NL2036211B1 - Process for manufacturing roof tiles using the rapid firing method - Google Patents

Abstract

In a first aspect, the invention relates to a method for producing a roof tile from clay (1), comprising the steps of providing the moist, unprocessed clay (1); producing an aqueous clay suspension (2); separating an excess fraction from the suspension (2), the excess fraction consisting of grains whose grain diameter is greater than a defined value; granulating the suspension (2) to produce a clay granulate (3); placing the clay granulate (3) in a compression mold (14); pressing the clay granulate in the compression mold (14), whereby the clay granulate (3) is compressed and formed into a roof tile shape; placing the roof tile shape in a kiln; and rapidly firing the roof tile shape. In another aspect, the invention relates to an installation (10) for producing a roof tile and to a roof tile.

Description

Process for manufacturing roof tiles using the rapid firing method

The invention relates to a method for producing a roof tile, an installation for carrying out the method and a roof tile obtained by the method.

State of the art

Roof tiles are usually manufactured using a wet pressing process. In this process, clay and/or loam is extracted from a quarry, then mixed and prepared for the pressing process. From the prepared clay mixture, an endless clay column is first extruded via an extrusion press. The clay string is then cut into so-called lumps. In a revolver press, in which plaster molds are placed to form the top and bottom of the roof tile, the lump is then given a shape that corresponds to the roof tile.

After the pressing process, the roof tile mould already has a so-called green strength, which allows the roof tile mould to be removed from the plaster press mould, stacked on drying frames and thus dried. The drying of the roof tile moulds serves to reduce the moisture content of the clay for the firing process and usually takes place over a period of 24 to 36 hours at a temperature between 80°C and 120°C. After drying, the roof tile moulds are placed on ceramic baking cassettes. The roof tile moulds are stacked together with the baking cassettes on kiln trolleys and transferred to the tunnel kiln, where the roof tile moulds are fired at temperatures between 980°C and 1100°C for a period of at least 24 hours.

The disadvantage of wet pressing is that the water that is bound in the clay mixture must escape from the clay and the press mould. If this does not happen, the water can leave pores in the baked roof tile that reduce the weather resistance of the roof tile. The moulds are therefore made of gypsum, which can absorb water due to its hygroscopic properties. However, it is also necessary to equip the gypsum moulds with drainage pipes. The production of gypsum moulds is labour-intensive and therefore expensive. Because the gypsum soaks through quickly, the lifespan of the moulds is short, which leads to frequent production stops because the moulds of the turret press have to be replaced regularly.

The moisture still in the roof tile mould must be reduced even further before the baking process, because otherwise the water that evaporates during the baking process leaves too many pores in the baked roof tile, which reduces the weather resistance of the roof tile. The pressed roof tile moulds are therefore transferred to drying frames and transferred to the drying process. The roof tile moulds must not be mechanically loaded during transfer, as this can lead to unwanted deformation. The roof tile moulds can also warp during the drying process or drying cracks can occur. The formed roof tiles must therefore be treated with the necessary care, which in turn requires a great deal of process engineering.

The energy consumption in the production of roof tiles is very high due to the drying and baking process and the long duration of these two processes. Since the tunnel kilns operate on natural gas, they also produce high CO: emissions. Another energetic disadvantage is that a large mass of kiln furniture (baking cassettes and kiln cars) is brought into the tunnel kiln. The kiln furniture has a high heat capacity and the heating and subsequent cooling of the kiln furniture leads to considerable heat losses.

In order to eliminate some of the disadvantages of the wet pressing process, DE 195 26 849 A1 proposes to produce roof tiles using the dry pressing process. In this process, the clay coming from the quarry is fed via feeders, tile makers, rolling machines and mixers to an intermediate warehouse. A granulate is then made from this prepared, digested, earth-moist clay by first extruding thin clay strips, which are cut into small shaped bodies after leaving the extruder and covered with dry clay grit to produce a moist clay granulate with an extremely large surface area. In this way, a pre-dried, free-flowing but still plastically kneadable granulate is produced, which is pressed into a green roof tile in a press. However, this theory is very difficult to realise in practice.

Because the water has already been removed before the pressing process, a large part of the shrinkage already takes place in the granulate and not, as is usual with wet pressing, during the drying of the roof tile shapes. This means that there are no more drying errors, which can cause deformation when the roof tiles are fired.

