Title of invention: Cooling device for hot-dip galvanized steel sheet
technical field
[One]
The present invention relates to a cooling device for a hot-dip galvanized steel sheet capable of reducing comb-shaped surface defects occurring at an edge portion of a hot-dip galvanized steel sheet when manufacturing a high corrosion-resistant plated steel sheet in a continuous hot-dip galvanizing process, for example.
background
[2]
In general, hot-dip galvanized steel sheet contains zinc (Zn), aluminum (Al), lead (Pb), etc. alone or a mixture of two or more, or magnesium (Mg), titanium (Ti), nickel (Ni), etc. in an appropriate concentration It refers to a plated steel sheet manufactured by passing the steel sheet through a molten plating bath added with
[3]
In the case of manufacturing a hot-dip galvanized steel sheet, an oxide film is formed on the surface of the plating layer by reacting with oxygen in the atmosphere when the molten metal attached to the surface of the steel sheet is solidified. This oxide film causes various defects in the plating layer by making the solidification rate and solidification characteristics of the molten metal non-uniform. lowers the
[4]
In particular, in a zinc-based plating bath to which a strong oxidizing material such as magnesium, titanium, or aluminum is added, the degree of oxide film formation becomes severe. Accordingly, in the case of coating the surface to improve corrosion resistance and aesthetics of the steel sheet, it is difficult to secure a beautiful and excellent painted surface.
[5]
In order to solve this disadvantage, when controlling the plating amount of the steel sheet lifted from the plating bath, the zinc oxidation A technique for producing a hot-dip galvanized steel sheet with improved surface quality by reducing the reaction is being put to practical use.
[6]
For example, in Korean Patent No. 1419585, by installing a sealing box on a plating bath and injecting nitrogen through a wiping nozzle inside the sealing box, the atmosphere in the sealing box is maintained as a non-oxidizing atmosphere. An oxide film is not formed on the surface of the plating layer.
[7]
On the other hand, when the coating amount of the highly corrosion-resistant plated steel sheet is thick, not only oxidative surface defects, but also comb-shaped surface defects occur at the edge portion of the hot-dip galvanized steel sheet. Since the generation mechanism of the comb pattern surface defects of the edge portion is different from that of the oxidative surface defects, a separate reduction means other than the sealing box was required.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[8]
Accordingly, an object of the present invention is to provide a device capable of reducing the comb-shaped surface defects occurring at the edge portion of the hot-dip galvanized steel sheet, thereby contributing to the realization of high quality and productivity improvement of, for example, high corrosion-resistant plated steel sheet.
means of solving the problem
[9]
A cooling device according to an embodiment of the present invention includes: a gas knife for controlling a plating thickness by spraying a wiping gas to a steel sheet that has passed through a plating bath; a defect prevention unit installed downstream of the gas knife and cooling the steel plate by spraying a cooling gas; and a moving unit driven to move the defect preventing unit.
Effects of the Invention
[10]
As described above, according to the present invention, a uniform solidification layer is generated in the width direction of the steel sheet through cooling of the center of the steel sheet, and due to this, when the steel sheet moves vertically, the uniform solidification layer of the plating surface layer is formed in the width direction of the steel sheet. As well as weakening the generated surface tension, as a result, the comb pattern surface defects are reduced, thereby obtaining the effect of improving the surface quality and productivity of the hot-dip galvanized steel sheet.
Brief description of the drawing
[11]
1 is a diagram schematically illustrating a hot-dip plating apparatus to which a cooling apparatus according to an embodiment of the present invention is applied.
[12]
2 (a) and (b) are views for explaining a mechanism of generating a comb-shaped surface defect occurring at an edge portion of a hot-dip galvanized steel sheet.
[13]
3 is a side view illustrating a cooling device according to an embodiment of the present invention.
[14]
4 is a perspective view illustrating an operating state of a cooling device according to an embodiment of the present invention.
