Gas wiping nozzle and method for manufacturing hot-dip metal coated metal strip

A gas wiping nozzle manufactured from parts divided along the slit length direction and maintains a gap in the width direction over the length direction in high temperature atmospheres and a method for manufacturing a hot-dip metal strip. In a gas wiping nozzle, a first and a second nozzle member are each divided along the length direction X of a slit into a plurality of nozzle members. The dimension of a divided face of the first nozzle member is 1.5T1 or more in a section of the first nozzle member where T1 is the thickness of the first nozzle member in the width direction Z of the slit, and the dimension of a divided face of the second nozzle member is 1.5T2 or more in a section of the second nozzle member where T2 is the thickness of the second nozzle member in the width direction Z of the slit.

TECHNICAL FIELD

The present invention relates to a gas wiping nozzle that blows gas onto a metal strip pulled up from a molten metal bath and adjusts the amount of a molten metal coated to a surface of the metal strip and a method for manufacturing a hot-dip metal coated metal strip using the gas wiping nozzle.

BACKGROUND ART

A hot-dip galvanized steel sheet, which is a type of hot-dip metal coated steel sheets, is widely used in fields such as building materials, automobiles, and home appliances. In these applications, an excellent appearance is required for the hot-dip galvanized steel sheet. Here, since the appearance after painting is strongly affected by surface defects such as uneven coating thickness, flaws, and adhesion of foreign matter, it is important that the hot-dip galvanized steel sheet has no surface defects.

In a continuous hot-dip metal coating line, normally, a steel strip as a metal strip annealed in a continuous annealing furnace in a reducing atmosphere passes through a snout and is introduced into a molten metal bath in a coating tank. The steel strip is pulled up above the molten metal bath via a sink roll and a support roll in the molten metal bath. Thereafter, the amount (hereinafter, also referred to as a basic weight amount) of molten metal coated is adjusted by blowing wiping gas from gas wiping nozzles located on both sides of the steel strip onto the surface of the steel strip and scraping off the excess molten metal coated to the surface of the steel strip and pulled up. Here, in order to correspond to various steel strip widths and also to cope with displacement in the width direction when the steel strip is pulled up, the gas wiping nozzle is normally configured to be wider than the width of the steel strip and extends outward from an end portion in the width direction of the steel strip.

In such a gas wiping method, hot metal wrinkles (also referred to as hot metal sagging) with corrugated flow pattern are often generated on the coated surface due to minute vibration of the steel strip or irregular hot metal flow on the coating layer due to the blowing of wiping gas. In a case where the coated surface of a coated steel sheet with such hot metal wrinkles is used as a coating base surface in an outer coating application, a surface texture of a coating film, particularly smoothness, is impaired, and thus the coated steel sheet cannot be used for an exterior sheet to be suitable for a coating treatment having an excellent appearance, which significantly affects the yield of the coated steel sheet.

In order to solve this problem, in the related art, for example, those described in PTL 1 are known.

A continuous hot-dip metal coating method described in PTL 1 is a method in which a steel strip is continuously immersed in a molten metal coating bath, and gas is blown from a gas wiping nozzle onto the steel strip immediately after being drawn out from the molten metal coating bath to control the amount of coating. The temperature T of the wiping gas blown from the gas wiping nozzle is controlled according to a D/B value represented by a ratio of the distance D between a tip end of the gas wiping nozzle and the steel strip, and a gas wiping nozzle gap B.

In addition, in the gas wiping method in the related art, a phenomenon that the edge portion of the steel strip may be supercooled from a central portion occurs during wiping, the steel strip may be warped, the amount of coating in the width direction may be uneven, and there may also be a problem of wasting a large amount of zinc in vain to guarantee the lower limit of the amount of zinc coated.

In order to solve this problem, for example, a method described in PTL 2 is known in the related art.

A wiping method in continuous hot-dip galvanizing described in PTL 2 is a method of heating wiping gas such that the temperature TG(° C.) of the wiping gas and the sheet thickness D (mm) of a steel strip to be coated satisfy the following equation (1), in the continuous hot-dip galvanizing, when the wiping gas is blown from a gas wiping nozzle to wipe the hot-dip zinc coating to the front and rear of the steel strip to be coated.
Wiping gas temperatureTG(° C.)≥−400D+400  (1)

In addition, as the gas wiping nozzle in the related art, for example, a nozzle described in PTL 3 is also known.

The gas wiping nozzle described in PTL 3 is a nozzle that blows gas onto a steel strip pulled up above a molten metal coating bath and adjusts a film thickness of a molten metal film coated to the surface of the steel strip. The gas wiping nozzle includes a first lip portion and a second lip portion that are provided so as to face each other and form a nozzle chamber into which gas is introduced, a slit formed between the end portions of the first lip portion and the second lip portion on the steel strip side, as a blowing port for gas blown from the nozzle chamber, and a fixing member provided on the slit side in the nozzle chamber and fixing the first lip portion and the second lip portion. In the fixing member, a plurality of first communication holes that communicate the slit side and the opposite side of the slit with respect to the fixing member is disposed side by side along the width direction of the steel strip.

According to the gas wiping nozzle described in PTL 3, even in a case where each part is reassembled in order to replace a part or all of the parts constituting the gas wiping nozzle, it is possible to suppress variations in a gap of the slit (hereinafter, also referred to as a slit gap) after assembly for each assembly.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the continuous hot-dip metal coating method described in PTL 1, the wiping method in the continuous hot-dip galvanizing described in PTL 2, and the gas wiping nozzle described in PTL 3 in the related art have the following problems.

In other words, in the continuous hot-dip metal coating method described in PTL 1 and the wiping method in the continuous hot-dip galvanizing described in PTL 2, a wiping gas is heated, and accordingly the periphery of the gas wiping nozzle becomes a high temperature atmosphere. The gas wiping nozzle itself is also heated as the wiping gas is heated. PTL 1 and PTL 2 do not describe whether the gas wiping nozzle is manufactured as a monobloc product in the length direction of the slit as a gas blowing port that is provided at the steel strip-side end of the gas wiping nozzle or is manufactured from divided parts. A gas wiping nozzle may be difficult to manufacture as a monobloc product depending on the material of the gas wiping nozzle, and may be manufactured from parts divided along the slit length direction. When a gas wiping nozzle is manufactured from parts divided along the slit length direction, and the periphery of the gas wiping nozzle becomes a high temperature atmosphere, the slit as the gas blowing port may have uneven gaps in the width direction orthogonal to the length direction depending on the assembling manner of the gas wiping nozzle, and a steel strip may have uneven coating amounts in the width direction of the steel strip, unfortunately.

In the gas wiping nozzle disclosed in PTL 3, a first lip portion and a second lip portion are fixed with a fixing member at the slit side in a nozzle chamber, and thus the slit gap can be prevented from varying after each assembly when some or all parts included in the gas wiping nozzle are exchanged.

In the gas wiping nozzle disclosed in PTL 3, however, each of the upper first lip portion and the second lip portion is manufactured as a monobloc product in the length direction of the slit as the gas blowing port, and each of the first lip portion and the second lip portion is not manufactured from parts divided along the slit length direction. Manufacturing each of the first lip portion and the second lip portion from parts divided along the slit length direction should cause a similar problem to that when the above gas wiping nozzle is manufactured from parts divided along the slit length direction.

The present invention is therefore intended to solve the related art problems and to provide a gas wiping nozzle that is manufactured from parts divided along the length direction of a slit as a gas blowing port, maintains a gap to be constant in the width direction orthogonal to the length direction of the slit over the length direction of the slit even in a high temperature atmosphere, and makes the coating amount on a steel strip constant in the width direction of the steel strip and a method for manufacturing a hot-dip metal strip using the gas wiping nozzle.

