Patent Application
20190212059
The present invention generally relates to metal forming lines such as continuous metal casting lines. In particular, it relates to a lining for a metallurgical vessel, such as a tundish, capable of reducing substantially the formation of oxide inclusions in the metal melt.
In metal forming processes, metal melt is transferred from one metallurgical vessel to another, to a mould or to a tool. For example, a tundish of large capacity is regularly fed with metal melt by a ladle transferring metal melt from a furnace to the tundish. This allows the continuous casting of metal from the tundish to a tool or mould. Flow of metal melt out of metallurgic vessels is driven by gravity through nozzle systems located at the bottom of the vessels, usually provided with a gate system to control (open or close) the flow of metal melt through said nozzle system. In order to resist the high temperatures of metal melts, the walls of the vessels are lined with refractory material.
Metal melts, in particular steel, are highly reactive to oxidation and must therefore be shielded from any source of oxidative species. Small amounts of aluminum are often added to passivate the iron in case oxidative species enter into contact with the melt. In practice, it appears that often this is not enough to prevent the formation of oxide inclusions in the melt that produce defects in a final part produced from the melt. It has been observed that a 10 kg steel casting may contain up to one billion non-metallic inclusions, most of them being oxides. Aggregated inclusions form defects. The defects must be removed from the final part by grinding or cutting. These procedures add to the production cost and generate large amounts of scrap.
Inclusions may be the result of reactions with the metal melt; these inclusions are known as endogenous inclusions. Exogenous inclusions are those in which the materials do not result from reactions of the metal melt, such as sand, slag, and debris of nozzles; exogenous inclusions are generally thicker than endogenous inclusions.
Endogenous inclusions comprise mostly oxides of iron (FeO), aluminium (Al2O3), and of other compounds present in, or in contact with the melt, such as MnO, Cr2O3, SiO2, TiO2. Other inclusions may comprise sulfides and, to a minor extent, nitrides and phosphides. Since metal melts are at very high temperatures (of the order of 1600° C. for low carbon steels) it is clear that the reactivity of an iron atom with an oxide is very high and reaction cannot be prevented.
To date, most measures to reduce the presence of inclusions in a steel casting involve retaining them in the metallurgical vessel in which they were formed. The present invention proposes a different solution by reducing substantially the formation of endogenous inclusions in a metallurgical vessel with simple, reliable, and economical means.
The present invention is defined by the attached independent claims. The dependent claims define various embodiments. In particular, the present invention concerns a lining for a metallurgical vessel for casting a metal melt. Examples of such metallurgical vessels comprise a floor, surrounded by walls over the whole perimeter of said floor, and an outlet, or multiple outlets, located on said floor characterized in that at least a portion of the floor and/or of the walls comprise means for creating in casting use an oxidation buffering layer at an interphase of metal melt extending from the interface between metal melt and the walls and floor of the metallurgical vessel, such that when in casting use, the metal flow rate in said oxidation buffering layer is substantially nil, and the concentration of endogenous inclusions, in particular oxides, in said oxidation buffering layer is substantially higher than in the bulk of the metal melt.
In a particular embodiment, the structure for creating in casting use an oxidation buffering layer comprises an immobilizing layer comprising metal and lining said floor and at least some of the walls of the vessel, said immobilizing layer being enclosed by layers of refractory material. The structure is thus constructed from a first or working layer of refractory material in contact with the metal melt in the vessel; underlying the first layer is a second layer containing metal; under the second layer is a third layer comprising a refractory material. In use, the metal may remain in the solid state in the second layer, or may be partially or completely converted to the liquid state in the second layer. A perforation is a channel or passage through a layer, enabling a fluid to pass from one side of the layer to the other. In particular embodiments of the invention, metal melt contained in the vessel may penetrate into porosity or perforations contained in the first layer of this immobilizing layer to become incorporated into the second layer. As the second layer is in close contact with the refractory material lining the walls and floor of a metallurgical vessel, said refractory material being identified as a major source of reagents for the formation of endogenous inclusions, be it by diffusion of the ambient air or by reaction of some of the components thereof, the metal in the second layer may, in the solid form, act as a barrier to reagents for the formation of endogenous inclusions or may, in the liquid form, retain a concentration of endogenous inclusions much higher than the bulk of the metal melt.
The first layer may be made of materials such as magnesia, alumina, zirconia, mullite, and combinations of any of these materials.
