Mould body and method for producing a mould body

Abstract

The invention relates to a mould body (1) for the continuous casting of metals from a metal melt and to a method for producing such a mould body (1), wherein the mould body (1) has a hot side (4) for contact with the metal melt and a cold side (5) for contact with a cooling liquid, wherein: the mould body (1) is made of copper or a copper alloy and the cold side (5) has at least one artificially weathered region (7); in this region (7) a copper patina is formed on the cold side (5); and the copper patina is impregnated with a hydrophobic impregnating agent and / or is sealed with a hydrophobic layer-forming sealant.

Description

[0001] Mold body and method for manufacturing a mold body

[0002] The invention relates to a mold body according to the features of claim 1 and a method for producing a mold body with the features of claim 5.

[0003] A mold is one of the most important components of a continuous casting plant. Solidification of the molten metal begins in the mold. Molds of the type in question are described, for example, in DE 1974305 A1. The basic structure consists of an outer steel frame and the actual shaping part of the mold, the mold body. The steel shell serves to position the mold body and ensure the necessary water circulation for cooling. The mold body is made of a material with high thermal conductivity, such as copper or a copper alloy. The mold body's primary function is to ensure the formation of a sufficiently thick, durable, and defect-free strand shell through continuous heat dissipation. Excessive heat dissipation, and thus excessively rapid cooling of the molten steel at the beginning of the solidification process, negatively impacts the surface quality of the strand.Microcracks and structural defects can occur. With angular casting strands, this can happen particularly in the corners, as the geometry results in greater cooling in these areas. It is known to reduce heat dissipation by applying a coating to the outside (DE 19747305 A1). The coating can be applied electroplated or as a thermal spray coating to the outside of the mold. However, a metal spray coating is comparatively complex to produce.

[0004] German patent DD 3 536 B1 discloses a continuous casting mold for producing blocks and ingots from crack-prone materials, wherein a layer of a material with a lower thermal conductivity than the mold material is applied to the outer wall of the mold facing the coolant. The thermal insulation on the outer wall of the mold facing the coolant can, for example, consist of a scale layer at least 0.25 mm thick. This layer can be produced by artificially accelerating scale formation, mimicking the conditions of natural scale growth. The thermal insulation effect of the oxide layer can be enhanced by applying a coating.

[0005] The invention is based on the objective of demonstrating a mold body and a method for producing a mold body in which heat dissipation can be effectively and cost-efficiently reduced locally by measures on the outside of the mold.

[0006] This problem is solved by a mold body having the features of claim 1 and by a method for producing such a mold body according to the features of claim 5.

[0007] The dependent claims relate to advantageous further developments of the invention.

[0008] The die body according to the invention is used for continuous casting of metals from a molten metal. The die body has an inner side, which is the hot side for contact with the molten metal. The die body has an outer side, which is the cold side for contact with a cooling liquid. The die body is made of copper or a copper alloy. According to the invention, the cold side has at least one artificially weathered area. In this artificially weathered area, a copper patina is formed on the cold side. The copper patina is impregnated with a hydrophobic impregnating agent and / or sealed with a hydrophobic film-forming sealant.

[0009] The invention takes advantage of the fact that copper and copper alloys have the property of forming a copper patina, which is formed from the substrate on which it is applied. Copper patina has a thermal conductivity of 1 to 2 W / mK. In comparison, the CuAg alloy, which can be used for die bodies, has a thermal conductivity of 377 W / mK. The copper patina acts as a thermal barrier against the copper material. This thermal barrier is produced by artificial weathering until it has a sufficient thickness to produce a significant physical effect, namely a reduction in heat dissipation. It preferably has a thickness of 20 to 30 µm.

[0010] The copper patina is not water-resistant. When a mold body is used in a water chamber of a mold, the cold side, which is in contact with the cooling fluid, usually cooling water, is permanently exposed to the coolant. Tests have shown that the copper patina would be eroded within a short time. Therefore, according to the invention, the copper patina is impregnated with a hydrophobic impregnating agent and / or sealed with a hydrophobic film-forming sealant.

[0011] Impregnation and sealing each prevent water from penetrating the copper patina. While impregnations penetrate the capillary system of the copper patina, sealants form a protective film on the surface of the copper patina. Impregnations can have a longer lifespan than sealants because they are effective within the copper patina and are therefore not subject to mechanical wear. They are generally not visually perceptible. Impregnations and sealants can be combined. The mold body according to the invention is, in particular, a tubular mold. The tubular mold can have a corner area or corner areas for producing a polygonal extruded profile. The artificially weathered areas are arranged, in particular, in the corner area to counteract overheating of the corner areas. This homogenizes the cooling process.Different textures with heat-insulating copper patina layers can be applied to the mold body. Therefore, there can be not just one artificially weathered area with the copper patina, but preferably several. In rectangular pipe molds, the artificially weathered areas with the copper patina are located particularly in the corners. Specifically, the copper patina can be applied to a roughened area on the hot side. This is particularly likely to be a previously sandblasted area.

