Molten metal pump, metal plate plating device, and method for manufacturing plated metal plate

Abstract

To provide a pump for molten metal that has a ceramic-made liner arranged on an inner surface of a casing opposed to an impeller and that prevents molten metal from entering between the casing and liner to prolong the lifetime of the pump itself.MEANS FOR SOLVING THE PROBLEM: An unshaped refractory is arranged between a casing and a liner arranged on an inner surface (impeller opposed surface) of the casing which corresponds to an impeller. Further, the unshaped refractory has a multi-layered structure of two or more layers, and is so arranged as to gradually decrease in coefficient of thermal expansion from the side of casing toward the liner, or uniformly vary in bulk density from the side of the casing toward the liner.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a molten metal pump used for transporting molten metal, a metal plate plating apparatus having the pump, and a method for producing plated metal plate using the plating apparatus. [Background technology]

[0002] When manufacturing plated metal sheets (plated metal sheets) such as zinc-plated steel sheets and aluminum-plated steel sheets, one method involves passing a metal sheet such as a steel sheet through a molten metal bath (plating bath) of the plating metal to form a plating metal layer on the metal sheet surface. In particular, for zinc-plated and aluminum-plated steel sheets such as steel sheets for automobiles, this method of continuously passing the steel sheet through such a molten metal bath (plating bath) is used because it allows for highly efficient production. The equipment used for this type of continuous production is called a continuous plating equipment.

[0003] In continuous coating equipment, steel sheets typically enter the coating bath through a snout. The snout has an atmosphere-controlled duct structure, one end of which is immersed in the coating bath. The steel sheet passes through the snout and enters the coating bath. Therefore, floating contaminants such as scum and dross tend to accumulate on the surface of the coating bath inside the snout. These contaminants are formed by reactions between metal components in the coating bath and components of the passing steel sheet. When these contaminants float on the bath surface, they are dragged along by the passing steel sheet, becoming entrained in the coating layer and leading to deterioration of coating quality. Therefore, floating contaminants on the bath surface inside the snout are discharged out of the snout using a push-pull system using a molten metal pump (see, for example, Patent Document 1).

[0004] Molten metal pumps (submerged pumps) used in coating baths generally consist of components such as a casing, impeller, shaft, and branch pipes (see, for example, Figure 1). The casing and branch pipes are made of heat-resistant cast steel that can withstand the temperature of the molten metal, but in areas where the molten metal flows at high speeds, erosion by the molten metal (especially aluminum) and corrosion due to contact between dissimilar metals (hereinafter, erosion and corrosion are collectively referred to as erosion in this specification) can become a problem, so the impeller and shaft are often made of ceramic.

[0005] The flow of molten metal becomes faster around the impeller, and the inner surface of the casing facing the impeller (the impeller-facing surface) is particularly exposed to the fast flow of molten metal. Although the casing is made of heat-resistant cast steel, it can be eroded by the flow of molten metal and, in the worst case, can be damaged. This erosion of the impeller-facing surface is severe, drastically shortening the life of the submerged pump. In other words, the erosion of the impeller-facing surface is the rate-limiting factor for the life of the submerged pump, and it also affects the repair plan for the entire plating equipment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-293107 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-117989 Summary of the Invention [Problem to be solved by the invention]

[0007] As a countermeasure against erosion on the impeller facing surface, for example, a method of forming a thermal spray coating 13 of wear-resistant metal as shown in Figure 4(a) has been proposed. However, even if a wear-resistant metal is sprayed, the penetration of molten metal cannot be completely prevented due to the through pores in the spray coating, and the sprayed metal ends up peeling off in parts, so the erosion suppression effect is limited.

[0008] It is also possible to use ceramic for not only the impeller but also the casing. However, although ceramics are resistant to wear, they are weak to impacts, so if the casing were also made of ceramic, it would be difficult to handle and there would be a risk of it being damaged during installation. Furthermore, the price would be significantly higher, making it impractical.

