Method of forming sealed refractory joints in metal-containment vessels, and vessels containing sealed joints

Abstract

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, e.g. a metal-contacting trough. The method involves introducing a mesh body made of metal wires into a gap between metal-contacting surfaces of adjacent refractory sections of a vessel so that the mesh body is positioned beneath the metal conveying surfaces, and covering the mesh body with a layer of moldable refractory material to seal the gap between the metal-contacting surfaces. Other embodiments relate to a vessel formed by the method and a vessel section with a pre-positioned mesh body suitable for preparing a sealed joint with other such sections.

Claims

1. A vessel for containing molten metal, the vessel formed by two or more refractory vessel sections positioned end to end, wherein each section is formed of a respective section body that is a monolithic trough-shaped part, wherein the vessel includes a sealed joint between adjacent ends of the sections, wherein the sealed joint comprises: a gap between the adjacent vessel sections; a groove within the gap and that extends at least across a bottom of the trough shape of one of the adjacent vessel sections; a mesh body made of metal wires introduced into the gap and located within the groove; 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 vessel sections, wherein the mesh body prevents the moldable refractory material from penetrating further in the gap than a lower surface of the groove.

2. The vessel of claim 1, wherein the mesh body contains a quantity of refractory paste.

3. The vessel of claim 1, wherein the metal used to form the mesh body is resistant to attack by molten aluminum.

4. The vessel of claim 1, wherein the metal used to form the mesh body is chosen from the group consisting of NiCr based alloys, stainless steel and titanium.

5. The vessel of claim 1, wherein the metal wires are woven together to form a woven metal fabric for the mesh body.

6. The vessel of claim 5, wherein the woven metal fabric has mesh openings having dimensions small enough to resist penetration by molten metal.

7. The vessel of claim 6, wherein the mesh openings have a size in a range of 1 to 5 mm.

8. The vessel of claim 6, wherein the mesh openings have a size in a range of 2 to 3 mm.

9. The vessel of claim 1, wherein the mesh body has a plurality of layers laid one over another.

10. The vessel of claim 9, wherein the layers of woven metal mesh are rolled up over each other to form an elongated rope.

11. The vessel of claim 10, wherein the elongated rope is covered with a woven tubular sleeve made of metal.

12. The vessel of claim 11, wherein the layers of woven metal mesh have mesh openings, and wherein the woven tubular sleeve has mesh openings of the same size or a smaller size than the mesh openings of the one or more layers.

13. The vessel of claim 1, wherein the moldable refractory material is selected from the group consisting of materials made of silica/alumina and pastes containing aluminosilicate fibers.

14. The vessel of claim 1, wherein the refractory vessel sections have a molten metal-contacting surface formed therein, and wherein the groove is located beneath the molten metal-contacting surface.

15. The vessel of claim 14, wherein the mesh body has an uncompressed width wider than the width of the groove.

16. A vessel section for a metal containment vessel, the vessel section comprising a body defining a monolithic trough-shaped part of refractory material and having a metal-contacting surface formed therein, and having a transverse groove at one end of the body, the transverse groove extending across at least the bottom of the trough and having a metal mesh rope pre-positioned in the transverse groove leaving room in the transverse groove for an overlying coating of a moldable refractory material, wherein when vessel sections are placed end to end, the transverse groove is within a gap between the adjacent vessel sections and the metal mesh rope in the transverse groove prevents the moldable refractory material from penetrating further in the gap than a lower surface of the transverse groove.

17. The vessel section of claim 16, wherein the transverse groove extends at least across a bottom of the trough shape of the vessel section.

18. The vessel section of claim 16, wherein at least one of: the metal used to form the metal mesh rope is resistant to attack by molten aluminum; the metal used to form the metal mesh rope is chosen from the group consisting of NiCr based alloys, stainless steel and titanium; the metal mesh rope includes metal wires woven together to form a woven metal fabric having mesh openings with dimensions small enough to resist penetration by molten metal; the metal mesh rope has a plurality of layers laid one over another; the metal mesh rope is covered with a woven tubular sleeve made of metal; the transverse groove is located beneath the metal-contacting surface; or the metal mesh rope has an uncompressed width wider than the width of the transverse groove.

