JP6880943B2 - Manufacturing method of molten aluminum plated steel wire - Google Patents

Description

The present invention relates to a method for producing a molten aluminum plated steel wire. More specifically, the present invention relates to, for example, a method for manufacturing a molten aluminum plated steel wire that can be suitably used for an automobile wire harness or the like.

In the present specification, the hot-dip aluminum-plated steel wire is a steel wire plated with aluminum by immersing the steel wire in a hot-dip aluminum plating bath and then continuously pulling the steel wire from the hot-dip aluminum-plated bath. Means. Further, the molten aluminum plating bath means a plating solution of molten aluminum.

Conventionally, copper wire has been used as an electric wire used for a wire harness of an automobile. However, in recent years, since weight reduction has been required, it is desired to develop an electric wire using a metal wire which is lighter than a copper wire.

As a metal wire that is lighter than a copper wire, a hot-dip Al-plated steel wire in which a steel core wire is subjected to hot-dip aluminum plating has been proposed (see, for example, claim 1 of Patent Document 1). The hot-dip Al-plated steel wire is a material steel wire made of a steel core wire or a material steel wire having a zinc-plated layer or a nickel-plated layer on the surface of the steel core wire, which is continuously immersed in a vapor-phase space after being immersed in a hot-dip aluminum plating bath. (See, for example, paragraph [0024] of Patent Document 1).

Further, as a method for producing a molten aluminum plated steel wire, a method for producing a molten aluminum plated steel wire by immersing the steel wire in a molten aluminum plating bath and then continuously pulling the steel wire from the molten aluminum plating bath. Therefore, when the steel wire is immersed in the molten aluminum plating bath and then pulled up from the molten aluminum plating bath, it is stable on the bath surface and the steel wire at the boundary between the steel wire and the bath surface of the molten aluminum plating bath. A nozzle having an inner diameter of 1 to 15 mm is arranged so that the tip of the nozzle is located at a distance of 1 to 50 mm from the steel wire in contact with the chemical member, and 200 to 800 from the tip of the nozzle. A method for producing a molten aluminum-plated steel wire, which comprises blowing an inert gas having a temperature of ° C. at a volume flow rate of 2 to 200 L / min toward the boundary between the steel wire and the bath surface of the molten aluminum plating bath. It has been proposed (see, for example, Patent Document 2). According to the above-mentioned manufacturing method, an excellent effect is obtained that a molten aluminum-plated steel wire having a uniform wire diameter and in which aluminum ingots are hard to adhere to the surface can be efficiently manufactured.

However, when the molten aluminum plated steel wire is manufactured by the above method, there is a possibility that an uneven thickness portion having a large difference in the thickness of the plated coating between the thick portion and the thin portion of the plated coating of the obtained molten aluminum plated steel wire may occur. Since the wire diameter of the steel wire becomes non-uniform when the molten aluminum-plated steel wire is wire-drawn, the wire may be broken when the wire is drawn at high speed, or the molten aluminum after the wire drawing may occur. There is a risk that the so-called "wire habit" will increase on the plated steel wire.

Japanese Unexamined Patent Publication No. 2014-185355 Japanese Unexamined Patent Publication No. 2015-134961

The present invention has been made in view of the above-mentioned prior art, and it is difficult for an uneven thickness portion having a large difference in the thickness of the plating coating between the thick portion and the thin portion of the plating film of the molten aluminum plated steel wire to occur on the surface. An object of the present invention is to provide a method for producing a molten aluminum-plated steel wire capable of efficiently producing a molten aluminum-plated steel wire to which an aluminum ingot does not easily adhere.

The present invention
(1) After immersing the steel wire in the molten aluminum plating bath, the steel wire is continuously pulled up from the molten aluminum plating bath through the dipping member immersed in the molten aluminum plating bath to obtain the molten aluminum plated steel. A method of manufacturing a wire, in which a stabilizing member is formed at the boundary between the molten aluminum plated steel wire pulled up from the molten aluminum plating bath and the bath surface of the molten aluminum plating bath, and the bath surface of the molten aluminum plating bath and the said. The horizontal slide amount L1 of the steel wire when it is brought into contact with the molten aluminum plated steel wire and the stabilizing member is pressed against the steel wire, and from the bath surface of the molten aluminum plating bath to the contact point between the dipping member and the steel wire. To adjust the value of the ratio (L1 / L2) to the shortest length L2 to 0.006 to 0.2 and spray the inert gas to the position facing the stabilizing member via the molten aluminum plated steel wire. A method for producing a molten aluminum-plated steel wire, characterized in that an inert gas having a temperature of 600 ° C. or higher is blown from the tip of the nozzle to the boundary portion at a pressure of 0.1 to 25 kPa.
(2) The method for manufacturing a molten aluminum-plated steel wire according to (1) above, wherein the steel wire is a steel wire made of carbon steel or stainless steel, and (3) the temperature of the molten aluminum plating bath is set to the temperature of the molten aluminum plating bath. The method for producing a molten aluminum-plated steel wire according to (1) or (2) above, which is adjusted so as to be higher than the melting point by 15 ° C. or more.

According to the method for manufacturing a hot-dip aluminum-plated steel wire of the present invention, it is difficult for an uneven thickness portion having a large difference in the thickness of the plating film between the thick part and the thin part of the plated steel film of the hot-dip aluminum plated steel wire to occur, and aluminum is formed on the surface. An excellent effect is achieved that a molten aluminum-plated steel wire on which lumps do not easily adhere can be efficiently produced.

It is a schematic explanatory drawing which shows one Embodiment of the manufacturing method of the hot-dip aluminum plated steel wire of this invention. It is schematic cross-sectional view which shows one Embodiment of the steel wire introduction part control apparatus shown in FIG. It is schematic cross-sectional view which shows one Embodiment of the bath surface control apparatus used for the steel wire introduction part control apparatus shown in FIG. 1 and FIG. In the method for manufacturing a molten aluminum plated steel wire of the present invention, the horizontal slide amount L1 of the steel wire when the stabilizing member is pressed against the steel wire and the contact point between the dipping member and the steel wire from the bath surface of the molten aluminum plating bath. It is a schematic explanatory drawing at the time of adjusting the value of the ratio (L1 / L2) with the shortest length L2 up to. FIG. 5 is a schematic explanatory view of a boundary portion between a steel wire and a bath surface of the hot-dip aluminum plating bath when the steel wire is pulled up from the hot-dip aluminum plating bath in the method for manufacturing a hot-dip aluminum-plated steel wire of the present invention.