[15]
5 (a) and (b) are front views illustrating a defect preventing unit that can be used in a cooling device according to an embodiment of the present invention.
[16]
6 (a) and (b) are front views illustrating a modified example of a defect preventing unit that can be used in a cooling device according to an embodiment of the present invention.
Best mode for carrying out the invention
[17]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same components are given the same reference numerals as much as possible even though they are indicated on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.
[18]
1 is a diagram schematically illustrating a hot-dip plating apparatus to which a cooling apparatus according to an embodiment of the present invention is applied.
[19]
The hot-dip plating apparatus includes: a plating tank 1 in which molten metal 2 is accommodated; a gas knife (3) for controlling the plating thickness by spraying the wiping gas (4) on the steel sheet (S) drawn upward from the plating bath; And it is spaced apart from the gas knife and includes a frame (5) provided to surround the upper region to which the steel sheet is transferred.
[20]
Optionally, the hot-dip plating apparatus may further include a sealing box 10 surrounding the gas knife 3 and the frame 5 and isolating the hot water surface of the plating bath 1 from the surrounding atmosphere.
[21]
For example, in the continuous hot-dip galvanizing process, the steel sheet (S) is annealed in a heat treatment furnace (not shown) and then enters the plating bath (1) filled with the molten metal (2) through a snout (6). The direction is changed through the sink roll (7) in the plating bath and proceeds upward.
[22]
On the upper part of the sink roll 7, there are a stabilizer roll 8 and a collector roll 9, and these rolls push the front and back surfaces of the steel plate S while pressing the steel plate by tension. It plays a role in suppressing the rebound and vibration of
[23]
After being immersed in the plating bath 1, when exiting the plating bath, the molten metal 2 is attached to the surface of the steel sheet S, and the plating thickness of the molten metal is sprayed by the gas knife 3 installed at the top of the plating bath. It can be controlled by the wiping gas (4).
[24]
A pair of gas knives 3 is provided, so that the amount of plating on one side and the other side of the steel plate S can be adjusted.
[25]
The gas knife 3 may be connected to the frame 5 by a gas supply pipe (not shown), and the frame surrounds the upper region of the gas knife to which the steel plate S is transferred.
[26]
The wiping gas 4 may be supplied to the gas knife 3 through the frame 5 and the gas supply pipe. As the wiping gas, an inert gas such as nitrogen or argon may be used.
[27]
As described above, the sealing box 10 may surround the gas knife 3 and the frame 5 and isolate the molten metal surface of the plating bath 1 from the surrounding atmosphere. This sealing box leaves only the doorway 11 formed with a minimum area so that the steel plate S can pass vertically, and shields around the steel plate S that has passed through the plating tank 1 . In addition, between the sealing box and the hot water surface of the plating bath is sealed by a sealing member (not shown).
[28]
By injecting an inert gas such as nitrogen or argon into the sealed space formed by the sealing box 10, the residual oxygen concentration can be lowered to form an inert atmosphere, that is, a non-oxidizing atmosphere. In addition, in order to maintain a non-oxidizing atmosphere in the sealed space in the sealing box, the gas knife 3 continuously injects an inert gas such as nitrogen or argon as the wiping gas 4 .
[29]
The doorway 11 of the sealing box 10 is formed to have an opening area larger than the cross-sectional area of ​​the steel sheet so as not to come into contact with the steel sheet in order to prevent scratches on the plating layer of the steel sheet when the steel sheet S is vertically passed.
[30]
2 (a) and (b) are views for explaining a mechanism of generating a comb-shaped surface defect occurring at an edge portion of a hot-dip galvanized steel sheet.