However, the dry pressing process known from the current state of the art has the disadvantage that the granulate production described there requires a lot of process engineering. In addition, the many individual steps entail high investment and operating costs for the associated machines and systems.

Goal

The invention is based on the aim of developing a process and a system for the production of roof tiles, whereby the process has low energy consumption and the lowest possible

CO: emissions and where the system can be used to produce high quality roof tiles at low production costs and short production times.

Description of the invention

The main features of the invention are set out in claims 1, 14 and 15.

Embodiments are the subject of claims 2 to 13.

According to the invention, the problem is solved by a method for producing a clay roof tile, the method comprising the following steps: — Providing the moist, untreated clay; — Generating an aqueous clay suspension; — Separating an excess grain fraction from the suspension, the excess fraction comprising grains whose grain diameter is larger than a defined value; — Granulating the suspension to produce a clay granulate; — Applying the clay granulate to a compression mould; — Pressing the clay granulate in the compression mould, whereby the clay granulate is compressed and formed into a roof tile shape, — Transferring the roof tile shapes to a roller kiln and — Firing the roof tile shapes in a rapid firing process with reduced CO: emissions.

For the purposes of this disclosure, a rapid firing process is understood to mean a firing process in which one or more roof tile shapes are fired for a maximum of 4 hours at temperatures between 950 °C and 1100 °C. The method according to the invention preferably provides for clay preparation for further processing in a dry pressing process. Due to the low moisture content of the clay granulate, long-life steel molds can be used during pressing, which makes the time-consuming and energy-intensive drying of the roof tile shapes before firing unnecessary. Since the roof tile shapes already have a high degree of dimensional stability after pressing, they can be fired in a roller kiln without kiln furniture. This eliminates the energy losses that occur in tunnel or chamber kilns due to the heating and cooling of the kiln furniture. The term "dry pressing" is to be understood as a pressing step in which the pressed roof tile shape has a moisture content of 20% or less, preferably 10% or less and in particular preferably 4% or less after the pressing process.

The clay can come from one well ("single source" clay). Coordination of the clay mixture from different clay types is not necessary because of the minor importance of plastic properties for the process according to the invention.

According to the invention, the roof tile shapes are baked in a roller kiln using the so-called rapid baking process, in which the baking times for roof tiles are between one and four hours. The shorter baking times compared to conventional baking processes lead to a lower energy requirement and thus to a reduction in CO: emissions. There are also significant time and cost savings. Due to the low tonnage in the combustion chamber, it is also possible to start and stop the firing process at short notice, which allows flexible operating times to be achieved. This makes it possible, for example, to avoid cost-intensive production times such as weekends or holidays because the roller kiln can be stopped and started up quickly.

Roof tiles are usually fired in tunnel or chamber kilns. A large number of brick shapes are stacked on the appropriate cassettes to form a unit and fired in the kiln for at least 16 hours. This process requires a sufficiently large combustion chamber, which in turn leads to poor heat distribution and also costs a lot of energy.

In addition, starting up and shutting down the kiln, i.e. heating up and cooling down, takes a long time, which makes it difficult to use the kiln flexibly. In contrast, the roller kiln is fired in a single layer. The firing channel of the kiln is designed as small as possible to increase the firing capacity of the kiln and thus to be able to fire the material faster.

At the same time the combustion chamber must be as small as possible in relation to the required output. The only limiting factor here is the breaking load of the rollers.

The use of a roller kiln also has the advantage that the roller kiln can be used climate neutrally compared to kilns that are normally used in brick kilns, such as tunnel kilns or chamber kilns. The roller kiln can, for example, operate electrically or on hydrogen.

Tunnel kilns are very difficult to operate with hydrogen or electricity.

It is also conceivable that the process includes a quality inspection step after pressing the clay granulate into roof tile shapes. Here, defective or unsatisfactory molded products can be returned to the slurry production process and reprocessed there. The quality inspection step can be performed in particular on a random basis.