In the method for producing a hot-dip aluminum-plated steel wire of the present invention, as described above, the steel wire is dipped in the hot-dip aluminum plating bath and then the steel wire is dipped in the hot-dip aluminum plating bath. It is a method of manufacturing a molten aluminum plated steel wire by continuously pulling it from a molten aluminum plating bath, and at the boundary between the molten aluminum plated steel wire pulled up from the molten aluminum plating bath and the bath surface of the molten aluminum plating bath. When the stabilizing member is brought into contact with the bath surface of the molten aluminum plating bath and the molten aluminum plated steel wire and the stabilizing member is pressed against the steel wire, the horizontal slide amount L1 of the steel wire and the molten aluminum plating bath The value of the ratio (L1 / L2) of the shortest length L2 from the bath surface to the contact point between the dipping member and the steel wire is adjusted to 0.006 to 0.2, and the molten aluminum plated steel wire is used. A nozzle for spraying the inert gas is arranged at a position facing the stabilizing member, and the inert gas having a temperature of 600 ° C. or higher is sprayed from the tip of the nozzle to the boundary portion at a pressure of 0.1 to 25 kPa. It is characterized by that.

According to the method for manufacturing a molten aluminum-plated steel wire of the present invention, since the above operation is adopted, the thickness difference between the thick portion and the thin portion of the plated coating of the molten aluminum-plated steel wire is large. It is possible to efficiently manufacture a molten aluminum-plated steel wire in which a portion is unlikely to be formed and an aluminum ingot is unlikely to adhere to the surface.

Hereinafter, the method for producing a hot-dip aluminum-plated steel wire of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described in the drawings.

FIG. 1 is a schematic explanatory view showing an embodiment of the method for manufacturing a hot-dip aluminum-plated steel wire of the present invention.

In the method for producing a hot-dip aluminum-plated steel wire of the present invention, the hot-dip aluminum-plated steel is obtained by immersing the steel wire 2 in the hot-dip aluminum-plated bath 1 and then continuously pulling the steel wire 2 from the hot-dip aluminum-plated bath 1. Wire 3 is manufactured.

Examples of the steel material constituting the steel wire 2 include stainless steel and carbon steel, but the present invention is not limited to these examples.

The stainless steel is an alloy steel containing 10% by mass or more of chromium (Cr). Examples of the stainless steel include austenitic steels, ferritic steels, martensitic steels and the like specified in JIS G4309, but the present invention is not limited to these examples. Specific examples of the stainless steel include stainless steels such as SUS301 and SUS304 whose austenite phase is generally considered to be semi-stable; stable austenite-based stainless steels such as SUS305, SUS310 and SUS316; SUS405, SUS410L, SUS429, SUS430 and SUS434, Ferrite-based stainless steels such as SUS436, SUS444, and SUS447; martensite-based stainless steels such as SUS403, SUS410, SUS416, SUS420, SUS431, and SUS440, and chromium-nickel-manganese-based stainless steels classified in the SUS200 series. However, the present invention is not limited to such an example.

Carbon steel is a steel material containing 0.02% by mass or more of carbon (C). Examples of carbon steel include steel materials specified in the JIS G3506 hard steel wire rod standard, and steel materials specified in the mild steel wire rod standard of JIS G3505, but the present invention is limited to such examples. It is not something that is done. Specific examples of carbon steel include hard steel and mild steel, but the present invention is not limited to these examples.

Among the steel materials, stainless steel and carbon steel are preferable from the viewpoint of increasing the tensile strength of the molten aluminum plated steel wire 3.

The diameter of the steel wire 2 is not particularly limited, and it is preferable to appropriately adjust the diameter according to the use of the molten aluminum plated steel wire 3. For example, when the molten aluminum-plated steel wire 3 is used for an automobile wire harness or the like, the diameter of the steel wire 2 is usually preferably about 0.05 to 0.5 mm.

The steel wire 2 may be degreased before being subjected to hot-dip aluminum plating. The degreasing of the steel wire 2 is performed, for example, by immersing the steel wire 2 in an alkaline degreasing solution, washing it with water, neutralizing the alkali adhering to the steel wire 2, and washing it again with water to perform degreasing. This can be done by a method of performing electrolytic degreasing by energizing the steel wire 2 in a state where 2 is immersed in an alkaline degreasing solution. The alkaline degreasing liquid may contain a surfactant from the viewpoint of improving the degreasing power.

Further, from the viewpoint of efficiently forming a smooth aluminum plating film on the steel wire 2, the surface of the steel wire 2 is pre-plated before being immersed in the molten aluminum plating bath 1. May be good. Examples of the metal constituting the pre-plating treatment include zinc, nickel, chromium, and alloys thereof, but the present invention is not limited to these examples. Further, the plating film formed on the surface of the steel wire 2 by the pre-plating treatment may be formed of only one layer, or may be formed of a plurality of plating films made of the same or different metals.

In FIG. 1, the steel wire 2 is sent out from the delivery device 4 of the steel wire 2, is continuously conveyed in the direction of arrow A, and is immersed in the molten aluminum plating bath 1 in the plating bath 5.

When the steel wire 2 is a steel wire 2 made of carbon steel, even if the steel wire 2 is degreased, rust may occur on the surface of the steel wire 2 before hot-dip aluminum plating is performed. It is preferable to degreas the steel wire 2 from the delivery device 4 to the molten aluminum plating bath 1. The degreasing of the steel wire 2 made of carbon steel can be performed by the same method as the degreasing of the steel wire 2.

Only aluminum may be used in the molten aluminum plating bath 1, and if necessary, other elements may be contained within a range that does not impair the object of the present invention. Examples of the other elements include nickel, chromium, zinc, silicon, copper, iron and the like, but the present invention is not limited to these examples. When these other elements are contained in aluminum, the mechanical strength of the plating film (not shown) can be increased, and thus the tensile strength of the molten aluminum-plated steel wire 3 can be increased. Among the other elements mentioned above, although it depends on the type of steel wire, it suppresses the formation of an iron-aluminum alloy layer having brittleness between the iron contained in the steel wire and the aluminum contained in the plating film. However, silicon is preferable from the viewpoint of efficiently plating the steel wire 2 by increasing the mechanical strength of the plating film and lowering the melting point of the molten aluminum plating bath 1.