[31]
In general, when the steel sheet S is vertically moved after being immersed in the plating bath 1, the edge portion of the steel sheet is cooled faster than the center portion of the steel sheet due to the latent heat of the steel sheet. As such, due to the temperature difference between the edge portion and the center portion of the steel sheet, non-uniform solidification is generated in the surface layer portion of the plating layer in the width direction of the steel sheet. As shown in (b) of Figure 2, the plating layer (P) occurs faster solidification at the edge portion of the steel sheet compared to the center portion of the steel sheet, and the solidification proceeds gradually toward the center.
[32]
Looking at the velocity distribution in the plating layer (P), the speed of the adjacent plating layer adjacent to the surface of the steel sheet (S) in the plating layer is the same as the moving speed (U 0 ) of the steel sheet , and the speed approaches 0 as it goes to the unsolidified surface of the plating layer. do. However, since the surface layer portion of the plating layer at the edge portion of the steel sheet is in a solidified state, the speed of the surface layer portion of the plating layer at this edge portion has a non-zero value. As it moves toward the center of the steel sheet, the plating layer is present in an unsolidified state.
[33]
Therefore, the surface layer portion of the plating layer has a different speed depending on the position in the width direction of the steel sheet (S), and the speed of the edge portion of the surface layer portion of the plating layer is higher than that of the center portion (U 1 > U 2 > U as shown in (a) of FIG. 2) 3 ).
[34]
In addition, since gravity acts in the opposite direction to which the steel plate S moves, the plating layer P, which is still in a non-solidified state, may be sufficiently affected by gravity.
[35]
As a result, due to the speed difference and the action of gravity appearing in the surface layer portion of the plating layer, surface tension is generated in the width direction from the edge portion of the steel sheet S toward the center, and accordingly, surface defects in the shape of a comb pattern are caused in the diagonal direction.
[36]
For example, when the coating amount on one side of the steel sheet is 250 g/m 2 or more, a comb pattern surface defect occurs in an oblique direction at the edge portion of the steel sheet, and the comb pattern may have a length of about 300 mm in severe cases.
[37]
As described above, since the comb pattern surface defect is different from the oxidative surface defect and its generation mechanism is different, it cannot be solved only with the sealing box 10 described above. In particular, in order to secure high quality when manufacturing a highly corrosion-resistant plated steel sheet, it is important to reduce not only oxidative surface defects, but also comb-shaped surface defects at the edge that occur in the thick plating layer (P).
[38]
3 is a side view illustrating a cooling device according to an embodiment of the present invention, and FIG. 4 is a perspective view illustrating an operating state of the cooling device according to an embodiment of the present invention.
[39]
As shown in these drawings, the cooling device according to an embodiment of the present invention injects a wiping gas 4 (refer to FIG. 1) to the steel sheet S that has passed through the plating bath 1 (refer to FIG. 1). Gas knife (3) for adjusting the plating thickness; a defect prevention unit 20 installed downstream of the gas knife and cooled by spraying a cooling gas 24 on the steel plate; and a moving unit 30 which drives the defect preventing unit to move.
[40]
The cooling device according to an embodiment of the present invention performs cooling by mainly spraying a cooling gas 24 to the central portion of the steel sheet S, so that the plating layer P in the width direction of the steel sheet P; see Fig. 2 (b). ) to generate a uniform solidification, so that the generation of comb-shaped surface defects at the edge of the steel sheet is suppressed.
[41]
The steel sheet S whose surface is plated by the molten metal 2 (refer to FIG. 1) in the plating bath 1 is withdrawn from the plating bath, and then the plating amount is controlled by the gas knife 3 .
[42]
The gas knife 3 can control the plating amount by spraying an inert gas such as nitrogen or argon to the steel sheet S, and removing the excess molten metal 2 from the steel sheet.
[43]
The steel sheet S in a state where the plating amount is controlled is passed through the defect preventing unit 20 constituting the main part of the present invention following the gas knife 3, and this defect preventing unit applies the cooling gas 24 to the center of the steel sheet. It can be sprayed with focus.
