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(11) | EP 0 736 363 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Die means, particularly for pressing ceramic tiles |
| (57) The die for pressing ceramic tiles makes for greater uniformity of pressing by compensating
for differences of density occurring when loading the matrix with the powders to be
pressed; the die (P) has a cavity closed on the side facing the clay mixture to be
pressed by means of an elastic membrane (5) peripherally anchored to the body of said
die (P), said elastic membrane (5) being associated to a stiffening plate (111, 316,
362, 372) the cavity may contain an incompressible fluid (11). |
[0001] The invention concerns die means, particularly for pressing ceramic tiles, according to the preamble of claim 1.
[0002] IT-A-1104511 discloses a method and a device for achieving uniform pressing of ceramic tiles. The method envisages the application to the free surface of the clay mixture introduced into the opening of the die, during the action of pressing, of an elastic moulding surface, or elastic membrane, held in firm contact with the clay mixture, to form one face of the tile, by means of an incompressible fluid: this, to neutralize the effects of zones of disuniform density in the body of the formed tile which would cause uneven shrinkage on firing, with consequent variations in the size, or linearity, of the sides of the tile and/or of the planarity of its surface and with the additional possibility of cracking or breakage. Outside the cavity, the membrane is provided with an external portion of a more resistant material.
[0003] The method and the device according to IT-A-1104511 have introduced the fundamental concept of an incompressible fluid, for example, oil, acting on an elastic membrane and interposed between the punch and the membrane.
[0004] However, said method and device do not always enable sufficiently flat (back) surfaces, and hence sufficiently uniform tile thickness, to be readily achieved, particularly in the case of large formats.
[0005] We are aware of a die in which an auxiliary punch base has, on its front face, a chessboard-like array of large flat squares surrounded by channels for the distribution of the liquid, communicating with the internal surface of the overlying membrane by means of large, corresponding square alveoli, forming part of an intermediate punch-plate superimposed on said auxiliary punch base; the smooth inner surface of the overlying (vulcanized) membrane is moulded to afford an array of large, flat square protruding bosses surrounded by channels corresponding exactly to the aforesaid configuration of the upper face of said base of auxiliary punch. This type of mould is also described as forming part of the prior art in IT-U-MI93000071, Fig. 1 and in IT-A-MI92002158, page 3.
[0006] EP-A-0556163, which is per se an intermediate document but concerns the same type of mould, discloses a mould having a plurality of cavities defined by a lattice to which a membrane is anchored; however the lattice cannot be provided with a membrane obtained by vulcanized elastomeric substance, such as rubber or resin, since, when the liquid elastomeric substance is poured on the lattice, the cavities become completely filled with the elastomeric substance and no room is therefore available for the incompressible fluid.
[0007] IT-U-214739 discloses a punch for uniform pressing of ceramic tiles, comprising a plurality of cavities among which a lattice is inherenty defined, said cavities containing an incompressible fluid, i. e. oil, and being closed on the side facing the clay mixture to be pressed by means of an elastic membrane, the elastic membrane comprising a central zone and a preripheral zone, those parts of the membrane not covering the cavities being anchored to the body of said punch at respective peripheral and intermediate anchoring zones, each cavity being intermediately occupied by a respective piston and serving as a guide for allowing axial movements of the piston inwardly and outwardly with respect to the cavity.
[0008] Each piston is further externally provided with a seal for the incompressible fluid peripherally engaged with the internal surface of the respective cavity in order to prevent oil from coming into contact with the membrane.
[0009] In that mould, however, the pistons deteriorate the corresponding edges of the membrane when they move into the cavities to compensate disuniform density of the clay mixture. Furthermore, when the membrane has to be formed, particularly by vulcanization, the pistons have to be inserted into the cavities before the liquid elastomeric membrane is poured to coat the face of the punch: therefore a difficulty arises in that the pistons cannot be located at precise axial positions inside the cavity, being it essential, for proper functioning, that each piston be located at intermediate sections of the respective cavity, so that they can be moved outwardly, under the pression of the oil, and also inwardly, under the pression of the clay mixture. Correct positioning of the pistons is also essential in order to avoid excessive variations of thickness of the membrane.
