METHOD FOR MANUFACTURING A ROOF TILE

Description

[0001] The invention relates to a method for producing roof tiles. Roof tiles are typically manufactured using the wet pressing process. In this process, clay and loam are mined from a pit, then mixed, processed, and stored in a wet press ready for production. From the prepared clay mixture, a continuous strand of clay is first extruded through an extrusion press, which is then cut into so-called lumps. In a turret press, into which plaster molds are inserted for forming the top and bottom of the roof tile, the lump is given a shape corresponding to the roof tile. After the pressing process, the roof tile already has a so-called green strength, which allows the green roof tile to be removed from the plaster mold and stacked on drying frames for drying.The green roof tile is dried over a period of 24 to 36 hours at a temperature preferably between 80°C and 120°C. This reduces the moisture content of the roof tile to less than 2%. If the surface of the roof tile is to be engobed or glazed to achieve different colors, the roof tiles are first separated for surface coating, then placed on firing cassettes and finally stacked together with the firing cassettes in the tunnel kiln cars. The firing process takes place in the tunnel kiln over a period of 24 to 36 hours at a temperature between 980°C and 1100°C. The fired roof tiles are then unloaded from the tunnel kiln car, separated from the firing cassettes, and sent for packaging.

[0002] To crush and homogenize the clay and loam components during raw material processing, and to later obtain a moldable clay mixture for the extrusion process, water is added to the clay mixture several times. The clay stored in the slump house has a moisture content of approximately 15% to 18%, which is increased to 18% to 20% by adding more water shortly before the extrusion press.

[0003] During the pressing process, it is important to ensure that the water bound in the clay mixture can escape from the clay and the pressing mold. If the water does not escape, it remains in the clay mixture and leaves pores in the fired roof tile, reducing the roof tile's resistance to freeze-thaw cycles. Therefore, the pressing molds are made of gypsum and equipped with drainage pipes so that water is extracted from the clay due to the hygroscopic properties of the gypsum. However, the service life of the gypsum molds is short, so that the plaster molds of the turret press must be replaced frequently, leading to production interruptions. Furthermore, the separate production of the plaster molds is labor-intensive and expensive.

[0004] Another disadvantage is that the roof tile still has a high moisture content of approximately 18% after pressing. The water still contained in the clay must be removed from the green roof tile during drying to achieve a moisture content of less than 2%, which is permissible for the firing process. Due to the significant water removal, significant shrinkage occurs and thus leads to drying defects in the roof tiles.

[0005] Drying roof tiles also involves high investment costs, due to the high purchase price of a dryer and the space required for such a system. Furthermore, loading the dryer involves significant handling effort. During operation, the dryer generates significant energy costs due to the long drying times and high drying temperatures.

[0006] To eliminate the disadvantages inherent in the wet pressing process, DE 195 26 849 A1 proposes producing roof tiles using the dry pressing process. In this process, the clay emerging from the pit is conveyed to an intermediate storage facility via a feeder, pan mill, rolling mills, and mixer. Granules are then produced from this prepared, dispersed, earth-moist clay by first extruding thin clay strands. These strands are then cut into small molds after exiting the extruder and coated with dry clay dust, creating moist clay granules with an enormously large surface area that dry quickly. This produces pre-dried, free-flowing, yet still plastically deformable granules, which are then pressed in a press to form a green roof tile.

[0007] Due to the drying process of the granules, the green roof tiles have very low residual moisture content, allowing steel press molds to be used instead of short-life plaster molds. Furthermore, the green roof tiles require little or no drying prior to firing. Since the water is removed prior to pressing, the primary shrinkage occurs in the granules and not, as is common with wet pressing, during the drying of the green roof tiles. Therefore, drying defects that can manifest as warping during firing of the roof tiles are eliminated.

[0008] However, the use of steel molds has not proven successful in the production of roof tiles. In order to fulfill their function on the roof, roof tiles usually have projections, such as head and side seams, lugs for hanging the roof tile on the roof battens, stiffening ribs or stacking points. In order to form the projections of the roof tile, the depth of the steel mold must be significantly greater in the area of ​​the projections than in other areas. Although these indentations in the mold are filled with clay material, such as clay granules, when the mold is filled, they are less compacted during the pressing process. As a result, the roof tiles have lower green strength and increased porosity in the area of ​​the projections, which can often lead to cracking or the projection breaking off during demolding and later due to freeze-thaw interactions.Further methods for producing roof tiles are known in the prior art, for example from US 2,918,715 A, JP 2003-320513 A. JP H06-122112 A discloses a method for producing a roof tile from clay according to the preamble of claim 1.

[0009] The invention is therefore based on the object of providing a method for producing a roof tile using the dry pressing process, which enables a more uniform compaction of the clay material and thus improves the strength and resistance of the roof tile to external influences.

