Pressing apparatus and method

The invention relates to an apparatus and method for forming ceramic objects from powder or ceramic granules or another ^' similar material, by pressing. The ceramic powder intended for forming objects, for example crockery, or tiles, is compacted in suitable pressing moulds, prevalently using an isostatic pressing process. The non-isostatic process in fact causes differences in compacting or density of the powder material that cause a different shrinkage of the powder material during the firing step. This means that objects are obtained that have irregular shapes, or have variable mechanical features, or, in extreme cases, objects that fracture during firing. In the isostastic forming process isostatic moulds are used that are shaped so as to press the powder material at a constant pressure to ensure homogenous density of the objects after pressing.

Isostatic moulds comprise a first half mould and a second half mould that are mutually movable between a rest position in which the first and the second half mould are mutually spaced apart and do not interact together, and an operating position in which the first and the second half mould are moved near to press the ceramic powder. The first half mould, by acting, for example, as a die of the pressing mould, comprises a cavity into which the ceramic powder to be pressed is poured. The second half mould acts as a punch of the pressing mould and is provided with a buffer that defines a pressing surface, i.e. the surface intended for coming into contact with the ceramic powder to compact the ceramic powder, which is deformable.

The. pressing surface consists of a flexible membrane shaped so as to bound a pocket into which an incompressible liquid is inserted, for example oil, so that the membrane is interposed, in use, between the material to be compacted and the incompressible liquid.

In the preparation of the buffer, the oil is introduced inside the pocket so as to swell the pocket.

The quantity of oil introduced into the pocket determines the pressure of oil inside the pocket in conditions of rest of the buffer.

Further, the quantity of oil in the pocket varies the deformability of the membrane during the pressing step compared with the rest condition: too small a quantity of oil limits the deformability of the membrane during the pressing step and therefore the isostatic capacities of the mould, too great a quantity of oil deforms the flexible membrane excessively, prejudicing the durability thereof. When the buffer is pushed against the ceramic powder in the ^• die, the oil pushes the elastic membrane against the material to be pressed.

During pressing, the zones of the mould in which there is a greater thickness of powder, push, via the flexible membrane, the oil, moving the oil at a constant pressure inside the pocket, to the zones of the mould in which there is a smaller thickness of powder.

Consequently, the flexible membrane is deformed, following the irregularities of the powder material in the mould. In this manner, the powder material is pressed at a constant pressure, i.e. at a constant force per surface unit, and possible charging lacks of homogeneity of the powders in the die of the mould are compensated.

Objects are thus obtained with thicknesses that may not be uniform but which have homogenous densities, inasmuch as the same specific pressing pressure acts on all the points. In this manner, the irregularities of shape of the objects after firing are limited. In this manner, during the step of glazing of the pressed objects the colours are further absorbed in a homogenous manner. During the pressing step, the pressure reached by the oil inside the pocket depends on the pressing force applied by the isostatic mould.

The isostatic pressing can also be achieved in multicavity moulds, comprising a die in which a plurality of containing cavities is provided in which the material to be compacted and a plurality of pressing buffers is poured. Each pressing buffer is arranged for interacting with the ceramic material of a respective containing cavity of the die and is provided with a respective flexible membrane. Each buffer is further provided with a containing pocket into which the incompressible fluid is inserted. The pockets of the various buffers can be connected hydraulically together so that, during the pressing step, the oil can flow from one buffer to the other, to try to compensate for possible charging differences between the various cavities of the die of the mould. A drawback of known isostatic moulds is that they do not enable possible oil leaks to be compensated for. The oil leaks are difficult to avoid and the decrease of oil in the pockets of the buffers prejudices over time the isostatic capacity of the moulds. In fact, the decreasing of the quantity of oil decreases the thrust force of the oil on the membrane .

Further, as the quantity of oil decreases, the compensating effect due to the oil becomes ineffective. Thus the membrane is not deformed in a manner corresponding to . the charge differences of the cavity of the die and differing pressing forces are established in the various zones of the mould. Thus the ceramic material is not pressed in isostatic conditions . A further drawback of known moulds is that they are not very versatile, i.e. they are suitable for working only in certain preset pressing conditions.

For example, known moulds are not suitable for working at pressing pressures that differ between various pressing cycles . Further, it is not possible to vary the deformability of the membrane during operation of known moulds .

In order to vary the deformability of the membrane it is in fact necessary to lock the mould, empty the pocket containing the oil, and pour a quantity of oil into the pocket that is such as to obtain the desired deformation of the membrane for a set pressing pressure.

With the varying of the deformability of the membrane in a pressing operation, it is necessary to repeat the aforesaid operations . This entails considerable delays to the productive cycle. The aforesaid operations also have to be performed if it is desired to change the oil inside the pockets of the buffers. Thus the oil inside the buffers is changed rarely, in order ' to avoid excessive production slowdowns. As the chemical and physical properties of the oil are lost over time, it may be progressively corrosive in relation to the material with which it is in contact, damaging, for example, the elastic membrane.

