Apparatus for manufacturing hot-dip galvanized steel sheet and method of manufacturing the same

Abstract

Provided is a technique for producing a hot-dip galvanized steel sheet having few surface defects. A production apparatus for a hot-dip galvanized steel sheet includes: a molten zinc container that stores molten zinc; a furnace nose that is disposed so as to dip an end portion in a molten zinc bath in the molten zinc container and supplies a steel sheet into the molten zinc bath; a submerged roll that is disposed so as to dip in the molten zinc bath in the molten zinc container and winds the steel sheet around; a support roll that is disposed above the submerged roll so as to dip in the molten zinc bath and is arranged in contact with one or both sides of a lifting side of the steel sheet; and a rectifier plate that is disposed above the submerged roll and has a rectification mechanism that controls the flow of the molten zinc in the molten zinc container, the rectifier plate being disposed so that the shortest distance from a lower end position to the surface of the submerged roll is in a range of greater than 0 mm and 50 mm or less, and the lower end position is in a range from the horizontal direction end portion of the furnace nose side of the submerged roll to the center axis of the submerged roll when viewed from above.

Description

Technical Field

[0001] This invention relates to an apparatus for manufacturing hot-dip galvanized steel sheets, and more specifically, to an apparatus for manufacturing hot-dip galvanized steel sheets with fewer surface defects, and to a method for manufacturing hot-dip galvanized steel sheets using the apparatus. Background Technology

[0002] Hot-dip galvanized steel sheets, especially galvanized steel sheets, are widely used in building materials, automobiles, and home appliances. Moreover, in these applications, hot-dip galvanized steel sheets require excellent appearance regardless of the presence or absence of coating. While the appearance after coating is obviously uncoated, it is highly susceptible to surface defects such as blemishes and foreign matter adhesion; therefore, the absence of these surface defects is crucial.

[0003] Hot-dip galvanized steel sheets are typically manufactured by immersing the steel sheet in a molten zinc bath (hereinafter sometimes referred to as a plating bath or bath) in a continuous hot-dip galvanizing equipment. Submerged rollers and support rollers are present in the plating bath and are in contact with the steel sheet. The steel sheet, which is to be plated, is annealed in an annealing furnace, and then immersed in the molten zinc bath through the furnace nose. The plating process is performed by controlling the amount of adhesion using a gas wiping device. At this time, there is a problem that oxides of molten zinc generated in the furnace nose adhere to the plated part, becoming a defect. This defect is referred to below as a zinc ash defect. To prevent this zinc ash defect, it is necessary to control the flow of the molten zinc bath and suppress the flow of zinc oxide adhering to the plated part. As a technique for controlling the flow of the molten zinc bath, Patent Document 1 can be cited as an example. Patent Document 1 discloses an apparatus having a rectifying mechanism disposed above the submerged rollers and controlling the flow of molten zinc in the molten zinc container, which can suppress the slag entrapment at the support rollers.

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-224457 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, the following issues must be addressed in the aforementioned prior art.

[0008] That is, the technology described in Patent Document 1 is a technique for controlling the flow of so-called bottom slag, which has a higher density and is more prone to settling than molten zinc, on the surface side of the plating bath. Here, the flow generated by the collision between the accompanying flow of the steel plate entering the molten zinc bath and the accompanying flow based on the rotation of the submerged roller is called "collision flow". In Patent Document 1, the zinc ash generated in the furnace nose and transported along with the collision flow is not considered. In particular, the distance between the lower end of the rectifier plate and the surface of the submerged roller is large, making it impossible to suppress the collision flow from the rectifier plate to the support roller side. Therefore, there is a problem that the zinc ash comes into contact with the lifted steel plate, becoming a surface defect.

[0009] This invention was made to solve the aforementioned problems, and its object is to provide an apparatus for manufacturing hot-dip galvanized steel sheets with fewer surface defects, thus reducing the occurrence of zinc ash defects. Furthermore, a method for manufacturing hot-dip galvanized steel sheets using this manufacturing apparatus is proposed.

[0010] Methods for solving problems

[0011] The inventors conducted flow analysis in a hot-dip galvanized steel sheet manufacturing apparatus. The results showed that the flow within the molten zinc bath varied depending on the positional relationship between the rectifier plate and the submerged roller. In particular, they discovered a flow mechanism that could suppress the adhesion of zinc oxide generated within the furnace nose to the steel strip surface.

