METHOD AND DEVICE FOR THE PRODUCTION OF CERAMIC FIBER COMPOSITES WITH VARIABLE GEOMETRY

Description

[0001] The present invention relates to a method and a device for producing ceramic fiber composites with variable geometry by means of a vacuum pressure infusion process.

[0002] Ceramic fiber composites (CMCs) essentially consist of two main components: a ceramic fiber component and a ceramic matrix that surrounds and holds the fibers together. By appropriately combining these two main components, damage-tolerant failure of the otherwise typically brittle ceramics can be achieved. Damage-tolerant failure can be achieved in different ways and depends, among other things, on the matrix system used, the fibers used, and the fiber-matrix bonding.

[0003] Oxide-ceramic fiber composites (ox-CMC) are typically so-called "weak matrix composites" (WMC) and are characterized by a weak, porous matrix composed of fine ceramic particles of the matrix material. The matrix functions as the weak interface to achieve favorable failure behavior, resulting in quasi-ductile material behavior (similar to metals).

[0004] Ox-CMCs are usually produced from particulate, often water-based or solvent-based slip systems with defined solid contents. Compared to non-particulate polymer systems, the particulate nature of the slip makes it difficult to completely and evenly infiltrate all fiber bundles and the interfiber bundle spaces. Furthermore, the water or solvent contained in the slip must be removed by drying to obtain a dry, moldable green body (preform). For this reason, the infusion processes known and established from polymer technology cannot be readily transferred to the production of ox-CMCs.

[0005] Different technologies are currently known for the production of long-fiber reinforced ceramic fiber composites: hand infiltration / doctoring processes and hand lamination (lay-up), prepreg technologies, winding technology (e.g. WHIPOX) and infusion processes.

[0006] The fundamental disadvantage of lay-up, prepreg, and winding processes, as described in EP 3 768 405 A1, is the greater or lesser necessity of manual process steps to produce the shaped and dried green body. This results in limited automation, cost-effectiveness, and reproducibility of the process and / or material quality. These disadvantages are most pronounced in hand infiltration and lay-up processes, which are produced almost exclusively using manual processes. While the infiltration of semi-finished fiber products such as fabrics can be at least partially automated and, to a limited extent, scaled up using appropriate methods and tools, the production of shaped parts, even with prepreg processes, is usually only carried out using manual lay-up techniques.

[0007] The winding process, as disclosed in EP 1 734 024 B1, demonstrates a comparatively high degree of automation, but only for the production of simple, rotationally symmetrical components. The production of simple plate geometries or other complex-shaped components also requires cutting and manual forming of the wound body during the winding process. Furthermore, the winding process cannot be parallelized (manufactured in parallel) and cannot be scaled to higher quantities in a comparatively economical manner.

[0008] Further disadvantages are the production time and the required labor. Manual lay-up processes, in particular, are very time-consuming and labor-intensive, depending on the complexity of the component. Furthermore, the quality of the final workpiece depends on the skills of the operator and is therefore susceptible to a wider variation in quality. The winding process is also relatively time-consuming, as the structure must be built up by depositing individual fiber bundles on the winding core, turn by turn. Due to the high time and labor expenditure, the quantities that can be produced are also limited. Furthermore, the processes are usually restricted to a specific fiber architecture or fiber preform. Thus, only individual continuous fiber bundles can be processed using the winding process. Lay-up and prepreg processes almost exclusively process 2D fiber fabrics. The respective manufacturing process can also be applied to other fiber architectures, e.g.Fiber braids or 3D fiber preforms are only partially or not at all feasible.

[0009] An infusion process without a fixed tool using a vacuum bag to produce CMC is also known. However, the disadvantages are the complex setup (long process time) and resource efficiency with regard to consumables (e.g., vacuum film, sealing tape). This process is therefore also inefficient, especially for the production of larger quantities of the same component. Furthermore, infiltration pressure (vacuum negative pressure) and the resulting compression of the fiber layers by the vacuum bag cannot be separated from one another. This can lead to problems because, on the one hand, lower pressure enables better infiltration with a minimum of air inclusions, but at the same time, the greater compression prevents complete infiltration of the fiber bundles. In addition, the fiber volume content (FVG) cannot be arbitrarily adjusted, which reduces the range of material properties that can be realized.

