Isostatic pressing means

Abstract: The pressing means, particularly for the isostatic pressing of ceramic tiles (41), enables a greater ease of fabrication and vulcanisation; it comprises at least one die (1) having a plurality of intercommunicating chambers (2) containing incompressible fluid (F) and closed by an elastic membrane (12) anchored to walls (208) separating said chambers (2); inside each chamber (2) there being inserted, in an intermediate position between said fluid (F) and said membrane (12), an element (4, 4a, 4b, 70, 71) for controlling the deformation of the membrane (12); each said control element (4, 4a, 4b, 70, 71) is anchored to said membrane (12) and has a zone close to said membrane (12) a certain distance from said walls (208) so as to define, in said membrane (12), a perimetric elastic joint (12a) connecting said control element (4, 4a, 4b, 70, 71) to the respective walls (208), said control element (4, 4a, 4b, 70, 71) co-operating with respective positioning means (14, 16, 25, 17, 18, 19, 21, 26, 27, 28, 29, 30, 31, 65, 69, 111, 90, 212, 216, 218, 305, 308) that maintain each said control element (4, 4a, 4b, 70, 71) in a predetermined position within the relative chamber (2) during the forming of the membrane (12).

Description: The invention concerns an isobaric die for ceramic tiles, particularly suitable for forming tiles with a uniform pressing intensity and controlled thickness. IT-A-1104511 describes a die in which the ceramic tiles are pressed with the action of an elastic modelling membrane, for example made of rubber, delimiting a chamber in a relative semi-die into which an incompressible fluid, for example oil, is introduced; with such a die it is possible to achieve a homogeneous density of the pressed tile thereby limiting undesirable dimensional variations in the tile during the subsequent firing. The same patent also proposes the use of stiffer plates applied to the external surface of the elastic modelling membrane in order to prevent it from deforming excessively. Moreover, in this patent, whilst introducing the fundamental concept of the homogeneous pressing of ceramic tiles, a tendency has been found for the pressed items to have a non-uniform thickness. EP-A-0556163 describes an isostatic die having a membrane, or rubber plane, underneath which there are chambers positioned close to each other and intercommunicating, the membrane being securely anchored to the outside edge of the die and to the ribs defined by the partition walls of the various chambers, said chambers being filled with incompressible fluid. During pressing, the membrane, in the areas corresponding to the chambers, is able to move sufficiently to transmit the pressing force to the tile in a uniform manner; at the ribs separating one chamber from the adjacent one, where the membrane with its rigid response remains constantly level, there are imprints which form the support appendages on the rear of the tile. To obtain such a die in practice requires the die to be manufactured in two parts. A first part consists of a plate with perforations in the areas corresponding to the chambers: the membrane is vulcanised on this perforated plate with the use of two matrixes, one reproducing the form of the surface of the rear of the tile, the other having a number of appendages, or protuberances, that define the inside of each chamber. The first part of the die is then assembled, by means of numerous screws and seals, to a second part of the die that has channels which render the chambers intercommunicating. Such a manufacturing method, as well as requiring lengthy and expensive machining operations, is also unreliable as regards the strength and the sealing action of the numerous seals. EP-A-0620089 proposes obtaining said chambers on the face of a single die body, creating the intercommunication channels on the base of said chambers, isolating the upper part of the each chamber with a plug made of elastic material, then vulcanising the membrane on top using a low pressure matrix. IT-A-MO930162 describes an analogous die in which, in order to avoid filling the chambers during vulcanisation, there is a layer of sand covered with a sheet of plastic material, it being possible to eliminate the layer of sand after vulcanisation. All these construction methods, however, are still very laborious and costly. A serious problem with tiles pressed with prior art isostatic dies is the highlighting of the support appendages on the front face of the tile after firing: this is due to the fact that, during pressing, if in one area of the tile there is not enough powder, or the powder has a lower density, the areas corresponding with the appendages will be pressed considerably less than the areas between said appendages. This gives rise to an unacceptable alteration in the surface lustre on the opposite side of the tile reproducing the design of the underlying appendages. This highlighting is accentuated by the fact that the elastic membrane tends to become bulged, concave, substantially spherical in form, with considerable lack of homogeneity of pressing between the central zone and the outside zones close to the appendages. A further serious defect arises when the bulge of the membrane occurs outwards from the body of the tile, that is, when the bulge extends beyond the ideal plane formed by the extremity of the appendages: this gives rise to corresponding surface convexity in the top face, during the softening of the tile in the firing phase. The defect described above is reduced with the adoption of the utility model IT-U-214739, which describes a die having a plurality of intercommunicating seats in which are inserted sliding pistons forming a seal. An elastically deformable membrane is positioned between the active extremities of said pistons and the powder to be pressed, the membrane, clearly, only being able to move in proximity to each single piston and in parallel planes. Such