Ceramic filter, in particular for filtering molten metals, and method of manufacturing same

Abstract

The present invention relates in general to a ceramic filter, in particular for filtering molten metals, for example aluminum melts, and to a method of manufacturing same.

Description

[0001] Ceramic filter, in particular for filtering metal melts, and method for its production

[0002] Description

[0003] The present disclosure relates generally to the field of ceramic filters, in particular for filtering molten metals, and a method for producing them.

[0004] Ceramic filters are used for a variety of applications, particularly for filtering molten metals, such as aluminum melts or melts containing aluminum.

[0005] The Schwartzwalder process is often used to manufacture filters. This involves impregnating a foam body with a slip by squeezing it between rollers, for example, so that the ceramic mass of the slip is placed on the foam. The foam coated with the slip is then dried, sprayed with slip again, dried again, and then fired.

[0006] However, this process only allows for a limited pore size range for the foam pores. For very coarse-pored filters with less than 7 PPI (pores per inch), foam is unsuitable as a carrier material, as such large pores cannot be produced in conventional foams.

[0007] However, many applications are currently being developed in which filtration through very coarse-pored foams or foam ceramics is necessary, which, however, cannot be produced using the conventional method described above.

[0008] One way to produce such foams or foam ceramics is by printing foams. In recent years, the development of so-called 3D printers (also known as "additive manufacturing") has progressed rapidly, allowing for an efficient and rapid way of printing parts.

[0009] However, difficulties arise with the direct printing of additive manufacturing ceramic or inorganic materials. Such processes, such as selective laser sintering, often involve extensive equipment and consume a lot of energy, which seems impractical from a sustainability perspective.

[0010] It is also known to use three-dimensional models in the production of coarse-pored foams, which periodically repeat from a network of composite polyhedra, as described, for example, in DE 11 2014 001 464 T5. These structures are often very complex and, overall, lead to the formation of a three-dimensional periodic structure of high symmetry. This can be disadvantageous because, due to reduced turbulent flow, it can make it difficult for contaminants to adhere to the filter surface and for the material flow to settle.

[0011] There is therefore a need for ceramic filters with large pores (foam pores), which are particularly suitable for filtering metal melts, as well as for a process for their production, which at least somewhat mitigates the weaknesses of the state of the art.

[0012] Object of the invention

[0013] The object of the invention is to provide a foam and a cellular foam ceramic with large pores (so-called foam pores) and a method for producing such a foam and such a foam ceramic, which at least partially overcome or at least mitigate the known weaknesses of the prior art.

[0014] Summary of the Invention The object of the invention is achieved by the subject matter of the independent claims. Preferred or specific embodiments can be found in the description, the figures, and the dependent claims of the disclosure.

[0015] The disclosure therefore relates, according to a first aspect, to a precursor for a ceramic filter or a ceramic filter, in particular for a filter suitable for filtering metal melts, wherein the structure of the precursor comprises a plurality of sections, wherein the sections are cellular or cellular in structure, in particular open-cell / open-cellular, comprising foam pores and webs connecting them, and wherein at least one section has a non-periodic structure.

[0016] In the present disclosure, the term "cellular" is used synonymously with the English technical term "cellular," which is used in English to describe a foam. Likewise, in the present disclosure, the terms "cellular" and "cellular" (the latter being a translation of the English term "cellular") are used synonymously.

[0017] Open-cell or open-cellular describes a foam which has a permeable structure, i.e. in which the walls of the individual pores of the foam no longer contain any material and the structure is formed by the webs between the individual pores of the foam.

[0018] A "non-periodic" structure is a structure that has no symmetry; such a structure may also be referred to as "heterogeneous" in the context of the present disclosure.

[0019] Within the scope of the present disclosure, a distinction is made between different pores with regard to the filter and (if applicable) the precursor. This is also explained further below with reference to Fig. 1 of the disclosure. The precursor and / or the precursor (if applicable) comprise correspondingly different pores, which differ in terms of their formation and / or, more specifically, their size. Within the scope of the present disclosure, a distinction is made between foam pores, the largest pores, the so-called web pores, which can occur particularly inside a web, and ceramic pores, fine pores, which are usually present in a ceramic due to the material.

[0020] The filter according to the present disclosure is one which is particularly suitable for filtering (or synonymously for filtering or filtration) molten metals.

[0021] In the context of the present disclosure, a precursor for a filter is generally understood to mean a structure which serves as a template for the filter to be produced. In particular, this precursor can be understood as a coarse-pored foam. In general, the precursor can have a cylindrical or prism-like structure, i.e. a round cross-section, for example a circular cross-section, or a polyhedral cross-section, as well as a height. The shape of a straight cylinder or prism is particularly preferred. Of course, an irregular cross-section or an irregular base area is also possible and, in general, any desired geometries are possible depending on the area of ​​application of the later filter. For the sake of simplicity, the structure of the precursor and the precursor is described below as an example.The filter is explained using a cylinder, although it should be understood that other geometries are also possible, and a cylinder was used only for the sake of clarity. The following explanations apply, with the necessary modifications, to pre-stages or filters with other geometries.