Solution to Problem

To solve the problems, a gas wiping nozzle pertaining to an aspect of the present invention is configured to blow a wiping gas onto a metal strip pulled up from a molten metal bath and adjust an amount of a molten metal coated to a surface of the metal strip. The gas wiping nozzle includes a first nozzle member and a second nozzle member, and has a slit as a gas blowing port between the first nozzle member and the second nozzle member, at a metal strip side end of the gas wiping nozzle. Each of the first nozzle member and the second nozzle member is divided along the length direction of the slit into a plurality of nozzle members, the dimension of a divided face of the first nozzle member is 1.5T1or more in a section of the first nozzle member that is cut in the length direction of the slit, at at least one point on the depth direction orthogonal to the length direction of the slit where T1is the thickness of the first nozzle member in the width direction of the slit, and the dimension of a divided face of the second nozzle member is 1.5T2or more in a section of the second nozzle member that is cut in the length direction of the slit, at at least one point on the depth direction orthogonal to the length direction of the slit where T2is the thickness of the second nozzle member in the width direction of the slit.

A method for manufacturing a hot-dip metal coated metal strip pertaining to another aspect of the present invention includes disposing a pair of the gas wiping nozzles described above on both surface sides of a metal strip pulled up from a molten metal bath, and blowing wiping gas from each slit of the pair of gas wiping nozzles to each surface of the metal strip to adjust an amount of molten metal coated to both surfaces of the metal strip, continuously manufacturing a hot-dip metal coated metal strip.

Advantageous Effects of Invention

According to the gas wiping nozzle and the method for manufacturing a hot-dip metal coated metal strip pertaining to the present invention, a gas wiping nozzle that is manufactured from parts divided along the length direction of a slit as a gas blowing port, maintains a gap to be constant in the width direction orthogonal to the length direction of the slit over the length direction of the slit even in a high temperature atmosphere, and makes the coating amount on a steel strip constant in the width direction of the steel strip and a method for manufacturing a hot-dip metal strip using the gas wiping nozzle can be provided.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be now described with reference to the drawings. The embodiments illustrated below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the material, shape, structure, arrangement, and the like of the component parts in the following embodiments.

In addition, the drawings are schematic. Therefore, it should be noted that a relationship, ratio, and the like between a thickness and a plane dimension are different from the actual ones, and there are parts where the relationship and ratio of the dimensions are different between the drawings.

FIG.1illustrates a schematic configuration of continuous hot-dip metal coating equipment provided with a gas wiping nozzle according to an embodiment of the present invention.

The continuous hot-dip metal coating equipment1illustrated inFIG.1is equipment for continuously coating molten metal to the surface of a steel strip S as a metal strip by immersing the steel strip S in a molten metal bath4made of the molten metal, and then bringing the molten metal into a predetermined amount of coating.

The continuous hot-dip metal coating equipment1includes a snout2, a coating tank3, a sink roll5, and a support roll6.

The snout2is a member having a rectangular cross section perpendicular to the traveling direction of the steel strip S, which partitions a space through which the steel strip S passes. The upper end of the snout2is connected to, for example, the outlet side of a continuous annealing furnace, and the lower end is immersed in the molten metal bath4stored in the coating tank3. In the present embodiment, the steel strip S annealed in the continuous annealing furnace in a reducing atmosphere passes through the snout2and is continuously introduced into the molten metal bath4in the coating tank3. Thereafter, the steel strip S is pulled upward from the molten metal bath4via the sink roll8and the support roll6in the molten metal4.

Wiping gas is blown onto both surfaces of the steel strip S pulled upward from the molten metal bath4from a pair of gas wiping nozzles10(slits14described later) disposed on both surface sides of the steel strip S and the amount of molten metal coated to both surfaces of the steel strip S is adjusted. Thereafter, the steel strip S is cooled by cooling equipment (not illustrated) and guided to a subsequent step, and the hot-dip metal coated steel strip S is continuously manufactured.

Here, each of the pair of gas wiping nozzles10disposed on both surface sides of the steel strip S includes a nozzle header15and a first nozzle member11disposed on the upper side and a second nozzle member12disposed on the lower side that are connected to the nozzle header15, as illustrated inFIG.2. The first nozzle member11and the second nozzle member12are provided to face each other, and the slit14as a gas blowing port is formed so as to extend elongated in the length direction X between the end portions11cand12c, on the steel strip S side, of the first nozzle member11and the second nozzle member12. Each gas wiping nozzle10is disposed on each surface side of the steel strip S so that the length direction X of the slit14is along the sheet width direction of the steel strip S, the width direction Z orthogonal to the length direction X of the slit14is along the sheet length direction of the steel strip S, and the depth direction Y of the slit14is along the sheet thickness direction of the steel strip S. The width direction Z of the slit is the same as the vertical direction of the gas wiping nozzle10. The wiping gas is blown from the slit14toward one surface of the steel strip S from one of the gas wiping nozzles10. In addition, the wiping gas is blown from the slit14toward the other surface of the steel strip S from the other gas wiping nozzle10. As a result, excess molten metal is scraped off on both surfaces of the steel strip S, the amount of coating (molten metal) is adjusted, and the amount of coating is made uniform in the sheet width direction and the sheet length direction of the steel strip S. In order to correspond to various sheet widths of steel strip S and to cope with displacement in the width direction when the steel strip S is pulled up, each gas wiping nozzle10is configured to be longer than the sheet width of steel strip S so that the length of the slit14is longer than the sheet width of steel strip S, and extends outward from an end portion of the steel strip S in the width direction.

The nozzle header15of each gas wiping nozzle10is formed in an approximately rectangular shape extending in the length direction X, the depth direction Y, and the width direction Z and is made from a metal such as chrome molybdenum steel. To the base end (rear end) of the nozzle header15, a gas supply pipe17is connected, and a gas supply path16communicating the gas supply pipe17with a hollow portion13described later is formed.

The first nozzle member11placed at the upper side is divided, as illustrated inFIG.2, along the length direction X of the slit14on a plurality of divided faces20into a plurality of (three in the present embodiment) nozzle members11A,11B,11C, as described in detail later. Each nozzle member11A,11B,11C includes, as illustrated inFIG.2toFIG.4, a flat plate portion11aextending in the length direction X and the depth direction (front-to-rear direction) Y and having a certain thickness T1, a flange portion11bprotruding upward from the rear end of the flat plate portion11a, and the above-described inclined end portion11cextending obliquely downward from the front end of the flat plate portion11a. Below the flat plate portion11aof each nozzle member11A,11B,11C, a hollow portion-forming space13aforming the hollow portion described later is formed.

The second nozzle member12placed at the lower side is also divided, as illustrated inFIG.2, along the length direction X of the slit14on a plurality of divided faces20into a plurality of (three in the present embodiment) nozzle members12A,12B,12C. Each nozzle member12A,12B,12C includes, as illustrated inFIG.2toFIG.4, a flat plate portion12aextending in the length direction X and the depth direction (front-to-rear direction) Y and having a certain thickness T2, a flange portion12bprotruding downward from the rear end of the flat plate portion12a, and the above-described inclined end portion12cextending obliquely upward from the front end of the flat plate portion12a. Above the flat plate portion12aof each nozzle member12A,12B,12C, a hollow portion-forming space13bforming the hollow portion described later is formed.

The first nozzle member11and the second nozzle member12are joined vertically and are fixed with the shim members30described later, and a rear end face11baof the flange portion11bof the first nozzle member11and a rear end face12baof the flange portion12bof the second nozzle member12are connected to a front face of the nozzle header15. The hollow portion-forming space13aformed by the first nozzle member11and the hollow portion-forming space13bformed by the second nozzle member12accordingly form a hollow portion13.