[0012] The hot-dip galvanized steel sheet manufacturing apparatus of the present invention advantageously solves the above-mentioned problems. It is an apparatus for manufacturing hot-dip galvanized steel sheets by immersing the steel sheet to be galvanized in a molten zinc bath, causing the molten zinc to adhere to the surface of the steel sheet to form a coating. The apparatus is characterized by comprising: a molten zinc container for storing molten zinc; a furnace nose, provided with its end immersed in the molten zinc bath within the molten zinc container, and supplying the steel sheet to be galvanized into the molten zinc bath; and a submerged roller, provided with its end immersed in the molten zinc bath within the molten zinc container, and supplying the steel sheet to be galvanized. The submerged roller is equipped with a support roller, which is positioned above the submerged roller in such a way that it is immersed in the molten zinc bath and is arranged in contact with one or both sides of the lifting side of the steel sheet to be plated; and a rectifier plate, which is positioned above the submerged roller and has a rectifier mechanism for controlling the flow of molten zinc in the molten zinc container, wherein the rectifier plate is configured such that the shortest distance from its lower end position to the surface of the submerged roller is greater than 0 mm and less than 50 mm, and the lower end position, when viewed from above, is located from the horizontal end of the submerged roller on the furnace nose side to the central axis of the submerged roller.

[0013] It should be noted that, in the hot-dip galvanized steel sheet manufacturing apparatus of the present invention, (a) the width of the rectifier plate is greater than or equal to the width of the steel sheet to be galvanized, and (b) the thickness of the rectifier plate is 9 mm or more, and having ribs or the like is a more preferred solution.

[0014] The method for manufacturing hot-dip galvanized steel sheet of the present invention, which advantageously solves the above-mentioned problems, is characterized by comprising the following steps: using the hot-dip galvanized steel sheet manufacturing apparatus of any of the above-mentioned claims, immersing the steel sheet to be galvanized in a molten zinc bath, so that molten zinc adheres to the surface of the steel sheet to be galvanized to form a coating.

[0015] Invention Effects

[0016] According to the present invention, since the lower end of the rectifier plate disposed above the submerged roller of the molten zinc bath is positioned close to the submerged roller, the flow that causes zinc oxide generated in the furnace nose to adhere to the surface of the exit steel strip of the molten zinc bath can be suppressed. As a result, zinc oxide adhesion to the steel strip can be prevented, the generation rate of zinc ash defects can be significantly reduced, and thus productivity is improved, making it industrially useful. Attached Figure Description

[0017] Figure 1 This is a schematic concept diagram illustrating a manufacturing apparatus for hot-dip galvanized steel sheets according to one embodiment of the present invention.

[0018] Figure 2 This is a schematic conceptual diagram illustrating the flow of the molten zinc bath involved in the above embodiments.

[0019] Figure 3 This is a schematic diagram illustrating the flow of molten zinc in a conventional rectifier plate. Detailed Implementation

[0020] The embodiments of the present invention will now be described in detail. It should be noted that the accompanying drawings are schematic and may sometimes differ from reality. Furthermore, the following embodiments illustrate apparatus and methods for embodying the technical concept of the present invention, and do not specify the structure as described below. That is, the technical concept of the present invention can be modified in various ways within the scope of the claims.

[0021] Figure 1 The schematic diagram illustrates a hot-dip galvanized steel sheet manufacturing apparatus according to one embodiment of the present invention. The hot-dip galvanized steel sheet manufacturing apparatus 10 includes: a molten zinc container 1 for storing molten zinc Z; a furnace nose 2 disposed with its ends immersed in the molten zinc bath; and submerged rollers 4 and support rollers 5 and 6 immersed in the molten zinc bath. In this embodiment, a rectifier plate 7 is included, which has a rectification mechanism for controlling the flow of molten zinc within the molten zinc container 1. The hot-dip galvanized steel sheet manufacturing apparatus 10 may also include a coil feeding device (not shown), an uncoiler, an annealing furnace, a gas wiping device, an alloying furnace, a coil winding device, etc.

