WO1996015888A1

WO1996015888A1 - A method for compacting powders, and a relative apparatus

Info

Publication number: WO1996015888A1
Application number: PCT/EP1995/004560
Authority: WO
Inventors: Carlo Antonio Camorani; Maris Algeri
Original assignee: Carlo Antonio Camorani; Maris Algeri
Priority date: 1994-11-22
Filing date: 1995-11-20
Publication date: 1996-05-30
Also published as: IT1269274B; CN1062504C; BR9509806A; AU4174396A; ITMO940159A0; ITMO940159A1; CN1173154A; DE69529997D1; EP0793565B1; EP0793565A1

Abstract

A method for compacting powders comprises forming a layer (8, 8a) of powders on conveying means (2) which conveys it to a die (9), isolating a portion of said layer (8, 8a) inside a frame (11) of said die (9), by bringing said frame (11) adjacent to said conveying means (2), and compacting the portion of said layer (8, 8a) isolated by said frame (11), by means of a punch (10) of said die, descending inside said frame (11); an apparatus for forming ceramic articles comprises conveying means (2) for conveying a layer of powders (8, 8a) to a die (9), said die (9) comprising a punch (10) movable in a substantially orthogonal direction to said layer (8, 8a), associated with a relative cross-member (62) to cause the pressing of the powders and a frame (11), movable in a substantially orthogonal direction to said layer (8, 8a) independently of said punch (10), inwardly slidably engageable with said punch, serving as isolating means for isolating a portion of said layer (8, 8a) on said conveying means (2).

Description

A method for compacting powders, and a relative apparatus.

The invention concerns a method and relative apparatus for forming powders, that is, a procedure for manufacturing pressed ceramic, particularly paving or lining tiles. The prior art comprises forming methods whereby the matrix of a die for ceramic materials is filled with powders, or mixtures of powder and granules, in one or more phases, prior to it being pressed to obtain a compacted article which is then sent to be fired, after, possibly, it has been dried.

Such methods entail lengthy idle times when loading the matrix, in as much as the trolley used for distributing the powders has to be made to advance in order to fill the matrix and, subsequently, in order to enable the punch of the press to be lowered, said trolley has to be retracted at a moderate speed so as to avoid disturbing the distribution of the powder beneath it.

Loading the matrix by means of a trolley is not at all satisfactory, in that it implies an intrinsic undesirable lack of homogeneity in the distribution of the powders, caused mainly by the mixing and/or uncontrolled displacement of the powders themselves with the movement of the trolley, depending also on factors that are variable with time in an unpredictable manner, for example, depending on the environmental conditions, or the physical state of the powders to be treated, its granulometry, humidity, pour rate and other factors besides. Furthermore, the stroke of the press has to include a deaeration phase, that is, an initial portion of the down stroke of the punch into the matrix has to be carried out at a reduced velocity to enable the air inside the mass of powder being pressed to escape: this in order to avoid the formation of lenticular pockets of air inside the mass which, when the thrust exerted by the punch ceases, tends to cause the article to disintegrate. Furthermore, with prior art forming methods, obtaining even simple chromatic effects, involving, for example, the distribution of particles, or other powdered materials, or granules, onto the surface of the article to be pressed, is highly problematical: in fact, highly complex and costly devices have to be used to load a number of layers of powders in the matrix of the press, superimposed on each other, bringing about a considerable reduction in productivity and considerable increase in costs. Such prior art may be subject to considerable improvements with a view to eliminating said drawbacks.

From the foregoing emerges the need to resolve the technical problem of inventing a new method for pressing ceramic articles in which it is possible to obtain estimable aesthetic effects whilst maintaining high productivity and with an increase in quality,- all this in the context of a production apparatus that is particularly simple and functional: needing, in particular, to avoid defects due to lack of homogeneity in the distribution of the powders to be pressed during loading.

A further aspect of the technical problem is that of achieving a greater rapidity and efficiency in feeding the ceramic presses.

In the context of the present invention the term "layer of powders" signifies both a homogeneous layer of pulverulent material and a layer consisting of a plurality of separate layers superimposed on each other, that may also comprise decorating substances.

The term "powders" is used to represent powder of various granulometries and/or various colours, even mixed together. The term "decorating substances" signifies substances selected from the group comprising: powders, ceramic paints, colour in the form of powder or liquid solution, ceramic mixtures and their combinations.

The invention resolves said technical problem by adopting a method for forming ceramic articles, comprising forming a layer of powders on conveying means which conveys it to a die, subsequently, isolating a portion of said inside a frame of said die, the frame having an outline substantially corresponding to the profile of the article to be compacted, by bringing, from above, said frame adjacent to said conveying means, and compacting the portion of said layer isolated by said frame, still positioned on said conveying means, by means of a punch of said die, which engages internally slidably with said frame.

In a particularly advantageous version, the method comprises preparing of a homogeneous, continuous mass of said powders, pre-compacting of said mass to obtain a flat pre-formed semifinished product that has peripheral dimensions that are slightly smaller than that of the pressed tile, and pressing of said pre-formed semifinished product.