The bottom face of the inclined end portion11cat the steel strip S side of the first nozzle member11and the top face of the inclined end portion12cat the steel strip S side of the second nozzle member12are flat faces facing together, and the above-described slit14as a gas blowing port is formed between the flat faces. The slit14is thin, extends in the length direction X as described above, and has a length L1in the length direction X (seeFIG.2), a width or a gap L3in the width direction Z orthogonal to the length direction X (seeFIG.3), and a depth L2in the depth direction Y orthogonal to the length direction X (seeFIG.3). The slit14may have any dimensions, but the length L1of the slit14is set in consideration of a margin for the width of a steel strip S and may be set, for example, at about 1,500 to 2,500 mm. The gap L3of the slit14may be set, for example, at about 0.5 to 3.0 mm. The depth L2of the slit14may be set, for example, at about 5 to 30 mm.

The slit14communicates with the hollow portion13in the depth direction Y. The hollow portion13functions as a pressure equalizing portion, and a wiping gas introduced from the gas supply pipe17through the gas supply path16into the hollow portion13is blown at a uniform pressure over the length direction X of the slit14.

Each gas wiping nozzle10includes, as illustrated inFIG.2toFIG.4, a pair of shim members30that adjust the gap L3in the width direction Z orthogonal to the length direction X of the slit14.

These shim members30also function to fix the first nozzle member11and the second nozzle member12. To fix the first nozzle member11and the second nozzle member12with these shim members30, each of the first nozzle member11and the second nozzle member12, specifically, each of the nozzle members11A,11C and the nozzle members12A,12C has a groove28,29into which the shim member30is fitted as illustrated inFIG.4.

The first nozzle member11, the second nozzle member12, and the shim members30are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, which has a low wettability to a molten metal such as molten zinc, is unlikely to undergo plastic deformation, and has a low linear expansion coefficient. Specifically, examples of the ceramic material include, but are not limited to, alumina, sialon, silicon nitride, zirconia, barium titanate, hydroxyapatite, silicon carbide (SiC), and fluorite, and examples of the carbon material include, but are not limited to, graphite. Graphite oxidizes and volatilizes in a highly oxidizing atmosphere, and thus the surface layer thereof is preferably coated with silica or the like.

Invar and tungsten have a low linear expansion coefficient but undergo plastic deformation and thus are unsuitable as the materials of the first nozzle member11, the second nozzle member12, and the shim members30, especially as the material of the shim members30.

The ceramic material, the carbon material, the carbon fiber-reinforced carbon composite material, or the ceramic-based composite material preferably has a flexural strength of 600 MPa or more preferably 800 MPa or more. Hence, the ceramic material is preferably zirconia, silicon nitride, sialon, or the like. By using such a material, the members are unlikely to undergo plastic deformation, and deformation can be substantially suppressed at a disruptive strength or lower.

If zinc adheres to the first nozzle member11and the second nozzle member12to clog the slit14during operation of the apparatus, the zinc adhesion amount partially increases on a part corresponding to the clogged part, and a linear defect is formed on a steel strip S in the same direction as the traveling direction of the steel strip S. The zinc adhering to the first nozzle member11and the second nozzle member12is thus removed by a special jig. In the removing, a nozzle surface having a low hardness may be cracked or chipped. To prevent such cracking or chipping, the ceramic material, the carbon material, the carbon fiber-reinforced carbon composite material, or the ceramic-based composite material preferably has a Vickers hardness of 800 Hv or more and more preferably 1,000 Hv or more. For a similar reason, the ceramic material, the carbon material, the carbon fiber-reinforced carbon composite material, or the ceramic-based composite material preferably has a fracture toughness of 5 MPa·m1/2or more.

When a high-temperature gas is used as the wiping gas, a nozzle material having a thermal shock resistance of not higher than the temperature of the high-temperature gas may cause cracking. The ceramic material, the carbon material, the carbon fiber-reinforced carbon composite material, or the ceramic-based composite material desirably has a thermal shock resistance of not less than the temperature of a used wiping gas, preferably has a thermal shock resistance of 430° C. or more, and more preferably has a thermal shock resistance of 600° C. or more.

From the viewpoint of suppressing nozzle deformation by heat, the first nozzle member11(nozzle members11A,11B,11C) and the second nozzle member12(nozzle members12A,12B,12C) preferably has a linear expansion coefficient of not more than ½ of the linear expansion coefficient of the nozzle header15fixed to the first nozzle member11and the second nozzle member12and more preferably not more than ⅓ of that. As the material of the nozzle header15, for example, stainless steel or the like is used, and the linear expansion coefficient thereof is about 10 to 18×10−5/K.

When a ceramic material is selected as the material unlikely to undergo plastic deformation, to manufacture the first nozzle member11and the second nozzle member12, a monobloc product having a typical nozzle width of 1,500 mm or more is difficult to manufacture due to, for example, the restriction of the size of a furnace for sintering ceramics. When a carbon material is selected as the material unlikely to undergo plastic deformation, to manufacture the first nozzle member11and the second nozzle member12, similarly, a monobloc product having a typical nozzle width of 1,500 mm or more is difficult to manufacture due to, for example, the restriction of the size of a die used for forming.

When a carbon fiber-reinforced carbon composite material or a ceramic-based composite material is selected to manufacture the first nozzle member11and the second nozzle member12, similarly, a monobloc product having a typical nozzle width of 1,500 mm or more is difficult to manufacture due to the restriction of a furnace for forming. Hence, when a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material is selected to manufacture the first nozzle member11and the second nozzle member12, as described above, the first nozzle member11is divided along the length direction X of the slit14on a plurality of divided faces20into a plurality of (three in the present embodiment) nozzle members11A,11B,11C, and the second nozzle member12is divided along the length direction X of the slit14on a plurality of divided faces20into a plurality of (three in the present embodiment) nozzle members12A,12B,12C.

In the present embodiment, as illustrated inFIG.4, in a section of the first nozzle member11that is cut in the length direction X of the slit14, at at least one point on the depth direction Y orthogonal to the length direction X of the slit14, the dimension (D1+D2+D3) of the divided face20of the first nozzle member11is 1.5T1or more where T1is the thickness of the first nozzle member11in the width direction Z of the slit14, and in a section of the second nozzle member12that is cut in the length direction X of the slit14, at at least one point on the depth direction Y orthogonal to the length direction X of the slit14, the dimension (D1+D2+D3) of the divided face20of the second nozzle member12is 1.5T2or more where T2is the thickness of the second nozzle member12in the width direction Z of the slit14.

T1and T2may be the same thickness or different thicknesses where T1is the thickness of the first nozzle member11in the width direction Z of the slit14, and T2is the thickness of the second nozzle member12in the width direction Z of the slit14.

The reason for the dimension of the divided face20being 1.5T1or 1.5T2or more will next be described. When each of the first nozzle member11and the second nozzle member12is divided along the length direction X of the slit14on a plurality of divided faces20into a plurality of nozzle members11A,11B,11C,12A,12B,12C, the divided face20can have a linear shape parallel with the nozzle thickness direction (the width direction Z of the slit14) and have a length equal to each thickness of the first nozzle member11and the second nozzle member12in the width direction Z of the slit14, and an adhesive can be applied onto the divided faces20for assembly, as illustrated inFIG.5.