If damage to the membrane is considerable, oil leaks may occur through the membrane, with considerable deterioration to the operation of the mould, and loss of the isostatic properties of the mould.

Further, in the event of damage, the membrane has to be replaced, and this entails increases in production costs and considerable production slowdowns. A still further drawback of known isostatic moulds is that they do not enable pressing conditions to be checked directly.

It is in fact not possible to determine the actual isostaticity of the pressing operation and/or the pressing pressure of the mould.

In order to check the actual isostatic operation of known moulds and/or pressing pressure, it is necessary to measure the density of the pressed object, before firing, possibly at different points of the object, or to check whether the object pressed after firing has dimensions that conform to desired dimensions.

It is thus possible that a certain number of objects obtained at non-isostatic pressure or at a pressing pressure value that is different from the desired one, those having a density that is variable or different from the desired density, have to be eliminated, with consequent time and financial losses that are also considerable.

The drawbacks listed above are more evident in known multicavity isostatic moulds . In fact, it is quite difficult to obtain with multicavity moulds of known type homogenous pressing of the ceramic material charged into the different cavities.

In a known multicavity mould that has the pockets of the various buffers hydraulically insulated from one another, each buffer acts in a manner that is substantially independent of other buffers, i.e. as if it were a buffer of a single-cavity mould. A mould of this type, in addition to having the aforesaid drawbacks, does not enable it to be assured that during pressing the various buffers act in the same manner on the powder material arranged in the respective cavities .

In a known multicavity mould having the pockets of the various buffers connected to one another hydraulically, the oil, during the pressing step, is moved between the pockets of the various buffers contained therein. The flow of the oil in the various pockets and above all in the conduits that join the various pockets together, is subject to a certain loss of load.

Thus in different pockets oil pressure values that are even very different from one another may be reached during the pressing step.

This means that the powder material in the various cavities is not compacted in the same manner and that the different pressed objects have density values that are very different from one another. At the end of the pressing step, the pockets of the various buffers that are mutually connected may be at pressures that

are different from one another, especially if there has been a transfer of oil between the various pockets. Such pressure differences generate an oil flow between the various pockets that is suitable for making the pressure of the oil in the various pockets homogenous .

Nevertheless, the flow of oil between the various pockets is limited and is not sufficient to make the pressure homogenous in the various pockets of the buffers in the time elapsing between two successive pressing cycles. Thus the various buffers are not at the same pressure at the start of a subsequent pressing step.

Consequently, during successive pressing cycles, the various buffers press the powder material at pressures that are different from one another. In the various cavities objects are thus obtained that have different densities from one another.

Further, the pressure differences between the various pockets during a pressing cycle influence compacting of the powder material in the subsequent pressing cycle. This causes differences in the density of the pressed objects even between subsequent pressing cycles.

An object of the invention is to improve known pressing moulds . Still another object is to provide pressing moulds that enable isostatic pressing conditions to be maintained over time.

Still a further object is to provide pressing moulds that enable the pressing pressure value of the powder material to be kept constant over time. Still a further object is to provide pressing moulds that enable objects to be obtained in subsequent pressing cycles that have almost the same density values.

A still further object is to provide multicavity pressing moulds in which the pressing pressure between the various cavities is homogenous .

A still further object is to provide multicavity pressing moulds in which the pressing pressure of the various cavities is maintained almost constant over time.

A further object is to provide isostatic moulds in which it is possible to check pressing conditions directly.

In a first aspect of the invention a pressing apparatus is provided for pressing powder material to obtain pressed objects, comprising half-mould means provided with chamber means into which an incompressible fluid is insertible, said chamber means being closed at least on a side facing said powder material by flexible membrane means, characterised in that said apparatus comprises a regulating system for varying in the desired manner the quantity of said fluid in said chamber means during a pressing cycle of said apparatus. In an embodiment, said regulating system comprises collecting tank means for collecting a certain quantity of said fluid, and supplying means for sending a further quantity of said fluid to said chamber means, for example from said tank means, to vary in the desired manner the quantity of said fluid in said chamber means .

In an embodiment, said supplying means comprises pump means for pumping said fluid into said chamber means. In a further embodiment, said supplying means further comprises discharging means for evacuating said fluid from said chamber means to said tank means .

In a further embodiment, said regulating system further comprises valve means for opening/closing conduit means interposed between said chamber means and said tank means, to enable/prevent the passage of said fluid in said conduit means .

In another embodiment, the regulating system further comprises pressure transducing means for measuring the pressure of said fluid in said chamber means. The presence of the pressure transducing means enables the pressure in the half-mould means to be detected to know the

operating pressure of the half-mould means at any desired moment of the pressing cycle.

It is further possible to detect the effective operating isostaticity of the pressing apparatuses in a pressing cycle. In this manner it is possible to detect whether pressure value that is made in the chamber means during the pressing step is different from the desired pressing pressure values.

It is further possible to know the actual pressing pressure of a pressing cycle in real time. In an embodiment, the half-mould means comprises punch means.

