Ceramic mold control device

Abstract: A control device for ceramic molds which consist of a die-plate (11) provided with at least one forming cavity (10) for receiving at least one layer of material to be compacted by pressing, and in which the base of said at least one cavity is defined by a die (8) which is fixed to the lower plate of the mold, and with which there cooperates an overlying die caused to travel vertically by the mold operating press, comprises, within a body (19, 123) to be fixed perpendicular to the press bed (2), two coaxially aligned overlying pistons (26, 15), of which the upper piston (26) supports said lower plate (6), whereas, in combination with an axially adjustable annular piston (18) interposed between the first two pistons (26, 15), the lower piston (15) defines the downward stroke of said upper piston (26), which corresponds to the desired depth of loading of said at least one layer in said cavity (10).

Description: This invention relates generally to ceramic tile manufacture, and in particular concerns a control device for molds used for producing ceramic tiles. As is well known, molds of various types are used in tile manufacture, all comprising: an intermediate plate, commonly known as the die-plate, provided with at least one forming cavity into which a layer of material to be compacted, such as atomized clay, is loaded, possibly with the addition of an upper layer of a different material such as powdered ceramic glaze, a lower plate provided upperly with at least one forming die which defines the base of said at least one cavity, and an upper plate which is fixed to the vertically mobile cross-member of a ceramic press and is provided lowerly with at least one die to cooperate with the opposing (lower) die to compact the material present in said at least one cavity, and hence form the tile, see for example EP-A-0211449. The aforesaid elements constitute the essential parts of known ceramic molds, of which the following main types can be identified: so-called "entering punch" molds in which the die-plate is stationary in height, and the dies for forming the exposed face of the tile, commonly known as "exposed face" dies, are fixed to the lower plate, whereas the dies for forming the laying face of the tile, commonly known as "reverse face" dies, are fixed to the upper plate; so-called "mirror-plate" dies in which the die-plate moves in height during each pressing step and the "exposed face" and "reverse face" dies are fixed respectively to the upper and lower plates of the mold; so-called "reverse mirror" molds in which the die-plate is movable and the "exposed face" and "reverse face" dies are fixed to the upper and lower plates respectively, and so-called "double mirror" molds in which the "exposed face" and "reverse face" dies are positioned inversely to the preceding case and are associated with a counter-die and with the mold die-plate respectively, said counter-die and mold die-plate being able to travel vertically relatively to the corresponding dies. The said main types of ceramic molds, and others which are no more than modified models deriving from the preceding, are well known to the expert of the art and therefore other details will not be described. For the present description it is however important to clarify the procedure involved in one complete cycle comprising loading said at least one forming cavity and pressing/discharging a tile. After forming a tile, the upper die is raised on command by the cross-member of the ceramic press, and the lower die moves to the level occupied by the upper face of the die-plate. The lower die is lifted by the mould lower plate, the tile being extracted from the forming cavity by said lifting, ready to be removed. At this point a suitable loading trolley (for example for atomized clay) receives permission to advance and hence remove the tile from the die-plate, with a slight delay the lower die then lowering to a predetermined level. In this manner the thickness is defined for the atomized clay, which the trolley can now discharge into the forming cavity. At this point the mold is practically ready for pressing a tile, commonly known as a support or biscuit, which may or may not be glazed after firing. The same mold is often used to form other types of product such as so-called "pressure-glazed" tiles, and tiles with a multi-component support, these being prepared by pressing two different materials together. With particular but not exclusive reference to pressure-glazed tiles, after loading the clay the lower die is further lowered to free the upper part of the forming cavity. In the part freed in this manner, the same or a different trolley then deposits a layer of powdered ceramic glaze on the clay. After this the lower die moves to its lower end-of-travel position with the lower operating plate resting against the bed of the ceramic press. At this point the upper die is lowered to form the (pressure-glazed) tile, after which the upper die is raised, followed by the lower die to move the tile into its discharge position, after which a further loading/pressing cycle begins. However during the use of such molds it often happens that the operating parameters with which the final characteristics of the tiles are closely linked vary even several times during one production period. For example it can happen that the clay characteristics such as its moisture content, its average particle size and the ratio of finer particle quantity to coarser