Methods and systems for manufacturing refractories

Abstract

A method 100 of manufacturing a refractory 204 for continuous casting, the method comprising; forming, via freeze casting, a precursor structure 201 of the refractory 204; impregnating the precursor 2

Description

TECHNOLOGICAL FIELD Examples of the disclosure relate to methods and systems for manufacturing refractories. Some examples, though without prejudice to the foregoing, relate to methods and systems of manufacturing refractories for continuing casting. BACKGROUND Refractories (e.g. such as Alumina / graphite refractories comprising Alumina and graphite ceramic material bonded with carbon) are specialized materials / items / objects that may be used in a continuous casting process (e.g. to line / protect various components of a continuous casting process - not least such as tundishes and molds). Certain examples of refractories may include, not least for example: tundish linings / impact pads, shrouds (e.g. ladle shrouds and subentry shrouds), and nozzles (e.g. subentry nozzles). Conventional methods and systems for manufacturing refractories in continuous casting are not always optimal. Typically, refractories for continuous casting are manufactured via isostatic pressing wherein a refractory is made from pressed ceramic material, which may be pressed / pressurized to a high pressure, e.g. such as of the order of 40,000 psi («2,800 kg / cm2). Manufacturing refractories via isostatic pressing may not be optimal. Refractories manufactured via isostatic pressing may have low thermal shock resistance and may require heating prior to use. Isostatic pressing imposes many restriction on isostatic mold design. Accordingly, a degree of design freedom for a refractory manufactured via isostatic pressing may be limited (for instance, feasible / viable shapes manufacturable via isostatic pressing may be limited and it may not be possible to form complex shapes). Refractory objects manufactured via isostatic pressing may have a poor net shape and, after forming a refractory object via isostatic pressing, machining may be required. The manufacturing of refractory objects via isostatic pressing may be a sensitive / non-robust process with a high level of rejects / failures of the resultant refractories. Isostatic molds may be expensive to manufacture. Establishing manufacturing facilities for isostatic pressing may require high investment capital. Refractory objects manufactured via isostatic pressing may be expensive to manufacture. In some circumstances it can be desirable to improve methods and systems for manufacturing refractories. 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. One or more aspects / examples of the present disclosure may or may not address one or more of the background issues. BRIEF SUMMARY According to various, but not necessarily all, examples of the present invention there are there are provided examples as claimed in the appended claims. Any examples and features described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention. According to various, but not necessarily all, examples there is provided a method of manufacturing a refractory for continuous casting, the method comprising: forming, via freeze casting, a precursor structure of the refractory; impregnating the precursor structure of the refractory with a carbon precursor; and pyrolysing the impregnated precursor structure of the refractory to form the refractory. According to various, but not necessarily all, examples there is provided a refractory manufactured in accordance with the above-mentioned method. According to various, but not necessarily all, examples there is provided: an Alumina / graphite refractory; a refractory object of a continuous casting process; a lining of a component of a continuous casting process a shroud, a ladle shroud; a submerged entry shroud; a nozzle; a submerged entry nozzle; and an impact pad for a tundish. manufactured in accordance with the above-mentioned method. According to various, but not necessarily all, embodiments there is provided one or more apparatuses or a system comprising means for performing at least part of one or more methods described herein. The following portion of this 'Brief Summary’ section describes various features that can be features of any of the examples described in the foregoing portion of the 'Brief Summary' section mutatis mutandis. In some but not necessarily all examples, forming the precursor structure via freeze casting comprises forming the precursor structure from a powder of a ceramic material mixed with a colloid of ceramic material. In some but not necessarily all examples, the precursor structure comprises at least one of the following: a green body ceramic structure of the refractory; and a porous ceramic structure. In some but not necessarily all examples, the precursor structure comprises at least one of the following: Alumina; Silica; Zirconia; Silicon Carbide; and Graphite. In some but not necessarily all examples, impregnating the precursor structure comprises at least one of the following: vacuum impregnating the precursor structure with the carbon precursor; pressure impregnating the precursor structure with the carbon precursor; and soaking the precursor structure with the carbon precursor. In some but not necessarily all examples the carbon precursor comprises at least one of the following: a solution-based organic precursor; an organic liquid precursor; an organic resin; an organic polymer; a liquid resin; a ceramic binder; and an antioxidant. In some but not necessarily all examples, the method further comprises carbonising the precursor structure to form the refractory, wherein the carbonising comprises: the impregnation of the precursor structure, and the pyrolysis of the impregnated precursor. In some but not necessarily all examples, the pyrolyzing comprises firing the impregnated precursor structure in an inert environment and / or a reduced atmosphere firing environment. In