Method of manufacturing roof tiles using a rapid firing process

Abstract

According to a first aspect, the invention relates to a method for manufacturing a roof tile made of clay (1), comprising the steps of: providing the unprepared wet clay (1); producing an aqueous clay slurry (2); removing an oversize fraction from the slurry (2), wherein the oversize comprises grains that have diameters greater than a defined value; granulating the slurry (2) to produce a granular clay material (3); introducing the granular clay material (3) into a pressing mold (20); pressing the granular clay material in the pressing mold (20), wherein the granular clay material (3) is compressed and formed into a roof tile molding; transferring the roof tile molding to a roller kiln; and firing the roof tile molding using a rapid firing method.According to another aspect, the invention relates to a unit (10) for manufacturing a roof tile and a roof tile. Figure 1.

Description

Title of the invention: Method of manufacturing roof tiles using a rapid firing process

[0001] The present invention relates to a method for manufacturing roof tiles, a unit for carrying out the method and roof tiles obtained using said method. State of the art

[0002] Roof tiles are generally manufactured using a wet pressing process. With this process, clay and / or loam is extracted from a quarry, then mixed and prepared for the pressing operation. From the prepared clay mixture, a continuous column of clay is first extruded using an extrusion press. The clay column is then cut into lumps. In a rotary press in which gypsum molds have been inserted in order to shape the upper and lower part of the roof tiles, respectively, the lumps are given a shape that corresponds to the roof tiles. After the pressing operation is completed, the roof tile castings already have a green strength, which allows the roof tile castings to be removed from the plaster mold, stacked on drying trays and then dried.Drying roof tile casts reduces the moisture content of the clay before firing and is usually carried out at a temperature between 80°C and 120°C for 24 to 36 hours. Once drying is complete, the roof tile casts are placed on ceramic firing cassettes. The roof tile casts are stacked with the firing cassettes on firing trolleys and then transferred to the tunnel kiln, where they are fired at temperatures between 980°C and 1100°C for at least 24 hours.

[0003] Wet pressing processes have the disadvantage that the water present in the clay mixture must be drained from the clay and the pressing mold. If this is not the case, the water can leave the pores of the fired roof tiles, which reduces the weather resistance of the roof tiles. The pressing molds are thus made of gypsum, which can absorb water due to its hygroscopic properties. In addition, it remains necessary, however, to equip the gypsum pressing molds with drainage pipes. The manufacture of gypsum pressing molds is labor-intensive and therefore expensive. Since gypsum quickly absorbs moisture, the service lives of the pressing molds are short, which causes frequent production stoppages, due to the need to regularly replace the pressing molds of the rotary presses.

[0004] The moisture remaining in the roof tile castings must be further reduced before firing. Otherwise, the water that evaporates during firing will leave an excessive amount of pores within the fired roof tiles, which will reduce the weather resistance of the roof tiles. The pressed roof tile castings are therefore transferred to drying trays and dried. During their transfer, the roof tile castings must not be subjected to any mechanical stress. Otherwise, undesirable deformation may occur. In addition, the roof tile castings may deform during drying, or drying cracks may occur. The castings must therefore be treated with special care, which involves technical complexity.

[0005] The amount of energy consumed in the manufacture of roof tiles is very high, due to drying and firing, and the long duration of these two processes. Since tunnel kilns are fueled by natural gas, high CO2 emissions are also produced. From an energy point of view, it is also unfavorable to introduce a large number of firing aids (firing cassettes and trolleys) into tunnel kilns. Firing aids have a high heat capacity, and their heating and subsequent cooling cause considerable heat losses.

[0006] In order to eliminate certain disadvantages of wet pressing, patent DE 195 26 849 A1 proposes to manufacture roof tiles using a dry pressing process. In this case, the clay leaving the quarry is fed to a temporary storage device via a feeding system, a millstone crusher, rolling mills and a mixer. From this prepared, broken and wet clay, a granular material is produced by first extruding fine columns of clay, which are cut into small pieces after leaving the extruder, and are covered with dry clay dust, so that a wet granular clay material that has a very large surface area is formed. Thus, the objective is to produce a pre-dried, flowable but still plastically deformable granular material, which is pressed into a green roof tile in a press. However, this teaching is very difficult to implement in practice.