In an embodiment, the punch means comprises a plurality of pressing elements, each provided with a respective chamber of said chamber means containing the incompressible fluid.

The chambers of the various pressing elements of the plurality of moulds can be hydraulically connected together so that the fluid can flow between one chamber and the other of said chamber means .

Each chamber can be provided with a pressure transducer of said pressure transducing means to detect the pressure of said fluid in each chamber.

The regulating system is shaped so as to vary the quantity of fluid in each chamber.

The regulating system enables homogenous pressure values to be achieved in the various chambers of the half-mould means. In this manner, it is possible to obtain, in the various cavities, pressed objects having an homogenous density from one another.

It is further possible to restore in the various chambers the same pressure values that there were at the start of the pressing step.

It is further possible to restore in the various chambers the same quantity of fluid that there were at the start of the pressing step.

In a second aspect of the invention, a method is provided for pressing a powder material, comprising introducing an incompressible fluid into chamber means defined in half-mould

pressing means, said chamber means being closed at least on a side facing said powder material by flexible membrane means, operating said half-mould means to press said powder material to obtain pressed objects, regulating in a desired manner the quantity of said fluid in said chamber means, characterised in that said regulating comprises varying in a desired manner said quantity of said fluid in said chamber means during said operating. In an embodiment, said regulating comprises collecting a certain quantity of said fluid in collecting tank means.

In another embodiment, said regulating comprises sending a further quantity of said fluid to said chamber means and/or to said tank means for varying in the desired manner the quantity of said fluid in said chamber means . In another embodiment, said regulating comprises measuring the pressure of said fluid in said chamber means. Comparing the measured pressure value with reference pressure values can also be provided. Owing to the invention, it is possible to vary as desired the quantity of oil located in the chamber means of the half- mould means during operating steps of said half-mould means. This consequently enables the pressing pressure of the half- mould means and therefore the density of the obtained pressed objects to be varied. Owing to the invention, it is if necessary possible, in a simple manner/ to increase the quantity of fluid in the chamber means .

This enables, for example, possible leaks of incompressible fluid to be prevented or the pressing pressure of the half- mould means to be increased.

It is further possible, in an equally simple and immediate manner, to decrease the quantity of fluid located in the chamber means to reduce suitably the pressing pressure of the half-mould means. Owing to the invention, it is further possible to vary the quantity of fluidlocated in the chamber means during

operation of the half-mould means, by exploiting the steps in which the half-mould means are not active.

This enables pressing apparatus downtime and therefore slowdowns in the productive cycle to be avoided. It is thus further possible to renew the fluid located in the chamber means, preventing deterioration thereto and consequent damage to the component of the half-mould means, in particular to the membrane that_ closes the chamber means. In this manner the life of the half-mould means is considerably extended.

The invention can be better understood and implemented with reference to the attached drawings that illustrate some embodiments by way of non-limiting example, in which: Figure 1 is a schematic view of a regulating system according to the invention for a pressing apparatus provided with an isostatic buffer;

Figure 2 is a view like the one in Figure 1 showing a regulating system for a pressing apparatus provided with two distinct buffers. With reference to Figure 1, there is shown a regulating system 1 for a portion of mould, for example a punch, of a pressing apparatus, which is not shown, for pressing powder ceramic material . The pressing appa'ratus is used to press powder or granular ceramic material to obtain pressed objects, such as, for example, tiles, which are subsequently subjected to firing. The pressing apparatus can therefore comprise a forming press of ceramic tiles . The pressing apparatus comprises a mould portion and a further mould portion that are mutually movable between a removed position in which the mould portion and the further mould portion are spaced away from one another and do not interact together, and a work position in which the mould portion and the further mould portion interact to press the ceramic material that is interposed therebetween.

In the embodiment in Figure 1, the mould portion comprises a punch, and the further mould portion comprises a die provided with a cavity into which a desired quantity of ceramic material to be pressed is introduced. The cavity of the die is shaped so as to form the visible part of the object to be pressed.

The die comprises a box that is suitable for defining side walls of the cavity. A lower member cooperates with the box to define a bottom of the forming cavity. In an embodiment, the die is fixed and the punch is movable in relation to the latter to interact with the ceramic material contained in the cavity of the die.

The die may comprise a plurality of cavities and the punch may comprise a plurality of pressing elements, each pressing element being suitable for coupling with a corresponding cavity to form simultaneously a' plurality of objects. At least the punch or the die of the pressing apparatus comprises a buffer provided with an isostatic device to press the ceramic material at homogenous pressure. In an embodiment that is not shown, the isostatic device is provided in the buffer of the die. In this case, the buffer of the die can be further provided with a regulating system according to the invention. In the embodiment shown, the isostatic device is provided in a buffer 2 associated with the punch of the pressing apparatus .

The buffer 2 comprises a body and a pressing surface 4 intended for coming into contact with the ceramic material during the pressing step of the pressing apparatus. The pressing surface 4 is shaped so as to form the non- visible part of an object to be pressed in the pressing apparatus, for example a tile.