A plating film (not shown) made of aluminum or an aluminum alloy is formed on the surface of the hot-dip aluminum-plated steel wire 3. The lower limit of the content of the other element in the plating film is 0% by mass, but from the viewpoint of fully expressing the properties of the other element, it is preferably 0.3% by mass or more, more preferably 0. It is 5.5% by mass or more, more preferably 1% by mass or more, and preferably 50% by mass or less, more preferably 20% by mass or less, still more preferably 15 from the viewpoint of suppressing potential difference corrosion due to contact with the aluminum wire. It is mass% or less.

Elements such as nickel, chromium, zinc, copper, and iron may inevitably be mixed in the molten aluminum plating bath 1.

The lower limit of the bath temperature of the molten aluminum plating bath 1 is a temperature equal to or higher than the melting temperature of the molten aluminum plating bath 1 when manufacturing the molten aluminum plated steel wire, and is usually the melting point of the molten aluminum plating bath 1 under normal pressure. It is the above temperature.

When the bath temperature of the hot-dip aluminum plating bath 1 is adjusted to a temperature 15 ° C. or higher higher than the melting point of the hot-dip aluminum plating bath 1, the thickness difference between the thick portion and the thin portion of the plating film is large. It is possible to obtain a molten aluminum-plated steel wire 3 in which a portion is hardly generated and an aluminum ingot hardly adheres to the surface.

Therefore, from the viewpoint of obtaining the molten aluminum plated steel wire 3 in which the uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film is hardly generated and the aluminum ingot hardly adheres to the surface, the molten aluminum is obtained. It is preferable to adjust the bath temperature of the plating bath 1 to a temperature 15 ° C. or higher higher than the melting point of the molten aluminum plating bath 1, and the bath temperature of the molten aluminum plating bath 1 is 20 ° C. higher than the melting point of the molten aluminum plating bath 1. It is preferable to adjust the temperature to a higher temperature.

The upper limit of the bath temperature of the molten aluminum plating bath 1 is preferably 800 ° C. or lower, more preferably 780 ° C. or lower, and further preferably 750 ° C. or lower from the viewpoint of improving thermal efficiency.

Further, the bath temperature of the molten aluminum plating bath 1 is preferably 680 to 720 ° C. from the viewpoint of efficiently producing the molten aluminum plated steel wire 3 in which aluminum lumps do not easily adhere to the surface.

The bath temperature of the molten aluminum plating bath 1 is such that a temperature sensor in which the thermocouple is inserted in a protective tube for protecting the thermocouple is placed at a depth of about 300 mm from the bath surface of the molten aluminum plating bath 1. It is a value when it is immersed in the vicinity of the steel wire 2 pulled up from the plating bath 1 and measured.

In the present invention, from the viewpoint of efficiently producing the molten aluminum-plated steel wire 3 in which the aluminum ingot does not easily adhere to the surface, the steel wire 2 is heated before the steel wire 2 is immersed in the molten aluminum plating bath 1. It is preferable to pass the steel wire 2 through the steel wire introduction unit control device 8 having the bath surface control device 7 for preventing the oxide film from adhering to the surfaces of the heating device 6 and the steel wire 2.

Examples of the steel wire introduction unit control device 8 include the steel wire introduction unit control device 8 shown in FIG. 2, but the present invention is not limited to such an example. FIG. 2 is a schematic cross-sectional view showing an embodiment of the steel wire introduction unit control device 8 shown in FIG. The steel wire introduction unit control device 8 includes a heating device 6 and a bath surface control device 7.

As shown in FIG. 2, the heating device 6 has a tubular heating device main body 6a made of a steel material such as stainless steel. The inside 6b of the heating device main body 6a is hollow so that the steel wire 2 can be passed in the direction of arrow B.

Examples of the heating gas ventilated to the heating device 6 include air, an inert gas such as nitrogen gas, argon gas, and helium gas, but the present invention is not limited to these examples. Absent. Among these, the heating gas discharged from the lower end 6d of the heating device 6 is ventilated into the inside from the introduction port of the upper end 7a of the bath surface control device 7 arranged below the heating device 6, and the inside thereof. The inert gas is preferable from the viewpoint of preventing the molten aluminum plating bath 1 in the bath surface control device 7 from being oxidized by creating an inert gas atmosphere. Since the temperature of the heating gas varies depending on the type of steel wire 2 used and conditions such as its diameter, wire speed, and flow rate of the heating gas, it cannot be unconditionally determined. Therefore, the temperature of the steel wire can be determined according to the conditions. It is preferable to adjust so that 2 is appropriately heated.

The heating temperature of the steel wire 2 is preferably 60 ° C. or higher, more preferably 80 ° C. or higher, still more preferably 150 ° C. or higher, still more preferably 200 ° C. or higher, from the viewpoint of efficiently producing the molten aluminum-plated steel wire 3. There is, and the upper limit thereof cannot be unconditionally determined because it differs depending on the type of steel wire 2, etc., but in consideration of energy efficiency, it is usually preferably 1000 ° C. or lower, more preferably 900 ° C. or lower, still more preferably. It is 800 ° C. or lower. The heating temperature is a temperature measured based on the method described in the following examples.

The length of the heating device main body 6a shown in FIG. 2 may be any length as long as it can be adjusted so that the steel wire 2 is heated to a predetermined temperature, and is not particularly limited. , 1 to 5 m. Further, the diameter of the inside 6b of the heating device main body 6a varies depending on the diameter of the steel wire 2 used and its type, and therefore cannot be unconditionally determined, but is usually 1.5 to 1.5 to the diameter of the steel wire 2. It is about 50 times. For example, when a steel wire 2 having a diameter of 0.2 mm is used, the diameter of the inside 6b of the heating device main body 6a is preferably about 0.3 to 10 mm.

A branch pipe 6e having a heating gas vent 6c is arranged on the side surface of the heating device main body 6a. By ventilating the heating gas from the heating gas vent 6c of the branch pipe 6e, the steel wire 2 passed through the heating device 6 can be heated, and a heater (not shown) is provided in the branch pipe 6e. May be arranged to heat the heating gas ventilated in the branch pipe 6e by the heater. In the embodiment shown in FIG. 2, seven branch pipes 6e are arranged, but the number of branch pipes 6e is not particularly limited, and the number of the branch pipes 6e may be only one. Or, it may be about 2 to 10 pieces.

