The invention relates to improvements for improving the functionality and durability of isostatic buffers, that are in particular suitable for pressing ceramic tiles. The prior art comprises numerous types of isostatic moulds the common feature of which is to exert pressing force on the powders to be compacted with a flexible diaphragm pushed by a pressurised liquid so as to standardise pressing force. A mould for ceramic tiles generally consists of two plates, a lower and an upper one, called "buffers" in jargon, that slide axially inside a containing frame, called "die" in jargon. The reciprocal approach of these two buffers compacts the powder contained between them, the isostatic mechanism is usually contained in one of these buffers.

In a first category of isostatic buffers, an example of which is disclosed in EP 0736363, the diaphragm is anchored peripherally to the rigid edge of the buffer whereas the internal zone is free to fluctuate on the isostatic liquid together with a stiffening slab.

In a second category, an example of which is disclosed in EP 0556163, the diaphragm, in addition to be anchored on the peripheral edge of the buffer, is also anchored to rigid intermediate zones, at which the diaphragm remains coplanar and does not behave with an isostatic effect.

The isostatic pressing normally carried out in the field of ceramic tiles with the buffers of both the aforementioned categories is defined "passive" as the increase of pressure of the liquid, already present inside one of the buffers is induced through reaction in the gradual reciprocal approach of the latter, the overall volume of isostatic liquid in the circuit remaining constant. Otherwise, isostatic pressing is defined as "active" if, whilst the mould is already in a stable closing position, the pressure increase is

obtained through the introduction from without of the pressurised liquid.

Isostatic moulds exert uniform pressing on the material, compensating the loading differences in the pressing space with corresponding variations of thickness in the pressed product . When these loading deformities are of slight degree, the isostatic mould exerts the function that is proper to it without drawbacks. When, as is not infrequent, the loading deformity becomes significant, the diaphragm is subject to excessive displacement with risk of detachment or breaking.

This drawback is very frequent and damaging, especially when, in order to make pressing uniform in all the different parts of a mould, the isostatic liquid is connected in a single circuit that connects all the various isostatic buffers to enable free transfer of liquid from a buffer to the other.

In this case, in fact, if a space of the mould or a portion thereof remains devoid of or lacking in powder, during the pressing step all the liquid of the isostatic zone transfers to this zone, making the. diaphragm explode; simultaneously in the other buffers, the diaphragm that is no longer supported by the isostatic liquid is squashed against the bottom of the buffer losing totally the isostatic effect and above all risking, in certain circumstances, becoming torn.

This is dangerous because what has happened is not always noticed and therefore in addition to the damage caused by replacement of the moulds sometimes much more serious damage occurs that is due to production rejects.

In order to overcome these drawbacks, the general tendency of manufacturers has been to construct the most rigid and fixed diaphragm and to reduce the volume of liquid, thereby falling into an increasingly poor and unsatisfactory hydrostatic trend.

Furthermore, devices have also been adopted for

controlling the hydraulic circuit of these moulds. The device disclosed in IT1287436 has only the function of enabling the volume of liquid inside each single buffer to be adjusted manually to standardise pressing between the various buffers, thus preventing the various buffers of the same mould from being connected with each other .

The devices disclosed in IT1104511, IT1257506 and IT1262666 comprise means for controlling the pressure and/or the volume of isostatic liquid in the pressing step, configured for overcoming technical drawbacks that are different from those that the present invention intends to overcome . Buffers of the type EP 0736363 that are sometimes preferred for the aesthetic results on the pressed product are nevertheless very vulnerable near the elastic joint arranged peripherally around the stiffening slab, because, if adequate counterpressure of the powder is lacking, this joint constitutes a preferential leak route for the highly pressurised liquid.

In IT1257667, EP1291145, EP1403016, isostatic buffers are disclosed with a diaphragm that is anchored to fixed intermediate zones and with movable zones of the diaphragm cooperating with respective axially sliding pistons that have a stop preventing movement toward outside. The function of this movement limit is to prevent overstressing of the diaphragm in the event of faults in loading the mould space or avoiding deformation that is too clearly visible on the back of the tile. This type of buffer is also very vulnerable in the case of great loading fault. As the pressures in question may also be greater than 500 bar, on the body that comprises these movement stops and on the fixing screws enormous stress is exerted that is such as to damage the buffer.

In IT1257667 there is also disclosed a system for

connecting together the isostatic buffers through channels obtained in the supporting plate. The connection between the channel of the buffer and the channel of the plate underneath is indirectly obtained by interposing two pistons, one of which is arranged in the buffer and the other in the supporting plate, coupled mechanically by means of struts. The function of this piston seal is not to disperse the liquid during the step of assembling and disassembling the buffer. This mechanism greatly limits compensation capacity because, in the pressing step, as the washers of the two pistons are subject to extrusion (cyclical pressure acts on them only on one side) , the great friction of the washers against the wall tends to immobilise the pistons, furthermore causing rapid deterioration of the washers with consequent loss of the liquid. In IT1257667 and EP1291145 also being able to replace the front part of the buffer without intervening on the isostatic liquid is provided for, which remains sealed in the base of the buffer. The proposed solutions are nevertheless incomplete for the following reasons :

- the interchangeable slab also performs the function of ■ limiting the movement of the pistons with an abutment surface thereof, it therefore has to be very tough and firmly anchored to the base body not only in the peripheral zones but also in many intermediate zones, as a result the active compensation surface has to be very limited, also to enable the insertion of multiple screws for fixing into the intermediate rigid zones of the buffer, furthermore, this also involves numerous manufacturing and assembling processes;

- the manufacture of the diaphragm in the interchangeable slab thus conceived is very laborious because two moulding dies are necessary, one for the external face with the conformation of the tile, and one for the internal face for obtaining the seats of the pistons, furthermore, the

mechanical processes have to be very precise ^" to have a minimal play between pistons and corresponding seats;

- both the external diaphragm and the seal washer of the pistons become subjected to great extruding action. This is a very serious drawback, as the intrusion of the diaphragm into the gap present around the piston tends to jam the piston, reducing greatly compensation sensitivity. Similarly, the problem of extrusion is present in the seal washer on the piston. It is certainly true that anti- extrusion washers or stiffer elastomers can be used, nevertheless these ' solutions will inevitably lead to reducing compensation sensitivity.