a type of die, whilst partially eliminating the typical defect described previously, is difficult to make, requiring a high degree of precision in the machining of the seats and of the relative pistons, and is consequently also very costly; furthermore, the inevitable leakage of the liquid past the sliding seals causes the formation of permanent pockets of liquid between the piston and the membrane; during the pressing phase the membrane is subject to intrusion in the space between the piston and the seat, this causing the membrane to tear and blocking the axial sliding of the piston. Furthermore, the liquid seal being achieved by means of seals sliding against the seat, the seals will be subject to extrusion and the pistons, which for isostatic operation have to perform their axial movements at the maximum pressure, will have their movements severely hampered by the friction of the seal against the seat. Furthermore, in this last known system, the in-situ construction of the membrane is difficult for the following reasons: 1) the possibility, when the membrane is subjected to the vulcanising thrust, of the pistons moving down and coming to rest on the base of their respective seats; 2) the tendency of the pistons to become blocked in their seats, due to the inevitable infiltration of the material of the membrane in the clearance between each piston and its seat. Furthermore, in prior art isostatic dies, it has been found to be very difficult to make the ducts connecting the chambers: in fact, a network of long transverse holes, orthogonal to each other, are made through the body of the die communicating with holes which are perpendicular with respect to the base of each chamber. Alternatively (see IT-A-MI922158) there are four holes in the base of each chamber inclined in a "V" shape towards the outside in such a way that they communicate with the holes made in the adjacent chambers. There are also, in the area closest to the base of said walls, passages made by cutting, at four points in each chamber, by means of a small radial milling cutter whose axis of rotation is orthogonal to the face of the die. All these systems are extremely expensive due to the time required for the machining and to the particular type of machine tool required. Such prior art may be subject to considerable improvements with a view to eliminating, or significantly reducing, said drawbacks. The technical problem of this invention is that of inventing an isostatic die that makes it possible to eliminate pressing defects in ceramic tiles. A further aspect of the technical problem is that of inventing an isostatic die that may be constructed in a very simple and economic manner in which, in particular, it is possible to obtain the chamber communication ducts in an extremely simple manner. The invention resolves said technical problem by adopting pressing means, particularly for the isostatic pressing of ceramic tiles, comprising at least one die having a plurality of communicating chambers containing incompressible fluid and closed by an elastic membrane which has an external surface that reproduces the rear of the tile and an internal surface anchored to walls separating said chambers, inside each chamber there being inserted, in an intermediate position between said fluid and said membrane, a control element for controlling the deformation of the membrane, characterised in that each said control element is anchored to said membrane and has a zone close to said membrane detached from said walls so as to define an elastic peripheral joint in said membrane connecting said control element to said respective walls, said control element co-operating with respective positioning means that maintain each said control element in a predetermined position within the relative chamber during the formation of the membrane. The control element for controlling the deformation of the membrane is advantageously made of a stiffer material than that of the membrane. In an advantageous version, there are a plurality of intercommunicating chambers containing incompressible fluid and closed by an elastic membrane having an external surface that reproduces the rear of the tile and an internal surface anchored to walls separating said chambers, inside each chamber there being inserted, in an intermediate position between said fluid and said membrane, a substantially rigid control element for controlling the deformation of the membrane; said control element has, at its end close to said membrane, a peripheral zone detached from the walls of the chamber where there is an elastic sealing joint; said control element being anchored to said membrane and co-operating with respective positioning means that maintain each said element in a predetermined position within the relative chamber during the forming of the membrane. Said positioning means may consist of a collapsible positioning element, that is to be collapsed by means of a force acting on the membrane after said membrane has been formed. Said substantially rigid element may also have oscillating movements, that is, not constrained to parallelism. The seal against the incompressible fluid between said mobile rigid element and the wall of the corresponding chamber is obtained by the presence of a joint which is securely anchored to said rigid element and to the wall of the corresponding chamber, said joint permitting axial movements of the rigid element purely by elastic deformation, that is, without sliding contact between different surfaces. Said joint may advantageously be made of the same material as said membrane and be integrated with it. A method is now described for the vulcanisation of the membrane onto the body of the die with the use of a matrix, forming the external and active face of the die, placed in a position below said die. The product constituting the elastic membrane should preferably be in liquid form prior to vulcanisation, such that it may