[0009] Patent Document 2 proposes a casing in which a ceramic liner (referred to as a cassette in Patent Document 2) is placed on the surface facing the impeller, which is susceptible to erosion by molten metal (Fig. 4(b)). The placement of this ceramic liner has a certain effect on preventing casing erosion. However, there is a large difference in the thermal expansion coefficient between the ceramic and the metal material (such as heat-resistant cast steel) that makes up the casing. Even if the liner is fitted into the casing at room temperature, the temperature of the molten metal bath is high during operation, and the difference in thermal expansion creates a gap between the liner and the casing. It has been found that molten metal penetrates this gap and erodes the metal material of the casing. Furthermore, it has been found that a large gap between the ceramic liner and the casing can, in some cases, induce vibration of the liner, potentially causing damage.

[0010] Therefore, the present invention aims to provide a molten metal pump in which a ceramic liner is placed on the surface of the inner casing facing the impeller (impeller-facing surface), in which the problem is to prevent molten metal from entering between the casing and the liner and to extend the life of the pump itself. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and have obtained the following findings. (a) It was discovered that by placing an amorphous refractory between the casing and a liner placed on the impeller-facing surface of the casing, even if a gap occurs due to the difference in thermal expansion between the casing and the liner at high temperatures, the amorphous refractory can fill the gap and prevent molten metal from entering. For example, even if the casing is made of heat-resistant cast steel and the liner is made of ceramics, by placing an unshaped refractory material between them, it is possible to prevent molten metal from penetrating into the gap between them (gap sealing effect).

[0012] (b) Furthermore, it was found that the gap sealing effect can be improved by making the monolithic refractory into a multi-layer structure of two or more layers.

[0013] (c) In the case of a multi-layer structure, it has been found that the gap sealing effect can be further improved by making the thermal expansion coefficient of the monolithic refractory higher on the casing side. Note that the thermal expansion coefficient is treated as synonymous with the thermal expansion coefficient and the linear expansion coefficient.

[0014] (d) Alternatively, in the case of a multi-layer structure, it has been found that the bulk density of the monolithic refractory material should be different, preferably arranged so that it changes uniformly from the casing side, thereby alleviating the thermal stress caused by the difference in thermal expansion between the casing and the liner and enhancing the gap sealing effect. The present invention was made based on the above findings, and the gist of the present invention is as follows.

[0015] [1] A molten metal pump having at least a tubular casing and an impeller disposed inside the casing, a liner is disposed on at least a portion of the inner surface of the casing that faces the impeller; A molten metal pump characterized in that a castable refractory material is disposed between the liner and the casing. [2] The molten metal pump according to [1], wherein the monolithic refractory has a multi-layer structure of two or more layers extending from the casing to the liner. [3] A molten metal pump as described in [1] or [2], wherein the thermal expansion coefficient of the monolithic refractory material is between the thermal expansion coefficients of the casing and the liner, and is arranged so that it decreases in order from the casing side to the liner side. [4] A molten metal pump as described in [2], wherein the bulk density of the monolithic refractory material is arranged so as to uniformly change from the casing side to the liner side. [5] The molten metal pump according to any one of [1] to [4], wherein the casing is made of heat-resistant cast steel and the liner is made of ceramics. [6] The molten metal pump according to any one of [1] to [5], wherein a mold release agent is disposed between the casing and the monolithic refractory. [7] The molten metal pump according to any one of [1] to [6], wherein the molten metal has an aluminum (Al) content of 50 mass % or more. [8] A plating apparatus for a metal plate, comprising the molten metal pump according to any one of [1] to [6]. [9] [8] A method for producing a plated metal sheet, characterized by using the plating apparatus described in [8]. [Effects of the Invention]