The pressing surface 4 is obtained in a deformable membrane 5, in particular made of elastomeric material, for example vulcanised rubber.

The membrane 5 is shaped so as to bound a chamber or pocket 6 provided inside the body of the buffer 2. Inside the pocket 6 there is an incompressible fluid, for example oil, suitable for achieving homogenous pressing pressure on the ceramic material .

The pocket 6 comprises an inlet 7 and is connected to the regulating system 1 to regulate the quantity of oil in the pocket 6. The regulating system 1 comprises an arrangement of conduits 8 inside which the oil flows. The arrangement of conduits 8 is connected to the inlet 7 of the pocket 6 and extends between the pocket 6 and a collecting tank 9 inside which a certain quantity of oil is contained. The arrangement of conduits 8 comprises a conduit portion 10 extending between the inlet 7 of the pocket 6 and a connecting zone 11. The arrangement of conduits 8 further comprises a supply conduit 12, and a discharge conduit 13 that both extend from the connecting zone 11 to the collecting tank 9. Along the supply conduit 12 there is provided a pump 14 for pumping the oil from the collecting tank 9 to the pocket 6. Along the supply conduit 12 a supply valve 15 is further provided for opening/closing the supply conduit 12 to enable/prevent the flow of oil from the collecting tank 9 to the pocket 6.

Along the discharge conduit 13 there is provided a discharge valve 16 shaped so as to open/close the discharge conduit 13 to enable/prevent the flow of oil from the pocket 6 to the collecting tank 9. Along the conduit portion 10 coupling means 17 is provided that is shaped so as to connect, or disconnect, the inlet 7 of the pocket 6 to, or from the conduit portion 10. The coupling means 17 may, for example, comprise a quick release joint. The coupling means 17 comprises a first half coupling 18 connected to the conduit portion 10 and a second half

coupling 19 connected to the inlet 7. When the first half coupling 18 and the second half coupling 19 are connected together, the oil can flow freely through the conduit portion 10 to the pocket 6, or vice versa, from the pocket 6 to the conduit portion 10.

When the first half coupling 18 and the second half coupling 19 are disconnected, the first half coupling 18 prevents the part of oil located in the conduit portion 10 being able to exit from the end of the conduit portion 10 delimited by the first half coupling 18 and the second half coupling 19 ^■ prevents the oil in the pocket 6 being able to exit the pocket 6 through the inlet 7.

The coupling means 17 can be disconnected to separate the buffer 2 from the regulating system 1, for example, during mounting of the mould or during maintenance operations .

Along the conduit portion 10 there is further provided a measuring device 20 for measuring the pressure of the oil inside the pocket 6. The measuring device 20 comprises a pressure transducer 21 provided with a sensor that detects the value of the pressure in the conduit portion 10 and thus inside the pocket 6, and a switch that transforms the detected pressure value into an electric signal. The regulating system 1 further comprises driving means, which is not shown, arranged for driving the regulating system 1 to regulate the quantity of oil in the pocket 6, as better explained below.

The regulating system 1 further comprises a control unit, which is not shown, for operating the driving means to command operation of the regulating system ^* 1, or in other words of the supply valve 15, of thedischarge valve 16 and of the pump 14.

The control unit can bearranged so as to store predefined pressure values entered by an operator and consequently to drive the regulating system 1 to vary the quantity of oil in

the pocket 6 so as to reach, in the pocket 6, the predefined pressure values.

In the operation of the pressing apparatus, an operator prepares the buffer 2 by setting a preload Pl pressure value corresponding to the pressure value that it is desired to make inside the pocket 6 when the buffer 2 is in a rest condition, i.e. when the buffer 2 is not in the ceramic material pushing or pressing step.

Subsequently, manually or automatically via the central control unit and/or the driving means, the regulating system

1 is driven to supplying to the pocket 6 an initial quantity of oil so as to reach, in the pocket 6, the preloading pressure value Pl .

The supply valve 15 is opened to enable the oil to flow from the collecting tank 9 to the pocket 6 and the pump 14 is driven to pump the oil from the collecting tank 9 to the pocket 6 to fill the pocket 6 progressively with the initial quantity of oil. The discharge valve 16 is closed.

The transducer 21 detects the instantaneous pressure value during filling of the pocket 6.

The measuring device 20 compares the detected pressure value with the set preload Pl pressure value.

When the quantity of oil inside the pocket 6 is such that in the pocket 6 the preload Pl pressure value is reached, the supply valve 15 is closed so as to block the flow of oil from the collecting tank 9 to the pocket 6. The pump 14 is also locked.

The passage of the oil in the arrangement of conduits 8 can be enabled or prevented manually or automatically by the driving means and/or the control unit acting on the opening and closing of the supply valve 15.

Subsequently, the pressing apparatus is driven to press the ceramic material previously supplied to the cavity of the die of the apparatus. The punch with which the buffer 2 is associated is approached progressively to the die and is subsequently pushed until a pressing position is reached.

