Technical Field The invention relates to a process for pressing ceramic tiles, as well as a device for realising the process.

Background Art In the field of ceramic tiles, an extremely important objective has always been to obtain products which are both aesthetically and technically excellent.

With particular reference to ceramic tiles made of vitrified stoneware, whether planed or not or glazed or not, the search for ever-improving aesthetic effects is combined with the excellent technical characteristics this type of material can offer.

Among the most advanced aesthetic effects are those known as three- dimensional, which are generally created on the visible surface of the tile; these effects are those of natural stone, showing veins and so on.

At present these effects are achieved by using a number of different techniques.

Generally, however, in order to obtain them on vitrified stoneware it is preferable to carry out the necessary operations before and during the pressing stage of the ceramic tiles.

For example, the prior art teaches solutions which vary, more or less incidentally, the mix of raw materials constituting the tile mixture when the press supply hopper is filled.

It is also possible to use hoppers equipped with specially-shaped grids, or use special colouring materials, optimised to achieve three-dimensional aesthetic

finishes.

All of these processes, which obviously can also be used in combination, though guaranteeing rapid and economic production cycles, are not able to produce ceramic tiles having particularly sophisticated three-dimensional effects, which today's market is increasingly demanding.

A more refined process involves the use of more than one pressing cycle, either carried out by a same press or using several different presses. For each successive pressing cycle the hopper is topped up, in predetermined or incidental proportions, with various quantities of high-quality material, so as to create on the visible surface of the tiles a composite multi-level structure giving a good reproduction of natural stone with a three-dimensional effect of depth.

This process, however, has considerable drawbacks.

First of all, the production cycles implementing this type of effect are very slow and expensive.

Also, this solution requires the use of"mirror"dies, i. e. dies whose work surface corresponds to the upper surface (i. e. the top surface) of the tile. This leads to large wastage of high-quality materials every time the hopper is cleaned of excess material; this operation being necessary before each successive pressing stage.

Another solution consists in the use of a semi-finished clay blank, pre-pressed in an initial preliminary pressing stage, which is subsequently subjected to the addition of various quantities of high-quality material with the aim of obtaining the desired aesthetic effects.

The"real"pressing of the tile, including the high-quality materials, is done subsequently.

With respect to the previous solution, this process has the advantage of allowing more rapid and economical production cycles, though the technical and aesthetic results of the finished product are inferior.

In addition, given the considerable fragility of the semi-finished tile blank, there is always the risk that one of the blanks could break when placed on the press die; an ensuing pressing operation could lead to damage both to the die and the press.

The present invention has the aim of obviating the drawbacks in the prior art.

In particular, the main aim of the invention is to make available a pressing process for ceramic tiles, as well as a device for realising the process, wherein high-quality three-dimensional aesthetic effects can be obtained, all by using simple apparatus and with rapid and economical production times.

A further aim of the invention is to make available a pressing process for ceramic tiles as well as a device for realising the process, which are particularly suitable for obtaining three-dimensional aesthetic effects on vitrified stoneware ceramic tiles.

A further aim of the present invention is that it provides a pressing process for ceramic tiles as well as a device for realising the process which are able to minimise material wastage, and in particular wastage of high-quality material used for obtaining the desired aesthetic effects.

Finally, a further aim of the present invention is to make available a pressing process for ceramic tiles, as well as a device for realising the process, which can largely be obtained through the use of standard plant equipment, easily obtainable on the market.

These aims and others besides are all attained by a process for pressing ceramic tiles, which is characterised in that it comprises the stages of : loading a container having at least one frame and at least one extractable bottom wall, with a forming material, for example clayey powder materials; introducing the container internally of a press, for example in a bottom die of the press, the bottom die being in a loading position; extracting the bottom wall of the container, positioning the bottom wall externally of the press; extracting the frame,

positioning it externally of the press; bringing the bottom die into a pressing position, and pressing the forming material.