[0010] Main features of the invention are defined in claim 1. Embodiments are subject of claims 2 to 6.

[0011] To achieve the object, which is not claimed, in a press mold for producing a roof tile from clay, having a first mold half and a second mold half, wherein the mold halves are movable relative to one another between a pressing position, in which the mold halves essentially delimit a receiving space which reproduces the shape of the finished roof tile, wherein the surface of the first and the second mold half each reproduces a surface of the roof tile, and a filling position, in which the mold halves are spaced apart from one another and a plastically deformable clay material can be filled into the first and / or the second mold half, it is provided that the first and / or the second mold half has at least one depression which reproduces a projection of the finished roof tile, wherein in and / or on the depression a first pressure element is provided which can be moved between a starting position,in which the first pressure element is set back with respect to the shape of the finished roof tile, and a compaction position in which the first pressure element partially reproduces the surface of the shape of the roof tile, and is designed to be movable. On the surface of the first and / or the second mold half, at least one second pressure element is provided, which is designed to be movable between a starting position in which the second pressure element protrudes or is set back with respect to the shape of the finished roof tile, and a compaction position in which the second pressure element partially reproduces the surface of the shape of the roof tile, wherein the second pressure element is moved during or after the movement of the mold halves into the pressing position into the compaction position or after completion of the pressing process back to the starting position. The first and / or the second pressure element is a pressure pad which has a pressure medium-fillable,volume-variable pressure chamber, wherein a pressure line is provided for supplying and / or discharging the pressure medium, wherein the movement of the pressure elements takes place by the inflow or outflow of the pressure medium into the pressure chamber.,

[0012] The first pressure element can be moved to the compaction position after the mold has been closed or the mold halves have been moved into the pressing position. This allows the first pressure element to further compact the clay material in areas where sufficient compaction is not achieved by moving the mold halves, for example, in depressions that represent ribs or projections of the finished roof tile. This can increase the strength of the roof tile in these areas, resulting in greater strength and resistance to external influences.

[0013] During compaction, the compression element presses into the surface of the roof tile, creating an embossed pattern in the compacted areas. This embossing gives the roof tile a distinctive appearance and remains intact even after the firing process. Depending on the number, size, and arrangement of the compression elements used, different embossed patterns are created on the surface of the roof tile.

[0014] After the pressing process, the first pressure element can be moved back to its starting position, allowing the pressed roof tile to detach from the respective mold half in the recesses, simplifying demolding. This reduces the risk of damage to the pressed roof tile during removal from the mold due to the roof tile sticking to one of the mold halves.

[0015] For example, at least one first pressure element is provided on each of the opposing surfaces of the recess. The first pressure elements can be arranged mirror-inverted with respect to a plane of symmetry of the recess, so that the projection is compressed on both sides. In particular, the opposing pressure elements can be coupled to one another to ensure that the projection is compressed to the same extent on both sides.

[0016] The first pressure element can, for example, be located at the base of the recess, i.e., at the transition from the recess to the surface of the mold half. This compacts the clay material in the heavily stressed areas of the base of a projection, thereby increasing the stability of the roof tile.

[0017] At least one second pressure element can be provided on the surface of the first and / or second mold half, which is designed to be movable between a starting position, in which the pressure element protrudes or is recessed relative to the shape of the finished roof tile, and a compaction position, in which the pressure element partially reproduces the surface of the roof tile. This second pressure element enables, for example, subsequent compaction of the clay material outside the recesses.

[0018] The second pressure element can be coupled to a first pressure element provided in the recess, wherein the coupling is designed such that when the second pressure element moves from a protruding position into the compaction position, the corresponding first pressure element is forced from the recessed position into the compaction position. In this embodiment, no further compaction takes place in the region of the second pressure element; instead, the second pressure element is used to move the first pressure element into the compaction position. The second pressure element can be used as a control element. Preferably, however, the first and second pressure elements are mechanically coupled, so that the pressure acting on the second pressure element causes the first pressure element to move into the compaction position.

[0019] The coupling of the first and second pressure elements enables easier control of the movement of the first and second pressure elements between their respective starting positions and the respective compaction positions. By moving the mold halves into the pressing position, the clay material exerts pressure on the second pressure element, which moves the second pressure element into the compaction position. By moving the second pressure element into the compaction position, the first pressure element coupled to the second pressure element is also moved into the compaction position, eliminating the need for a separate control for the first pressure element.