In the embodiment shown in FIG. 2, a gap D is provided between the lower end 6d of the heating device 6 and the upper end 7a of the bath surface control device 7 arranged below the heating device 6. The gap D is preferably about 3 to 10 mm from the viewpoint of efficiently discharging the heating gas from the gap D. The gap D does not necessarily have to be provided, and the heating device 6 and the bath surface control device 7 may be formed of separate members, and both may be integrated by, for example, screw fitting. When the heating device 6 and the bath surface control device 7 are integrated, if necessary, the heating device 6 or a discharge port (not shown) for discharging the heating gas ventilated inside the heating device 6 is provided. It may be provided on the side surface of the bath surface control device 7.

In the present invention, for example, an energization heating device, an induction heating device, or the like can be used instead of the heating device 6.

Examples of the bath surface control device 7 include the bath surface control device 7 shown in FIG. 3, but the present invention is not limited to such an example.

FIG. 3 is a schematic cross-sectional view showing an embodiment of the bath surface control device 7 used in the steel wire introduction unit control device 8 shown in FIGS. 1 and 2.

As shown in FIG. 3, the bath surface control device 7 has a tubular body 9 having a through hole 9a for passing the steel wire 2 in the direction of arrow C inside the bath surface control device 7. The total length L of the bath surface control device 7 is usually preferably 30 to 500 mm, more preferably 40 to 300 mm, still more preferably 50 to 100 mm.

The tubular body 9 has an immersion region 9b for immersing in the molten aluminum plating bath 1 from one end of the side immersed in the molten aluminum plating bath 1 to the virtual line P shown in FIG. 3 along the longitudinal direction. .. The length of the immersion region 9b is usually preferably 2 to 20 mm, more preferably 5 to 15 mm or more.

In the longitudinal direction of the tubular body 9, the length of the portion not immersed in the molten aluminum plating bath 1 is usually preferably 5 mm or more, more preferably 10 mm or more.

Ratio of the area of the opening of the through hole 9a of the tubular body 9 to the area of the cross section of the steel wire 2 used for hot-dip aluminum plating (so-called cross section of the steel wire 2) [of the through hole 9a of the tubular body 9 The value of [Area of opening / Area in cross section of steel wire 2] is preferably 3 or more from the viewpoint of smoothly introducing the steel wire 2 into the through hole 9a of the tubular body 9, and is oxidized to the steel wire 2. From the viewpoint of preventing the film from adhering, the amount is preferably 4000 or less, more preferably 3000 or less, still more preferably 2000 or less, and even more preferably 1000 or less.

The shape of the opening of the through hole 9a included in the tubular body 9 is arbitrary, may be circular, or may be any other shape. The gap (clearance) between the opening of the through hole 9a of the tubular body 9 and the steel wire 2 is preferably 10 μm or more from the viewpoint of preventing the inner wall of the through hole 9a of the tubular body 9 from sliding with the steel wire 2. , More preferably 20 μm or more, still more preferably 50 μm or more, and even more preferably 100 μm or more.

As shown in FIG. 3, the opening of the through hole 9a of the tubular body 9 includes the opening 9d and the tubular body 9 in the introduction port 9c for introducing the steel wire 2 into one end of the tubular body 9. It is an opening 9f in the discharge port 9e for discharging the steel wire 2 at the end. The area and shape of the opening 9d and the opening 9f may be the same or different, but the steel wire 2 is smoothly passed through the through hole 9a of the tubular body 9, and the tubular body 9 is formed. As shown in FIG. 3, from the viewpoint of avoiding sliding between the inner wall of the through hole 9a and the steel wire 2 and efficiently manufacturing the molten aluminum-plated steel wire 3 in which the plating film is formed on the entire surface, as shown in FIG. It is preferable that the area and shape of the opening 9d and the opening 9f are the same.

If necessary, the steel wire 2 that has passed through the steel wire introduction unit control device 8 is immersed in the molten aluminum plating bath 1.

The wire passing speed of the steel wire 2 is 100 m / min or more from the viewpoint of efficiently producing the molten aluminum-plated steel wire 3, and suppresses the scattering of the oxide film formed on the surface of the molten aluminum-plated bath 1. From the viewpoint of efficiently producing the molten aluminum-plated steel wire 3 in which the oxide film hardly adheres to the surface, the concentration is preferably 1000 m / min or less, more preferably 800 m / min or less.

The time (plating time) for the steel wire 2 to be immersed in the hot-dip aluminum plating bath 1 is adjusted so that the thickness of the plating film formed on the surface of the steel wire 2 becomes a predetermined thickness. The time (plating time) for the steel wire 2 to be immersed in the hot-dip aluminum plating bath 1 varies depending on the required thickness of the plating film, the bath temperature of the hot-dip aluminum plating bath 1, and the like, and therefore cannot be unconditionally determined. Usually, it is about 0.3 to 1 second.

Next, as shown in FIG. 1, after immersing the steel wire 2 in the molten aluminum plating bath 1, the steel wire 2 is immersed in the molten aluminum plating bath 1 via the dipping member 10. By pulling up from the bath surface 10 of 1, the plating film of the molten aluminum plating bath 1 is formed on the surface of the steel wire 2, and the molten aluminum plated steel wire 3 is obtained.

When the steel wire 2 is continuously pulled up from the molten aluminum plating bath 1, the steel wire 2 is unlikely to have an uneven thickness portion having a large difference in thickness between a thick portion and a thin portion of the plating film, and is unlikely to occur on the surface of the steel wire 2. From the viewpoint of efficiently producing the molten aluminum-plated steel wire 3 to which the aluminum ingot does not easily adhere, it is preferable to pull it up in the vertical direction.

As shown in FIG. 4, the stabilizing member 12 is formed on the bath surface of the molten aluminum plating bath 1 at the boundary between the molten aluminum plated steel wire 3 pulled up from the molten aluminum plating bath 1 and the bath surface of the molten aluminum plating bath 1. The horizontal slide amount L1 of the steel wire 2 when the stabilizing member 12 is pressed against the steel wire 2 by contacting the 11 and the molten aluminum plated steel wire 3, and the dipping member 10 from the bath surface 11 of the molten aluminum plating bath 1 The value of the ratio (L1 / L2) with the shortest length L2 to the contact point with the steel wire 2 is adjusted to 0.006 to 0.2. In the present invention, since the above operation is adopted, it is difficult for an uneven thickness portion having a large difference in thickness between a thick portion and a thin portion of the plating film to occur, and it is difficult for an aluminum block to adhere to the surface. The molten aluminum plated steel wire 3 can be efficiently manufactured.