The process involves the use of at least one pressing device for ceramic tiles comprising a container for a forming material, characterised in that the container comprises a frame and an extractable bottom wall, the bottom wall being translatable on the frame and being mobile, with respect to the frame between a first position in which the extractable bottom wall is inserted in the frame and a second position in which the extractable bottom wall is removed from the frame.

Disclosure of Invention Further characteristics and advantages will better emerge from the detailed description that follows of some preferred though not exclusive embodiments of a pressing process for ceramic tiles, as well as a device for realising the process, with reference to the accompanying figures of the drawings, which are provided as a non-limiting illustration of the invention, and in which: figure 1 shows a view from above of a pressing device for ceramic tiles, the object of the present invention; figure 1 a is a side view of a pressing device for ceramic tiles of the invention, with the bottom wall removed from the frame of the device; figure lb is a side view of the pressing device for ceramic tiles of the invention, with the bottom wall inserted in the frame of the device; figures 2 and 3 represent two different views, respectively frontal and lateral, of the pressing device for ceramic tiles of the invention; figure 4 is a schematic view of the stage of insertion of the device of the invention, inside the operative space of a press for ceramic tiles, the insertion stage being contemporary to the expulsion of a finished tile from the press; figure 5 is a schematic view of the extraction stage of the bottom wall of the supply device of the present invention from the operative zone of the press;

figure 6 is a schematic view of the stage of depositing the ceramic powders inside the die of a press; figure 7 is a schematic representation of the extract from of the supply device of the invention, by now emptied of the ceramic powders and without the bottom wall, from the operative zone of the press; figures 8 and 9 are schematic views of the pressing stage, relating to the process for pressing ceramic tiles of the invention.

With reference to the figures of the drawings, 1 denotes in its entirety a device for realising the pressing process for ceramic tiles which is object of the present invention (see figures 1,2 and 3).

The device 1 essentially consists of a container for the material, or rather for a mixture of forming materials, for example clayey powder materials 3.

The container 1 in effect functions as a supply tray or hopper for a ceramic tile press, and comprises a frame 2 having a plurality of frontal walls 24a and lateral walls 24c, and a bottom wall 25 which is extractable and which is translatably mounted on the frame 2 and is mobile between a first position in which the bottom wall 25 is inserted in the frame 2 (see figure lb) and a second position in which the bottom wall 25 is removed or mostly removed from the frame 2 (see figure la).

The frame 2 can be equipped with a known-type internal grid, not shown in the figures, for example a beehive-type grid.

The bottom wall 25 comprises and is solidly constrained to a portion of anchorage 22 having special guide means 23 for operatively connecting with special and known means for movement and control, not shown in the figures.

The frame 2 and the bottom wall 25 are preferably both made of metal, for example the frame 2 can be made of steel and the bottom wall 25 of aluminium.

The bottom wall 25 is made to all necessary specifications, well known to experts

in the field, to give a perfect and regular planarity and dimensional stability.

The reciprocal motion of the frame 2 and the bottom wall 25 is made possible for example by use of special grooved guides (not illustrated in the enclosed figures) made directly in the body of the frame 2, for example at its lateral walls 24c; the extractable bottom wall 25 slides in and out of these guides.

In a preferred embodiment of the invention, ball bearing guides 26 are used, mounted externally and parallel to the lateral walls 24c of the frame.

The bearing guides 26 are mounted solidly on the frame 2 and the bottom wall 25 and enable reciprocal motion between the bottom wall 25 and the frame 2, minimising friction and offering sufficiently rapid operating speeds.

The bearing guides 26 also guarantee perfect alignment between the frame 2 and the bottom wall 25, which is indispensable to correct functioning of the device 1.

The frontal walls 24a of the frame 2 define, together with the lateral walls 24c, the volume of the internal space of the loading tray or hopper, which will be filled with clayey powder material 3 during the process of the invention.

