Field of the Invention

The present invention relates to the casting of steel slabs and more specifically to upper tundish nozzles used in such casting. Most specifically, the invention relates to argon injected upper tundish nozzle designs by which argon leakage therefrom is minimized/eliminated.

Background of the Invention

The present invention relates to an improved design for upper tundish nozzle. The nozzle is designed to be used in continuous casting of steel into slabs. Figure 1 depicts a cross section of such a continuous casting line. The line includes a ladle 1 which continuously brings fresh steel to the tundish 2. The tundish 2, controls the flow therefrom into the casting mold 3.

Figure 2 is a closer view of the tundish 2 and the casting mold 3 and specifically shows the position of the upper tundish nozzle 4, which is the focus of the present invention. The upper tundish nozzle 4 collects the molten steel from the tundish 2 and directs the steel through a gate valve and into the casting mold 3.

Figure 3 is a simplified cross section of an upper tundish nozzle 4. The upper tundish nozzle 4 is composed of a ceramic inner portion 6 and a protective can 5 which houses and protects the fragile ceramic inner portion 6.

The ceramic inner portion 6 of such nozzles are often formed from a porous, gas permeable refractory material which may be a ceramic oxide of aluminum, silicon, magnesium, chromium, or zirconium, or mixtures thereof. Alternatively, and more preferably, the ceramic inner portion 6 of the nozzle may be formed of a ceramic material having pierced/tunneled holes in the ceramic to provide set gas flow paths within the ceramic inner portion 6.

The porous, gas permeable refractory material and/or the pierced/tunneled holes provide flow paths for Argon gas which is injected into the upper tundish nozzle 4 during continuous casting to deter clogging of the upper tundish nozzle 4 with solid inclusions. The argon flow also affects the flow pattern of steel in the upper tundish nozzle 4, the gate valve and subsequently in the casting mold 3.

As alluded to above, the inside surface of the ceramic inner portion 6 of the upper tundish nozzle 4 defines a bore for conducting a flow of liquid steel. The outside surface of the ceramic inner portion 6 is enveloped in a protective can 5. The protective can 5 can be formed of metallic sheet material, such as steel, that may be spaced apart from the outside surface of the ceramic inner portion 6 in order to define one or more annular, gas conducting spaces. The argon gas is injected into the upper tundish nozzle 4 via a gas injection port 7. Figure 3 indicates the argon gas injection port 7, as well as the argon flow path which includes the argon pressure/distribution manifold 8 and individual gas injection channels 8'. The gas injection channels 8' exit into the interior bore of the upper tundish nozzle 4 through gas injection holes 8". The distribution of the gas injection channels 8’ and size/position of the gas injection holes 8" are designed and modeled to provide the proper gas flow into the bore of the upper tundish nozzle 4. The inert gas flows through the gas flow paths 8,8' in the ceramic inner portion 6. The argon eventually escapes through the gas injection holes 8” in the ceramic inner portion 6 as argon bubbles. These bubbles may advantageously form a fluid film over the surface of the bore within the upper tundish nozzle 4 that prevents that molten metal from making direct contact with the inner surface forming the bore. By insulating the bore surface from the molten metal, the fluid film of gas prevents the small amounts of alumina that are present in such steel from sticking to and accumulating onto the surface of the nozzle bore. The prevention of such alumina deposits is important, as such deposits will ultimately obstruct the flow of molten steel until it congeals around the walls of the bore, thereby clogging the upper tundish nozzle 4. Such a clogged nozzle 4 necessitates the shutting down of the casting process and the replacement of the nozzle 4.

While such upper tundish nozzles 4 have generally shown themselves to be effective in retarding the accumulation of bore-obstructing alumina deposits, the inventors have observed a number of shortcomings associated with such nozzles. One specific issue relates to leakage of argon gas, i.e. the loss of argon from the system in areas that are not the gas injection holes 8” of the inner bore surface of the upper tundish nozzle 4. Such leaks can occur when cracks 9 in the inner ceramic portion 6 intersect with the argon pressure/distribution manifold 8 and/or the individual gas injection channels 8'. Such leaks can jeopardize the proper function of the gas in pathways to the interior bore of the upper tundish nozzle 4. If the gas leaks are serious enough it could interfere with forming a protective fluid film over the surface of the nozzle bore. The pressure of the inert gas must be maintained at a level high enough to overcome the considerable backpressure that the molten steel applies to the surface of the bore. Ideally, the gas pressure should be just enough to form the desired film. If it is too high, the gas can stir the steel excessively, thus creating additional defects. Thus, the control of the gas pressure and flow is critical and must be maintained within a narrow range. Any significant leak can jeopardize the desired delicate pressure balance. Further such argon loss is an added expense to production and therefore should be minimized if possible.

Clearly, there is a need for an improved upper tundish nozzle 6 design that minimizes or eliminates the leakage mechanisms inherent in the prior art designs.

Summary of the Invention

The present invention relates to a leak-proof gas injected upper tundish nozzle. The gas injected upper tundish nozzle 4 may include a protective can 5, and a ceramic inner portion 6 disposed within the protective can 5. The ceramic inner portion 6 may have gas flow pathways therein. The gas flow pathways may have been formed using a sacrificial mold 6* when producing the ceramic inner portion 6. The nozzle may also include a gas injection port 7 attached to the protective can 5. The gas injection port 7 may allow for the injection of gas through the protective can 5 and into the gas flow pathways within the ceramic inner portion 6. A gas flow seal 11 may be formed on the interior surfaces of the gas flow pathways within the ceramic inner portion 6. The gas flow seal 11 may block gas leakage from the gas flow pathways into any cracks in the ceramic inner portion 6. The gas flow seal 11 may be formed of nickel or an alloy of nickel.