[0016] The present invention can extend the service life of molten metal pumps used in the production of plated metal sheets, thereby extending the maintenance intervals of not only the molten metal pumps but also the plating equipment, resulting in improved productivity and reduced repair costs. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing an example of an overall cross section of a molten metal pump according to the present invention. [Figure 2] 1 is a schematic diagram showing an example of a partial cross section of the impeller and its surroundings of a molten metal pump according to the present invention. [Figure 3]1 is a schematic diagram showing an example of a cross section of an impeller-facing surface of a molten metal pump according to the present invention. [Figure 4] Fig. 4(a) is a schematic diagram showing an example of a partial cross section of the impeller and its periphery in a conventional molten metal pump, where Fig. 4(b) is a conceptual diagram showing the case where a thermal spray coating is formed on the casing, and Fig. 4(b) is a conceptual diagram showing the case where only a liner is arranged. DETAILED DESCRIPTION OF THE INVENTION

[0018] The molten metal pump according to the present invention is used to transport molten metal, and the type of metal and its application are not particularly limited. Here, the description will be given mainly of a molten metal pump used in the production of hot-dip galvanized steel sheets and hot-dip aluminized steel sheets (hereinafter, both are collectively referred to as plated steel sheets) as an example.

[0019] As mentioned above, in the production of coated steel sheets, steel sheets are continuously passed through a molten metal bath (coating bath). During this process, to remove floating foreign matter such as scum and dross from the surface of the coating bath (bath surface), especially floating foreign matter in the snout, a molten metal pump (sometimes called a submerged pump or simply a pump) is placed in the bath, and a flow is created on the bath surface using a push-pull system to remove the floating foreign matter.

[0020] Figure 1 shows a schematic cross-sectional view of an example of a submerged pump. Pump 1 in Figure 1 is an example of a push-side pump (the pump that pushes molten metal toward the bath surface). The pump in Figure 1 includes a tubular casing 2, an impeller 3 inside the casing that rotates to create a flow in the molten metal, a shaft 4 connected to the impeller and positioned along the casing's axial axis, a motor 5 (e.g., an air motor) for rotating the shaft, and a branch pipe 6 for discharging the molten metal. The submerged pump in Figure 1 rotates the impeller 3 to create a flow of molten metal in the axial direction of the casing (upper side in the figure), which is then discharged to the bath surface 7 through the branch pipe 6. This is a so-called axial flow pump. While the rotation of impeller 3 primarily drives the molten metal in the axial direction of the casing (upper side in the figure), centrifugal force due to the rotation of impeller 3 also creates a flow toward the inner surface of the casing. This flow toward the inner surface of the casing erodes the casing 2. To prevent this erosion, a liner 10 is placed on the inner surface of the casing that faces the impeller (impeller-facing surface).

[0021] The impeller-facing surface refers to the portion of the inner surface of the casing with which the flow of molten metal generated by the impeller collides. Since the purpose of the liner 10 is to prevent erosion of the inner surface of the casing, it can be considered to be the portion of the inner surface of the casing 2 where erosion is a concern. For example, in the case of an axial flow pump as shown in FIG. 1, when viewed in cross section, it is preferable that the liner 10 include a portion of the inner surface of the casing 2 extending from a position corresponding to the lower end of the impeller (the end on the suction side of the molten metal) to a length corresponding to 1.2 to 3.0 times the impeller height (the distance from the upper end of the impeller (the end on the discharge side of the molten metal) to the lower end of the impeller in the direction of the flow of the molten metal (the axial direction of the casing)). It is sufficient that the liner 10 is disposed on at least a portion of the impeller-facing surface. Of course, it is preferable that the liner 10 be disposed over the entire surface of the impeller-facing surface, but this can be appropriately selected depending on the pump structure.

[0022] Figure 1 shows an example of an axial flow pump, but the pump type (centrifugal pump, mixed flow pump, etc.) is not particularly limited. Even with pump types other than axial flow pumps, it is good to consider the part of the inner surface of the casing where the flow of molten metal caused by the impeller collides, or the part of the inner surface of the casing where erosion is a concern, as the impeller facing surface.

[0023] The pump material is not particularly limited, but typically, metal materials are used for non-moving parts such as the casing 2 and branch pipe 6, while ceramics are used for moving parts such as the shaft 4 and impeller 3. Because the bath temperature is high, around 460°C for hot-dip galvanizing and around 680°C for hot-dip aluminizing, heat-resistant cast steel or stainless steel is typically used for the casing 2 and branch pipe 6. Ceramics used for the impeller 3 and other components generally have high-temperature resistance and are corrosion-resistant and abrasion-resistant to molten metals, so the type of ceramic is not particularly limited. For example, the ceramic can be appropriately selected from sialon, Si3N4, SiC, SiN, ZrO2, alumina (Al2O3), etc.