[0007] Since the water has already been removed before pressing, the majority of the shrinkage already occurs within the granular material and not, as is common with wet pressing, during drying of the roof tile castings. Drying defects, which can become visible as a result of deformation during firing of the roof tiles, thus no longer occur.

[0008] However, the dry pressing of the prior art has the disadvantage that the production of granular material described is associated with a high level of complexity. technique. In addition, the many steps involve significant investment and operating costs in terms of machines and units. Subject of the invention

[0009] An object of the invention is to provide a method and a unit for manufacturing roof tiles, the method having low energy consumption and minimal CO2 emissions, and the unit being capable of manufacturing high-quality roof tiles with low production costs and short production times. Description of the invention

[0010] The main features of the invention are described in the claims.

[0011] A process for manufacturing roof tiles composed of clay is described herein, and comprises the following steps: • providing unprepared wet clay; • the production of an aqueous clay suspension; • the elimination of an oversized fraction from the suspension, the oversized fraction comprising grains which have diameters greater than a defined value; • granulation of the suspension to produce a granular clay material; • the introduction of the granular clay material into a pressing mold; • pressing the granular clay material in the pressing mold, the granular clay material being compressed and formed into a roof tile molding, • transferring the roof tile molding to a roller kiln, and • firing the roof tile using a rapid firing process with reduced CO2 emissions.

[0012] A rapid firing method in the context of the present description is to be understood as a firing method in which one or more roof tile castings are fired at temperatures between 950°C and 1100°C for a maximum of 4 hours. In the method according to the present description, preference is given to preparing clay for further processing by means of dry pressing. The low moisture content of the granular clay material means that long-life steel molds can be used for pressing, and the time-consuming and energy-intensive drying of the roof tile castings before firing can thus be eliminated. Since the roof tile castings already exhibit high dimensional stability after pressing, they can be fired in a roller kiln without firing aids.Thus, energy losses in tunnel or chamber kilns due to heating and cooling of the baking aids can be ignored. The term "dry pressing . » should be understood to mean a pressing process in which the pressed roof tile molding has a moisture content of 20% or less, preferably 10% or less, and preferably 4% or less after pressing.

[0013] The clay may come from a single quarry ("single source" clay). There is no need to adjust the clay mixture composed of a plurality of clays, since the plastic properties are less important for the method according to the invention.

[0014] It is conceivable that the step of introducing the granular clay material into the pressing mold is followed by the step of removing excess granular material from the pressing mold. Furthermore, it is conceivable that the introduction of the granular clay material into the pressing mold is carried out using a filling screen, and / or that the introduction of the granular clay material into the pressing mold is carried out by blowing the granular material into the pressing mold, and / or that the introduction of the granular clay material into the pressing mold is carried out by sucking the granular material into the pressing mold.

[0015] According to the present description, the firing of the roof tile castings is carried out in a roller kiln using a rapid firing method, in which the firing times of the roof tiles are between one hour and four hours. The reduced firing times compared to conventional firing methods result in a reduction in energy requirements and thus a reduction in CO2 emissions. Furthermore, the savings in terms of time and costs are considerable. Furthermore, due to the reduced gauge in the firing chamber, it is possible to start or stop firing within a very short time, which allows for flexible operating times. This makes it possible, for example, to avoid costly manufacturing periods, such as weekends or holidays, since the roller kiln can be stopped and restarted quickly.

[0016] Roof tiles are usually fired in tunnel kilns or chamber kilns. Several tile castings are stacked on cassettes that have suitable refractory properties in order to form a unit, and fired in the kiln for at least 16 hours. This operation requires a sufficiently large firing chamber, which in turn causes poor heat distribution and requires a large amount of energy. In addition, a considerable amount of time is required to start and stop the kiln, i.e. for heating and cooling, which makes flexibility in using the kiln difficult. Conversely, single-layer firing takes place in a roller kiln. The firing channel of the kiln is as small as possible, in order to increase the firing power of the kiln and, thus, to be able to fire the material more quickly. In addition, the firing chamber must be as small as possible compared to to the desired result. Only the breaking load of the rollers is a limiting factor in this case.