In the above method, however, the nozzle members11B,12B that are located at the center in the length direction X of the slit14and are not fixed vertically by a pair of shim members30are easily affected by a force in the width direction (Z direction inFIG.1) orthogonal to the length direction of the slit14, and heat deformation by an ejected high-temperature gas causes slippages31on the divided faces20in directions of expanding the gap of the slit14as illustrated inFIG.6. In addition to this, nozzle cleaning for removing zinc clogged in the slit14or the internal pressure of a gas may cause slippages31on the divided faces20. The slippages31deform the hollow portion13as illustrated inFIG.6, and the gap of the slit14deforms in the nozzle width direction. From a slit14having a different gap shape, a gas is ejected in varies amounts in the length direction X of the slit14to vary the wiping performance in the length direction X of the slit14. As a result, the coating amount on a steel strip S cannot be uniformized in the width direction of the steel strip S. As illustrated inFIG.6, if a slit14has a larger gap, zinc splashed by a wiping gas is more likely to enter the slit14. As a result, the slit14clogged with zinc is likely to cause uneven linear adhesion (linear marks).

To solve the problems, the nozzle members11B,12B located at the center in the length direction X of the slit14are required to be prevented from deforming in the width direction Z of the slit14, or the fastening force between the nozzle members11A,11B,11C,12A,12B,12C is required to be increased. In the present embodiment, as illustrated inFIG.4, in a section of the first nozzle member11that is cut in the length direction X of the slit14, at at least one point on the depth direction Y, the dimension (D1+D2+D3) of each divided face20of the first nozzle member11is 1.5T1or more where T1is the thickness of the first nozzle member11(the thickness of the flat plate portion11a) in the width direction Z of the slit14, and in a section of the second nozzle member12that is cut in the length direction X of the slit14, at at least one point on the depth direction Y, the dimension (D1+D2+D3) of each divided face20of the second nozzle member12is 1.5T2or more where T2is the thickness of the second nozzle member12(thickness of the flat plate portion12a) in the width direction Z of the slit14.

InFIG.4, each divided face20of the first nozzle member11and the second nozzle member12has a step20b. In other words, each divided face20of the first nozzle member11includes a first linear portion20alinearly extending downward from the top face of the first nozzle member11(flat plate portion11a), a step20blinearly extending outward from the lower end of the first linear portion20ain the length direction X of the slit14, and a second linear portion20clinearly extending downward from an end of the step20bto the bottom face of the first nozzle member11(flat plate portion11a). Each divided face20of the second nozzle member12includes a first linear portion20alinearly extending upward from the bottom face of the second nozzle member12(flat plate portion12a), a step20blinearly extending outward from the upper end of the first linear portion20ain the length direction X of the slit14, and a second linear portion20clinearly extending upward from an end of the step20bto the top face of the second nozzle member12(flat plate portion12a).

The total dimension (D1+D2+D3) of the dimension D1of the first linear portion20a, the dimension D2of the step20b, and the dimension D3of the second linear portion20cof each divided face20is 1.5T1or more for the first nozzle member11and is 1.5T2or more for the second nozzle member12.

If the dimension (D1+D2+D3) of each divided face20is less than 1.5T1or 1.5T2, the divided face20has a similar shape to that illustrated inFIG.5, and the nozzle members11B,12B located at the center in the length direction X of the slit14easily move in the width direction Z of the slit14. The effect by the shape including the step20bis thus unlikely to be exerted.

If the dimension (D1+D2+D3) of each divided face20is more than 5T1or 5T2, the effect of improving the fastening force between the nozzle members11A,11B,11C,12A,12B,12C reaches the limit, and a divided face20having an excessively large dimension may crack. Hence, the upper limit of the dimension of the divided face20of the first nozzle member11is preferably 5T1, and the upper limit of the dimension of the divided face20of the second nozzle member12is preferably 5T2.

To make each divided face20have a dimension of 1.5T1or more or 1.5T2or more, each divided face20of the first nozzle member11and the second nozzle member12may have a taper shape that inclines with respect to the width direction Z of the slit14(vertical direction) as a gas wiping nozzle10pertaining to a first alternative embodiment and illustrated inFIG.7. In this case, each divided face20is inclined such that the dimension E1of the divided face20is 1.5T1or more for the first nozzle member11and is 1.5T2or more for the second nozzle member12. Even in this case, the upper limit of the dimension E1of each divided face20is preferably 5T1or 5T2.

In the cases illustrated inFIG.4andFIG.7, typically, the gap of a slit14tends to expand due to the internal pressure of a gas or heat effect, and thus the nozzle division is designed under the concept of suppressing the gap expansion of the slit14.

In contrast, a gap shrinkage of the slit14may become problematic. In such a case, a divided face20having such a shape as illustrated inFIG.8orFIG.9suppresses the gap shrinkage of the slit14.

FIG.8illustrates a section of a gas wiping nozzle pertaining to a second alternative embodiment, and each divided face20of a first nozzle member11and a second nozzle member12has a symmetrical shape to the shape of each divided face20illustrated inFIG.4. In other words, each divided face20of the first nozzle member11includes a first linear portion20alinearly extending downward from the top face of the first nozzle member11(flat plate portion11a), a step20blinearly extending inward from the lower end of the first linear portion20ain the length direction X of the slit14, and a second linear portion20clinearly extending downward from an end of the step20bto the bottom face of the first nozzle member11(flat plate portion11a). Each divided face20of the second nozzle member12also includes a first linear portion20alinearly extending upward from the bottom face of the second nozzle member12(flat plate portion11a), a step20blinearly extending inward from the upper end of the first linear portion20ain the length direction X of the slit14, and a second linear portion20clinearly extending upward from an end of the step20bto the top face of the second nozzle member12(flat plate portion12a), where signs are not illustrated inFIG.8.

The total dimension (D1+D2+D3) of the dimension D1of the first linear portion20a, the dimension D2of the step20b, and the dimension D3of the second linear portion20cof each divided face20is 1.5T1or more for the first nozzle member11and is 1.5T2or more for the second nozzle member12.

FIG.9illustrates a section of a gas wiping nozzle pertaining to a third alternative embodiment, and each divided face20of a first nozzle member11and a second nozzle member12has a symmetrical shape to the shape of each divided face20of the first nozzle member11and the second nozzle member12of the gas wiping nozzle10pertaining to the first alternative embodiment and illustrated inFIG.7.

When each of the first nozzle member11and the second nozzle member12is divided along the length direction X of the slit14on a plurality of divided faces20into a plurality of nozzle members, unlike the case illustrated inFIG.4(each member is divided into three members), each member may be divided into four nozzle members11A,11B,11C,11D,12A,12B,12C,12D, as a gas wiping nozzle pertaining to a fourth alternative embodiment and illustrated inFIG.10.

To make each divided face20have a dimension of 1.5T1or more or 1.5T2or more, each divided face20of the first nozzle member11and the second nozzle member12may have such a fitting face shape that a concave face20dand a convex face20eof the adjacent divided nozzle members11A and11B,11B and11C,11C and11D,12A and12B,12B and12C,12C and12D fit together, as the gas wiping nozzle pertaining to the fourth alternative embodiment and illustrated inFIG.10. The adjacent divided nozzle members11A and11B will be described as an example. The divided face20has such a key shape that the concave face20dformed on the nozzle member11A fits the convex face20eformed on the nozzle member11B.

In the gas wiping nozzle10pertaining to the fourth alternative embodiment and illustrated inFIG.10, the divided faces20have substantially the same dimension, and thus the dimension of the divided face20formed in the first nozzle member11will be described. The dimension of the divided face20is the sum of the dimension F1of a first linear portion linearly extending downward from the top face of the first nozzle member11(flat plate portion11a), the dimension F2of a second linear portion linearly extending outward from the lower end of the first linear portion in the length direction X of the slit14, the dimension F3of a third linear portion linearly extending downward from an end of the second linear portion, the dimension F4of a fourth linear portion linearly extending inward from the lower end of the third linear portion in the length direction X of the slit14, and the dimension F5of a fifth linear portion linearly extending downward from an end of the fourth linear portion to the bottom face of the first nozzle member11(flat plate portion11a).