The supply of the powders, and/or granules, to the pre- compacting station being advantageously achieved with the distribution of said powders, in a continuous layer that has a substantially uniform thickness and density. Said layer being obtained with dropping said mass of powders in a controlled manner from a relative batching means, for example, a hopper with a adjustable outlet section for pouring said mass of powders onto an underlying conveyor belt.

Alternatively, the powders may be poured onto a table movable with a reciprocating straight-line motion between a loading position under the hopper and a pre-compacting position under the corresponding press.

Before pressing, decorating substances may advantageously be distributed, for example, powders, that have varying granulometries and/or colours, even co-ordinated with those of the base, on the layer of powders, and/or granules, and/or on the top surface of the pre-formed semifinished products. The distribution of said decorating substances may take place, in particular, on the stretch of said conveyor, or table, included between said hopper and the pre-compacting station of the layer of powders.

Alternatively, in order to prevent, in particular, the decorating substances from causing variations in thickness, with, consequently, possible defects in the pressing, the distribution of the decorating substances may be effected directly on said conveyor, or said table, upstream of said hopper.

The decorating substances may consist of powders, ceramic paints, in liquid or powder form, or mixes of these, or of coloured clay-based mixtures.

All this being achieved with the most varied types of distributing devices, for example, drop feed from a conveyor belt, or roller, or feed from a hopper, or with serigraphic applications.

In a further aspect of the invention, the apparatus for the formation of the ceramic articles comprises conveying means for conveying a layer of powders to a die, said die comprising a punch that may move in a direction that is substantially orthogonal to said layer, which is associated with a relative cross-member to cause the powders to be pressed and with a frame that may move in a direction that is substantially orthogonal to said layer, independently of said punch, being shaped so as to couple with it and to enable said punch to slide inside it, said frame also being such as to isolate a portion of said layer on said conveying means.

In a particularly advantageous version, the apparatus comprises batching means for the continuous dosage of predetermined quantities of powders onto underlying first conveying means that transfer said powders in the form of a substantially continuous layer towards a pre-compacting die; the apparatus also having second conveying means to transfer the pre-compacted articles to a pressing station. In a particularly advantageous version, said first conveying means consist of a conveyor belt wound in a closed loop on a number of rollers, at least one of which being motorised, said belt having an active section passing through said pre-compacting station.

The pre-compacting station advantageously includes a punch held above said belt which is lowered onto the powders to be pre-compacted inside a frame which is vertically mobile in co-ordination with the movements of the punch,- a striking block being positioned beneath said belt to operate, with its top surface, as a sliding plane for the belt once the thrust of the press ceases.

This enables the pre-compaction of ceramic articles to be achieved in a particularly simple manner without inducing inconsistencies in its composition.

In an advantageous version, the belt is driven with intermittent motion, with advancement phases alternating with static phases to achieve the pre-compaction of the powders; said batching and/or distributing devices being coupled to relative driving means in a direction that is substantially parallel to the longitudinal direction of the conveyor belt; said driving means being such as to enable a constant relative velocity to be maintained between the conveyor and said batching and/or distribution devices. This offers the added advantage of a further improvement in the uniformity of loading by limiting load displacement and the consequent forces of inertia set up by dynamic actions. In another advantageous version, said conveyor belt is driven in a continuous uniform motion and the pre- compacting station has relative driving means that transfer the pre-compacting die in a horizontal direction substantially parallel to the longitudinal direction of said conveyor.

This enables a further improvement in the uniformity of distribution of the powders enabling a highly homogeneous degree of compaction to be achieved. Further advantages offered by this invention are: the possibility of obtaining new and estimable aesthetic effects with increased productivity and contained costs. In a particularly advantageous version, the pressing die for the pre-compacted semifinished products is made to co¬ operate with a device for the continuous extraction and/or supply of pressed tiles, advantageously consisting of a pair of chains closed in a loop on corresponding pinions, driven synchronously, the chains being connected to each other by transverse elements acting as impellers for said tiles and/or said pre-compacted semifinished products. This enables the further advantage of reducing the time required to load and evacuate the pressing die. It is to be noted that the increase in productivity is due in particular to the drastic reduction in the time required to load the pressing die, due to the elimination of the movements of the powders, and/or granules, in the area close to the matrix of the die.

Furthermore, with the method according to the invention, the increase in productivity is also due to the reduction in the pressing times, in that, with the introduction of the pre-compacting phase of the powder, the deaeration of the soft mass occurs for the most part before it is pressed.