[0022] Since, due to the porous or cellular structure of the precursor, only a small portion of the cylinder volume is actually filled with material, the outer lateral dimension of the precursor can be approximately understood as the diameter for the cross-sectional dimension. The same applies to the height of the cylinder or precursor. The sections of the precursor each have a cellular / cellular structure, namely open-celled in particular. This means that the precursor comprises cells or foam pores, i.e. spatial sections that have an approximately polyhedral shape. The foam pores are connected to one another by webs, or the individual foam pores border one another via common edges and / or surfaces. The edges of the foam pores can also be understood or referred to as webs.If the precursor is open-celled, or synonymously open-celled, then the sides or surfaces of the foam pores are open, i.e., not covered with material, and only the edges of the foam pores remain as ridges connecting the individual foam pores. The transition from one foam pore to another, which is enclosed by ridges, is also called a cell window.

[0023] While the above statements also apply generally to open pores, they apply in particular to the precursors and filters considered here, especially to the so-called foam pores, which are also the largest pores of the filter or precursor according to the present disclosure.

[0024] At least one section of the precursor has a non-periodic or heterogeneous structure. As explained above, a non-periodic structure means that the section comprising such a structure is not periodically structured, i.e., it does not have periodically recurring structures. The section can thus also be described as non-symmetrical with respect to the foam pores that form the section. The (abstracted polyhedral) shape of the individual foam pores therefore does not vary according to any symmetry laws, and their sequence within the section exhibits no order. Such a structure of the section is also referred to as "heterogeneous" in the context of the present disclosure.

[0025] For example, this is possible by scanning the structure of a naturally occurring biological sponge and using it at least partially as a template for the precursor of the ceramic filter according to embodiments. Such an actually occurring structure of a foam, be it a biological sponge, for example, or a polymer foam obtained by known methods, is also referred to as a "real structure" in the context of the present disclosure.

[0026] In general, without limitation to a specific embodiment, the provision of such a non-periodic or heterogeneous structure can be carried out as follows:

[0027] A) Firstly, a real structure model can be used, which is obtained, for example, from a tomographic scan, for example using computed tomography. Such a real structure can, as explained above, be that of a biological sponge or a chemically produced foam, for example a polyester foam or similar, for example also of so-called heterogeneous foam structures. The scan is preferably carried out in such a way that the corresponding size and dimension of the template is scanned. Finer structures, for example with pores in the micrometer range, can then be subsequently converted to the desired dimension. By using such a scan of a real foam structure and the creation of a section of a foam based on it, the structures are always based on the same master foam. A similarity of the resulting properties is assumed.This makes it possible to produce components, such as filters, with a reproducible microstructure. As explained above, the master foam can be scaled in terms of cell size and web width (for example, via external dimensions).

[0028] In the context of the present disclosure, a real structure is understood to be a structure that actually exists, i.e., an actually existing structure that is embodied and accessible to a scan. The model of this structure obtained by means of the scan, i.e., its capture in the form of data, is referred to as a "real structure model." It is possible to make modifications, for example, by non-uniform scaling, without fundamentally changing the real structure. For example, elliptical (foam) pores with preferred directions can then be generated, i.e., if desired, anisotropic properties of the foam and thus of the filter can be obtained. If a variation of the structures is desired, different foams can be scanned, and thus different components or different sections within a component can be realized with different structures.

[0029] B) In the second variant, the starting point is also a real structure model based on tomography measurements, but so-called skeletonized structures are used. The real structure determined by scan is divided into a large number of mathematically defined units. By varying the parameters, the web diameters can be precisely modified and the cross-section types can also be adapted (from triangular and round to octagonal or polygonal). In this case, certain web diameters can be partially reduced or enlarged, e.g. at the interstices, to avoid material accumulation. The interstices are the points where at least two webs of the foam meet, in particular at least three webs. In addition, it is possible to generate a uniform web diameter, which leads to an improvement in the mechanical material properties in particular.Furthermore, the skeletonized structures allow for structuring of the web surface, which can improve or optimize the coating behavior with a ceramic slurry. Furthermore, the web diameter can be randomly varied at selected locations using mathematical operations, which also results in non-periodic structures. However, these selected locations do not affect mechanical stability. On the contrary, targeted thickening or thinning can have a direct, positive influence on turbulent flow. This allows for structural optimization.

[0030] C) A third variant is based on the use of two or more different periodic structures in the process according to B), including possible modifications (thickness, diameter, cross-section), which have the same or different web diameters and are interlaced in such a way that random connection points are possible via the ceramic slurry (capillary forces at appropriate spacing). Using various transformation operations, the structures can now be combined with one another much more easily than with the real structure models, provided the web diameter is the same or similar, usually with the aid of an external bounding box to stabilize the bond. Due to the identical web diameter, the coating has the same structure at all points.Two closely adjacent bridges that are not connected to each other in the polymer state can now be connected by the capillary forces of the slurry (depending on its viscosity), resulting in a composite with a non-periodic structure in the final ceramic. Due to the random connections between the regular substructures, the final composite is always non-periodic.

[0031] All three variants can also be produced using direct 3D ceramic printing. In case C), capillary forces are automatically utilized by additional impregnation for bonding and a lower print resolution. However, such 3D ceramic prints are currently rather expensive.

[0032] This at least partial formation of the precursor (and correspondingly of the resulting ceramic filter, or synonymously, ceramic filter) is advantageous. This approach makes it possible to achieve better filtration results. It has been shown that such non-periodic structures, for example, bionic structures like those of a sponge, achieve a better filtration effect than periodically constructed precursors or filters.

[0033] This is not fully understood in the specialist literature. However, it appears that a periodic structure in the filter reduces turbulent flow, which impairs the filtering effect. In general, filters and their precursors, as already partially described above, including ceramic filters made from filter precursors, have a cellular structure. This means that these filters have a foam-like structure, with the foam pores generally being open, allowing air to pass from one side of the filter to the other. This is also referred to as "open-cell" or open-cellular, i.e. the structure comprises various foam pores, each of which has an open side, and the (foam) pores of the structure are connected to one another by webs.The structure can be understood as being composed of polyhedra, where the edges of the polyhedra represent the webs and the polyhedral surfaces are open.