[0010] Particularly with regard to flexible applicability and the automated, near-net-shape production of complex components, there is a need for a process with which CMC, in particular ox-CMC, can be produced in any three-dimensional geometry. The present invention therefore aims to avoid the disadvantages known from the prior art and to provide a process with which CMC, and in particular ox-CMC, can be produced in any three-dimensional geometry.

[0011] DE 10 2020 106043 A1 discloses a tool for producing components from ceramic fiber composite materials according to the preamble of claim 1.

[0012] Surprisingly, it has been found that the object underlying the present invention is achieved by a vacuum-pressure infusion and drying process. In a first embodiment, the present invention thus relates to a tool for producing components from ceramic fiber composites by infusing fibers with a slurry in a cavity, wherein the slurry contains water and / or solvent as well as particles or precursors therefor. wherein the tool comprises a die, whereby a cavity is located inside the tool, which cavity is delimited by the die, the top side and the bottom side of the tool, characterized in that the tool has at least one device for increasing the pressure inside the cavity and / or for supplying the slurry into the cavity, at least one device for retaining the particles or precursors of the slurry inside the cavity and for removing the contained water and / or solvent is present inside the die, and the die has at least one device by means of which the pressure inside the cavity can be reduced and / or excess water and / or solvent can be removed,wherein the at least one device for retaining the particles or precursors of the slip in the interior of the cavity and for removing the contained water and / or solvent is arranged in the die or the top or bottom of the tool in such a way that water and / or solvent can be removed from the cavity, wherein the die is formed from a solid material which does not deform during use, and wherein the tool preferably further comprises at least one heating device which enables the heating of the cavity.

[0013] The tool according to the invention thus has a top side and a bottom side. The lateral boundary is provided by the die. The tool further comprises a punch, wherein the punch rests positively against the inner wall of the die and is vertically displaceable in its position within the die, forming a cavity between the punch and die. The punch thus represents the top side of the tool. Furthermore, the tool preferably has a cavity arranged spatially below the at least one device. Water / solvent from the slip can be collected in the cavity and removed from the cavity via the at least one device.

[0014] According to the invention, the slip comprises ceramic and / or silicate particles as well as water and / or solvent. Furthermore, it is possible according to the invention for the slip to comprise not the particles themselves, but rather precursors therefor. These are precursors of the particles, the particles then forming during the material production process. Any description of slip particles below always includes the associated precursors. Suitable ceramic particles include, for example, oxide ceramic particles or nitride ceramic particles. Suitable precursors are sufficiently described in the prior art and are known to the person skilled in the art.

[0015] The water and / or solvent in the slip are also referred to below as the fluid. This includes water and / or solvent in the liquid or gaseous state. Likewise, water and / or solvent can be present in both liquid and gaseous form. In particular, they are removed from the tool in gaseous form, as the application of negative pressure can change the state of the fluid. Suitable solvents include glycerin or other alcohols. These can be used alone or in combination with water. Glycerin alone or in combination with water is particularly preferred.

[0016] The fibers can be in the form of woven fabrics, non-woven fabrics, braids, or similar fiber preforms made from long or continuous fibers, as well as from a wide variety of short fiber preforms such as fleece, felt, paper, or similar, each in 1D, 2D, or even 3D fiber structures. According to the invention, the fibers are ceramic, silicate, mineral, and / or glass fibers. Basalt fibers or pyrolyzed natural fibers can also be used.

[0017] In a further embodiment, the object underlying the present invention is achieved by a process for producing components from ceramic fiber composite materials by infusion of fibers with a slip containing water and / or solvent, characterized in that (a) introducing the fibers into the cavity of a previously described tool, (b) closing the tool, (c) reducing the pressure inside the tool compared to the ambient pressure, (d) optionally thermally treating the fibers inside the tool, (e) introducing a first slip containing water and / or solvent into the cavity, wherein the slip may have a pressure higher than the ambient pressure, (f) reducing the pressure inside the tool and optionally thermally heating the tool and removing water and / or solvent from the cavity, (g) optionally repeating steps (e) and (f) once or more times, using a slip which is the same or a different slip than the first slip, and (h) subsequently shaping the resulting green body from the tool and sintering it in a furnace.