take on a horizontal surface configuration naturally when it is poured. The forming matrix is placed, on the lower face of a normal vertical axis heating press, with the forming face facing upwards, said matrix having an external perimetric edge protruding upwards and such that the body of the die to be vulcanised may easily enter inside it. Above the matrix, previously treated with a non-stick agent, a measured quantity of liquid substance constituting the membrane is poured and which is contained by said external edge; once the surface of said substance has become level the body of the die with the chambers facing downwards is made to descend until it comes into contact with the external edge of the matrix; during this phase the system may be pressurised with the introduction of compressed gas, that is pressurised, in one of the communication holes: this in order to aid the conformation of the membrane to the matrix, adhesion of membrane in the areas of contact with the die and the elimination of any bubbles of gas. The side of the die to be vulcanised will have been previously sanded and treated with suitable adhesive substances applied by brush or spraying. The advantages obtained with this method are: precise and controllable height of the chambers due to the possibility of using a measured quantity of levelled liquid resin; reduction in costs caused by the use of rubber plugs, sand, isolating film whose application require a considerable amount of time; strong and reliable adhesion of the membrane during operation, aided by the formation of a concave meniscus of elastomer on the lateral surfaces of the chambers. The invention is illustrated in detail with the help of the attached drawings which illustrate some embodiments. Figure 1 is a partial section of the die, showing, on the left, the configuration after the membrane has been applied and, on the right, a phase of operation, with collapsible positioning element in the form of a strut; Figure 2 is a section as in the previous one showing a collapsible positioning element in the form of an open ring. Figure 3 is an enlarged perspective view of the collapsible positioning element of Figure 2; Figures 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15 are all sections as in Figure 1, each with a different version of collapsible positioning element; Figure 16 is a partial section of a die during the phase of the application of the membrane, using a particular method of forming, that is, with the matrix positioned underneath said die; Figure 17 is a plan view of the positioning element shown if Figure 16; Figure 18 is a perspective view of the positioning element in Figure 4; Figures 19, 20, 21, 22, 23 and 25 are all enlarged and interrupted sections, with reference to Figure 2, of the area of the membrane comprised between the rigid element and the wall of the chamber; Figures 24 and 26 are all enlarged and interrupted sections, with reference to Figure 1, of the area of the membrane comprised between the rigid element and the wall of the chamber; Figure 27 is a cross-section of an isostatic die for pressing ceramic tiles, in a version with membrane control elements in the form of a tessera which, during vulcanisation, rest on, and are centred by, a collapsible support element; Figure 28 is a section as in Figure 27, but at the end of the stroke of permanent deformation of the collapsible support elements: Figure 29 is a section as in Figure 27, but relative to the punch in operation, that is showing the collapsible supports crushed on the bottom of their respective cavities; Figure 30 is a section as in Figure 27, but with support element for each tessera which is collapsible and in the form of a saucer; Figure 31 is a section as in Figure 30, but at the end of the stroke of deformation of the collapsible supports; Figure 32 is a section as in Figure 31, but relative to the die during operation; Figure 33 is a section as in Figure 27, but relative to variants of the collapsible support with the tessera centred on the internal edge of said support, and, respectively, with occluding sphere; Figure 34 is a section as in Figure 27, but with the tesserae supported on a collapsible tablet after vulcanisation and showing how the tesserae may be associated with occluding rings supported peripherally; Figure 35 is a section as in Figure 34, but at the end of the stroke of permanent deformation of the collapsible support elements; Figure 36 is a section as in Figure 34, but relative to the die during operation; Figure 37 is a vertical, interrupted section of a die according to the invention, with temporary collapsible support element being annular in form, as in the one in Figure 12; Figure 38 is a section as in those of Figures 27, 29, but with the tesserae exposed on the pressing surface; Figure 39 is an interrupted perspective view of a collapsible support element consisting of a composite plate with corrugated internal layer; Figure 40 is a vertical section of an isobaric die for tiles, prior to vulcanisation in accordance with the method of the present invention; Figure 41 is a vertical section of the hollow matrix for vulcanising the die in Figure 40, containing the fluid substance for forming the membrane; Figure 42 is a section as in those of Figures 40 , 41, but showing the coupling between the die and the matrix during vulcanisation; Figure 43 is a partial perspective view of the body of the die of Figure 40, but prepared for receiving elements for controlling the deformation of the membrane; Figure 44 is a perspective view of a control element that is to be vulcanised inside the membrane; Figure 45 is an interrupted section of the body of the mould shown in figure 43 having the elements shown in figure 44 inserted in it and coupled with the vulcanizing matrix; Figure 46 is an interrupted and repeated section, showing, on the left, the phase at the beginning of vulcanisation and, on the right, at the end of