which elements are predisposed to be pressed one against the other to exert a pressing action on a material which has been previously placed between the facing surfaces 10 and 20 of the elements.
In the illustrated example the element 1 is fixed to the structure 9 of the press 8, while the element 2 is mobile in a vertical direction and actuated by a hydraulic cylinder which is not shown in the figures of the drawings.
The press 8 is used as a forming machine for forming ceramic products, especially slabs and/or tiles, starting from a layer of soft powder material 11 which initially contains a considerable quantity of air.
The machine is equipped with an apparatus which has the aim of removing the air from the material during the press-forming stage, which apparatus essentially includes a plurality of holes on at least one of the two faces the soft material 11 comes into contact with. The holes are in contact with the outside environment and are distributed over the whole contact surface. The air initially contained in the soft material 11 is expelled following a compression action exerted on the material 11, and passes through cavities situated directly below the holes, which cavities are in direct contact with the outside environment.
The holes are denoted by reference number 3 and are distributed over an active surface 6, destined to come into direct contact with the powder material 11, of a flat body 5, which body 5 exhibits, on a face thereof opposite to the active surface 6, a plurality of the above-mentioned cavities 4, which are interconnecting.
The cavities 4 are in free communication with the outside through openings 12 at the edges of the flat body 5.
The flat body 5 exhibits, on the opposite side to the active surface, reliefs 7, the ends of which identify a rest surface, by which the body 5 is rested on the surface 20 of the element 2 - although the ends of the reliefs 7 could equally be rested and fixed on the surface 10 of element 1.
The flat body 5 is materially constituted by a mobile belt provided with intermittent motion and synchronised with the pressing action exerted by the first element 1 and the second element 2, which intermittent belt motion is in a perpendicular direction to that of the pressing action.
The loading of the soft powder material 11 can therefore take place away from the press 8, on the part of the belt which is not yet located between the first element 1 and the second element 2.
In particular, the flat body 5 is highly elastically deformable, at least in those parts thereof not occupied by the reliefs 7, and can preferably be made of an elastomer material. This characteristic gives good isostatic results during the pressing phase.
Lateral containment elements can be constrained to the surface 10 or the surface 6 of the flat body 5, which elements should be highly elastically deformable; their task is to laterally contain the pressing material, including during press-forming.
During the press-forming operation, which is done in a single stage with no pauses, air removal is achieved by means of the holes 3, through which the air initially contained in the powder material 11 is compressed is expelled into firstly the cavities 4 and then the outside environment, passing through the openings 12 predisposed at the lateral sides of the flat body 5.
The cavities 4, which are quite large, are in fact the spaces not occupied by the reliefs 7, which are not very elastically deformable so that during compression the height of the cavities is prevented from being significantly reduced.
The homogeneous distribution of the holes 3 over the surface of the material to be pressed enables a homogeneous removal of air to be obtained, giving a final press-formed product which is structurally very homogeneous. The homogeneous distribution of the holes 3 also enables the maximum pressure needed to achieve press-forming to be much lower than that required by traditional techniques.
The invention is also rather simple and is very adaptable to use in a production line where the press-former is of the type schematically illustrated in the figures of the drawings, i.e. with the upper element 1 (punch) fixed and the lower element 2 (bottom die) mobile and actuated by a hydraulic cylinder; and with the material loading functions, the containment of the material during the press-forming phase, and the pressed-material unloading operation being performed by a continuous belt constituted by a flat body 5 having intermittent predetermined step-motion, and being synchronised with the press-former 8 work cycle.

Claims

A press-forming apparatus for ceramic products from softpowder material in which the material is pressed between facing surfaces of an upper element (1) and a lower element (2) which are pressed one against another, at least one of the two surfaces being provided with a plurality of holes (3) which are in communication directly with cavities (4) which freely communicate with the outside environment; at least the one of the two surfaces which is provided with the plurality of holes (3) being an active surface (6), destined to come into direct contact with the powder material, of a flat body (5), which flat body (5) affords, on a face situated opposite to the active surface (6), a plurality of the intercommunicating cavities (4) which freely communicate with the outside environment by means of openings afforded at edges of the flat body (5); the flat body (5) exhibiting, on the opposite face to the active surface (6), reliefs (7) having extremities which create a rest surface by means of which the flat body (5) can be rested on one of the facing surfaces; the flat body (5) resting, by means of the rest surface created by the ends of the reliefs (7), on the surface (20) of the lower element (2) which faces the surface (10) of the upper element (1);
characterised in that the flat body (5) is constituted by a mobile belt provided with intermittent motion, which belt is synchronised with a pressing action exerted by the first element (1) and by the second element (2), and which intermittent motion moves in a perpendicular direction to the pressing action; a loading of the powder material being carried out at a part of the mobile belt which is not interposed between the first element (1) and the second element (2).
. The apparatus of claim 1, characterised in that the flat body (5) exhibits characteristics of high elastic deformability, at least at its parts which are not directly occupied by the reliefs (7).