[0017] In addition, roller kilns have the advantage of being able to be used without impacting the environment, unlike kilns generally used in tile factories, such as tunnel kilns or chamber kilns. For example, the roller kiln can operate using electricity or hydrogen. It is very difficult to operate tunnel kilns using hydrogen or electricity.

[0018] It is also conceivable that the method comprises a quality control step after pressing the granular clay material to form roof tile castings. Here, defective or unsatisfactory castings may be returned to the process to produce a slurry, in which they are prepared again. More particularly, the quality control step may take place randomly.

[0019] The pressing is preferably carried out in a pressing mold, which may have a first mold half and a second mold half. In this case, the mold halves may be movable relative to each other between a pressing position in which the mold halves substantially delimit a space that reproduces the shape of the finished roof tile and a filling position in which the mold halves are spaced apart from each other and a plastically deformable molding material may be placed in the first and / or second mold half.The first mold half and / or the second mold half have at least one recess which reproduces a projection of the finished roof tile molding, in which recess a first pressure element is provided within and / or at the recess which is movable between a starting position in which the first pressure element is recessed relative to the shape of the finished roof tile mold and a pressing position in which the first pressure element transversely reproduces the surface of the roof tile molding. The roof tile pressing process therefore further comprises the following steps: . • providing the pressing mold, in which the mold halves are in the filling position and the at least one first pressing element is in the starting position, • filling the space with granular clay material, • moving the mold halves into the pressing position, in which the granular clay material is compressed, • moving the at least one pressure element into the compression position, in which the granular clay material is compressed in the area of ​​the first pressure element.

[0020] Since the first pressure element is moved into its compression position after the pressing mold has been closed, the first pressure element subjects the granular clay material to additional compression in areas in which the movement of the mold halves alone does not allow sufficient compression, for example in recesses that reproduce projections of the finished roof tile molding. This can increase the stability of the roof tile molding in said areas, and thus the roof tile molding has better stability and greater resistance to external influences. The additional compression can be carried out mechanically, semi-isostatically and / or isostatically.

[0021] During compression, the pressure element presses the surface of the roof tile molding, as a result of which the surface of the roof tile is embossed in the areas subjected to the additional compression. The embossing gives the roof tile a characteristic appearance and is preserved even after firing. Depending on the number, size and arrangement of the pressure elements used, different embossing patterns are thus created on the surface of the roof tile.

[0022] The aforementioned projections may be on the top of the roof tile molding and / or on the bottom of the roof tile molding. For example, the top of the roof tile molding may have an overlap and a side overlap, and the bottom of the roof tile molding may be provided with fixing lugs, mounting points, closed guards and reinforcing ribs.

[0023] After the pressing is completed, the first pressing element is preferably moved to the starting position, whereupon the pressed roof tile molding can be detached from the respective mold half in the area of ​​the recesses, and demolding is simplified. The mold halves are then moved to the filling position and the roof tile molding is removed from the pressing mold. The risk of damage to the pressed roof tile when removing it from the pressing mold due to the roof tile sticking to one mold half can thus be reduced.

[0024] Preferably, a guide for the first and / or second mold half is provided, the guide, together with the mold halves, fully delimiting the space in the filling position and in the pressing position. This guide may comprise several guide parts and can be moved into a demolding position before the mold halves are opened. With dry pressing, the clay has a relatively high elastic recovery within the pressed granular clay material. The elastic recovery is about 0.7% to 1%. If the pressing mold is opened within the guide which laterally delimits the space for removal of the pressed roof tile molding, the pressed roof tile molding will expand and become stuck in the guide, as a result of which the tile molding of pressed roof tile may be damaged or may be more difficult to remove from the pressing mold. In order to avoid these problems, the guide is moved laterally, i.e. parallel to the direction of extension of the mold halves, into a demolding position which is at a distance from the mold halves and in which the pressed roof tile molding cannot rest against the guide, even in the event of elastic recovery of the granular clay material, and, thus, the roof tile molding can expand in the direction of extension substantially parallel to the surface of the mold halves.