- lastly, in the case of EP1291145 the inevitable slow leak from the washers of the pistons, once the space between the washer and the diaphragm has filled with liquid, leads to the immobility of the pistons, or to the detachment of the diaphragm or any way to loss of the liquid. It is to point out that in the isostatic buffers of this type a low ratio of active movable surface with respect to the stiff surface, in addition to procuring poor compensation capacity, may also cause a serious visibility drawback of the rigid zones in the front face of the tile, what in jargon is defined as "brand transparency". This drawback occurs in the zones of the tile where loading of the material is poorer, here in fact, whereas at the diaphragm the pressure transmitted to the material corresponds to the normal envisaged value, in the adjacent rigid zones thickness remains high and the material is scarcely pressed.

In a normal atomised ceramic paste the pressing forces are transmitted to the thickness of the tile mainly in the pressing direction and also, with a gradually decreasing influence, in diverging directions (it can be hypothesised with reasonable approximation that the critical angle within which the forces are transmitted with still

significant influence is approximately 50-60° with respect to the pressing direction) . Thus if the size of these zones with poor pressing is of a size of magnitude comparable to the thickness of the tile this pressing difference is also manifested on the visible surface of the tile, on the other hand, if the zone of poor pressing is less wide, and is thus of an order of magnitude corresponding to a fraction of the thickness of the tile, this pressing difference diminishes progressively in thickness and does not appear on the visible face. In other words, when the poorly pressed zones are narrow, a hypothetical point of the face in view will be influenced by a surface portion of the back that comprises only a small part of these narrow zones with low pressing. This "transparency" phenomenon is also accentuated by the fact that the less the isostatic surface extends the more it is induced to move in thickness to compensate. A compromise for overcoming this problem of transparency consists of compensating in a hydrostatic manner, also at the support ribs, in this case, however, the support surface is no longer coplanar and, as the support of the tile becomes coplanar during the firing softening step, possible unevenness of planarity may appear to be unacceptable on the visible face of the tile. It is thus important to have the possibility of checking the mobility of the support ribs to eliminate the "transparency" defect, keeping the drawback of non-planarity within tolerable limits . A first object of the present invention is an isostatic buffer provided with the possibility of interchanging the part subject to wear keeping the isostatic liquid circuit sealed, with a wide compensation surface in maintaining a support surface of the back of the tile tending to be parallel to the visible face, with significant compensation sensitivity that is resistant, economically regenerable and, in an advantageous embodiment, with safe control of the mobility limit of the diaphragm.

A second object of the present invention is to prevent excessive movements of the diaphragm of the isostatic buffers that are hydraulically connected together, also in the presence or great loading faults and without noticeably stiffening the mobility of the diaphragm in the normal working field thereof .

A third object of the present invention is to obtain that in the event of accidental breakage of one of the isostatic buffers or of the hydraulic connecting circuit, the damage is limited only to that damaged portion and that the continuation of the pressing may be possible with the functionality of the mould only partially limited. A fourth object of the present invention is to obtain that, in the isostatic buffers connected hydraulically together, the presence of a preset minimum volume of liquid is always ensured in each of the buffers . A fifth object of the present invention in an advantageous embodiment is to obtain a simple and rapid change of the isostatic buffers, without any intervention on the connecting hydraulic circuit, maintaining maximum compensating capacity and without drawbacks due to great loading faults . A sixth object of the present invention in an advantageous embodiment is to enable hydrostatic connection of the isostatic buffers without dangers of leaks of liquid in any operating step.

A seventh object of the present invention in an advantageous embodiment is to enable the functionality of every single isostatic buffer to be monitored, reporting, with precise indications, or with alarms, variations in the volume of liquid present in each single buffer throughout the pressing cycle. Some of these objects are achieved in a first aspect of the invention through a buffer for isostatic pressing of tiles, comprising:

-a base body with a face provided with, a plurality of cavities closed by respective movable walls, said cavities being intercommunicating and filled with liquid; -a slab the external surface of which defines the pressing plane, coupled in a removable way with said face, said slab having movable portions corresponding to said movable walls and adjacent stationary portions suitable for forming the supporting protrusions of the tile; characterised in that the space defined between said movable portions and said stationary portions, in the thickness comprised between said liquid and said pressing plane, has substantial continuity of incompressible material.- In a second aspect of the invention a mould is provided for passive isostatic pressing comprising a plurality of isostatic buffers interconnected by a connecting network suitable for transmitting the pressure of the liquid in the pressing step, characterised in that each of said buffers is connected to a hydraulic device suitable for defining the volume of liquid that can flow into each of said isostatic buffers.

In a third aspect of the invention a buffer support base with rigid zones is provided that is suitable for solidly supporting isostatic buffers, comprising a channel for interconnecting with a liquid said isostatic buffers, characterised in that inside said rigid zones there are elastically movable diaphragms hermetically closing cavities underneath obtained in the body of said buffer support base, said cavities being full of said liquid and connected to said channel.

In a fourth aspect of the invention a buffer is provided for isostatic pressing comprising an active face provided with a movable wall placed to close a chamber full of liquid, characterised in that the face opposite said active face comprises an elastically movable diaphragm arranged to close a cavity communicating with

said chamber, the space comprised between said movable wall and said elastically movable diaphragm being full of said liquid.

In a fifth aspect of the invention a buffer is provided for isostatic pressing provided with a movable wall placed to close a chamber in which a liquid is present, characterised in that it comprises a detecting means for detecting the position of- said movable wall and a flow- adjusting means of said liquid, said- adjusting means interacting with said checking means.