The second layer may be made of steel, aluminum, alloys or combinations of any thereof.
Various embodiments of the present invention are illustrated in the attached Figures:
As can be seen in the depiction of a casting apparatus 10 in
The second assumption which led to the present invention was that oxidation reagents originate at the walls and floor of the metallurgical vessel. In particular, it is believed that oxidation reagents come from two main sources:
This second assumption was validated by lab tests.
The solution, therefore, proceeded from these two starting assumptions:
The inventors developed the following solution for preventing the formation of endogenous inclusions in the bulk of the metal melt. If it were possible to immobilize the atoms forming the metal melt close to the source of oxidative species, i.e., the walls and floor of a metallurgical vessel, a “passivating layer” or a “buffering layer” would form which would be left to oxidize but, since diffusion is very slow and absent any significant flow, the oxidation reaction would not spread to the bulk of the metal melt. This principle is illustrated schematically in
It is clear that although oxidation reactions have been mentioned in the above explanation, the same applies mutatis mutandis to other reactions such as the formation of sulfides, nitrides, and phosphides, which reaction rates with atoms such as Fe are also diffusion controlled.
Various devices or means for forming an oxidation buffering layer can be utilized according to the present invention. In a first embodiment, the device takes the form of a lining structure in which a metal layer or metal component is sandwiched or enclosed between two layers of refractory material. The enclosed metal lining structure may be used to line part or all of the floor of a refractory vessel, and may be used to line part or all of the walls of a refractory vessel. The outer or enclosing layers of the enclosed metal lining structure are made of a substantially non oxidative material with respect to the metal melt.
The outer or enclosing layers of the enclosed metal lining structure should be made of a material not reactive with metal melts, in particular low carbon steels. Certain embodiments of the invention are characterized by the absence of silicates. The materials used for making tundish foam filters are suitable for making the outer or enclosing layers of the present invention. In particular, zirconia, alumina, magnesia, mullite and a combination of these materials may be suitable for forming the outer or enclosing layers of the present invention and are readily available on the market.
The second layer is configured to maximize the area of metal that is in a plane parallel to the walls of the vessel. If the metal of the second layer is in solid form, it physically prevents oxidation agents from passing from the third layer to the first layer and consequently into the volume of the metal melt. If the metal in the second layer is converted, partially or completely, to the molten form, metal atoms in contact with the refractory lining enter in contact with oxidation reagents, such as diffusing oxygen or components of the refractory lining, and rapidly react forming oxides, in particular FeO in low carbon steel melts. Any metal melt, however, is essentially trapped within the second layer, and cannot flow significantly into the bulk of the molten metal contained within the vessel. Since the diffusion controlled spreading of the oxidation reactions is very slow in still metal melts, the reaction will propagate extremely slowly through the thickness, δ, of the lining structure. The metal melt flowing over the lining structure is therefore not contacted by oxidation reagents until the oxidation reaction has proceeded through the thickness, δ, of the layer, which can take longer than a casting operation.
It is clear from the above explanation that refractory materials used in casting operations can be used in the first and third layers of the lining structure of the present invention. The first layer and third layer may be monolithic or composed of panels.
The metal incorporated into the second layer may be provided in any form having two orthogonal dimensions that are significantly larger than a third, or thickness, dimension, such as in the form of foil, sheets, panels, slurry or compressed powder. To ensure that the first layer remains fixed with respect to the third layer during metallurgical forming operations, the metal in the second layer may have the form of sheets or panels separated by a distance into which a refractory material can be placed. In certain embodiments of the invention, metal sheets or panels constituting the second layer may be provided with transverse holes to accommodate refractory material, such as the refractory material constituting the first layer so that, when the sheet or panel is pressed into the third layer, or when the refractory material of the first layer is applied over the sheets or panels, refractory penetrates the holes and forms standoffs that fix the position of the first layer with respect to the third layer. In certain embodiments of the invention, metal sheets or panels constituting the second layer may be provided with dimples or protrusions so that, when the sheet or panel is pressed into the third layer, or when the refractory material of the first layer is applied over the sheets or panels, receiving geometries for the dimples or protrusions are formed in the first layer or third layer to engage the second layer to the first layer or the third layer.