[0022] The steel sheet to be coated 3 is continuously fed from the furnace nose 2 into the molten zinc bath stored in the molten zinc container 1. The steel sheet to be coated 3 is wound around the submerged roller 4, changing its travel path from the entry direction to the lifting direction. Figure 1 In this example, the back-side support roller 5 on the inward-curling side of the lifted steel sheet 3 relative to the submerged roller 4 and the surface-side support roller 6 on the outer side of the lifted steel sheet 3 relative to the submerged roller 4 are arranged in contact with the steel sheet 3. The back side of the steel sheet to be coated is referred to as the B side, and the surface side is referred to as the F side. The support rollers 5 and 6 may also be arranged above the submerged roller 4 and on one side of the steel sheet 3.

[0023] In this embodiment, the rectifier plate 7 disposed above the submerged roller 4 is characterized in that it is disposed in the following manner.

[0024] 1) The shortest distance a from the lower end of the rectifier plate 7 to the surface of the submerged roller 4 is in the range of greater than 0 mm and less than 50 mm.

[0025] 2) When viewed from above, the lower end of the rectifier plate 7 is located from the horizontal end of the submerged roller on the nose side to the central axis CL of the submerged roller 4. That is, the distance b between the lower end of the horizontal rectifier plate 7 and the horizontal end of the submerged roller 4 on the nose side is positive in the direction toward the central axis CL, and is above 0 and below the radius of the submerged roller 4.

[0026] The inventors, having observed that conventional rectifier plates described in Patent Document 1 could not suppress zinc ash defects, conducted actual machine observations and flow simulations. The results revealed a relationship between the lower end position of the rectifier plate 7 and the suppression of zinc ash defects. The mechanism is considered as follows. Figure 2 This is a schematic diagram conceptually illustrating the flow of molten zinc bath under the configuration of the rectifier plate 7 in this embodiment. Figure 3 This is a conceptual diagram illustrating the flow of molten zinc in a conventional rectifier configuration that produces zinc ash defects.

[0027] Zinc oxide generated within the furnace nose 2 is carried into the molten zinc bath along with the accompanying flow of the steel sheet 3 to be coated. This zinc oxide, being less dense than the molten zinc, floats within the bath and moves with the flow. Furthermore, it is believed that zinc oxide adheres to the steel sheet, is pressed down by the rollers, and becomes zinc ash defects. Figure 2 , 3 As shown, the flow of the steel sheet 3 supplied from the furnace nose 2 collides with the flow accompanying the rotation of the submerged roller 4 on the upper surface side, forming an upward-spraying impact stream. This impact stream contains zinc oxide.

[0028] like Figure 3 As shown, in the conventional case, the lower end of the rectifier plate 7A contacts the impact flow, distributing the flow of the molten zinc bath towards the support roller side. In this embodiment, by positioning the rectifier plate 7 within the aforementioned range, as... Figure 2 As shown, the impact flow does not distribute to the support roller side, allowing zinc oxide to float on the bath surface 8 between the extension line of the furnace nose 2 and the rectifier plate 7. Therefore, zinc ash defects can be reduced.

[0029] The condition for the lower end position of the rectifier plate 7 required in this embodiment needs to be met throughout all operations involved in the manufacture of the galvanized steel sheet. For example, the submerged roller 4 is thinned during operation, with its radius decreasing by approximately 15 mm. Furthermore, the rectifier plate 7 is positioned close to the submerged roller 4 without contacting it, thus being constantly under load due to the accompanying flow of molten zinc, sometimes deforming towards the furnace nose side by approximately 40 mm. There are many limitations to the installation of the moving device for the rectifier plate 7. Specifically, there are many auxiliary devices around the molten zinc container 1 of the hot-dip galvanized steel sheet manufacturing apparatus 10, making the installation of the moving device for the rectifier plate 7 physically difficult and requiring excessive investment. Therefore, considering the thinning of the submerged roller 4 and the deformation of the rectifier plate 7, it is preferable to move the initially positioned lower end of the rectifier plate 7 horizontally towards the central axis CL of the submerged roller 4 by a predetermined amount. By designing the rectifier plate 7 in this way, it is possible to manufacture galvanized steel sheets that require no maintenance and have few surface defects.

[0030] It should be noted that the material of the rectifier plate 7 is preferably SUS316L. From the viewpoint of suppressing deformation, the thickness of the rectifier plate 7 is preferably 9mm or more. On the other hand, an excessively heavy rectifier plate 7 may make installation difficult, so a thickness of 15mm or less is preferred. From the viewpoint of preventing deformation, it is preferable that the rectifier plate 7 has reinforcing ribs extending along the width direction of the plated steel sheet 3.