[0034] Various processes are known for producing such a filter, and in particular, it may be possible to produce such a filter using so-called "additive manufacturing." In the prior art, three-dimensional models in the form of complex polyhedra that repeat periodically are often created. As explained above, however, this has the disadvantage of a suboptimal filtration effect.

[0035] This is at least reduced in at least one section of the filter pre-stage and accordingly also in the ceramic filter resulting from such a pre-stage, so that overall a better filtration effect can be achieved.

[0036] In the present disclosure, the terms "filter pre-stage" and "pre-stage" are used synonymously. Furthermore, the terms "ceramic filter" and "ceramic filter" are used synonymously. Where reference is made to a "filter," this also refers to a ceramic filter / ceramic filter.

[0037] According to one embodiment, the precursor comprises a polymer. In general, it is advantageous if the polymer is a sustainable polymer, for example based on natural materials such as cellulose, polylactic acid (PLA), or starch, or is produced using a sustainable manufacturing process. In general, within the scope of the present disclosure, a manufacturing process for a polymer is considered sustainable if the process is more sustainable than the production of a conventional polymer product, i.e., less material is used overall or other savings in materials and / or energy are possible. The precursor according to the present disclosure is preferably produced using 3D printing and is thus advantageous and correspondingly sustainable compared to conventional foam production processes, since energy-intensive reticulation is no longer necessary and no waste is generated.

[0038] According to one embodiment of the disclosure, the polymer comprises at least one filler, or several fillers, in particular one or more ceramic fillers such as ceramic powder. Generally, without limitation to one embodiment, the polymer can be a thermoplastic polymer.

[0039] If the polymer comprises one or more fillers, particularly in the form of ceramic fillers, it may be advantageous to choose a high filler content, i.e., a high ceramic filler content, preferably of at least 50 vol. However, it may also be advantageous to use one or more metallic fillers, either alone or in combination with one or more ceramic fillers. This is because a metallic filler can be converted into an oxide when the organic component is burned out, thus also resulting in a ceramic filter.

[0040] In the context of the present disclosure, a ceramic is generally understood to mean an inorganic, non-metallic material. A ceramic is preferably an at least partially crystalline material, which can also preferably have a porous structure, in particular with fine pores, which in the context of the present disclosure are also referred to as ceramic pores, which can, for example, be in the range of up to 1 pm to 30 pm pore size, for example 10 pm or 15 pm pore size. According to one embodiment, the precursor comprises a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections can be arranged offset from one another by an angle with respect to a longitudinal axis of the precursor, in particular such that a screw-like structure is or will be obtained with respect to the longitudinal axis.In particular, according to a particularly preferred embodiment, it can be provided that all sections of the preform are arranged offset by an angle, preferably at the same angle. By arranging the sections in a screw-like manner, a particularly advantageous filtration effect, for example, a quantity-optimized filtration effect, can be achieved.

[0041] As explained above, the precursor can be understood geometrically with regard to its outer lateral dimensions generally as a cylinder or prism, i.e., with two base surfaces that are spaced apart and preferably parallel to each other, preferably as a straight cylinder or a straight prism. The longitudinal axis is generally perpendicular to the base surface. In the case of offset sections, especially when all sections are offset by the same angle, it can be understood as a screw axis.

[0042] According to one embodiment, the precursor is designed to comprise a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections are arranged offset from one another with respect to an axis which forms an angle between more than 0 and less than 180°, preferably an angle of 90°, with the longitudinal axis.

[0043] The axis is therefore one which is preferably arranged perpendicular to the longitudinal axis.

[0044] In general, interlacing the structures around at least one axis, and preferably around two axes, is advantageous because it increases the tortuosity of the structure. This, in turn, promotes the development of turbulent flow and generally improves the filtration efficiency of a ceramic filter built on such a structure.

[0045] According to a further embodiment, the foam pores have a pore size of 300 μm and 5 mm, preferably between 1.5 mm and 2.5 mm. The pore size is generally understood to mean the maximum dimension of a pore, without limitation to a specific type of pore, such as a foam pore, a ridge pore, or a ceramic pore within the meaning of the disclosure.

[0046] Such a design is particularly advantageous if, for example, the production of a ceramic filter for the filtration of metallic melts is intended.

[0047] According to yet another embodiment, the webs have a roughness R a from 2.5 pm to 150 pm, preferably at most 100 pm, and / or the webs have an average thickness between 100 pm and 5 mm.

[0048] The mean thickness of the web is generally understood to be the arithmetic mean of the lateral dimension of the web perpendicular to its length, the largest lateral dimension of the web.

[0049] The roughness of the ridges can be adjusted by selecting the precise manufacturing process and / or the material used. Keeping the ridges rough within the aforementioned limits increases the surface area of ​​the filter precursor, and when the precursor is coated with a ceramic slurry (also known as slurry coating or impregnation), the slurry adheres better to the precursor. This leads to greater strength of the ceramic filter and is therefore particularly preferred.

[0050] According to a further aspect, the disclosure also relates to a ceramic filter, in particular for filtering metal melts, particularly preferably aluminum melts. The ceramic filter generally comprises a structure comprising several sections, wherein the sections are cellular / cellular in structure, in particular open-cell or open-cellular, i.e., comprising foam pores and the webs connecting them, and wherein at least one section has a non-periodic structure. The ceramic filter or ceramic filter according to the disclosure is particularly suitable for the filtration of metal melts, for example aluminum-containing melts or aluminum melts.

