This invention relates to molten metal containment structures used for conveying, treating or holding molten metals, particularly such structures incorporating refractory or ceramic molten metal-containing vessels made from or including two or more pieces or sections. More particularly, the invention relates to methods of providing sealed joints between such pieces or sections to prevent leakage of molten metals from the vessels at the joints.
Molten metal containment vessels, e.g. metal-conveying troughs and launders, are often employed during metal treatment or casting operations and the like, for example to convey molten metal from one location, such as a metal melting furnace, to another location, such as a casting mold or casting table. In other operations, such vessels are used for metal treatments, such as metal filtering, metal degassing or metal transportation. Vessels of this kind are often constructed from two or more shaped sections made of refractory and/or ceramic materials that are resistant to high temperatures and to degradation by the molten metals intended to be contained therein. The vessel sections are brought into close mutual contact and may be held within an outer metal casing or the like provided for support, proper alignment and protection against damage. Sometimes, such vessels are provided with sources of heat to ensure that the molten metals do not cool unduly or solidify as they are held within the vessels. The sources of heat may be electrical heating elements positioned above or beneath the vessels or enclosures for conveying hot fluids (e.g. combustion gases) along the inner or outer surfaces of the vessels.
It is of course important to ensure that molten metal does not leak out of the vessels at the interface between two abutting sections, whether the vessels are heated or not. However, it is especially important to avoid metal leakage when sources of heat for the vessel are provided because the molten metal may cause catastrophic damage to electrical heating elements or other heating means. It is therefore usual to provide a sealed joint between adjacent vessel sections, e.g. by providing a layer of refractory paper between the adjacent sections to accommodate thermal expansion or contraction. A refractory sealant may also be forced into the gap between abutting surfaces of adjacent sections. It is also known to provide sections with a surface groove spanning the abutting sections and to fill the groove with a refractory rope covered with a moldable refractory sealant to fill the joint and to form a smooth interconnecting surface between the vessel sections. However, all such joints deteriorate with time and use due to thermal cycling, especially when used in heated vessels, and the joints eventually allow a direct leak path to appear between the vessel sections.
There is therefore a need for further ways of providing sealed joints for metal-holding and metal-containment vessels.
An exemplary embodiment of the invention provides a method of preparing a reinforced refractory joint between refractory sections of a vessel used for containing or conveying molten metal. The method comprises introducing a mesh body made of metal wires (preferably of a metal that is resistant to attack by the molten metal contained in the vessel) into a gap between metal-contacting surfaces of adjacent refractory sections of the vessel so that the mesh body is positioned beneath the metal-contacting surfaces, and covering the mesh body with a layer of moldable refractory material (preferably in the form of a malleable paste) to seal the gap between the metal-contacting surfaces.
The mesh body forms a flexible and compressible support for the moldable refractory material. Furthermore, in case the refractory material becomes cracked or broken, the mesh body holds the pieces in place and maintains the joint seal. The mesh body preferably has mesh openings of a size (e.g. 1-5 mm, more preferably 2-3 mm) that resist penetration by the molten metal due to surface tension forces (metal meniscus or wetting angle), and also a thickness or number of layers that creates a tortuous or convoluted path for any molten metal that does penetrate the surface of the mesh body, thereby making penetration completely through the mesh body unlikely. It is also advantageous to employ a metal for the mesh body that is not easily wetted by the molten metal, i.e. it may be less than fully wetted. Although completely non-wetted metals would be desirable, they may not have the other desirable characteristics, e.g. resistance to attack by the molten metal.
Preferably, an enlarged groove is formed in or close to a metal-contacting surface of at least one of the vessel sections to form part of the gap between the adjacent the sections. Such a groove provides a positive location for the mesh body and, without such a groove, the gap between the sections has to be made large enough to provide space for the mesh body. The groove may be formed so that the sides of the groove are closer together than the diameter or width of the mesh body, whether the mesh body is used with or without impregnating refractory paste. Advantageously, the width of the groove is 0 to 15% narrower than the nominal (uncompressed) width of the mesh body prior to its insertion into the groove, although the groove may preferably have a width in a range of up to 15% wider or up to 50% narrower than the width of the mesh body (or, expressed in the alternative, the uncompressed width of the mesh body is preferably 0 to 15% wider than the width of the groove, etc.). The groove is typically incorporated into the vessel section as it is cast, or may be ground or cut into the end region of a trough section already formed, e.g. at the time of installation or repair of the vessel. The groove may be made rectangular (including square), part-circular or of any other desired profile. The groove may be located at the metal-contacting surface or beneath it buried within the gap. In the latter case, the mesh body is virtually fully enclosed within the groove on all sides, except at the gap, and the moldable refractory paste is used to seal the gap above the mesh body, but may or may not actually contact the mesh body. Moreover, the groove may be located entirely within one of the vessel sections or, alternatively, parts of the groove may be formed in both sections of an adjoining pair so that the sections line up to form the groove when the vessel is assembled.