vulcanisation; Figure 47 is a section as in Figure 46, but in a variant with support elements for the saucer-shaped control elements; Figure 48 is a partial and interrupted front view of the active face of the die, prior to vulcanisation, in a further variant in which the element for controlling the deformation of the membrane is supported on the body of the punch so that it may slide; Figure 49 is section IL-IL of Figure 48; Figure 50 is a partial, interrupted plan view of a die without membrane showing seats for the control elements made in two variants, with and without support shoulder for the relative edges; Figure 51 is section LI-LI of Figure 50, during the vulcanisation of the membrane; Figure 52 is a perspective view of a variant of rigid control element with end plate in the shape of a star; Figure 53 is an interrupted section of two variants of the die, on the left during the vulcanisation phase, on the right during operation respectively with and without the collapsible support element; Figure 54 is an interrupted section of a further variant with membrane control elements having annular outside edge, during the operation phase and showing the possible movements of the membrane; Figure 55 is an interrupted vertical section of an isobaric die with rigid control elements associated with an occluding ring that may be subjected to plastic deformation; Figure 56 is a section as in Figure 55, but during operation; Figure 57 is a section as in Figure 55, but showing an element for controlling the deformation of the membrane in the shape of a saucer engaged in an annular support. The isostatic die for tiles comprises a metallic body 1, on whose active surface there are chambers 2 intercommunicating by means of straight connecting ducts 108. Inside the chambers 2 is inserted a rigid element 4 which is maintained in position axially, during the vulcanisation of the membrane 12, by means of a wire-like collapsible positioning element 14 made of a metal that may subjected to plastic deformation, for example, copper, inserted in a suitable seat 15, 15a made in the base of the chamber 2; the seat 15, 15a may also be made in the element 4 and the wire-shaped element 14 may be inserted in the relative seat before the rigid element 4 is inserted in its chamber 2. The wire-shaped element 14, acting as a strut, is positioned between the base of each chamber 2 and the relative rigid element 4 for controlling the deformation of the membrane 12. As shown in Figures 4 and 18, the collapsible element may consist of a tessera 25 having a quadrangular plan view shape, provided with folds 25b, obtained, for example, directly from stamped plate. The folds 25b form protuberances on which the rigid membrane control element 4 is placed during the vulcanisation of said membrane. As shown in Figures 2 and 3 the collapsible positioning element 14 may consist of a wire-shaped element 16, 16a suitably folded in the form of a ring (for example made of copper, lead or tin) and placed on the base of the chamber 2, it being possible for said wire-shaped element to have a square cross-section. As shown in Figure 5, the axial positioning elements may consist of protuberances 17 arranged radially around the control element 4 which are destined to be sheared with the forced movement of the element 4 as described earlier. In a further version as described, as shown in Figure 6, the positioning element consists of a flat metal sheet 18 that may be subjected to plastic deformation obtained by punching and therefore extremely economical; the forced movement of the control element 4 in this case causes permanent deformation of the edge 18a of said sheet. Figure 7 shows a positioning element consisting of a piece of wire 19 (or a small bar) with its extremities inserted in suitable hollows 20 made in the walls of the chamber 2 and which is destined to be sheared by the relative control element 4 after vulcanisation. In Figure 8, the positioning element consists of a concave tessera 21 obtained, for example, by punching-drawing from sheet metal that may be subjected to plastic deformation and which is destined to be flattened against the base of the chamber 2, as shown on the right side of said Figure; naturally, said concave tessera 21 may also be introduced up-side-down and, moreover, it may have any other suitable shape. As shown in Figure 9, the positioning element is divided into two parts, that is it comprises a collapsible element, here shown as a plurality of spheres 27, made of a material that may be subjected to plastic deformation, for example, lead, above which there is a rigid tessera 28 which supports the seal 22 around the control element 4; it is to be noted how said collapsible element 27 may also be replaced by any one of the other types of collapsible elements already described or described herewith. In Figure 10 the positioning element consists of a bevel ring 29, suitably drawn to diverge towards the membrane 12, matched to the peripheral form of the respective chamber 2: the ring 29, during the forming phase of the membrane, also holds up the seal ring 22. Figure 13 shows a particular version of rigid element 4, obtained from stamped plate: the rigid element has a hollow form facing the respective chamber 2 suitable for receiving the incompressible fluid: this enables the rigid element 4 to be easily obtained with any plan view shape, even non-circular, and already provided with, at the edge facing the membrane 12, a suitable seat for the seal 22. In all the examples described so far, there needs to be a seal against the liquid elastomer poured during the forming phase of the membrane between the top of the control element 4 and the lateral walls 2a of the chamber 2; said seal may be achieved with a toroidal seal ring 22 or even with ring with a flat section 23. In the examples shown in Figures 11, 12, 14 and 15, on the other hand, the seal against the elastomer is achieved directly