[0018] The result is a workpiece made of a ceramic fiber composite, with the workpiece or green compact having the shape of the tool. The two embodiments and preferred embodiments are described in more detail below. Features disclosed for one embodiment can also be applied to other embodiments. All features can be combined with one another in any desired manner.

[0019] In Fig. 1 An embodiment of a device not claimed is shown. It shows: Reference symbol 1 Tool 2 Stamp (upper part of the tool) 3 Attached frame for sealing the tool 5 Porous membrane (solid) for selective filtration of fluid and solid in the slurry 6 Perforated insert for mechanical support of 5 8 Pressure connection and reservoir for slurry for infusion 9 Infusion channel 10 cavity 11 (a) Facilities for water / solvent removal and pressure reduction 12 Die (lower part of the tool) 13 cavity (matrix)

[0020] According to the invention, the fibers (4) are first inserted into the interior of the cavity (13). The fibers (4) can be in the form of woven fabrics, scrims, braids, or similar fiber preforms made from long or continuous fibers, as well as from a wide variety of short fiber preforms such as fleece, felt, paper, or the like, each in 1D, 2D, or even 3-dimensional fiber structures. According to the invention, the fibers are ceramic, silicate, mineral, and / or glass fibers. According to the invention, mixtures of different types of fibers are thus included, whereby the material properties of the fiber composites can be adjusted as desired. Different fibers can be incorporated at different positions in the tool and thus in the product, or mixtures can be distributed arbitrarily inside the tool. Preferably, only one type of fiber (4) is used. In particular, the fiber (4) is a ceramic fiber (4).

[0021] The cavity (13) determines the shape of the final green compact. The fibers should follow the geometry of the cavity so that the fibers (4) are present at all positions in the final green compact in the desired concentration and orientation.

[0022] The fibers (4) are, for example, in the form of a textile, which is introduced above the at least one device (5, 6) for retaining the particles / precursors of the slurry (7) inside the cavity (13) and for discharging the contained water and / or solvent into the cavity (13). The device can be, for example, a porous membrane. Furthermore, there can be solid structures to support the membrane.

[0023] After the fibers (4) are inserted into the cavity, the pressure inside the cavity (13) is reduced. In a preferred embodiment, the punch (2) is first moved downward toward the die (12). The adjusted gap establishes the final green compact thickness. The fiber composite green compact can be precisely adjusted using the gap and the textile volume.

[0024] As far as the terms "top", "bottom", "above" or "below" are used in the present application, these are to be understood in such a way that the tool (1) as in the Fig. 1 shown and top and bottom correspond to such an orientation in space.

[0025] If the punch (2) and die (12) are positioned relative to one another such that the cavity (13) has the shape of the future green compact, the pressure inside the tool (1) is reduced via the at least one device (11, 11a). This can be achieved by connecting a vacuum pump to the at least one device (11, 11a).

[0026] The reduction in pressure serves primarily to distribute the slip evenly inside the cavity. If the tool does not have a punch (2), the pressure is reduced as described above. The shape of the cavity is then determined by the die (12) and fixture (5, 6).

[0027] The pressure is reduced to a pressure below ambient pressure. This reduces any air bubbles that may be present. The pressure is preferably reduced to 800 mbar or less, preferably to 500 mbar or less, in particular to 250 mbar or less, particularly preferably to 100 mbar or less, particularly preferably from 80 mbar to 10 mbar, preferably from 60 mbar to 20 mbar.

[0028] If the fibers are coated with a size, for example, the tool (1) can preferably be heated by an existing heating device according to the invention. This allows temperatures of up to 700°C, preferably from 200°C to 600°C, to be reached inside the cavity (13). This removes the size and removes it as a gaseous product through the device (11, 11a) and / or via a connection (8) and an infusion channel (9).

[0029] According to the invention, one or more devices can be provided between the at least one device (11, 11a) and the vacuum pump, in which substances and / or compounds which are removed from the interior of the tool, such as burnt-off coating, are collected so that they do not reach the vacuum pump.