In addition, FIG. 4 shows the horizontal slide amount L1 of the steel wire 2 when the stabilizing member is pressed against the steel wire and the immersion from the bath surface of the molten aluminum plating bath in the method for manufacturing the molten aluminum plated steel wire of the present invention. It is schematic explanatory drawing at the time of adjusting the value of the ratio (L1 / L2) with the shortest length L2 to the contact point between a member and a steel wire.

The dipping member 10 is arranged so as to come into contact with the steel wire 2 without pushing the stabilizing member 12 into the steel wire 2. As the material of the dipping member 10, since it is used by dipping it in the molten aluminum plating bath 1, for example, a metal or ceramic having a melting point higher than the heating temperature of the molten aluminum plating bath 1 can be mentioned. Is not limited to such examples. Examples of the shape of the immersion member 10 include a cylinder, a polygonal column, and the like, but the present invention is not limited to these examples. When the dipping member 10 is, for example, a cylindrical dipping roll, its diameter is not particularly limited and is usually about 200 to 500 mm. The dipping member 10 may be fixed without rotating. It may be installed so as to rotate along the traveling direction of the steel wire 2.

The shortest length L2 from the bath surface 11 of the molten aluminum plating bath 1 to the contact point between the dipping member 10 and the steel wire 2 is an uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film. From the viewpoint of efficiently producing the molten aluminum-plated steel wire 3 in which the aluminum lumps are less likely to adhere to the surface, the thickness is preferably 10 to 500 mm, more preferably 20 to 400 mm.

By pulling up the steel wire 2 immersed in the molten aluminum plating bath 1 from the bath surface 11 of the molten aluminum plating bath 1, the molten aluminum plating bath 1 adheres to the surface of the steel wire 2, and the molten aluminum plated steel wire 3 is obtained. Be done. As shown in FIG. 5, when the steel wire 2 is pulled up from the molten aluminum plating bath 1 in the direction of arrow E, the plating bath 1 is lifted along with the molten aluminum plated steel wire 3 pulled up from the molten aluminum plating bath 1. As a result, the meniscus 18 is formed. When the tip 18a of the meniscus 18 extends upward, the tip 18a of the meniscus 18 solidifies into an aluminum ingot, and the aluminum ingot may adhere to the plating film 19 of the molten aluminum-plated steel wire 3 as a foreign substance. ..

Therefore, in order to prevent foreign matter such as an aluminum ingot from adhering to the surface of the molten aluminum plated steel wire 3 by suppressing the tip 18a of the meniscus 18 from extending excessively upward, the steel wire 2 is provided. When pulling up from the hot-dip aluminum plating bath 1, the stabilizing member 12 is placed in the hot-dip aluminum plating bath at the boundary between the hot-dip aluminum-plated steel wire 3 pulled up from the hot-dip aluminum plating bath 1 and the bath surface 11 of the hot-dip aluminum plating bath 1. A nozzle 13 for in contacting the bath surface 11 of No. 1 and the molten aluminum-plated steel wire 3 and blowing an inert gas at a position facing the stabilizing member 12 via the molten aluminum-plated steel wire 3 is arranged.

Note that FIG. 5 shows the boundary between the steel wire 2 and the bath surface 11 of the hot-dip aluminum-plated bath 1 when the steel wire 2 is pulled up from the hot-dip aluminum-plated bath 1 in the method for manufacturing a hot-dip aluminum-plated steel wire of the present invention. It is a schematic explanatory drawing. In the embodiment shown in FIG. 5, the stabilizing member 12 is shown in a state when it is not pushed into the molten aluminum plated steel wire 3.

Examples of the stabilizing member 12 include a stainless steel square bar having a heat-resistant cloth material 12a wound on the surface thereof. Examples of the heat-resistant cloth material 12a include woven fabrics and non-woven fabrics containing heat-resistant fibers such as ceramic fibers, carbon fibers, aramid fibers, and imide fibers, but the present invention is limited to these examples only. is not it. The heat-resistant cloth material 12a brings the surface (new surface) of the heat-resistant cloth material 12a to which aluminum is not adhered into contact with the steel wire 2 from the viewpoint of suppressing the adhesion of aluminum ingots to the surface of the molten aluminum-plated steel wire 3. Is preferable.

It is preferable that the stabilizing member 12 is in contact with both the bath surface 11 of the molten aluminum plating bath 1 and the molten aluminum plated steel wire 3 at the same time. When the stabilizing member 12 is brought into contact with both the bath surface 11 of the molten aluminum plating bath 1 and the molten aluminum plated steel wire 3 at the same time in this way, the pulsation of the bath surface 11 of the molten aluminum plating bath 1 is suppressed. As a result, the pulsation of the meniscus 18 is suppressed, so that the plating film 19 can be uniformly formed on the surface of the steel wire 2.

When the stabilizing member 12 is brought into contact with the molten aluminum-plated steel wire 3, in order to apply tension to the molten aluminum-plated steel wire 3 from the viewpoint of suppressing minute vibration of the molten aluminum-plated steel wire 3. The stabilizing member 12 is pressed against the molten aluminum plated steel wire 3. The horizontal slide amount L1 of the steel wire 2 when the stabilizing member 12 is pressed against the molten aluminum plated steel wire 3 is stable from the steel wire 2 to the steel wire 2 when the stabilizing member 12 is not pressed against the steel wire 2. The amount of change to the steel wire 2 when the chemical member 12 is pressed, in other words, the amount of bending of the steel wire 2 by the stabilizing member 12.

The horizontal slide amount L1 of the steel wire 2 is not particularly limited, but it is difficult for an uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film 19 to occur, and an aluminum lump is formed on the surface. From the viewpoint of efficiently producing the hard-to-adhere molten aluminum-plated steel wire 3, the thickness is preferably 0.15 to 80 mm, more preferably 0.2 to 60 mm.

