EP1961537A2

EP1961537A2 - Mold for forming clay tiles and method for obtaining said mold

Info

Publication number: EP1961537A2
Application number: EP08100609A
Authority: EP
Inventors: Simone Dutto
Original assignee: Bongioanni Stampi Srl
Current assignee: Bongioanni Stampi Srl
Priority date: 2007-02-21
Filing date: 2008-01-17
Publication date: 2008-08-27
Also published as: EP1961537A3; ITTO20070124A1

Abstract

A mould (41) for forming clay tiles (59), comprising a pair of half-moulds (43, 45), wherein at least one of the half-moulds (43, 45) is equipped with a supporting element (47, 49) which has associated therewith a forming element (51, 53), preferably made of polyurethane. The invention also concerns a method for obtaining said mould.

Description

The invention relates to a mould for forming clay tiles and a method for obtaining said mould.
Clay tiles are a well known product of brickwork industry. They are used almost everywhere in the world to cover buildings in general, and they can have different shapes and sizes depending on the use, the custom and the geographical region where they are to be used.
Tiles can be made of different materials, but no doubt clay is still nowadays the most widespread raw material thanks to its low cost, lightness, impermeableness and insulating capability, as well as to its great availability and easy workability.
As known, clay mixed with water becomes plastic and it can be moulded. The subsequent drying eliminates mixing water, and a further baking eliminates chemically combined water. Thus, the obtained product cannot become softened due to humidity.
Clay tiles are generally manufactured by compression, by forming a biscuit of raw clay (the so called "green clay") inside a pair of half-moulds and by subsequently subjecting the product thus formed to a drying and baking step in a kiln.
Tile forming generally takes place by means of presses, e.g. mechanical or hydraulic presses, where the half-moulds forming the whole mould are approached to each other and exert a compression force generally exceeding 1,000 KN.
A mechanical tile press is disclosed for instance in document EP-A-0847849 .
Referring to Figs. 1a and 1b, a prior art mechanical tile press is schematically shown. In the illustrated example, the tile press comprises a machine body (1), forming the supporting structure of the press, a press assembly, comprising some members that will be discussed in detail below, and a deburring and laying assembly (17). The press assembly comprises a gear set (2), which is driven by an electric motor (3) and drives a cam shaft (4) and a Maltese cross (5). Cam shaft (4) drives, through an orthodromic cam system (6), a "compressor" or pressing head (7) on which the upper half-moulds are mounted (generally one to four half-moulds depending on the press type), and converts the rotary motion into an up-and-down reciprocating rectilinear motion. Maltese cross (5) is fixedly connected to a multiple-face drum (8), generally with six faces, on which the lower half-moulds are mounted (the number of which corresponds, for each drum face, to the number of the upper half-moulds), and it converts the continuous rotary motion of a gear wheel into the intermittent rotary motion of the drum.
Cam shaft (4) also drives a rod-and-crank device (9) that drives deburring assembly (17) by means of two levers (11), directly or through a gear driving transmission (10). The deburring assembly is to remove pressing defects from the articles, take the articles from the half-moulds and lay them onto suitable supports in order they can be subjected to drying and baking. Deburring assembly (17) is guided in its taking and laying movement by a shaft (13) slidable in a guide (14) pivotally connected to the machine body or frame (1) and it performs a reciprocating rotary motion between two end points of its stroke, namely a point of article taking from the drum, corresponding to the view of Fig. 1a, and the article laying point, corresponding to the view of Fig. 1b.
As known, a correct forming of the clay tile inside the mould can take place only if the half-moulds have suitable characteristics, in particular if the distance between opposite surfaces of the half-moulds is within the limits determined by the design of the tile to be obtained, if the excess clay coming out from the half-mould edges when the half-moulds are moved towards each other is correctly removed during the compression phase, and if the formed tile is easily detached when the half-moulds are separated.
Of course, such characteristics must be maintained with time, even after a high number of pressing operations: actually, if for instance the distances become modified due to the mould wear, or if excess clay is not properly removed, or if the tile is not uniformly detached from the moulds, thereby leaving residuals on the concerned half-mould surfaces, the resulting article will be of low quality and possibly is to be discarded.