In a sixth aspect of the invention a method is provided for controlling the movement of the movable wall of an isostatic buffer during the pressing cycle, said movable wall being placed to close a chamber in which a liquid is present, characterised in that it provides for detecting the position of the said movable wall with a detecting means and modifying the flow of said liquid with a flow-adjusting means interacting with said detecting means . The invention can be better understood and implemented with reference to the attached drawings that illustrate some embodiments thereof by way of non-limitative example, in which: Figure 1 is a schematic and fragmentary section view of an isostatic buffer according to the first aspect of the invention, during an operative condition;

Figure 2, 3 and 4 are views like the one in Figure 1, in three further versions according to the first aspect of the present invention; Figure 5 is the view of the buffer in Figure 4, decomposed, and in a non-operative condition; Figure 6 is a view like the one in Figure 4 in a further version according to the first aspect of the present invention; Figure 7 is a schematic view of the apparatus according to the second, third and fourth aspect of the present

invention, in a configuration with three buffers;

Figure 8 is a schematic view of the apparatus according to the second, third and fourth aspect of the present invention, in a configuration with two buffers; Figure 9 is a schematic and section view of a detail in

Figure 7 and Figure 8;

Figure 10 is a schematic and section view of a detail like the one in Figure 9, in a different, diaphragm, embodiment ; Figure 11 is a section view of a detail like the one in

Figure 9, in an embodiment integrated inside a buffer;

Figure 12 is a section view of a detail like the one in

Figure 10, in an embodiment integrated inside a buffer;

Figure 13 is a section view of a detail like the one in Figure 10, in an embodiment integrated inside a buffer support base;

Figure 14 is a section view of a detail like the one in

Figure 10, is an embodiment split between buffer and buffer support base; Figure 15 is a section view of the detail in Figure 14 , in an operating step.

Figure 16 is a schematic and fragmentary section view of an isostatic buffer according to the fifth and sixth aspect of the invention,- Figure 17 and Figure 18 are sections of a detail in

Figure 16 in different operating steps;

Figure 19 is a schematic and fragmentary section view of an isostatic buffer according to the fifth and sixth aspect of the invention, in a different form; Figure 20 • is a schematic plan view of the buffer in

Figure 19 that illustrates a possible version of the connecting network;

Figure 21 is a schematic and fragmentary section view of a buffer according to the fifth and sixth aspect of the invention in a further embodiment;

Figure 22 and Figure 23 are views like the one in Figure

21 in different operating steps;

Figure 24 is a perspective view of a detail in Figure 21 • highlighting a detecting and adjusting device.

Figures 25, 26, 27 and 28 are plan views of the detail in Figure 24 in two different forms and in two different operating steps.

Figure 29 is a section of a detail in Figure 21 highlighting a version of the detecting and adjusting device . Figure 30 and 31 are sections of a different detecting and adjusting device in different operating steps.

Figure 32 and 33 are sections of a further different detecting and adjusting device in different operating steps. Figure 34 is a section view of a further version of the detecting and adjusting device, in an operating step.

Figure 35 and 36 are partial section views of a buffer according to the fifth and sixth aspect of the invention in two further versions . Figure 37 is a section of a detail of the buffer according to the fifth and sixth aspect of the invention that illustrates a different type of expansion chamber.

With reference to Figure 1, the isostatic buffer 1 comprises a base body 2 a face 3 of which has a plurality of cavities 4 closed by a diaphragm 5 on which rigid tesseras 6 are firmly anchored. Around each of the cavities 4 there are elastic rings 7 arranged in seats 8 leading directly onto the face 3. The main function of these elastic rings 7 is to enable the diaphragm 5 to be formed "in situ" without invading the space below the rigid tesseras 6, and to form "anti-peeling" lips 9 on the diaphragm 5.

In the disclosed embodiment, the cavities 4, in a plan view of the face 3, have a square perimeter with rounded corners and are arranged in an orderly ^ΛX chequered" arrangement but may have any other shape and arrangement .

The diaphragm 5, the external face B of which is substantially flat, is firmly anchored to the base body 2 in all the contact zones and extends in a subtle layer F also over the entire face 3 of the base body 2. The cavities 4 are full of liquid 10 and communicate hydraulically by means of channels 11 obtained in base body 2.

Below each of the rigid tesseras 6 a detecting means 12 is arranged consisting of a stem 13 the top of which rests on the bottom of the tessera 6 and which follows the movement thereof. The stem 13 runs axially to the inside of a hole 14, enabling the passage of the liquid 10 through longitudinal grooves 15 obtained in the walls of the hole 14. An adjusting means 16 consisting of a shutter 17 that, pushed by a spring 19, can form a hermetic seal by resting on the conical surface 18 is connected to the stem 1. When the shutter 17 rests on the conical surface 18 , the passage of liquid 10 between the cavity 4 and the corresponding channel 11 is prevented and the stem 13 protrudes with respect to the bottom 20 of the cavity 4 by a dimension Z.

The conical seat 18 is obtained in a removable element 21, which is screwed tight and is coplanar with, the bottom of the cavity 4.

The external face B of the base body 2 has a plate 22 resting on it that is fixed to the perimeter in a removable manner with a series of gripping screws 23. The plate 22 obtained from a steel slab is provided with through openings 24 , peripherally corresponding to the seats 8 and is integrated with an elastomer 25 that fills the entire space of the openings 24. The elastomer 25 extends from the bottom of the openings 24, so as to define a flat coplanar surface at the base of the ribs 26 up to the opposite face where the pressing surface 27 is defined. The plate 22 that is thus composed has movable

portions 28 consisting of. elastomer 25 only, surrounded by- stationary portions 29 that comprise the steel ribs 26. The pressing surface 27 at the stationary portions 29 has hollows 30 intended to mould the rear support projections of the tile. The diaphragm 5 of the base body 2 is thus perfectly coupled with the elastomer 25 of the slab 22 without discontinuity or interstices and the movability of the movable portions 28 is obtained through elastic deformation of an annular joint S, that extends in a thickness Y without interruption from the liquid 10 to the pressing surface 27 and consists of two overlapping parts in contact, a first part Sl belonging to said base body 2, a second part S2 belonging to said slab 22. This conformation enables soft elastomers to be used without ■ danger of breakages or extrusions and without friction, even at higher pressures as there is no sliding between different surfaces.