[0051] The ceramic filter according to the disclosure therefore replicates the structure of the pre-stage, so that the statements concerning the pre-stage also apply to the ceramic filter accordingly.

[0052] The ceramic filter according to the disclosure can generally be particularly suitable for the filtration of molten metals, as explained above. This implies that the ceramic filter according to the disclosure is preferably generally designed such that it can withstand the corresponding harsh conditions that arise in the corresponding application, i.e., in particular, has a correspondingly high mechanical and / or thermal resistance. This can be demonstrated, for example, by thermal shock tests. In general, the ceramic filter can be designed such that it has an initial inert strength of at least 2.5 + 0.5 MPa, preferably with a porosity of approximately 70 + 5%.Inert strength is understood to be a strength which is determined at high test speeds (more than 1.5 mm / minute) in order to minimize subcritical crack growth within a test specimen, for example a ceramic filter.

[0053] For example, according to one embodiment, the initial inert strength at a porosity of 60% is preferably at least 1+0.5 MPa, and at a porosity of 90%, at least 0.5+0.25 MPa. According to one embodiment, the ceramic filter is designed to withstand at least one, preferably three, thermal shock with a temperature jump of, for example, ΔT=580 K, generally between an ΔT of at least 100 K and an ΔT of at most 1200 K, at which the strength is preferably halved at most while maintaining structural integrity. In other words, according to embodiments of the present disclosure, the ceramic filter is designed to remain operational at temperature differences between at least 100 K and at most 1200 K, for example, of 600 K or 580 K.According to one embodiment, the Weibull modulus value m as a measure of the strength dispersion is 4+0.5 for up to three thermal shock cycles and 5.5+0.5 without thermal shock. In general, the Weibull modulus can be at least 2 after up to three thermal shock cycles and at least 3 without thermal shock. According to yet another embodiment of the ceramic filter, the damage parameter D is between 0.15 and 0.9, for example between 0.42 and 0.58, for the increasing number of thermal shock cycles.

[0054] In other words, the ceramic filter, in particular for the filtration of metal melts, according to one embodiment has an initial inert strength of at least 2.5+0.5 MPa, preferably with a porosity of the ceramic filter of 70+5%.More generally, without being limited to a specific embodiment of the ceramic filter, the ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, with the structure comprising a plurality of sections, as generally described for the ceramic filter according to the present disclosure, can be designed with an initial inert strength of at least 0.5+0.25 MPa, preferably with a porosity of the ceramic filter of 90% and / or with an initial inert strength of at least 1+0.5 MPa, preferably with a porosity of the ceramic filter of 60%, wherein generally an upper limit of the strength can be 90 MPa, in particular also 70 MPa, and / or with a thermal shock resistance with at least one temperature jump and up to a maximum of three temperature jumps between at least 100 K and a maximum of 1200 K and a damage parameter D between 0.15 and 0.9.In this way, sufficient mechanical and / or thermal strength of the ceramic filter is ensured, particularly for use in filtering molten metals, for example, aluminum melts. In particular, this means that even after one or more thermal shock cycles, the ceramic filter is still suitable and can be used for the corresponding application, for example, filtering molten metals, such as aluminum melts. In general, within the scope of the present disclosure, the information on porosity refers to the volume of the corresponding body, for example, the filter. With a porosity of, for example, 90%, 90% of the volume is present as pores and only 10% of the volume is occupied by a ceramic material.

[0055] According to one embodiment of the ceramic filter, it comprises several sections, at least two sections having the same non-periodic structure. The at least two sections can be arranged offset from one another by an angle with respect to a longitudinal axis of the ceramic filter, in particular such that a helical structure is or will be obtained with respect to the longitudinal axis. As explained, this is advantageous for the filtration effect of the ceramic filter to be achieved.

[0056] To increase the tortuosity of the ceramic filter, according to a further embodiment, it can alternatively or additionally be provided that the filter has several sections, at least two sections having the same non-periodic structure, the at least two sections being offset from one another with respect to an axis which forms an angle of between more than 0 and less than 180°, preferably an angle of 90°, with a longitudinal axis of the ceramic filter. As stated, the ceramic filter replicates the structure of the precursor in a corresponding manner, at least partially or even completely, although certain differences may exist, for example, with regard to the formation of the interstices, the precise dimensions of the foam pores and / or the webs, and the resulting pore sizes.

[0057] According to one embodiment of the ceramic filter, the foam pores have a pore size between 300 μm and 5 mm, preferably between 1.5 mm and 2.5 mm, which is advantageous for the filtration of, for example, metallic melts. Further applications of the ceramic filter according to embodiments include, for example, general conversion applications for liquid or gaseous media.

[0058] According to a further embodiment, the ceramic filter is designed such that the webs have an average thickness of between 200 μm and 10 mm, preferably at most 8 mm, particularly preferably at most 5 mm, and / or that the webs have a tubular structure, and / or wherein the webs comprise web pores, wherein the web pores preferably have a web pore size of between 30 μm and 300 μm. In general, this is advantageous for the formation of a sufficiently stable filter. Although web pores generally lead to a reduction in the mechanical properties, this reduction is acceptable if the web pores are within the range described above, since they also contribute to dewatering of the ceramic material during the firing process and can therefore also have a positive influence on the resulting strength of the ceramic material.

