JP2003155548A - Hot dipping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for continuously manufacturing plated articles with high productivity and high thermal efficiency even if hot dipping is carried out in of a molten zinc bath and a molten zinc-aluminum alloy bath. SOLUTION: A material to be plated, hanging on a first hanger, is immersed in a molten zinc bath having a temperature T1 ranging from 440 to 480 deg.C for >=100 s to undergo hot dipping and then immersed, while being held at >=300 deg.C without water cooling, in a molten zinc-aluminum alloy bath having a temperature T2 lower by 15 to 30 deg.C than the temperature T1 for 30 to 100 s to undergo hot dipping, and the resultant plated article is cooled. After the cooling, the first hanger is replaced by a new second hanger in a replacement step and put to use in the first plating step. The zinc-aluminum alloy contains 1 to 10 wt.% aluminum. This method is useful as a continuous process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-bath hot dip plating method for hot dip plating using a hot dip zinc bath and a hot dip zinc-aluminum alloy bath.

[0002]

2. Description of the Related Art Hot-dip galvanizing is widely used to impart corrosion resistance to corrosive steel products. However, in hot dip galvanizing, if the immersion time is lengthened to improve the corrosion resistance, the Fe—Zn alloy layer develops, the corrosion resistance does not improve so much, and so-called “burning” occurs, impairing the surface appearance. On the other hand, in order to improve the corrosion resistance, hot dipping with a zinc alloy containing aluminum has been proposed. However, when a steel product is hot-dipped with a zinc-aluminum alloy, an unplated portion is likely to be formed.

Therefore, it has been proposed to carry out hot dip galvanizing and then hot dip zinc-aluminum alloy plating.
For example, Japanese Unexamined Patent Publication No. 52-30233 discloses a hot dip plating method in which a surface of a steel material is hot dip galvanized and then aluminum-zinc alloy is hot dip plated.
This document describes an example of immersing in a zinc plating bath at 460 ° C. for 10 seconds and then immersing in an Al—Zn alloy bath at 500 ° C. for 20 seconds. Japanese Unexamined Patent Publication No. 57-35672 discloses a first step of hot dip galvanizing a steel material,
Then, a hot dip galvanizing method is disclosed including a second step of applying a zinc alloy plating containing 0.1% or more of aluminum. This document describes that the first stage plating is performed for about 2 to 3 minutes, and the second stage plating is performed for about 3 to 7 minutes. Further, an example is described in which a steel material is immersed in a molten zinc bath at 460 ° C. for 2 minutes, the steel material is gently pulled up from the zinc bath, and immersed in an alloy bath (430 ° C.) containing 5% of aluminum for 5 minutes to perform plating. .

In Japanese Patent Publication No. 63-63626, the object to be plated is treated at a high temperature (500-600 ° C., preferably 530-300).
Immediately after immersing in a molten zinc bath at 560 ° C. and taking it out, 450 ° C. or less (preferably 400 to 450)
℃) molten aluminum zinc alloy bath (aluminum content 3 ~
7%) and a hot dip galvanizing method is disclosed. According to this document, an object to be plated taken out from a molten zinc bath is immediately melted, that is, while the temperature of the object to be plated does not significantly decrease and the pure zinc layer outside the Fe—Zn alloy layer on the surface is not oxidized. Immersion in an alloy bath is also described.

Japanese Patent Publication No. 19299/1992 discloses a temperature of 4
30 to 460 ° C., immersion time 0.5 minutes to less than 2 minutes, first step of performing hot dip galvanizing at a pulling rate 1 to 2 m / minute, temperature 430 to 460 ° C., immersion time 0.5 minutes to 1 minute And a second step of performing hot dip zinc-aluminum alloy plating at a pulling rate of 0.5 to 3.5 m / min.
In this document, dipping at 440 ° C. for 1 minute, pulling up at a speed of 1 m / min for hot dip galvanization, and 430 ° C. for 0.5
An example is described in which the molten zinc-aluminum plating is performed by immersing for ~ 1 minute and pulling up at a speed of 1-3 m / min.

In such a two-bath plating method or a two-step plating method, usually, the object to be plated is hung on a hanger and transferred, dipped and pulled up in each plating bath. Repeated use of the same hanger in such a process will contaminate the molten zinc bath or molten zinc alloy bath. In particular,
When the molten zinc bath of the first bath is contaminated by the aluminum component attached to the hanger, an unplated portion is produced. That is, when the object to be plated is hung on a hanger and immersed in the molten zinc bath of the first bath for hot dip galvanizing, and the object to be plated hung on the hanger is further immersed in the molten zinc-aluminum alloy bath of the second bath. The components adhering to the hangers in the first bath mix into the second bath and contaminate the second bath. In particular, after performing hot dip zinc alloy plating in the second bath, hanging a new object to be plated on the hanger used for hot dip zinc alloy plating, and hot dip galvanizing in the first bath, the aluminum component adhered to the hanger The first bath is contaminated, an unplated portion is generated, and the first bath once contaminated becomes unusable.

Therefore, in reality, in order to prevent contamination by aluminum, the first special hanger is used to
After hot dip galvanizing in the bath, cooling by water cooling removes the object to be plated from the first exclusive hanger, transfers the object to the second exclusive hanger and hangs it, and melts it in the molten zinc alloy bath of the second bath After plating and cooling with water, the plated product is removed from the second dedicated hanger. That is, the first dedicated hanger is used only for hot dipping in the first bath,
The exclusive hanger is used only for hot dipping in the second bath.