[0025] At least one second pressure element may be provided on the surface of the first and / or second mold half, which is movable between a starting position in which the second pressure element protrudes or is recessed relative to the shape of the finished roof tile molding and a pressing position in which the second pressure element transversely reproduces the surface of the shape of the roof tile molding, the second pressure element being moved into the pressing position during or after the mold halves have moved into the pressing position and returning to the starting position after the pressing operation has been completed. Said second pressure element allows, for example, additional pressing of the clay material outside the recesses.

[0026] Preferably, the second pressure element is, however, coupled to a first pressure element provided in the recess. The first pressure element is pushed from the recessed position to the compression position as a result of the movement of the second pressure element between the protruding position and the compression position. In this embodiment, the second pressure element is used to move the first pressure element into the compression position. In this case, the second pressure element can be used as a control element. Preferably, the first and second pressure elements are, however, hydraulically coupled, and thus, the pressure exerted on the second pressure element allows the movement of the first pressure element into the compression position.

[0027] The coupling of the first and second pressure elements makes it easier to control the movement of the first and second pressure elements between the respective starting position and the respective compression position. Due to the movement of the mold halves into the pressing position, the clay material exerts pressure on the second pressure element, as a result of which the second pressure element is moved into the compression position. Due to the movement of the second pressure element into the compression position, the first pressure element coupled to the second pressure element is also moved into the compression, and no separate actuation of the first pressure element is thus necessary.

[0028] Furthermore, a simple demolding of the roof tile molding from the mold is possible. For example, the second pressure element, in the starting position, protrudes beyond the shape of the finished roof tile molding and is moved into the compression position as a result of the pressure increasing during the movement of the mold halves into the pressing position. Due to the coupling of the first and second pressure elements, the first pressure element is moved into the compression position. When the mold is opened, i.e. when the mold halves are moved into the filling position, the pressure on the second pressure elements is reduced, and they can thus return to the protruding position, whereupon the pressed roof tile molding is lifted and detached from the mold surface.The first pressure element coupled to the second pressure element simultaneously returns to the starting position, which is recessed relative to the shape of the roof tile, as a result of which the roof tile molding can also be detached from the respective mold half in the area of ​​the recess. Overall, the roof tile does not adhere to the respective mold half afterwards, or only very slightly, and thus the risk of damage when removing the roof tile can be reduced.

[0029] Preferably, several first pressure elements and / or several second pressure elements are provided, the first pressure elements and / or the second pressure elements being coupled to each other. Sufficient compression of the clay material can be achieved with one pressure element. When using several pressure elements, preferably with a reduced surface area, the compression can be better controlled, or the pressing operation can be controlled so that the compression is in each case carried out on the clay material in a defined area at a defined pressure.

[0030] According to a preferred embodiment, the pressure elements are designed so that a compression of the granular clay material of approximately 2:1 can be achieved. This means that the initial volume of the granular clay material can be reduced by half using the pressure elements preferred here. For this purpose, the pressure elements may be made of a sufficiently hard and flexible material, which must also have the same expansion properties as the material of the pressing mold halves. Preferably, the pressure elements may be made of steel, for example.

[0031] After filling with the granular clay material, the mold halves can be moved into an aeration position between the filling position and the pressing position, in which the air present in the space can escape therefrom.

[0032] During the manufacture of the suspension and, therefore, at the beginning of the described process, it is further possible to remove the undersized fraction and the oversized fraction using a sieve or a filter. More particularly, the removal is carried out using a wet sieving process. A wet sieving process allows the removal of unwanted grain sizes from the suspension without the need for prior drying of the suspension. In addition, wet sieving can prevent clogging of the sieve meshes, which can occur with small grain sizes during wet sieving. Alternatively, the removal can be carried out using a centrifuge or a cyclone separator.