It is to be noted that, with the implementa ion of the method according to the invention and the embodiment of the relative apparatus for its implementation, the damaging effects caused by the variations in time of the physical, granulometric and flow characteristics of the powders and/or granules are eliminated: in fact, these variations occur in a time interval that is always much longer than the time required for the distribution onto the conveyor belt of the layer of powders relative to the formation of a tile: this all contributes towards improving the homogeneity of loading and the quality of the final pressing. Some embodiments of the invention are illustrated in the seventeen tables of drawings attached, wherein: Figure 1 is a schematic side view of an apparatus for forming ceramic articles, in a version with a pair of consecutive pressing stations;

Figure 2 is a partially sectioned side view of the pre- compacting press for the semifinished products in the starting phase of the pressing;

Figure 3 is a partially sectioned side view of the pre- compacting press for the semifinished products in the pressing phase;

Figure 4 is a partially sectioned side view of the pre- compacting press for the semifinished products in the removal phase;

Figure 5 is a partially sectioned side view of the pre- compacting press for the semifinished products in the return to initial position phase,-

Figure 6 is a partially sectioned side view of the press for pressing ceramic tiles in the extraction phase of the pressed tile;

Figure 7 is a partially sectioned side view of a press as in Figure 6 in the starting phase of the pressing,- Figure 8 is a partially sectioned side view of a press as in Figure 6 in the pressing phase;

Figure 9 is a partially sectioned and interrupted side view of an apparatus for the embodiment of the method according to the invention, in a version with distribution of the decorating substances upstream of the batching means for the distribution of the mass of powders and/or granules making up the body of the tile;

Figure 10 is a Cartesian diagram with, on the ordinate, the velocity of the conveyor, shown with a continuous line, and the velocity of the batching means and/or distributing means, shown with a dotted line, and with time on the abscissa, referring to a version of apparatus having conveyor belt driven with intermittent motion; Figure 11 is a diagram, referring to the same version of apparatus, with, on the ordinate, the space covered by the conveyor, shown with a continuous line, and, with a dotted line, the space covered by the batching and/or distributing means, and with the time elapsed on the abscissa; Figure 12 is a schematic vertical section of a die for pressing pre-compacted semifinished products having a device for loading and evacuating the matrix, in the extraction phase of the formed tile;

Figure 13 is a section as in Figure 12, but in the starting phase of the pressing,-

Figure 14 is a section as in Figure 12, but in the phase where the semifinished product is loaded and the punch is cleaned by means of a rotary brush device,-

Figure 15 is an enlarged lateral section of the die of Figure 12, but with a rotary brush device for alternately cleaning the base of the matrix and the punch, in the phase at the end of the pressing;

Figure 16 is a vertical section as in Figure 15, but in the extraction phase of the pressed tile;

Figure 17 is a section as in Figure 15, but in the starting phase of the pressing;

Figure 18 is a section as in Figure 15, but in the initial extraction phase of the pressed tile;

Figure 19 is a section as in Figure 15, but showing the cleaning of the active face of the punch with the driving device shown in a dotted line,-

Figure 20 is a section as in Figure 15, but showing the introduction of a pre-compacted article in the matrix of the die,-

Figure 21 is a plan view of Figure 19;

Figure 22 is a section as in Figure 19, but in a variation relating to the device for extracting the pressed tiles, acting also as a device for feeding them to the matrix of the die,- Figure 23 is a section as in Figure 22, but in the configuration during the cleaning of the active face of the punch;

Figure 24 is a side view as in Figure 1, but in a variation where the return stretch of the conveyor belt passes through the pre-compacting die;

Figure 25 is section XXV-XXV of Figure 1, but highlighting the striking block of the pre-compacting press supported straddling the return stretch of the conveyor belt; Figure 26 is a transverse section as in Figure 25, but in a variation with the striking block of the pre-compacting press supported flexibly on the relative base; Figure 27 is a plan view of an apparatus according to the invention, but in a version with a line for pre-compacting the powders extending in a direction parallel to the pressing line, said lines being interconnected by means of conveying means arranged perpendicularly to both lines,- Figure 28 is a schematic side view of a forming apparatus according to the invention, in a version with single stage pressing, during the advancement phase of the conveyor; Figure 29 is a schematic view as in Figure 28 during the pressing phase,-

Figure 30 is a partial, schematic side view of the dosing devices for distributing the powders and/or granules, showing the relative actuating means,- Figure 31 is a top view of Figure 30; Figure 32 is a section XXXII-XXXII of Figure 28; Figure 33 is a section as in Figure 32, but during the pressing phase;

Figure 34 is section XXIV-XXXIV, partial and enlarged, of Figure 32;

Figure 35 is a view in direction XXXV-XXXV of Figure 32; Figure 36 is section XXXVI-XXXVI of Figure 35; Figure 37 is a section as in Figure 32, in a version with the frame supported on the base and the bottom of the isobaric version of the pressing die; Figure 38 is a section as in Figure 37, but during pressing;

Figure 39 is a section as in Figure 32, in a variant with the frame connected rigidly to the cross-member,- Figure 40 is a section as in Figure 39, but during pressing;

Figure 41 is a side view as in Figure 9, but with distributing means that are able to form an undulated layer of powders and/or granules.

The apparatus 1 for forming ceramic articles, i. e. ceramic tiles, comprises conveying means, consisting, for example, of a conveyor belt 2 wound in a closed loop on rollers, at least one of which is coupled to driving means, having a straight, upper active section resting on a support plane 4.