The horizontal slide amount L1 of the steel wire 2 when the stabilizing member 12 is pressed against the steel wire 2 and the shortest length L2 from the bath surface 11 of the molten aluminum plating bath 1 to the contact point between the immersion member 10 and the steel wire 2 As for the value of the ratio (L1 / L2) to, it is difficult for an uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film 19 to occur, and the aluminum lump does not easily adhere to the surface. From the viewpoint of efficiently producing the aluminum-plated steel wire 3, it is adjusted to 0.006 to 0.2, preferably 0.01 to 0.06.

A nozzle 13 for blowing the inert gas at a position facing the stabilizing member 12 is arranged via the molten aluminum-plated steel wire 3. The tip 13a of the nozzle 13 is arranged so that the inert gas can be sprayed on the boundary between the steel wire 2 and the bath surface 11 of the molten aluminum plating bath 1. The distance (shortest distance) from the steel wire 2 to the tip 13a of the nozzle 13 is preferably from the viewpoint of avoiding contact between the tip 13a of the nozzle 13 and the steel wire 2 and efficiently manufacturing the molten aluminum-plated steel wire 3. A viewpoint of obtaining a molten aluminum-plated steel wire 3 having a thickness of 1 mm or more, hardly causing an uneven thickness portion having a large difference in thickness between a thick portion and a thin portion of the plating film 19, and hardly adhering an aluminum ingot to the surface. Therefore, it is preferably 50 mm or less, more preferably 40 mm or less, still more preferably 30 mm or less, still more preferably 10 mm or less, and even more preferably 5 mm or less.

The inner diameter of the tip 13a of the nozzle 13 is determined by accurately spraying the inert gas discharged from the tip 13a of the nozzle 13 onto the boundary between the steel wire 2 and the bath surface 11 of the molten aluminum plating bath 1. From the viewpoint of efficiently producing the wire 3, the thickness is preferably 1 mm or more, more preferably 2 mm or more, and there is almost no uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film 19. From the viewpoint of obtaining the molten aluminum-plated steel wire 3 to which the aluminum ingot hardly adheres to the surface, the thickness is preferably 15 mm or less, more preferably 10 mm or less, still more preferably 5 mm or less.

The inert gas can be supplied from the inert gas supply device 14 to the nozzle 13 via the pipe 15 as shown in FIG. 1, for example. In order to adjust the flow rate of the inert gas, for example, a flow rate control device (not shown) such as a valve may be provided in the inert gas supply device 14 or in the pipe 15.

The inert gas means a gas that is inert to the molten aluminum. Examples of the inert gas include nitrogen gas, argon gas, helium gas and the like, but the present invention is not limited to these examples. Among the inert gases, nitrogen gas is preferable. The inert gas may contain, for example, oxygen gas, carbon dioxide gas, etc., as long as the object of the present invention is not impaired.

The pressure of the inert gas discharged from the tip 13a of the nozzle 13 is adjusted to 0.1 to 25 kPa. In the present invention, when the steel wire 2 is immersed in the molten aluminum plating bath 1 and then pulled up from the molten aluminum plating bath 1, the bath surface of the molten aluminum plated steel wire 3 and the molten aluminum plating bath 1 is pulled from the tip 13a of the nozzle 13. Since the pressure of the inert gas to be sprayed on the boundary portion with 11 is adjusted to 0.1 to 25 kPa, the uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film 19 It is possible to obtain a molten aluminum-plated steel wire 3 in which almost no aluminum lumps adhere to the surface.

The pressure of the inert gas discharged from the tip 13a of the nozzle 13 is 0.1 kPa or more from the viewpoint of obtaining the molten aluminum-plated steel wire 3 on which almost no aluminum lumps adhere to the surface, and the thickness of the plating film 19 is thick. From the viewpoint of obtaining the molten aluminum-plated steel wire 3 in which a large difference in thickness between the portion and the thin portion is hardly generated, the thickness is 25 kPa or less, preferably 20 kPa or less, more preferably 15 kPa or less, still more preferably 3 kPa or less. is there.

The pressure of the inert gas discharged from the tip 13a of the nozzle 13 is made of stainless steel having an inner diameter of 0.5 mm in the inert gas in the nozzle 13 at a distance of 2 mm from the tip 13a of the nozzle 13. This is a value when the tip of the tube and the tip 13a of the nozzle 13 are inserted so as to face each other and the gas pressure of the inert gas applied to the tip of the tube is measured by a pressure sensor.

The volumetric flow rate of the inert gas discharged from the tip 13a of the nozzle 13 is preferably 2 L (liter) / min or more, more preferably 5 L, from the viewpoint of efficiently preventing the oxidation of the meniscus portion 18 of the molten aluminum plating bath 1. It is / min or more, more preferably 10 L / min or more, and there is almost no uneven thickness portion having a large difference in thickness between the thick portion and the thin portion of the plating film 19, and almost no aluminum lump adheres to the surface. From the viewpoint of obtaining the molten aluminum-plated steel wire 3, it is preferably 200 L / min or less, more preferably 150 L / min or less, and further preferably 100 L / min or less.

As for the temperature of the inert gas discharged from the tip 13a of the nozzle 13, there is almost no uneven thickness portion in which the thickness difference between the thick portion and the thin portion of the plating film 19 is large, and most of the aluminum lumps are formed on the surface. From the viewpoint of obtaining the molten aluminum-plated steel wire 3 that does not adhere, the temperature is 600 ° C. or higher, preferably 610 ° C. or higher, more preferably 620 ° C. or higher, and from the viewpoint of improving thermal efficiency, preferably 1000 ° C. or lower, more preferably 800 ° C. or higher. Below, it is more preferably 750 ° C. or less.

The temperature of the inert gas discharged from the tip 13a of the nozzle 13 is, for example, set in the inert gas at a distance of 2 mm from the tip 13a of the nozzle 13 discharged from the tip 13a of the nozzle 13. , It is a value when measured by inserting a thermocouple for temperature measurement such as a sheath thermocouple having a diameter of 1.6 mm.

The pulling speed when pulling the hot-dip aluminum-plated steel wire 3 from the bath surface 11 of the hot-dip aluminum plating bath 1 is not particularly limited, and exists on the surface of the hot-dip aluminum-plated steel wire 3 by appropriately adjusting the pulling speed. Since the thickness of the plating film 19 can be adjusted, it is preferable to adjust the thickness appropriately according to the thickness of the plating film 19.