some but not necessarily all examples the refractory comprises at least one of the following: an Alumina / graphite refractory; a refractory object of a continuous casting process; a lining of a component of a continuous casting process a shroud, a ladle shroud; a submerged entry shroud; a nozzle; a submerged entry nozzle; and an impact pad for a tundish. While the above examples and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples can comprise any or all of the features described in respect of other examples, and vice versa. Also, it is to be appreciated that any one or more or all of the features, in any combination, may be comprised in / implemented by / performable by an apparatus or a method as desired, and as appropriate. Actions and / or functions described herein can be performed in any suitable way using any suitable method. The description of a function should additionally be considered to also disclose any means suitable for performing that function. The description of an action or a function should additionally be considered to also disclose any means suitable for performing that function and / or action. BRIEF DESCRIPTION OF THE DRAWINGS Some examples will now be described with reference to the accompanying drawings in which: FIG. 1 schematically illustrates a method in accordance with an example of the subject matter described herein. DETAILED DESCRIPTION FIG. 1 schematically illustrates a flow chart of an example of a method 100 of manufacturing a refractory 204 for continuous casting. The refractory 204 may be not least for example: an Alumina / graphite refractory (for instance, by way of example, consisting of: »70% Alumina, »20% Graphene, and »10% other / additives) a refractory object / item for continuous casting (e.g. continuous casting of metal such as steel, Aluminium or iron in foundries not least such as iron and steel foundries); a lining of a component of a continuous casting process (e.g. impact pad) a shroud (e.g. a ladle shroud and a submerged entry / subentry shroud), and a nozzle (e.g. a submerged entry / subentry nozzle). FIG. 1 can, in effect, be considered to illustrate a plurality of methods in the sense that FIG. 1 can be considered to illustrate one or more actions performed by / at a plurality of apparatuses / devices. FIG. 1 can therefore be considered to illustrate a plurality of individual methods performed by each respective individual apparatus / device of a system of a plurality of the apparatuses / devices. In block 101 of the method 100, a precursor structure 201 of the refractory is formed via a freeze casting process. Freeze casting, which can also be referred to as: ice-templating or freeze alignment, is a known / established method of forming a ceramic object. In the freeze casting process, a powderof a ceramic material (e.g. powdered Alumina AI2O3) may be mixed with colloid of a ceramic material (e.g. colloidal Silica SiO2) and the mixture may then be formed into a shape of the refractory and undergo a freeze casting process, e.g. via a freeze casting system / machine device, undergoing a freezing operation (that sets a shape of the structure) followed by a thawing operation (following which thee shape is retained) resulting in the formation of the refractory precursor structure 201. The freeze casting process of block 101 may be performed by one or more suitable devices / machines that are configured to perform the above-mentioned steps involved in the freeze casting process. Such devices / machines may thereby be considered as providing a freeze casting system for carrying out the freeze casting process of block 101 to form the refractory precursor structure 201. The refractory precursor structure 201 resulting from the freeze casting process of block 101 may be a low density and / or porous green body ceramic structure of the refractory. The refractory precursor structure may be made from / comprise at least one of the following: Alumina; Silica; Zirconia; Silicon Carbide; and Graphite. In block 102, the precursor refractory structure 201 is impregnated with a carbon precursor 202 to form an impregnated refractory precursor structure 203. It is to be appreciated that the precursor refractory structure may be impregnated with a carbon precursor via any appropriate impregnation technique, not least for example vacuum impregnation, pressure impregnation, soaking, spraying and / or bathing the precursor refractory structure with a carbon precursor such that the carbon precursor is forced / pushed / soaked into the various pores, internal pathways and interior of the precursor refractory structure so as to block, fill and / or seal the same. The carbon precursor may comprise at least one of the following: a solution-based organic precursor; an organic liquid precursor; an organic resin; an organic polymer; a liquid resin; a ceramic binder; and an antioxidant. The impregnation process of block 102 may be performed by one or more suitable devices / machines that are configured to perform the above-mentioned steps involved in the impregnation process. Such devices / machines may thereby be considered as providing an impregnation system for carrying out the impregnation process of block 102 to form the impregnated refractory precursor structure 203. In block 103, the impregnated precursor refractory structure 203 is pyrolised to form the resultant refractory 204. The pyrolyzing may comprise firing the impregnated precursor refractory structure 203 in an inert environment and / or a reduced atmosphere firing environment (i.e. firing the impregnated precursor refractory structure substantively in the absence of oxygen, e.g. a kiln firing environment where the amount of available oxygen is intentionally reduced). In this regard, the impregnated precursor refractory structure 203 is pyrolysed so as to form the refractory 204 in which the ceramic material of the impregnated precursor refractory structure has been sintered / fused / vitrified and the carbon