The active section of the conveyor belt 2 has above it a batching means, for example, a hopper 5, for. the distribution of the powders, that are destined to make up the body of the pressed tile 6, the opening of the hopper having a vertical batching blade 7, vertically adjustable in order to vary the thickness of the layer 8 of powders. The conveyor belt 2 passes through the pre-compacting die 9, including a punch 10 positioned above the belt 2, sliding inside a matrix 11, and a striking block 12 positioned beneath the conveyor belt 2 to support it during the compaction so as to obtain a pre-formed article 17. As shown in Figure 2, the striking block 12 may have an upper plate 12a, directly in contact with the lower face of the conveyor belt 2, made of a porous material, obtained, for example, by sintering, for example metal, or other suitable material: in this case the conveyor also being made of a gas-permeable material, that is, porous, for example fabric.

With the striking block 12 in conjunction with conveyor belt 2 and, possibly, plate 12a being made of gas-permeable materials a more rapid deaeration of the mass of powder is obtained in the pre-compaction, with an increase in productivity and improved quality.

The pre-compaction pressure may be vary widely, depending on the type of powders used, the degree of final pressing, the aesthetic effect required for the final product and other factors besides.

The pre-compaction pressure, however, has to be such as to permit a pre-compacted semifinished product to be obtained that is sufficiently resistant to enable it to be transferred and handled towards the pressing station without it being damaged.

The pre-compaction of said powders and/or granules is such that a flat pre-formed semifinished product is obtained that has peripheral dimensions that are slightly smaller than those of the pressed tile and a thickness that is slightly greater than that of the pressed tile. The die 9 may be stationary, wherein case the layer 8 is made to advance intermittently with the batching means 5 being coupled to driving means not shown acting in a longitudinal direction F parallel to the direction of conveyor belt 2.

Alternatively, in the case where it is preferable to have a continuous motion of said layer, the pre-compaction die 9 may be made mobile with intermittent motion synchronous with the speed of translation of the active section of the conveyor belt 2 in the direction indicated by arrow Fl, by means of substantially horizontal driving means parallel to the direction of the conveyor belt 2.

Between the batching means 5 and the pre-compacting die 9 there may be distributing means 13, 14 for distributing powders onto the layer 8, in order to improve the appearance of the pressed tile, or to give it particular physical, or mechanical properties.

Said distributing means, which may be chosen from a wide range, for example, of decorating machines for ceramic tiles, amongst which there also are serigraphy machinery, may consist of, for example, hoppers 15, whose outlet section is controlled by a corresponding batching roller 16, whose peripheral surface is smooth, or even etched, to project non coherent decorating elements continuously, or even intermittently.

A powder, or granule, batching means 14 may consist of a pair of vibrating, superimposed sieves 14a, 14b, the lower sieve 14b being suitably screened in order to deposit the loose material onto predetermined areas of the layer 8. At the end of the conveyor belt 2, the pre-compacted articles 17, produced by die 9, are transferred onto second conveying means, advantageously comprsing, for example, a roller conveyor 18, with motorised rollers 18a, to feed the press 19. Between the end of said conveyor belt 2 and the roller conveyor 18 there is a hopper 20 that collects and recycles excess powder 19a sending it to batching means 5 by means of conduits not shown.

There may be other distributing means 21 for powdered material on the roller conveyor 18, similar to distributing means 13, 14 described previously.

Transferring means, i. e. an impeller 22 for the pre-formed articles 17 and/or the pressed tiles 6 is movable on the roller conveyor 18 with reciprocating motion. As illustrated in Figures 2 to 5, the frame 11 of the compacting die 9 has lower edges 23 having wedge-shaped sections in a plane perpendicular to the conveyor belt: in this way it is possible to achieve an optimal separation from the layer 8 of powders of the mass destined to form the tile 6, without altering the density of the layer 8: the particular shape of the edges 23 determine the formation of mounds 24 of excess material in the area corresponding to the external edges of the frame 11. When the pre-compaction is concluded the die 9 is activated in its return stroke in a direction F2 opposite to Fl, as shown in Figure 5.

As shown in Figure 6, the pre-formed article 17 is sent, by means of the second conveying means, for example, a roller conveyor 18, to press 19 for the formation of the tile 6 and its removal, by a further motorised roller conveyor 25, possibly supplied by oscillating feeder arm 25a with suction pad 25b.

As shown in Figure 7, the impeller 22, driven towards the press 19 in the direction indicated by arrow F3, is pulled back in the opposite direction, as indicated by arrow F4, at the end of the advancement stroke with a stretch of rising inclined trajectory to avoid interference with the article already ready to be inserted in the press. The press 19 has punch 26, matrix 27 with mobile base 28. Figure 9 shows how the batching means for the powders and/or granules that go to make up the body of the pressed tile 6 may feed, by means of distributing means 13, 14, the conveyor belt 2 on which a layer 29 of decorating substance, or even a number of superimposed layers 29, 29a, has already been distributed.