[0020] Furthermore, easy demolding of the roof tile from the mold is possible. For example, the second pressure element protrudes beyond the shape of the finished roof tile in the starting position and is moved into the compaction position by the pressure that increases when the mold halves are moved into the pressing position. By coupling the first and second pressure elements, the first pressure element is moved into the compaction position. When the mold is opened, i.e. when the mold halves move into the filling position, the pressure on the second pressure elements is reduced so that they can move back into the protruding position, whereby the pressed roof tile is lifted and released from the surface of the mold. The first pressure element coupled to the second pressure element is simultaneously moved back into the starting position offset with respect to the shape of the roof tile, whereby the roof tile can also be released from the respective mold half in the area of ​​the recess.Overall, the roof tile then adheres little or not at all to the respective half of the mould, so that the risk of damage when removing the roof tile can be reduced.

[0021] Preferably, a plurality of first pressure elements and / or a plurality of second pressure elements are provided, wherein the first pressure elements and / or the second pressure elements are coupled to one another and / or to each other. Adequate compaction of the clay material can be achieved with one pressure element. If a plurality of, preferably small-area pressure elements are used, compaction can be better controlled, or the pressing process can be controlled such that compaction occurs in a defined area with a defined pressure on the clay material.

[0022] In a preferred embodiment, the first and / or second pressure element is a pressure pad having a variable-volume pressure chamber that can be filled with an incompressible pressure medium, wherein a pressure line is provided for supplying and / or discharging the pressure medium. A pressure pad can be very effectively controlled via the pressure or volume of the filled pressure medium. In addition, such pressure pads are low-maintenance. Particularly with pressure pads, the use of several small-area pressure elements has the advantage of enabling better control of compaction or targeted compaction in defined areas of the roof tile surface. In addition, wear on the pressure pads can be reduced because the pressure pads can be dimensioned and arranged in such a way that the pressure pads have no or only a few bending points.

[0023] The use of pressure pads also enables easy coupling of first and / or second pressure pads. For example, the pressure lines of at least one first and / or at least one second pressure pad are connected to each other. The pressure pads can be connected to each other via the pressure lines according to the principle of communicating tubes. This results in pressure equalization between the individual pressure pads, so that the pressure in the pressure pads is approximately the same, resulting in compaction in the area of ​​the various pads at the same pressure.

[0024] For example, the pressure pads form a closed system in which the pressure medium is introduced at a slight overpressure of approximately 5 Pa to 7 Pa. If a higher pressure is exerted on one pressure pad, pressure equalization occurs within the closed system, whereby the pressure pad is pressed in, for example, and another pressure pad, which is subject to a lower pressure, is raised. For example, a first pressure element designed as a pressure pad is coupled to a second pressure pad designed as a pressure pad. Since the second pressure element is arranged on the surface of the mold half, high pressure is exerted on it when the mold is closed, so that this pressure pad is pressed in slightly until it is in the compaction position. Since the first pressure element is arranged in the recess, a lower pressure acts on it.Through the coupling with the first pressure pad, the pressure medium flows into the first pressure pad, causing it to be lifted and also moved into the compaction position. With a closed system, compaction of the clay material in the depressions is possible without additional control for the pressure elements.

[0025] A further advantage of such a coupling of first and second pressure elements designed as pressure pads is the easy demolding of the roof tile from the mold. If the pressure is reduced after the pressing process by moving the mold halves apart, the pressure on the second pressure elements decreases. The pressure medium flows from the first pressure elements back into the second pressure elements. The first pressure elements move back into the filling position, allowing the pressed roof tile to be released from the respective mold half in the area of ​​the recesses. The pressure medium flowing into the second pressure elements causes the second pressure elements to bulge, so that the roof tile is lifted and released from the surface of the mold half.

[0026] Alternatively or additionally, a pressure generating device can be provided to provide the pressure medium, with at least one pressure line connected to the pressure generating device. For example, the pressure elements can be individually connected to the pressure generating device in order to be able to control them individually. In an alternative embodiment, however, several pressure elements that are coupled or connected to one another can also be connected jointly to the pressure generating device.

[0027] The surface of the first and / or second mold half can have a flexible coating. The pressure element can in particular be arranged beneath the coating and / or be formed at least in sections by the coating. The coating can be formed by a membrane or a film and have a surface that prevents or at least reduces adhesion of the clay material, thus facilitating removal of the pressed roof tile from the mold. In addition, the membrane can be used to produce a roof tile surface without steps or ledges. It is also possible for a membrane or coating to be provided only on the mold half that has pressure elements.

[0028] The mold halves can have a base body made of metal, in particular tool steel.

[0029] In a preferred embodiment, a guide is provided for the first and / or second mold half, wherein the guide, together with the mold halves, completely defines the receiving space in the filling position and in the pressing position. This prevents the clay material from escaping from the receiving space during and after the filling process.

[0030] For example, the clay material can be introduced into the mold under overpressure so that pre-compaction can occur as soon as the clay material is poured in.

