TECHNOLOGICAL FIELD

Examples of the present disclosure relate to a ceramic foundry filter and a method of manufacturing the same. Some examples, though without prejudice to the foregoing, relate to a ceramic foam foundry filter for filtering molten metal, such as Steel, and a method of manufacturing the same.

BACKGROUND

Conventional ceramic foundry filters for filtering metal, e.g. such as Steel, are not always optimal. Typically, ceramic foundry filters for filtering Steel are made from a monolithic porous ceramic foam structure, whose ceramic material is made from Zirconia (Zr02 - Zirconium Dioxide). Such a conventional Zirconia based ceramic foam structure is typically formed by coating a Reticulated Polyurethane Foam (RPF) with a Zirconia based slurry. This is fired at a temperature of around 1 ,650 - 1 ,700°C. By contrast a conventional SiC, Silicon Carbide, based ceramic foam filter (formed by coating an RPF with a Silicon Carbide based slurry) is typically fired at around 1 ,200 °C.

The higher the firing temperature, the greater the degree of shrinkage of the resultant ceramic filter. Accordingly, a resultant conventional Zirconia based ceramic foam filter shrinks to a greater extent than an equivalent resultant conventional Silicon Carbide based ceramic foam filter (which is fired at a lower temperature). The degree of shrinkage of conventional Zirconia based ceramic foam filters can cause, not least, the following issues:

the resultant conventional Zirconia based ceramic foam filter may undergo asymmetric deformations or even crack due to shrinkage during the firing process. This may limit the transverse size/span of conventional Zirconia based ceramic foundry foam filters, e.g. typically to dimensions less than 200mm, a high manufacture rejection rate (e.g. of the order of 30%) of the resultant conventional Zirconia based ceramic foam filters, and the resultant conventional Zirconia based ceramic foam filter may have low fidelity to the initial shape/dimensions of the pre-fired porous filter structure (e.g. the pre-fired pore size may decrease during firing thereby increasing the pores per inch (PPI) of the resultant conventional Zirconia based ceramic foam filter. This can reduce the filter’s efficiency and prolong pouring time during a casting process by reducing the flow rate of the molten metal. This may slow the filtering process and could lead to the molten metal freezing during the casting process, e.g. in the filter or in the crucible during the casting process.

Furthermore, such high firing temperatures will increase energy consumption and manufacturing costs due to:

increased energy consumption required to reach such higher firing temperatures,

high grade equipment required, e.g. able to withstand the higher temperature (i.e. high temperature kilns),

longer manufacturing production time due to the longer time required to reach the required high temperature as well as cooling time thereafter,

increased amount of expensive raw materials (Zirconia) required. Due to the shrinkage, the density of the resultant Zirconia based ceramic foam filter increases. Also, due to the shrinkage, a larger pre-fired filter is required for a give sized post-fired filter. Hence there is an increased amount of raw material/Zirconia required to make a resultant conventional Zirconia based ceramic foam filter of a given size than would be the case if there were less shrinkage.

For such reasons as those set out above, conventional Zirconia based ceramic foam filters may be around 10 times as expensive as a conventional Silicon Carbide based ceramic foam filters. However, whilst a conventional Silicon Carbide based ceramic foam filter is suitable for filtering molten Iron, if is refractory characteristics are not as good as those of a conventional Zirconia based ceramic foam filter and a conventional Silicon Carbide (SiC) based ceramic foam filter is not optimally suitable for filtering molten Steel due to the higher temperatures involved.

It is useful to provide an improved ceramic foundry filter for filtering molten metal. One or more aspects/examples of the present disclosure may or may not at least partially address one or more of the background issues.

The listing or discussion of any prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge.

BRIEF SUMMARY

According to one or more examples of the disclosure there is provided a ceramic foundry filter for filtering molten metal, the filter comprising:

a filter structure made from a first refractory material, and

a coating, over the filter structure, of a second refractory material different to the first refractory material, wherein the second refractory material comprises Zirconium dioxide.

According to one or more examples of the disclosure there is provided a method of manufacturing a ceramic foundry filter, the method comprising: coating a filter structure made of a first refractory material in a mixture comprising a second refractory material, different to the first refractory material, wherein the second refractory material comprises Zirconium dioxide.

In certain examples, the ceramic foundry filter is a ceramic foam foundry filter. In certain examples, the ceramic foundry filter is for filtering molten Steel.