by the collapsible positioning element. In Figure 11, the positioning element 30 consists of a tessera having a recessed seat suitable for centring the rigid element 4; the tessera may be drilled to enable the free passage of incompressible fluid when in the collapsed position. In Figure 12, said positioning element 31 is analogous to the preceding one, though, in this case, the centring coupling is made in the control element 4. The control element in Figure 15 also has a centring recess, but the collapsible element 32 is initially drawn so that it diverges towards the base of the respective chamber 2 and is destined to be flattened on the base of the chamber after vulcanisation. Figure 14 shows a positioning element in two parts 28, 29, as in Figure 9, in which however the seal against the elastomer is achieved by means of a flat seal 33. Figures 16 and 17 show a system for the positioning the element 4 in such a way that it is effective even with the die turned upside-down, this being necessary to carry out the forming of the membrane with the matrix 7 positioned underneath; this system offers the particular advantage of not requiring the means 22, 23 for obtaining the seal against the liquid elastomer. Also, as the element 4 only requires a rough surface finish, the rigid element 4 in this case may advantageously be obtained from plate by punching or cutting with water jet, or laser beam, without further machining. Furthermore, positioning with secure constraints on element 4 is not required as the forming of the membrane takes place with very low loads on element 4. The annular positioning element 26 may be obtained directly by cutting a sheet of elastomer material thereby also being extremely economical. In this case the preparation is also extremely simple in that it involves introducing into each chamber 2 an element 26 that has to enter without interference with a small amount of lateral clearance; subsequently, a rigid element 4 has to be placed on each element 26, then, using a flat thruster the elements 4 are made to enter, with automatic axial levelling, into the respective annular element 26; the introduction may be achieved without folding the internal edge of the element 26 or, instead, by causing it fold as shown on the right side of Figure 16, in either case the positioning is guaranteed in that as the element 26 expands elastically it becomes blocked against the lateral walls of the chamber; this slight blocking though, does not impede the normal movement the element 4 needs to be able to perform during operation. In all the examples shown, the seal against the incompressible fluid F between said mobile rigid element 4 and the wall of the corresponding chamber 2 is obtained with the presence of a joint 12a securely anchored to said rigid element and to said wall of the corresponding chamber, said seal enabling axial movements of the rigid element 4 purely by elastic deformation, that is, without sliding contact between different surfaces. Figures 19 and 26 highlight a particular problem in the movements of the element 4 in conjunction with toroidal seal 22. If the seat for said seal 22 is made in the element 4 (Figure 19), element 4 is free to descend into the chamber 2, as shown in Figure 20, in that an empty zone is created above the seal 22; on the other hand, upward movement of element 4, that is, out of the chamber 2, is prevented in that this can only occur if the membrane 12 tears or it detaches from the edge 35. To counteract this drawback, it is convenient to provide a clearance of amplitude G between the element 4 and the respective wall through which it is possible for the seal to extrude, the dimension G being up to 80% of the value of the diameter D of the section of the seal, otherwise the seat will have to shaped as in Figures 23, 24, 25 and 26, in which there is an ample chamfer of amplitude H, indicatively up to 80% of the value of the diameter D of the section of the seal. Naturally, there is the same problem when the seat is made in the wall of the chamber (Figure 24), in this case impeding movement downwards. This problem does not arise in the solutions shown in Figures 9 and 10: this because in these cases during vulcanisation the seal 22 is held by elements 28 and 29 which are not constrained to the rigid element 4. A further important advantage of the invention as described in the preceding versions with respect to the prior art, is that it is possible, in an extremely precise and simple manner, to assign a maximum stroke to the movement of the element 4 towards the base of the chamber 2: this is possible by suitably sizing the collapsible support elements. In the version shown in Figures 27 to 33, the control elements, or tesserae, 4 may have smooth lateral surfaces and be inserted with a considerable amount of clearance in the respective seats, or chambers 2, who also have smooth lateral surfaces. The bottom of each control element 4 may be made to co-operate with a collapsible support element 65 consisting of a flat central element 66, provided with an axial through hole 67, and peripherally provided with a concave annular edge defining a seat for centring the relative control element 4. the central hole 67 has to be situated correspondingly with the hole 60 in the body 1 to enable the passage of the fluid F through the relative distribution duct 61. When the elastomer material constituting the membrane 12 is subjected, at the end of the forming phase with the forming matrix 36, to the action of a punch P (Figure 28) comprising an elastic active surface, or an active surface with appendages protruding in correspondence with the tesserae 4, the collapsible support 65 is flattened against the base of the chamber 2 and the tessera remains in stable contact with the membrane: an annular joint 12a made of the material of the membrane 2 that allows the floating movements of each tessera 48 is positioned between the lateral walls