[0010] The dies according to EP-A-0556163 and IT-U-214739 are to be considered as traditional non-isostatic dies, in the regions defined betwen adjacent cavities. Thus, non-uniform pressing is obtained in the parts of the tiles corresponding to those regions.
[0011] Such prior art may be subject to further improvements with a view to eliminating the said drawbacks.
[0012] A primary object of the present invention is to find isostatic die means that need not be built up of several transverse component parts to enable a membrane to be attached to intermediate supports.
[0014] A further object is to control the thickness of the soft layer of powders to be pressed, so as to obtain uniform thickness and density in the body of the pressed tile.
[0015] According to the invention, die means are provided, comprising two dies, punch and matrix, at least one die having a cavity closed on the side facing the clay mixture to be pressed by means of an elastic membrane peripherally anchored to the body of said die, characterised in that said elastic membrane is associated to a stiffening plate.
[0016] In a advantageous embodiment, the stiffening plate is continuous and fixed to said membrane in such a way that the whole surface of said plate facing the powders to be pressed is anchored to said elastic element.
[0017] In another embodiment, the stiffening plate is provided with a plurality of through-apertures, so that said memrane is anchored to said plate at least in the zones defining the border of said apertures on the side of the plate facing away from the powders to be pressed.
[0018] It is to be noted that the stiffening plate has the additional function of allowing the distribution of the incompressible fluid in the cavity of the relative semi-die.
[0019] It is to be noted, furthermore, that, on completion of the membrane-shaping process, the stiffening plate can be eliminated, for example, by a chemical process, whereby a substance that will corrode said plate, but not the membrane, is introduced into the cavity, or by a physical process, whereby, for example, the semi-die is heated to a temperature at which the plate melts, while the membrane remains firmly attached to the cavity.
[0020] It is to be noted, furthermore, that the holes for the introduction and discharge of the incompressible fluid protrude from the bottom of the cavity through a spot-facing that can be blocked with a plug during the moulding of the elastic membrane, the plug remaining partially incorporated in the membrane itself.
[0021] In order to prevent said membrane adhering to the bottom of the cavity, those areas of the bottom of the cavity of the die where the membrane should not adhere can be sheathed in plastic, or paper, with holes punched where said apertures occur.
[0022] In another embodiment, the cavity communicates with a device controlling the volume of fluid in the cavity of the said at least one die, said controlling device serving to alter the deformation of said membrane during pressing.
[0023] The advantages offered by this invention are: lower manufacturing costs; lower running costs; possibility of renovating the die; improved functionality; possibility of adopting various, not only square, designs; maximum stability in the areas of adhesion; possibility of transforming traditional punches, even if en bloc, into punches according to the invention by the simple application of a distributing plate to, or above, the active surface of the punch itself; possibility of more efficient moulding of the membrane; greater protection of the membrane; possibility of greater control over the flexing of the membrane, reduction in surface defects; ease of removal of pressed items, facilitated particularly with the adoption of the device regulating the volume of fluid.
[0024] Some embodiments of the invention are illustrated, by way of example, in the accompanying drawings, in which:
Figure 1 is a vertical section of a die according to the invention in which a plate of flexible material is inserted between the elastic membrane and the smooth upper face of the punch to transmit the pressure to the entire surface in a more uniform manner by the elimination of the forces that tend to deform the elastic membrane in the horizontal plane and allow bending only in a vertical direction;
Figure 2 is a section as in Figure 1, but after the introduction of the liquid;
Figure 3 is a section as in Figure 1, but relating to the pressing phase of the product;
Figures 4 and 8 show, in a sectioned side view, a improved die with elastic membrane having adjustable trim, in particular during the loading phase of the mixture;
Figures 5 and 9 show, in a sectioned side view, a die according to the invention in the loading phase in two different embodiments corresponding to Figure 4 and 8;
Figure 6 shows the die according to the invention in use, without the introduction of liquid between membrane and cavity;
Figure 9 shows, again in a sectioned side view, the die illustrated in Figure 31 during the loading phase prior to pressing;
Figure 10 shows a pressing phase carried out with the combined use two embodiments of the present invention, one lower die, acting as a baffle plate, with pre-positioned membrane, and one upper die acting as a punch with pressure-equalizing fluid;
Figures 11 and 12 are sections as in Figures 4 and 5 in a version of design of the elastic means that act also as a seal;
Figures 13 and 14 are sections as in Figure 12, but relating to different versions of coupling joint between moulding and stiffening plate and elastic membrane;
Figures 15 and 16 are sections as in Figures 11 and 12, but relating to further versions of the die according to the invention, in which the moulding stiffening plate is divided in two parts, an innermost part one having the function of defining the chamber of fluid during moulding and an outermost part, which is floating, acting as a stiffener;
Figures 17 and 18 are sections as in Figures 11 and 12, but relating to further versions with single-piece moulding and stiffening plates and elastic membrane enveloping the plate on both its surfaces that lie in planes that are substantially parallel to the moulding plane;
Figure 19 is a section as in Figure 12, but relating to a further embodiment, in which the moulding and stiffening plate is divided in two parts, the innermost part being simply a frame in the base of the cavity of the corresponding die.