[0024] Figure 2 shows a cross-sectional view of the impeller and its surroundings in the molten metal pump 1 shown in Figure 1. The inner surface of the casing and the liner 10 are assembled at room temperature. In conventional submerged pumps, a small gap 12 is sometimes provided between the casing 2 and the liner 10 to facilitate assembly (see, for example, Figure 4(b)). The casing may be deformed, particularly during repairs, and a gap is sometimes provided between the casing and the liner to account for this. Furthermore, when the pump is placed in the bath, both the casing and the liner expand due to the high temperatures described above. However, if the casing 2 is made of metal and the liner 10 is made of ceramic, the difference in thermal expansion between them will widen the gap. If a gap is created, molten metal will penetrate there and erode the casing. For this reason, in the present invention, a castable refractory 11 is placed between the casing 2 and the liner 10 in advance. By disposing the monolithic refractory 11, even if a gap widens due to the difference in thermal expansion between the casing 2 and the liner 10 at high temperatures, the gap can be filled with the monolithic refractory, preventing the molten metal from contacting the casing 2 and preventing erosion of the casing 2. For example, the thermal expansion coefficient of heat-resistant cast steel is 14 to 16 × 10 -6 / K (500℃), whereas for ceramics, for example, SiC is 3.7×10 -6 / K (400℃), 2.8 × 10 for Si3N4 -6 / K (400℃), 3.0×10 for sialon -6 / K (20 to 800°C). The thermal expansion coefficient of monolithic refractories is approximately 5 to 10 × 10 -6 / K, which is an intermediate thermal expansion coefficient between that of metal materials and ceramics. Therefore, by placing the monolithic refractory 11 between the casing 2 and the liner 10, it is expected to function as a buffer layer between them.

[0025] The material of the monolithic refractory is not particularly limited. It may be appropriately selected from alumina, clay, silicon carbide, fused silica, magnesia, mortar, etc. From the viewpoint of impact resistance at high temperatures, alumina or silicon carbide monolithic refractories are preferred.

[0026] The monolithic refractory 11 may have a single layer or a multi-layer structure of two or more layers. A multi-layer structure of two or more layers is preferable. Figure 3 shows a case where the monolithic refractory has two layers. The multi-layer structure enhances the functional effect of the monolithic refractory as a buffer layer between the casing 2 and the liner 10. For example, the thermal expansion coefficient of the monolithic refractories 11 (11A, 11B) may be set to a value between the thermal expansion coefficients of the casing 2 and the liner 10, and the thermal expansion coefficients of the monolithic refractories, including the monolithic refractories, may be arranged so that they change sequentially from the casing to the liner. For example, if the liner is made of ceramic and the casing is made of metal, the thermal expansion coefficient of the monolithic refractory 11B on the liner side may be smaller than the thermal expansion coefficient of the monolithic refractory 11B on the casing side. This inclined arrangement from the perspective of thermal expansion coefficients can buffer thermal stress due to the difference in thermal expansion between the casing 2 and the liner 10, thereby preventing damage to the monolithic refractory 11. Therefore, the gap between the casing and the liner can be stably filled, the attack of the molten metal on the casing 2 can be reduced, and erosion can be suppressed.