The gas flow passages may include a gas pressure/distribution manifold 8 and individual gas injection channels 8'. The sacrificial mold 6* may include a protomanifold 8* and proto-injection channels 8** formed of sacrificial material. The gas flow seal 11 may be formed by depositing nickel or nickel alloy onto the proto-manifold 8* and proto-injection channels 8** by a method selected from the group consisting of electroless plating, nickel foil strips, sputtering, physical vapor deposition, chemical vapor deposition, plasma deposition, and metal printing. Additional nickel or nickel alloy may be deposited into the gas pressure/distribution manifold 8 and individual gas injection channels 8' after the sacrificial mold 6* has been removed from the ceramic inner portion 6.

The protective can 5 may be formed of a metal material such as, for instance, a steel material. The ceramic inner portion 6 may be formed from a refractory material consisting of a ceramic oxide of one or more of aluminum, silicon, magnesium, chromium, or zirconium, or mixtures thereof. The gas distribution channels 8' may have gas outlets 8" to release the gas into the steel flowing within the upper tundish nozzle 4.

The gas flow seal 11 may be formed by depositing nickel or nickel alloy into the gas pressure/distribution manifold 8 and individual gas injection channels 8' after the sacrificial mold 6* has been removed from the ceramic inner portion 6 without deposition of nickel/nickel alloy onto the sacrificial mold 6*.

Brief Description of the Drawings

Figure 1 depicts a cross section of such a continuous casting line in which the upper tundish nozzle of the present is preferably used;

Figure 2 is a closer view of the tundish and the casting mold and specifically shows the position of the upper tundish nozzle;

Figure 3 is a simplified cross section of an upper tundish nozzle; Figure 4A is a cross-sectional view of a sacrificial mold 6* useful for the present invention;

Figure 4B is a 3D depiction of a sacrificial mold 6* useful for the present invention;

Figure 4C is a cross-sectional depiction of a sacrificial mold 6* onto which a nickel or nickel alloy sealant layer 11 has been deposited;

Figure 5 depicts a cross-sectional depiction of an upper tundish nozzle 4 including the inventive sealing solution.

Detailed Description of the Invention

The present invention is an improved argon injected upper tundish nozzle 4 which minimizes/eliminates unwanted leakage of inert gas (such as argon) therefrom.

The upper tundish nozzle 4 of the present invention is the type that contains preformed argon pressure/distribution manifold 8 and individual gas injection channels 8' as shown in Figure 3. The preformed argon pressure/distribution manifold 8 and individual gas injection channels 8' are formed within the ceramic inner portion 6 during manufacture of said upper tundish nozzle 4.

The ceramic inner portion 6 of the upper tundish nozzle 4 is generally formed by hydrostatic pressing of powdered ceramic materials. For this type of upper tundish nozzle 4, the preformed argon pressure/distribution manifold 8 and individual gas injection channels 8' are formed by isostatic pressing of the powdered ceramic material around a sacrificial mold. After the isostatic pressing, the mold is then removed leaving the argon pressure/distribution manifold 8 and individual gas injection channels 8'. Figure 4A is a cross-section of such a sacrificial mold 6* and Figure 4B is a 3D depiction thereof. The mold 6* contains the design for the argon flow system including the proto-manifold 8* and the proto-injection channels 8**. Figure 4C is a cross- sectional depiction of the sacrificial mold 6* onto which a nickel or nickel alloy sealant layer 11 has been deposited onto the surface of the proto-manifold 8* and protoinjection channels 8** portions thereof.

Figure 5 depicts a cross-section of the upper tundish nozzle of present invention specifically showing the nickel or nickel alloy sealant layer 11 as it remains on the inner surfaces of the preformed argon pressure/distribution manifold 8 and individual gas injection channels 8' after the sacrificial mold 6* has been removed. The nickel or nickel alloy sealant layer 11 helps to reduce or eliminate the loss of argon from the upper tundish nozzle 4 through cracks and/or pores within the inner ceramic portion 6 thereof. It is believed that this seal 11 remains ductile at the elevated temperatures which helps to prevent cracks from leaking.

The inventors electroplated nickel onto a sacrificial mold 6* and used it to isostatically press to form an upper tundish nozzle 4. While the inventors have used electroplating to deposit the nickel seal 11 . Other viable techniques include electroless plating, nickel foil strips, sputtering, physical vapor deposition, chemical vapor deposition, plasma deposition, metal printing and the like. What is important is not how the nickel got into position, but rather forming the nickel seal 11 onto the inner surface of the argon pressure/distribution manifold 8 and individual gas injection channels 8' of the ceramic inner portion 6.

Further, while the nickel sealant layer 11 may be formed onto the sacrificial mold 6*, it may alternatively be formed by gaseous or liquid deposition onto the inner surface of the argon pressure/distribution manifold 8 and individual gas injection channels 8' after the ceramic inner portion 6 has already been formed. Additionally, both pre- production deposition of the nickel/alloy sealant 1 1 onto the sacrificial mold 6* and postproduction of deposition of additional nickel/alloy sealant 1 1 may be combined to form the final product.