particle quantity can change, and as is well known to the expert of the art these characteristics can result in even fairly large variations in the final tile thickness and in various problems during their firing. In addition in the case of pressure-glazed tiles it can prove convenient to vary the thickness of the glaze to be deposited on the clay, for example to at least partly remedy the effects due to the aforesaid variations, or to give the tiles a more resistant exposed surface. Moreover, it often happens that the forming cavity is filled in a non-uniform manner, or that the various mold parts are inaccurately positioned relative to each other, or are subjected to incorrect relative movement during pressing. Consequently in such situations the relative positions of the mold parts must be controlled in order to obtain tiles of practically constant thickness. To solve this complex problem the Applicant has already provided a support and adjustment column, illustrated and described in Italian patent application No. 46814 A/90, to which reference should be made for further details. The column of this document comprises a hydraulic cylinder which is to be fixed to the press on which the ceramic mold is mounted, which contains a damper piston for supporting the mold die-plate, and on which there are slidingly mounted two telescopic pistons one inserted into the other, of which the outer one is intended to support the mold lower plate, whereas the inner one determines the lowering stroke of said lower plate, corresponding to the amount of loading of the desired layer of powdered material, such as clay, into the forming cavity or cavities of said die-plate. In addition, said two telescopic annular pistons are associated with a surrounding bush for defining the upward stroke of the outer piston, where this latter determines the loading of said layer of clay, the thickness of said layer being varied according to requirements by adjusting the axial position of said bush. Specifically, said adjustment is made by a screw-nut device provided between the bush and an outer body, and by a worm-helical gear linkage operated by an electronic card micromotor. Respective screw-nut adjustment means are also interposed between said damping piston and the mould die-plate and between said hydraulic cylinder and the mold lower plate, the first adjusting the height of the die-plate and the second defining the upward end-of-travel position of said outer annular piston. Sensor means are also provided associated with said surrounding bush, and are combined with the hydraulic circuit which operates the inner annular piston, in order to determine (if necessary) an intermediate lower (or backward) position for the inner annular piston before it reaches its downward end-of-travel position. In this manner, a layer of powdered ceramic glaze (or other material in powder or granular form) can be deposited on the layer of clay (or other material) fed into the forming cavity or cavities of the die-plate. Although the aforesaid column has proved suitable for its purpose, the following problems have arisen. Firstly it has been found that the clamping between the die-plate and the mold lower plate provided by said damping piston and outer annular piston can, by virtue of adjustment inaccuracies or severe operating conditions, give rise to small misalignment between said two pistons and hence imperfect alignment between the forming cavity and the respective dies, with consequent excessive rubbing between them and fairly rapid wear. Secondly, adjusting the screw-nut means provided between the damping piston and mold die-plate and between the hydraulic cylinder and mold lower plate has proved relatively lengthy and complicated. This is because said means are located in a region between the mold lower plate and die-plate which is of difficult access and is normally covered by fairly thick compact layers of dust. Relatively lengthy adjustment times result in rather substantial production losses, which assume a certain importance given the production rate of modern processing lines. In addition, the column of the cited document comprises a relatively large number of component parts, making it rather complex and bulky, and also relatively very costly. Moreover, it has been found that said constructional complexity can give rise, as has unfortunately happened, to mistakes in adjustment and maintenance, resulting in often irreparable damage both to the column and to the respective ceramic mold. The main object of the present invention is to provide a ceramic mold control device which solves the initially discussed problems and overcomes the aforelisted drawbacks, within the framework of a simple and rational construction. Said object is attained by a device as defined in the accompanying claims. The features and constructional merits of the invention together with its manner of operation will be apparent from the detailed description given hereinafter with reference to the accompanying drawings, which show a preferred embodiment thereof by way of non-limiting example. Figure 1 is a sectional elevation of the invention; Figure 2 is a partly sectional view of the hydraulic actuator for controlling the device of Figure 1; Figure 3 is a view in the direction III of Figure 2; Figure 4 is a schematic view from above showing a ceramic mold fitted with devices according to the invention; Figure 5 is a partly sectional front elevation of the preceding figure; and Figure 6 is a partly