[0025] The Figures show: a punch P, corresponding to the back of the tile and having a membrane 5, for example of vulcanized rubber and adapting itself to the disuniformity of the mass of mixture placed in the mould of the die to obtain a uniform compression in the mass itself, in its every point during pressing.
[0026] Elastic membrane 5 also having intermediate indentations 104 and an indented peripheral border 9 whose base is coplanar with those of indentations 6 that, during pressing, form the so called "feet" or support ribs on the back of the tile, or their complements.
[0027] There are also a number of holes 107 for the introduction of liquid 11, for example oil, after the membrane has been moulded, after the possible chemical disintegration and/or physical elimination of the material of the plate, for example, by making use of the same hole; hole 107 being closeable with plug 325 (Figures 4 and 11) to prevent it from becoming filled with the material the membrane is made of when it is poured or else when it is being moulded. The plug itself - for example, cylindrical - penetrates in a corresponding hole in a plate 111, when still in situ, and, together with one or more other analogous plugs, act as a reference pin for the plate.
[0028] The elastic membrane 5 may be stiffened transversely by means of, advantageously, inextensible fibres inserted in it, during vulcanization: this prevents marked undulation, whilst conserving longitudinal elasticity.
[0029] It is to be noted that the feet or ribs on the back of the tile can be of any other convenient form, for example, even of the type having cells in the form of a honeycomb.
[0031] The Figures also show: a top face of punch P having anchorage grooves 102, even having sides diverging downwards thereby creating undercut, covered with adhesive substance, and peripheral frame 103 with internal face similarly treated: grooves 102 being filled by appendages 103a of the elastic membrane; 104, grooves on the external surface of elastic membrane 5 vulcanized in situ, reproducing in relief the design of the back of the tile to be formed.
[0032] The plate 111 is of a thickness that ranges, for example, from a few tenths of a millimeter to a few millimeters and is interposed between the bottom surface of a cavity in the body of punch P and the lower, smooth surface of membrane 5 that provides an extensive and continuous vulcanized anchorage surface 112 (Figure 2) so as to avoid rippling and therefore excessive undulation.
[0033] In this case, with the presence of plate 111, which in practice stiffens membrane 5, the intermediate anchorage areas of the membrane/plate assembly are eliminated, except in the peripheral areas.
[0034] It is to be noted that plate 111 is able to absorb the loads set up in the membrane caused by disuniformities in the density and/or composition of the powders to be pressed; in particular, the plate has to have a modulus of elasticity that enables it to deflect elastically and to compensate for the differences in reaction loads transmitted by the powder to the membrane: the adoption of a continuous floating plate has the advantage of being able to compensate deformation during pressing over wide areas.
[0035] The Figures also show: 114 (Figure 3), the punch and 115, the matrix of the die; 116, the external peripheral anchorage zone of the membrane; 301 (Figure 4) is a die including a punch P in which there is at least one cavity, or recess, 303 in which a deformable membrane 5 in elastic material, for example rubber, is anchored, for example, by vulcanization, or glueing, which is anchored on a plate 111 of a stiffer material than that forming membrane 5, for example a metal. Membrane 5 is, as a rule, vulcanized on plate 111 and has a peripheral lip 306 so shaped to be inserted in a corresponding seat 307 of the recess. Between the metallic plate 111 and the plane of said recess an elastic means is interposed acting also as a peripheral seal 308, anular and deformable, which ensures sealing whilst permitting relative perimetric displacement between plate and imprint.