[0012] Measurements and calculations have shown that the corners of a non-inventive die without artificially weathered areas are over 30°C cooler than the central surfaces of the die. This temperature difference, combined with the cooling of the corner area from two sides, leads to greater shrinkage in the corner area, which in turn can cause longitudinal cracks. In a comparative analysis, the calculations were repeated for a die with artificially weathered corner areas and a corresponding copper patina. It was found that the patina on the corner areas increases the corner temperature by 20°C, thus reducing the temperature difference compared to the central surfaces. This means that the cooling is more homogeneous overall and the strand growth is more uniform. As a result, the quality of the steel strand is improved.

[0013] The inventive measure for reducing heat dissipation is effective and more cost-efficient than other measures that do not use a heat-insulating functional surface formed from the substrate itself, but instead provide an applied coating made of other materials.

[0014] To create the heat-insulating areas of the mold body, the cold side is first masked to expose those areas that should not be artificially weathered. Such a mask can, for example, be glued to the surface of the mold body. The exposed areas can optionally be roughened before or after masking, e.g., by sandblasting, to increase the surface area for the formation of the copper patina.

[0015] After masking, the areas to be artificially weathered are brought into contact with at least one patination solution one or more times. Patination can be achieved by immersion, wetting, or spraying. Without the use of a patination solution, the formation of a copper patina would take several years. Patination solutions accelerate the process. Before wetting with these chemicals, the surface to be weathered is degreased, if necessary, and mechanically roughened as described above, in particular by sandblasting. Patination, i.e., the application of the patination solution, can be carried out in several stages. The copper patina is produced by a reaction of one or more chemicals with the copper surface under specific conditions. This can involve aging or weathering in a maturation chamber. Once a predetermined patina quality is reached, the surface can be further treated.The resulting copper patina forms a porous layer of copper salts, such as brochantite, paratacamite, malachite, or any mixtures thereof. Once the copper patina has formed, it is brought into contact with a fixative.

[0016] The fixing agent can be an impregnating agent or a sealant. An impregnating agent penetrates the capillaries of the copper patina and fixes it from the inside. A sealant, alternatively or additionally, forms a coating on the surfaces outside the capillaries. Both the impregnating agent and the sealant are hydrophobic. By varying the ratio of impregnating agent and / or sealant, different viscosities can be applied. The correlation between porosity, viscosity, and penetration depth leads to an increase in the hydrophobic properties and the adhesion resistance of the copper patina, and thus to an improvement in its service life.

[0017] The microporosity of copper patina is generally advantageous, as it allows the sealant or impregnating agent to penetrate the patina and ensure good adhesion. The sealant or impregnating agent is hydrophobic and, in particular, permanently elastic. Any solvent it contains leaches out over time, causing the patina layer to harden. The success of the coating depends on the removal of dust, dirt, grease, and moisture before applying the sealant or impregnating agent. The liquid sealant or impregnating agent can be applied by brushing, spraying, or dipping. The surface can be impregnated or sealed several times in succession (wet-on-wet method) or immersed in the sealant or impregnating agent for at least 15 minutes.

[0018] After impregnation or sealing, drying takes place, which can be done at slightly elevated temperatures, such as 40°C for several hours. The copper patina can withstand light use after just a few hours of curing. Drying should take place at least 3°C ​​above the dew point temperature.

[0019] Complete curing can take 7 to 14 days. This waiting period should be observed before the mold body is used as intended. It is considered particularly advantageous that the mold body does not need to be stored at the production site for 7 to 14 days. Curing can occur during transport of the mold body from the production site to the point of use. Curing can, of course, also take place after transport to the customer or even at the point of use. Even before complete curing, the fixed copper patina is mechanically resilient enough that it will not be damaged during transport.

[0020] The special feature of the inventive method is that no coating in the sense of a surface covering is applied to the mold body, consisting exclusively of additive materials that differ from the substrate of the mold body, for example, a thermal spray coating. The chemicals for patination merely stimulate patina formation. The copper patina consists primarily of the copper material of the mold body itself. The physical effect of the thermal insulation is attributable to the copper patina and not to the impregnating agent or the sealant. The latter serve to fix the copper patina and not to alter the thermal insulation in the patinated areas. The inventive method for producing a mold body is not only suitable for use with pipe molds. The term "mold body" encompasses any geometry of a forming mold body, i.e.,also sections or areas of multi-part molds, in particular mold plates, several of which together define a mold cavity.