[0033] One aspect of the invention provides a unit for manufacturing roof tiles using the method according to the present disclosure. The unit comprises, more particularly, a feeder for supplying unprepared clay, a grinder for producing a slurry, a granulator for producing a granular clay material, a pressing mold for dry pressing the granular clay material to form a roof tile molding, and a roller kiln for performing rapid firing.

[0034] In addition, a crusher for pre-fragmenting the unprepared clay material into clay pieces of a defined size may be provided, the crusher being upstream of the mill or being part of the mill. The mill may be a pendulum mill, a vertical roller mill or a ball and agitator mill. Optionally, the mill may include a sorter for removing excess material (such as undersized and oversized fractions), the sorter more particularly including a screen.

[0035] Preferably, the unit further comprises a glazer adapted to finish the surfaces of the roof tile castings. For example, the castings may be glazed, embossed, coated or engobed in the glazer.

[0036] According to another aspect, the invention provides a roof tile composed of clay which has been manufactured using the method described herein. Description of the figures

[0037] Other features, details and advantages of the invention will become more apparent from the wording of the claims and the following description of exemplary embodiments based on the drawings. In the figures: [[Fig.l]] illustrates a schematic representation of a unit for manufacturing roof tiles composed of clay; [[Fig.2]] illustrates a flowchart of a method of manufacturing roof tiles composed of clay according to a first exemplary embodiment; [[Fig.3]] illustrates a flowchart of a method of manufacturing roof tiles composed of clay according to a second exemplary embodiment; [[Fig.4a]] illustrates a pressing mold for manufacturing roof tiles according to a preferred embodiment in a filling position; [[Fig.4b]] illustrates the pressing mold of [Fig.4a] in a closed pressing position.

[0038] [Fig.l] illustrates a schematic representation of a unit 10 for manufacturing roof tiles composed of clay 1. The illustrated unit 10 is primarily adapted to carry out the method according to the present description. The unit 10 illustrated in [Fig.l] comprises a feeder 11 which supplies the untreated quarry clay to a mill 12. In the mill 12, a suspension 2 is produced from the clay. According to the method described herein, the undersized fraction and the oversized fraction can also be removed in the mill.

[0039] The prepared suspension 2 is then supplied to the granulator 13, which transforms the suspension 2 into a granular clay material 3 which has a defined moisture content. As illustrated in [Fig.l], the granulator 13 may be, for example, a drying tower.

[0040] The unit 10 of [Fig.l] further comprises a temporary storage device 14, which is designed to store and dry the granular clay material 3. Preferably, the temporary storage device 14 comprises one or more silos. Preferably, the granular clay material 3 has a solids content of less than 15%, more particularly from 1% to 11% after granulation of the suspension 2.

[0041] As a further section, the unit 10 comprises a pressing mold 20 for dry pressing the granular clay material 3 into a roof tile molding. Finally, the pressed roof tile moldings are transferred to a roller kiln 16 suitable for firing the tile moldings using a rapid firing process, i.e. in less than 4 hours.

[0042] As illustrated in [Fig.l], the unit 10 may also include a glazer 15. The castings may be, for example, glazed, embossed, coated or printed (by "digital printing", for example) and / or engobed before being fired in the roller furnace 16.

[0043] [Fig. 2] illustrates, in the form of a flowchart, steps S1 to S8 of the method, according to the present description, for manufacturing roof tiles composed of clay 1 according to a first exemplary embodiment.

[0044] The first step is step S1: providing the unprepared wet clay 1. The clay 1 is advantageously supplied to the unit 10 from a nearby quarry. Thus, long transport routes and associated costs can be avoided or reduced. There is no need to adjust the clay mixture composed of a plurality of clays, since the plastic properties are less important.