By making each divided face20of the first nozzle member11and the second nozzle member12have such a fitting face shape, the fastening force between the nozzle members11A,11B,11C,11D,12A,12B,12C,12D is increased, and even if an external force is applied to the divided faces20to expand or shrink the gap of the slit14, the gap expansion or shrinkage is appropriately suppressed.

To make each divided face20have a fitting face shape, the fitting face shape may be a dogleg shape.

To make each divided face20have a dimension of 1.5T1or more or 1.5T2or more, each divided face20of the first nozzle member11and the second nozzle member12may have such a shape that the adjacent divided nozzle members11A and11B,11B and11C,11C and11D,12A and12B,12B and12C,12C and12D are engaged, as a gas wiping nozzle pertaining to a fifth alternative embodiment and illustrated inFIG.11.

In the gas wiping nozzle10pertaining to the fifth alternative embodiment and illustrated inFIG.11, the dimension of each divided face20is the total dimension (D1+D2+D3) of the dimension D1of a first linear portion20a, the dimension D2of a step20b, and the dimension D3of a second linear portion20cas with the gas wiping nozzle10illustrated inFIG.4, is 1.5T1or more for the first nozzle member11, and is 1.5T2or more for the second nozzle member12. The gas wiping nozzle10pertaining to the fifth alternative embodiment and illustrated inFIG.11is an example in which a nozzle is divided into four members. For example, when divided into five members, the nozzle may have such a structure as a gas wiping nozzle10pertaining to a sixth alternative embodiment and illustrated inFIG.12.

To increase the fastening force between nozzle members11A,11B,11C,12A,12B,12C, pins32may be used to connect the divided nozzle members11A and11B,11B and11C of the first nozzle member11and the divided nozzle members12A and12B,12B and12C of the second nozzle member12as in a gas wiping nozzle pertaining to a seventh alternative embodiment and illustrated inFIG.13or in a gas wiping nozzle pertaining to an eighth alternative embodiment and illustrated inFIG.14. This increases the fastening force between the divided nozzle members11A and11B,11B and11C,12A and12B,12B and12C.

The pin32may have a rectangular cross-sectional shape or a circular cross-sectional shape. In the gas wiping nozzle pertaining to the seventh alternative embodiment and illustrated inFIG.13, when the pin32is inserted into the step20bof the divided face20in the width direction Z of the slit14, the dimension of the pin32in the slit length direction X should be less than the dimension D2of the step20b.

In the gas wiping nozzle pertaining to the eighth alternative embodiment and illustrated inFIG.14, when the pin32is inserted into the taper-shaped divided face20in the width direction Z of the slit14, the dimension of the pin32in the slit length direction X should be less than the dimension between one end of the taper-shaped divided face20and the other end.

In the gas wiping nozzle pertaining to the seventh alternative embodiment and illustrated inFIG.13and the gas wiping nozzle pertaining to the eighth alternative embodiment and illustrated inFIG.14, when pins32are inserted as illustrated inFIG.15, any number of the pins32may be inserted in the slit length direction X and the slit depth direction Y at any positions.

A method of fixing the first nozzle member11and the second nozzle member12will next be described with reference toFIG.1toFIG.4.

The first nozzle member11and the second nozzle member12are first assembled. Before assembling the first nozzle member11and the second nozzle member12, the nozzle member11A and the nozzle member11C of the first nozzle member11are grooved from the rear end face11bato form grooves28, and the nozzle member12A and the nozzle member12C of the second nozzle member12are grooved from the rear end face12bato form grooves29.

To assemble the first nozzle member11, the adjacent nozzle members11A,11B are fitted on the divided face20, and an adhesive for ceramics is applied to fix the adjacent nozzle members11A,11B. The adjacent nozzle members11B,11C are fitted on the divided face20, and an adhesive for ceramics is applied to fix the adjacent nozzle members11B,11C. Accordingly, the assembling the first nozzle member11is completed.

To assemble the second nozzle member12, the adjacent nozzle members12A,12B are fitted on the divided face20, and an adhesive for ceramics is applied to fix the adjacent nozzle members12A,12B. The adjacent nozzle members12B,12C are fitted on the divided face20, and an adhesive for ceramics is applied to fix the adjacent nozzle members12B,12C. Accordingly, the assembling the second nozzle member12is completed. Examples of the adhesive used to assemble the first nozzle member11and the second nozzle member12include, but are not limited to, an adhesive mainly containing zirconia and silica, an adhesive mainly containing alumina, and an adhesive mainly containing silica.

The assembled first nozzle member11is placed at the upper side, and the assembled second nozzle member12is placed at the lower side. To the grooves28of the first nozzle member11and to the grooves29of the second nozzle member12, shim members30are fitted from the end faces11ba,12baof the first nozzle member11and the second nozzle member12in a direction parallel with the extending direction of the grooves28,29. For the fitting, a similar adhesive to the above is applied to the grooves28of the first nozzle member11and the grooves29of the second nozzle member12.

Accordingly, the first nozzle member11and the second nozzle member12are fixed.

The rear end face11baof the fixed first nozzle member11and the rear end face12baof the second nozzle member12may then be connected to the front-end face of the nozzle header15with fixing members such as screws (not illustrated).

When the gas wiping nozzle10pertaining to the present embodiment is placed in a high temperature atmosphere, and a high-temperature gas is ejected from the slit14, heat deformation during the ejection would cause slippages on the divided faces20in directions of expanding the gap L3of the slit14. In the present embodiment, as illustrated inFIG.4, in a section of the first nozzle member11that is cut in the length direction X of the slit14, the dimension (D1+D2+D3) of each divided face20of the first nozzle member11is 1.5T1or more where T1is the thickness of the first nozzle member11(the thickness of the flat plate portion11a) in the width direction Z of the slit14, and in a section of the second nozzle member12that is cut in the length direction X of the slit14, the dimension (D1+D2+D3) of each divided face20of the second nozzle member12is 1.5T2or more where T2is the thickness of the second nozzle member12(thickness of the flat plate portion12a) in the width direction Z of the slit14. Hence, the nozzle members11B,12B located at the center in the length direction X of the slit14are prevented from deforming in the width direction Z of the slit14, or the fastening force between the nozzle members11A,11B,11C,12A,12B,12C is increased. Accordingly, the divided faces20do not slip in directions of expanding the gap L3of the slit14due to heat deformation, and the gap L3in the width direction Z orthogonal to the length direction X of the slit14is maintained to be constant over the length direction X of the slit14. Accordingly, the gas ejection amount is constant in the length direction X of the slit14, and the wiping performance does not fluctuate in the length direction X of the slit14. As a result, the coating amount on a steel strip S is uniformized in the width direction of the steel strip S.

In the gas wiping nozzle10pertaining to the present embodiment, the upper limit of the dimension (D1+D2+D3) of the divided face20of the first nozzle member11is 5T1, and the upper limit of the dimension (D1+D2+D3) of the divided face20of the second nozzle member12is 5T2. This prevents the nozzle members11A,11B,11C,12A,12B,12C included in the first nozzle member11and the second nozzle member12from cracking.

InFIG.2, when each of the first nozzle member11and the second nozzle member12has a divided face20having a dimension of 1.5T1or more or 1.5T2or more in a section of the members cut at at least one point in the depth direction Y, the slit14maintains a constant gap. Under the condition, however, the first nozzle member11(the nozzle members11A,11B,11C) and the second nozzle member12(the nozzle members12A,12B,12C) may crack. To suppress the cracking, the region in the depth direction Y where the dimension of each divided face20of the first nozzle member11and the second nozzle member12is 1.5T1or more for the first nozzle member11and 1.5T2or more for the second nozzle member12is preferably a region having a dimension of not less than ⅓ of the full dimension L (seeFIG.3) in the depth direction of each of the first nozzle member11and the second nozzle member12and is more preferably a region having the same dimension as the full dimension L.