19. A vessel section for a metal containment vessel, the vessel section comprising a body of refractory material and having a metal-contacting surface formed therein, and having a transverse groove at one end of the body, the transverse groove extending at least across a bottom of a trough shape of the vessel section and having a metal mesh rope pre-positioned in the transverse groove leaving room in the transverse groove for an overlying coating of a moldable refractory material, wherein when vessel sections are placed end to end, the transverse groove is within a gap between the adjacent vessel sections and the metal mesh rope in the transverse groove prevents the moldable refractory material from penetrating further in the gap than a lower surface of the transverse groove.

20. The vessel of claim 19, wherein at least one of: the metal used to form the metal mesh rope is resistant to attack by molten aluminum; the metal used to form the metal mesh rope is chosen from the group consisting of NiCr based alloys, stainless steel and titanium; the metal mesh rope includes metal wires woven together to form a woven metal fabric having mesh openings with dimensions small enough to resist penetration by molten metal; the metal mesh rope has a plurality of layers laid one over another; the metal mesh rope is covered with a woven tubular sleeve made of metal; the transverse groove is located beneath the metal-contacting surface; or the metal mesh rope has an uncompressed width wider than the width of the transverse groove.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a refractory trough section having a groove at one end suitable for forming a sealed joint;

(2) FIG. 2 is an end view of the trough section of FIG. 1 showing the end having the groove formed therein;

(3) FIG. 3 is top plan view of the abutting ends of two trough sections of the kind shown in FIGS. 1 and 2 having a sealed joint formed there-between;

(4) FIG. 4 is a transverse cross-section of the sealed joint of FIG. 3 taken on the line IV-IV showing the internal construction of the joint;

(5) FIG. 5 is a longitudinal cross-section of one type of sealed joint formed between adjacent trough sections;

(6) FIG. 6 is a longitudinal cross-section similar to that of FIG. 5 but showing an alternative type of joint formed between adjacent trough sections;

(7) FIG. 7 is a longitudinal cross-section similar to that of FIG. 5 but showing a further alternative type of joint formed between adjacent trough sections;

(8) FIG. 8 is an enlarged view of a woven mesh layer suitable for use in exemplary embodiments;

(9) FIG. 9 is a top plan view of the woven layer of FIG. 8 showing the tubular nature of the woven layer;

(10) FIG. 10 is an end view of a rolled-up bundle formed from the tubular woven piece of FIGS. 8 and 9; and

(11) FIG. 11 is a side view of the bundle of FIG. 10 showing how the bundle may be covered by a tubular woven sleeve to keep the bundle together and form a flexible rope.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(12) FIGS. 1 and 2 of the accompanying drawings show one section 10A of a molten metal-containment vessel in the form of an elongated metal-conveying trough 10 (see FIG. 3). The trough 10 is formed by positioning two or more such sections end to end to create a trough of any desired length. Although not shown in these views, the sections are normally held within an open-topped metal casing of a molten metal containment or distribution structure, so that the sections are held by the casing against relative movement and are protected from damage. The section 10A has a U-shaped channel 11 formed by an inner channel surface 12. In use, the channel 11 is partially filled with molten metal up to a maximum level 14 (FIG. 2) as the molten metal is conveyed through the trough. The parts 12A of the surface 12 below the level 14 are thus in contact with molten metal during use of the apparatus and form molten metal-contacting surfaces. The trough section is formed by a body 15 which is a solid cast block of refractory material having resistance to both heat and attack by molten metal. For example, the body may be made of any one of the refractory materials exemplified earlier provided they may be shaped and formed into a suitable vessel section. Particularly preferred are alumina, silicon carbide, nitride-bonded silicon carbide (NBCS), fused silica, and combinations of these materials. One longitudinal end 16 of the trough section is provided with an enlarged groove 17 of rectangular cross-section that extends into the body 15 of the trough section from the inner surface 12 and runs completely from one side of the trough section to the other. When two such trough sections are placed in longitudinal alignment, with one grooved end adjacent to a non-grooved end, the groove 17 is closed on all sides except at the inner surface 12. As an alternative, each end of the trough section 10 may be provided with a half-width groove so that a groove 17 of full width is formed between such trough sections when the grooved ends are positioned together. This latter alternative has the advantage that the remainder of the gap between trough sections (i.e. the part below the groove 17) is positioned immediately under the centerline of the groove, rather than at one side thereof, and is therefore more protected against leakage for reasons that will become apparent below.