[0059] In the context of the present disclosure, a tubular configuration or structure is generally understood to mean that the webs can be hollow, whereby it is not necessary for the cross-section of the cavity to be round or elliptical. Rather, the area of ​​such a cross-section through the web, in particular the cross-section of the cavity, can be formed in any desired manner, for example, as a polygon or also round or elliptical, or generally irregularly defined.

[0060] The webs further comprise web pores. In the context of the present disclosure, the term "web pores" generically refers to the pores of the web, which form, for example, in the form of an internal cavity in the webs and which can result from the decomposition of the precursor polymer during the firing process. As stated, these generally have a web pore size between 30 μm and 300 μm. However, it should also be noted that the webs of the ceramic filter, since they comprise ceramic, can generally comprise even finer pores, as is typical for ceramics, and which can range, for example, between 1 μm and 30 μm. These finer pores are also referred to as ceramic pores in the context of the present disclosure, where reference is made to them.These ceramic pores, as well as the ridge pores, can generally be advantageous, as they can facilitate the dewatering of the ceramic material during the firing process and thus lead to improved mechanical stability of the material. Additionally, it can be advantageous if the material is porous and includes ridge pores, as this generally reduces the weight of the ceramic filter. The aforementioned ridge pore sizes in the range between at least 30 μm and 300 μm are advantageous for this purpose.

[0061] According to one embodiment of the ceramic filter, it comprises a ceramic comprising aluminum oxide as the main material and a secondary phase, wherein the ceramic is preferably free of P2O5 or comprises P2O5 between 0.5 and 3.5 wt.%. Suitable compositions for the ceramic of the ceramic filter can be found, for example, in the applicant's own application with the file number WO 2022 / 084413 A1.

[0062] However, it is generally also possible and may be preferable to choose a ceramic with a different composition, such as SiC or ZrO2. The choice of material generally depends on the intended application of the ceramic filter.

[0063] According to one embodiment, the ceramic of the ceramic filter comprises the following components in wt% on an oxide basis:

[0064] AI2O3 67 to 95, especially 75 to 95

[0065] Ei2O 0 to 5, preferably 0.3-5, preferably 0.3 to 0.5

[0066] SiO2 0 to 25, preferably 5 to 25, preferably 10 to 25

[0067] B2O3 0 to 5, preferably 0.1 to 5, preferably 0.3 to 1.5 and / or wherein the content of B2O3 is at most 500 ppm, based on the weight

[0068] CaO 0 to 20, preferably 0.1 to 20, preferably 0.1 to 10, particularly preferably

[0069] 0.1 to 2 P2O5 0 to 10, preferably at most 10 wt.%, particularly preferably at most 7 wt.%, most preferably at most 5 wt.%

[0070] According to a further embodiment, the ceramic of the ceramic filter comprises the following components in wt% on an oxide basis:

[0071] AI2O3 75 to 95

[0072] Li2O 0 to 5, preferably 0.3-5, preferably 0.3 to 0.5

[0073] SiO2 0 to 25, preferably 5 to 25, preferably 10 to 25

[0074] B2O3 0 to 5, preferably 0.1 to 5, preferably 0.3 to 1.5 and / or wherein the content of B2O3 is at most 500 ppm, based on the weight

[0075] CaO 0 to 20, preferably 0.1 to 20, preferably 0.1 to 10, particularly preferably

[0076] 0.1 to 2

[0077] P2O5 0 to 10, preferably at most 10 wt.%, particularly preferably at most 7 wt.% and most preferably at most 5 wt.%.

[0078] Within the scope of the present disclosure, the specification of the components thus relates to the chemical composition of the material. Therefore, if, within the scope of the present disclosure, a ceramic comprises, for example, 90 wt.% Al2O3, this is understood to mean the total aluminum oxide content of the ceramic. In this case, Al2O3 in the foam ceramic can be present both in the form of Al2O3 and in the form of other compounds, for example, in the form of an aluminum silicate.

[0079] According to yet another embodiment, the ceramic of the ceramic

[0080] Filters the following components in vol.%, based on the solid content: a-AbOs (corundum) 85 to 95

[0081] Quartz 0.8 to 2

[0082] Cristobalite 0 to 2. According to a further aspect, the disclosure also relates to a method for producing a ceramic filter, in particular for filtering metal melts, particularly preferably aluminum melts, preferably a ceramic filter according to one embodiment. The method comprises the steps:

[0083] - Providing a precursor for a filter, in particular for filtering metal melts, in particular preferably aluminum melts, in particular a ceramic filter, in particular a ceramic filter according to one embodiment, preferably a precursor according to one embodiment, wherein the provision of the precursor preferably comprises:

[0084] Providing a model of a cellular, preferably non-periodic, structure and forming a precursor,

[0085] - preferably providing a slip for a ceramic material, - preferably forming a precursor coated with a ceramic slip, wherein the forming is carried out by means of an additive process, and

[0086] - preferably firing the precursor coated with the ceramic slip to obtain a ceramic filter.

[0087] The step of providing a model of a cellular structure can generally include:

[0088] - scanning, preferably by means of computer tomography, a real structure of a foam, for example a biological foam or a plastic foam, to obtain a model of a cellular, non-periodic structure,

[0089] - if necessary, scaling the model to the desired dimension of the preliminary stage,

[0090] - if necessary, modify the real structure, for example in the form of non-uniform scaling,

[0091] - Selecting a section of the real structure,

[0092] - Optionally, subdividing the real structure into a multitude of mathematically defined units using a model and modifying the real structure to obtain a skeletonized structure, whereby the structure can be partially modified, for example, with regard to web diameters and / or other parameters. For example, the mathematically defined units can be general geometric bodies or surfaces, such as cylinders, triangles, cubes, polyhedra in general, etc.