In the gas wiping nozzle10pertaining to the present embodiment, all the first nozzle member11, the second nozzle member12, and the shim members30are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, which has a small linear expansion coefficient, and the members have no difference in linear expansion coefficient. Accordingly, the gap L3in the width direction orthogonal to the length direction X of the slit14as a gas blowing port is maintained to be constant over the length direction X of the slit even in a high temperature atmosphere.

Although using a nozzle header15also made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material is further effective in maintaining the gap L3of the slit14to be constant, it is difficult to prepare a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material capable of withstanding a high-pressure wiping gas (capable of withstanding at least 60 kPa), and thus the nozzle header15is not made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material.

In the gas wiping nozzle disclosed in PTL 3, a first lip part and a second lip part are fixed with a fixing member at the slit side in a nozzle chamber, and thus the slit gap can be prevented from varying after each assembly when some or all parts included in the gas wiping nozzle are exchanged.

In the gas wiping nozzle disclosed in PTL 3, however, the fixing member to fix the upper and lower nozzle members, bolts used to fix the fixing members, and the like are made from a metal, and thus the fixing members, the bolts, and the like lengthen in a high temperature atmosphere. This changes the slit gap, and the slit gap cannot be maintained to be constant in the slit length direction.

In contrast, in the gas wiping nozzle10pertaining to the present embodiment, not only the first nozzle member11and the second nozzle member12are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, but also the shim members30are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material. In addition, the shim members30function to fix the first nozzle member11and the second nozzle member12. This eliminates members that fix the first nozzle member11and the second nozzle member12but function to expand the gap L3of the slit14in a high temperature atmosphere. The shim members30are made from a material unlikely to undergo plastic deformation and thus maintain the constant gap L3of the slit14as a gas blowing port in the length direction X of the slit14even in a high temperature atmosphere.

If shim members30have no function to fix the first nozzle member11and the second nozzle member12, and the first nozzle member11and the second nozzle member12made from a ceramic material are fixed with metal bolts, the first nozzle member11and the second nozzle member12made from a ceramic material needs bolt holes, and metal bolts should be inserted into the bolt holes. In this case, torque during fastening the metal bolts or thermal expansion may damage the first nozzle member11and the second nozzle member12made from a ceramic material.

In contrast, in the gas wiping nozzle10pertaining to the present embodiment, not only the first nozzle member11and the second nozzle member12are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, but also the shim members30are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material. In addition, the shim members30function to fix the first nozzle member11and the second nozzle member12. Hence, the first nozzle member11and the second nozzle member12are not damaged by torque during fastening metal bolts or thermal expansion.

A gas wiping nozzle pertaining to a ninth alternative embodiment will next be described with reference toFIG.16andFIG.17.

The gas wiping nozzle10illustrated inFIG.16andFIG.17has substantially the same basic configuration as the gas wiping nozzle10illustrated inFIG.4, but differs from the gas wiping nozzle10illustrated inFIG.4in that pins33are used to connect the grooves28of the first nozzle member11to the shim members30, and pins33are used to connect the grooves29of the second nozzle member12to the shim members30.

Each section of the grooves28of the first nozzle member11and the grooves29of the second nozzle member12illustrated inFIG.16andFIG.17has a rectangular shape. The grooves28of the first nozzle member11extend forward from the rear end face11ba(seeFIG.3). The grooves29of the second nozzle member12extend forward from the rear end face12ba(seeFIG.3). Corners28ain the grooves28and corners29ain the grooves29may have a curved shape. This suppresses stress concentration to prevent breakage of the shim member30.

The shim member30has a rectangular parallelepiped shape and has a sectional shape allowing the shim member to be fitted into the groove28of the first nozzle member11or the groove29of the second nozzle member12. As illustrated inFIG.17, the shim member30has a width C1of about 5 to 20 mm corresponding to the width of the groove28,29, and the shim member30has a height C2of about 5 to 40 mm.

To fix the first nozzle member11and the second nozzle member12, the shim members30are fitted into the grooves28of the first nozzle member11and the grooves29of the second nozzle member12. A plurality of pins33are used to connect the grooves28of the first nozzle member11to the shim members30and to connect the grooves29of the second nozzle member12to the shim members30. As described above, in the seventh alternative embodiment, the shim members30can be fitted before the first nozzle member11and the second nozzle member12are combined, and this enables assembly without inserting shim members30from the rear end faces11ba,12baof the first nozzle member11and the second nozzle member12into the grooves28,29. Hence, shim members30may be provided at a plurality of points in depth direction Y of the first nozzle member11and the second nozzle member12, and this enables highly accurate holding of the gap L3of the slit14.

As for pins33, in the present embodiment, a total of four pins33are used: two pins are used to connect the grooves28of the first nozzle member11to the shim members30; and two pins are used to connect the grooves29of the second nozzle member12to the shim members30, as illustrated inFIG.16. To provide shim members30at a plurality of points in the depth direction Y of the first nozzle member11and the second nozzle member12, the number of pins may be increased according to the number of shim members30.

To connect the groove28of the first nozzle member11to the shim member30, the shim member30is fitted into the grooves28,29, and then a pin33is inserted from the side face of the first nozzle member11into the shim member30to a predetermined depth C3, as illustrated inFIG.16andFIG.17. Similarly, to connect the groove29of the second nozzle member12to the shim member30, the shim member30is fitted into the grooves28,29, and then a pin33is inserted from the side face of the second nozzle member12into the shim member30to a predetermined depth C3, as illustrated inFIG.16andFIG.17.

In the present embodiment, each pin33is formed in a circular cylinder having a diameter C4of about Φ1to 10 mm, and the insertion depth C3of the pin33is about 1 to 15 mm, provided that the insertion depth C3of the pin33<the width C1of the shim member30, and the diameter C4of the pin33<the height C2of the shim member30. Each pin33is also preferably made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material. Each pin33preferably has a flexural strength of 600 MPa or more and more preferably 800 MPa or more. Hence, the ceramic material is preferably zirconia, silicon nitride, sialon, or the like.

When the gas wiping nozzle10illustrated inFIG.16andFIG.17is placed in a high temperature atmosphere, for example, when a wiping gas is heated, and accordingly the gas wiping nozzle10itself is heated, the nozzle header15made from a metal (seeFIG.1andFIG.2) would expand in the vertical direction or in the width direction Z of the slit14due to thermal expansion. Accordingly, the first nozzle member11and the second nozzle member12would move vertically apart due to the expansion. The first nozzle member11and the second nozzle member12are, however, connected to the shim members30with the pins33, and the shim members30are unlikely to undergo plastic deformation. Hence, the first nozzle member11and the second nozzle member12do not move vertically apart. The first nozzle member11and the second nozzle member12do not move vertically apart, and thus the gap L3of the slit14formed between the inclined end portions11c,12cat the steel strip S side of the first nozzle member11and the second nozzle member12is maintained.

Next, in the manufacturing of the steel strip S, it is preferable to control the temperature of the wiping gas so that the temperature T (° C.) of the wiping gas immediately after being blown from the slit14of the gas wiping nozzle10satisfies TM−150≤T≤TM+250 in relation to the melting point TM(° C.) of the molten metal. When the temperature T (° C.) of the wiping gas is controlled in this range, cooling and solidification of the molten metal can be suppressed, so that uneven viscosity is unlikely to occur and the occurrence of hot metal wrinkles can be suppressed. On the other hand, when the temperature T (° C.) of the wiping gas is less than TM−150° C. and is too low, the temperature T does not affect the fluidity of the molten metal and is not effective in suppressing the occurrence of hot metal wrinkles. In addition, when the temperature T (° C.) of the wiping gas is higher than TM+250° C., alloying is promoted and the appearance of the steel sheet is deteriorated.