[0021] The invention is explained below with reference to the embodiment shown in Figure 1.

[0022] Figure 1 shows a mold body 1 in a perspective view. It is a tubular mold with a square cross-section. The mold body 1 is used for continuous casting of steel. The arrow indicates the pouring direction G. The mold body 1 defines a mold cavity 2 with a pouring end 3 for molten metal. The mold body 1 itself is made of a copper alloy.

[0023] The inner, shaping side of the mold body 1 is referred to as the hot side 4. The opposite outer side is referred to as the cold side 5 because it is cooled. For this purpose, the mold body 1 is positioned within a support frame that supports it. A cooling fluid is circulated through a cooling gap between the outer side and the support frame.

[0024] The outer corner regions 6 of the mold body 1 are rounded. Within these corner regions 6, at a distance from the end-face inlet opening 3, are artificially weathered regions 7. In this example, the artificially weathered regions 7 are almost twice as wide as the rounded corner regions 6. They extend parallel to the corner regions 6, which are specifically defined by the outer radius of the mold body 1, and are therefore strip-shaped, running parallel to and spaced apart from each other, just like the corner regions 6. The area of ​​the artificially weathered regions 7 is smaller than the area of ​​the non-artificially weathered regions located in the middle of the side walls of the mold tube 1.

[0025] The artificially weathered areas 7 possess a copper patina, not shown in detail, which is further impregnated with a hydrophobic impregnating agent and / or sealed with a hydrophobic film-forming sealer. The artificially weathered areas 7 were mechanically roughened before patination, e.g., by sandblasting. The artificially weathered areas 7 are each strip-shaped and extend parallel to the corner areas 6 in the longitudinal direction of the mold body 1 to the exit side of the mold body 1 at the lower end in the image plane.

[0026] The copper patina has a thickness of 20 to 30 pm. It has a thermal conductivity of 1 to 2 W / mK.

[0027] Reference mark:

[0028] 1 - Mold body

[0029] 2 - Mold cavity

[0030] 3 - End of forehead

[0031] 4 - Hot side of 1

[0032] 5 - Cold side of 1

[0033] 6 - Corner area

[0034] 7 - artificially weathered area

[0035] G - Casting direction

Claims

Patent claims 1. Mold body (1 ) for continuous casting of metals from a molten metal, having a hot side (4) for contact with the molten metal and a cold side (5) for contact with a cooling liquid, wherein the mold body (1 ) is made of copper or a copper alloy and wherein the cold side (5) has at least one artificially weathered area (7), wherein a copper patina is formed in this artificially weathered area (7), wherein the copper patina is impregnated with a hydrophobic impregnating agent and / or sealed with a hydrophobic film-forming sealant.

2. Mold body (1) according to claim 1, characterized in that it is a tubular mold, wherein the tubular mold has corner areas (6), wherein artificially weathered areas (7) are arranged in the corner areas (6).

3. Mold body (1 ) according to claim 1 or 2, characterized in that the copper patina has a thickness of 20 to 30 pm.

4. Mold body (1 ) according to one of claims 1 to 3, characterized in that the copper patina is arranged on a mechanically roughened area of ​​the cold side (5).

5. Method for producing a die body (1) according to one of claims 1 to 4, characterized in that a mask is applied to the cold side (5) which leaves out the areas (7) to be artificially weathered, wherein after masking the areas (7) to be artificially weathered are brought into contact with at least one patina liquid one or more times to form a copper patina in the artificially weathered areas (7), wherein the formed copper patina is brought into contact with a hydrophobic impregnating agent and / or sealed with a hydrophobic film-forming sealer.

6. Method according to claim 5, characterized in that the copper patina is produced with a thickness of 20 to 30 pm.

7. Method according to claim 5 or 6, characterized in that the areas (7) to be artificially weathered are roughened before contact with the patination liquid.

8. Method according to claim 7, characterized in that the areas (7) to be artificially weathered are sandblasted.

9. Method according to one of claims 5 to 8, characterized in that the copper patina with the impregnating agent and / or with the sealant is allowed to harden for 7 to 14 days before the mold body (1) is used as intended.

10. Method of claim 9, characterized in that the curing takes place during the transport of the mold body (1) from its place of manufacture to the place of use.

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