material of the carbon precursor used to impregnated the precursor refractory structure has formed a network of carbon bonds internally and externally of the resultant refractory 204. The pyrolyzing process of block 103 may be performed by one or more suitable devices / machines that are configured to perform the above-mentioned steps involved in the pyrolyzing process. Such devices / machines may thereby be considered as providing a pyrolyzing system for carrying out the pyrolyzing process of block 103 to form the refractory 204. As schematically illustrated with respect to 104, the: impregnation of carbon 202 into the precursor refractory structure 201 in block 102 to form the impregnated precursor refractory structure 203, and the pyrolysis of the impregnated precursor refractory structure 204 in block 103 can effectively be considered as subjecting the freeze dried precursor refractory structure 201 to a carbonising procedure, i.e. forming a carbonaceous residue, so as to form the refractory 204. Typically, conventional ceramic objects made using a conventional freeze casting process result in porous / low density ceramic objects - which are unsuitable for use as refractories. However, in order to make objects formed via freeze casting suitable for use as refractories, the precursor structure resulting from the freeze casting process underdoes the carbonising process 104. In this regard, the porous / low density refractory precursor structure 201 may be formed into a high density refractory item 204 via the carbonising process 104 in which the pores of the porous / low density refractory precursor structure 201 are filled / blocked with the carbon pre-cursor to form a high density ceramic structure of the refractory. In certain particular examples, the precursor refractory structure could be pyrolysed at 900°C but the resultant ceramic structure post pyrolysis, i.e. the refractory, might be able to withstand temperatures of 1,700°C. The ability to use lower temperatures advantageously may reduce the amount of shrinkage that the precursor refractory structure undergoes. Advantageously, this may thereby reducing the amount of deformation and give rise to an improved net shape with a higher fidelity of the resultant ceramic object / refractory as compared to the initial precursor refractory structure. Furthermore, the reduced temperature requirements and resultant reduced amounts of shrinkage also reduces the risk of cracking and hence failures / rejects of the end / resultantly formed refractory. The reduced temperature requirement may also reduce the cost and timescales to manufacture refractories as high temperature kilns may not be required and heating / cooling times may be reduced. Yet further, the carbonising of the precursor refractory structure so as to introduce a network of carbon bonding therein may increase the structural strength and integrity as well as the rigidity and density of the resultant refractory. As used herein, a "precursor” may be used to refer to a substance from which another substance is formed, such as a carbon precursor via which, following carbonisation (e.g. in the pyrolysis of block 102), a network of carbon bonding is formed. The carbon precursor may, for instance, comprise a liquid resin, powdered carbon, a ceramic binder, a ceramic material, an antioxidant, and a rheological additive. In certain examples, the carbon precursor comprises a phenolic liquid resin, in other examples the carbon precursor may comprise a carbon slurry. The use of an antioxidant in the carbon precursor material may be particularly advantageous for forming the refractory (since the refractory is required to have high temperature resilience as well as a high degree of structural strength and integrity). The carbon in the network of carbon bonds in the resultant (post-pyrolysis) refractory may oxidise in temperatures in excess of 600°C in the present air. Thus, the use of antioxidants in the carbon precursor material can reduce such oxidisation and enable use of the resultant ceramic object temperatures in excess of 600°C in the presence of air. Carbonisation of the precursor refractory structure is also advantageous since carbon is non-wetting upon application of liquid / molten metals. The above described method of may provide a cheap and reliable technology to manufacture refractories for continuous casting (not least Alumina / graphite refractories "composite" refractories comprising ceramics - mainly Alumina and graphite - bonded with carbon), e.g. to replace similar refractories produced via iso-static pressing. Such refractories produced via iso-static pressing can be very expensive to make, and manufacturing facilities for the same can require huge capital investment to establish. Whereas, refractories manufactured according to the present disclosure may be more reliable manufactured (fewer rejects) cheaper to make, and manufacturing facilities for the same can require a much lower capital investment to establish as compared to iso-static pressing manufacturing facilities. Refractories manufactured according to the method 100 of FIG. 1 (i.e. involving freeze casting to form ceramic precursor refractory items followed by carbon impregnation and pyrolysis of the same to produce refractory items for continuous casting, e.g. of metals such as steel, Aluminium, or iron) may provide the following advantages: 1. Improved net shape forming where there may be no need for machining after forming. Refractories made via isostatic pressing are usually machined to produce uniform shapes - which can be expensive and can be a source of health hazards. 2. No need for heating prior to use because the refractories may have much more thermal shock resistance than refractories made via isostatic pressing. 3. Improved freedom in design of the refractories. Isostatic pressing imposes many restriction on mold design for isostatically pressed objects. 4. Cheaper molds (for the freeze casting) than isostatic molds. 