A problem encountered in designing a mould for forming clay tiles is thus how to maintain the mould characteristics unchanged with time, in order the forming result too is of constant quality.
The already mentioned almost worldwide diffusion of clay tiles and the different traditions existing in the different geographical areas make it necessary to build moulds for obtaining different tile shapes and sizes, depending on the country where the tiles are to be used. Among the most well-known tile types, we may mention e.g. the bent tile, the plain roofing tile, the Dutch tile, the Roman tile, each type being generally made according to a number of variants for special uses, such as for instance for ridges, hips and rooflights.
This need, jointly with the usually very low cost of the clay tiles, gives rise to another problem also encountered in the same design area, namely how to provide a method of making moulds for forming clay tiles, which method can be used worldwide, for any clay tile shape and size, with reduced manufacture and maintenance costs.
Moreover, clay tile production is diversified not only depending on the geographical region where the tiles are to be used, as already mentioned, but also depending on the quality of the resulting product. Actually, it is known that industrial countries in Northern Europe demand for instance clay tiles having perfectly finished surfaces, in particular without burrs or deformations, whereas developing or less rich countries still have a high demand also of clay tiles of lower quality, in particular on the surface that is to be directed towards the inside of the cover and consequently generally is not visible from the outside.
A further problem related with clay tile production is thus how to obtain an article with high surface quality and high resistance, while keeping manufacturing costs low.
The above problems have lead, with time, to investigating different solutions for making the moulds in which clay tiles are formed.
A first prior art solution uses a mould in which each of both half-mould has a shell of aluminium alloy equipped with a plaster cast. The plaster cast adheres to the inner surface of the half-mould reproducing the shape to be given to the tile and defines the surface which will be in contact with clay during compression.
Plaster, thanks also to its porosity, has proved with time the best material for obtaining optimum results from the aesthetical viewpoint in clay tile production. Moreover, plaster allows an easy removal of the tile once it has been formed by compression in the mould.
One of the drawbacks of such solution however is that the plaster cast, due to the fragility of the material, the pressure exerted during compression and the clay slip, undergoes a rather quick wear and thus it must be frequently replaced. Moreover, for the same reasons, plaster generally does not allow exceeding press speeds of 16 - 18 beats/minute and thus does not allow a high productivity.
Replacing the plaster cast necessarily entails stopping the press, removing the mould, removing the worn cast (e.g. by means of high-pressure water jets) and depositing a new cast.
All those operations, besides entailing the press stop, the duration of which can possibly be reduced by providing spare moulds ready for use, also entails a deterioration of the shell of aluminium alloy and is to be effected by skilled workers, capable of carrying out the above operations and especially the last phase of deposition of the new cast. This last phase demands using a suitable counter-mould or matrix for each half mould and pouring liquid plaster into the hollow space formed between the half-mould and the corresponding counter-mould or matrix.
Even if the solution based on aluminium alloy and plaster therefore on the one side affords the advantages of optimum aesthetical results for the article and allows easily carrying out small changes to the tile shape, for instance to correct errors or to suit the client's requirements, by merely modifying the matrix that generally is made on resin, it demands on the other side a frequent restoration of the plaster cast due to the wear. Thus, it is a technique widely used in countries where a high quality of the end product is demanded.
A second solution frequently employed in constructing moulds for clay tiles uses a mould in which each of both half-moulds has a shell of aluminium alloy, which reproduces the shape to be given to the tile and is covered with a resin cast adhering to the mould.
According to this technique, in order to increase the resin duration, to allow an easy removal of the clay tile and to obtain aesthetically better results for the article, the resin casts of both half-moulds are further coated with a sheet or membrane of thin rubber, which is deformed during compression.