[44]
These defect prevention units 20 may be disposed on both sides of the steel plate (S) in progress, one on each, that is, as a pair. In addition, each defect preventing portion may be horizontally positioned over at least the center of the steel sheet in the width direction.
[45]
The defect prevention unit 20 includes a tubular body 21 having at least one nozzle 22 , and a supply pipe 23 connected to the body and supplying a cooling gas 24 to the body.
[46]
The length of the main body 21 (the length extending in the direction parallel to the width direction of the steel plate S) may be shorter than the width of the steel plate, for example, considering the width of the actually manufactured steel plate, the length within the range of about 1000 ~ 1600mm It is preferable to have, but is not necessarily limited thereto.
[47]
The nozzle 22 provided in the body 21 may be formed in a hole shape or a slit shape.
[48]
5 (a) and (b) are front views illustrating a defect preventing unit that can be used in a cooling device according to an embodiment of the present invention. The main body 21 of the defect prevention part 20 shown in FIGS. 5 (a) and (b) is provided with a plurality of hole-type nozzles 22 arranged in a direction parallel to the width direction of the steel plate (S). .
[49]
As shown in (a) of FIG. 5 , a plurality of nozzles 22 may be formed as holes having the same diameter and may be arranged in a line at least.
[50]
In addition, as shown in FIG. 5B , the nozzle located at the center of the main body 21 among the plurality of nozzles 22 has the largest diameter, and the nozzles are arranged in such a way that the diameter of the nozzle decreases toward both ends of the main body. can be In this case, a larger flow rate of the cooling gas 24 may be injected toward the center compared to both edge portions of the steel plate S.
[51]
6 (a) and (b) are front views illustrating a modified example of a defect preventing unit that can be used in a cooling device according to an embodiment of the present invention. The main body 21 of the defect prevention part 20 shown in FIGS. 6 (a) and (b) is provided with a slit-type nozzle 22 extending in a direction parallel to the width direction of the steel plate (S).
[52]
6A , the nozzle 22 may have the same width over the entire length of the slit.
[53]
Alternatively, as shown in (b) of FIG. 6 , the nozzle 22 may be formed in such a way that the width of the slit is greatest at the center of the body 21 and the width of the slit decreases toward both ends of the body. In this case, a larger flow rate of the cooling gas 24 may be injected toward the center compared to both edge portions of the steel plate S.
[54]
On one side of the body 21, it may be connected to a supply pipe 23 for supplying a cooling gas 24 made of compressed air or an inert gas such as nitrogen or argon, and the supplied cooling gas is supplied to the nozzle ( 22), so that it can be cooled mainly in the center of the width direction of the steel plate (S).
[55]
As will be described later, since the position of the defect prevention part 20 is variable, it is better to use a corrugated pipe or a flexible tube made of a material such as fiber, rubber, or resin as the supply pipe 23 to cope with this. good.
[56]
Again, referring to FIGS. 3 and 4 , the defect preventing unit 20 is connected to the moving unit 30 so that its position is changed, so that it can respond according to the position where the comb-shaped surface defect of the edge part occurs. Here, the occurrence position of the comb pattern surface defect may be changed according to the moving speed (U 0 ) of the steel plate (S ), the width of the steel plate, the amount of plating, and the like.
[57]
The moving unit 30 may optionally be implemented as a linear motion guide. Such a moving part, the support part 31; The bolt shaft 32 is installed extending from the support and rotates in the forward and reverse direction through the driving force of the driving unit 35 connected to one side; and a moving block 33 connected to the main body 21 of the defect prevention unit 20 and provided with a nut unit 34 reciprocating along the bolt axis by screwing with the bolt shaft.
[58]
The support part 31 may be installed on the upper surface of the sealing box 10 . However, the present invention is not necessarily limited thereto, and for example, it may be installed on the frame 5 supporting the gas knife 3 . The support part may include a bearing (not shown) for supporting the bolt shaft 32 .