The pressing process preferably takes place in a press mould, which may have a first mould half and a second mould half. The mould halves may be designed to move relative to each other between a pressing position, in which the mould halves essentially define a receiving space reproducing the shape of the finished roof tile, and a filling position, in which the mould halves are spaced apart and a plastically deformable moulding compound can be filled into the first and/or second mould half. The first mould half and/or the second mould half have at least one cavity reproducing a projection of the finished roof tile casting, in which a first pressure element is arranged in and/or on the cavity, which is designed to move between a starting position, in which the first pressure element is set back relative to the shape of the finished roof tile casting, and a compacting position, in which the first pressure element reproduces the surface of the roof tile casting in sections. Accordingly, the method for pressing the roof tile further comprises the following steps: — Providing the press mould, the mould halves being in the filling position and the at least one first pressure element being in the starting position, — Filling the clay granulate into the receiving chamber, — Bringing the mould halves into the pressing position, whereby the clay granulate is compressed, — Bringing the at least one pressure element into the compacting position, whereby the clay granulate is compacted in the area of the first pressure element.

By moving the first pressure element into the compaction position after the press mold is closed, the first pressure element ensures that the clay aggregate is re-compacted in places where sufficient compaction is not achieved by simply moving the mold halves, for example in the recesses that form the projections of the finished roof tile mold. This can increase the strength of the roof tile mold in these places, so that the roof tile mold is stronger and more resistant to external influences.

During compaction, the pressure element presses itself into the surface of the roof tile form, giving the surface of the roof tile a relief in the post-compacted areas. The relief gives the roof tile a characteristic appearance that is retained even after the baking process.

Depending on the number, size and arrangement of the pressure elements used, different relief patterns are created on the surface of the roof tile.

The above-mentioned protrusions can be located at the top and/or bottom of the roof tile form. For example, the roof tile form can have a top and side seam at the top and be provided with suspension eyes, stacking points, batten protectors and stiffening ribs at the bottom.

Once the pressing process is completed, the first pressure element is preferably moved to the starting position, which releases the pressed roof tile form from the respective mold half in the area of the notches and facilitates demoulding. The mold halves are then moved to the filling position and the roof tile form is removed from the press mold. This reduces the risk of damage to the pressed roof tile when it is removed from the press mold due to the roof tile sticking to one mold half.

Preferably, there is a guide for the first and/or second mold half, whereby the guide together with the mold halves completely delimits the receiving space in the filling and pressing position. The guide can consist of several guide parts and can be brought into a demoulding position before the mold halves are opened. In the dry pressing process, clay shows a relatively high degree of back-expansion of the pressed clay granulate. The back-expansion is approximately 0.7% to 1%. When the press mold is opened to remove the pressed roof tile form within the guide that laterally delimits the receiving space, the pressed roof tile form expands and clamps in the guide, which can damage the pressed roof tile form or make it more difficult to remove it from the press mold. To avoid such problems, the guide is moved laterally, i.e. parallel to the direction in which the mold halves extend, to a demoulding position at a distance from the mold halves, in which the pressed tile mold cannot rest against the guide even if the clay pellets expand back, so that the tile mold can expand in the direction of expansion which is essentially parallel to the surface of the mold halves.

At least one second pressure element can be arranged on the surface of the first and/or second mold half, which is designed to be movable between a home position, in which the second pressure element projects or is set back relative to the shape of the finished roof tile form, and a compaction position, in which the second pressure element reproduces the surface of the shape of the roof tile form in sections, the second pressure element being moved into the compaction position during or after moving the mold halves to the pressing position or back to the home position after completion of the pressing process. This second pressure element makes it possible, for example, to re-compact the clay material outside the recesses.

Preferably, however, the second pressure element is coupled to a first pressure element in the recess. The first pressure element is pushed from the recessed position into the compaction position by the movement of the second pressure element from the projecting position into the compaction position. In this embodiment, the second pressure element is used to move the first pressure element into the compaction position. The second pressure element can be used as an operating element. Preferably, however, the first and second pressure elements are hydraulically coupled so that the pressure acting on the second pressure element moves the first pressure element into the compaction position.

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 compaction position. By moving the mold halves into the pressing position, the clay material exerts pressure on the second pressure element, causing the second pressure element to move into the compaction position. The movement of the second pressure element into the compaction position also moves the first pressure element coupled to the second pressure element into the compaction position, so that no separate control is required for the first pressure element.