The process involves the use of at least one device 1 of the above-described type, one or more supply containers or trays or hoppers for a ceramic tile press, consisting of at least one frame 2 having a bottom wall 25 which is extractable or in any case mobile with respect to the frame 2.

In a preferred embodiment, a plurality of containers or trays or hoppers of the above-described type is used.

The containers (or trays or hoppers) will be described hereinafter in general terms as"trays".

The trays (see figure 4) are generally transported by special and known means for movement, such as one or more belt systems, to a plurality of loading stations 10, which in turn can be made by setting up one or more specially equipped hoppers

in series. The hoppers can be, for example, equipped with sieves, screens or the like.

The trays are loaded at the hoppers with the forming material, or rather with a mixture of forming materials, which are generally clayey powder materials 3.

In the process of the invention the ceramic tile is subjected to pressing with the upper face thereof (i. e. the surface which will be in view) facing downwards, that is, facing the bottom die of the press, while the laying side of the tile is upwards- facing, i. e. facing the upper die of the press.

The supply hoppers therefore deposit first the oxides and or colorants, which are the higher-quality materials which give the finished tile the desired three- dimensional aesthetic effect, and thereafter the base clay, which is destined to constitute the body of the tile, i. e. the structural support of the tile.

In a possible application of the invention, there could be a succession of at least five supply stations (not shown in the figures).

At a first station a silk-screen composition of powder could be deposited on the extractable bottom 25 of the tray.

At a second station, a plurality of composite solids could be laid by free-fall into the tray. The solids could contain sands, for example semi-fired clays, fluxes, glazes and so on.

At a third station colouring oxides could be added here and there to create the same aesthetic effect as the veins in natural stone.

At a fourth station a mixture of ceramic colorants could be added to give the tile its overall colour.

At a fifth and final station, the tray could be loaded with base clay, i. e. the material which goes to make up the tile body.

After the final loading stage, it is preferable to proceed to a smoothing stage of the forming material in order to make sure the tile has a homogeneous thickness,

and to remove waste or excess clay material from the tray.

All of the final work is done on the clay base of the tile, and not the high-quality materials (oxides, colorants and so on), which makes for considerable savings of expensive materials.

At this point at least one tray has been filled and is ready to be positioned at the die of the press.

The tray is therefore positioned on a special press-loading truck 6, which generally comprises a flat and smooth surface, for example made of teflon, or at least covered with a layer of teflon. The flat and smooth surface is obviously coplanar to the plane of the press.

The press-loading truck 6 comprises known and suitable means for movement 9, for braking and starting, command and control, and operatively associates with at least one or preferably a plurality of supply trays of the above-described type.

It is usually possible to associate at least three trays of the above-described type to the press-loading truck 6.

Through the press-loading truck the trays are introduced into the operative space of the press: this is schematically illustrated in figure 4.

In figure 4, a container 1 i. e. a tray according to the present invention, is mounted on the press-loading truck 6 and inserted in a press 4 for ceramic tiles.

The press 4 is equipped with a die consisting of two semi-dies, a namely a bottom die Sa and a top die 5b.

When the tray is inserted into the press 4, precisely the bottom die Sa, the bottom die Sa is in a first position, which can for example be called the loading position.

In this loading position, the bottom die Sa is at the same level as the press-loading truck 6.

The insertion (by the truck 6) of the tray internally of the operating space of the press 4 coincides with the removal from the same operating space of an already-

formed ceramic tile 7. This is possible because a pusher organ 12 is solidly associated to the press-loading truck 6 and pushes the formed tile out.

During this stage of the operation the top die 5b is located in a first position, which can, like the first position for the bottom die Sa, be termed a loading position.

In the loading position, the top die 5b is distanced from the bottom die 5a so that enough space is created in the pressing zone for easy insertion of the press- loading truck 6.

The press 4 loading stage is followed by a rapid extraction of the mobile bottom wall 25 (see figure 5) of the tray, through the use of special and known means of movement and control, not illustrated in the figures, which engage the portion of anchorage 22 and the guides 23 of the bottom wall 25.