5. Less sensitive process which means less rejects. 6. Manufacturing facilities for refractories can be built near steel mills rather than shipped for thousands of miles around the world. Refractories can be very heavy, and have to be packaged in very expensive boxes and complected packaging. 7. Capital investment for isostatic pressing facilities may be around £10-£20 million, while capital investment for freeze casting may be less than £0.1 Million. Various, but not necessarily all, examples of the present disclosure can take the form of a method, an apparatus, or a system. The component blocks of FIG. 1 are functional and the functions described can be performed by a single physical apparatus / device or a collection / system of apparatuses / devices duly configured to perform the described functionality. The blocks illustrated in FIG. 1 can represent actions in a method or functionality performed by an apparatus / system. It will be understood that each block and combinations of blocks illustrated in FIG. 1 as well as the further functionality described above, can be implemented by various means such as hardware / machines / devices, under control of software including one or more computer program instructions. For example, one or more of the functions described above can be performed by a duly configured apparatus or system comprising means for performing the above described functionality. Accordingly, the blocks support: combinations of means for performing the specified functions; and combinations of actions for performing the specified functions. It will also be understood that each block, and combinations of blocks, can be implemented by special purpose hardware-based systems which perform the specified functions or actions. Various, but not necessarily all, examples of the present disclosure provide both a method and corresponding apparatus comprising various modules or means that provide the functionality for performing / applying the actions of the method. The modules or means can be implemented as hardware. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Features described in the preceding description can be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions can be performable by other features whether described or not. Although features have been described with reference to certain examples, those features can also be present in other examples whether described or not. Accordingly, features described in relation to one example / aspect of the disclosure can 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, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as set out in the claims. The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X can comprise only one Y or can comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one...” or by using "consisting”. As used herein, a description of an action should also be considered to disclose enabling, and / or causing, and / or controlling that action. The term "means" as used in the description and in the claims may refer to one or more individual elements configured to perform the corresponding recited functionality or functionalities, or it may refer to several elements that perform such functionality or functionalities. Furthermore, several functionalities recited in the claims may be performed by the same individual means or the same combination of means. For example performing such functionality or functionalities may be caused in an apparatus by a processor that executes instructions stored in a memory of the apparatus. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or 'for example’, 'can’ or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some or all other examples. Thus 'example', 'for example’, 'can' or 'may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. In this description, references to "a / an / the" [feature, element, component, means ...] are used with an inclusive not an exclusive meaning and are to be interpreted as "at least one" [feature, element, component, means ...] unless explicitly stated otherwise. That is any reference to X comprising a / the Y indicates that X can comprise only one Y or can comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use 'a’ or 'the' with an exclusive meaning then it will be made clear in the context. In some circumstances the use of 'at least one’ or 'one or more' can be used to emphasise an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature (or combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative method features and structures which offer equivalent functionality to the specific examples of such method features and structures 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 method features and structures which provide equivalent functionality unless such alternative method features or structures are explicitly excluded in the above description of the examples of the present disclosure. The examples of the present disclosure and the accompanying claims can be suitably combined in any manner apparent to one of ordinary skill in the art. Separate references to an "example”, "in some examples” and / or the like in the description do not necessarily refer to the same example and are also not mutually exclusive unless so stated and / or except as will be readily apparent to those skilled in the art from the description. For instance, a feature, structure, process, block, step, action, or the like described in one example may also be included in other examples, but is not necessarily included. Whilst endeavouring in the foregoing specification to draw attention to those features of examples of the present disclosure believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present disclosure. Further, while the claims herein are provided as comprising specific dependencies, it is contemplated that any claims can depend from any other claims and that to the extent that any alternative embodiments can 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.