More precisely, the resin cast of the lower half-mould is generally coated with a rubber membrane secured to the half-mould by means of a frame generally comprising a set of rods and fastened by means of screws along the edge of each half-mould. On the contrary, the resin cast of the upper half-mould is coated with a rubber sheet which is periodically unwound from and wound onto one roller of a pair of rollers located at the sides of the half-mould.
By this solution, results of fairly good quality, even if lower than that attainable by means of the plaster cast, are obtained, the interventions on the cast are reduced, since the resin cast is much more resistant, and hence lasting, than the plaster cast, but the rubber is to be frequently replaced since it is subjected to breakings.
Another drawback of such a solution is the need to make a set of holes in the resin to allow air to flow, which is indispensable for the operation of the vacuum system with which the press is to be equipped in order to enable detaching the rubber from the tile, whereby tile detachment from the mould is made easier. Actually, being the rubber airproof, in the absence of a system for creating vacuum between the rubber and the resin, clay detachment once the tile has been formed would be difficult.
A further solution, less frequently employed in constructing moulds for clay tiles, uses a mould in which each half-mould has a shell of aluminium alloy, which reproduces the shape to be given to the tile and is equipped with a vulcanised rubber coating that directly adheres to the mould following the shape thereof, and defines the surface intended to come into contact with clay.
This solution, even though it ensures better results, in terms of quality of the clay tile, than those attainable with the mould with a resin cast, is however scarcely utilised because of the difficulties in removing the rubber when the latter is worn or cut. Indeed, in such case, the rubber must be removed by combustion.
Another solution employed in constructing moulds for clay tiles uses half-moulds of stainless steel. That solution has the advantage that it does not require plaster or resin casts and that it dispenses with using the rubber sheet or membrane, but, besides being expensive and making execution of modifications difficult, it has the drawback that it requires application of an electric current through the mould (this being also referred to as "electroshock phase") for detaching the tile at the end of the forming, and that it does not ensure the quality of the result, since the metal of the half-moulds is subjected to a slow, but inexorable wear.
Thus, it is a first object of the present invention to provide a mould for forming clay tiles, which does not have the drawbacks of the prior art discussed above.
It is a second object of the present invention to provide a method of making a mould for forming clay tiles, which allows attaining an optimum quality of the resulting article and reducing the costs of the production process.
The above and other objects are achieved by the mould and the method as claimed in the appended claims.
An advantage of the invention with respect to the state of the art is that the support and forming functions are allotted to two independent elements that are mutually associated and preferably are easily separable. In this way, contrary to what has occurred till now with the known solutions, where the supporting element itself gives the shape and is at most coated with a layer of a material making detachment easier and/or improving the quality, it is possible to obtain different shapes by acting only on the forming element. Consequently, according to the invention, a plurality of forming elements can be provided and used in combination with a same half-mould, without need of interventions for modifying the support element and with the advantage that the forming element can be used again.
Advantageously, according to the invention, clay tiles can also be obtained having a high surface quality, substantially equal to that attainable with plaster, with a higher productivity.
A further advantage of the invention is also that the tile pattern can be replaced by simple operations that are in the reach of any technician, without need of sending the mould to the manufacturer.
Always in accordance with the invention, the mould with a polymer coating, in particular of polyurethane, can advantageously be used without applying further protective overcoatings, e.g. of rubber, or overcoatings making tile detachment easier, thereby reducing costs and machine stops.
Actually, according to the invention, it is possible to obtain a reduction of the machine stops for replacing the rubber or the plaster and, consequently, a higher productivity with lower management costs and with a simplification of the press, which moreover allows attaining high speeds, exceeding 20 beats/min and of the order of 25 beats/min, such as attainable with resin cast moulds.
The invention will now be described with reference to the accompanying drawings, which show preferred but not exclusive embodiments, and in which:

Figs. 1a and 1b schematically show a prior art mechanical tile press;
Fig. 2 is perspective cross-sectional view of a mould made in accordance with the invention;
Fig. 3 is a longitudinal cross-section of the mould shown in Fig. 2;
Fig. 4 is a transversal cross-section of the mould shown in Fig. 2.

Referring to Figs. 2 to 4, there is schematically shown a mould for forming clay tiles, generally denoted by reference numeral 41, according to a preferred embodiment of the invention.
Mould 41 comprises a pair of half- moulds 43, 45, a lower and a upper half-mould, respectively, according to the orientation of the Figures, which haif-moulds can be associated, in a known manner, for instance with a press for forming clay tiles such as that schematically shown in Fig. 1.
According to the invention, at least one of half- moulds 43, 45 comprises a respective supporting element 47, 49, made for instance of aluminium alloy, which is associated with a forming element 51, 53, i.e. an element giving the shape to one of the tile faces.
According to a preferred embodiment of the invention, forming element 51, 53 is made of polymeric material.
Preferably, according to the invention, the polymeric material is chosen out of the polyurethane family, for instance nolyether-based or polyester-based polyurethanes in which the most utilised pre-polymers are based on TDI, NDI and MDI with cross-linking agents such as Butandiol, Mobca, Lonzacure and Etacure.
According to this embodiment of the invention, the method of constructing the mould will advantageously comprise a step in which the polymeric material, preferably polyurethane, in fluid condition, is poured into a matrix mould (not shown) and subsequently hardened in order to obtain the forming element and give it the desired shape, complementary to the shape of the tile that is to be obtained by subsequently using said forming element inside the tile mould.
Advantageously, according to this embodiment of the invention, no rubber sheet or membrane covering the exposed surface of forming element 51, 53 is to be provided, with a considerable saving of material and a considerable increase in plant productivity.
In the alternative, in other embodiments of the invention, forming element 51, 53 can be made of resin, e.g. a thermosetting resin, metal, e.g. steel or aluminium alloy, or any other suitable material.
In such case, the method of making the mould will advantageously comprise a step in which the material of the forming element is moulded or formed in a matrix die or mould (not shown) or is machined in order to obtain the forming element and give it the desired shape, complementary to the shape of the tile that is to be obtained by subsequently using said forming element inside the tile mould.
According to this exemplary embodiment of the invention, forming element 51, 53 has a thickness in the range 15 to 45 mm and an average thickness in the range 20 to 30 mm, so that its consistency is such that it maintains its shape even when removed from the associated half-mould.
According to the invention, forming element 51, 53 is preferably associated with the corresponding supporting element 47, 49 in removable manner, and is retained in a seat 44, 46, defined in the supporting element, by means of a frame 55, 57 surrounding each half- mould 43, 45. The frame is made of a single piece or is defined by a plurality of rods and is secured to the corresponding supporting element 47, 49 e.g. by means of screws 48.
As better shown in Figs. 3 and 4, forming elements 51, 53 are advantageously retained within seats 44, 46 defined in supporting elements 47, 49 by means of edges 56, 58 of the corresponding frames 55, 57, which edges slightly project, e.g. by a few millimetres, into seats 44, 46 and against which the corresponding forming element abuts.
Advantageously, according to the invention, it will be sufficient unscrewing screws 48 locking frame 55, 57 to release the frame and the corresponding forming element 51, 53 and to replace the latter, either because it is worn or because differently shaped tiles are to be formed.
According to the invention, supporting element 47, 49 is preferably made with plane and smooth internal surfaces so as to define a corresponding seat 44, 46 having no roughness, so that the shape of a tile 59, formed inside the mould in the hollow space defined between both forming elements 51, 53, is determined by the shape of the surfaces of said forming elements 51, 53.
Preferably, according to the invention, a step will be provided in which said supporting element 47, 49 is machined in order to form said seat 44, 46.
Advantageously, the described solution allows using the same half-mould with different forming elements, in order to obtain tiles with different shapes, without need of modifying the half-mould.
Always in accordance with the invention, it is however possible that at least one of the internal surfaces of supporting elements 47, 49 defining the corresponding seat 44, 46 for the forming element, has projections and/or recesses that determine wholly or in part the tile shape by defonning forming element 51, 53, and/or that cooperate with forming element 51, 53 for retaining it inside half- mould 43, 45.
Forming element 51, 53 obtained according to the invention is moreover of lightweight and cheap construction and allows the press manufacturer to supply the end user with forming elements of which the number and the shapes are sufficient for considerably reducing the machine stops and for obtaining a plurality of different tiles.
It is also possible to envisage a mould where only one of the half-moulds is made in accordance with the invention, and a second half-mould is made in accordance with the prior art. In such manner, mixed solutions can be obtained in which for instance the lower half-mould, intended to form the bottom tile face, is made in accordance with the invention, and the upper half-mould is made with the plaster cast technique, or vice versa.
In order to further facilitate tile detachment from the mould at the end of the forming, it is also possible to envisage a step in which an electric current is applied through both half-moulds.