The spacing between the major surface of the first layer facing away from the bulk of the metal melt and the surface of the third, or backing, layer facing towards the bulk of the metal melt, or the thickness of the second layer, may be in the range from and including 0.01 mm to and including 10 mm, from and including 0.01 mm to and including 20 mm, from and including 0.01 mm to and including 50 mm, from and including 0.01 mm to and including 100 mm, from and including 0.01 mm to and including 150 mm, from and including 0.05 mm to and including 10 mm, from and including 0.05 mm to and including 20 mm, from and including 0.05 mm to and including 50 mm, from and including 0.05 mm to and including 100 mm, from and including 0.05 mm to and including 150 mm, from and including 0.1 mm to and including 10 mm, from and including 0.1 mm to and including 20 mm, from and including 0.1 mm to and including 50 mm, from and including 0.1 mm to and including 100 mm, from and including 0.1 mm to and including 150 mm, from and including 0.5 mm to and including 10 mm, from and including 0.5 mm to and including 20 mm, from and including 0.5 mm to and including 50 mm, from and including 0.5 mm to and including 100 mm, from and including 0.5 mm to and including 150 mm, from and including 1 mm to and including 20 mm, from and including 1 mm to and including 30 mm, from and including 1 mm to and including 50 mm, from and including 1mm to and including 100 mm, from and including 1 mm to and including 150 mm, from and including 2 mm to and including 30 mm, from and including 2 mm to and including 50 mm, from and including 2 mm to and including 100 mm, and from and including 2 mm to and including 150 mm.
According to the present invention, a lining structure for a refractory vessel may comprise (a) a first layer having a first layer first major surface and a first layer second major surface disposed opposite to the first layer first major surface, and (b) a second layer having a second layer first major surface and a second layer second major surface disposed opposite to the second layer first major surface, wherein the first layer second major surface is in contact with, or in communication with, the second layer first major surface; and (c) a nonperforated third layer having a third layer first major surface in communication with the second layer second major surface, wherein the second layer comprises a metal component having a major surface parallel to, or adjacent to, the second layer first major surface, or to the third layer first major surface. The first layer, second layer and third layer may all be oriented in parallel. A nonperforated layer is a layer which has not been subjected to a procedure producing a channel or passage through the layer and enabling a fluid to pass form one side of the layer to another. A major surface is a surface having an area greater than the median value for all surfaces of an object. The area of the metal component surface parallel to, or adjacent to, the third layer first major surface, or to the second layer first major surface, may have a value from and including 50% to and including 100%, from and including 50% to and including 99%, from and including 50% to and including 95%, from and including 80% to and including 95%, or from and including 80% to and including 99% of the area of the third layer first major surface, or of the area of the second layer first major surface. The first layer of the lining structure may comprise a refractory material such as magnesia, alumina, zirconia, mullite, and combinations of these materials. The third layer of the lining structure may comprise a refractory material such as magnesia, alumina, zirconia, mullite, and combinations of these materials. The metal component in the second layer may contain passages between the second layer first major surface and the second layer second major surface. The passages may be filled with refractory material to produce support structures between the first layer and the third layer. The sum of the cross-sectional areas of the passages in the metal component, or the sum of the cross-sectional areas of support structures passing through the metal component, may have a value from and including 0.1% to and including 10%, from and including 0.5% to and including 10%, or from and including 1% to and including 10%, from and including 0.1% to and including 30%, from and including 0.5% to and including 30%, and from and including 1% to and including 30% of the area of the second layer first major surface.
The second layer of the lining structure may comprise a metal component constructed from foil, sheet, panel or a volume of slurry or compressed powder having the greater two dimensions of three orthogonal dimensions oriented parallel to the second layer first major surface, wherein the summed area in a plane parallel to a major plane of the second layer, of all gaps or interruptions in the metal component in the second layer is less than the summed area in a plane parallel to a major plane of the second layer, of the metal component in the second layer. In certain embodiments of the invention, the summed area in a plane parallel to a major plane of the second layer, of all gaps or interruptions in the metal component in the second layer (defined as “a1”) and the summed area in a plane parallel to a major plane of the second layer, of the metal component in the second layer (defined as “a2”) may have a ratio r=a1/a2 such that r is equal to or less than 1.0, equal to or less than 0.5, equal to or less than 0.1, equal to or less than 0.05, equal to or less than 0.02, equal to or less than 0.01, equal to or less than 0.007, equal to or less than 0.005, or equal to or less than 0.002.