[0031] Furthermore, there is no particular limitation on the thickness of the steel sheet 3 to be coated; for example, it is 0.4 to 3.5 mm. The thinner the steel sheet 3 to be coated, the faster the plate passing speed and the faster the collision flow, thus making it easier to generate zinc ash defects. Therefore, the effects of the present invention are more easily achieved when the thickness of the steel sheet 3 to be coated is 0.4 to 1.2 mm.

[0032] Example

[0033] (Example 1)

[0034] Use according to Figure 1 The manufacturing apparatus for hot-dip galvanized steel sheets was used, and the lower end position of the rectifier plate was changed to investigate the zinc ash defect rate on the steel sheet surface. The results are summarized in Table 1. Regarding the zinc ash defect rate, the trajectory of simulated zinc oxide particles was calculated using flow analysis software, and the proportion of particles reaching the galvanized steel sheet relative to all particles was set. As can be seen from the results in Table 1, the invention significantly reduces the zinc ash defect rate compared to the comparative example.

[0035] [Table 1]

[0036] (Example 2)

[0037] Next, using the rectifier plate configuration under condition No. 3 in Table 1, the plate deformation, i.e., warpage, for each plate thickness was investigated. Table 2 summarizes the warpage of the plated steel plates after 20,000 tons of plate passing. By setting the plate thickness to 9.0 mm, the deformation of the rectifier plate can be significantly reduced.

[0038] [Table 2]

[0039] In this instruction manual, the unit of mass "t" is 1000 kg.

[0040] Label Explanation

[0041] 10. Manufacturing equipment for hot-dip galvanized steel sheets

[0042] 1. Molten zinc container

[0043] 2. Furnace nose

[0044] 3. (The steel plate to be plated) (the part to be plated)

[0045] 4 Submerged Rollers

[0046] 5 (Back side) Support rollers

[0047] 6 (Surface side) support rollers

[0048] 7 Rectifier Board

[0049] 7A (conventional) rectifier board

[0050] 8. Facial Massage

[0051] CL (center shaft of submerged roller)

[0052] Z-molten zinc.

Claims

1. An apparatus for manufacturing hot-dip galvanized steel sheet, wherein the steel sheet to be galvanized is immersed in a molten zinc bath, so that the molten zinc adheres to the surface of the steel sheet to form a coating, wherein... The apparatus for manufacturing the hot-dip galvanized steel sheet includes: Molten zinc containers for storing molten zinc; The furnace nose is provided such that its end is immersed in the molten zinc bath in the molten zinc container, and the steel sheet to be plated is supplied to the molten zinc bath; The submerged roller is arranged in such a way that it is immersed in the molten zinc bath in the molten zinc container and is used to hang the steel sheet to be plated; A support roller is positioned above the submerged roller, immersed in the molten zinc bath, and in contact with one or both sides of the lifting side of the steel sheet to be plated; and A rectifier plate is disposed above the submerged roller and has a rectifier mechanism for controlling the flow of molten zinc within the molten zinc container. The rectifier plate is configured such that the shortest distance from the lower end to the surface of the submerged roller is greater than 0 mm and less than 50 mm, and when viewed from above, the lower end is located from the horizontal end of the submerged roller on the furnace nose side to the central axis of the submerged roller.

2. The apparatus for manufacturing hot-dip galvanized steel sheet according to claim 1, wherein, The width of the rectifier plate is greater than or equal to the width of the steel plate being plated.

3. The apparatus for manufacturing hot-dip galvanized steel sheet according to claim 1, wherein, The rectifier plate has a thickness of 9mm or more and has ribs.

4. The apparatus for manufacturing hot-dip galvanized steel sheet according to claim 2, wherein, The rectifier plate has a thickness of 9mm or more and has ribs.

5. A method for manufacturing hot-dip galvanized steel sheet, wherein, The process includes the following steps: Using the apparatus for manufacturing hot-dip galvanized steel sheet according to any one of claims 1 to 4, the steel sheet to be galvanized is immersed in a molten zinc bath, so that molten zinc adheres to the surface of the steel sheet to form a coating.

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