KR810000590B1 - Method for repairing ingot moulds or mould stools - Google Patents

Abstract

An erosion cavity in an ingot mould stool or the bottom of a mould is repaired by placing in the cavity a metal-producing exothermic reaction mixt. including a metal oxide having vol.<=1.5 times than that of the cavity, igniting the mix. to form a melt contained entirely in the cavity, and allowing the melt to sep. into metal and slag phases and to solidify so that the metal is bound to the bottom of the cavity and the slag is attached to the metal to form the exposed surface of the repair. The prepferred exothermic material is a stoichiometric mixt. of powd. Al (-100-+400 mesh) and Fe2O3 (<=-35 mesh) and is used for repairing cast Fe moulds.

Description

Repair method of mold and surface plate

1 is a cross-sectional view of a corroded mold surface and the materials required to carry out the invention.

2 is a cross-sectional view of a mold surface plate repaired by the method of the present invention.

Figure 3 deposits a wear resistant monolithic ceramic liner at the bottom,

Cross-sectional view of a large end up (BEU) ingot mold installed in accordance with another embodiment of the present invention.

4 is a cross-sectional side view of the ingot mold of FIG. 3 after welding the ceramic bottom liner.

The present invention relates to a method for repairing an ingot mold and a surface plate and a low hermetic ingot mold at a relatively low cost using an aluminum thermite reduction (ATR) metal welding method for repair.

Practical methods of repairing damaged molds and surface plates during use have been urgently requested by steelmakers because the performance of the molds and surface plates is directly related to the cost of steel production. The main reasons why molds and plates, usually made of cast iron, become defective or waste products are cracks in the mold walls and plate sheets or corrosion of the mold base and plate sheets. Conventional bulk welding methods for repairing molds and plates are expensive, time consuming, and often unsatisfactory because the welds crack or fall off. In order to improve the welding method and fix the weldment, V or u-shaped notches or grooves or dovetail grooves are installed on the surface and the notches are welded with welding metal. This method is usually successful but very expensive. Attempts to fill cracks and craters with ceramics have failed. Steel plates embedded in gaps and holes outside the mold have been used to close gaps in the mold and prevent further spread, but these repairs are still completely satisfactory because molten metal enters the gaps and holes, making ingot stripping extremely difficult. It is not.

One known repair method is to first groove along the damaged part of the mold wall. Drive several nails and bolts into the damaged area with the head exposed in the groove. The grooves are filled with weld metal to ensure the first breakage of the weld metal.

Aluminum Termination and Reduction (ATR) technology has been used in the past to repair castings such as ingot molds and mold plates. In such a method, it is common to considerably perform the surface conditioning treatment before the metal is deposited. For example, many people have thought that it is important to undercut the casting surface to remove the surface scale of the structure so that the welded metal is fixed so that the welded metal does not fall off, even if it is not bonded to the casting.

It has also been considered that the casting needs to be preheated to ensure good welded welded metal.

부피의 용착된 금속을 생기게 하므로 ATR분말과 ATR반응 생성물을 수선되는 부분에 한정시키기 위해 격납용 주위(containment perimeter)를 사용하는 것이 늘 필요했었다.ATR powder of given volume is about

Because of the volume of deposited metal, it was always necessary to use a containment perimeter to limit the ATR powder and ATR reaction product to the repaired area.

That is, the volume of ATR powder used to fill a given volume of crater with the same volume of ATR deposited metal should be five times larger. Therefore, a fire resistant ambient system is needed to directly confine the ATR powder to the cavity being filled. It is also necessary to likewise define the molten reaction product having a larger volume than the cavity. In other words, a larger volume of slag is inevitably generated to produce a metal having the same volume as the cavity volume. Even after the reaction has proceeded, the reaction product remains molten and a heavier metal product will fill the cavity to the bottom while the slag portion accumulates in the stomach in a limited volume by the fire resistant ambient system.

After the reaction product solidifies, the surrounding system and the superposed slag are removed and the deposited metal remains in the cavity.

The present invention relates to a method for repairing large castings, such as ingot molds and surface plates, and in particular, a method for welding the corrosion crates formed thereon, using an exothermic reduction reaction such as aluminum thermite reduction reaction, and does not require the above-mentioned complicated process. . The method of the present invention does not require any surface conditioning, no preheating or ambient system.

The chemical reaction can be expressed as follows.