In particular embodiments of the invention, the second layer may comprise a plurality of stand-off structures protruding from the first major surface of the third layer, disposed to hold the metal component of the second layer in position. In particular embodiments of the invention, the second layer may comprise a plurality of stand-off structures protruding from the second major surface of the first layer, disposed to hold the metal component of the second layer in position. The standoff structures may be formed in any suitable geometry, such as spheres, cylinders, conic sections, or prisms of polygons. The first layer and third layer may be provided with receiving geometries so that the standoff structures are immobilized when the first layer is installed with respect to the third layer.
In particular embodiments of the invention, the second layer may comprise a sacrificial structure in contact with the metal component of the second layer. The sacrificial structure is configured so that, when it is removed by combustion, heat, chemical or physical action, the metal in the second layer will be able to expand with increasing temperature without damaging the structural integrity of the refractory layers with which it is in contact. In some embodiments of the invention, some or all of the perforations or holes in metal sheets or other metal components in the second layer may be filled with sacrificial material to accommodate volume expansion of the metal on heating. Sacrificial structures may be constructed of cellulosic, plastic, or other organic materials, graphitic materials, glasses, permeable minerals, gaseous materials or metals, and combinations thereof. The material used in the sacrificial structure may take the form of a sheet, powder, sprayed slurry or gel. The sacrificial structure is placed in contact with the metal in the second layer, as part of the process of assembling the second layer in the preparation of a lining according to the invention. One or more refractory materials are then applied to the sacrificial structure to provide, after removal of the sacrificial structure, first and second layers according to the present invention.
The sacrificial structure may have a volume in the range from and including 0.05% to and including 20%, from and including 0.05% to and including 15%, from and including 0.05% to and including 10%, 0.05% to and including 5%, from and including 0.05% to and including 2%, from and including 0.05% to and including 1%, from and including 0.05% to and including 0.5%, from and including 0.1% to and including 20%, from and including 0.1% to and including 15%, from and including 0.1% to and including 10%, from and including 0.1% to and including 5%, from and including 0.1% to and including 2%, from and including 0.1% to and including 1%, from and including 0.1% to and including 0.5%, from and including 0.2% to and including 20%, from and including 0.2% to and including 15%, from and including 0.2% to and including 10%, from and including 0.2% to and including 5%, from and including 0.2% to and including 2%, from and including 0.2% to and including 1° A, from and including 0.2% to and including 0.5%, of the volume of the metal with which it is in communication.
In particular embodiments of the invention, the first layer may have a thickness in the range in the range from and including 1 mm to and including 150 mm, in the range from and including 1 mm to and including 100 mm, in the range from and including 1 mm to and including 50 mm, in the range from and including 5 mm to and including 150 mm, in the range from and including 5 mm to and including 100 mm, in the range from and including 5 mm to and including 50 mm, in the range from and including 10 mm to and including 150 mm, in the range from and including 10 mm to and including 100 mm, or in the range from and including 10 mm to and including 50 mm.
In particular embodiments of the invention, the second layer may have a thickness in the range from and including 0.01 mm to and including 150 mm, in the range from and including 0.01 mm to and including 100 mm, in the range from and including 0.01 mm to and including 50 mm, from and including 0.05 mm to and including 150 mm, in the range from and including 0.05 mm to and including 100 mm, in the range from and including 0.05 mm to and including 50 mm, from and including 0.1 mm to and including 150 mm, in the range from and including 0.1 mm to and including 100 mm, in the range from and including 0.1 mm to and including 50 mm, in the range from and including 0.5 mm to and including 150 mm, in the range from and including 0.5 mm to and including 100 mm, in the range from and including 0.5 mm to and including 50 mm, in the range from and including 1 mm to and including 150 mm, in the range from and including 1 mm to and including 100 mm, in the range from and including 1 mm to and including 50 mm, in the range from and including 5 mm to and including 150 mm, in the range from and including 5 mm to and including 100 mm, in the range from and including 5 mm to and including 50 mm, in the range from and including 10 mm to and including 150 mm, or in the range from and including 10 mm to and including 100 mm, or the range from and including 10 mm to and including 50 mm.
The present invention also relates to the use of the lining structure as previously described in a refractory vessel, and to a metallurgical vessel having an interior and an exterior, wherein the interior of the metallurgical vessel comprises a lining structure as previously described.
The present invention also relates to a process for the minimization of oxidation of a molten metal during transfer, comprising (a) transferring molten metal to a vessel having a lining structure as previously described, and (b) transferring the molten metal out of the vessel.