In one embodiment, a quantity of moldable refractory material in the form of a to paste is worked into the mesh body before the mesh body is introduced into the gap between the adjacent refractory sections.
According to another exemplary embodiment of the invention, there is provided a vessel for containing molten metal formed by two or more refractory vessel sections positioned end to end having a sealed joint between adjacent ends of the vessel sections. The sealed joints comprise a mesh body made of metal wires introduced into a gap between the adjacent vessel sections, and a layer of moldable refractory material overlying the mesh body in the gap and sealing the gap against molten metal penetration between the refractory sections. The mesh body itself may contain a quantity of refractory paste.
According to yet another exemplary embodiment, there is provided a vessel section for a molten metal containing vessel, the vessel section comprising a body of refractory material having a metal-conveying channel formed therein, and having a transverse groove at one end of the body, the groove having a metal mesh rope pre-positioned in the groove leaving room in the groove for an overlying coating of a moldable refractory material.
Preferably the vessel is shaped and dimensioned for use as an elongated metal-conveying trough having a channel formed therein, or as a container for a molten metal filter, a container for a molten metal degasser, a crucible, or the like.
The vessel is normally intended for containing molten aluminum and aluminum alloys, but could be used for containing other molten metals, particularly those having similar melting points to aluminum, e.g. magnesium, lead, tin and zinc (which have lower melting points than aluminum) and copper and gold (that have higher melting points than aluminum). Preferably, for a particular molten metal intended to be contained or conveyed, a metal should be chosen for the mesh that is unreactive with that particular molten metal, or that is at least sufficiently unreactive that limited contact with the molten metal would not cause excessive erosion or absorption of the mesh. Titanium is a good choice for molten aluminum, but has the disadvantage of high cost. Less expensive alternatives include, but are not limited to, Ni—Cr alloys (e.g. Inconel®) and stainless steel.
When the vessel is a trough, the trough may have an open metal-conveying channel that extends into the body of the trough or trough section from an upper surface. Alternatively, the channel may be entirely enclosed by the body, e.g. in the form of a tubular hole passing through the body of the trough from one end to the other.
Although the sealed joint of the exemplary embodiments may be formed just between metal-contacting surfaces of adjacent vessel sections, the joint may alternatively be formed between all parts of adjacent trough sections.
The sealed joint of the exemplary embodiments may be formed between vessel sections, e.g. trough sections, that are either heated or unheated. If heated trough sections are joined in this way, they may form part of a heated trough structure according to U.S. Pat. No. 6,973,955 issued to Tingey et al. on Dec. 13, 2005, or pending U.S. patent application Ser. No. 12/002,989, published on Jul. 10, 2008 under publication no. US 2008/0163999 to Hymas et al. (the disclosures of which patent and patent application are specifically incorporated herein by this reference). The patent to Tingey et al. provides electrical heating from below and from the sides, and the patent application to Hymas et al. provides heating by means of circulating combustion gases. In still further alternative embodiments, heating means may be located inside or above the refractory vessel itself.
The term “refractory material” as used herein to refer to metal containment vessels is intended to include all materials that are relatively resistant to attack by molten metals and that are capable of retaining their strength at the high temperatures contemplated for the vessels. Such materials include, but are not limited to, ceramic materials (inorganic non-metallic solids and heat-resistant glasses) and non-metals. A non-limiting list of suitable materials includes the following: the oxides of aluminum (alumina), silicon (silica, particularly fused silica), magnesium (magnesia), calcium (lime), to zirconium (zirconia), boron (boron oxide); metal carbides, borides, nitrides, silicides, such as silicon carbide, particularly nitride-bonded silicon carbide (SiC/Si3N4), boron carbide, boron nitride; aluminosilicates, e.g. calcium aluminum silicate; composite materials (e.g. composites of oxides and non-oxides); glasses, including machinable glasses; mineral wools of fibers or mixtures thereof; carbon or graphite; and the like.