The batching means may include, under a hopper 5 containing the powder, an upper conveyor belt 30 that deposits the powder on the conveyor belt 2 by gravity feed. This prevents the distribution of the decorating substances 29, 29a from being disturbed by the distribution, onto the same conveyor belt, of the powder that will form the body of the tile.

It is preferable if the powders are dropped very gently from the upper conveyor belt, this being achievable by inclining said conveyor belt in the advancement direction Fl of the layer of powder, in such a way as to limit to the minimum possible value the vibrations to which the powders are subjected.

Instead of the inclined conveyor belt, an inclined slide 30a may be provided in association with a conveyor with a horizontal upper active section.

To compensate for possible irregularities in the thickness that may arise as a result of the drop feed distribution from the upper conveyor belt 30, also taking into consideration the presence of the decorating substances 29, 29a, a blade 31 may advantageously be provided, supported transversely over conveyor 2 to scrape the upper surface of the layer 8.

A powder preparation apparatus arranged as in Figure 9 enables the tiles to be pressed with their top side facing downwards, which enables the use of normal "plunger" type punches.

Obtaining tiles with their top sides facing downwards is equally possible with the other versions of apparatus, on turning the pre-compacted semifinished products over by means of normal overturning devices for ceramic tiles. It is to be noted that the distribution of the powdered material, or granules, even made up of, for example, powdered or atomised ceramic paints or clays, or mixtures thereof, may take place even only in the central part of the layer 8, that is, that part of it that is to be pre- compacted prior to the final pressing.

In this way contamination is avoided in the recycling of the mass of loose material that makes up the body of the tile with the powdered granulate material that constitute the decorative pattern on the top face of the layer 8. It is to be noted also that with the method and apparatus according to the invention it possible to obtain new and more estimable aesthetic effects, unattainable with prior art forming procedures.

In particular, the punch 10 of the pre-compaction die may have a convex active surface, so as to obtain a concave top surface in the pre-compacted semifinished product which may be filled with paint and/or clay grains, or powders, by means of distributing means 16, 21.

Furthermore, grains, or granulate material, may be distributed on the top face of the pre-compacted article, designed to impart particular decorative motifs to the support, which become incorporated in the mass of the support during pressing. This enables a defect inherent in the methods according to the prior art to be eliminated, whereby the distribution of granules in a mass of powder constituting the main body of the tile entails the granules sinking during pressing up to a point where they almost disappear beneath its top surface making it necessary to perform the costly procedure of smoothing the article after it has been pressed or after firing.

On the other hand, adopting the method and the apparatus according to the present invention, it is possible to obtain ceramic tiles with the main body in a low cost material and a surface layer made of a more valuable and aesthetically pleasing material.

This type of tile may otherwise only be manufactured by resorting to the so called "double loading" forming methods, which involve considerable time wasting and high costs.

The diagrams in Figures 10, 11 refer to a stepped advancement of the conveyor belt 2, and therefore of the layer 8, and refer to a condition included between a time TO at the beginning of the cycle and a time Tl relating to the end of the movement in one step.

As shown in Figure 10 the variation of the relative speed of the conveyor belt 2, that is, of the layer of powders 8, with respect to batching means 13, 14 and/or distributors 5 is such that the relative speed Vrel of the layer with respect to the batching means and/or distributors, that is, the difference in ordinate between the continuous line diagram of the speed VI and the dotted line of V2 is kept constant at all times during the cycle.

This is achieved in a particularly advantageous way by applying a constant acceleration at all times during the cycle, which may be obtained with straight-line variations, in function of time, in the speed diagrams relating to said layer and to said distributor and/or batching means. In this way the particular advantage is obtained whereby a layer 8 is obtained that has a uniform thickness and homogeneous density.

Furthermore, limiting the dynamic loads on the powders prevents them from being mixed prior to the pre-compaction. Deriving from this is the diagram of the space SI covered by the layer 8 and the space S2 covered by the distributor and/or batcher as shown in Figure 11.

It is to be noted that the function obtained for the difference between curves SI and S2 is linear. As shown in Figure 12, the die 19 may be equipped with a device 32 for extracting the pressed tiles 6 from the sliding plane of the relative matrix 27, said device being made up of a pair of chains 33 each closed in a loop on respective geared pinions 34, free to rotate, 34a motorised, these last being interconnected to a shaft 35 coupled to driving means not shown, by means of driving cogs 36 and chain transmission 37 (Figure 19) . The pair of chains 33 is interconnected by at least one transverse element 35, acting as impeller, advantageously by a pair of such impellers, positioned opposite each other, one connecting the pair of lower, active stretches of said chains, the other connecting the upper, return stretch.

Figure 14 shows how there may be a pair of impellers 22, 22a, integral with one another, the first of which, further back, for inserting the semifinished products in the press 19, the other, further forward, for extracting the pressed tiles 6.