of the tessera 4 and the lateral walls of the respective chamber 2. Figure 32 shows an isobaric punch 1, inserted in a matrix M of a die for ceramic tiles during the pressing of a tile 41 by means of punch PZ. The membrane may be limited to the set of annular joints 12a, that is, the control elements 4 may even not be covered with the elastomer material on the active face during pressing, as shown in Figure 38. The collapsible support 65 may be shaped as in a saucer 69 (Figures 30 and 33, left side), possibly with a central hole for occluding element 70, acting as control element 4, destined to be an integral part of the membrane 2. The occluding element may also consist of a sphere 71, as shown on the right side of Figure 33. The surface of the collapsible element 65 facing the membrane 2 may advantageously be coated with a layer of non-stick material in order to prevent the undesirable adhesion, during vulcanisation, of the collapsible supports to the membrane. Figure 34 shows a collapsible support element 111 having, on the side facing the membrane, a shape which is complementary to that of the respective control element 4, that is, with a flat central surface and raised edges for centring the control element. The collapsible support element 111 may be made of a material that may be volumetrically reduced, such as for example, expanded polystyrene, destined to be flattened, as shown in 111a, on the base of the respective chamber 2 after the membrane 2 has been formed. Figure 37 shows a flat temporary collapsible support element, for example, in the shape of a ring 31, positioned with overhang in a stepped seat 73 made in the alveolus, or chamber 2. This particular conformation of the temporary support element is preferable for its simplicity, in that it enables the use of commercially available rings, or washers, with significant savings. After vulcanisation, the ring 31 may be deformed in the direction of the base of the seat 2 by means of a preliminary pressing stroke P: to make such a deformation possible, the width of each tessera 48 is preferably less than the minimum width D2 of the relative chamber 2. Figure 38 shows how the control elements 4a may be exposed on the pressing surface, in this case there being a corresponding break in that part of the membrane 12: the tesserae 4a are each connected to the respective chambers 2 by means of annular joints 12a. The collapsible support element may also consist of a panel 90 (Figure 39) of composite material, comprising a pair of external layers 91 between which a reducible layer 92 is inserted, for example, made of a corrugated metallic material. The reduction of element 90 may be achieved by flattening on the base of the respective cavity 2. Figure 40 shows an isostatic die for ceramic tiles during forming using the method as described in the present invention. The metallic body 1 is prepared, on whose active face there are the chambers 2, interconnected by means of communication channels 62. A matrix 204 (Figure 41) for forming the active face of the body 1 has its surface coated with non-stick material; the matrix has a perimetric frame 205 for containing the liquid elastomer material 210, (for example, a polymer such as CYANAPREME of the American company AIR PRODUCTS of ALLENTOWN) that is poured into it. Once the liquid elastomer in the filled and possibly preheated matrix 204 is perfectly level, the body 1, previously treated with an adhesive substance and preheated, is brought into contact with it and maintained in position, as shown in Figure 42. After the vulcanisation the matrix 204 may be detached leaving the die ready with the empty spaces 215 in the chambers 2 to be filled with the incompressible fluid through the holes 61, 62 provided. It is to be noted that in this procedure the use of a press is not strictly necessary in that no pressure is exerted between the body 1 and the matrix 209, the weight of the body 1 itself being sufficient. The press, however, is useful in applying the detaching action of the matrix, or, in the case it should be necessary to apply a higher pressure for the introduction of a fluid, for example compressed gas, during the vulcanisation phase; said fluid, introduced through holes 61, can aid the adaptation of the elastomer 210 to the matrix 204, reduce the formation of bubbles and improve the adhesion of the elastomer 210 to the ribs 208; it can also enable the use other different types of elastomer, not in liquid form. This forming method enables the die to be made in other advantageous versions, some of which are described in the preceding Figures (for example, Figure 16, 17) in which there are elements for controlling the deformation of the membrane inserted in the respective cavities. As shown in Figure 43, the communication channels may be obtained by cutting the ribs 208 along their entire height by means of a disc milling cutter with axis parallel to the plane of the face of the die, possibly mounted in series for a more rapid execution. The relative cuts may also be made by means of an angle cutter, in this way the four cuts in the respective four ribs will be carried at the same time. The external part 209a of the cuts 209 will be filled with elastomer, whereas in the lower part 209b - that is, the part closer to the base of the cavity - will remain empty to allow the passage of the liquid. It is to be noted that, given the considerable width of the cut 209, the elastomer contained in it will not be able to move in an appreciable and damaging manner, said cut will instead improve anchorage of the membrane 12 to the ribs 208. The membrane 12 inside each chamber 2 is associated with a preferably rigid element for controlling the deformation of the membrane 4. The control element 4 is maintained in position during the vulcanisation phase by means of an elastic support 212, already vulcanised, or simply glued to the relative element 4; the pre-assembled unit 213 is then