According to one or more examples of the disclosure there are provided examples as claimed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of various examples of the present disclosure that are useful for understanding the detailed description and certain embodiments of the invention, reference will now be made by way of example only to the accompanying drawings in which:

Figure 1 schematically illustrates an example of an apparatus according to the present disclosure;

Figure 2 schematically illustrates a further example of an apparatus according to the present disclosure;

Figure 3 schematically illustrates a method according to the present disclosure;

Figure 4 schematically illustrates a further method according to the present disclosure; and

Figure 5 schematically illustrates a yet further method according to the present disclosure;

The Figures are not necessarily to scale. Certain features and views of the figures may be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures may be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the Figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures.

DETAILED DESCRIPTION The Figures schematically illustrate a ceramic foundry filter 100 for filtering molten metal, no† leas† for example in a direct pour casting process. The filter 100 comprises:

a filter structure 101 made from a firs† refractory material 102, and a coating 103, over the filter structure 102, of a second refractory material 104 different†o the firs† refractory material 102, wherein the second refractory material 104 comprises Zirconium dioxide.

For the purposes of illustration and no† limitation, in some examples the filter structure may be a Silicon Carbide based ceramic foam filter structure (e.g. formed via coating an RPF in a Silicon Carbide slurry)†ha† is provided with a coating of a Zirconia based ceramic material †o thereby produce a composite, i.e. non-monoli†hic, ceramic foam filter having an internal Silicon Carbide based ceramic foam filter structure with an external layer/coating of Zirconia. The provision of such a filter structure may provide structural and mechanical support†o the Zirconia based coating layer. Since the Zirconia based layer need no† be self-supporting, this enables a thin coating of the Zirconia based coating layer†o be used (i.e. as compared†o a conventional monolithic Zirconia based ceramic foam filter) . This may provide several advantages, no† leas† such as reducing the firing temperature required †o manufacture the resultant composite Silicon Carbide and Zirconia ceramic foam filter, as well as reducing the amount of Zirconia raw material required.

The reduction in firing temperature advantageously may reduce the amount of shrinkage the resultant composite ceramic filter undergoes. Advantageously, this may reduce the amount of deformation/cracking - enabling larger ceramic filters†o be manufactured. This may also reduce the amount the resultant filter’s PPI increases - enabling an increase in filtering efficiency and flow rate as well as reduced risk of freezing. The reduced temperature requirement may also reduce the energy requirements and time scale†o manufacture the resultant filter as lower firing temperatures may be used and consequently heating/cooling times may be reduced. The reduced amount of shrinkage ye† further also additionally reduces the amount of Zirconia raw material requirement. All such benefits may help reduce manufacturing costs.

Ye† further, in some examples the resultant composite filter, i.e. a filter structure made from a firs† refractory material coated in a Zirconia based second refractory material, may provide improved structural strength and integrity (as compared†o a monolithic Zirconia based filter). The provision of such a composite filter may prevent the propagation of cracks in the body of the composite filter and hence reduce/preven† catastrophic failures/breakages of the composite filter, e.g. upon impact of a molten metal stream. In addition†o an increase in strength, a mode of failure of the composite filter may change, from a previously typical mode of breaking catastrophically into two or three pieces upon impact of the molten metal (as may be the case of previous monolithic filters),†o an entirely different mode of failure in which the damage caused by the impact of the molten metal†o the composite filter (having a Zirconium coating) is limited †o the area of impact only, e.g. the upper surface of the composite filter, leaving the res† of the composite filter intact. This may provide considerable advantages since it may reduce/preven† catastrophic failure and broken filter pieces from lodging themselves into the casting rendering the casting unusable, whilst reducing the thickness of the composite filter thereby improving flow rate, reducing pouring time and helping†o improve the casting quality.

Certain examples may be particularly advantageous as a ceramic foundry filter, e.g. such as a composite ceramic foam foundry filter, for filtering molten metal (no† leas†, for example, ferrous metals such as iron or steel or non- ferrous metals such as aluminium, copper, bronze, etc.) . Certain examples may be particular advantageous for filtering molten Steel e.g. in a direct pour casting process, where filters with high refractory qualities (i.e. superior †o those required for filtering molten Aluminium or Iron) as well as high structural s†reng†h/in†egri†y are required. Figure 1 focuses on the functional components necessary for describing an example of a ceramic foundry filter 100 according†o the present disclosure. The filter comprises a filter structure 101 made from a firs† refractory material 102. In this example, the filter structure is a porous filter structure comprising a plurality of open channels/pores/cells 101’. In this example, the filter structure is a ceramic foam filter structure, made of the first refractory material (such a filter structure being formed via coating a RPF in a slurry of the first refractory material and firing the same to produce the ceramic foam filter structure 101. [Where the first refractory material comprises Silicon Carbide, such a filter structure may correspond to a conventional Silicon Carbide ceramic foundry foam filter for filtering Iron]).