A rotary brush 38 may be associated with the pair of impellers 22, 22a to clean the lower active surface of the punch 26 and/or the mobile base 28 of the matrix 27. As shown in Figures 15 to 23, a rotary cleaning brush device 38 may be positioned between the stretches of chain 33, driven by chain 38a, supported on a pair of end limbs 39, the cleaning device being mobile between two positions on opposite sides of the punch 26 and being made to brush over, alternately, the upper surface of the mobile base 28 and the lower surface of the punch 26.

Figures 22, 23 show how the chains 33 are interconnected by a set of four transverse elements 35 that have both the function of removing the pressed tiles and of feeding the semifinished products to the pressing die.

The distance between one transverse element 35 and the next, as well as the number of transverse elements and the distance between centres of the pinions 34, 34a, are conditioned by the format of the tiles to be pressed. Figure 24 shows how the return stretch of the conveyor belt 2, with reference to the version of apparatus having the conveyor belt with intermittent step-by-step advancement motion, may pass through the pre-compac ion die 9 between the active stretch of the same conveyor belt and the striking block 12a by means of a pair positioning rollers 3a, with, possibly, the interposition of a plate, not shown, of material with a low coefficient of friction. This greatly simplifies the operation of substituting the conveyor belt when it becomes worn.

Figure 25 shows how the striking block 12, 12a is positioned straddling the conveyor belt 2 by means of a pair of lateral elements, or sills 12b, running longitudinally with respect to the conveyor belt 2 on the base 43 of the supporting structure 12c of the pre- compaction press so as to form a cavity I, sufficiently large to permit the passage through it of the return stretch of the conveyor belt 2.

Figure 26 shows how the striking block 12, 12a may be supported by elastic means 40, on a base plate 41 fixed to the base 43 and interconnecting the columns forming the load bearing structure 12c of the press 19 so as to form a cavity I, of variable amplitude, to allow the passage of the return stretch of the conveyor belt 2: when the punch 10 and the frame 11 descend towards the conveyor belt 2 to pre-compact the area of layer 8 that is to be formed, the block 12, 12a is lowered to a point where it blocks both the active and the return stretch of the conveyor belt 2 against the plate 41; when the pre-compaction thrust ceases, elastic elements 40 lift the striking block 12, 12a so that the conveyor belt is free to be advanced by another step so as to bring the next portion of layer 8 to the press 19.

Figure 27 shows a layout of an apparatus including a pre- compaction line, defined by the longitudinal extent of the conveyor belt 2, and a pressing line, defined by the positioning of the rollers of the roller conveyors 18, 25: between said pre-compaction line and said pressing line are positioned third conveying means 44, for example a pair of closed loop belts wound on corresponding pairs of pulleys. The semifinished products transiting on said third conveying means may be subjected to various types of applications to decorate their top faces, or to further processing, such as, for example, drying, brushing, or other treatments besides.

Figures 28 to 41 show a version of the apparatus with single pressing phase, structurally analogous to the apparatus as in the previous Figures: therefore the compacting press 19 may directly form the ceramic tiles; a layer 29b of decorating substances may be distributed on the layer 8.

With particular reference to Figures 30, 31, driving means is described which is able to ensure that a constant relative velocity is maintained, as in the diagram as in Figures 10, 11, between the conveyor belt 2 and the distributing means 5, 13: to this end the conveyor 2 has an end roller 3 coupled to relative actuating means, first transmitting means 50, for example, comprising a chain wound on a driving sprocket wheel 51, that is coupled to relative actuating means 52, and a driven wheel 53, made integral with roller 3. Second actuating means 54, for example consisting of a further chain, are placed between a further driven sprocket wheel 54a (Figure 31) , integral with the same roller 3, and an idler sprocket wheel 55 supported on the side of the conveyor belt 2. The chain 54 is wound on a driving wheel 56, coupled to relative independent actuating means 57, in a section of it having a profile as in an omega due to the deviation upwards induced by a pair of idler wheels 58. The sprocket wheels 56, 58 are supported on a trolley 59 which supports the distributing means 5, 13, for distributing said powders.

The independent actuating means 57 impart a constant speed of rotation to the relative drive wheel 56, therefore, when the conveyor belt 2 is stationary, that is during the working strokes of the punch 10 and of the matrix 11, the trolley moves towards the roller 3 distributing a layer 8 of uniform density; when an end-of-stroke position has been reached signalled by a first sensor 60, the actuating means 52 are activated in uniformly accelerated motion, so that the trolley may slow down progressively, stop and invert its direction of movement, initiating its movement away from the roller 3; having followed the uniform deceleration and acceleration ramps, the trolley moves away from the roller 3 at a noticeably constant velocity with respect to the conveyor belt 2 whilst the distributing means 5, 13 continue to distribute a uniform layer of powders on the layer 2.

A limit switch 61 determines the stoppage of the machine should the trolley 59 fail to invert its motion, as could occur should the actuating means 52 jam up, or due to machine stoppage caused by an interruption in the operating cycle of the press.