[0036] Punch P has holes 107 to introduce fluid in chamber "C" which is defined by the base of the punch, plate and perimetric elastic medium prior to the introduction of the fluid due to the plate 111 resting on elastic medium 308.
[0037] In the plane of cavity 303 there are closed seats 310 in which elastically deformable spacer elements 311 are inserted, for example, helical springs, that permit the adjustment of the trim of the plate during the loading phase of the product to be pressed and which retract partially or entirely into their seats during the pressing.
[0038] In the plane of the imprint there can be threaded holes 312 (Figure 8) for adjusting screws 313 that support the plate 111 during the loading phase of the product to be pressed.
[0039] The top end of threaded holes 312 can open out into cylindrical seats 314 in which can be placed corresponding elastically deformable spacer elements 311: advantageously, the screws have support caps 315 at their top end: said screws have the further function of adjusting the preloading of spacer elements 311 so as to vary the trim of the membrane during the loading of the powders.
[0040] In the version illustrated in Figure 7, the plate 316 has a greater thickness and the membrane is in contact only with its rear surface: the punch has a peripheral step with sharp corner in relation to which a first perimetric elastic element 308a and a second perimetric elastic element 308b are assembled: between step 319 and the corresponding seat 320 of plate 316 a seal 321 is assembled made of a material such as rubber.
[0041] Turning now to Figure 11, 322 indicates a moulding matrix for the membrane that has protuberances 323 distributed that create in membrane 5 indentations which will create the so-called "feet" or support ribs on the back of the tile.
[0042] During the vulcanization phase, plate 111 is kept in the correct position with the insertion through punch P of pins 325, that is a pair adjusting-screw dowels 313a.
[0043] In Figures 5, 7 and 10 fluid 11 introduced in chamber C has been represented schematically with closely spaced dots: the seal is ensured by lip seal 306 cooperating with perimetric elastic media 308 or with seals 308a, 308b.
[0045] Figures 6 and 9 show how the screws 313 enable the positioning of the various areas of the plate 111 at the desired elevations, functioning as reference elements for the plate during the moulding phase.
[0046] Figure 10 shows a further possible use for the invention: it shows how punch P can be used as an upper pressure-equalizing punch and made to interact with another beneath whose sole function is a controlling one; adjusting screws 313 adjusts the trim of the plate, enabling thicknesses S1 and S2 of the material to be pressed to be predetermined.
[0047] Figures 15, 16 show a further structural variation of the die, in which plate 111 is divided in two parts, one a floating, stiffening element 362 for membrane 5, the other fixed to the base of the cavity, for example, by means of screws 363, in such a way that its outer edge extends inside the seat in the base of the cavity for the lip 306 of the elastic membrane 5, so as to create an undercut seal 361 to prevent the fluid from leaking: in a particular case not shown the lip can cover entirely the underside of the plate 111 acting as a sealing a support element for the plate.
[0048] In the version of Figure 15, elastic elements 360 are inserted between the floating, stiffening part 362 of membrane 5 and the sides of the seat of lip 306: these elastic elements have the function of lifting membrane 5 after pressing and of centering stiffening floating plate 362 in relation to the cavity of the corresponding die.
[0049] Intermediate layer 364 of membrane 5 is anchored to stiffening plate 362 and distanced from underlying moulding plate 111, so as to include a truncated cone stopper 365 in relation to each fluid inlet hole 107.
[0050] Figures 40, 41 show a version of die in which the plate 111 is made adherent on both its sides to membrane 5, as in the version of Figure 9: with respect to this version, however, lower layer 367 of the said membrane has rim 366 inserted in a groove in the base of the cavity of the corresponding die, the height of rim 366 being such as to define chamber C for the fluid. Layer 367 and the corresponding rim 366 can be pre-formed as hollow caps, or even integral 368, 369 with membrane 5 as shown in Figure 18, in which case there also being elastic elements 360 for the formation of chamber C.