[0045] Once arrived at the unit 10, the untreated quarry clay 1 can be directly processed into an aqueous suspension 2 in the mill 12, according to step S2. The suspension 2 can, among other things, be better homogenized than the granular clay material 3. In addition, the subsequent removal processes can also be better carried out compared to conventional processes when the clay 1 is present in the form of an aqueous suspension 2. The conditioning of the starting material in order to form a suspension 2 is preferably carried out with the water supply and with the aid of dissolvers and agitators, which can be integrated into the mill 12. At the end of step S2, the suspension 2 has a solids content of 20 to 70%, preferably a solids content of between 55% and 65%.

[0046] This step is followed by step S3: the removal of an oversized fraction from the suspension 2, the oversized fraction comprising grains that have diameters greater than a defined value. Ideally, the particle size of the subsequent granular material 3 should be between 120 pm and 1000 pm. This is ensured by removing grains that have a diameter greater than 1000 pm, in each case, from the suspension 2. In a further step S3.1 (see [Fig. 3]), grains that have a diameter less than 120 pm can also be removed from the suspension 2.

[0047] The removal of the oversize fraction and / or the undersize fraction from the suspension 2 is followed by step S4: granulation of the suspension 2 to produce a granular clay material 3. In order to achieve the best possible pressing result, the granular clay material 3 must have a residual moisture content of between 2% and 6%. This prevents shrinkage of the roof tile castings during pressing. The granulation process S4 can be carried out, for example, using spray or atomization drying in a suitable granulator 13.

[0048] The next step is step S5: introducing the granular clay material 3 into a pressing mold 20. In order to produce the roof tile castings, the granular clay material 3 obtained from step S4 is preferably injected under pressure into the pressing mold 20 of the unit. This step is directly followed by step S6: pressing the granular clay material 3 into the pressing mold 20, the granular clay material 3 being compressed and shaped into a roof tile casting. Once the desired amount of granular clay material 3 has been introduced into the pressing mold 20, the mold halves of the pressing mold 20 are moved from the filling position to the pressing position, in which the pressing mold 20 reproduces the shape of the finished roof tile.

[0049] The next step, step S7, comprises the following: transferring the roof tile molding to a roller kiln 16 for firing. In the last step, step S8, the The roof tile molding is then fired to form a roof tile using rapid firing. The firing process according to step S8 is preferably carried out in a single-layer placement mode. Thus, as much of the radiant energy from the furnace 16 as possible can be used for heat transfer to the roof tiles.

[0050] [Fig. 3] illustrates a flowchart comprising steps S1 to S8 of the method for manufacturing roof tiles composed of clay 1 according to a second exemplary embodiment. The method illustrated in [Fig. 3] differs from the method illustrated in [Fig. 2] in that the method of [Fig. 3] comprises the additional intermediate steps S 1.1, S2.1, S3.1 and S4.1.

[0051] Step Sl.l follows step S1 and comprises the following: crushing the clay blocks present within the clay 1 into clay pieces, the clay pieces having an average diameter of 5 cm or less. Crushing or grinding of relatively large clay blocks into clay pieces of less than 5 cm on average may be carried out, for example, in the crusher 12 and serves to prepare the unprocessed material from the pile for subsequent steps.

[0052] Step S2.1 follows step S2 and comprises the following: adding additives to the suspension 2. The additives facilitate the homogenization of the suspension 2 and more particularly serve to give the roof tiles their desired properties, for example in order to maintain the solids content within the suspension as high as possible.

[0053] Step S3.1 follows step S3 and comprises the following: removing an undersized fraction from the suspension 2, the undersized fraction comprising grains that have diameters smaller than a defined value. Ideally, the particle size of the subsequent granular material 3 should be between 120 pm and 1000 pm. This is ensured by removing grains that have a diameter smaller than 120 pm from the suspension 2. Step S3.1 may be carried out at the same time as step S3.

[0054] Step S4.1 follows step S4 and comprises the following: storing the granular clay material 3 in at least one suitable storage device 14. The temporary storage device 14 is preferably a silo. Storage in a temporary storage device 14 contributes to the homogenization of the granular material 3, and, during this phase, for example, an equalization of slight differences in moisture content within the granular material 3 may occur. The operation of the temporary storage device may last from a few hours to a few days - depending on the production requirements.