[0030] The slurry (7) is then infused into the cavity (13) of the tool (1). The infusion does not occur solely because the pressure inside the cavity is lower than that in the ambient air. In addition, the slurry (7) itself is introduced into the cavity (13) at increased pressure. This combination of pressure and vacuum produces a CMC (ceramic fiber composite material) in which the slurry (7) penetrates the fibers and the spaces between the fibers (4) or the spaces between fiber bundles particularly well. The slurry is added to the cavity (13) through a connection (8) and an infusion channel (9). These can be fed directly through the die (2) into the cavity (13). According to the invention, it is also possible for the infusion channel (9) to be fed through the punch (2), if present. The exact position depends on the shape of the tool (1).It is only important that infiltration of the tissue with the slip is made possible, i.e. that the slip is introduced into the cavity (13).

[0031] This results in CMCs with improved strength compared to previous manufacturing processes. Furthermore, the fiber volume content can be reduced while maintaining the same strength, allowing for cost-effective products without compromising the material properties.

[0032] In addition, CMCs produced by the method according to the invention and / or with a tool (1) according to the invention have a more homogeneous porosity and fewer defects in the structure than CMCs produced by known methods.

[0033] According to the invention, the slip (7) is thus introduced into the cavity (13) at a pressure that is higher than the ambient pressure. The pressure does not arise from pressure being exerted on the punch (2). The slip (7) itself is introduced into the tool (1) at overpressure. This overpressure is preferably 100 bar or less, in particular it is in the range from 1 bar to 50 bar, preferably from 2 bar to 30 bar, particularly preferably from 3 bar to 20 bar. The pressure depends on the precise design of the tool, i.e. on the size, geometry and materials of the components.

[0034] After the inventive pressure-vacuum infusion (DVI) of the slip (7) into the cavity (13), further compaction can occur. In a preferred embodiment, this can be achieved by moving the punch (2) toward the die (12). The die (12) can also be moved toward the punch (2). Additional pressure can be exerted on the interior of the cavity (13) through the pressure connection (8).

[0035] According to the invention, it is possible for a further pressure-vacuum infusion of a slip (7) to subsequently take place into the interior of the tool (1). The now infiltrated slip (7) can be the same or a different one than the slip (7) used in the first pass. The slips (7) used can differ, for example, in the proportion of ceramic particles or the size of the particles they contain or the particle size distribution. The slips (7) can also differ in their chemical composition. In particular, the particles in the slip (7) can differ in their chemical composition. Likewise, the proportion of particles in the slip (7) can be different in each case. According to the invention, the pressure-vacuum infusion can also be repeated several times until the desired properties are achieved. However, it is preferred if the DVI of at least one slip (7) takes place once or twice.

[0036] The workpiece is then dried inside the cavity (13). Preferably, the drying also takes place at a pressure lower than ambient pressure. Preferably, a vacuum is applied with a pressure of 100 mbar or less, in particular 50 mbar or less, preferably 20 mbar or less, and particularly preferably 10 mbar or less.

[0037] In the method according to the invention or in the device according to the invention, water and / or solvent contained in the slip is separated from the particles also contained in the slip. For this purpose, at least one device (5, 6) for retaining the particles of the slip (7) inside the cavity (13) is present inside the tool. Excess water and / or solvent are collected, for example, in the cavity (10). If a negative pressure is applied, these evaporate and can be removed via the at least one device (11, 11a) either from the cavity (10) or directly from the cavity (13).

[0038] According to the invention, drying is preferably assisted by heating. For this purpose, the workpiece is heated inside the tool to a temperature in the range of 30 °C to 400 °C, preferably 60 °C to 200 °C.

[0039] The mold (1) is then opened, and the dried workpiece (green compact) can be removed from the mold. Subsequently, sintering takes place in a furnace in the conventional manner.

[0040] Due to the drying process already performed in the mold (1), the green compact is dimensionally stable and can be easily removed from the mold without deformation. This is particularly relevant for complex green compact geometries. The resulting dimensional accuracy and surface quality exceed those of all known manufacturing processes. This is highly advantageous from both an economic and ecological perspective, as the cost- and energy-intensive process of (mechanical) post-processing can be completely or partially eliminated.