The punch with which the buffer 2 is associated can be moved, for example, by means of a hydraulic movement device. The punch and the die are moved towards or away from one another according to operating steps defining a pressing cycle. The pressing cycle comprises a loading step, in which the punch and the die are spaced apart from one another to enable the forming cavity to receive the ceramic material to be pressed, a pushing step, in which the punch and the die cooperate for pressing against the ceramic material arranged in the forming cavity to form the pressed object, and an ejection step, in which the punch and the die are moved mutually to enable the pressed object to be extracted from the forming cavity, for example owing to a pushing action exerted on the object pressed by the bottom of the forming cavity.

During the pushing step the membrane 5 interacts with the ceramic material to press the ceramic material. During the pushing step of the pressing cycle, the oil inside the pocket 6 is progressively subjected to increasing pressure values .

When, in the pushing step, the buffer 2 is in the pressing position the oil in the pocket 6 is subjected to a maximum pressure value defined as a pressing value P2. The value of the pressing pressure P2 depends on the pushing force of the buffer 2 against the ceramic material and on the quantity of oil located in the pocket 6.

The aforesaid pressing pressure value P2 influences the density of the object obtained with the apparatus and is usually decided a priori by the operator. At the start of a pressing cycle, the regulating system 1 has already provided the pocket 6 with oil up to a set preload value Pl, so the supply valve 15 and the discharge valve 16 are both closed. During pressing, the membrane 5 is deformed according to the arrangement of ceramic material, pressing on the latter with a homogenous pressing pressure.

During pressing, the measuring means 20 measures the pressure value of the oil in the pocket 6 and compares the pressure value with the desired pressing pressure value P2. On the basis of the pressure value measured by the measuring means 20, the regulating system 1 can be activated substantially instantaneously, i.e. during the pushing step, or during the other steps of the pressing cycle, for example during the ejecting step e/o the charging step, so as to regulate the pressure of the oil in the pocket 6 until a desired value is obtained during the current pushing step or during the step of the subsequent pressing cycle. In the embodiment in which the regulating system 1 is activated during the pushing step, when the detected pressure value is less than pressing pressure value P2 , the regulating system 1 is driven, in a similar manner to what was seen previously for the preloading operation, for example by the control unit, to supply a further quantity of oil to the pocket 6. The supply valve 15 is thus opened and the pump 14 is activated. The further quantity of oil supplied to the pocket 6 is such that in the pocket 6 the oil reaches a pressure value corresponding to the desired pressing pressure value P2. When the measuring device 20 measures an instantaneous pressure value of the oil in the pocket 6 equal to the pressing pressure value P2 , the regulating system 1 is deactivated, i.e. the supply valve 15 is closed and the pump 14 is stopped to interrupt any further flow of oil from the collecting tank 9 to the pocket 6. If, on the other hand, in the pushing step the measuring device 20 detecϋs a pressure value in the pocket 6 that is substantially the same as the pressing pressure value P2, i.e. within a preset tolerance range, the regulating system 1 is not activated, for example by the control unit, the supply valve 15 remaining closed and the pump 14 remaining inactive.

In the embodiment in which the regulating system 1 is activated during the other steps of the pressing cycle and not during the pushing step, when the detected pressure value is less than pressing pressure value P2, the regulating system 1 supplies the pocket 6, similarly to what is disclosed above, with a preset quantity of oil, modifying the preload pressure Pl by an interval δQ1 until the pressure of oil in the pocket 6 reaches a value set by the sum Pl+δQl . The interval δQ1 can naturally have a positive value to increase the preload pressure Pl, or a negative value, to decrease the preload pressure Pl. During the next pressing cycle, the measuring device 20 detects the instantaneous pressing pressure, which is compared with the pressing value P2. If the instantaneous pressing pressure is still different from the pressing value P2 , the regulating system 1, during the ejection step or the charging step, it sends a further quantity of oil, for example such as to vary the current preload pressure Pl+δQl by a further interval δQ2, so that in the pocket 6 the oil reaches a pressure preload value equal to P1+δQ1+δQ2. The further interval δQ2 may be the same as the interval δQ1. The preload pressure is thus modified by subsequent steps δQ1, δQ2,... δQN, until a pressing cycle is obtained in which the value of the instantaneous pressing pressure is the same as the desired pressing pressure value P2. Naturally, each of the intervals δQl, δQ2,... δQN of the subsequent steps may have a positive value to increase the preload pressure by sending oil to the pocket 6, or a negative value, to reduce the preload pressure by making oil exit from the pocket 6. In other words, in order to reach the desired pressing pressure value P2 , ad each step or pressing cycle positive or negative compensations of the preload pressure can be. set. When the measuring device 20 measures an instantaneous pressure value of the oil in the pocket 6 that is substantially the same as pressing pressure value P2 , i.e.

within a preset tolerance range, the regulating system 1 remains deactivated for the entire pressing cycle. In both the embodiments disclosed above, the regulating system 1 enables the pressing pressure P2 to be reached by sending to the pocket 6 a minimum quantity of oil that is sufficient to obtain the desired isostatic effect. The defects in the pressed object are thus much reduced. If the pocket 6 contains an excessive quantity of oil, the regulating system 1 can be activated, for example by the control unit, to extract a certain quantity of oil from the pocket 6.