[0055] According to one embodiment, the cooking channel of the oven must be as small as possible, in order to increase the cooking power of the oven and, thus, to be able to bake the material more quickly. Here, another advantage of the described process is that the resulting roof tile castings can be baked without the usual baking aids (such as H- or U-shaped cassettes), since they already have sufficient dimensional stability during the dry pressing stage. Thus, baking aids can be eliminated, saving space and reducing costs, but also increasing the baking efficiency of the kiln. In addition, a roller kiln has the advantage of being able to be used without any environmental impact, unlike the kilns typically used in tile factories. For example, the roller kiln can be operated using electricity or hydrogen.

[0056] [Fig. 4a] illustrates the pressing mold 20 in a filling position in which the mold halves 22, 24 are spaced apart from each other and a clay material can be placed in the space. To fill the pressing mold 20, a filling device 42 is provided and can inject the clay material into the space 30 with an overpressure, using compressed air. The injection is carried out in an injection direction E substantially parallel to the surface 34, 38 of the first and second mold halves 22, 24.

[0057] From the filling position illustrated in [Fig.4a], the mold halves 22, 24 can be moved towards each other in a pressing direction P, towards the pressing position illustrated in [Fig.4b], in which the gap 30 substantially reproduces the shape of the roof tile 18. One of the mold halves 22, 24 can be fixed in place and, thus, only the other mold half 22, 24 is moved. However, it is also possible that the two mold halves 22, 24 can be moved and are moved towards each other during the pressing operation for the roof tile 18. The guide elements 28 are movable in a withdrawal direction R substantially perpendicular to the pressing direction P, towards a withdrawal position in which the guide elements 28 are spaced apart from the mold halves 22, 24. The mold halves 22, 24 each have a main body 44, 46 made of steel, preferably tool steel.In addition, the surfaces 34, 38 each have a coating 48, 50 which, in the embodiment illustrated here, is formed of a layer of PU in each case. The coating 48, 50 reduces the adhesion of the filled clay material to the surfaces 34, 38 of the mold halves 22, 24.

[0058] At or in the recess 40 a first pressure element 52 is provided which is formed by a pressure pad which has a pressure space 58 filled with an incompressible pressurizing agent 56. The first pressure element 52 has a pressure line 60 through which the pressurizing agent 56, such as oil, can flow into or out of the pressure space 58. The first pressure element 52 is provided at the base of the recesses 40, i.e. at the intersection with the surface 38 of the second half of mold 24 which faces the first half of mold 22.

[0059] In addition, at the surface 38 of the second mold half 24, a second pressure element 62 is provided, the structure of which substantially corresponds to that of the first pressure element 52. The second pressure element 62 has a pressure space 64 and a pressure line 66 which are filled with the pressurizing agent 56.

[0060] The pressure line 66 of the second pressure element 62 is connected to the pressure line 60 of the first pressure element 52, so that the pressurizing agent 56 can flow between the first and second pressure elements 52, 62. In addition, the pressure lines 60, 66 are connected to a pressure generator 68 which can supply the pressurizing agent 56 and / or adjust the pressure in the pressure lines 60, 66 and the pressure elements 52, 62. Preferably, the pressurizing agent 56 has an overpressure of approximately 5 Pa to 7 Pa. The pressure elements 52, 62 are each formed by a recess 70, 72 in the main body 46 of the second mold half 24 and the coating 50 in the form of a membrane.

[0061] In the filling position illustrated in [Fig. 4a], the second pressure element 62, in a starting position, is curved in the direction of the space 30, i.e. it protrudes beyond the shape of the finished roof tile 18 (dotted line). In the filling position, the first pressure element 52, in a starting position, is recessed relative to the shape of the finished roof tile 18.

[0062] The first and second pressure elements 52, 62 are coupled to each other by the pressure lines 60, 66 so that the first pressure element 52, following the movement of the second pressure element 62 into a compression position in which the second pressure element 62 transversely reproduces the shape of the finished roof tile, is moved outwardly by the pressurizing agent 56 which flows out of the second pressure element 62 and flows towards the first pressure element 52 into a compression position in which the first pressure element 52 also reproduces a section of the shape of the roof tile 18 (see [Fig. 4b]).