sectional side elevation of Figure 5. Firstly it should be noted that the device of the invention can be associated with any known type of ceramic mold, with a movable or fixed die-plate, and comprising any number of forming cavities of any shape and size. Consequently the mold parts specified hereinafter are in no way to be considered as limiting the present invention. For the same reason the mold support and operating press, the mold upper plate and the relative dies are not shown. Said figures, and in particular Figures 1, 5 and 6, show two plates 1 designed to rest on the press bed 2, and fixed to opposing sides of a bed protection platform 3 by screws 4. Each plate 1 is provided with two devices 5 according to the invention, said four devices 5 (see Figures 4, 5) supporting the mold lower plate 6 as described hereinafter. This latter comprises on its underside a block 7 (Figures 5, 6) and on its upper side a series of dies 8, such as reverse face dies for forming the laying side of the tiles. A dust protection bellows 9 (Figure 6) is provided between the block 7 and platform 3, the block 7 resting on the platform 3 during tile compacting. Said dies 8 are slidingly housed in forming cavities 10 provided in the mold die-plate 11, which is supported by four usual hydraulic dampers 12 fixed to the plates 1 as can be seen in Figures 4 to 6. It should be noted that said dampers 12 are connected to a common pressurized hydraulic reservoir, the operating pressure of which can be regulated as required. As can be seen in Figures 1 and 5, at each individual device 5 the plates 1 comprise a cylindrical recess with differing cross-sections, and with which there is associated a series of hydraulic oil feed/discharge ducts. From Figure 1 it can be seen that said cylindrical recess contains, fixed therein by screws 13, a coaxial flanged ring 14. Within this latter there slides under sealed conditions a piston 15 provided with an upper rod 16. Between said plate 1, ring 14 and piston 15 a chamber 17 is defined connected to a convenient hydraulic unit, such as the hydraulic circuit of the ceramic press. On the rod 16 there slides under sealed conditions an annular piston 18 which is inserted into a flanged bush 19 of differing cross-sections. This latter is fixed on the plate 1 at 20 (Figure 1), no description of the seal rings interposed between the components of the device 5 being given hereinafter as they are well illustrated. Between the two pistons 15 and 18 there is a chamber 21 from which there extends a duct 210 connected to a pressurized hydraulic reservoir. Basically, said chamber 21 acts as a damper. In addition between the annular piston 18 and the bush 19 there is defined an annular chamber 22 from which there extends a service duct 220 connected to the actuator 23 (see Figures 2, 3), to which reference will be made hereinafter. Again with reference to Figure 1 it will be seen that on the top of the bush 19 there is screwed a cap 123 which is locked by a ring nut 24 and is shaped as an inverted cup with a holed base. Said holed base is traversed by a rod 25 deriving from an underlying piston 26 slidable within the bush 19. The rod 25 is provided with a threaded hole 250 for fixing the plate 6 (die carrier) by means of a robust screw 251 (see Figure 6). It should be noted that between said screw 251 and the respective passage hole in the plate 6 there is a radial clearance of the order of a few tenths of a millimetre to allow automatic compensation of any slight horizontal slippage between the plate 6 and the die-plate 11. It should also be noted that said compensation is greatly facilitated by the fact that the die-plate simply rests on the dampers 12 (Figures 4 to 6), the combination of these features preventing excessive rubbing between the dies 8 and the cavities 10. Finally, above and below said piston 26 there are two chambers 27 and 28 respectively, from which respective service ducts 270 and 280 extend. The first 270 of said ducts is connected to a pressurized hydraulic buffer, the second 260 being connected to a convenient hydraulic unit such as the press hydraulic circuit. As can be seen in Figures 2 and 3, the actuator 23 comprises a hollow body 29 to one end of which the casing of a step-down unit is fixed, whereas the other end comprises four angularly equidistant cylinders 31. The body 29, the casing 30 and the cylinders 31 are closed by respective holed covers 290, 300 and 310. In the body 29 there is slidingly inserted an axially bored slider 32 the outward travel of which is determined by said step-down unit, whereas its return travel is determined by a compression spring 33 compressed between the cover 290 and the slider 32. This latter, at the end facing the cover 290, is pointed, for example as a frusto-conical or frusto-pyramidal point, against which the conjugate ends of four pistons 34 contained in said cylinders 31 rest. At the opposite end of each cylinder 31 there is provided a second piston 35, between said two pistons 34 and 35 there being interposed a compression spring 36. Between said pair of pistons 34 and 35 there is defined a chamber 360 into which the duct 220 connected to the chamber 22 opens (see Figure 1), an adjustable stop 37 being associated with the second piston 35 of said pair. This stop consists of a through screw screwed into the cover 310, its purpose being specified hereinafter. As can be seen in Figure 2, in said slider 32 there is a chamber 320 closed at one end (to the right in the