The oil flows in the conduit portion 10 and along the discharge conduit 13, the discharge valve 16 being open and the supply valve 15 being closed, and is collected in the collecting tank 9.

The defluxion of the oil from the pocket 6 to the collecting tank 9 is interrupted, closing the loading valve 16, when the measuring device 20 detects a desired pressure value in the pocket 6. The partial emptying of the pocket 6 is facilitated by the fact that the oil is pressurised. In order to empty the pocket 6, the movement device of the apparatus and thus the pressure force of the apparatus can also be exploited. With the regulating system 1, it is possible to vary rapidly the quantity of oil in the pocket 6 and obtain a pressed object effectively having the desired density. It is possible to increase the quantity of oil in the pocket 6, obtaining a further quantity of oil from the collecting tank 9. In this manner it is, for example, possible to compensate foraccidental oil leaks from the pocket 6.

The regulating system 1 enables the quantity of oil in the pocket 6 to be varied during operation of the apparatus, in particular during pressing or also, possibly, during the steps of the pressing cycle in which the buffer 2 does not interact with the ceramic material .

Thus, owing to the regulating system 1 it is not necessary to lock the apparatus to vary the quantity of oil in the pocket 6, in particular to compensate for oil leaks and/or to vary the pressing conditions of the apparatus. Further, the movement device of the punch that moves the punch, and the buffer 2 therewith, between the distanced, i.e. rest position, and the work, i.e. pressing position, can be used to push the oil from the pocket 6 to the collecting tank 9. In an embodiment, the regulating system 1 can be provided, alternatively, or in addition, with a further pump shaped so as to attract oil from the pocket 6 to the collecting tank 9. The regulating system 1 enables the exhaust oil to be removed easily from the buffer 2 to replace the exhaust oil with other oil. As is known, during use the chemical and physical properties of the oil tend to become modified and the oil tends to become corrosive to parts with which it is in contact, in particular with the membrane 5. Replacing the used oil enables the life of the buffer 2 to be increased significantly.

It is also possible to make partial emptying of the pocket 6 fast, performing this operation during operation of the apparatus, without the need to lock the apparatus. By suitably driving the regulating system 1, it is further possible to vary the pressing pressure value P2 at which to operate the apparatus by varying, i.e. increasing/decreasing, the quantity of oil in the pocket 6. In this manner, in successive pressing cycles, it is possible to obtain objects having densities that differ from one another .

The regulating system 1 enables the desired pressing conditions to be achieved, i.e. pressing pressure, quantity of oil in the pocket 6, in a very short time and without the need to lock the pressing apparatus.

In fact, in order to increase the quantity of oil in the pocket 6 the pump 14 is used whilst in order to decrease the quantity of oil in the pocket 6 the pushing force of the pressurised oil itself is exploited, or the movement device of the punch on which the buffer 2 is mounted, or a further pump .

The operator can possibly define a plurality of pressing pressure values Pp and a plurality of preload pressure values Pc for the oil in the pocket 6, so that the apparatus can work at distinct pressing pressure values to obtain objects that have densities that are also different from one another. The aforesaid pressing pressure values Pp and/or preload values Pc can be stored in the control unit of the regulating system 1. These values can be called up by the operator to drive the regulating system 1 to vary the quantity of oil in the pocket 6 on the basis of the particular pressing pressure value Pp and/or preload pressure value Pc chosen by the operator from the plurality of pressing pressure values Pp and/or. preload values Pc that have been stored.

The regulating system 1 disclosed above can also be used effectively for multicavity apparatuses,, i.e. apparatuses comprising a die provided with a plurality of containing cavities into which the material to be compacted is poured, and a plurality of pressing elements, each pressing element cooperating with a respective cavity of the plurality of containing cavities of the die. In this case, each pressing element and/or each cavity is provided with a buffer that is similar to what has been described with reference to Figure 1.

Each buffer is provided with a respective containing pocket into which the oil is inserted.

The pockets of the various buffers can be connected together in a known manner. In Figure 2 an alternative embodiment of the regulating system 100 is shown schematically that is to be used in an

apparatus provided with, a punch 3 comprising a first buffer

200 and a second buffer 201.

The parts of the regulating system IOO and respectively of the first and of the second buffer 200, 201, corresponding to what has been described with, reference to the regulating system 1 and to the buffer 2 of Figure 1 are indicated by the same numerical references and are not disclosed in detail below.

The regulating system 100 further comprises a conduit 22 joined to a second inlet 23 and a second chamber or second pocket 24 of the second buffer 201 and arranged for supplying the oil to/extracting the oil from the second pocket 24.

In an embodiment, the second pocket 24 can be connected to the pocket 6 by a connecting conduit that is not shown, which permits a flow of oil from the second pocket 24 to the pocket 6 and vice versa.