As shown in FIG. 1, in order to cool the molten aluminum-plated steel wire 3 in the process of pulling up the molten aluminum-plated steel wire 3 and efficiently solidify the plating film (not shown) formed on the surface. If necessary, the cooling device 16 may be arranged on the upper part of the nozzle 13. In the cooling device 16, the molten aluminum-plated steel wire 3 can be cooled by spraying, for example, a mist of gas or liquid onto the molten aluminum-plated steel wire 3.

As shown in FIG. 1, the molten aluminum-plated steel wire 3 manufactured as described above can be recovered by, for example, a winding device 17.

The thickness of the plating film existing on the surface of the molten aluminum-plated steel wire 3 suppresses the exposure of the base steel wire 2 during stranded wire processing, caulking, etc., and mechanically per unit diameter. From the viewpoint of increasing the strength, it is preferably about 5 to 10 μm.

The minimum thickness of the thin-walled portion of the plating film existing on the surface of the molten aluminum-plated steel wire 3 suppresses the exposure of the base steel wire 2 during stranded wire processing, caulking, etc., and has a unit diameter. From the viewpoint of increasing the mechanical strength per unit, it is preferably 1 μm or more, more preferably 2 μm or more.

The uneven thickness index of the molten aluminum plated steel wire 3 is such that it is difficult for an uneven thickness portion having a large difference in thickness between a thick portion and a thin portion of the plating film to occur, and it is difficult for an aluminum block to adhere to the surface of the molten aluminum. From the viewpoint of efficiently producing the plated steel wire, it is preferably 10 or less, more preferably 8 or less, and further preferably 4 or less.

The uneven thickness index of the hot-dip aluminum-plated steel wire 3 is an index indicating the uniformity of the plating film of the hot-dip aluminum-plated steel wire 3. The uneven thickness index of the hot-dip aluminum-plated steel wire 3 is calculated from the maximum and minimum thickness of the plating film.
[Unbalanced thickness index] = [Maximum thickness] / [Minimum thickness]
It is a value obtained based on.

If necessary, the molten aluminum-plated steel wire 3 obtained above may be drawn with a die or the like in order to have a desired diameter.

The hot-dip aluminum-plated steel wire obtained by the method for producing a hot-dip aluminum-plated steel wire of the present invention can be suitably used for, for example, a wire harness of an automobile.

Next, the present invention will be described in more detail based on Examples, but the present invention is not limited to such Examples.

Examples 1-99 and Comparative Examples 1-11
In each Example and each Comparative Example, a hot-dip aluminum-plated steel wire was manufactured based on an embodiment of the method for manufacturing a hot-dip aluminum-plated steel wire shown in FIG.

As the steel wire, a steel wire having the diameter shown in each table below and having the steel grades shown in each table is used, and the surface of the steel wire is not galvanized (of "pre-Zn" in each table). Those having a zinc-plated coating having an average thickness of 5 μm or less (indicated as “pre-Zn” in the column of “pre-Zn” in each table) were used. 37A described in the column of steel type of each table means a steel wire made of hard steel containing 0.37% by mass of carbon.

The steel wire not galvanized was degreased by immersing it in a degreasing solution of sodium orthosilicate to which a surfactant was added before immersing it in a hot-dip aluminum plating bath.

Further, before the steel wire was immersed in the molten aluminum plating bath, it was passed through the steel wire introduction unit control device 8 shown in FIG. 2, and the steel wire was preheated to about 400 ° C. by the heating device 6. Nitrogen gas was used as the heating gas. The preheating temperature was measured by preparing a steel wire to which a thermocouple was connected and passing the thermocouple together with the steel wire through a heating device 6 maintained at a predetermined temperature.

Further, as the bath surface control device 7 used in the steel wire introduction section control device 8 shown in FIG. 2, as shown in FIG. 3, the opening 9b and the discharge port at the introduction port of the through hole 9a of the tubular body 9 are provided. Using the bath surface control device 7 having the same shape, size, and area of the opening 9c in the above, the ratio of the area of the opening 9b of the through hole of the tubular body 9 to the area of the cross section of the steel wire [tubular body]. The area of the opening 9b of the through hole of 9 / the area in the cross section of the steel wire] is set to 57, and the steel wire is immersed in the molten aluminum plating bath for 0.3 to 1 second via the bath surface control device 7. I let you.

As a hot-dip aluminum plating bath, a hot-dip aluminum plating bath (aluminum purity: 99.7% or more, indicated as "Al" in the column of "type of hot-dip Al plating" in each table), and molten containing 4% by mass of silicon. Aluminum plating bath (indicated as "4% Si" in the "Type of molten Al plating" column of each table), hot-dip aluminum plating bath containing 8% by mass of silicon (of "Type of hot-dip Al plating" in each table) (Indicated as "8% Si" in the column), a hot-dip aluminum plating bath containing 11% by mass of silicon (indicated as "11% Si" in the "Type of hot-dip Al plating" column of each table) or 13% by mass. Using a hot-dip aluminum plating bath containing silicon (indicated as "13% Si" in the "Type of hot-dip Al plating" column of each table), the line speed (steel wire) shown in each table at the bath temperature shown in each table. After immersing the steel wire in the molten aluminum plating bath at the pulling speed of), the steel wire was pulled up from the molten aluminum plating bath.

Immersion member (diameter: 300 mm, material: carbon steel for machine structure S55C) is immersed in the molten aluminum plating bath, and the shortest length L2 from the bath surface of the molten aluminum plating bath to the contact point between the immersion member and the steel wire is 450 mm. The immersion member was brought into contact with the steel wire immersed in the molten aluminum plating bath.

At the boundary between the molten aluminum plated steel wire pulled up from the molten aluminum plating bath and the bath surface of the molten aluminum plating bath, the stabilizing member is brought into contact with the bath surface and the molten aluminum plated steel wire, and the stabilizing member is plated with molten aluminum. The horizontal slide amount L1 of the steel wire when pressing the steel wire and pressing the stabilizing member against the steel wire was set to 30 mm. As a result, the value of the ratio (L1 / L2) of the horizontal slide amount L1 of the steel wire to the shortest length L2 from the bath surface of the molten aluminum plating bath to the contact point between the dipping member and the steel wire is 0.067. Adjusted to. As the stabilizing member, a stainless steel square bar having a heat-resistant cloth material wrapped around the surface was used, and the contact length between the plated steel wire and the stabilizing member was adjusted to 5 mm.