figure) by a holed plug 321, and connected at its other end (to the left in the figure) to a hollow rod 322 which passes through the cover 290. The hollow rod 322 is connected via adjustable timed valve means to a hydraulic circuit the purpose of which is specified hereinafter. The chamber 320 of the slider 32 contains a piston 38, the rod 380 of which passes through said plug 321. Against the free end of said rod 380 there rests a coaxial push rod 30 connected at one end (to the left in Figure 2) to a helical gear 400 via a screw-nut linkage 40, at its other end (to the right in Figure 2) it being locked torsionally, but not axially, relative to the cover 300 by a key 41. Finally, a worm 401 with an electronic card-type operating motor (not shown) engages said helical gear 400. Lastly, it should be noted that the described actuator 23 is to be located on the press control panel, whereas the four devices 5 are preferably permanently associated with the ceramic press so that ceramic mold replacement is of low cost. The invention operates as follows. Firstly it should be noted that the positions of the piston 18 and piston 38 shown in Figures 1 and 2 respectively are purely indicative. It should also be noted that for a complete understanding of the operation of the invention reference is made hereinafter to the formation of multi-component tiles, such as pressure-glazed tiles by a mold of the mirror-plate type as specified in the introduction. After a lower layer of atomized clay and an upper layer of powdered ceramic glaze have been deposited in known manner in the cavities 10, the block 7 of the plate 6 is rested on the platform 3 (see Figure 6) and the die-plate 11 is completely raised. With this configuration the pistons 26 and 15 (see Figure 1) are completely lowered, and the rod 16 of the lower piston 15 is spaced from the upper piston 26. On termination of this filling, the mold upper plate (not shown) is lowered, by which said upper plate pushes the die-plate 11 downwards, the corresponding upper dies (not shown) cooperating with the lower dies 8 to form the tiles (of pressure-glazed type, also not shown). After this forming, commonly known as "pressing", the mold upper plate is raised, followed by the die-plate 11 which is urged by the dampers 12 (Figures 5, 6). Almost simultaneously the chambers 28 and 17 (Figure 1) are pressurized so that the dies 8 move to the level of the upper face of the die-plate 11, whereas the lower piston 15 rests against the annular piston. At this point the loading trolley or trolleys (not shown) advance to remove the tile which has just been formed, and before the clay loader reaches the cavity 10 the piston 26 is lowered to rest against the rod 16. This travel determines the layer quantity of clay to be deposited in the cavity 10. After the clay loader has passed but before the arrival of the glaze loader a determined quantity of oil is fed into the chamber 320, with the result that the slider 32 advances slightly (towards the left). This produces an outward movement of the pistons 34 and hence a corresponding contraction of the chambers 360, from which oil is forced into the corresponding chambers 22. This results in an identical lowering of the annular piston 18 and of the two pistons 15 and 26, and hence also of the mold lower plate 6. This further lowering determines the thickness of the layer of ceramic glaze to be deposited on the clay, said glaze thickness being adjusted as required by operating the valve means associated with the hollow rod 322. It should be noted that the thickness of the clay deposited in the cavities 10 can also be adjusted according to requirements, this being done by withdrawing or advancing the push rod 39 (see Figure 2) independently of the filling/emptying of the chamber 320 by the actuator 23 (Figure 2). After the glaze loader has returned to its rest position, the previously fed oil is removed from the chamber 320, and the chambers 28 and 17 are discharged. In this manner the pistons 26 and 15 return to their respective rest positions and the mold is ready for the next pressing. If after suitably checking the formed tiles it is found that they have defects due to non-uniform loading of the forming cavities 10, the positions of the pistons 35 are adjusted by the screws 37. Obviously this adjustment is made independently of the filling/emptying adjustment of the chamber 320 and independently of the advancement/withdrawal adjustment of the push rod 39 (Figure 2). It is apparent that adjusting the operating position of one or more of said pistons 35 results in a corresponding variation in the plane in which the mold lower plate 6 lies during the loading of the clay (or other material) and during the loading of the glaze (or different material). It is also possible to adjust the height and lie of the die-plate 11 (see Figure 6), for example by placing shims below one or more of the dampers 12, and to adjust the end of the upward stroke of the piston 26, by means of the cap 123 (Figure 1). If tiles for glazing after firing are to be obtained, it is necessary only to exclude the adjustment determined by the chamber 320 (see Figure 2). The merits and advantages of the invention are apparent from the aforegoing and from an examination of the accompanying figures. The invention is not limited to that illustrated and described, but covers all technical equivalents to the aforesaid means and their combinations, if implemented within the context of the following claims.