[0051] In this way, then, the invention as described fulfills its objects, in particular in the way in which chamber C between plate 111 and imprint 303 remains defined without the intervention of thrust of the pressurized fluid that is introduced, due to the prior lifting of the plate itself which, on completion of the vulcanization phase, is supported on perimetric elastic elements 308, or on spacer elements 311; furthermore, it can assume a non planar configuration, but predetermined as required, in readiness for the loading of the material to be pressed.
[0052] In the version of Figure 11, perimetric elastic means 308, being toroidal in form, is substituted with elastic means 350 having a trapezoidal section, and cooperates with lip 306 of membrane 5: this providing increased safety against leakage of the liquid.
[0053] In the version of Figure 13, the peripheral coupling joint between membrane 5 and plate 111 consists of a plurality of annular extensions 352, for example, a pair of extensions, defining, between them, a groove 353 in which the moulding membrane is anchored: the said annular extensions can be of different thicknesses, one with respect to the other, and may, furthermore, penetrate into lip 306 of membrane 5 to differing depths; furthermore, they can be parallel to each other or inclined with respect to one another.
[0054] Figure 14 shows how the lip 306 can have a pair of opposing appendages 354, one penetrating plate 111, the other penetrating the body of punch P: this to further improve sealing against leakages of the fluid.
[0055] In Figure 19, the lower portion of the moulding plate is limited to a peripheral frame 372 extending towards the seat of lip 306 so as to divide it into two limbs during moulding, in a way analogous to that of Figure 35.
[0056] Each limb of lip 306 can have an annular sealing appendage 370, 371 inserted in corresponding grooves respectively in the body of matrix P and in floating plate 111.
[0057] Frame 372 can be fixed to the base of the cavity by means of screws 363, or simply placed on it, in both cases the said frame being treated with a non-stick agent so as not to adhere to the material making up membrane 5 during moulding: this contributes to improving the coupling of the membrane to the semi-die.
[0059] It is to be noted that elastic elements 308, 350 have the double function of lifting the plate and of sealing against fluid leakage from chamber C, whereas elastic elements 311, 360 do not have a sealing function, being therefore isolated, that is, peripherally interrupted to allow the passage of fluid into the cavity.
[0060] Furthermore all the elastic elements mentioned above can be inserted between the sides of the seat for lip 306 and floating plate 111, to contribute advantageously to its centering in the cavity of the corresponding semi-die.
[0061] The invention as described is susceptible to numerous changes andvariations all included in the domain of the present invention.
1. Die means, comprising two dies, punch and matrix, at least one die (P) having a cavity
closed on the side facing the clay mixture to be pressed by means of an elastic membrane
(5) peripherally anchored to the body of said die (P), characterised in that, said
elastic membrane (5) is associated to a stiffening plate (111, 316, 362, 372).
2. Die means according to claim 1, wherein said cavity contains an incompressible fluid
(11).
3. Die means according to claim 1, or 2, wherein said plate (111, 316, 362) has at least
a face pointing outwardly of said cavity which is joined to said membrane (5).
4. Die means according to claim 1, wherein elastically deformable spacer means (308,
311, 360, 360, 366) is interposed between said plate and an inner portion of said
cavity.
5. Die means according to any preceding claim, wherein said plate (316) is peripherally
extended above said cavity and up to the outer edge of said die.
6. Die means according to claim 2, wherein said spacer means (308, 350) extends perpherally
and continuously around said cavity so as to serve as sealing means.
7. Die means according to any preceding claims, wherein the bottom of said cavity has
a peripheral depression (102, 307) in which the inner part (103a, 306) of the membrane
(5) is inserted.
8. Die means according to claims 1 and 2, wherein an isolating cap (366, 367) is interposed
between said plate (111) and said incompressible fluid (11) so that the plate (111)
is not in direct contact with said fluid.
9. Die means according to claims 1 and 2, wherein the bottom part of said cavity is provided
with an at least peripherally extending plate-shaped element (111, 372) fixed thereto.