As already said, the slab 22 can be advantageously fixed only peripherally, so as to have more soft compensating surface 28. Intermediate fixing is not necessary because the slab 22 during pressing will anyway remain adhering to the body 2, in fact the stationary portions 29 are subject to the pressure of the powder but not to the pressure of the liquid 10. Also in the case of pressing without the presence of powder the diaphragm 5 can only rise by a limited amount H, and this shift will be easily assisted by the elastic yielding of the elastomer 25 and possibly also by slight flexing of the slab 22, which in this case will be able to distance itself from the surface B without harm.

In' the pressing step, the elastomer 25 also exerts pressure on the side walls 32 of the openings 24. As there is no adequate counterpressure on the external wall 33, it is advisable, in order to remain within the steel' s tensile strength limits, for the width G of the ribs 26 not to be less than approximately a sixth of the width of

the openings 24. Nevertheless, a peripheral snap-fit 34 may be provided between the slab 22 and the base body 2 so that these forces generated by the pressure are discharged on the base body 2. In this case, the ribs 26 can have a more limited width G so as to increase to the maximum the movable compensating- surface 28.

As shown in Figure 2, instead of the snap-fit 34 cylinders 37 can be adopted that are inserted precisely into holes obtained on the two coupled flat surfaces, this can be advantageous, machining flat surfaces without protrusions being simpler.

The fixing screws 23 can also be inserted on the pressing plane side, in this case it will be appropriate to cover the heads of the screws with elastomer caps the top of which is coplanar with the pressing plane 27. Instead of the screws 23 a suitable magnetic fixing can also be adopted. The choice of thickness of the slab 22 does not have any functional limitations except for those connected with the mechanical machining thereof . It may therefore be appropriate to construct a disposable type of slab 22, approximately 4-6 mm thick, or less, so as to use the minimum quantity of steel and elastomer 5. The precision of the openings 24 is not critical, so the latter can be obtained by shearing, laser-cutting or any other appropriate system so as to maximise construction economies .

The projecting edge 35 of the slab 22 is advantageously obtained by applying and welding hard material, this also enables machining to remove material to obtain the lowered plane 36 to be avoided.

It is shown that, unlike what happens in the buffers manufactured according to the prior art, also the higher pressure exerted without the presence of powders cannot damage the buffer 1 as the pressure will be borne entirely and easily by the shutters 17.

The independent control of the movement H on each of the movable portions 28 makes this buffer 1 completely resistant to any loading fault. Even with the most anomalous load, such as could for example be a complete lack of powder in a large corner, at each of the cavities 4 of the corner without powder only the limited quantity of liquid 10 could arrive that is suitable for lifting the stiff tessera 6 to point H and all the other zones will continue to act isostatically because of the presence of the liquid 10. In the case of known isostatic buffers this hypothetical condition would produce disastrous effects as all the liquid of the buffer, and of all the other connected buffers, would be concentrated in this limited zone, which would therefore explode. The buffer 1 shown in Figure 2, differs, in addition to the snap-fit 34, 37 system already illustrated, by the fact that the interchangeable slab 22 does not have the ribs 26. The slab 22 thus consists of a steel C frame with the interior completely full of elastomer 25. Also in this case the movability of the movable portions 28 is obtained through elastic deformation of an annular joint S that extends without interruption from the liquid 10 to the pressing surface 27. Here, nevertheless, depending on the thickness of the slab 22 and on the yieldability of the elastomer 25, there will be a certain mobility of the pressing surface 27 also at the hollows 30. In Figure 3 an intermediate solution is illustrated that provides a reticulated body R with ribs 26 that is independent of the frame C, of a height N that is less than the height of the frame C so as to have at the hollows 30 an adequate thickness M of elastomer 25. This body R, obtained from a steel slab or obtained through moulding of plastics or elastomer materials of great hardness, is inserted inside the frame C and included during the vulcanisation step in the elastomer 25.

In the example shown in Figures 4 and 5 the body R is

arranged recessed by an amount P with respect to the supporting plane of the frame C and this recess is occupied by an elastomer slab 38. This embodiment enables a certain mobility of the pressing surface 27 to be obtained even at the hollows 30 and high pressure of the pressing surface to be maintained at the same time due to the presence of a limited thickness M of elastomer 25. This feature is particularly useful when for example in the body mixture of the ceramic tiles for aesthetic purposes there are large and hard granules . If the latter are in fact pressed with a soft surface they would remain protruding with respect to the bordering surface, causing an unacceptable alteration of the support surface 30 of the tile. It is pointed out that these adaptations can be implemented by simply replacing the slab 22 or even only the elastomer slab 38, without intervening on the hydraulic circuit . As shown in Figure 6, the frame C has a wider width and extends further inside the buffer beyond the outermost hollow 30a. This enables a frame C to be obtained that is sturdier and better anchored to the base 2 but with movable portions 28a of the external perimeter with a more reduced area. The frame can also extend as far as to comprise the second hollow 30b, or also more internally, thus enabling the movable portions -28 to all be kept the same size.

As shown in Figures 2, 4, 5 and 6, in the slab 38 and. in the elastomer 25 heavy-duty fibres 39 are advantageously included that are arranged parallel to the pressing surface 27. This enables the load on the internal wall 32 of the frame C to be lightened because the slabs 25, 38, whilst remaining flexible and movable in the normal direction to the pressing surface 27, will be unextendable in the direction parallel to the pressing surface 27. The fibres 39 can extend tightly gripping also on the frame C.