3MeO + 2Al → 3Me + Al ₂ O ₃ + Thermal

In the above formula, MeO is an oxide of a metal to be deposited such as hematite (Fe ₂ O ₃ ), Al is an aluminum fuel, and Al ₂ O _{3, which} is an oxide of aluminum, is a main component of slag generated as a result of the reaction. A new and important step in the process of the invention is the proper disposal of the ATR charge when the ATR reaction is initiated. The ATR charge, which consists of a stoichiometric mixture of aluminum and iron oxide, is placed in a damaged area such as a corrosion hole. As the reaction occurs and the superheated metal is produced in contact with the substrate surface rather than in the crucible as usual, it utilizes the heat of reaction efficiently and thus enhances the binding of the deposited metal to the steel substrate.

It is a primary object of the present invention to provide a method of repairing large castings such as ingot molds and surface plates which do not require casting surface preparation, preheating and ambient systems.

It is yet another object of the present invention to provide a rapid and economical method of repairing ingot molds and surface plates as well.

It is a further object of the present invention to provide a method which is possible without the need for sophisticated or expensive equipment in repairing an ingot mold or a surface plate.

Another object of the present invention is to provide a method of repairing a mold surface without transferring it from the ingot car to which it is mounted.

It is yet another object of the present invention to provide a method of forming a high melting point, wear resistant ceramic shield on a fused metal. This object will become more apparent by reference to the following detailed description and accompanying drawings.

As shown in FIG. 1, the mold surface 10 was eroded during use such that the crater 12 was on the surface surface.

Sufficient amount of reaction mixture 12 accumulates to fill crater 12 so that small hills 16 of exothermic reaction mixture 14 are formed into sieve crater 12 having a surface plate placed on the ingot carafe. Ideally about 50% and excess mixture 14 is required. As can be seen, the 50% excess is hemispherical on crater 12. The mixture 14 is preferably an aluminum thermite reduction (ATR) reaction mixture. The mixture is composed of about 3 parts of powdered iron oxide and 1 part of aluminum powder. The iron oxide is good in Fe ₂ O ₃ and should not be finer than 200 mesh, and has a fine size of at least -35 mesh. It is good to have a size between about-100-400 meshes. Other fuels that may be used instead of aluminum include magnesium, calcium, silicon and calcium-silicon alloys or mixtures thereof. The ATR mixture 14 ignites with a flame, flame or hot filament. The reaction results in the formation of a superheated melt comprising the metal phase 20 (FIG. 2) and the slag phase 22. The heavier metal phase quickly separates from the melt and settles to the bottom where it is metallurgically bonded to the surface. The oxide scale of any metal on the mold surface is melted or chemically reduced like the slag phase 22 on top.

This “in situ” bulk deposition method effectively utilizes the heat of reaction to clean the surface and descale, thus increasing the formation of additional filler material welded to the surface. Upon cooling, the metal phase 20 is welded to the surface plate 10. The overlying slag phase 22 is firmly attached to the underlying metal phase 20 so that, although temporary, it can provide additional corrosion protection.

In previous efforts to deposit ATR metals in such cavities as described above, base metal castings preheated prior to application of the ATR mixture to ensure sufficient heat between the solid-liquid surfaces to weld the ATR metals to the cavity walls. I thought I should. However, in the practice of the present invention, such preheating is neither necessary nor desirable. Moreover, before the present invention, the existence of slag phases was detrimental, and thus it was considered that such slag phases should always be removed. Since the slag phase was removed, it was necessary to provide sufficient ATR mixture to fill the whole crate with the reactive metal. The slag statue on top is then destroyed and discarded.

Since a large amount of deposited metal was needed, a correspondingly large amount of ATR mixture was required. As noted above, this required the installation of a fire-resistant containment system around the cavity to contain the extra ATR mixture and reaction product to allow the next metal to enter the cavity. Indeed, it is known that loose ATR mixtures need to have a volume of approximately six times the common volume. However, in this practice where both reaction products, ie the metal phase and the slag phase fill the cavity, the ATR mixture should have a volume of 1.5 times the crater volume to fill the crater. Thus, a fire resistant ambient system is unnecessary and can be repaired effectively without the need for any equipment.