In addition, a method for raising the temperature of the wiping gas supplied to the gas wiping nozzle10is not particularly limited. Examples thereof include a method for heating with a heat exchanger and raising the temperature to supply, and a method for mixing the combustion exhaust gas of the annealing furnace with air.

In addition, examples of the hot-dip metal coated metal strip manufactured by applying the gas wiping nozzle and the method for manufacturing the hot-dip metal coated metal strip according to the present embodiment include a hot-dip galvanized steel strip. The hot-dip galvanized steel strip includes both a coated steel sheet (GI) that is not subjected to an alloying treatment after the hot-dip galvanized treatment and a coated steel sheet (GA) that is subjected to the alloying treatment. However, the hot-dip metal coated metal strip manufactured by applying the gas wiping nozzle and the method for manufacturing the hot-dip metal coated metal strip according to the present embodiment is not limited thereto, and includes all hot-dip metal coated steel strips containing other molten metals such as aluminum and tin other than zinc.

The embodiments of the present invention have been described, but the present invention is not limited to them, and various modifications and improvements can be made.

For example, the number of divided members of each of the first nozzle member11and the second nozzle member12is three or four in the above description but may be two or five or more.

In a section of the first nozzle member11that is cut in the length direction X of the slit14, the dimension of each divided face20of the first nozzle member11is at least 1.5T1or more where T1is the thickness of the first nozzle member11in the width direction Z of the slit14, and in a section of the second nozzle member12that is cut in the length direction X of the slit14, the dimension of each divided face20of the second nozzle member12is at least 1.5T2or more where T2is the thickness of the second nozzle member12in the width direction Z of the slit14. The shape of each divided face20is not limited to the shapes illustrated inFIG.4,FIG.7,FIG.8,FIG.9,FIG.10,FIG.11, andFIG.12.

The thickness of the flat plate portion11aof the first nozzle member11and the thickness of the flat plate portion12aof the second nozzle member12are set constant, but may be inconstant.

The upper limit of the dimension of the divided face20of the first nozzle member11is 5T1, and the upper limit of the dimension of the divided face20of the second nozzle member12is 5T2, but the upper limits may be more than 5T1and 5T2, respectively.

All the first nozzle member11, the second nozzle member12, and the shim members30are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, but each of the first nozzle member11, the second nozzle member12, and the shim members30is not necessarily made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material.

All the first nozzle member11, the second nozzle member12, and the shim members are made from a ceramic material, a carbon material, a carbon fiber-reinforced carbon composite material, or a ceramic-based composite material, but all the first nozzle member11, the second nozzle member12, and the shim members are not necessarily made from the same material. However, all the first nozzle member11, the second nozzle member12, and the shim members are preferably made from the same material. This can certainly eliminate a difference in linear expansion coefficient among the first nozzle member11, the second nozzle member12, and the shim members.

Two independent shim members are not necessarily provided in the length direction X of the slit14. For example, as long as a shim member is partly fitted in grooves of the first nozzle member11and grooves of the second nozzle member12, the shim member may be an integral shim member having a connection part that connects portions fitted in the grooves of the nozzle members.

When pins33are used to connect the groove28of the first nozzle member11to the shim member30and to connect the groove29of the second nozzle member12to the shim member30, the section of the groove28,29is not limited to a rectangular shape but may be a dovetail groove shape, a T-groove shape, and other shapes. The sectional shape of the shim member30may be changed according to the sectional shape of the grooves28,29. The shape of the pin33is not necessarily a circular cylinder but may be a rectangular parallelepiped or other shapes.

EXAMPLES

A continuous hot-dip metal coating equipment1having the basic configuration illustrated inFIG.1was used to manufacture a hot-dip galvanized steel strip by introducing a steel strip S having a sheet thickness of 1.0 mm and a sheet width of 1,200 mm into a molten zinc bath at a sheet speed of 2.0 m/s. A gas wiping nozzle10has a slit14having a length L1of 1,800 mm, a depth L2of 20 mm, and a width (gap) L3of 1.2 mm. The quotient of the dimension of a divided face20of nozzle members11A to11C,12A to12C divided by the nozzle thickness T is as illustrated in Table 1 over the entire dimension in the depth direction Y. During experiments, the molten zinc coating bath had a temperature of 460° C., and the gas temperature T was 500° C. at the tip of the wiping nozzle. The wiping gas used was a mixed and adjusted gas of a flue gas from a combustor with air. The molten zinc coating bath had a melting point TMof 420° C.

The gas wiping nozzles of Invention Examples 1 to 14 and Comparative Examples 1 to 5 will next be described.

In Invention Examples 1 to 14 and Comparative Examples 1 to 5, sialon had a flexural strength of 980 MPa, a Vickers hardness of 1,620 HV, a fracture toughness of 6 MPa·m1/2, a thermal shock resistance of 650° C., and a linear expansion coefficient of 3.2×10−6/K. Chrome molybdenum steel had a yield stress of 400 MPa, a Vickers hardness of 300 HV, a fracture toughness of 236 MPa·m1/2, and a linear expansion coefficient of 11.2×10−6/K.

Invention Example 1

In Invention Example 1, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.4, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.4, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 12 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. The first nozzle member11and the second nozzle member12were each assembled. During the assembling, the adjacent nozzle members11A and11B,11B and11C,12A and12B,12B and12C were fixed with an adhesive mainly containing zirconia and silica. Next, the assembled first nozzle member11was placed at the upper side, and the assembled second nozzle member12was placed at the lower side. Substantially the same adhesive as above was applied to grooves28of the first nozzle member11and grooves29of the second nozzle member12, and the shim members30having a rectangular parallelepiped shape were fitted into the grooves28,29of the first nozzle member11and the second nozzle member12. The nozzle header15was finally fixed to the first nozzle member11and the second nozzle member12.

Invention Example 2

In Invention Example 2, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.4, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.4, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 78 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 3

In Invention Example 3, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.7, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.7, the divided face20had a taper shape, in which E1was 32 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 4

In Invention Example 4, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.7, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.7, the divided face20had a taper shape, in which E1was 98 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 5

In Invention Example 5, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.13, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.13, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 12 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. Definitions of D1, D2, D3, and T are the same as inFIG.4. Each divided face20of the first nozzle member11and the second nozzle member12was subjected to drilling at two points in the nozzle depth direction Y with a tolerance of 8 mm+10 μm. In the first nozzle member11and the second nozzle member12, the adjacent nozzle members11A and11B,11B and11C,12A and12B,12B and12C were fixed on the divided faces20with an adhesive mainly containing zirconia and silica. Next, an adhesive mainly containing zirconia and silica was applied to the drilled portions, and two pins32prepared to have a diameter of 8 mm with a tolerance of −10 μm were inserted into the drilled portions arranged in the slit depth direction Y as illustrated inFIG.13andFIG.15. Next, the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica, and the nozzle header15was finally fixed to the first nozzle member11and the second nozzle member12.

Invention Example 6

In Invention Example 6, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.14, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.14, the divided face20had a taper shape, in which E1was 32 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. Definitions of E1and T are the same as inFIG.7. Each divided face20of the first nozzle member11and the second nozzle member12was subjected to drilling at two points in the nozzle depth direction Y with a tolerance of 8 mm+10 μm. In the first nozzle member11and the second nozzle member12, the adjacent nozzle members11A and11B,11B and11C,12A and12B,12B and12C were fixed on the divided faces20with an adhesive mainly containing zirconia and silica. Next, an adhesive mainly containing zirconia and silica was applied to the drilled portions, and two pins32prepared to have a diameter of 8 mm with a tolerance of −10 μm were inserted into the drilled portions arranged in the slit depth direction Y as illustrated inFIG.14andFIG.15. Next, the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica, and the nozzle header15was finally fixed to the first nozzle member11and the second nozzle member12.