In addition, the roof tile mold can be easily removed from the press mold. For example, the second pressure element protrudes from the home position over the shape of the finished roof tile mold and is brought into the compaction position by the increasing pressure when the mold halves are brought into the pressing position. By coupling the first and second pressure elements, the first pressure element is brought into the compaction position. When the press mold is opened, i.e. when the mold halves are moved to the filling position, the pressure on the second pressure elements is reduced so that they can move back to the protruding position, whereby the pressed roof tile mold is lifted and released from the surface of the press mold. The first pressure element coupled to the second pressure element is simultaneously moved back to the home position, which is set back relative to the shape of the roof tile, whereby the roof tile mold can also release from the respective mold half in the area of the notch. Overall, the roof tile will then hardly or not at all adhere to the respective mould half, so that the risk of damage when removing the roof tile can be reduced.

Preferably, a number of first pressure elements and/or a number of second pressure elements are present, whereby the first pressure elements and/or the second pressure elements are coupled to each other and/or to each other. Sufficient compaction of the clay material can be achieved with one pressure element. If multiple, preferably small-scale pressure elements are used, the compaction can be better controlled or the pressing process can be controlled in such a way that the compaction always takes place in a defined area with a defined pressure on the clay material.

Preferably, the compression elements are designed in such a way that they can be used to achieve a compaction of the clay granulate of approximately 2:1. This means that the original volume of the clay granulate can be reduced by half using the preferred compression elements. For this purpose, the compression elements can be made of a correspondingly hard and resilient material, which should also have the same expansion properties as the material of the mould halves. Preferably, the compression elements can be made of steel, for example.

After the clay granulate has been filled, the mold halves can be placed in a venting position between the filling position and the pressing position, allowing the air in the receiving area to escape from the receiving area.

When preparing the suspension and thus at the beginning of the process according to the invention, it can also be determined that the separation of the undersized fraction and the oversized fraction is carried out using a sieve or a filter. In particular, it is considered to carry out the separation using a wet sieving process. A wet sieving process makes it possible to remove unwanted grain sizes from the suspension without having to dry the suspension first. Wet sieving can also prevent clogging of the sieve meshes, which can occur with small grain sizes in dry sieving processes. Alternatively, the separation can be carried out using a centrifuge or a cyclone separator.

Another aspect of the invention is an installation for the production of roof tiles according to the method of the invention. The installation comprises in particular a feeder for raw clay, a mill for producing a slurry, a granulating device for producing clay granulate, a press mold for dry pressing the clay granulate into a roof tile shape and a roller kiln for carrying out a rapid baking process.

There may also be a crushing plant to pre-crush the raw clay material into clay pieces of a certain size, whereby the crushing plant can be connected upstream of the mill or can also be part of the mill. The mill can be a pendulum mill, a roller bowl mill or a stirred ball mill. Optionally, the mill can have a sorting device for separating excess material (e.g. undersize and oversize fractions), whereby the sorting device can mainly consist of a screen.

Preferably, the system also includes a glazing device suitable for processing the surfaces of the roof tile shapes. The formed roof tiles can be glazed, relief-formed, coated or engobed in the glazing device, for example.

In a further aspect, the invention relates to a clay roof tile produced according to the method described herein.

Figure description

Further features, details and advantages of the invention will be apparent from the wording of the claims and from the following description of the embodiments with reference to the drawings. These show:

Fig. 1 shows a schematic representation of an installation for the production of a clay roof tile;

Fig. 2: A flowchart of a method for producing a clay roof tile according to a first example of an embodiment;

Fig. 3 is a flowchart of a method for producing a clay roof tile according to an example of a second embodiment;

Fig. 4a shows a press mould for producing a roof tile according to a preferred embodiment in a filling position;

Fig. 4b shows the press mold of Fig. 4a in closed pressing position.

Fig. 1 shows a schematic representation of an installation 10 for the production of clay roof tiles 1. The installation 10 shown is particularly suitable for carrying out the process according to the invention. The exemplary installation 10 in Fig. 1 consists of a feeder 11, which feeds the untreated clay to a mill 12. In the mill 12, a suspension 2 is made from the clay. According to the process described here, the undersized and oversized fractions can also be removed in the mill.

The prepared suspension 2 is then fed to the granulating machine 13, which converts the suspension 2 into a clay granulate 3 with a certain moisture content. As can be seen in Fig. 1, the granulating apparatus 13 can be, for example, a spray dryer.