[0063] The invention is not limited to one of the embodiments described above, but can be modified in many ways.

[0064] All features and advantages emerging from the claims, description and drawings, including structural details, arrangements and method steps, may be essential to the invention both individually and in a wide variety of combinations.

[0065] List of references Sn Step n 1 Clay 2 Suspension 3 Granular clay material 10 Unit 11 Feeding device 12 Crusher 13 Granulator 14 Temporary storage device 15 Ice Cream Maker 16 Roller oven 18 Roof tile 20 Pressing mold 22 First half of mold 24 Second half of mold 25 Guide 28 Guide Elements 30 Space 34, 38 Surface 40 Recess 42 Filling device 44, 46 Main body 8, 50 Coating 52 First pressure element 56 Pressurizing agent 58, 64 Pressure space 60, 66 Pressure line 62 Second pressure element 70, 72 Recess

Claims

Claims

1. A unit (10) for manufacturing a roof tile, the unit comprising: a feeder (11) for supplying unprepared wet clay (1); a grinder (12) for producing an aqueous clay slurry (2); a granulator (13) for converting the slurry (2) into a granular clay material (3); a pressing mold (20) for dry-pressing the granular clay material (3) into a roof tile molding; and a roller kiln (16) for firing the tile moldings using a rapid firing method.

2. A method of manufacturing a roof tile comprising the following steps: S1 - providing the unprepared wet clay (1); S2 - producing the aqueous clay slurry (2); S3 - removing an oversize fraction from the slurry (2), wherein the oversize fraction comprises grains that have diameters greater than a defined value; S4 - granulating the slurry (2) to produce a granular clay material (3); S5 - introducing the granular clay material (3) into the pressing mold (20); S6 - pressing the granular clay material into the pressing mold (20), wherein the granular clay material (3) is compressed and formed into a roof tile molding; S7 - transferring the roof tile molding to the roller kiln (16), and S8 - firing the roof tile molding using a rapid firing method.

3. Method according to the preceding claim, characterized in that it further comprises the following step after step S1: S 1.1 - crushing the clay blocks present within the clay (1) into pieces of clay, in which the pieces of clay have an average diameter of 5 cm.

4. Method according to any one of claims 2 and 3, characterized in that it further comprises the following step after step S2: S2.1 - the addition of additives to the suspension (2).

5. A method according to any one of claims 2 to 4, characterized in that it further comprises the following step which follows step S3: - S3.1 the elimination of an undersized fraction from the suspension (2), in which the undersized fraction comprises grains which have diameters less than a defined value.

6. Method according to any one of claims 2 to 5, characterized in that it further comprises the following step after step S4: S4.1 - storing the granular clay material in at least one temporary storage device (15), and more particularly a silo.

7. A method according to any one of claims 2 to 6, characterized in that the aqueous suspension (2) has a solids content of 20% to 70%, more particularly 55% to 65%, before granulation.

8. Method according to any one of claims 2 to 7, characterized in that the grains of the oversized fraction each have a diameter greater than 1000 pm.

9. Method according to claim 5, characterized in that the grains of the undersized fraction each have a diameter of less than 120 pm.

10. A method according to any one of claims 2 to 9, characterized in that the granular clay material (3) has a solids content of less than 15%, more particularly 1% to 11%, after granulation of the suspension (2).

11. Method according to any one of claims 2 to 10, characterized in that the pressing of the granular clay material (3) is carried out by dry pressing.

12. A method according to any one of claims 5 to 11, characterized in that the removal of the undersized fraction and the oversized fraction is carried out using a screening process in each case.

13. Method according to any one of claims 2 to 12, characterized in that step S 1.1 is carried out in a pendulum mill or in a vertical roller mill.

14. A roof tile made of clay, characterized in that the roof tile has been manufactured by the method according to any one of claims 2 to 13.

Images