These heavy-duty fibres 39 may be, for example: glass fibre, carbon fibres, Kevlar ^® fibres of the Dupont company, metal fibres .

With reference to Figure 7, the hydraulic clutches of three isostatic buffers 101, that are provided with a movable active wall 102, are connected to an interconnecting network 103 with interposed hydraulic devices 104. The hydraulic device 104, as shown in Figure 9, consists of a tubular body 105 with a cylindrical internal wall 106 closed at the end by the covers 107 that have two respective conduits 117 and 118 in the axis that lead internally into --conical seats 137, 138. On the cylindrical wall 106 a piston 108 runs in a sealed manner that can move between two end abutting positions defined by the sealed contact of the protrusions 135, 136 of the piston 108 against the conical seats 137 138. The piston 108 provided with a seal washer 113 is normally maintained during the inactive step in an intermediate position with respect to the two end positions through the action of two opposing springs 114.

The conduits 117 and 118 are intercommunicating by means of a bypass 119 provided with a closing valve 120 as shown in Figure 7.

The tubular body 105 advantageously consists of non- ferromagnetic material and a magnet 121 is fixed to the piston 108 the movement of which can be displayed on the outside by a ferromagnetic sphere 122 that follows the movement thereof and/or be reported by magnetic alarm sensors 123, 124 (for example Reed bulbs) with an adjustable position.

Figure 8 shows a special connection case where a sole hydraulic device 104 is present that is connected to two buffers 102.

After connecting the buffers 101 as in Figure 7 and

filling all the cavities and the circuit with liquid 10, the mould can operate. • If loading of the various recesses does not display great deformity, the mould will act in the normal manner, compensating pressing in an optimal manner. The operator in charge of the control will in all cases have the opportunity of monitoring the operation of each single buffer 1, controlling the position taken up by the sphere indicators 122 at each step of the pressing cycle. In other words he will be able to realise at first sight whether a given recess has been loaded with too much powder or on the other hand with little powder or whether drawbacks of other type are occurring in the mould (mechanical deformation, asymmetry in movements, etc.) and can then intervene preventively with the appropriate adjustments.

If, on the other hand, a serious loading fault occurs, such as for example a complete lack of powder in one of the six recesses of a mould, the apparatus will act as explained below. At the start of the pressing step, the five buffers 101 that act on the recesses where there is the powder will start to expel the liquid 10 that will thus move to the buffer 101 corresponding to the empty recess. Through the conduit 117 the liquid 10 will enter the chamber 115 moving the piston 108, which, by overcoming the resistance of the spring 114, will reach the stroke-end limit, closing the conduit 118 with the shutter 136. At this point pressure in the chamber 115 will continue to rise until it reaches the maximum pressing value without any further transfer of liquid 10..

The powder of the five recesses will thus have been pressed in a perfectly isostatic manner and without any damage to the corresponding buffers 101. Also the- buffer corresponding to the empty recess will not have, suffered any damage as only the quantity of liquid 10 moved by the piston 108 will have reached it. Furthermore, in the-

meantime, through activation of the sensor 124 the pressing cycle will have been stopped and/or an alarm will have been reported.

The apparatus 104 can also be used to prevent the liquid 10 from being able to completely leave a buffer 101 during the pressing step, this is particularly important so that none of the buffers can lose isostatic effect or suffer damage. It is to point out that the hydraulic devices 104 do not noticeably reduce the freedom of movement of the diaphragm of the buffer 101 in the preset field of work. The only resistances introduced are those of the springs 114 and those of the friction of the washer 113 against the walls 106. Furthermore, this washer 113 works in optimal conditions because it is not subject to extrusion as the pressure of the liquid 10 in the two chambers 115, 116, even at the end of the stroke, is balanced (the only difference is due to the slight load of the springs 114) . This is important because in this way the washer 113 can be optimised to have maximum seal against leaks with minimum friction on the wall 106, without concern about seal performance at high pressure. This important operating feature arises from the fact that the elastic sealing means 113 extends without interruption between the isostatic liquid 10 of the buffer 101 and the isostatic liquid 10 connected directly or indirectly to the other buffers 101. Therefore, also in conditions of high pressure, it is undeformed and in a substantial .condition of hydrostatic equilibrium. The friction against the wall 106 on which it runs, is even at high pressure substantially the same as that that occurs without pressure. Several washers 113 can also be used, but between them there must be the liquid 10 so that hydrostatic equilibrium ' is assured. Substantially, continuity between the elastic sealing

means and the liquid 10 must occur.

In order to compensate for possible "false settings" of the apparatus generated by leaks of liquid 10 through the washer 113, all the bypass valves 120 may be opened occasionally manually or automatically during the non- pressing step. In this way normal operating conditions are restored, i.e. an equilibrium of- the pressure of the liquid 10 will be obtained in the non-pressing phase of all the buffers 101, at the same time all the pistons 108 will return to the normal intermediate rest position.

This opening of the bypass can also be used to restore (manually or automatically) the normal volume of liquid 10 inside the circuit, through control of the pressure of the liquid 10 during the non-pressing phase.

In Figure 10 the hydraulic device 104 consists of a lenticular casing formed by two peripherally bolted spherical caps 130, 131 in the interior of which the two chambers 115, 116 are separated by an elastomer wall 132. The central part of the wall 132 has rigid protrusions 133 on both faces that are suitable for resting sealingly against the outlet of the channels 117, 118. In Figure 11 the hydraulic device 104 is housed in the body 134 of an isostatic buffer 101. In this case the interconnecting network 103 will be housed in the base block. The hydraulic coupling between ^' the buffer 101 and base block can be obtained with known seal devices that are able to ensure closure of the relative outlets even with the buffer dismantled.