[0031] To allow air contained in the clay material or the mold to escape, the mold may have vents. For example, vents are provided between the mold halves and the guide.

[0032] Optionally, a filling device for introducing a, in particular pre-dried, clay material can be provided, wherein the filling device has an overpressure injection device.

[0033] The object is further achieved by a method for producing a clay roof tile as described in claim 1.

[0034] Preferably, a guide is provided for the first and / or second mold half, wherein the guide, together with the mold halves, completely defines the receiving space in the filling position and in the pressing position. The guide can have multiple guide parts and can be moved into a demolding position before the mold halves are moved into the filling position. In the dry pressing process, clay exhibits a relatively large recovery of the pressed clay material. The recovery is approximately 0.7 - 1.0%. If the press mold is opened within the guide that laterally defines the receiving space to remove the pressed roof tile, the pressed roof tile expands and becomes jammed within the guide, which can damage the pressed roof tile or make it more difficult to remove from the press mold.In order to avoid such problems, the guide is moved laterally, i.e. parallel to the direction of extension of the mold halves, into a removal position spaced from the mold halves, in which the pressed roof tile cannot rest against the guide even if the clay material stretches back, so that the roof tile can expand in the direction of extension essentially parallel to the surface of the mold halves.

[0035] The second pressure element is preferably coupled to a first pressure element provided in the recess. The first pressure element is urged from the recessed position to the compression position by the movement of the second pressure element from the protruding position to the compression position.

[0036] The pressing mold may comprise a filling device for introducing a particularly pre-dried clay material, wherein the filling device comprises an overpressure injection device and the filling device injects the clay material into the receiving space with overpressure, wherein the clay material is pre-compacted.

[0037] After the clay material has been filled, the mold halves can be moved into a venting position between the filling position and the pressing position, in which air contained in the receiving space escapes from the receiving space.

[0038] The clay material is preferably injected in a direction substantially parallel to the surface of the first and / or second mold half.

[0039] The clay material is preferably produced using the following steps: Providing the moist, unprocessed clay, drying the clay to a defined moisture content, grinding the dried clay to a broken grain in a mill, and separating out an undersize whose grain size is below a defined grain size range and separating out an oversize whose grain size is above a defined grain size range.

[0040] In principle, in a dry pressing process, the shrinkage associated with the removal of water already takes place in the raw material before it is introduced into the pressing mold. Because the clay is dried at the beginning, it has only a low moisture content, which nevertheless means it is still plastically deformable. In this way, the clay material can be poured directly into the pressing mold without the addition of further water and pressed there into a roof tile. In the prior art process, however, the clay coming from the stockpile is first processed into granules, which are then dried. This step is omitted in the process according to the invention. The clay coming from the stockpile is dried by the addition of heat without further processing, so that it can then be ground into a clay material made from broken grains.

[0041] The resulting clay material made from broken grains has better mold filling properties than build-up or spray granules. Large gaps remain between the individual broken grains, which are only reduced during the pressing process when the broken grains are pushed together. The broken grain forms fewer gaps between the individual broken grains, which are reduced during the pressing process when the broken grains are pushed together. If you compare the microstructure of a roof tile produced according to the invention and a roof tile made from build-up or spray granules under an electron microscope, you can see that the broken grain has fewer, but larger, pores after compaction than the build-up or spray granules. The structure also differs. Due to the more angular surface structure of the broken grain, interlocking and / or interlocking occurs during the pressing process.Wedging of the grains, which leads to increased green strength and better sintering of the roof tile.

[0042] Further features, details, and advantages of the invention will become apparent from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. They show: Fig. 1 a view of a roof tile produced by a method according to the invention, Fig. 1a a perspective view of the embossed pattern on the underside 14 of the roof tile, Fig. 2 A sectional view of the roof tile from Fig. 1 , Fig. 3 a press mold for producing the roof tile from Fig. 1 in a filling position, Fig. 4 the mold Fig. 3 in closed pressing position, Fig. 5a - 5e Process steps of a process for producing the roof tile from Fig. 1 , and Fig. 6a schematic representation of a plant for the production of the clay material of the roof tile from Fig. 1 .

[0043] In the Figures 1 and 2 a clay roof tile 10 is shown. Figure 1 shows a view of the underside 14 of the roof tile 10, Figure 2 shows a sectional view along the axis AA from Figure 1 The roof tile 10 has a top side 12 and a bottom side 14, wherein in the embodiment shown here, the top side 12 forms the visible side of the roof tile 10. A plurality of projections 16 are formed on the top side 12 of the roof tile 10. A plurality of projections 18 are formed on the bottom side 14. The projections 18 form, for example, head or side folds, lugs for hanging the roof tile on the roof battens, stiffening ribs, or stacking points. Depending on the type of projections, these can extend in sections over the bottom side 14 of the roof tile (see also Figure 1 ).