It is possible to create productive cycles which have a rapid extraction speed of the bottom wall 25 since the bottom wall 25 is very light.

The extraction of the bottom wall 25 of the tray is preferably done at the same time (more or less) as the insertion of the tray in the bottom die 5a of the press 4.

With this synchronisation, if the extraction movement of the bottom wall 25 is done in an opposite direction to previous or, even better, contemporaneous movement of the whole tray as it enters the press 4, a special dynamic compensation effect is achieved, by means of which the ceramic powders 3 which constitute the tile to be pressed, when falling towards the bottom die Sa following the extraction of the bottom wall 25 of the tray (see figure 6), stay in their original order or composition.

This dynamic compensation effect is especially important for the high-quality components of the materials, i. e. the oxides, glazes, etc. , in effect the materials which will give the desired three-dimensional aesthetic effect to the finished tile.

As these higher-quality materials are initially at the bottom of the tray, close to or in contact with the bottom wall 25 thereof, they will benefit directly from the dynamic compensation effect and will deposit on the bottom die 5 a without being mixed up with the other materials, so that they will have more or less the same configuration as before the drop, and the resulting aesthetic effect in the finished tile will not be compromised.

The material dropping stage into the bottom die 5a is made easier by the fact that the bottom die 5a, subsequently to the extraction of the bottom wall 25, lowers and is brought into an intermediate position below the plane defined by the press- loading truck 6 (see figure 6). The forming material therefore deposits gently inside the bottom die 5a.

Once the clayey powder material 3 has been deposited inside the bottom die 5a, the now-empty tray can be removed by extraction of the press-loading truck 6 (see figure 7). During this stage any excess forming material on the laying surface of the tile is removed by skimming, done by special means 13 for skimming which are solidly constrained to the press-loading truck 6.

At this point the pressing operation can begin.

Usually the pressing cycle begins by bringing the lower die 5a into a third position, which we can term the pressing position (see figure 8).

When the bottom die 5a is in the pressing position, it is best positioned to receive the top die 5a-this is to say that the pressing operation can now take place (see figure 9) without risking damage to the press 4 or the various apparatus connected thereto.

The pressing operation is achieved by lowering the top die 5b into a second position, i. e. a pressing position, on the bottom die 5a.

After the pressing is complete, the bottom 5a and top dies 5b are returned to their loading configuration, that is, into their original positions. The press 4 therefore

opens and a new work cycle can begin, with the ingress of a new tray and a contemporaneous expulsion of the just-formed tile.

Cycle times can be further improved by using a plurality of trays, so that the press 4 can work in a continuous cycle, following the same times usually used for normal trays, i. e. those which are not equipped with the mobile bottom wall 25.

The plurality of trays is moved by known and suitable means for moving the material, which means transport the trays during both the press loading and unloading stages, as well as during the tray-loading stage in conjunction with the loading stations.

The material movement means can be assembled in various ways and configurations. For example, in the accompanying figures of the drawings, reference is made to a solution which sees the movement of the trays on two different planes, one for supply to the press and another for recycling the empty trays towards the loading stations.

However, other solutions can be adopted which involve tray movement on a single plane, for example along a circuit having a horseshoe configuration, and others besides.

The invention achieves its set aims.

In particular, the invention makes available a process for pressing ceramic tiles, as well as a device for realising the process, which enables high-quality three- dimensional aesthetic effects to be obtained, using simple apparatus and with fast and economical production cycles. The process and the device are particularly, though not exclusively, suitable for use in vitrified stoneware tile manufacture.

The invention further makes available a ceramic tile pressing process and a device for realising the process, which minimises waste of forming material, especially high-quality material used for obtaining the desired aesthetic effects.

Finally, the invention makes available a pressing process for ceramic tiles, as well as a device for realising the process, which is to a considerable extent achieved through the use of known and standard plants and apparatus.