[59]
The driving unit 35 may be a driving motor capable of forward and reverse rotation. Accordingly, when the bolt shaft 32 is rotated by the rotational drive of the driving unit, the moving block 33 and the body 21 of the defect prevention unit 20 are linearly reciprocated by the action of the nut portion 34 screwed to the bolt shaft. will move
[60]
The moving block 33 may be fixedly connected to at least one end of the main body 21 of the defect prevention unit 20 . The nut part 34 may be formed integrally with the moving block in the form of a through hole, or may be made separately and then firmly attached to the moving block.
[61]
In FIG. 3 , unexplained reference numeral 36 denotes a stopper that blocks the movement of the moving block 33 .
[62]
Additionally, the moving unit 30 may further include at least one guide (not shown) installed to extend parallel to the bolt shaft 32 . In this case, a guide hole (not shown) is formed in the moving block 33 provided at either end of both ends of the main body 21 of the defect prevention unit 20, and the guide hole is inserted into the guide, and the moving block ( 33) and the main body 21 are able to move smoothly.
[63]
On the other hand, as shown in more detail in FIG. 4 , when the two moving parts 30 connected to the main body 21 of the defect prevention part 20 are disposed one on each side of the support part 31 , the moving part 30 . A power transmission unit 40 may be interposed between and the driving unit 35 .
[64]
The power transmission unit 40 may include a side gearbox 41 , a connecting shaft 42 , and a central gearbox 43 when a driving motor is employed as the driving unit 35 .
[65]
Two side gearboxes 41 are arranged and may be installed on the support unit 31 together with the driving unit 35 . This side gearbox is connected to the moving part 30 , more specifically, the bolt shaft 32 .
[66]
In addition, the central gearbox 43 is connected to the rotation shaft of the driving unit 35 .
[67]
Each of the two connecting shafts 42 may have one end connected to the side gearbox 41 and the other end connected to the central gearbox 43 . In such a connection shaft, for example, first gears such as bevel gears and worm gears are formed at both ends, and accordingly, the ends of the bolt shaft 32 of each moving part 30 and the ends of the rotation shaft of the driving part 35 are respectively A second gear such as a bevel gear or a worm wheel may be formed.
[68]
Accordingly, it is possible to simultaneously operate the two moving parts 30 connected to both sides of the main body 21 of the defect prevention part 20 by one driving part 35 , that is, one driving motor.
[69]
Here, the configuration, connection relationship, and operation relationship of the moving unit 30 , the driving unit 35 , and the power transmission unit 40 are not limited to the above-described examples.
[70]
For example, as the moving unit 30 and the driving unit 35 that provide a driving force so that the main body 21 of the defect prevention unit 20 or the moving block 33 connected to the main body can reciprocate, it is equipped with an operating rod. Any actuator such as a hydraulic cylinder may be applied.
[71]
Also, the plurality of driving units 35 may be respectively connected to the plurality of moving units 30 without a power transmission unit.
[72]
In addition, when a single driving unit 35 without a power transmission unit drives the moving unit 30 connected to one side of the main body 21 of the defect prevention unit 20, a guide is disposed on the other side of the main body 21 to provide a moving block (33) may be guided.
[73]
Hereinafter, the operation of the cooling device according to an embodiment of the present invention will be briefly described.
[74]
The steel sheet S to which the molten metal 2 is attached through the plating bath 1 is wiped by the wiping gas 4 ejected through the gas knife 3 to adjust the plating amount. When the sealing box 10 is installed, the ejected wiping gas forms an inert atmosphere in the sealing box, so that an oxide film is not formed on the surface of the plating layer.
[75]
The driving unit 35 is operated to move the defect preventing unit 20 according to the moving speed (U 0 ) of the passing steel sheet (S) , the width of the steel sheet, the plating amount, etc., and this defect preventing unit moves the driving unit 35 and the moving unit ( 30), the position at which the cooling gas 24 is injected from the defect prevention unit can be changed by descending or rising by the driving.