The configured structure of the invention may be formed by providing a base panel of a refractory material, such as an ultralow cement alumina castable, and spraying a tundish lining material, such as a magnesite spray material containing from and including 70 wt % magnesite to and including 100 wt % magnesite, on the base panel to form a third layer. A metal component sheet is then securely pressed against the magnesite spray material on the base panel to form a second layer. An alumina-based material, such as a material containing from and including 80 wt % alumina to and including 100 wt % alumina, is then sprayed on the second layer to form a first layer. Support structures for the metal component may be formed by pressing the metal component sheet against the third layer so that the material of the third layer surrounds the metal component sheet or so that the material of the third layer is forced into transverse opening in the metal sheet. In another embodiment of the invention, metal powder may be used to form the metal component or layer, and the refractory material in the first and third layers may be provided in the form of a dry-vibratable refractory lining. In yet another embodiment of the invention, a metal-containing slurry may be sprayed onto the third layer to form the metal component or layer.
The refractory materials may be applied by gunning, spray, trowelling, casting, dry-vibration application, shotcreting, grouting, pouring, injection, or placement of preformed pieces. The refractory materials may then be dried, cured or stabilized to solidify them as necessary. The resulting layered structure is then exposed to physical or chemical action to remove or transform any sacrificial structures to provide a volume to accommodate the thermal expansion of the metal component.
The second layer may have a thickness from and including 0.01 m, 0.02 mm, 0.05 mm, 0.10 mm, 0.25 mm, 0.50 mm, 1 mm, 2 mm, 3mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm to and including 5 mm, 6 mm, 7, mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm.
A vessel constructed according to the present invention may be used in metallurgical processes. A method of use may include introducing a molten metal into a vessel having a lining according to the present invention, and subsequently removing the molten metal from the vessel through a nozzle.
For testing, base panels are prepared from an ultralow cement alumina castable similar to the material used as safety lining inside a steel tundish. The dimensions of each base panel are 36 inches×24 inches×5 inches (90 cm×60 cm×12.5 cm). First, a tundish lining material (Basilite, a lightweight magnesite-based spray material containing >70 wt % magnesia) is sprayed over the base panel to about 1 inch (2.5 cm) thickness, using a Basilite spray machine. Metal component sheets (20 inches×12 inches, or 50 cm×30 cm) having different opening configurations are securely pressed against the Basilite lining. Then, an alumina based material (alumina>80 wt %) is sprayed to a thickness of about 1 inch (2 cm) over the surface.
In the construction of selected panels, passages or openings will be provided in the metal component sheets. The volumes of these openings will be filled with refractory material during the construction of the panel, so that direct contact is made, through the openings, between the linings in contact with each of the surfaces of the metal component sheets.
Metal components are air dried and then fired at 1000 degrees F. for three hours to provide information on the drying behavior of the lining as well as the structural integrity.
A MgO crucible (12 inches in height and 7.5 inches ID) is used for testing. A metal hollow cylinder with desired thickness and 5.5-6 inches OD and 10.5 inches tall is placed in the center of the crucible. The metal hollow cylinder may be provided with perforations between an interior lateral surface and an exterior lateral surface. These perforations may be filled with a sacrificial material during the construction of the crucible. The space between the inner wall of the MgO crucible and the outer wall of the metal cylinder is filled with a tundish lining material (such as Basilite). Then a cylindrical metal mandrel is placed in the centre of the crucible already containing the hollow metal cylinder. Then the space between the inner wall of the metal cylinder and the mandrel is filled with a tundish lining material (mostly high alumina). The mandrel is removed after drying the crucible at 230 degrees F. for an hour. Then the crucible is dried at 450 degrees F. for 24 hrs and then fired at 2700 degrees F. for five hours. The crucible is then examined.
Numerous modifications and variations of the present invention are possible. It is, therefore, to be understood that within the scope of the following claims, the invention may be practiced otherwise than as specifically described.
This application is a U.S. national stage application, filed under 35 U.S.C. § 371, of International Application No. PCT/US17/47049, which was filed on Aug. 16, 2017, and which claims priority to U.S. Provisional Application Ser. No. 62/378,706, filed on Aug. 24, 2016, the contents of which are incorporated by reference into this specification.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US17/47049 | 8/16/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62378706 | Aug 2016 | US |