Examples of different ways in which the joint can be formed are illustrated in
In the embodiment of
A further exemplary embodiment is shown in
The metal mesh rope 20 may be any kind of metal mesh piece or body, but is preferably of a kind as shown in
The moldable refractory paste 21 used in the exemplary embodiments may be any kind of paste made of a refractory material that hardens and is resistant to attack and abrasion by molten metal. The paste may be, for example, a commercially available product commonly used for refractory repair, e.g. an alumina/silica paste such as Pyroform EZ Fill® sold by Rex Materials Group of P.O. Box 980, 5600 E. Grand River Ave., Fowlerville, Mich. 48836, U.S.A., or a paste containing aluminosilicate fibers such as Fiberfrax LDS Pumpable® sold by Unifrax LLC, Corporate Headquarters, 2351 Whirlpool Street, Niagara Falls, N.Y., U.S.A. Such materials should be used according to the manufacturers' instructions, and are generally cured with an external added heat source (such as a gas burner) or by using the heat provided by the trough itself when put into use. The EZ fill product cures to form a solid and relatively brittle final mass, but the metal mesh body prevents the mass from forming a continuous crack all the way through the joint. The LDS Pumpable material cures to form a more fibrous and flexible mass and the metal mesh body helps it to retain sufficient solidity to resist erosion by the molten metal. The softness of the mass allows it to accommodate some of the thermal expansion and contraction of the trough. While the above materials are preferred, pastes of any of the refractory materials exemplified earlier may be use when the can be obtained in moldable paste form.
When sealed joints are formed according to the methods of the exemplary embodiments, the joints can be easily removed by breaking through the upper layer of molded refractory material and then removing the metal mesh rope filling. This allows a trough section, even a central section, to be removed from an operational trough when necessary for maintenance or repair. The trough section may then be returned to the trough or replaced and the joint re-formed in the indicated manner.
It is also possible to pre-prepare trough sections with metal mesh ropes installed in end grooves and held in place, e.g. by means of a thin underlayer of moldable refractory paste. When such a trough section is used, it may simply be positioned end to end with other trough sections and then the joints completed by filling them in with the moldable refractory paste and smoothing off the joint surface.
In the above embodiments, the trough 10 may be an elongated molten metal trough of the kind used in molten metal distribution systems suitable for conveying molten metal from one location (e.g. a metal melting furnace) to another location (e.g. a casting mold or casting table). However, according to other exemplary embodiments, other kinds of metal containment and distribution vessels may employed, e.g. as in-line ceramic filters (e.g. ceramic foam filters) used for filtering particulates out of a molten metal stream as it flows, for example, from a metal melting furnace to a casting table. In such cases, the vessel includes a channel for conveying molten metal and a filter positioned in the channel. Examples of such vessels and molten metal containment systems are disclosed in U.S. Pat. No. 5,673,902 which issued to Aubrey et al. on Oct. 7, 1997, and PCT publication no. WO 2006/110974 A1 published on Oct. 26, 2006. The disclosures of the aforesaid U.S. patent and PCT publication are specifically incorporated herein by this reference.
In another exemplary embodiment, the vessel acts as a container in which molten metal is degassed, e.g. as in a so-called “Alcan compact metal degasser” as disclosed in PCT patent publication WO 95/21273 published on Aug. 10, 1995 (the disclosure of which is incorporated herein by reference). The degassing operation removes hydrogen and other impurities from a molten metal stream as it travels from a furnace to a casting table. Such a vessel includes an internal volume for molten metal containment into which rotatable degasser impellers project from above. The vessel may be used for batch processing, or it may be part of a metal distribution system attached to metal conveying vessels. In general, the vessel may be any refractory metal containment vessel positioned within a metal casing. The vessel may also be designed as a refractory ceramic crucible for containing large bodies of molten metal for transport from one location to another. All such alternative vessels may be used with the exemplary embodiments of the invention provided they are made of two or more sections that are joined end-to-end.
This application is a divisional of U.S. patent application Ser. No. 12/928,353, filed Dec. 8, 2010 and entitled “METHOD OF FORMING SEALED REFRACTORY JOINTS IN METAL-CONTAINMENT VESSELS, AND VESSELS CONTAINING SEALED JOINTS,” which claims the priority right of prior U.S. provisional patent application Ser. No. 61/283,886 filed Dec. 10, 2009 entitled “METHOD OF FORMING SEALED REFRACTORY JOINTS IN METAL-CONTAINMENT VESSELS, AND VESSELS CONTAINING SEALED JOINTS.” The entire contents of each are incorporated herein for all purposes by this reference.
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Number | Date | Country | |
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Number | Date | Country | |
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Number | Date | Country | |
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Parent | 12928353 | Dec 2010 | US |
Child | 15164100 | US |