[0044] The roof tile 10 is fixed with the Figures 3 and 4 mold 20 shown. Preferably, a dry pressing process is used in which, as explained below, a pre-dried clay material, for example a pre-dried clay granulate or a pre-dried broken grain, is used.

[0045] The pressing mold 20 has a first, upper mold half 22 and a lower, second mold half 24. The first mold half 22 essentially forms the upper side 12 of the roof tile 10. The second mold half 24 essentially forms the underside 14 of the roof tile 10. Furthermore, a guide 26 with several guide elements 28 is provided, which, together with the mold halves 22, 24, completely enclose a receiving space 30. Between the mold halves 22, 24 and the guide 26, only ventilation openings 32 are provided, through which air can escape from the receiving space 30 before and during the pressing process.

[0046] On the surface 34 of the first mold half 22, a plurality of recesses 36 are provided, which represent the projections 16 on the upper side 12 of the roof tile 10. On the surface 38 of the second mold half 24, a plurality of recesses 40 are provided, which, as explained below, represent the projections 18 of the roof tile 10 in the pressing position of the pressing mold 20.

[0047] In Figure 3 The mold 20 is shown in a filling position in which the mold halves 22, 24 are spaced apart from one another and a clay material can be filled into the receiving space. For filling the mold 20, a filling device 42 is provided, which can inject the clay material into the receiving space 30 using compressed air at overpressure. The injection takes place in an injection direction E substantially parallel to the surface 34, 38 of the first and second mold halves 22, 24, respectively.

[0048] From the Figure 3In the filling position shown, the mold halves 22, 24 can be moved in a pressing direction P towards each other into the position shown in Figure 3 shown pressing position, in which the receiving space 30 essentially reproduces the shape of the roof tile 10. One of the mold halves 22, 24 can be fixed in place, so that only the other mold half 24, 22 is moved. However, it is also possible for both mold halves 22, 24 to be moved and to be moved towards one another during the pressing process of the roof tile 10.

[0049] The guide elements 28 are movable in a removal direction R running substantially perpendicular to the pressing direction P into a removal position in which the guide elements 28 are spaced apart from the mold halves 22, 24.

[0050] The mold halves 22, 24 each have a base body 44, 46 made of steel, preferably tool steel. Furthermore, the surfaces 34, 38 each have a coating 48, 50, which in the embodiment shown here is formed from a polyurethane layer. The coating 48, 50 reduces the adhesion of the filled clay material to the surfaces 34, 38 of the mold halves 22, 24.

[0051] A first pressure element 52 is provided on or in the recess 40. This pressure element is formed by a pressure pad having 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 is provided at the base of the recesses 40, i.e., at the transition to the surface 38 of the second mold half 24 facing the first mold half 22.

[0052] Furthermore, a second pressure element 62 is provided on the surface 38 of the second mold half 24, the structure of which essentially corresponds to the structure 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.

[0053] 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, 62. Furthermore, the pressure lines 60, 66 are connected to a pressure generating device 68, which can provide the pressure medium 56 and / or adjust 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.

[0054] 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 designed as a membrane.

[0055] In the Figure 3 In the filling position shown, the second pressure element 62 is curved in a starting position toward the receiving space 30, thus protruding beyond the shape of the finished roof tile 10 (see dashed line). In the filling position, the first pressure element 52 is set back in a starting position relative to the shape of the finished roof tile 10.

[0056] The first and second pressure elements 52, 62 are coupled to one another by the pressure lines 60, 66 in such a way that the first pressure element 52 is moved outwards into a compaction position by moving the second pressure element 62 into a compaction position in which the second pressure element 62 partially reproduces the shape of the finished roof tile, by the pressure medium 56 flowing out of the second pressure element 62 and flowing into the first pressure element 52, in which the first pressure element 52 also reproduces a section of the shape of the roof tile 10 (see Figure 4 ).

[0057] To produce a roof tile 10, a pre-dried clay material 78, preferably made of pre-dried, crushed clay, is injected under pressure into the mold 20 by the filling device 42. The mold halves 22, 24 are each in the filling position ( Figure 5a ).

[0058] Once the desired amount of clay material 78 has been introduced into the press mold 20, the mold halves are moved in the pressing direction P into the pressing position in which the press mold 20 reproduces the shape of the finished roof tile 10 ( Figure 5b ). During the movement of the mold halves 22, 24, air contained in the receiving space 30 can escape through the vent openings 32. For example, a vent position can be provided between the filling position and the pressing position to ensure complete escape of the air from the receiving space 30.