[76]
The cooling device of the present invention mainly sprays the cooling gas 24 to the center of the steel sheet S, and also rapidly cools the center of the steel sheet. By doing so, uniform solidification of the plating layer (P) is induced in the width direction of the steel sheet, and consequently, generation of comb-shaped surface defects at the edge portion of the steel sheet is suppressed.
[77]
Therefore, according to the cooling device of the present invention, a uniform solidification layer is generated in the width direction of the steel sheet through cooling of the center of the steel sheet, and due to this, when the steel sheet moves vertically, the uniform solidification layer of the plating surface layer is the width of the steel sheet In addition to weakening the surface tension generated in the direction, as a result, the comb pattern surface defects are reduced, thereby obtaining the effect of improving the surface quality and productivity of the hot-dip galvanized steel sheet.
[78]
The above description is merely illustrative of the technical spirit of the present invention, and various modifications and variations will be possible without departing from the essential characteristics of the present invention by those skilled in the art to which the present invention pertains. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.
Industrial Applicability
[79]
As described above, the present invention is useful, for example, when manufacturing a highly corrosion-resistant plated steel sheet in a continuous hot-dip galvanizing process.
Claims
[Claim 1]
a gas knife for controlling the plating thickness by spraying a wiping gas to the steel sheet that has passed through the plating bath; a defect prevention unit installed downstream of the gas knife and cooling the steel plate by spraying a cooling gas; and a moving unit driving the defect preventing unit to move.
[Claim 2]
The cooling apparatus according to claim 1, wherein the defect prevention unit includes a tubular body having at least one nozzle, and a supply pipe connected to the body and supplying a cooling gas to the body.
[Claim 3]
The cooling device according to claim 2, wherein a length of the main body is shorter than a width of the steel plate.
[Claim 4]
The cooling device according to claim 2, wherein the main body includes a plurality of hole-type nozzles arranged in a direction parallel to a width direction of the steel plate.
[Claim 5]
The cooling apparatus according to claim 4, wherein the nozzle located at the center of the main body has the largest diameter among the plurality of nozzles, and the diameter of the nozzle decreases toward both ends of the main body.
[Claim 6]
The cooling device according to claim 2, wherein the main body includes a slit-type nozzle extending in a direction parallel to a width direction of the steel plate.
[Claim 7]
The cooling device according to claim 6, wherein the nozzle has the largest width at the center of the main body and decreases toward both ends of the main body.
[Claim 8]
The method of claim 2, wherein the moving unit comprises: a support; a bolt shaft that is installed extending from the support and rotates in a forward and reverse direction through a driving force of a driving unit connected to one side; and a moving block connected to the main body of the defect prevention unit and provided with a nut unit that is screwed with the bolt shaft to reciprocate along the bolt shaft.
[Claim 9]
9. The method of claim 8, wherein the support part is installed on a frame supporting the gas knife or on the upper surface of a sealing box that surrounds the gas knife and the frame and isolates the hot water surface of the plating bath from the surrounding atmosphere. cooling system.
[Claim 10]
The cooling apparatus according to claim 8, wherein the moving unit further comprises at least one guide extending parallel to the bolt shaft and guiding the movement of the defect preventing unit.
[Claim 11]
The cooling apparatus according to claim 8, wherein when the two moving parts connected to the main body of the defect prevention part are disposed on the support part, a power transmission part is interposed between the moving part and the driving part.
[Claim 12]
12. The method of claim 11, wherein the power transmission unit comprises: two side gearboxes respectively connected to the moving unit; a central gearbox connected to the rotation shaft of the driving unit; and two connecting shafts each having one end connected to the side gearbox and the other end connected to the central gearbox.
[Claim 13]
The cooling apparatus according to claim 12, wherein a first gear is formed at both ends of the connecting shaft, and a second gear is formed at an end of the moving part and an end of the rotation shaft of the driving part.