[0041] According to the invention, the stamp (2) can be made, for example, of a ceramic, plaster, or other mineral material and / or steel. In particular, the stamp (2) is designed to exhibit low thermal expansion, so that its shape remains consistent throughout the entire process. Overall, the material of the stamp (2) is selected to exhibit high abrasion resistance compared to the materials of the slip (7). The deformability should be low in order to obtain green specimens whose shape corresponds to that of the tool (1).

[0042] According to the invention, the die (2) can have a coating on its underside, i.e., the side that comes into contact with the slurry (7) and the fibers (4), which allows for good separation. This allows the green compact to be easily removed from the mold after production.

[0043] According to the invention, materials are also selected for the die (12) which have low thermal expansion, high abrasion resistance to slip and fibres and low deformability even at temperatures up to 600 °C.

[0044] In Fig. 2 a closed tool with fibers (4) and slip (7) is shown. Fig. 3 This figure schematically shows a method according to the invention as described above. These and the following figures each show tools (1) having a punch (2).

[0045] According to the invention, the tool has an element (14) on the underside of the stamp (2), whereby a further cavity (13a) is created between the underside of the stamp and the device (14), so that slip (7) flows through the infusion channel (9) into the cavity (13a) and from there is distributed homogeneously in the hollow space (13), wherein the element (14) is perforated, so that slip (7) can flow from the further cavity (13a) into the hollow space (13). Such an embodiment according to the invention is described in Fig. 4 shown.

[0046] In a further preferred embodiment, elements (16, 16a) can be present inside the cavity (13) that define the geometry of the cavity (13). One possible design of the elements (16, 16a) is shown in Fig. 5The presence of these elements allows for the production of 2D or 3D structures from CMC. These elements also enable the production of 3D structures with complex geometries and highly reproducible properties.

[0047] According to the invention, the device (8, 8a) for increasing the pressure inside the cavity (13) and / or for supplying the slip (7) into the cavity (13) is arranged on the upper side of the plunger (2) and is connected to the cavity (13) via an infusion channel (9) in the plunger (2). Such an arrangement is described in Fig. 1 shown.

[0048] However, it is also possible according to the invention that the device (8, 8a) for increasing the pressure inside the cavity (13) and / or for feeding the slip (7) into the cavity (13) is present in the region of the die (12) and is located above the at least one device (5, 6) for retaining the particles of the slip (7) inside the cavity (13) and for removing the water and / or solvent contained therein. Such an embodiment is described in Fig. 6shown. The operating direction of the tool is reversed here, so that not only is fluid removed via the devices (11, 11a), but the former infusion channel (9) can also be used as an outlet for a fluid (11b). The infusion of the slurry (7) into the cavity (13) then takes place via a hollow, perforated element (17) which is arranged inside the cavity (13). Preferably, the element (17) is arranged such that it divides the cavity (13) into two separate areas. Slip (7) can then be introduced into these areas via the element (17) and pressure can be applied in the same way.

[0049] Textiles (fibers (4)) are inserted above (4b) and below (4c) the perforated element (17), which, after infusion with slip (7) and drying, produce two separate workpieces. A further porous filter (5a) can be inserted above the upper textile (4b) to separate the fluid and the particulate components of the slip (7) during the drying process. The fluid from this part is removed via a device arranged above the element (17). This device (11b) can preferably correspond to the infusion channel (9) of a different design. In a preferred design, a further perforated element (6a) can be introduced into the cavity (13) between the upper filter (5a) and the plunger (2), so that a new cavity (10b) is created above the perforated element (6a) and below the plunger (2) for the planar removal of the fluid.

[0050] Alternatively, the device (8, 8a) for increasing the pressure inside the cavity (13) and / or for supplying the slip into the cavity (13) is arranged inside the cavity (13), wherein the device (8, 8a) is surrounded by an element (17a) via which the slip (7) is introduced into the cavity (13). Fig. 7shows such an embodiment schematically. In this embodiment, the infusion takes place via a hollow, perforated element (17a) which is arranged inside the cavity (13), but does not divide it into two separate areas. Above and below the perforated element (17a), also inside the cavity (13), between the punch (2) and the perforated element (17a) or between the die (12) and the perforated element (17a), two separate, porous membranes (5b / c) with the outer contour of the later workpiece can be incorporated into the matrix. This creates a new cavity (13c) between the perforated element (17a) and the membranes (5b / c). The membranes (5b / c) are designed analogously to the devices (5 / 6) and enable the filtration of fluid and solid (particles) in the slip (7). They therefore enable the production of even complex geometries.