With reference to Figures 32, 33, a cross-member 62 of a press through which passes a conveyor belt 2 is coupled at its lower side to a frame 11 by means of a plurality hydraulic cylinders 63, connected hydraulically in series in such a way as to avoid deflection of the frame during pressing and to maintain parallelism with respect to the plane of the conveyor belt 2. The arrangement in series enables the creation of an hydraulic transmission between cylinders 63 connected to each other in such a way as to maintain the stems 64 of said cylinders acting on various zones of the surface of the frame 11 at the same time. In particular, each cylinder 63 has a stem protruding from a chamber of the cylinder containing the pressurised fluid: the connection between the cylinders is such that one chamber is connected on the side from which the relative stem protrudes to the chamber of another cylinder on the opposite side from which the stem protrudes. The active sections of the chambers have to be the same in order to guarantee the same stroke of stems 64. The branches 65 of hydraulic circuit connecting cylinders 63 coupled together, have an inlet 66 for supplying oil and for maintaining a constant volume of oil in the circuit, by means of a solenoid valve not shown.

The frame 11 has lateral appendages 67 which come to rest, at the end of the pressing stroke, on lateral abutments 68 protruding from the block 12.

Furthermore, the frame may have an intermediate baffle 70, having a concave bottom face 71 in the shape of a V involved with conduits 72 pointing upwards to discharge powders trapped between the walls of the concave face 71 during the pressing stroke.

Alternatively, as shown in Figures 37 and 38, in the place of the intermediate baffle 70, there may be a blade 73, with the bottom edge 73a tapered towards layer of powders 8.

Vertical driving means for driving the frame 11 may be positioned between the block 12 and the appendages 67. The punches 10 are driven by moving the cross-member 62 in a manner not shown.

The striking block 12 may have isobaric zones 75, defined by a membrane 76 delimiting a cavity with a number of compartments containing incompressible fluid, positioned below the conveyor belt 2 in a zone corresponding to that of the punch 10; the conveyor belt may have impressions 78 defining the supporting zones of the tile being formed and their alternate cavities 78a.

Alternatively, the membrane 79 may delimit a single chamber 80 for the incompressible fluid.

A stiffening plate 81 may be positioned between membrane 79 and the rear face of the conveyor belt 2.

With reference to Figures 39 and 40, the frame 11 is supported by the cross-member 62 by means of distancing elements 82 fixed to the appendages 67, together with the punches 10.

Vertical driving means 83 are positioned between the punches 10 and the cross-member 62, consisting, for example, of hydraulic cylinders having stems 84 integral with said punches.

In this way it is possible to carry out the pressing stroke, shown in Figure 40, of the punches 10 when has the frame 11 of the die is positioned on the conveyor belt 2. Figure 41 shows a structure of the distributing means 5, 13 suitable for obtaining the distribution of the powders in a layer 8 having a undulated bottom layer 8a, defining cavities 78b.

This is caused by a dosing drum 85 with a concave external surface such that the quantity of powders discharged onto the underlying layer 2 is not constant.

In practice, the materials, dimensions and details of execution may be different from but technically equivalent to those described without departing from the juridical domain of the present invention.

In as much, the pre-compaction die, for example, may be associated with a number of presses by means of conveying means for the semifinished products, such as, for example, motorised roller conveyors, with conveyors arranged in straight lines or with perpendicular offshoots, or other besides .

It is to be understood that the trasferring means, i. e. impeller 22, 22a, 25, 25a, 25b, feeding the press with the pre-compacted articles 17, or extracting the pressed tiles 7 may be associated with forming apparatus for forming ceramic articles different from those described in the present specification.

Claims

1. A method for compacting powders, wherein it comprises forming a layer (8, 8a) of powders on conveying means (2) which conveys it to a die (9) , subsequently isolating a portion of said layer (8, 8a) inside a frame (11) of said die (9) , the frame (11) having an outline substantially corresponding to the profile of the article (6, 17) to be compacted, by bringing, from above, said frame (11) adjacent to said conveying means (2) , and compacting the portion of said layer (8, 8a) isolated by said frame (11), while it is still positioned on said conveying means (2) , by means of a punch (10) of said die, which slidably engages internally with said frame (11) .

2. A method as claimed in claim 1, wherein said article (6, 17) is removed from said die (9) by moving said frame (11) away from said conveying means (2) before, or more quickly than, the punch (10) .

3. A method as claimed in claim 1, wherein said layer of powders (8, 8a) is has a substantially uniform thickness and omogeneous density.

4. A method as claimed in claim 1, wherein the manufactured article (17) after being removed from said die

(9) is at least pressed again.

5. A method as claimed in any one of the preceding claims, wherein, before being pressed, and/or before being pressed again, a layer of decorating substances (29b) is distributed on said layer of powders (8, 8a) and/or on said pressed article (17) .

6. A method as claimed in claim 5, wherein said layer of decorating substances (29b) is involved only with the part of said layer (8, 8a) destined to be isolated by said frame (11) .

7. A method as claimed in any one of the preceding claims, wherein in one of the faces of said layer (8) cavities (78a, 78b) are formed in which decorating substances (29, 29a) are introduced.