(13) FIGS. 3 and 4 show adjoining parts of two trough sections 10A and 10B. These sections are positioned end to end and are provided with a sealed joint 24 according to one preferred exemplary embodiment. FIG. 3 is a plan view from the top and FIG. 4 is a cross-section along the line IV-IV of FIG. 3. Rectangular groove 17 is filled with and sealed by a combination of a metal mesh body in the form of a flexible, compressible rope 20, and a moldable refractory paste 21. A smooth surface 22 is preferably formed from paste 21 at the outer surface of the groove 17, at least in the region of the surface part 12A of the trough section that contacts molten metal during use. This assures a smooth laminar flow of metal over sealed joint 24 and thereby reduces erosion.

(14) Examples of different ways in which the joint can be formed are illustrated in FIGS. 5, 6 and 7. As shown in FIG. 5, metal mesh rope 20 is first inserted into the groove 17 and pushed to the bottom of the groove, for example by means of a hand-tool such as a blunt chisel or thin tamping device (not shown). The metal mesh rope 20 is then covered by a layer of the moldable refractory material 21 pushed into the groove and made smooth at surface 22 by means of a hand-tool such as a trowel (not shown). The metal mesh of the rope should preferably not be exposed at the surface 22 and is preferably covered by a layer of the refractory paste having a thickness of up to 1.9 cm ( inch). The moldable refractory material 21 is then allowed to dry, harden and possibly cure before the trough sections are used to convey molten metal (as represented by arrow 25). The trough sections 10A and 10B are supported above an electrical heating element 26 within an outer metal casing (not shown), although heating elements of the same kind may alternatively or additionally be provided along the sides of the trough section. The metal mesh rope 20 extends horizontally completely across the groove 17, as does the moldable refractory material 21, so that molten metal cannot penetrate into the groove 17 and down into the gap 27 between the adjacent trough sections 10A and 10B. The heating element 26 is therefore protected from contact with molten metal from the interior of the trough and is thus protected from damage and degradation by the metal. The moldable refractory material 21 adheres to the metal mesh rope 20 as it dries and cures so that the metal mesh provides a durable support and reinforcement for the moldable refractory material 21. This allows the use of a softer and more flexible moldable refractory material than would be the case if the groove had to be filled solely with a moldable refractory material itself. The metal mesh also allows the sealed joint 24 to expand and contract with heating cycles and also allows the moldable refractory material 21 to expand and contract in the same way, thus minimizing the likelihood of cracking. However, should the moldable refractory material 21 develop a crack or fissure, molten metal from the trough section will not penetrate far into the groove 17 because the metal mesh body of the rope 20 resists such penetration, especially if the mesh size of the metal mesh is relatively small, e.g. 1-5 mm and more preferably 2-3 mm, or smaller, so that the molten metal meniscus bridges the mesh openings and resists metal penetration. Penetration is also discouraged if the body is made up of two or more layers so that a tortuous or convoluted path through the body must be taken by the molten metal if it is to fully penetrate the rope 20.

(15) In the embodiment of FIG. 6, the metal mesh rope 20 is first impregnated with a moldable refractory paste material 28, which may be the same as or different from the moldable refractory material 21 employed above the rope. The impregnation of the paste into the metal mesh rope can be done, for example, by providing a flat strip of woven mesh material, working the moldable refractory paste 28 into the mesh openings, and then rolling the flat strip into a roll to form the rope 20. The refractory-impregnated rope is then used in the same way as that of FIG. 5 to form a sealed joint 24. The refractory paste impregnated into the rope in the embodiment of FIG. 6 introduces more refractory material into the joint, and allows for better adhesion of the rope with the moldable refractory 21 and also with the sides and the bottom of the groove 17. In both embodiments of FIGS. 5 and 6, an amount of moldable refractory material may, if desired, be worked into the groove 17 before the rope 20 is inserted in order to provide a layer of refractory material beneath the rope 20. While such an arrangement is not shown in FIGS. 5 and 6, it is illustrated in FIG. 4.