[0051] In this new cavity (13c), the fiber (4d) is draped around the porous element (17a) and supplied with slurry (7) via the connection (8a), through which pressure can also be applied in the same way. The process then continues in the same manner (infusion, drying, demolding). The hollow, porous element (17a) can be removed as a whole and reused or removed as a lost mold from the green body of the CMC, for example, chemically or thermally.

[0052] The tool (1) according to the invention can be used alone or in an arrangement of several tools (1). Such an arrangement can comprise two, three, or more tools (1). These can each be designed identically, so that the same workpiece can be produced simultaneously in multiple copies. The arrangement can also have several different configurations of the tool (1), so that different workpieces can be produced simultaneously.

[0053] An example of an arrangement is shown in Fig. 8 and Fig. 9 shown. In Fig. 8 similar unstressed tools (1) are combined with each other, whereas in Fig. 9 an embodiment with different tools (1) is shown.

[0054] The tool (1) can therefore be adapted to be part of an arrangement in which the matrix is ​​divided into smaller segments, such as 2x2 or 3x3 etc. ( Fig. 8This significantly increases usability, flexibility, and economic and resource efficiency. The tool (1) itself can also be mirrored along the horizontal axis of the die (12). For this adaptation, an attachment (2a) to the punch (2) can be used, which connects several punches via a master infusion channel (9b). New cavities (13d) are created in the individual chambers, in which workpieces can be formed. The drainage of the separated fluid during the drying process is connected via horizontal channels (11c).

[0055] This adaptation / variant can be combined with any of the aforementioned variants, whereby the allocation in each matrix can be identical or can be varied to further increase utilization and variability. This is exemplified in Fig. 9 shown.

[0056] A technological solution was thus found that enables both the infusion and drying of the infiltrated CMCs in a closed mold. The infusion and drying processes take place in a continuous process without any manual intermediate steps. At the end of the process, a fully formed and dried green body can be removed from the mold. The process according to the invention can thus be considered a process for the automated production of ceramic fiber composites.

[0057] Infusion can be performed using vacuum, pressure, or a combination of both. The additional pressure applied to the slurry can achieve a better infusion result and minimize any air inclusions compared to prior art methods.

[0058] Furthermore, production time and labor can be significantly reduced. The prepared infusion mold only needs to be filled with fibers and any accessories such as peel ply.

[0059] The use of a fixed mold and automated production promise consistent quality and high reproducibility of the resulting fiber composites. This is particularly important for the production of larger quantities of the same product. The surface quality and dimensional accuracy are so good that, depending on the application, no or very little post-processing of the workpiece is required, increasing cost-effectiveness and resource efficiency.

[0060] The material thickness or the compression of the fiber layers (fiber volume content) can be adjusted as desired via the gap between the lower mold and the upper mold, i.e. the size of the cavity (13).

[0061] The process is flexible and versatile and can be used for a wide variety of fiber architectures and fiber preforms such as 2D or 3D fabrics, braids or short fiber felts.