In Figure 12 the hydraulic device 104 of the diaphragm 132 type, like the one in Figure 10, is integrated into the buffer 101. In this case one of the cap surfaces is obtained directly in the body of the buffer 101 whilst the other cap is obtained in the closing cover 140, locked with suitable means 141 on the body of the buffer

101 .

The hydraulic devices 104, both of the cylinder type with piston 108, and of the type with diaphragm 132, can be arranged inside each base, block 139, as shown in Figure 13, or in the common plate 170 below that holds all the base blocks 139. A sensor 142 that is able to detect the distance Dl of the magnetic body 143 incorporated in the diaphragm 132, will send a signal to a remote control station. With reference to Figure 14 and 15 the invention is applied in such a way as to allow a quick replacement of the buffers 101 keeping the hydraulic circuit perfectly sealed. The buffer 101 has in the rear face thereof a cavity 145 with a pseudospherical surface with a channel 118 that leads into the chamber 146 under the pressing diaphragm 147. The cavity 145 is closed by a circular elastomer diaphragm 148 the external face of which in rest status is coplanar with or protrudes slightly from the rear face 144 of the buffer. The diaphragm is kept in position by a flange 149 fixed firmly to the body of the buffer 101 with screws 150 and the whole cavity is filled with liquid 10. If the isostatic buffer has to contain the liquid 10 at a certain pressure to be able to mould the chambers 146, it will be appropriate to have the diaphragm 148 conformed with a certain concavity facing outside so that it does not assume an excessively protruding shape due to the internal pressure of the liquid 10. The buffer support base 139 has at each diaphragm 148, a cavity 151 with a diaphragm 152 that is symmetrical with and faces the diaphragm of the buffer 101. The cavity 151 has a hole 153 on the bottom that widens in a portion with a conical shape 154 and leads into the face opposite the plate 139 where there is a closing cap 156.

In the space between the closing cap 156 and the conical surface 154 a shutter 157 is arranged that is kept pushed against this conical surface 154 by a spring 158. The shutter 157 has a stem 159 that rests on the central part of the diaphragm 152 and in rest conditions keeps the hole 153 open. The stem 159 runs axially inside the hole 153, enabling the passage of the liquid 10 through longitudinal grooves 160 obtained in the walls of the hole 153 or of the stem 159. All the spaces 155 are intercommunicating by means of the channels 161 and all these watertight cavities are filled with liquid 10, for example hydraulic oil. The buffers 101 can be mounted on the base 139 keeping them locked with the known magnetic means and at this point the mould is ready for operating.

^• The diaphragms 148 152 resting on one another thus define a transferring zone of the hydrostatic pressure, all the buffers 101 will work isostatically transferring the liquid 10 through deformation of the diaphragms 148, 152, which will remain firmly coupled. Furthermore the volume of liquid 10 that can leave or enter any buffer will be well defined as these diaphragms 148, 152 move within a precise limit. Downward movement is limited by resting on the surface 151, upward movement is limited by the intervention of the shutter 157, which, as visible in Figure 15, will exclude any further passage of liquid 10 through the hole 153.

The intervention of this shutter 157 is very important because otherwise a serious loading fault could cause the buffer 101 to become detached from the base 139. As the diaphragms 148, 152 must have a good working surface, preferably around 5% of the surface of the buffer 101 so that average movement in the two directions of approximately 5 mm (average total movement 10 mm.) produces diaphragm 147 mobility of approximately 0.4-0.5 mm, and since, as already said, the pressure can

reach 500 bar, in the event of loading deformity, it may for example happen that on a buffer of 400x400 mm detachment force of approximately 40 tons is exerted, that can hardly be contrasted by a magnetic attack. In the case of the present invention with the presence of the shutter 157, the force of detachment that is exerted on the buffer 101 is only the force that the diaphragm 148 opposes to elastic deformation thereof as shown in Figure 15. (Pressure is completely excluded by the shutter 157 before the diaphragm 148 comes to touch the surface 145) . Even if a diaphragm 148 of very rigid elastomer is hypothesised, this force will be limited to a few tens of N. It is furthermore shown that not having sliding walls between different materials, movement of the diaphragms 148,- 152 occurs without friction also at higher operating pressure. They in fact" move elastically in conditions of maximum equilibrium inside the liquid 10, so there is maximum compensation sensitivity, just as the duration of these diaphragms 148, 152 will be significant.

It is advantageous that in rest conditions at least one of the two diaphragms 148, 152, has slightly protruding convexity to better ensure perfect coupling of the two diaphragms 148 152 in any operating step.

It is to point out that the buffers 101 and the buffer support bases 139 constructed with the seal diaphragms 148, 152, are absolutely watertight in any operating condition, not having any sealing member subject to sliding on a different surface.

Adjustment of the end position of the diaphragm 148 can be obtained by ^" varying the length of the stem 159 with suitable spacers, or replacing in the interface between the two diaphragms 152 148 suitable lenticular spacers 163 in elastomer material. For this purpose, as shown in Figure 14, the lower diaphragm consists of two distinct

part, the lower part 152 that is recessed with respect to the plane 162 of the plate 139, the upper part 163 that is removable and snap-fitted inside the flange 149. The peripheral edge 164 of this interchangeable pad 163 5 will be kept on the plane 162, the internal part can be flat or be provided with convexity or concavity according to requirements .

The diaphragms 148, 152, 161, 163, which define a transfer zone of hydrostatic pressure, will be

10 advantageously arranged in the axis of the buffer 101, so that the buffer 101 can be mounted in various axial rotation positions.