(16) A further exemplary embodiment is shown in FIG. 7. In this embodiment, a groove 17 is formed by two semi-cylindrical depressions 17A and 17B formed, respectively, in end faces of trough sections 10A and 10B. The rope 20 is inserted into the groove 17 when the trough 10 is assembled from sections 10A and 10B, and it is almost completely enclosed within the bodies of the trough sections, except for the gap 27 between the trough sections (which is preferably kept as small as possible). The gap above the groove is then filled with a moldable refractory material 21. Preferably, the refractory material is made to penetrate deeply into the gap to enter the groove 17 and contact the metal mesh rope 20, at least at the top thereof. However, the refractory material may merely fill the gap above the groove 17, thus sealing the trough against metal penetration. By locating the groove 17 below the metal-contacting surfaces of the trough sections, the gap required to be filled with the refractory paste is minimized and cracks are less likely to develop and to propagate through this material. Any molten metal that does penetrate into the groove 17 has to pass through the rope 20 before it reaches the lower parts of gap 27 and, as indicated above, the characteristics of the rope make such penetration difficult and unlikely.

(17) The metal mesh rope 20 may be any kind of metal mesh piece or body, but is preferably of a kind as shown in FIGS. 8 to 11 of the accompanying drawings. A thin flexible metal wire 30 may be woven to form an open-weave fabric using a simple warp and weft arranged at right angles, but is preferably woven with open circular loops 31 as shown in FIG. 8 to form a woven piece 32. The woven piece may be made with any suitable dimensions, but is preferably woven in the form of a tube 33 as shown in FIG. 9 of any suitable axial length between the open ends of the tube. The woven tube may then be flattened as represented by the arrows in FIG. 9, and then, starting from one open end of the flattened tube, the woven piece may be rolled up to form a tubular bundle 34 as shown in FIG. 10 (although the winding of the tubular bundle is generally much tighter than illustrated). If still greater bulk is required, two or more flattened woven tubes may be wound together to form the bundle. As shown in FIG. 11, the tubular bundle 34 is preferably covered by a tubular woven metal sleeve 35 to hold the bundle together and to form the rope 20 used in the manner shown in the earlier embodiments, e.g. as shown in FIG. 5. A rope of this kind preferably has a thickness (diameter) of 5 mm to 1.9 cm ( 3/16 inch to inch). The woven tubular sleeve 35 preferably has mesh openings of the same size or smaller than those of the layers forming the tubular bundle 34. The tubular sleeve 35 prevents the bundle 34 from unrolling but maintains the flexible nature of the bundle. If a rope 20 of the kind shown in FIG. 6 is required, i.e. a rope impregnated with moldable refractory paste, the bundle 34 of FIG. 10 may be unrolled and the moldable refractory paste worked into the mesh. The bundle may then be re-rolled and used in this form, or even with the outer sleeve 35 re-applied (if the greater dimension resulting from the included moldable refractory paste permits such re-use). Woven metal products of this kind may be obtained, for example, from Davlyn corporation of Spring City, Pa. 19475, USA. A particularly preferred product from Davlyn is a 1 cm ( inch) flexible mesh cable having a construction similar to that shown in FIGS. 8 to 11. The wire is made of Inconel, which is an NiCr based alloy. This alloy is particularly resistant to high temperatures and is especially suitable for sealing the joints of externally-heated trough sections designed to reach high temperatures, e.g. up to about 900 C. There is also a version of the product that is made of stainless steel, which is more suitable for unheated troughs where the only source of heat is the molten metal itself.

(18) 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.

(19) 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.

(20) 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.

(21) 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.

(22) 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.