[0059] By moving the mold halves 22, 24 in the pressing direction P, a pressure acting in the pressing direction P is generated on the clay material 78, by which the clay material 78 is compacted. The pressure also acts on the second pressure element 62, designed as a pressure cushion, so that it is compressed until it partially reproduces the shape of the finished roof tile 10, i.e., is in the compaction position ( Figure 5c ).

[0060] Due to the volume reduction and the pressure increase of the second pressure element 62, the pressure medium 56 flows out of the second pressure element 62 and via the pressure lines 60, 66 into the first pressure element 52. In the recesses 40, the pressure generated by the displacement of the mold halves 22, 24 is lower, so that the clay material 78 is less compacted and less pressure is exerted on the first pressure element 52. The first pressure element 52 can thereby expand and move into the compaction position, in which the first pressure element 52 partially reproduces the shape of the finished roof tile 10.

[0061] By moving the first pressure element 52 into the compaction position, additional pressure is exerted on the clay material 78 in the depression 40, acting essentially transversely to the pressing direction P or perpendicular to the surface of the depression 40 in the region of the first pressure element 52. This pressure further compacts the clay material 78 in the region of the depression 40, so that the roof tile 10 has greater strength in this area due to the increased compaction. The roof tile 10 compacted in this way has high resistance to freeze-thaw cycles.

[0062] To remove the pressed roof tile 10, the guide elements 28 are first moved into the removal position ( Figure 5d). The clay material used in the dry pressing process has a relatively large recovery, which also acts perpendicular to the pressing direction P. If the mold halves 22, 24 are moved into the filling position in order to remove the pressed roof tile 10, the roof tile 10 can expand parallel to the surfaces 34, 38 of the mold halves 22, 24, so that the pressed roof tile 10 could become jammed on the guide 26. By moving the guide elements 28 into the removal position, the roof tile 10 can expand unhindered.

[0063] Subsequently, the mold halves 22, 24 are moved into the filling position against the pressing direction P. By moving the mold halves 22, 24 against the pressing direction P, the pressure on the clay material 78 and thus on the second pressure element 62 is reduced. The pressure medium 56 can flow at least partially from the first pressure element 52 back into the second pressure element 62 ( Figure 5e ).

[0064] As a result, the first pressure element 52 is moved back to the starting position, in which the first pressure element 52 is offset with respect to the shape of the pressed roof tile 10, whereby the roof tile 10 can detach from the second mold half 22 in the region of the recess 40. Furthermore, the roof tile 10 is additionally lifted by the bulging second pressure element 62 and thus also detaches from the surface 38 of the second mold half 24. The roof tile 10 is therefore released from the surface 38 of the second mold half 24 when the pressing mold 20 is opened, so that the roof tile 10 can be easily removed from the pressing mold 20.

[0065] The first pressure element 52 further compacts the clay material 78 in the area of ​​the recesses 40, so that the roof tile 10 has a high degree of stability. The second pressure element 62 can additionally apply a structure or embossing to the underside 14 of the roof tile 10.

[0066] In Fig. 1a the embossed pattern on the underside 14 of the roof tile 10 is shown in perspective.

[0067] First and second pressure elements 52, 62 were used for subsequent compaction, with the first pressure elements 52 being arranged in the recesses 40 of the mold half 24 such that they can subsequently compact the surfaces 170 of the roof tile 10 that extend substantially transversely to the pressing direction P. Such surfaces 170 are located, for example, on the flanks of the stiffening ribs 172 or at transition regions 174 for interlocking the roof tile 10.

[0068] The second pressure elements 52, on the other hand, are arranged in the flat surfaces of the pressing mold 20 so that they are perpendicular to the pressing direction P and can further compact the flat surfaces 176 of the roof tile 10, which are located, for example, between the stiffening ribs 170.

[0069] Since each pressure element 52, 62 presses into the surface of the roof tile 10 during compaction, a single embossing 178 is created on the surface of the roof tile 10 in each re-compacted area.

[0070] Depending on the roof tile model, the number, size, shape, and arrangement of the printing elements 52, 62 used may vary. The individual embossings 178, as a whole, give the roof tile 10 a characteristic appearance or embossed pattern that is retained even after the firing process.

[0071] The upper side 12 of the roof tile 10 forms the visible side exposed to the weather. Except for structurally required recesses or projections 16, this surface is therefore designed to be as smooth as possible. Since no moving parts or pressure elements are provided on the surface 34, this surface 34 can optionally also be designed without a coating 48 in order to achieve the smoothest possible upper side 12 of the roof tile 10.

[0072] In principle, it is possible to use a large pressure pad or a large first or second pressure element 52, 62. However, if such a large pressure pad extends over edges of the surface 34, 38 of the respective mold half 22, 24, the pressure pad will have bending points that can quickly wear out due to the high stress. Furthermore, achieving the contour accuracy of the roof tile is more difficult with a large pad. For this reason, several small pressure pads are used, whereby the pressure lines of the pressure pads can be connected to one another.

