Patent Application
20240375174
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.
The present invention relates to an improved design for an upper tundish nozzle. The nozzle is designed to be used in continuous casting of steel into slabs.
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, 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.
In operation of an upper tundish nozzle 4 having a porous ceramic inner portion 6, pressurized inert gas (such as argon) is permeated through the annular space between the outside surface of the ceramic inner portion 6 and the protective can 5 that may circumscribe it while molten metal flows through the bore of the upper tundish nozzle 4. The inert gas flows through the gas flow paths 8 in the porous ceramic inner portion 6. The argon eventually escapes the porous ceramic inner portion 6 as argon bubbles 9. 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 inner bore surface of the upper tundish nozzle 4. Such leaks can jeopardize the function of the gas in penetrating to the interior bore of the upper tundish nozzle 6. 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 4 design that minimizes or eliminates the leakage mechanisms inherent in the prior art designs.
The present invention relates to a leak-proof gas injected upper tundish nozzle. The nozzle includes a protective can and a ceramic inner portion disposed within the protective can. The ceramic inner portion preferably has gas flow pathways therein. The nozzle further includes a gas injection port attached to the protective can which allows for the injection of gas through the protective can and into gas flow pathways within the ceramic inner portion.
The nozzle also includes at least one gas flow seal formed between the protective can and the ceramic inner portion. The gas flow seal blocks gas leakage from the gap between the protective can and the ceramic inner portion. The gas flow seal may be formed from nickel or an alloy of nickel.
The gas flow seal may be formed by depositing nickel or nickel alloy into any gaps between the protective can and the ceramic inner portion by a method selected from the group consisting of electroplating, electroless plating, nickel/alloy foil strips, sputtering, plasma vapor deposition, and metal printing.
In one embodiment, the gas flow seal may be formed by electroplating nickel or nickel alloy into any gaps between the protective can and the ceramic inner portion. The nickel or nickel alloy may be electroplated across the gap on the exterior of the protective can and the exterior of ceramic inner portion. The nickel or nickel alloy may be electroplated across the gap on the exterior of the protective can and the exterior of the ceramic inner portion after the protective can and ceramic inner portion have been formed into a unitary piece.
The nickel or nickel alloy may be deposited onto one or both of the interior surface of the protective can and the exterior surface of the ceramic inner portion. Preferably, the nickel or nickel alloy may be deposited onto one or both of the interior surface of the protective can and the exterior surface of the ceramic inner portion before the protective can and ceramic inner portion have been formed into a unitary piece.
The protective can may be formed of a metal material, preferably steel. The ceramic inner portion may be formed from a porous ceramic material and the gas flow pathways may comprise the pores within the porous ceramic material. The ceramic inner portion may be is formed from a gas permeable refractory material consisting of a ceramic oxide of one or more of aluminum, silicon, magnesium, chromium, or zirconium, or mixtures thereof.
The ceramic inner portion may not be porous or gas permeable and the gas flow pathways may be formed directly into the body of the ceramic inner portion. The gas flow pathways may include a gas distribution manifold and gas distribution channels. The gas distribution channels may have gas outlets to release the gas into the steel flowing within the upper tundish nozzle.
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 inventors pressure tested an as received commercial upper tundish nozzle 4 to determine if there were leaks in the gaps between the protective can 5 and the ceramic inner portion 6 thereof. The nozzle pressurized and a soapy water solution was applied to the gaps. Bubbles formed, indicating significant leakage of the gas.
The inventors electroplated nickel onto the upper tundish nozzle 4 in areas that completely overlapped the gap between the protective can 5 and the ceramic inner portion 6. After the electroplating of the seal 11, 11′, the nozzle was again pressure tested and it was seen that the leaks had been plugged. This was of course at room temperature and not at steel casting temperatures.
Next the can with the electroplated nickel seals 11, 11′ was subjected to thermal testing by pouring liquid steel into the nozzle using a 100 lb open air furnace. The pour went from a ladle through the upper tundish nozzle 4 into an ingot mold under the nozzle. After the steel solidified, the nozzle was examined, and it was found that the electroplated nickel seal 11,11′ was completely intact and even survived a direct metal splash.
The present inventor envisions two different types of nickel seals. The first type of nickel seal 11 is described above. It is applied externally to cover the gaps between the protective can 5 and the ceramic inner portion 6. This type of seal 11 is generally applied after the upper tundish nozzle 4 is formed.
Alternatively, the nickel material may be applied to one or both of the protective can 5 and the ceramic inner portion 6 before the upper tundish nozzle 4 is formed. The nickel is deposited strategically on the protective can 5 and/or ceramic inner portion 6 to form the nickel seal 11′ there between.
While the inventors have used electroplating to deposit the nickel seals 11,11′. Other viable techniques include electroless plating, nickel foil strips, sputtering, plasma deposition, metal printing and the like. What is important is not how the nickel got into position but rather forming the nickel seal 11,11′ between the protective can 5 and the ceramic inner portion.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/058717 | 9/24/2021 | WO |