Further, a nozzle having an inner diameter of the tip shown in each table is arranged so that the tip of the nozzle is located at a position 2 mm away from the molten aluminum plated steel wire, and the temperature is adjusted from the tip of the nozzle to the temperature shown in each table. The obtained inert gas (nitrogen gas) was sprayed on the boundary between the molten aluminum plated steel wire and the bath surface of the molten aluminum plating bath at the volumetric flow rate and pressure shown in each table.

By performing the above operations, a hot-dip aluminum-plated steel wire having a plating film having an average thickness shown in each table was obtained.

Next, as the performance of the hot-dip aluminum-plated steel wire, the adhesiveness of the aluminum ingot and the uniformity of the plating film were examined based on the following method. The results are shown in each table.

[Adhesion of aluminum block]
A 300 m long molten aluminum plated steel wire is run at a passing speed of 100 m / min, and the outer diameter of the molten aluminum plated steel wire is measured over the entire length of the molten aluminum plated steel wire, and the outer diameter is locally increased. The presence or absence of the convex part was examined. The adhesiveness of the aluminum ingot was evaluated based on the following evaluation criteria by visually observing whether or not the aluminum ingot adhered to the convex portion having a locally large outer diameter.
(Evaluation criteria)
◯: No adhesion of aluminum lumps is observed.
X: Adhesion of aluminum lumps is observed.

[Uniformity of plating film]
The cross section of the hot-dip aluminum-plated steel wire was observed to determine the maximum and minimum thickness of the plating film. More specifically, a 300 mm test piece was arbitrarily cut out from the molten aluminum-plated steel wire, and six test pieces were cut out from the test piece, and then the test piece was embedded in a resin and embedded. The cross section of the molten aluminum plated steel wire was exposed by cutting the resin and polishing the cut cross section. This cross section was observed with an optical microscope (magnification: 500 times), and the maximum thickness and the minimum thickness of the plating film were measured. The average value of the largest thickness of the plating film of the six test pieces is defined as the maximum thickness of the plating film, and the average value of the smallest thickness of the plating film of the six test pieces is defined as the minimum thickness of the plating film. did.

From the maximum and minimum thickness of the plating film obtained above, the formula:
[Unbalanced thickness index] = [Maximum thickness] / [Minimum thickness]
The uneven thickness index was calculated based on the above, and the uniformity of the plating film was evaluated based on the following evaluation criteria.
(Evaluation criteria)
⊚: Unbalanced thickness index is 4 or less ○: Unbalanced thickness index exceeds 4 and 10 or less ×: Unbalanced thickness index exceeds 10

〔Comprehensive evaluation〕
Based on the evaluation results of the adhesiveness of the aluminum ingot and the uniformity of the plating film, a comprehensive evaluation was performed according to the following evaluation criteria.
(Evaluation criteria)
⊚: The evaluation of the adhesiveness of the aluminum ingot is ◯, and the evaluation of the uniformity of the plating film is ◎ (excellent).
◯: All evaluations of the adhesiveness of the aluminum block and the plating film are ◯ (excellent).
X: In the evaluation of the adhesiveness of the aluminum ingot and the plating film, either is x (failed).

Examples 100-135 and Comparative Examples 12-18
In Example 7, the states of the hot-dip aluminum plating bath, the nozzle, the inert gas and the wire were changed as shown in Tables 6 to 8 to obtain a hot-dip aluminum-plated steel wire having a plating film. Using the obtained hot-dip aluminum-plated steel wire, the adhesiveness of the aluminum ingot and the uniformity of the plating film were examined as the performance of the hot-dip aluminum-plated steel wire in the same manner as in Example 7. The results are also shown in Tables 6-8.

From the above results, according to each embodiment, it is difficult for an uneven thickness portion having a large difference in the thickness of the plating coating between the thick portion and the thin portion of the plating coating to occur, and it is difficult for aluminum lumps to adhere to the surface of the molten aluminum. It can be seen that plated steel wire can be manufactured efficiently.

The hot-dip aluminum-plated steel wire obtained by the production method of the present invention can be suitably used for, for example, a wire harness of an automobile.

1 Hot-dip aluminum plating bath 2 Steel wire 3 Hot-dip aluminum-plated steel wire 4 Sending device 5 Plating bath 6 Heating device 7 Bath surface control device 8 Steel wire introduction part control device 9 Tubular body 9a Through hole 9b Immersion area 9c Introduction port 9d Opening 9e Outlet 9f Opening 10 Immersion member 11 Bath surface of molten aluminum plating bath 12 Stabilization member 12a Heat resistant cloth 13 Nozzle 13a Nozzle tip 14 Inert gas supply device 15 Piping 16 Cooling device 17 Winding device 18 Meniscus 18a Meniscus Tip 19 Plating film

Claims (3)

After immersing the steel wire in the hot-dip aluminum plating bath, the hot-dip aluminum-plated steel wire is manufactured by continuously pulling the steel wire from the hot-dip aluminum plating bath through a dipping member immersed in the hot-dip aluminum plating bath. How to do
At the boundary between the molten aluminum plated steel wire pulled up from the molten aluminum plating bath and the bath surface of the molten aluminum plating bath, the stabilizing member is brought into contact with the bath surface of the molten aluminum plating bath and the molten aluminum plated steel wire. The ratio (L1) of the horizontal slide amount L1 of the steel wire when the stabilizing member is pressed against the steel wire and the shortest length L2 from the bath surface of the molten aluminum plating bath to the contact point between the dipping member and the steel wire. Adjust the value of / L2) to 0.006 to 0.2 and adjust
An inert gas having a temperature of 600 ° C. or higher is provided from the tip of the nozzle to the boundary portion by disposing a nozzle for blowing the inert gas at a position facing the stabilizing member via the molten aluminum plated steel wire. A method for producing a molten aluminum plated steel wire, which comprises spraying the gas at a pressure of 0.1 to 25 kPa. The method for manufacturing a molten aluminum-plated steel wire according to claim 1, wherein the steel wire is a steel wire made of carbon steel or stainless steel. The method for producing a molten aluminum-plated steel wire according to claim 1 or 2, wherein the temperature of the molten aluminum plating bath is adjusted to be 15 ° C. or higher higher than the melting point of the molten aluminum plating bath.

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