[0073] The production of the pre-dried clay material 78 takes place, for example, in the Figure 6 schematically illustrated plant 100, which together with the press mold 20 is part of a manufacturing plant 200 for a roof tile 10.

[0074] The plant 100 has a feeding device 102, for example, a box feeder, which feeds the unprocessed clay material coming from a stockpile 104 to the plant 100. A crushing device 106 is provided downstream of the feeding device 102, which crushes the clay material into clay lumps of a defined size. The clay lumps preferably have a maximum size of 60 mm.

[0075] A dryer 108 is provided downstream of the crushing device 106 to dry the clay lumps. Drying is preferably carried out such that the clay introduced into the mold 20 has a residual moisture content of approximately 2%-4%. The dryer 108 can be any type of dryer. Depending on the drying capacity of the dryer 108, larger clay lumps can also be dried, or pre-crushing can be omitted.

[0076] Downstream of the dryer 108, a mill 110 is provided, which grinds the pre-dried clay material to a defined size. The mill 110 is, for example, a pendulum mill, a roller mill, or a stirred ball mill. A sorting device 112 is provided in the mill 110 or immediately downstream of the mill 110, in which an undersize, whose grain size lies below a defined grain size range, and an oversize, whose grain size lies above a defined grain size range, are sorted out. The grain size range preferably has a grain size between 0.1 mm and 0.6 mm.

[0077] From the sorting device 112, the crushed grain is conveyed to a silo 114, where the clay material is temporarily stored. The intermediate storage in the silo 114 homogenizes the crushed clay material, resulting in a more uniform structure. From the silo 114, the clay material 78 is fed to the mold 20 and processed into a roof tile 10.

[0078] Behind the press mold 20, a glazing and / or engobing device 116 and a firing kiln 118 are also provided.

[0079] The moist, unprocessed clay coming from the stockpile 104 is pre-crushed in the crushing device 106, whereby this pre-crushing merely serves to ensure a faster and more uniform drying process. The clay lumps are then dried to a defined residual moisture content, which is selected so that the clay material 78 has a residual moisture content of approximately 2% - 4% when introduced into the press mold 20. If the clay is directly processed into roof tiles, it can be dried to a residual moisture content of approximately 2%. If intermediate storage takes place, for example in a silo, during which further drying can take place, the residual moisture content is selected so that the clay has a residual moisture content of approximately 2% - 4% after intermediate storage, i.e., immediately before the roof tile is manufactured.

[0080] The pre-dried clay lumps are then crushed in mill 110, a broken grain with a defined grain size range is sorted out, and temporarily stored in silo 114. The undersize can be pelletized or granulated into larger granules and fed into the production cycle before the drying kiln 108 or before the mill 110. The oversize can be fed directly back into the mill 110.

[0081] Therefore, granules are not produced and then dried; instead, drying takes place before the clay material is crushed. The crushed grain has a more irregular structure, allowing the individual grains to interlock better during the pressing process. Furthermore, the crushed grain has better mold-filling properties. Fewer but larger pores are created, resulting in better compaction behavior.

[0082] The invention is not limited to one of the embodiments described above, but can be modified in many ways.

[0083] For example, a plurality of first pressure elements 52 and / or a plurality of second pressure elements 62 can be coupled to one another. However, it is also possible for only one first pressure element 52 to be coupled to a second pressure element 62, or for a plurality of first or second pressure elements 52, 62 to be coupled to a single second or a single first pressure element 62, 52.

[0084] The pressure chambers 58, 64 of the pressure cushions are each connected to one another according to the principle of communicating tubes, so that a pressure equalization takes place, by which the first and second pressure elements 52, 62 are moved into the compaction positions when the mold halves 22, 24 are moved into the pressing position.

[0085] Alternatively, the pressure in the pressure elements 52, 62 can also be adjusted by the pressure generating device 68, so that, for example, the second pressure elements 62 can also be set back in the starting position with respect to the shape of the pressed roof tile 10 and moved into the compaction position by increased pressure. In this embodiment, for example, the clay material 78 can also be further compacted in the region of the second pressure elements 62. By reducing the pressure in the first pressure elements 52 and increasing the pressure in the second pressure elements 62, the removal process of the roof tile 10 from the press mold 20 can also be facilitated in this embodiment.

[0086] For example, only first pressure elements 52 may be present, which are coupled to a pressure generating device 68.