The devices exemplified in Figures 13, 14 and 15 refer to the lower buffers of the mould, nevertheless, they

15 can also refer to the- upper buffers, considering the Figures to be rotated by 180°. Also in the apparatus of Figures 14 and 15 a detecting system detecting the axial position of the diaphragms 148, 152 can be advantageously applied, for example with a sensor

20 arranged in the cap 156 or in the base 139 that is suitable for detecting the position of the shutter 157. It is to pint out that the apparatus according to the invention can be used as a safety system for the prevention of mould faults and breakages, and, no less

25 important, can also be used as a base for monitoring important pressing parameters that are not otherwise detectable with any other known means. For this purpose, the indicator 122 in Figure 9 can be replaced by a linear magnetic sensor or by another system that is

30 _. suitable for sending the signal to computerised remote control unit so that these data can be displayed on a screen and possibly be recorded and processed to show possible cyclical anomalies. Modifications of a practical-applicational nature can be

35 made to the invention without thereby falling outside the scope of inventive idea as claimed.

Thus for example the hydraulic device 104 may have stroke end abutments with adjustable positioning, replacing for example spacer rings 160 arranged between the cap 107 and the body 105 or axially adjusting from the exterior appropriate screw abutments .

With reference to Figure 16, the isostatic buffer T comprises a movable wall 201 provided with a stiffening slab 202 covered with an elastomer 203 vulcanised on site that seals a chamber 204 underneath that is full of liquid 10. The approaching or distancing movement of the slab 202 with respect to the bottom of the cavity 206 obtained in the body 207 of the buffer T is suitably followed by the elastic deformation by the peripheral elastomer 203 joint 208. The chamber 204 is connected through the manifold 209 to other similar buffers T arranged in the same pressing mould. Between the manifold 209 and the chamber 204 a detecting means 2210 is arranged that consists of a stem 211 resting on the bottom of the slab 202 and which is suitable for following the movement thereof. The stem 211 slides axially inside a hole 212 enabling the passage of the liquid 10 through longitudinal grooves Bl obtained in the walls of the hole 212 or of the stem 211. The hole 212 expands in a conical shape 213 and leads into the rear wall of the buffer T where there is a closing cap 214, and the space Sl comprised between the conical surface 213 and cap 214 communicates with the manifold 209. With the stem 211 an adjusting means is connected consisting of a shutter 215 that adapts to the conical surface 213, pushed by a spring 216. When the shutter 215 rests on the conical surface 213, the passage of liquid 10 is prevented and the stem 211 protrudes with respect to the bottom of the cavity 206 by a dimension Z.

In operation it is found that when the slab 202 is

raised with respect to the bottom 206 by an amount Zl that is less than the dimension Z, the buffer T acts normally, enabling the exchange of liquid 10 with the other buffers T through the manifold 209. When, however, the slab 202 rises above the dimension Z the hole 212 is sealed by the shutter 215 thereby preventing any further inlet transfer of liquid 10. Also higher pressure cannot damage the joint 208 or other parts of the movable wall 201 as this pressure will be entirely and easily supported by the shutter 215.

With reference to Figure 19 the face of the buffer T has a plurality of cavities 217 closed by a diaphragm 218 to which rigid tesseras 219 are firmly anchored. Elastic rings 220 are present the main function of which is to enable vulcanisation of the diaphragm 218 in situ without intruding on the space below the rigid tesseras 219. Below each of these cavities 217 there are abutting means 210 con shutters 215 similar to those already disclosed in the Figure 16. Operation is similar to what has been disclosed previously, nevertheless, this embodiment of the invention is also useful if the various buffers T of a mould are not connected hydraulically together, or when the buffer T of the mould is single. The independent control of the movement of the wall 201 on each of the plurality of movable zones makes this buffer T particularly resistant with respect to any powder- loading fault. Even if the most anomalous loading is hypothesised, such as for example could be a complete lack of powder in a large-sized corner, the buffer T ^' will be able to resist easily. In fact, at each of the cavities 217 corresponding to the corner without powder only the limited quantity of liquid 10 can arrive that is suitable for lifting the stiff tessera 219 up to the dimension Z and all the other zones will act in an isostatic manner through the presence of the liquid 10.

In the case of known isostatic buffers, this hypothesised condition would produce disastrous effects as all the liquid of that buffer and of all the other connected buffers would be concentrated in this small zone which would therefore explode.

In this embodiment in Figure 19 the entire mechanism comprising the stem/shutter 210, 215, the conical seat 213 and the spiral spring 216 is mounted from the inside of the cavity 217 by means of the body Q, provided with V notches suitable for screwing. This enables having a numerous series of closing caps 214 to be avoided, which closing caps 214, being cyclically subjected always to maximum pressure, could generate seal problems over time. In the case in Figure 19 the seal washer D of the body Q is stressed only in the case of lifting of the tessera 219 beyond the dimension Z, and therefore even a possible leak of one of these seals D does not affect the normal operation of the buffer T but only makes the protection mechanism ineffective in that specific cavity 217. The connecting channels between the cavities 217 consist of converging tilted holes U obtained on the bottom of the seats of the bodies Q. Alternatively, as shown by the broken line, the connection can also be made by means of holes Ml passing parallel to the plane of the buffer T.

As shown in Figure 20, in order to simplify execution and still maintain a good degree of safety, it may be appropriate to adjust with a single detecting means a plurality of interconnected cavities 217. For example, nine cavities 217 arranged 3x3 as a square could be interconnected to form a GR group, controlling with the detecting means 210 the diaphragm of the central cavity 217 of the GR group. Figures 21 to 23 show an embodiment of the invention that is particularly suitable for isostatic buffers T of the type with a single diaphragm with stiffening slab

202 .

On a peripheral part of the buffer T, in recesses 220 obtained on the bottom of the cavity 206, a detecting means is arranged consisting of elastic elastomer bodies 221 the slightly convex upper face 222 of which has through holes 223 which communicate through channels 225 with an expansion chamber 226. obtained in the body 207 of the buffer T or in the under-buffer locked thereupon. This expansion chamber 226 contains a rod that is sealingly slidable and is kept pushed to the part into which the channel 225 leads by a preloaded spring 228. The upper part 222 of the elastic body 221, in the undeformed condition, protrudes with respect to the bottom of the cavity 206 by a dimension Z and is kept squashed by a certain force by the slab 202 that thus occludes the hole 223.