positioned, applying a slight pressure, in each seat 214, said seat being shaped in such a way as to keep the element 4 centred and to permit lowering to the base of the cavity 2. Suitable calibration of the dimensions of the seat 214 and of the height of the support 212 enables a maximum lowering stroke C to be determined for the element 4. In this way it is possible to prevent the surface of the tile within the ribs from passing beyond the ideal plane formed by the extremities of said appendages. Figure 46 shows a different method for keeping the element 4 in position during the vulcanisation phase: in this case the base of the chamber 2 is shaped in such a way as to keep the element 4 centred when it is inserted in the chamber and the element remains attached to the base of the chamber 2 by means of movable means of connection, for example, magnets. Once the elastomer has reached a suitable degree of viscosity, the body 1 is de-magnetised and so the elements 4, falling, will partially sink into the elastomer and be held by it; the distance D will therefore be principally determined by the vulcanisation temperature and the moment when the de-magnetisation is carried out. Figure 47 shows a further advantageous system for keeping the element 4 positioned during the vulcanisation phase by means of a collapsible element 216 fixed, for example by gluing, to the base of the chamber 2 and to the control element 4; at the end of the vulcanisation operation the collapsible element 216 is flattened on the base of the cavity 2 with the action of pressure applied to the membrane 12, the expansion of the perimetric part of said collapsible element 216 in contact with the element 4 will cause it to detach and to be securely positioned on the base of the cavity, without any subsequent interference with the movement of element 11. A further advantageous version for keeping the control elements 4 in position is shown in Figures 48 and 49; a spring in the shape of a ring made of steel wire, suitably shaped to keep the element 4 centred and positioned axially is inserted in a groove 217 made in the lateral part of the chamber 2. In this case the walls of the chamber 2 next to the outer edge may be provided with a suitable inclination 219 in order to aid the insertion of said ring 218 and to obtain a joint 12a (not shown here) which is wider and less restrictive at the point where the membrane has to flex; said groove 217 may also be made in the external wall of the element 4 instead of in the wall of the chamber; furthermore, the spring 218 may be replaced by an elastomer seal ring, in this case it will be necessary to prevent the formation of a seal against the liquid, for example, by cutting a piece of said seal ring. As shown in Figure 51, a rigid element 4 is inserted inside the chambers 2 which has appendages 305 that interfere with the walls of the chamber 2 at the corners 306 so enabling the rigid element 4 to be maintained in a predetermined axial and radial position during the vulcanisation phase. The vulcanisation this case has to be obtained using the forming matrix placed in a position underneath the die, as already described with reference to the method of Figures 40, 41, 42. The appendages 305 may be positioned within a chamber 2 without any axial reference as shown on the left side of Figure 50 and 51, or on locators as shown on the right side of the same Figures, said locators advantageously aiding a more rapid and precise positioning of the control element 4 when it is inserted. Each appendage 305 may be an integral part of the element 4, that is, it may be made of the same material, or it may be made of a different material fixed to the control element 4. Should one wish to adopt a forming method for the membrane with the matrix positioned above the body of the die, said control element 4 will be provided with appendages 308 (Figure 53) which, as well as having the positioning function, will also perform the function of containing the mass of liquid elastomer, said appendages will therefore be suitably matched in suitable seats 309 in the chambers 2. As, with this forming method, the pressure exerted on the rigid element 4 is considerably higher, it may be convenient to momentarily support said rigid element 4 with a collapsible element - one of those already described - for example, a sphere 310 made of malleable material, such as lead or copper, placed in a suitable seat 311 and destined to be permanently deformed after vulcanisation. As shown in Figure 54, the control element 4 may protrude with respect to the appendage 308 towards the membrane 12, this in order to aid anchorage of the element 4 to the membrane. Furthermore, as shown on the right side of Figure 54, the base of the control element 4 may be inserted so that it may slide inside a seat 313, this in order to constrain the parallelism of the rigid element during the movement of the membrane 12. As shown in Figures 55 and 56, the control element 4 may be provided with a positioning element in the form of a ring 31, analogous to that of Figure 12, but inserted in a stepped seat made in the part of the element 4 closest to the membrane 12. The external edge of the ring 31 sits in a stepped seat made correspondingly on the walls of the relative cavity 2. This version makes it possible, in a simple manner, to obtain straight ducts 108, or ducts in the form of a "V" 62, in the walls 208 at the base of each cavity 2 in order to make said cavities intercommunicating and to allow the passage of the fluid F during pressing. Figure 57 shows a support element comprising a ring 31 coupled internally with a concave element 4b with concavity facing the membrane 12 and the external edge resting on the internal edge of the ring 31. During pressing, the movement of the membrane 12 towards the base of the chamber 2 causes the permanent deformation of the ring and consequently frees the concave element 4b from said ring.