The installation 10 of Fig. 1 also comprises an intermediate storage 14, which is designed to store and dry the clay granulate 3. Preferably, the intermediate storage 14 consists of one or more silos.

As a further machine component, the installation 10 comprises a press mould 14 for dry-pressing the clay granulate 3 into a roof tile shape. Finally, the pressed roof tile shapes are transferred to a roller kiln 16, which is suitable for baking the roof tile shapes in a rapid baking process, i.e. in less than 4 hours.

As shown in Fig. 1, the installation 10 may also include a glazing device 15. There, the molds can be glazed, embossed, coated, printed (e.g. "digital printing") and/or engobed, for example, before being fired in the roller kiln 16.

Fig. 2 shows in a flowchart the steps S1-S8 of the method according to the invention for the production of a clay roof tile 1 according to an example of the first embodiment.

First, step S1 is carried out: Provision of the moist, unprocessed clay 1. The clay 1 is preferably supplied to the installation 10 from a nearby pit. In this way, long transport routes and the associated costs can be avoided or reduced. Coordination of the clay mixture from different clay types is not necessary due to the minor importance of the plastic properties.

Once in the installation 10, the untreated quarry clay 1 can be processed directly into an aqueous suspension 2 in the mill 12 according to step S2. The suspension 2 can, among other things, be better homogenized than dry clay granulate 3. Furthermore, the subsequent separation processes can also be performed better compared to conventional processes if the clay 1 is available as an aqueous suspension 2. The conditioning of the starting material into a suspension 2 is preferably carried out by adding water and using unloaders and agitators, which can be integrated into the mill 12. At the end of step S2, the suspension 2 preferably has a solids content of 55% to 65%.

This is followed by step S3: separation of an oversized grain fraction from the suspension 2, the oversized fraction comprising grains whose grain diameter is larger than a defined value. Ideally, the grain size of the subsequent granulate 3 is between 120 µm and 1000 µm. To achieve this, grains with a diameter of more than 1000 µm are removed from the suspension 2. In a subsequent step S3.1 (see Fig. 3), grains with a diameter of less than 120 µm can also be removed from the suspension 2.

After separating the oversized and/or undersized grain fraction from the suspension 2, step S4 follows: granulating the suspension 2 into a clay granulate 3. In order to achieve the best possible pressing result, the clay granulate 3 must have a residual moisture content of 2% to 6%. This prevents the roof tile shapes from shrinking during the pressing process. The granulation process S2 can be carried out, for example, by spray or atomization drying in a suitable granulation machine 13.

Then follows step S5: The clay granulate 3 is introduced into a press mold 14. In order to produce the roof tile shapes, the clay granulate 3 obtained from step S4 is preferably injected under pressure into the press mold 14 of the system. This is immediately followed by step

S6: Pressing the clay granulate 3 into the press mold 14, whereby the clay granulate 3 is compacted and formed into a roof tile shape. Once the desired amount of clay granules 3 has been placed in the press mold 14, the mold halves of the press mold 14 are moved from the filling position to the pressing position, whereby the press mold 14 forms the shape of the finished roof tile.

The next step S7 comprises the following: Transferring the roof tile mold to a roller kiln 16 for baking the roof tile mold. In the last step S8, the roof tile mold is then baked to form a roof tile using the rapid baking process. The baking process according to S8 is preferably carried out in a single-layer setting method.

This allows as much of the radiant energy from oven 16 as possible to be used for heat transfer to the roof tiles.

Fig. 3 shows a flowchart with steps S1-S8 of the process for manufacturing a roof tile of Clay 1 according to a second embodiment. The process in Fig. 3 differs from the process in Fig. 2 in that the process according to Fig. 3 has the additional intermediate steps S1.1, S2.1,

S3.1 and S4.1 included.

Step S1.1 follows step S1 and comprises the following: Breaking clay lumps present in the clay 1 into clay pieces, the clay pieces having an average diameter of 5 cm or less. Breaking or grinding larger clay lumps into clay pieces that are on average smaller than 5 cm can take place, for example, in the mill 12 and serves to prepare the raw material from the stock for the following steps.