[0093] However, it is also possible that the step of providing a model of a cellular structure includes:

[0094] - Selecting at least two different periodic structures, wherein a subdivision into mathematically defined units takes place and wherein the thickness and diameter of webs and / or cross-sections of foam pores are recorded and modified in the structures, wherein these are interlaced in such a way that random connection points result.

[0095] As described above, the structure or structures being detected may inherently have smaller pore sizes than the foam pores specified within the scope of the present disclosure. However, it is understood that these pores of the structure are then scaled accordingly to the size range of the foam pores addressed within the scope of the present disclosure, so that in this regard, they are referred to as foam pores.

[0096] According to this embodiment, periodic structures are used, but these are transformed into non-periodic structures by impregnation with the ceramic slip, since in this step the capillary forces of the slip must be taken into account, which give the resulting ceramic filter its non-periodic structure.

[0097] In other words, providing a model of a cellular structure can involve providing a non-periodic structure. However, it is also possible to provide a periodic structure that is skeletonized in such a way that a non-periodic structure results when forming the ceramic filter, in particular during impregnation and / or the firing process. It can generally be provided that the ceramic filter is formed according to embodiments in such a way that, as explained above, a precursor is first provided, which can be produced in particular by means of 3D printing. Then, according to one embodiment of the method, it can be provided that a slurry for a ceramic material is provided, and in a further step, a precursor coated with the ceramic slurry is formed, the so-called impregnation or coating.This step is also carried out using an additive process, which is advantageous because it allows for targeted use of the slip itself, thus saving material. The precursor coated with the ceramic slip is then fired to produce a ceramic filter.

[0098] As explained, the provision of a pre-stage can generally be carried out as described in more detail above.

[0099] However, it can also generally be provided that the method for producing a ceramic filter, preferably a ceramic filter according to one embodiment, is carried out in such a way that a precursor is first provided, as described above, but this precursor is designed such that impregnation with a slip is not necessary. According to this embodiment of the method, the precursor is produced using a polymer which comprises a ceramic filler, wherein the filler content of the polymer is preferably at least 50 vol. %, and the precursor is fired to obtain a ceramic filter. The precursor is then fired, whereby the polymer decomposes and the ceramic filler sinters together to obtain a ceramic filter. This can be particularly advantageous from an efficiency perspective.

[0100] Examples

[0101] The invention is explained in more detail below using an example. For initial tests, we used the following material for the production of the printed

[0102] foam is used.

[0103] material

[0104] Polymer: Polyurethane TPU

[0105] Trade name: Luvosint TPU X92A-2 WT

[0106] Manufacturer: Lehmann & Voss & Co. KG, Germany

[0107] Printing process: Selective Laser Sintering SLS

[0108] The precursor obtained by this process is shown on the right in Fig. 4. The resulting ceramic filter (or ceramic filter) is shown in the left part of the figure.

[0109] The thermal shock behavior of ceramic filters according to various designs was investigated. For this purpose, ceramic filters were manufactured and measured for their geometric dimensions (height, diameter) and weight. The ceramic filters had a porosity of 67+3 vol%.

[0110] To determine thermal shock behavior, 15 samples are placed on a support plate and placed in an oven at room temperature. They are then heated to 600°C, which they maintain for one hour.

[0111] For each thermal shock cycle, a sample is taken, the furnace is closed, and the remaining samples are left at the corresponding high temperature for a holding time of one hour. The sample is placed in a water bath at room temperature. The sample is then removed and dried. The process is repeated with the next sample.

[0112] If multiple thermal shock tests are conducted consecutively, i.e., if the samples are quenched several times in succession, multiple furnaces are usually used, especially at least two, since the furnace must cool completely before each new cycle. The following table summarizes the strength values ​​for the ceramic filters:

[0113] The thermally shocked samples are then subjected to a compression test in an appropriate apparatus, with a feed rate of 2 mm / min.

[0114] The calculation of the so-called m-values, as listed in the table above, is carried out according to DIN 843-5 (maximum likelihood method). The corresponding measurement data of the strength as a function of the

[0115] Thermal shock cycles and the corresponding m-values ​​are also summarized in the diagram in Fig. 5.

[0116] Based on the data presented for the exemplary ceramic filters in the table above, it can be seen that the inert strength is reduced by 43% after one thermal shock cycle compared to the initial strength at room temperature; and by 58% after three thermal shock cycles compared to the initial strength at room temperature. This corresponds to the damage parameter D determined according to Münz as follows:

[0117] Difold = 0.42, Dafold = 0.58.

[0118] These results can be generalized as follows:

[0119] Ceramic filters according to the disclosure can generally be particularly suitable for the filtration of molten metals, as explained above. In particular, the ceramic filters according to the disclosure can be designed such that they generally, without limitation to a specific embodiment, withstand the corresponding harsh conditions arising in the corresponding application, i.e., in particular, they exhibit correspondingly high mechanical and / or thermal resistance.