Claims

We claim:

1. A method of manufacturing a refractory for continuous casting, the method comprising:forming, via freeze casting, a precursor structure of the refractory;impregnating the precursor structure of the refractory with a carbon precursor; and pyrolysing the impregnated precursor structure of the refractory to form the refractory.

2. The method of any previous claim, wherein forming the precursor structure via freeze casting comprises forming the precursor structure from a powder of a ceramic material mixed with a colloid of ceramic material.

3. The method of any previous claim, wherein the precursor structure comprises at least one of the following:a green body ceramic structure of the refractory; anda porous ceramic structure.

4. The method of any previous claim, wherein the precursor structure comprises at least one of the following:Alumina;Silica;Zirconia;Silicon Carbide; andGraphite.

5. The method of any previous claim, wherein impregnating the precursor structure comprises at least one of the following:vacuum impregnating the precursor structure with the carbon precursor;pressure impregnating the precursor structure with the carbon precursor; and soaking the precursor structure with the carbon precursor.

6. The method of any previous claim, wherein the carbon precursor comprises at least one of the following:a solution-based organic precursor;an organic liquid precursor;an organic resin;an organic polymer;a liquid resin;a ceramic binder; andan antioxidant.

7. The method of any previous claim, further comprising carbonising the precursorstructure to form the refractory, wherein the carbonising comprises:the impregnation of the precursor structure, andthe pyrolysis of the impregnated precursor.

8. The method of any previous claim, wherein the pyrolyzing comprises firing the impregnated precursor structure in an inert environment and / or a reduced atmosphere firing environment.

9. The method of any previous claim, wherein the refractory comprises at least one of the following:an Alumina / graphite refractory;a refractory object of a continuous casting process;a lining of a component of a continuous casting processa shroud,a ladle shroud;a submerged entry shroud;a nozzle;a submerged entry nozzle; andan impact pad for a tundish.

10. A refractory for continuous casting manufactured in accordance with any of the previous method claims.

11. A system comprising means for performing any of the previous method claims.

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