Step S2.1 follows step S2 and includes the following: Adding additives to the suspension 2. The additives facilitate the homogenisation of the suspension 2 and serve mainly to give the roof tiles their desired properties, for example to keep the solids content in the suspension as high as possible.

Step S3.1 follows step S3 and comprises the following: Separating an undersized grain fraction from the suspension 2, the undersized grain fraction consisting of grains whose grain diameter exceeds a defined value. Ideally, the grain size of the subsequent granulate 3 is between 120 µm and 1000 µm. To ensure this, grains with a diameter smaller than 120 µm are separated from the suspension 2. Step S3.1 can be performed simultaneously with step S3.

Step S4.1 follows step S4 and comprises the following: Storing the clay granulate 3 in at least one suitable intermediate storage 14, the intermediate storage 14 preferably being a silo. The storage in an intermediate storage 14 contributes to a further homogenization of the clay granulate 3, whereby in this phase, for example, small differences in moisture within the clay granulate 3 can be compensated. The intermediate storage process can take from several hours to several days, depending on the production requirements.

According to one embodiment, provision is made to advantageously make the firing channel of the kiln as small as possible in order to increase the firing capacity of the kiln and thus to be able to fire the material more quickly. Another advantage of the process described here is that the roof tile shapes obtained can be fired without the usual kiln furniture (e.g.

H or U cassettes), because they already come out of the dry pressing step with sufficient dimension stability. The kiln furniture can therefore be omitted, which saves space and costs and also increases the combustion efficiency of the kiln. The use of a roller kiln also has the advantage that roller kilns can be used in a climate-neutral way compared to the kilns normally used in brick kilns. The roller kiln can, for example, be operated electrically or on hydrogen.

In Fig. 4a, the press mold 14 is shown in a filling position in which the mold halves 22, 24 are spaced apart and a clay material can be filled into the receiving space. A filling device 42 is provided for filling the press mold 14, which can inject the clay material into the receiving space 30 by means of compressed air with overpressure. The injection takes place in an injection direction E which is substantially parallel to the surface 34, 38 of the first or second mold half 22, 24.

From the filling position shown in Fig. 4a, the mold halves 22, 24 can be moved towards each other in a pressing direction P to the pressing position shown in Fig. 4b, in which the receiving space 30 essentially reproduces the shape of the roof tile 18. One of the mold halves 22, 24 can be fixed in position so that only the other mold half 22, 24 is moved. However, it is also possible that both mold halves 22, 24 can be moved and moved towards each other during the pressing of the roof tile 18. The guide elements 28 can be moved in a removal direction R that is essentially perpendicular to the pressing direction P, to a removal position in which the guide elements 28 are spaced from the mold halves 22, 24. The mold halves 22, 24 each have a base body 44, 46 of steel, preferably tool steel. Furthermore, the surfaces 34, 38 each have a coating 48, 50, which in the embodiment shown here each consists of a PU layer. The coating 48, 50 reduces the adhesion of the filled clay material to the surfaces 34, 38 of the mold halves 22, 24.

On or in the recess 40 is arranged a first pressure element 52, which is formed by a pressure cushion with a pressure chamber 58 filled with an incompressible pressure medium 56. The first pressure element 52 has a pressure line 60 through which the pressure medium 56, for example oil, can flow into or out of the pressure chamber 58. The first pressure element 52 has a pressure line 60 through which the pressure medium 56, for example oil, can flow into or out of the pressure chamber 58. The first pressure element 52 is arranged at the base of the recesses 40, i.e. at the transition to the surface 38 of the second mold half 24 opposite the first mold half 22.

Furthermore, a second pressure element 62 is provided on the surface 38 of the second mold half 24, the structure of which largely corresponds to that of the first pressure element 52. The second pressure element 62 has a pressure chamber 64 and a pressure line 66, which are filled with the pressure medium 56.

The pressure line 66 of the second pressure element 62 is connected to the pressure line 58 of the first pressure element 52, so that the pressure medium 56 can flow between the first and second pressure elements 52, 82. Furthermore, the pressure lines 60, 66 are connected to a pressure generator 68, which can supply the pressure medium 56 and/or control the pressure in the pressure lines 60, 66 or the pressure elements 52, 62. Preferably, the pressure medium 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 base body 46 of the second mold half 24 and the coating 50 which is formed as a membrane.