[0087] Instead of the Figures 3 and 4Other pressure elements 52, 62 can also be used in addition to the pressure cushions shown, wherein the first and second pressure elements 52, 62 can be coupled to one another hydraulically or via a control system. List of reference symbols 10 roof tiles 64 printing room 12 Top of the roof tile 66 pressure line 14 Underside of the roof tile 66 pressure lines 16 Projections on the top of the roof tile 68 Pressure generating device 70 recess 18 Projections on the underside of the roof tile 72 recess 74 protective element 20 mold 76 protective element 22 mold half 78 Sound material 24 mold half 100 Attachment 26 guide 102 Feeding device 28 Guide elements 104 heap 20 mold 106 Crushing device 22 mold half 108 dryer 24 mold half 110 mill 26 guide 112 Sorting device 28 Guide elements 114 silo 30 recording room 116 Glazing and / or engobing device 32 Ventilation openings 34 surface 118 kiln 36 Deepening 170 surfaces of the roof tile running transversely to the pressing direction P 10 38 surface 40 Deepenings 172 Stiffening ribs 42 Filling device 174 Transition areas 44 Basic body 176 flat surfaces of the roof tile perpendicular to the pressing direction P 10 46 Basic body 48 Coating 50 Coating 178 Embossing 52 pressure element 200 manufacturing facility 56 Print medium 58 printing room E Injection direction 60 pressure line P Pressing direction 62 pressure element R Removal direction

Claims

1. Method for producing a roof tile (10) from clay, with a press mould (20) that has a first mould half (22) and a second mould half (24), wherein the mould halves (22, 24) are movable relative to one another between a pressing position, in which the mould halves (22, 24) substantially delimit a receiving space (30) that models the shape of the finished roof tile (10), wherein the surface (34) of the first mould half (22) and the surface (38) of the second mould half (24) model in each case a surface (12, 14) of the roof tile (10), and a filling position, in which the mould halves (22, 24) are spaced apart from one another and a plastically deformable clay material (78) can be filled into the first and / or the second mould half, wherein the first mould half (22) and / or the second mould half (24) has at least one recess (40) that models a protrusion (18) on the finished roof tile (10), wherein, in and / or on the recess (40), a first pressure element (52) is provided, which is configured to be movable between a starting position, in which the first pressure element (52) is set back with regard to the shape of the finished roof tile (10), and a compacting position, in which the first pressure element (52) partially models the surface (12, 14) of the roof tile (10), having the following steps of: - providing the press mould (20), wherein the mould halves (22, 24) are located in the filling position and the at least one first pressure element (52) is located in the starting position, - filling a predried, granular clay material (78) into the receiving space (30), - moving the mould halves (22, 24) into the pressing position, wherein the clay material (78) is compacted, - moving the at least one pressure element (52) into the compacting position, wherein the clay material (78) is compacted in the region of the first pressure element (52), wherein, at the surface (34, 38) of the first and / or the second mould half (22, 24), at least one second pressure element (62) is provided, which is configured to be movable between a starting position, in which the second pressure element (62) protrudes or is set back with regard to the shape of the finished roof tile (10), and a compacting position, in which the second pressure element (62) partially models the surface (12, 14) of the roof tile (10), wherein, while or after the mould halves (22, 24) are moved into the pressing position, the second pressure element (62) is moved into the compacting position, characterized in that the first and / or the second pressure element (52, 62) is a pressure pad that has a variable-volume pressure chamber (58, 64) that is fillable with a pressure medium (56), wherein a pressure line (60, 66) for supplying and / or discharging the pressure medium (56) is provided, wherein the pressure elements (52, 62) are moved by the pressure medium (56) flowing into or out of the pressure chamber (58, 64).

2. Method according to Claim 1, characterized in that, after completion of the pressing operation, the first pressure element (52) is moved into the starting position, then the mould halves (22, 24) are moved into the filling position, and the roof tile (10) is removed from the press mould (20).

3. Method according to Claim 2, characterized in that a guide (28) for the first and / or the second mould half (22, 24) is provided, wherein the guide (26), together with the mould halves (22, 24), fully delimits the receiving space (30) in the filling position and in the pressing position, wherein, before the mould halves (22, 24) are moved into the filling position, the guide (26) is moved into a demoulding position.

4. Method according to Claim 3, characterized in that that the second pressure element (62) is coupled to a first pressure element (52) provided in the recess (40), wherein, as a result of the second pressure element (62) being moved from the protruding position into the compacting position, the coupled first pressure element (52) is moved from the set-back position into the compacting position.

5. Method according to one of the preceding claims, characterized in that the pressure medium (56) is incompressible.

6. Method according to one of the preceding claims, characterized in that, after the clay material (78) has been filled in, the mould halves (22, 24) are moved into a venting position between the filling position and the pressing position, in which air contained in the receiving space (30) escapes from the receiving space (30).