8. A method as claimed in claim 7, wherein said cavities (78a, 78b) are obtained during the pressing of said layer (8, 8a) .

9. A method as claimed in any one of the preceding claims, wherein a portion (19a) of said layer (8, 8a) not isolated by said frame (11) is recovered to reconstitute a part of said layer (8, 8a) .

10. A method as claimed in any one of the preceding claims, wherein said layer (8, 8a) is obtained with the outflow of powders from distributing means (5, 13) movable in substantially uniform reciprocating motion with respect to said conveying means (2) .

11. A method as claimed in any one of the preceding claims, wherein advancement strokes of said frame (11) for bringing it adjacent to the conveying means (2) and following pressing strokes of said punch (10) alternate with controlled advancements of said conveying means (2) .

12. A method as claimed in claim 11, wherein said controlled advancements comprise a phase of substantially uniformly accelerated motion and a phase of substantially uniformly decelerated motion.

13. An apparatus for compacting powders, wherein it comprises conveying means (2) for conveying a layer of powders (8, 8a) to a die (9), said die (9) comprising a punch (10) movable in a substantially orthogonal direction to said layer (8, 8a) , associated with a relative cross- member (62) to cause the pressing of the powders and a frame (11) , movable in a substantially orthogonal direction to said layer (8, 8a) independently of said punch (10) , inwardly slidably engageable with said punch, serving as isolating means for isolating a portion of said layer (8, 8a) on said conveying means (2) .

14. An apparatus as claimed in claim 13, wherein said frame (11) has sides having a shape of cross section decreasing towards said conveying means (2) .

15. An apparatus as claimed in claim 13, wherein said conveying means (2) comprises a conveyor belt on which said powders are distributed in the form of a layer (8, 8a) by distributing means (5, 13), said belt being coupled to respective driving means (2) via first transmitting means (50) .

16. An apparatus as claimed in claim 15, wherein said distributing means (5, 13) are coupled to said conveying means (2) by second transmitting means (54) having independent driving means (57) .

17. An apparatus as claimed in claim 13, wherein further pressing means (19) are provided for pressing the articles

(17) , downstream of said die (9) , to further compact said articles (17) .

18. An apparatus as claimed in any one of claims 13 to 17, wherein upstream of said further pressing means (19) further distributing means (21) are provided for distributing decorating substances on said layer (8, 8a) and/or said articles (17) .

19. An apparatus as claimed in claim 13, wherein said die

(9) has protuberances in said punch and/or in said matrix enabling cavities (78a) to be obtained in said layer (8, 8a) .

20. An apparatus as claimed in claim 15, wherein said conveyor belt (2) is slidably coupled, at least in a position corresponding with that of the die (9) , with a fixed striking block (12) , that reacts against the thrust of the punch (10) during pressing.

21. An apparatus as claimed in claim 20, wherein said striking block (12) has a surface on which said belt (2) slides shaped like one of the faces of the article (6, 17) to be pressed and such that it may receive parts of the belt (2) during the deformation determined by said punch

(10) .

22. An apparatus as claimed in claim 20, wherein compensating means (75) for isostatic compensation are interposed between said conveyor belt (2) and said striking block (12) .

23. An apparatus as claimed in claim 13, or 20, wherein said conveying means (2) and/or the surface (12) of said striking block (12a) in contact with said conveying means is/are made of a gas-permeable material.

24. An apparatus as claimed in claim 13, or 14, wherein said frame (11) has at least one intermediate baffle (70, 73) extending between opposite sides of the frame (11) and defining in it pressing compartments of corresponding articles (6, 17), said at least one baffle (70, 73) lying in a plane which is substantially orthogonal to said layer (8,8a) .

25. An apparatus as claimed in claim 24, wherein said baffle (70) has a V-shaped lower surface (71) having a concave part pointing towards said conveying means (2) ; a plurality of holes (72) for the removal of surplus powder being provided at the innermost vertex of said "V" .

26. An apparatus as claimed in claim 13 and 23, wherein vertical driving means (74) for said frame (11) are interposed between said frame (11) and said striking block (12) .

27. An apparatus as claimed in claim 13, wherein said cross-member (62) is equipped with vertical driving means (63) .

28. An apparatus as claimed in claim 27, wherein said vertical driving means (63) comprises at least one pair of hydraulic cylinders (63) interconnected in series and defining an hydrostatic transmission.

29. An apparatus as claimed in claim 13 and 23, wherein said striking block (12) comprises abutting elements (68) limiting the stroke of the frame (11) towards the conveying means (2) .

30. An apparatus as claimed in claim 13, wherein said cross-member (62) is fixed to said frame (11) and is coupled to said punch (10) by means of an hydraulic cylinder (83) .

31. A die for forming ceramic tiles comprising a frame (11) that may be coupled internally with a punch (10) and having edges (23, 70, 73) which are thinner on the side of the underlying conveying means (2) .

32. Use of a conveyor belt (2) as a mobile base of a matrix for pressing plane ceramic articles (6, 17) .