The piping 22 comprises a branch 25 extending between the second inlet 23 and a further connecting zone 26 of the conduit 22. The branch 25 is connected to the inlet 23 by further coupling means 27, to couple the second inlet 23 to the conduit 22 to decouple the second inlet 23 from the conduit 22.

The further coupling means 27 is shaped in a similar manner to the coupling means 17 and comprises a first connector 28 associated with the branch 25 and a second connector 29 associated with the inlet 23. When the first connector 28 is coupled with the second connector 29, the oil can flow freely from the branch 25 to the second pocket 24 and, vice versa, from the second pocket 24 to the branch 25. When the first connector 28 and the second connector 29 are decoupled, they prevent the oil from exiting the parts with which they are respectively associated.

Along the branch 25 of the conduit 22, for example between the coupling means 27 and the further connecting zone 2-6, there is further provided a further measuring device 30 for

measuring the pressure of the oil inside the second pocket 24.

The further measuring device 30 comprises a further pressure transducer 31 for detecting the value of the pressure inside the second pocket 24 and generating an electric signal that is proportional to the detected pressure value. The piping 22 further comprises a supply pipe 32, and a discharge pipe 33 extending from the further connecting zone 26 respectively to a first joining zone 34 and to a second joining zone 35 provided respectively in the supply conduit 12 and in the discharge conduit 13 of the arrangement of conduits 8.

Along the supply pipe 32 there is provided a further supply valve 36 shaped so as to open/close the supply pipe 32 to enable/prevent the flow oil from the collecting tank 9 to the second pocket 24.

Along the discharge pipe 33 there is provided a further discharging valve 37 shaped so as to open/close the discharge pipe 33 to enable/prevent the flow of the oil from the second pocket 24 to the collecting tank 9.

In operation, an operator prepares the first buffer 200 and the second buffer 201, respectively setting a first and a second preload pressure value P3 , P4 that correspond to the pressure values desired respectively in the pocket 6 and in the second pocket 24 in rest conditions of the apparatus.

The first and the second preload pressure value P3, P4 may be the same as or different from one another.

The operator also sets a first pressing pressure value P5 and a second pressing pressure value P6 corresponding to the maximum pressure value to which the oil may be subjected respectively in the pocket 6 and in the second pocket 24 during the pressing step of the pressing apparatus. In particular, the operator may set a common pressing pressure value P7, i.e. the first pressing pressure value P5 and the second pressing pressure value P6 may be the same as one another.

The operator further sets a maximum deviation value M that is the same as the maximum pressure value that can be achieved between the pressure of the oil in the pocket 6 and the pressure of the oil in the second pocket 24, during the pressing step of the pressing apparatus. Setting a maximum deviation value M occurs in particular in the case of a common pressing pressure P7.

The maximum deviation value M influences the permitted density differences for objects formed respectively by the first and by the second buffer 200, 201.

The buffers 200, 201 are prepared starting manually or via the driving means, and/or the control unit, the regulating system 100, by hydraulically connecting the collecting tank 9 to the pocket 6 and to the second pocket 24 to introduce the desired quantities of oil therein.

The supply valve 15 is thus opened and the pump 14 is driven to direct a flow of oil into the pocket 6. The further supply valve 36 can be maintained closed until the first buffer 200 has been prepared. The measuring device 20 detects the pressure values inside the pocket 6 and the pump 14 sends oil to the pocket 6 until the latter reaches an oil pressure value that is substantially the same as the previously set first preload pressure value P3. The oil flow from the collecting tank 9 to the pocket 6 is interrupted, closing the supply valve 15.

At this point, the further supply valve 36 is opened to send oil to the second buffer 201, similarly to what has been disclosed for the first buffer 200. The pump 14 sends oil to the second buffer 201 through the supply pipe 32. The supply valve 15 is kept closed. When the quantity of oil inside the second pocket 24 is such that the pressure value detected by the further measuring device 30 is almost the same as the previously set second preload pressure value P4, the oil flow from the collecting tank 9 is interrupted, closing the further supply valve 36. The pump 14 is deactivated.

The pocket 6 and the second pocket 24 are hydraulically insulated from the collecting tank 9 and from the arrangement of conduits 8.

The preload operations can be performed simultaneously on the first buffer 200 and on the second buffer 201. In other words, the regulating system 100 can be activated so as to open substantially simultaneously both the supply valve 15 and the further supply valve 36. In this case, the pump 14 sends oil both to the pocket 6 and to the second pocket 24. Once the preload pressures P3 and P4 have been reached respectively in the pocket 6 and in the second pocket 24, the pump 14 stops and the supply valve 15 and the further supply valve 36 are both closed. The regulating system 100 can also be activated so as to regulate the pressure of the oil only in one of the pockets 6 and 24, without modifying the condition of the other pocket .

In the embodiment in which the pocket 6 and the second pocket 24 are connected by connecting conduit, during the preload operations, in the first buffer 200 and in the second buffer 201 a common preload pressure Pi is reached. Subsequently to preparing the first buffer 200 and the second buffer 201, the pressing apparatus is driven to press the previously supplied ceramic material in the various cavities of the die. The punch 3 is approached progressively to the die and is subsequently pushed until it reaches a pressing position.