The filter structure 101 may define one or more external surfaces (e.g. related to the overall external shape and contours of the filter structure) and internal surfaces (e.g. of the internal channels/pores/cells of the filter structure). The filter structure may define: a first major surface (e.g. an upper/top external surface on to which molten metal to be filtered may be poured, thereby in effect functioning as a primary filtering surface), a second major surface (e.g. a lower/bottom external surface), one or more side surfaces (e.g. a circumferential or perimeter external surface), and/or one or more internal surfaces (e.g. inner surfaces of the open channels/pores/cells internal of the filter structure). The filter structure may be substantially planer in its shape/form factor.

The filter structure 101 is provided with a coating 103 of a second refractory material 104 different to the first refractory material, wherein the second refractory material comprises Zirconium dioxide. In this regard, the filter structure 101 serves as a substrate to the coating/covering layer of the second refractory material that coats/lines the substrate in a covering coating layer. The coating may seep, infuse and penetrate the filter structure so as to coat both internal as well as external surfaces of the filter structure 101. The coating may be provided to one or more of the surfaces of the filter structure (e.g. one or more of its: external surfaces, infernal surfaces, first major surface, second major surface, one or more side surfaces, and/or inner surfaces of the open channels/pores/cells internal of the filter structure) so as †o substantially coat/line the same in a covering coating layer.

The right-hand side portion of Figure 1 schematically illustrates a cross- secfional cut through a filament of the coated filter structure (that is schematically illustrated in the left-hand side portion of Figure 1 ). This shows a par† of the (internal) filter structure 101” made from the firs† refractory material 102 being coated in a layer 103 of the second refractory material 104 comprising Zirconia.

The Zirconia coating may comprises a coating layer having one or more of: > 40%, > 50%, > 60%, > 70%, > 80%, > 90% and > 95% Zirconium dioxide by weigh† of the coating layer.

Table 1 below provides non-limiting examples of various possible Zirconia coating layer constituents as a % by weigh† of the coating layer itself.

TABLE 1 - Zirconia coating layer constituents:

The filter 100 may provide, in effect a composife/non-monolifhic filter structure formed of two differing refractory materials, wherein the refractory material of the oufer/exfernal boundary layer coating comprises Zirconium Dioxide.

Figure 2 illustrates an alternative example of a ceramic foundry filter 200 according to the present disclosure. The filter 200 comprises a filter structure

201 made from a first refractory material 202. In this example, the filter structure is a planer member made of the first refractory material that comprises a plurality of apertures 201’ therethrough (such as a pressed, perforated, punctured or extruded disk of the first refractory material).

The filter structure 201 is provided with a coating 203 of a second refractory material 204 different to the first refractory material, wherein the second refractory material comprises Zirconium dioxide. In this regard, the filter structure 201 serves as a substrate to the coating/covering layer of the second refractory material. The coating may be provided to one or more of the external and internal surfaces of the filter structure 201.

The right-hand side portion of Figure 2 schematically illustrates a cross- sectional cut through of a portion of the coated filter structure 201 " (that is schematically illustrated in the left-hand side portion of Figure 2). This shows a part of the (internal) filter structure 201 made from the first refractory material

202 being coated in a layer 203 of the second refractory material 204 comprising Zirconia.

As used herein,“filter structure” is a structure that is configured, e.g. by virtue of its shape, dimensions and configuration, so as to effect separating of wanted material from unwanted material. For example, the filter structure may be a multi layered lattice comprising suitably dimensioned pores/apertures/passageways through which a filtrate may pass but which contaminate may be trapped (as per Figure 1 ). In other examples, the filter structure may be a single layered member with suitably dimensioned apertures therethrough acting as a sieve (as per Figure 2). In some examples, the filter structure may be a ceramic structure made from the firs† refractory material, i.e. a“pos†-fired” ceramic filter structure. The filter structure may be, for example, one or more of: a porous ceramic structure, a ceramic foam structure, an open cell ceramic foam structure, a ceramic member comprising a plurality of apertures, and a Silicon Carbide ceramic foam filter. In some examples (as per Figure 2), the filter structure may be a perforated disk.