Claims

1. A mold (1) for producing components made of ceramic fiber composites by soaking fibers (4) with a slip (7) in a cavity (13), in which said slip contains water and / or solvent, as well as particles or precursors thereof, wherein said mold (1) includes a die (12), whereby a cavity (13) formed by the die (12), the upper side and the lower side of the mold (1) is present in the interior of the mold, characterized in that said mold (1) has at least one device (8, 8a) for increasing the pressure in the interior of the cavity (13) and / or for supplying the slip into the cavity (13), at least one device (5, 6) for retaining the particles or precursors of the slip (7) in the interior of the cavity (13) and for discharging the water contained therein and / or the solvent present in the interior of the die (12), and said die (12) has at least one device (11, 11a) by which the pressure in the interior of the cavity (13) can be reduced and / or excess water and / or solvent can be removed, wherein said at least one device (5, 6) is arranged within the die (12) in such a way that water and / or solvents can be removed through said at least one means (11, 11a), wherein said die (12) is formed from a solid material that does not deform during the application, and wherein said mold (1) preferably further has at least one heating device, which enables the cavity (13) to be heated, wherein said mold (1) further has a punch (2), wherein said punch (2) is placed close to the interior wall of the die (12) in a form-fitting manner and can be displaced vertically in the interior of the die (12), whereby a cavity (13) is formed between the punch (2) and the die (12), and characterized in that an element (14) is provided at the lower side of the punch (2), whereby another cavity (13a) is formed between the lower side of the punch and the element (14), so that slip (7) flows through an infusion canal into the cavity (13a), from where it is homogeneously distributed in the cavity (13), wherein said element (14) is perforated, so that slip (7) can flow from said other cavity (13a) into said cavity (13).

2. The mold according to claim 1, characterized in that it further has a cavity (10) that is arranged in a spatial direction below said at least one device (5, 6), wherein water / solvent of the slip can be collected in the cavity (10) and removed from the cavity through said at least one device (11, 11a).

3. The mold (1) according to at least one of claims 1 or 2, characterized in that elements (16, 16a) defining the geometry of the cavity (13) are present in the interior of the cavity (13).

4. The mold (1) according to at least one of claims 1 to 3, characterized in that said devices (8, 8a) for increasing the pressure in the interior of the cavity (13) and / or for supplying the slip (7) into the cavity (13) are provided at the upper side of the punch (2), and communicate with the cavity (13) through an infusion canal (9) in the punch (2).

5. The mold (1) according to at least one of claims 1 to 4, characterized in that said devices (8, 8a) for increasing the pressure in the interior of the cavity (13) and / or for supplying the slip (7) into the cavity (13) are present in the vicinity of the die (12), and are provided above said at least one device (5, 6) for retaining the particles of the slip (7) in the interior of the cavity (13) and for discharging the water contained therein and / or the solvent.

6. The mold (1) according to at least one of claims 1 to 5, characterized in that said devices (8, 8a) for increasing the pressure in the interior of the cavity (13) and / or for supplying the slip into the cavity (13) are provided in the interior of the cavity (13), wherein said devices (8, 8a) are surrounded by an element (17a), through which the slip (7) is introduced into the cavity (13).

7. An assembly for producing components from ceramic fiber composites by soaking fibers (4) with a slip (7) containing particles or precursors thereof and water and / or solvents, characterized in that it has two, three or more molds (1) according to at least one of claims 1 to 6.

8. A process for producing components from ceramic fiber composites by soaking fibers (4) with a slip (7) containing water and / or solvents, characterized in that (a) said fibers (4) are introduced into the cavity (13) of a mold (1) according to one or more of claims 1 to 6 or of an assembly according to claim 7, (b) the mold (1) is closed, (c) the pressure inside the mold (1) is reduced as compared to the ambient pressure, (d) optionally the fibers (4) within the mold are treated thermally, (e) a first slip containing water and / or solvents is introduced into the cavity (13), wherein said slip (7) has a pressure that is increased over the ambient pressure, (f) the pressure within the mold is reduced, and optionally the mold is heated thermally, and water and / or solvents are removed from the cavity (13), (g) optionally steps (e) and (f) are repeated once or several times, wherein a slip is used that is the same as or different from the first slip (7), and (h) subsequently, the green body obtained is demolded and sintered in an oven.

9. The process according to claim 8, characterized in that, the reduced pressure is lowered to a pressure below the ambient pressure in step (c), especially to 800 mbar or less, preferably to 500 mbar or less, specifically to 250 mbar or less, more preferably to 100 mbar or less, especially preferably to from 80 mbar to 10 mbar, most preferably from 60 mbar to 20 mbar.

10. The process according to claim 8 or 9, characterized in that the pressure in step (e) is 100 bar or less, especially from 1 bar to 50 bar, preferably from 2 bar to 30 bar, more preferably from 3 bar to 20 bar.