In the filling position according to Fig. 4a, the second pressure element 62 is bent into a starting position in the direction of the receiving space 30, i.e. protrudes beyond the shape of the finished roof tile 18 (dotted line). In the filling position, the first pressure element 52 is reset into a starting position relative to the shape of the finished roof tile 18.

The first and second pressure elements 52, 62 are connected to each other by the pressure lines 60, 66 in such a way that the first pressure element 52 is brought by the second pressure element 62 into a compaction position in which the second pressure element 62 reproduces the shape of the finished roof tile in parts, is moved outwardly by the pressure medium 56 flowing from the second pressure element 62 and flows into the first pressure element 52 to a compaction position in which the first pressure element 52 also reproduces part of the shape of the roof tile 18 (see Fig. 4b).

The invention is not limited to any of the embodiments described above, but can be modified in various ways.

All features and advantages resulting from the claims, the description and the drawing, including design details, spatial measures and method steps, may be essential to the invention, either individually or in various combinations.

List of reference symbols

No. Step 1 Clay 2 Suspension 3 Clay granulate 10 Installation 11 Feeder 12 Mill 13 Granulating device 14 Intermediate storage 15 Glazing equipment 16 Roller kiln 18 Roof tiles 20 Press mold 22 First mold half 24 Second mold half 26 Guide 28 Guide elements 30 Receiving space 34, 38 Surface 40 Floor 42 Filling device 44 46 Base body 48, 50 Coating 52 First pressure element 56 Pressure medium 58, 64 Pressure chamber 60 Pressure line 62 Second pressure element 70, 72 Recess

Claims (14)

Conclusions 1. A method for producing a clay roof tile (1), comprising the steps of: (81) Providing the moist, unprocessed clay (1); (82) Generating an aqueous clay slurry (2); (S3) Separating an oversized grain fraction from the slurry (2), the oversized grain fraction comprising grains whose grain diameter is larger than a defined value; (S4) Granulating the slurry (2) to produce a clay granulate (3); (S5) Applying the clay granulate (3) to a press mold (14); (S6) Pressing the clay granulate in the press mold (14), whereby the clay granulate (3) is compressed and formed into a roof tile shape; (S7) Transferring the roof tile shapes to a roller kiln and (S8) Firing the roof tile shapes in a rapid firing process. 2. A method according to claim 1, characterized in that the method according to step (S1) further comprises the following step: (S1.1) Breaking of clay lumps in the clay (1) into clay pieces, with the clay pieces having an average diameter of 5 cm. 3. A method according to any one of the preceding claims, characterised in that the method according to step (S2) further comprises the following step: (S2.1) Addition of additives to the suspension (2). 4. A method according to any one of the preceding claims, characterised in that the method further comprises the following step before step (S3): (S3.1) Separation of an undersized grain fraction from the suspension (2), the undersized grain fraction comprising grains whose grain diameter is smaller than a defined value. 5. A method according to any one of the preceding claims, characterised in that the method according to step (S4) further comprises the following step: (54.1) Store the clay granulate in at least one suitable intermediate storage facility (15), in particular a silo. 6. A method according to any one of the preceding claims, characterised in that the aqueous suspension (2) has a solids content of 20% to 70%, in particular 55% to 65%, before granulation. 7. A method according to any one of the preceding claims, characterised in that the grains of the oversized fraction each have a grain diameter greater than 1000 µm. 8. Method according to any one of claims 4 to 7, characterised in that the grains of the undersized fraction each have a grain diameter of less than 100 µm. 9. Method according to any one of the preceding claims, characterised in that the clay granulate (3) after granulation of the suspension (2) has a moisture content of less than 15%, in particular from 1% to 11%. 10. Method according to any one of the preceding claims, characterised in that the pressing of the clay granulate (3) is carried out by dry pressing. 11. Method according to any one of claims 4 to 10, characterised in that the separation of the undersized fraction and the oversized fraction always takes place in a sieving process. 12. A method according to any one of the preceding claims, characterised in that step (S1.1) is carried out in a pendulum mill or in a roller bowl mill. 13. Installation (10) for manufacturing a roof tile according to the method of any of the preceding claims. 14. Clay roof tile, characterised in that the roof tile is produced by a method according to any one of claims 1 to 12. -0-0-0-0-0-0-