In other examples, the filter structure may be a“pre-fired”, i.e. a precursor ceramic filter structure. The filter structure may be, for example, one or more of: a porous structure coated in the firs† refractory material, an open cell foam structure coated in the firs† refractory material, a reticulated foam structure coated in the firs† refractory material. In this regard, each of such precursor structures may serves as a substrate†o the coating/covering layer of the firs† refractory material. The coating of the firs† refractory material may seep, infuse and penetrate the precursor structure so as†o coa† both internal as well as external surfaces of the precursor structure. The coating of the firs† refractory material may be a coating of a slurry of the firs† refractory material. The slurry may be a mixture of a materials held in suspension in a liquid carrier medium / solvent (e.g. water or alcohol). The mixture comprising the ceramic material itself (i.e. in this case the firs† refractory material) along with other additives, no† leas† such as: rheological additives, suspension agent, binding agent (organic or inorganic binder), dispersion agent, starch and clay. In some particular examples, the filter structure is a reticulated polyurethane foam coated in a Silicon Carbide slurry. In some examples, the filter structure is a perforated disk made of the firs† refractory material.

The firs† refractory material may be any suitable refractory material, no† leas† for example: Silicon Carbide, Alumina or clay.

I† has been found†ha† the Zirconia coating adheres surprisingly well†o the filter structure made of a refractory material, no† leas† a firs† refractory material such as: Silicon Carbide, Silica, clay, Alumina (Aluminium Dioxide AI2O3).

Whilst reference is made†o the filter structure being made of/formed from the firs† refractory material, it is†o be appreciated†ha† the filter structure is no† necessarily purely made jus† of the firs† refractory material, bu††ha† other materials and additives may also be included. In some examples, the filter structure being made of/formed from the firs† refractory material relates†o the filter structure being predominately formed of the firs† refractory material, e.g. the firs† refractory material forms the greatest constituent of the refractory material/ceramic material of the filter structure.

Similarly, with regards†o references†o the coating being made of the second refractory material, namely Zirconia, it is†o be appreciated†ha† the coating is no† necessarily purely made jus† of the Zirconia, bu††ha† other materials, fillers, and additives may also be included, no† leas† for example: Alumina (AI2O3), Magnesium oxide (MGO), Calcium Oxide (CaO), Mullite, Y††ria / Yttrium Oxide (Y2O3), clay, Silica (S1O2), fused Zirconia Mullite. In some examples, references †o the Zirconia coating layer relate†o the coating layer being predominately formed of Zirconia, e.g. Zirconia forms the greatest constituent of the refractory material and/or ceramic material of the coating layer.

Figure 3 schematically illustrates a method 300 for use in manufacturing a foundry filter. In block 301 a filter structure, made of a firs† refractory material, is coated in a mixture comprising a second refractory material, different†o the firs† refractory material, wherein the second refractory material comprises Zirconium dioxide.

The filter structure is one or more of: a porous ceramic structure, a ceramic foam structure, an open cell ceramic foam structure, a ceramic member comprising a plurality of apertures, and a Silicon Carbide ceramic foam filter. In other examples, the filter structure is a pressed perforated ceramic disk, e.g. perforated†o provide a plurality of apertures†o provide filtering. The coating may be provided to one or more of the surfaces of the filter structure, e.g. one or more of its: external surfaces, infernal surfaces, first major surface, second major surface, one or more side surfaces, and/or internal surfaces of open channels/pores/cells internal of the filter structure. The coating may be via any appropriate coating technique, no† leas† for example: dipping, spraying and painting the Zirconium dioxide mixture onto the filtering structure, such †ha† a Zirconium dioxide based ceramic layer formed covering and providing an outer boundary layer†o the filtering structure formed of the firs† differing refractor material.

The mixture comprising Zirconium dioxide comprises one or more of: 10-90%, 20-80% and 45-75% Zirconium dioxide by weigh† of the mixture. The mixture may, for example be a slurry (e.g. a suspension of ceramic powdered precursor in a carrier, such as water,†ha† forms Zirconium dioxide when fired, or a suspension of Zirconium dioxide ceramic powder in a carrier) predominantly comprising Zirconium dioxide, albeit with additional materials and compounds, no† leas† one or more: rheological additive, suspension agent, binding agent (organic or inorganic binder), dispersion agent and starch. The slurry may also comprise one or more filler materials such as: Alumina, Mullite, Mullite Zirconia and fused Mullite Zirconia.

Table 2 below provides non-limiting examples of various possible Zirconia coating slurry constituents as a % by weigh† of the slurry itself.