Claims

A mould (41) for forming clay tiles (59), comprising a pair of half-moulds (43, 45), wherein at least one of the half-moulds (43, 45) is equipped with a supporting element (47, 49) which has associated therewith a forming element (51, 53).
The mould as claimed in claim 1, wherein said forming element (51, 53) has, on the face intended to form the tile (59), the shape to be given to said tile.
The mould as claimed in claim 1, wherein said forming element (51, 53) is removably associated with said supporting element (47, 49).
The mould as claimed in claim 1, wherein said supporting element (47, 49) includes a seat (44, 46) for said forming element (51, 53), the surface of said seat (44, 46) being substantially plane.
The mould as claimed in claim 3, wherein said forming element (51, 53) is retained in said supporting element (47, 49) by means of a peripheral frame (55, 57).
The mould as claimed in claim 5, wherein said peripheral frame (55, 57) is made of a plurality of rods.
The mould as claimed in claim 5, wherein said peripheral frame (55, 57) is made of a single piece.
The mould as claimed in claims 4 and 5, wherein said frame has an edge (56, 58) which slightly projects into the seat (44, 46) defined in the corresponding supporting element (47, 49) and against which the forming element (51, 53) associated therewith abuts.
The mould as claimed in claim 5, wherein said frame is secured to the corresponding supporting element (47, 49) by means of screws (48).
The mould as claimed in claim 1, wherein said forming element (51, 53) is made of polymeric material.
The mould as claimed in claim 10, wherein said polymeric material is chosen out of the polyurethane family.
The mould as claimed in claim 11, wherein said polyurethane family comprises polyether-based and polyester-based polyurethanes.
The mould as claimed in claim 1, wherein said forming element (51, 53) is made of resin, e.g. a thennosetting resin.
The mould as claimed in claim 1, wherein said forming element (51, 53) is made of metal, e.g. steel or aluminium alloy.
The mould as claimed in claim 1, wherein said forming element (51, 53) has a thickness in the range 15 to 45 mm.
The mould as claimed in claim 1, wherein said forming element (51, 53) has an average thickness in the range 20 to 30 mm.
A method of making a mould (41) for forming clay tiles (59), said mould comprising a pair of half-moulds (43,45), the method comprising the steps of:
- providing a supporting element (47, 49);

- providing a forming element (51,53);

- associating said forming element with said supporting element so as to define a first half-mould;

- providing a second half-mould.
The method as claimed in claim 17, wherein said forming element (51, 53) is removably associated with said supporting element (47, 49).
The method as claimed in claim 17, wherein said second half-mould is obtained by the same method used for obtaining the first half-mould.
The method as claimed in claim 18, comprising a step of securing said forming element (51, 53) to said supporting element (47, 49) by means of a frame (55, 57).
The method as claimed in claim 17, comprising a step of pouring a polymeric material into a matrix mould to mould said forming element (51, 53).
The method as claimed in claim 21, wherein said polymeric material belongs to the polyurethane family.
The method as claimed in claim 17, comprising a step of machining said supporting element (47, 49) to form a seat (44, 46) for said forming element (51, 53).
A press for forming clay tiles (59) inside a mould (41) comprising a pair of half-moulds (43, 45), characterised in that at least one of said half-moulds is obtained by means of the method as claimed in any of claims 17 to 23.
A forming element for use in the mould as claimed in claim 1 for forming clay tiles, characterised in that it has a pre-shaped face reproducing the shape of a tile face.
The element as claimed in claim 25, characterised in that it is made of a polymeric material.
The element as claimed in claim 26, wherein said polymeric material is chosen out of the polyurethane family.