[0027] Furthermore, when the monolithic refractory has a multi-layer structure, each layer of the monolithic refractory may be arranged at an inclination in terms of bulk density. That is, the layers of the monolithic refractory may be arranged so that the bulk density of the monolithic refractory changes uniformly (either increasing or decreasing) from the casing 2 side toward the liner 10 side. For example, the bulk density of the monolithic refractory 11B on the liner side may be increased sequentially compared to the bulk density of the monolithic refractory 11B on the casing side. Conversely, the layers may be arranged so that the bulk density decreases sequentially from the casing side. Since a low bulk density indicates a high porosity and a high bulk density indicates a low porosity, arranging the layers so that the bulk density increases from the casing 2 side toward the liner 10 means arranging the monolithic refractory layers so that the porosity decreases sequentially. This makes it easier to follow deformation due to thermal expansion, buffers thermal stress due to the difference in thermal expansion between the casing 2 and the liner 10, and suppresses destruction of the monolithic refractory 11. Therefore, the gap between the casing 2 and the liner 10 can be stably filled, reducing the attack of molten metal on the casing 2 and suppressing erosion. Preferably, a monolithic refractory layer with a low bulk density (high porosity) is arranged on the casing side with a high thermal expansion coefficient, and the bulk density increases toward the liner. This is because the lower bulk density (higher porosity) has better followability to the casing, which undergoes large deformation due to thermal expansion.

[0028] A release agent may be disposed between the casing 2 and the monolithic refractory 11, or between the liner 10 and the monolithic refractory 11, or both. By disposing the release agent, when inserting the monolithic refractory 11 between the casing 2 and the liner 10, the wettability of the monolithic refractory 11 to the casing 2 and the liner 10 is reduced, improving the fluidity of the monolithic refractory and facilitating insertion of the monolithic refractory. This allows the gap between the casing 2 and the liner 10 to be more stably filled, reducing the attack of molten metal on the casing 2 and suppressing erosion. The components of the release agent are not particularly limited as long as they are heat-resistant. For example, commercially available release agents, such as ZrO2-based release agents (containing 66% ZrO2 and 32% SiO2), can be used as appropriate.

[0029] The construction method for arranging the monolithic refractory is not particularly limited. For example, the pressing plate 8 at the bottom of the casing 2 may be removed, the liner 10 may be attached, and then the monolithic refractory 11 may be inserted between the casing 2 and the liner 10. After insertion, the monolithic refractory 11 may be dried and hardened, and then the pressing plate 8 may be fastened to the casing 2 with bolts or the like (not shown). Alternatively, before attaching the liner 10 to the casing 2, the monolithic refractory 11 may be applied to the casing 2, and after drying and hardening, the liner 10 may be attached. When forming a multi-layer structure of monolithic refractories, it is preferable to first apply the casing-side monolithic refractory 11A to the casing 2, dry and harden it, and then apply the liner-side monolithic refractory 11B. When forming a two-layer structure of a casing-side monolithic refractory and a liner-side monolithic refractory, it is preferable to use the harder of the two monolithic refractories as the casing-side monolithic refractory. To arrange a hard monolithic refractory inside the casing, an installation method such as wetting the hard monolithic refractory with water can be used. For a multi-layer structure of three or more layers, it is preferable to repeat the above installation method. After forming the required monolithic refractory layers, it is preferable to attach the liner 10 and secure it with a pressure plate. When a release agent is placed between the casing 2 and the monolithic refractory 11, the release agent may be applied to the inner surface of the casing 2 before applying the monolithic refractory, and then the monolithic refractory may be placed.

[0030] The bath temperature differs between the galvanizing bath used when producing hot-dip galvanized steel sheets and the aluminizing bath used when producing aluminized steel sheets. The bath temperature varies depending on the main metal components. As described above, the temperature of a galvanizing bath (Zn content of 50% by mass or more) is around 460°C, while the temperature of an aluminizing bath (Al content of 50% by mass or more) is around 680°C, with the aluminizing bath being higher. The higher the temperature, the more severe the corrosion of the metal material casing. The higher the temperature of the molten metal (e.g., aluminizing bath), the greater the contribution of the effects of the present invention.