TABLE 2 - Zirconia coating slurry constituents:

Figure 4 schematically illustrates a further method 400 for use in manufacturing a foundry filter. In block 301 a filter structure, made of a firs† refractory material, is coated in a mixture comprises Zirconium dioxide. In optional block 401 , the coated filter structure is dried. In block 402, the dried coated filter structure is fired. Optional block 401 may be omitted or combined with block 402. In firing block 402, the firing temperature may be up†o between: 1 ,200 - 1 ,500°C or 1 ,250-1 ,350°C. Advantageously, such a firing temperature is below that used for firing a conventional monolithic Zirconium dioxide based ceramic foundry foam filter.

Figure 5 schematically illustrates a yet further method 500 for use in manufacturing a foundry filter. In block 501 a filter structure if formed. The forming of the filter structure may comprise coating a structure in a first refractory material as indicated in block 502. The structure may be a precursor structure to the filtering structure and/or made from a non refractory material (i.e. that is burnt away during a subsequent firing process). In some examples, the structure is one or more of: a porous structure, an open cell foam structure, a reticulated foam structure, and a reticulated Polyurethane foam.

In optional block 503, the coated structure is dried to form the filtering structure. In optional block 504, the coated structure is fired. Optional drying block 503 may be omitted or combined with optional firing block 504. Optional firing block 504 may be omitted (i.e. the firing block 402 may be used in its place).

The duly formed filtering structure (being either a“pre-fired” filtering structure if optional firing block 504 is omitted, or a “post-fired” filtering structure if optional firing block 504 is carried out) then undergoes the process of blocks 301 , 401 and 402 as described above.

According to one aspect of the present disclosure, there is provided a foundry filter manufactured by any of the above described methods.

It will be understood that each block and combinations of blocks, can be implemented by various means, such as machines, hardware, firmware, and/or software including one or more computer program instructions. For example, one or more of the procedures described above may be embodied by computer program instructions for controlling a machine to perform the method actions. In this regard, the computer program instructions which embody the procedures described above may be stored by a memory storage device and performed by a processor.

Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. Accordingly, features described in relation to one example/aspect of the disclosure may include any or all of the features described in relation to another example/aspect of the disclosure, and vice versa, to the extent that they are not mutually inconsistent. Although various examples of the present disclosure have been described in the preceding paragraphs, if should be appreciated that modifications†o the examples given can be made without departing from the scope of the invention as set out in the claims. For example, whilst various examples of the filter have been discussed with respect†o ceramic foam filters, if is†o be appreciated that other examples of filters of the present disclosure need no† be ceramic foam filters, bu† could be, no† leas† for example, a ceramic member (such as a planer disk) comprising a plurality of apertures configures †o ac† as a filter. Whilst filtering with respect†o a direct pour casting process has been discussed above, it is †o be appreciated †ha† examples of the present disclosure could be used in other types of foundry filtering and/or casting processes, no† leas† for example a gating system of casting or die casting.

The term‘comprise’ is used in this document with an inclusive no† an exclusive meaning. That is any reference †o X comprising Y indicates †ha† X may comprise only one Y or may comprise more than one Y. If it is intended†o use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring†o“comprising only one ..." or by using“consisting”.

In this description, reference has been made †o various examples. The description of features or functions in relation†o an example indicates†ha† those features or functions are present in†ha† example. The use of the term ’example’ or‘for example’ or‘may’ in the†ex† denotes, whether explicitly stated or no†, †ha† such features or functions are present in a† leas† the described example, whether described as an example or no†, and†ha† they can be, bu† are no† necessarily, present in some or all other examples. Thus ‘example’,‘for example’ or‘may’ refers†o a particular instance in a class of examples. A property of the instance can be a property of only†ha† instance or a property of the class or a property of a sub-class of the class†ha† includes some bu† no† all of the instances in the class. In this description, references†o “a/ah/fhe” [feature, element, component, means ...] are †o be interpreted as “a† leas† one” [feature, element, component, means ...] unless explicitly stated otherwise.

Whilst endeavouring in the foregoing specification†o draw attention†o those features of examples of the present disclosure believed †o be of particular importance it should be understood†ha† the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred†o and/or shown in the drawings whether or no† particular emphasis has been placed thereon.

The examples of the present disclosure and the accompanying claims may be suitably combined in any manner apparent†o one of ordinary skill in the ar†.

Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Further, while the claims herein are provided as comprising specific dependencies, it is contemplated †ha† any claims may depend from any other claims and†ha††o the extent†ha† any alternative embodiments may result from combining, integrating, and/or omitting features of the various claims and/or changing dependencies of claims, any such alternative embodiments and their equivalents are also within the scope of the disclosure.