In the embodiments of the invention described above, it should be noted that in order to fill the cavity with metal and slag phases, the loose ATR mixture should have about 50% more volume than the cavity volume. However, it should be noted that the metal and slag phases do not need to completely fill the cavity. In fact, the top surface of the slag phase 22 may be lower than the top surface of the mold surface 10 without sacrificing any benefit. In some applications, it is desirable that the slag phase 22 be confined to the cavity walls so that the cavity is insufficiently filled. In addition to the above modifications, it is not necessary to apply the ATR mixture to the cavity at one time. For example, the cavity is partially filled with the ATR mixture, the mixture reacts and then more ATR mixture is added to react the mixture. If the reaction product from the first ATR mixture is still molten when the second ATR mixture is added, the two metal phases and the two slag phases combine to form substantially two phases as shown in FIG. However, in the second addition of the ATR mixture, four distinct layers are formed if the reaction product from the first ATR mixture is solidified. That is, the collision of metal and slag overlying from the original ATR mixture and the secondary metal and slag applied thereon from the secondary ATR mixture.

The above method of adding the ATR mixture twice provides the advantage that the upper slag layer formed when the secondary ATR mixture reacts is denser, less porous. The initial ATR reaction is believed to have some slag porosity because the reaction is in contact with a cast iron cast plate and the carbon in the cast iron reacts with oxygen in the ATR mixture to form CO ₂ . However, secondary ATR products are certainly less exposed to the cast iron surface and therefore produce less CO ₂ . It is interesting to note that when a second ATR mixture is added, slag with a high specific gravity occurs whether the first ATR reaction product solidifies or not.

In the above sphere, a method of filling the cavity created in the mold plate 10 is described. However, it should be noted that the same process can be used to fill the cavities in the bottom of the hermetic ingot mold. As far as the bottom hermetic ingot template is concerned, other embodiments of the invention have been successfully carried out with the whole bottom part having a monolithic slag layer. 3 and 4 illustrate embodiments of the invention described above for repairing a bottom hermetic ingot mold 30 having a corrosion cavity 32 at its bottom. In this embodiment of the present invention, the ATR reaction slag phase 36 is about 3 inches or less to fill not only part of the cavity 32 but also to create a thin layer of slag that can completely cover the bottom of the mold 30. Sufficient ATR mixture 34 is provided to cover the mold bottom with thickness. The metal phase 36 will be firmly bonded to the bottom of the cavity 32, while the slag phase 38 will adhere to the metal phase and the bottom of the ingot mold 30.

Ideally, the slag-like layer should not exceed about 1-2 inches because shorter ingot stripping takes place unless thicker deposits as well as special and very high ingot molds are involved.

In the above embodiments, it is good to have only the slag phase 38 fill the cavity 32 overflowing.

If the metal phase 36 covers the entire bottom of the ingot mold 30, a problem arises. In particular, if the metal layer is thick and the slag layer is thicker, the thickness of the mold will be greatly reduced. This makes the ingot casting fairly short. On the other hand, if such an upper metal layer is thin, the heat therein immediately dissipates to the mold bottom, so that the metal does not form a good bond with the mold bottom. Therefore, to obtain optimal results, the amount of ATR mixture used in this embodiment should be such that the entire metal phase can be contained in the cavity such that only the slag phase extends from the mold wall to the wall. This requires the volume of the ATR mixture used to be at least 1.5 times the volume of the cavity, i.e. more than necessary to fill only the cavity with metal and slag, and less than 5 times the volume of the cavity, i.e. to fill the cavity completely with metal.

Since the slag deposits overlying in each of the above embodiments are fragile, such a repaired plate or ingot mold will eventually cause the slag phase to break and fall off. Originally, for this reason, as noted above, it was thought that the slag phase should be removed before using the repair. In other words, it was feared that the slag phase would break when the tip was comforted in the casting ingot and the steel was injected into the mold. Contrary to these concerns, however, we applied the method to repair many plates and molds but did not see ingots contaminated with slag inclusions from the ATR repair. Thus, slag deposits not only cause ingot contamination but also provide the advantage of being less susceptible to corrosion during injection. Thus, the slag phase provides extra protection from corrosion and extends the life of the repaired plate or mold.

Claims (1)

Overheated metal and slag phases are placed in a cavity by heating a metal-generating pyrogenic reaction mixture containing metal oxides and having a volume of no more than 1.5 times the volume of the cavity (1.5 times or more for ingot moulds). Forming a melt, allowing the melt to be completely contained in the corrosion cavity, holding the melt for a time sufficient to separate the metal phase at the bottom and the slag phase thereon, allowing the melt to solidify and firmly bond the metal phase to the bottom of the cavity A slag phase is a method for repairing corroded cavities in the bottom of an ingot mold plate and a bottom hermetic metal mold or an ingot mold composed of being firmly attached to a metal phase.

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