[0031] While the above description has been given with reference to a submerged pump for producing coated steel sheets, the molten metal pump of the present invention can be applied to any coating equipment for metal sheets that has a molten metal bath, without any particular restrictions. It can also be applied to both push-type and pull-type coating equipment. Similarly, a coating equipment having a molten metal pump of the present invention can be used in any method for producing coated metal sheets by hot-dip coating. [Example]

[0032] Using a snout molten metal pump in a manufacturing device for hot dip aluminized steel sheets, experiments were conducted at the levels shown below to compare the service life (lifespan). A. WC spray coating (thickness 0.1 mm) (Figure 4(a)) A. Ceramic liner only (no monolithic refractory) (Figure 4(b)) C. A single layer of monolithic refractory material is placed between the casing and the liner (similar to Figure 2). D. Two layers of monolithic refractories are placed between the casing and the liner (similar to Figure 3). Thermal expansion coefficient of monolithic refractories: Casing side > Liner side Bulk density: Casing side > Liner side E. Two layers of monolithic refractories are placed between the casing and the liner (similar to Figure 3). Thermal expansion coefficient of monolithic refractories: Casing side > Liner side Bulk density: Casing side < Liner side

[0033] The molten metal pump used is shown in the schematic diagram in Figure 1, and the materials of each part are as follows: Casing: Heat-resistant cast steel Shaft: Ceramics (Sialon) Impeller: Ceramics (sialon) Branch pipe: heat-resistant cast steel Ceramic liner (common to levels B to E): Sialon Monolithic refractories (level C): High alumina mortar Bulk density: 2.13g / cm 3 Thermal expansion coefficient: 8.1 x 10-6 / ℃ Monolithic refractories (level E): 1st layer (casing side): High alumina mortar Bulk density: 2.13g / cm 3 Thermal expansion coefficient: 8.1 x 10 -6 / ℃ Second layer (liner side): High alumina monolithic refractory Bulk density: 2.10 g / cm 3 Thermal expansion coefficient: 5.7 x 10 -6 / ℃ Monolithic refractories (level O): 1st layer (casing side): High alumina mortar Bulk density: 2.0g / cm 3 Thermal expansion coefficient: 8.1 x 10 -6 / ℃ Second layer (liner side): High alumina monolithic refractory Bulk density: 2.10 g / cm 3 Thermal expansion coefficient: 5.7 x 10 -6 / ℃

[0034] The test was applied to a normal hot-dip aluminized steel sheet manufacturing process, and the casing and liner were checked during equipment repairs. The cumulative time spent threading the steel sheet until repairs were required was defined as the service life (lifespan). The test results are shown in Table 1.

[0035] [Table 1] [Industrial Applicability]

[0036] The present invention can be applied to a pump for molten metal, and the pump can be used, for example, in the production of hot-dip metal plating on metal sheets. [Explanation of symbols]

[0037] 1. Molten metal pump (submerged pump) 2 Casing 3 impeller 4 shafts 5 motors 6 branch pipes 7 Bath surface 8 Presser plate 10 Liner 11, 11A, 11B Monolithic refractories 12. Gap between casing and liner 13 Thermal spray coating

Claims

1. A molten metal pump having at least a casing made of a metal material and an impeller disposed inside the casing, a ceramic liner is disposed on at least a portion of the inner surface of the casing that faces the impeller; A molten metal pump characterized in that a castable refractory material is disposed between the liner and the casing.

2. 2. The molten metal pump according to claim 1, wherein said monolithic refractory has a multi-layer structure of two or more layers extending from said casing to said liner.

3. A molten metal pump as described in claim 1 or 2, wherein the thermal expansion coefficient of the amorphous refractory material is between the thermal expansion coefficients of the casing and the liner, and is arranged so that it decreases in order from the casing side to the liner side.

4. 3. The molten metal pump according to claim 2, wherein the bulk density of said monolithic refractories is arranged so as to uniformly change from said casing side to said liner side.

5. 5. The molten metal pump according to claim 1, wherein the casing is made of heat-resistant cast steel.

6. 6. The molten metal pump according to claim 1, wherein a release agent is disposed between the casing and the monolithic refractory.

7. 7. The molten metal pump according to claim 1, wherein the molten metal has an aluminum (Al) content of 50 mass % or more.

8. A metal plate plating apparatus comprising the molten metal pump according to any one of claims 1 to 6.

9. A method for producing a plated metal sheet, comprising using the plating apparatus according to claim 8.

Images