[0120] Evidence of this is the thermal shock tests that were carried out for ceramic filters according to embodiments. In general, the ceramic filter according to embodiments can therefore be designed such that it is constructed with an initial inert strength of at least 0.5 + 0.25 MPa, preferably at a porosity of the ceramic filter of 90% and / or with an initial inert strength of at least 1 + 0.5 MPa, preferably at a porosity of the ceramic filter of 60%, whereby an upper limit of the strength can generally be 90 MPa, in particular also 70 MPa, and / or with thermal shock resistance at at least one temperature jump and up to a maximum of three temperature jumps between at least 100 K and a maximum of 1200 K and a damage parameter D between 0.15 and 0.9. According to one embodiment of the ceramic filter, it is designed, for example, such that it is constructed, preferably at a porosity of approx.70+5%, an initial inert strength of at least 2.5+0.5 MPa.More generally, without being limited to a specific embodiment of the ceramic filter, the ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, with the structure comprising a plurality of sections, as generally described for the ceramic filter according to the present disclosure, can be designed with an initial inert strength of at least 0.5+0.25 MPa, preferably with a porosity of the ceramic filter of 90% and / or with an initial inert strength of at least 1+0.5 MPa, preferably with a porosity of the ceramic filter of 60%, wherein generally an upper limit of the strength can be 90 MPa, in particular also 70 MPa, and / or with a thermal shock resistance with at least one temperature jump and up to a maximum of three temperature jumps between at least 100 K and a maximum of 1200 K and a damage parameter D between 0.15 and 0.9.According to one embodiment, the ceramic filter is designed to withstand at least one, preferably three-fold, thermal shock with a temperature jump of, for example, ΔT=580 K, generally between ΔT of at least 100 K and ΔT of at most 1200 K, at which the strength is preferably at most halved while maintaining structural integrity. In other words, the ceramic filter according to the present disclosure is designed in embodiments such that it remains usable at temperature differences between at least 100 K and at most 1200 K, for example of 600 K or 580 K. According to one embodiment, the Weibull modulus value m as a measure of the scatter of strength is for up to three.

[0121] Thermal shock cycles at 4+0.5 and without thermal shock at 5.5+0.5. In general, the Weibull modulus can be at least 2 after up to three thermal shock cycles, and at least 3 without thermal shock. According to yet another embodiment of the ceramic filter, the damage parameter D is between 0.15 and 0.9, for example, between 0.42 and 0.58, for the increasing number of thermal shock cycles.

[0122] According to one embodiment, the ceramic filter, in particular for the filtration of metal melts, has an initial inert strength of at least 2.5+0.5 MPa, preferably with a porosity of the ceramic filter of 70+5 vol.%.

[0123] By designing the ceramic filter with the appropriate initial interstrengths and / or the appropriate thermal shock behavior, it has sufficient mechanical and / or thermal strength, in particular for the use of the ceramic filter for the filtration of metal melts, for example aluminum melts.

[0124] Description of the drawings

[0125] The invention is further explained below with reference to the figures. They show:

[0126] Fig. 1 shows a representation of different pores to explain their size difference,

[0127] Fig. 2 and 3 model representations of structures, Fig. 4 a photographic representation of a ceramic filter (or ceramic filter) and a precursor according to an embodiment, and

[0128] Fig. 5 is a diagram of the strength of ceramic filters as a function of thermal shock cycles.

[0129] Fig. 1 shows, by means of three representations on different scales, the different pores of the ceramic filter or the ceramic or the precursor according to the present disclosure.

[0130] The left-hand illustration shows a foam that may, by way of example, be part of a section of a precursor and / or a filter according to the disclosure. The white-bordered area indicates a foam pore, which may also be referred to as a cell. These cells or foam pores of the precursor or filter according to the disclosure generally have sizes between 300 μm and 5 mm.

[0131] In the black-bordered area of ​​the left-hand image, a ridge is marked, which is examined in more detail in the middle image, a scanning electron microscope image. The scale of the middle image in Fig. 1 is 1 mm. This is an image of a ridge in a ceramic filter that has already been obtained from a firing process, so that the organic matter of the precursor has already decomposed. As can be seen, this ridge has a pore in its center, which can form as a result of the decomposition of the organic material of the precursor and generally runs at least partially along the length of the ridge, without being limited to the example of the specific ceramic filter shown or illustrated in Fig. 1.Such a web pore can generally form in all webs of a ceramic filter according to the disclosure, and individual web pores of different webs can also connect with one another where the webs meet in interstices, even if this is not necessarily the case. The web pore in the illustration according to Fig. 1 is also outlined in white and can generally have sizes between 30 pm and 300 pm. Furthermore, an area of ​​the web made of ceramic material is outlined in black. In the right-hand illustration, this area has been zoomed in so that the fine structure of the ceramic is shown in a scanning electron micrograph. The white outline here shows an exemplary pore, which is also referred to as a ceramic pore in the context of the present disclosure and which results from the production of the ceramic by sintering during firing. The scale is also indicated here with 10 pm.In general, the ceramic pores can have a pore size between 1 and 30 pm.

[0132] Fig. 2 shows a model representation of a section of a structure according to a first embodiment. Here, a real structure of a foam was scanned, resulting in a model of a cellular, non-periodic structure, which is shown in detail in Fig. 2. The model can be scaled, if necessary, to the desired dimension of the precursor (and accordingly the filter), and also modified if necessary, for example, by means of a non-uniform scaling. A section was selected from the model obtained by scanning, which is shown here as an example in Fig.2, which can optionally be further subdivided, for example by dividing the real structure into a plurality of mathematically defined units by means of a model and modifying the real structure to obtain a skeletonized structure, wherein the structure can be partially modified, for example with regard to web diameters and / or other parameters.

[0133] The section of the structure can then be used generally for a section of the structure of the precursor and, accordingly, the ceramic filter.