There is a plurality of these elastic bodies 223 distributed in the periphery of the buffer T and cooperating with a plurality of respective expansion chambers 226 with a single chamber 226 on which all the channels 225 converge.

In this conditions, as long as the slab 202 remains lifted by a dimension less than the dimension Z it acts as a normal isostatic buffer as the slab 202 keeps all the holes 223 occluded and the liquid 10 all remains inside the cavity 204. When the slab 202 in the presence of a great loading fault is caused to lift up by a dimension Z2 greater than the dimension Z, it will lose contact with the elastic bodies 221 thus opening one or more holes 223. At this point, as shown in Figure 22 the liquid 10 will start to flow away to the chamber 226 overcoming the spring load 228. This flowing away will last until the lowering of the slab 202 again closes the holes 223. When the pressing cycle has finished the spring 228 will return the rod 227 to the stroke end and the liquid 10 will enter the chamber 204 through a

bypass 230 provided with one-way valve 231. This one-way valve 231 is necessary because as the holes 223 have a narrow section and the occluding force exerted by the slab 202 on these holes 223 is considerable, too high pressure would be necessary for reintroducing liquid 10.

Figures 25 to 28 show the particular operating mechanism • of the elastic element 221. In conditions of non- deformation, i.e. when the liquid 10 is not yet at operating pressure PR, the hole 223 has an open section (in the example in Figure 25 it has an oval shape, in the example in Figure 27 it has a square shape) . With the gradual increase in hydrostatic pressure PR it will tend to be squashed closed, the internal surfaces of the hole 223 coming into contact with each other, as shown in Figures 26 and 28. If the slab 202 rises excessively, it will be able to distance itself from the element 221 without hindrance as the hole 223 thus closed will not affect the hydrostatic equilibrium of the ^' slab 202. As soon as the slab 202 is detached the hole 223 returns to open, letting the liquid 10 flow away. This opening is induced by the elasticity of the material and by the hydrostatic pressure PR that is now also able to act progressively on the internal walls of the hole 223. If the hole 223 also .remains open during the pressing step, considerable force would be necessary to detach the slab 202. It should be borne in mind that at pressure of 500 bar, a hole 223 of the diameter of two millimetres generates a "suction effect" that requires force of over 150 N ^' to achieve detachment. The elastic elongation of the element 221 subject to this force could prevent or any way delay regular evacuation of the liquid 10. The body 221 may also have the shape of a continuous profiled section as shown in Figure 29. Wide zones of the buffer ^■ T can also be controlled without interruption, possibly maintaining a single discharge channel 225 as the connection thereto can be obtained

with a groove 232, obtained at the base of the shutter 221 or in the body 207 of the buffer T.

In Figures 30 and 31 the detecting and adjusting device comprises a hollow metal casing 234 screwed in the body 207 of the buffer T with the upper part coplanar with the bottom of the cavity 206. There are seal washers 235 and receiving surfaces 236 to enable screwing. Inside the casing 234 a bush 237 is arranged that slides axially without seal due to the presence of appropriate grooves 238. Within the bush 237 a shutter 239 can slide for a certain portion that is suitable for closing an opening 240 on the bottom of the casing 234. The shutter

239 is normally kept engaged against said opening 240 by a yielding spring 241 provided with locking ring 242. On the bottom of the casing 234 a compressed rigid spring 243 keeps the upper edge of the bush 237 resting against the slab 202.

During operation, small movements of the slab 202 do not cause shutter 239 movements and so the opening 240 remains closed. Overcoming a certain movement value of the slab 202 causes the shutter 239' to lift and the hole

240 enters in communication with the channel 225. The spring 243 has a load that is such as to be able to overcome the hydrostatic pressure corresponding to the hole section 240. In this embodiment no bypass channel is necessary for reintroducing the liquid 10 into the chamber 204, as, at the end of the pressing action, it is able to return through the hole 240 overcoming the slight force of the spring 241. In Figures 32 and 33 the detecting and adjusting device is a moulded plastic monobloc consisting of a relatively rigid upper ring 245 and of a lower shutter 246 that are connected by thin flexible strips 247 arranged to form a barrel surface. The shutter 246 and the upper ring 245 can easily approach and distance themselves from one another through the flexure of the strips 247, the

distancing is, however, permitted up to the point in which the strips 247 become taut. Keeping the ring 245 in contact against the slab 202 is obtained with the help of the compressed spring 248 that performs the same function as the spring 243.

The embodiment illustrated in Figure 34 differs from the one in Figures 32 and 33 inasmuch as the monobloc 249 is fixed directly to the slab 202 with a saw-tooth 250 snap-fitting, in this case the spring 248 thus becomes superfluous .

Figure 35 shows a detecting and adjusting device of the type shown in Figures 30 and 31, differing by the fact that here mounting and dismantling of the device is permitted by intervening from the bottom of the buffer T, with a wrench engaged in the appropriate seat 250 and after removing the cap 251, without any need to remove the diaphragm 218 and the slab 202.

The device in Figure 36, which also may be mounted and dismantled from the bottom of the buffer T, also comprises the expansion chamber 226 provided with a liner 252 in the end part of which there is a dust filter 253 and appropriate notches for receiving wrenches . Figure 37 illustrates a lenticular expansion chamber 255 in which the dividing function of the piston 227 is performed by a diaphragm 256 kept in position by a cover 257 and pressed by a spring 258. In all the illustrated cases, the function of the springs 228, 258 could be replaced or assisted by a fluid at suitable pressure. Modifications of a practical-applicational nature can be made to the invention without thereby falling outside the scope of the inventive idea as claimed.

Thus, for example, the seal of the element 21 and/or of the body Q can be achieved on a conical seat, omitting in this case the washer D.