When the punch 3 is in the pressing position, the oil in the pocket 6 and in the second pocket 24 is subjected to a certain pressing pressure.

The measuring device 20 and the further measuring device 30 detect the pressure values of the oil respectively in the pocket 6 and in the second pocket 24 and compare these values with the previously set pressing pressure values P5 and P6. If it is desired to obtain the same pressing pressure P7 in the pocket 6 and in the second pocket 24 the

measured pressure values of the oil are compared with the common pressing pressure value P7.

When the detected pressure value in the first and/or in the second pocket 6, 24 is less than the desired pressing pressure value P5, P6, or P7, the regulating system 100 is driven to supply to the pocket 6 and/or to the second pocket 24 a quantity of oil such as to reach the desired pressing pressure value P5, P6, or P7. On the other hand, if the measuring device 20 and/or the further measuring device 30 detect a pressure value that is greater than the desired pressing pressure value P5 , P6, or P7, the regulating system 100 extracts from the pocket 6 and/or from the second pocket 24 a quantity of oil such as to reach the desired pressing pressure value P5 , P6, or P7. The pressure values detected, during pressing, respectively by the measuring device 20 and by the further measuring device 30 are compared each other to calculate the pressure difference between the oil in the pocket 6 and in the second pocket 24. In the embodiment in which the various pockets are connected together, during the pressing step an oil flow occurs between the various pockets that are connected together from the pocket with greater pressure to the pocket with less pressure, which would tend to make the pressure values in the various pockets even.

Nevertheless, this flow is not sufficient to make the pressure values between the various pockets uniform. In all cases, if the actual pressure difference value between the oil in the pocket 6 and the oil in the second pocket 24 is greater than the set maximum deviation value M, the regulating system 100 varies the quantity of oil located in the pocket 6 and/or in the second pocket 24 so as to return the pressure difference value below the maximum deviation value M. The regulating system 100 is activated during the pressing or thrust step of the pressing cycle, or at the end of the

thrust step, i.e. in the ejection step or in the loading step.

In particular, by suitably driving the regulating system 100 at the end of the pressing or thrust step, it is possible to vary the quantity of oil in the pocket 6 and/or in the second pocket 24 to establish in the pocket 6 and in the second pocket 24 pressure values that are equal to the respective desired preload values P3 , P4. Alternatively, the regulating system 100 can modify the preload values P3 , P4 or Pi by a preset amount and check how the pressing pressure is modified in the pocket 6 and in the second pocket 24 during the thrust step of the next pressing cycle. The preload values are modified at each pressing cycle, for example as disclosed in relation to the embodiment of Figure 1, until the desired pressing pressure is achieved in the pocket 6 and in the second pocket 24. In this manner, it is prevented that the pressing conditions of the buffer 200 and of the second buffer 201 become progressively different from those intended, in particular if it is desired to reach a common pressing pressure P7 , it is avoided that the pressing conditions of the buffer 200 and of the second buffer 201 become progressively different from one another. Isostatic pressing conditions are further maintained in the various cavities of the apparatus .

Through the regulating system 100, it is possible to increase/decrease the quantity of oil in the pocket 6 and/or in the second pocket 24. In this manner it is possible to vary the density of the objects obtained in different pressing cycles, with an apparatus provided with the regulating system 100. ^' The .pump 14 is used to supply oil to the first buffer 200 and to the second buffer 201. In order to extract oil from the first buffer 200 and from the second buffer 201 the pressure of the oil in the buffers can be exploited, or the movement device of the punch 3 and, alternatively, or in

addition, a further pump can be used. This enables high oil capacity value to be obtained in the arrangement of conduits

8 and in the connecting conduit between the pocket 6 and the second pocket 24. Thus in the steps in which the punch 3 is not active it is possible to achieve the desired conditions in the pocket 6 and in the second pocket 24.

With the regulating system 100, it is possible, if desired, to operate the apparatus so that the oil in the pocket 6 has a pressing pressure value that is different from a further pressing pressure value of the oil in the second pocket 24.

In this manner, in the same pressing cycle objects having different densities from one another can be obtained.

Further, the regulating system 100 enables the desired pressing conditions to be obtained in a very short time and without the need to lock the pressing apparatus.

The pressing conditions can thus be easily varied between two consecutive pressing cycles.

The variation in the quantity of oil in the pocket 6 and/or in the second pocket 24 can be effected between two

^• consecutive pressing cycles, exploiting the rest steps of the punch, or also during the pressing step.

If desired, with the regulating system 100 it is further possible, during the pressing step, to empty completely the pocket 6 and/or the second pocket 24 and operate the apparatus without an isostatic device, i.e. in non-isostatic conditions .

Pressing pressure values that are different from one another can be possibly set for the first and the second buffer 200, 201 to obtain with the first and with the second buffer 200,

201 objects having densities that are different from one another.