Claims: A control device for ceramic molds which consist of a die-plate (11) provided with at least one forming cavity (10) for receiving at least one layer of material to be compacted by pressing, and in which the base of said at least one cavity is defined by a die (8) which is fixed to the lower plate (6) of the mold, and with which there cooperates an overlying die caused to travel vertically by the mold operating press, characterized by comprising, within a body (19, 123) to be fixed perpendicular to the press bed (2), two coaxially aligned overlying pistons (26, 15), of which the upper piston (26) supports said lower plate (6), whereas, in combination with an axially adjustable annular piston (18) interposed between the first two pistons (26, 15), the lower piston (15) defines the downward stroke of said upper piston (26), which corresponds to the desired depth of loading of said at least one layer in said cavity (10). A device as claimed in claim 1, characterized in that said two superposed coaxial pistons (26, 15) have respective projecting rods (25, 16), of which the first (25) emerges from said body (19, 123) to connect to said lower plate (6), whereas the second (16) passes through said annular piston (18) and enters the seat within which the upper piston (26) slides in order to define said downward stroke. A device as claimed in the preceding claims, characterized in that said superposed coaxial pistons (26, 15) each lie between an upper hydraulic damping chamber (27; 21) for achieving maximum lowering of the respective piston (26, 15), and a lower hydraulic chamber (28; 17) for achieving maximum raising of the respective piston (26, 15) and connected to an operating circuit, such as the press hydraulic circuit. A device as claimed in the preceding claims, characterized in that said annular piston (18) lies between said upper hydraulic damping chamber (27) associated with the lower piston (15), and a hydraulic control chamber (22) connected to a common actuator (23) controlling all the devices (5) supporting said lower plate (6). A device as claimed in claims 1 and 4, characterized in that said actuator (23) comprises a slider (32) which is constantly forced elastically against a threaded motorized adjustment rod (39), and further comprises, for each control chamber (22) of said devices (5), an inclined surface against which, by the effect of a rear thrust spring (36), there rests the conjugate end of a piston (34), the opposite end of which faces a hydraulic chamber (360) connected to the adjustment chamber (22) of the corresponding device (5). A device as claimed in claims 1, 4 and 5, characterized in that within said slider (32) there slides a piston (38) which at one end rests against said threaded rod (39) and at its other end faces a hydraulic chamber (320) for causing the slider (32) to advance independently of the action of said threaded rod (39). A device as claimed in claims 1, 4, 5 and 6, characterized in that said chamber (360), associated with the actuator (23) and connected to said control chamber (22) of the device (5), is defined by said piston (34) resting against the slider (32) and by an opposing piston (35) which at one end acts as a support for said thrust spring (36) and at the other end rests against an adjustment screw. A ceramic mold and its operating ceramic press, characterized by being provided with a series of devices (5) in accordance with claims 1 to 7, and in which the common actuator (23) for said devices is associated with the press control panel.

Inventors: BARDELLI LODOVICO, BARDELLI, LODOVICO
Applicants: MASS SPA, MASS S.P.A.
Application year: 1993
Main classification: B30B11
IPC codes: B30B11, B30B15, B28B3