Invention Example 7

In Invention Example 7, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.4, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.4, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 82 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 8

In Invention Example 8, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.7, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.7, the divided face20had a taper shape, in which E1was 102 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 9

In Invention Example 9, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.11, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into four nozzle members11A,11B,11C,11D,12A,12B,12C,12D (each nozzle member11A,11B,11C,11D,12A,12B,12C,12D had a length of 450 mm in the slit length direction X). As illustrated inFIG.11, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 12 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 10

In Invention Example 10, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.11, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into four nozzle members11A,11B,11C,11D,12A,12B,12C,12D (each nozzle member11A,11B,11C,11D,12A,12B,12C,12D had a length of 450 mm in the slit length direction X). As illustrated inFIG.11, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 78 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 11

In Invention Example 11, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.11, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into four nozzle members11A,11B,11C,11D,12A,12B,12C,12D (each nozzle member11A,11B,11C,11D,12A,12B,12C,12D had a length of 450 mm in the slit length direction X). As illustrated inFIG.11, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 82 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 12

In Invention Example 12, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.12, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into five nozzle members11A,11B,11C,11D,11E,12A,12B,12C,12D,12E (each nozzle member11A,11B,11C,11D,11E,12A,12B,12C,12D,12E had a length of 450 mm in the slit length direction X). As illustrated inFIG.12, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 12 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 13

In Invention Example 13, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.12, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into five nozzle members11A,11B,11C,11D,11E,12A,12B,12C,12D,12E (each nozzle member11A,11B,11C,11D,11E,12A,12B,12C,12D,12E had a length of 450 mm in the slit length direction X). As illustrated inFIG.12, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 78 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Invention Example 14

In Invention Example 14, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.12, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into five nozzle members11A,11B,11C,11D,11E,12A,12B,12C,12D,12E (each nozzle member11A,11B,11C,11D,11E,12A,12B,12C,12D,12E had a length of 450 mm in the slit length direction X). As illustrated inFIG.12, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 82 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Comparative Example 1

In Comparative Example 1, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.5, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.5, the divided face20had a linear shape parallel with the nozzle thickness direction, and each divided face20had a dimension of 20 mm, which was the same as the thickness T1of the first nozzle member11and the thickness T2of the second nozzle member12. The first nozzle member11and the second nozzle member12were each assembled with an adhesive mainly containing alumina and silica, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Comparative Example 2

In Comparative Example 2, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.4, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.4, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 8 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Comparative Example 3

In Comparative Example 3, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.7, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into three nozzle members11A,11B,11C,12A,12B,12C (each nozzle member11A,11B,11C,12A,12B,12C had a length of 600 mm in the slit length direction X). As illustrated inFIG.7, the divided face20had a taper shape, in which E1was 28 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Comparative Example 4

In Comparative Example 4, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.11, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into four nozzle members11A,11B,11C,11D,12A,12B,12C,12D (each nozzle member11A,11B,11C,11D,12A,12B,12C,12D had a length of 450 mm in the slit length direction X). As illustrated inFIG.11, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 8 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

Comparative Example 5

In Comparative Example 5, a first nozzle member11, a second nozzle member12, and shim members30made from sialon were used, and a nozzle header15made from chrome molybdenum steel was used. As illustrated inFIG.12, each of the first nozzle member11and the second nozzle member12was equally divided along the length direction X of the slit14into five nozzle members11A,11B,11C,11D,11E,12A,12B,12C,12D,12E (each nozzle member11A,11B,11C,11D,11E,12A,12B,12C,12D,12E had a length of 450 mm in the slit length direction X). As illustrated inFIG.12, the divided face20had a shape including a step20b, in which D1was 10 mm, D2was 8 mm, and D3was 10 mm. In a cut section, the first nozzle member11had a thickness T1of 20 mm, and the second nozzle member12had a thickness T2of 20 mm. In a similar manner to that in Invention Example 1, the first nozzle member11and the second nozzle member12were each assembled, and the shim members30having a rectangular parallelepiped shape were fitted into grooves28,29of the first nozzle member11and the second nozzle member12through an adhesive mainly containing alumina and silica. The nozzle header15was then fixed to the first nozzle member11and the second nozzle member12.

In Invention Examples 1 to 14 and Comparative Examples 1 to 5, the rate of the gap change of the slit14, the coating amount deviation on a steel strip S in the width direction, the occurrence rate of linear marks, and nozzle breakage (cracks) were evaluated. In the evaluation, the rate (%) of the gap change of the slit14is a value (%) expressed by the maximum gap in the length direction X of the slit14/the minimum gap×100, and a nozzle having a rate of less than 110(%) is acceptance. The coating amount deviation (%) on a steel strip Sin the width direction is a value (T) expressed by the maximum coating amount on a steel strip S in the width direction/the minimum coating amount×100, and a nozzle giving a deviation of less than 120(%) is acceptance. The occurrence rate (%) of linear marks is the rate of the length of a steel strip S in which a linear mark defect was visually identified in an inspection process to the length of a steel strip S manufactured in each condition, and a nozzle giving a rate of less than 0.4(%) is acceptance.

The results are illustrated in Table 1.

As apparent from Table 1, in Invention Examples 1 to 14 in which the divided face had a dimension of 1.5T or more, the rate of the gap change of the slit14, the coating amount deviation on a steel strip S in the width direction, and the occurrence rate of linear marks were significantly reduced as compared with Comparative Examples 1 to 5 in which the divided face had a dimension of 1 to 1.4T, and each nozzle in Invention Examples was acceptance.

In Comparative Example 1 in which the divided face had a linear shape parallel with the nozzle thickness direction, and the divided face had a dimension of 1T, in Comparative Examples 2, 4, and 5 in which the divided face had a shape including a step, but the divided face had a dimension of 1.4T, and in Comparative Example 3 in which the divided face had a taper shape, but the divided face had a dimension of 1.4T, each of the rate of the gap change of the slit14, the coating amount deviation on a steel strip S in the width direction, and the occurrence rate of linear marks was more than the acceptance standard, and each nozzle was failure.

In Invention Examples 7, 8, 11, and 14, the divided face had a dimension of more than 5T, and cracks were observed on each of the first nozzle member11and the second nozzle member12in nozzle overhaul inspection after manufacture, but the rate of the gap change of the slit14, the coating amount deviation on a steel strip S in the width direction, and the occurrence rate of linear marks satisfied the acceptance standards, and each nozzle was acceptance.

In each of Invention Examples 1 to 14 and Comparative Examples 1 to 5, the temperature of the wiping gas is controlled so that the temperature T (° C.) of the wiping gas immediately after being blown from the slit14of the gas wiping nozzle10satisfies TM−150≤T≤TM+250 in relation to the melting point TM(° C.) of the molten metal. Hence, no hot metal wrinkle defect was observed in each of Invention Examples 1 to 14 and Comparative Examples 1 to 5.

The above results reveal that, by using the gas wiping nozzle and the method for manufacturing the hot-dip metal coated metal strip pertaining to the present invention, in which the gas wiping nozzle is manufactured from members divided along the length direction X of the slit14as a gas blowing port, the gap L3in the width direction Z orthogonal to the length direction X of the slit14can be maintained to be constant over the length direction X of the slit14even in a high temperature atmosphere, and the coating amount on a steel strip S can be uniformized in the width direction of the steel strip S.

REFERENCE SIGNS LIST