[0134] Fig. 3 shows a model representation of the foam from Fig. 1. However, the structure has been mathematically modified here, so that the foam material in the interstices has been significantly reduced in order to achieve a reduction in the interstices material. This is not possible with conventional foams. Finally, as already explained for example in the disclosure, Fig. 4 shows a precursor obtained using the method according to the disclosure, which can be seen on the right in Fig. 4. The ceramic filter (ceramic filter) obtained in this way can be found in the left part of the figure.

Claims

1. Precursor for a ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, wherein the structure of the precursor comprises a plurality of sections, wherein the sections are cellular in structure, in particular open-cell, comprising foam pores and webs connecting them, and wherein at least one section has a non-periodic structure.

2. The precursor of claim 1, wherein the precursor comprises a polymer.

3. Precursor according to one of claims 1 or 2, comprising a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections can be arranged offset by an angle with respect to one another with respect to a longitudinal axis of the precursor, in particular such that a screw-like structure is or will be obtained with respect to the longitudinal axis.

4. Precursor according to one of claims 1 to 3, comprising a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections are arranged offset from one another with respect to an axis which encloses an angle of between more than 0 and less than 180°, preferably an angle of 90°, with a longitudinal axis of the precursor.

5. Precursor according to one of claims 1 to 4, wherein the foam pores have a pore size between 300 pm and 5 mm, preferably between 1.5 mm and 2.5 mm.

6. Precursor according to one of claims 1 to 5, wherein the webs have a roughness R a from 2.5 pm to 150 pm, preferably at most 100 pm, and / or wherein the webs have an average thickness between 100 pm and 5 mm.

7. Ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, comprising a structure comprising several sections, wherein the sections are cellular, in particular open-cell, comprising foam pores and webs connecting them, and wherein at least one section has a non-periodic structure.

8. Ceramic filter according to claim 7, with an initial inert strength of at least 0.5+0.25 MPa, preferably with a porosity of the ceramic filter of 90% and / or with an initial inert strength of at least 1+0.5 MPa, preferably with a porosity of the ceramic filter of 60%, wherein generally an upper limit of the strength can be 90 MPa, in particular also 70 MPa, and / or with a thermal shock resistance with at least one temperature jump and up to a maximum of three temperature jumps between at least 100 K and at most 1200 K and a damage parameter D between 0.15 and 0.

9.

9. Ceramic filter according to claim 7 or claim 8, comprising a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections can be arranged offset by an angle to one another with respect to a longitudinal axis of the ceramic filter, in particular such that a screw-like structure is or will be obtained with respect to the longitudinal axis.

10. Ceramic filter according to one of claims 7 to 9, comprising a plurality of sections, wherein at least two sections have the same non-periodic structure, wherein the at least two sections are arranged offset from one another with respect to an axis which encloses an angle of between more than 0 and less than 180°, preferably an angle of 90°, with a longitudinal axis of the ceramic filter.

11. Ceramic filter according to one of claims 7 to 10, wherein the foam pores have a pore size between 300 pm and 5 mm, preferably between 1.5 mm and 2.5 mm.

12. Ceramic filter according to one of claims 7 to 11, wherein the webs have an average thickness between 0.2 mm and 10 mm, preferably at most 8 mm, particularly preferably at most 5 mm, and / or wherein the webs have a tubular structure, and / or wherein the webs comprise web pores, wherein preferably the web pores have a web pore size between 30 pm and 300 pm.

13. Ceramic filter according to one of claims 7 to 12, wherein the ceramic filter comprises a ceramic comprising aluminum oxide as the main material and a secondary phase, wherein the ceramic is preferably free of P2O5 or contains max. 0.5 - 3.5% P2O5.

14. A method for producing a ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, preferably a ceramic filter according to one of claims 7 to 13, comprising the steps: - Providing a precursor for a filter, in particular a ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, preferably a precursor according to one of claims 1 to 6, - preferably providing a slip for a ceramic material, - preferably forming a precursor coated with a ceramic slip, the forming being carried out by means of an additive process, and - preferably firing the precursor coated with the ceramic slip to obtain a ceramic filter.

15. The method of claim 14, wherein providing the precursor comprises: providing a model of a cellular, preferably non-periodic, structure and forming a precursor.

16. The method of claim 14, wherein the step of providing a model of a cellular structure comprises: - scanning, preferably by means of computer tomography, a real structure of a foam, for example a biological foam or a plastic foam, to obtain a model of a cellular, non-periodic structure, - if necessary, scaling the model to the desired dimension of the preliminary stage, - if necessary, modify the real structure, for example in the form of non-uniform scaling, - Selecting a section of the real structure, - optionally subdividing the real structure into a plurality of mathematically defined units by means of a model and modifying the real structure to obtain a skeletonized structure, whereby the structure can be partially modified, for example, with regard to web diameters and / or other parameters, or - Selecting at least two different periodic structures, wherein a subdivision into mathematically defined units takes place and wherein the thickness and diameter of webs and / or cross-sections of foam pores are recorded and modified in the structures, wherein these are interlaced in such a way that random connection points result.

17. A method for producing a ceramic filter, in particular for filtering metal melts, in particular preferably aluminum melts, preferably a ceramic filter according to one of claims 7 to 13, preferably a method according to one of claims 14 to 16, wherein the production of the precursor is carried out by means of a polymer which comprises a filler, wherein the filler content of the polymer is preferably at least 50% by volume, and firing the precursor to obtain a ceramic filter.

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