Claims: Pressing means, particularly for the isostatic pressing of ceramic tiles (41), comprising at least one die (1) having a plurality of intercommunicating chambers (2) containing incompressible fluid (F) and closed by an elastic membrane (12) having an external surface that reproduces the rear of the tile (41) and an internal surface anchored to walls (208) separating said chambers (2), inside each chamber (2) there being inserted, in an intermediate position between said fluid (F) and said membrane (12), a control element (4, 4a, 4b, 70, 71) for controlling the deformation of the membrane (12), characterised in that each said control element (4, 4a, 4b, 70, 71) is anchored to said membrane (12) so as to follow movements of said membrane (12) during pressing and has a zone adjacent to said membrane (12) significantly spaced apart from said walls (208) so as to define, in said membrane (12), a perimetric elastic joint (12a) connecting said control element (4, 4a, 4b, 70, 71) to the respective walls (208), said control element (4, 4a, 4b, 70, 71) co-operating with respective positioning means (14, 16, 25, 17, 18, 19, 21, 26, 27, 28, 29, 30, 31, 65, 69, 111, 90, 212, 216, 218, 305, 308) that maintain each said control element (4, 4a, 4b, 70, 71) in a predetermined position within the relative chamber (2) during the forming of the membrane (12). Pressing means, as claimed in claim 1, in which each said control element (4, 4a, 4b, 70, 71) is made of a material which is stiffer than that of the membrane (12) Pressing means, as claimed in claim 1, in which said positioning means (14, 16, 25, 18, 19, 21, 25, 27, 28, 29, 30, 31, 65, 111, 90, 216) may be permanently deformed once the membrane (12) has been formed to disengage from the respective control element (4, 4a, 4b, 70, 71). Pressing means, as claimed in claim 1, characterised in that said positioning means (17) may be broken under the action of a pressing force to disengage from the respective control element (4, 4a, 4b, 70, 71). Pressing means, as claimed in claim 1, in which said positioning means (212, 308) may be deformed elastically under the action of a pressing force. Pressing means, as claimed in claims 3, or 4, or 5, in which said positioning means (17, 26, 218, 305) are each positioned between the walls (208) of the respective chambers (2) and the respective control element (4, 4a, 4b, 70, 71). Pressing means, as claimed in claims 3, or 4, or 5, in which said positioning means (14, 16, 25, 17, 18, 19, 21, 25, 27, 28, 29, 30, 31, 65, 111, 90, 212, 216, 308) are each positioned between the base of the respective chamber (2) and the respective control element (4, 4a, 4b, 70, 71). Pressing means, as claimed in one of the previous claims, in which each said control element (4, 4a, 4b, 70, 71) is associated with respective annular means for occluding (22, 23, 31, 33, 32) that prevent the passage of fluid material for the forming of the membrane (12) during vulcanisation. Pressing means, as claimed in claim 8, when dependent on claim 7, or on claim 6, in which a support element (28) for said means for occluding (22, 23, 31, 33, 32) is positioned between said control element (4) and the respective positioning means (14, 16, 25, 17, 18, 19, 21, 25, 26, 27, 28, 29, 30, 31, 65, 111, 90, 208, 212, 216, 305, 308).

Inventors: ALGERI MARIS, CAMORANI CARLO ANTONIO, ALGERI, MARIS, CAMORANI, CARLO ANTONIO
Applicants: ALGERI MARIS, CAMORANI CARLO ANTONIO, ALGERI, MARIS, CAMORANI, CARLO ANTONIO
Application year: 1996
Main classification: B28B3
IPC codes: B30B15, B30B5, B28B3, B28B7