However, even if the first bath is melt-plated and then cooled, since the first bath has a high melting temperature, it takes a long time to cool and the productivity of the plated product is greatly reduced. Further, in order to plate the object to be plated that has been cooled once in the second bath, it is necessary to raise the temperature of the object to be plated that has been cooled in the second bath, and the thermal efficiency is greatly reduced. Furthermore, when an object to be plated having a non-uniform thickness is hot-dipped, the thin-walled part of the object to be plated is exposed to a high temperature for a long time during hot-dip plating in the second bath, so that the plating layer grows. It is more likely to drop out. Furthermore, when cooling is performed after plating in the first bath, an oxide film is likely to be formed in the plating layer, and thus slag (oxidation residue) is likely to be formed in the second bath.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a two-bath hot-dip galvanizer capable of producing a plated product with high productivity even when hot-dip galvanizing using a hot-dip zinc bath and a hot-dip zinc-aluminum alloy bath. A method and hot dip system are provided.

Another object of the present invention is to cool an object to be plated, which is plated with a molten zinc bath, by water cooling or the like,
It is an object of the present invention to provide a two-bath hot-dip plating method and hot-dip plating system capable of performing hot-dip plating efficiently and greatly improving thermal efficiency.

Still another object of the present invention is to provide a two-bath hot dip plating method and hot dip plating system capable of effectively suppressing contamination of the hot dip plating bath and dropping of the plating layer.

[0012]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the inventors of the present invention melt-plated an object to be plated in a first bath in a state of hanging it on a hanger, and performed the first plating without cooling. After performing hot dip plating in 2 baths and cooling, if the hanger used for hot dip plating is replaced with a new hanger and is circulated for hot dip plating in the 1st bath, not only one hanger replacement work but also productivity The present invention has been completed based on the finding that the thermal efficiency can be significantly improved and that a continuous process can be realized by utilizing a circulation path or a circulation process.

That is, the hot dip plating method of the present invention is a method of suspending an object to be plated on a hanger, hot dip galvanizing, and hot dipping with a zinc-aluminum alloy.
A first plating step of hot dip galvanizing an object to be plated hung on a first hanger, and a second plating step of hot dip galvanizing with a zinc-aluminum alloy after the first plating step, After the second plating step, a step of cooling the plated product, and a replacement step of replacing the first hanger with a new second hanger and providing the first plating step after the cooling step. It is composed of. In this method, the object to be hot-dipped in the first plating step may be hot-dipped with a zinc-aluminum alloy while maintaining the temperature at 300 ° C or higher. In addition, after being subjected to the second plating step, the deposits may be removed from the first hanger and the first hanger may be reused as the second hanger. In the hot-dip plating method, in the first plating step, the object to be plated is immersed in a molten zinc bath at a temperature of T ₁ 440 to 480 ° C. for 100 seconds or more to perform hot-dip plating, and in the second plating step, the object to be plated is The temperature of the first plating step T ₁
It may be immersed for 30 to 100 seconds in a molten zinc-aluminum alloy bath having a temperature T ₂ lower than that by 15 to 30 ° C. for hot dipping. The zinc-aluminum alloy usually contains 1 to 10% by weight of aluminum. Also, zinc-
The aluminum alloy may further contain magnesium. Furthermore, after hot-dip plating in the second plating step, the plated product may be immersed in an aqueous solution containing a surfactant and cooled to prevent foaming of the plated layer.

The present invention is a continuous process, that is, hot dip galvanizing an object to be plated along a circulation path, and hot dipping with a zinc-aluminum alloy without water cooling,
A continuous hot dip plating method may be used in which the plated product is cooled, the first hanger is replaced with a new second hanger, and the work of performing the hot dip galvanizing is continuously performed.

The present invention is the hot-dip plating system, that is, a hot-dip plating system provided with a circulation path for sequentially performing hot-dip galvanizing and hot-dip zinc-aluminum alloy plating on an object to be plated while suspended on a hanger. First
While being hung on the hanger, the object to be plated is sequentially transferred along the circulation path to a molten zinc bath controlled to a predetermined temperature and a molten zinc-aluminum alloy bath controlled to a predetermined temperature for circulation. And a means for moving the molten zinc bath and the molten zinc-aluminum alloy bath to lower the object to be plated respectively, after a predetermined time has passed from the molten zinc bath and the molten zinc-aluminum alloy bath respectively Of elevating means for pulling up, timer means for counting the immersion time of the object to be plated in the molten zinc bath and the molten zinc-aluminum alloy bath, the molten zinc bath and the molten zinc-aluminum alloy bath An uncooled zone (or a cooling restraint zone), which is provided between the molten zinc-aluminum alloy bath and the uncooled zone for restraining the cooling of the molten plated matter Is provided in the circulation path on the side of the molten zinc, and a cooling means for cooling the hot-dip plated product is provided, and a hanger that has been subjected to the hot dip plating treatment is newly added to the circulation path on the downstream side of the molten zinc-aluminum alloy bath. Also disclosed is a hot dip system in which an exchange zone is provided for exchanging the secondary hanger.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION [Object to be Plated] The object to be plated applicable to the present invention is not particularly limited as long as hot dip galvanizing is possible, and even if it is a non-corrosive metal substrate, it is a corrosive metal group. It may be wood. Examples of the metal substrate include iron-based substrates containing iron (stainless steel, steel, etc.). Among these iron-based base materials, it is particularly preferable to apply to corrosive steel materials. The components and composition ratio of the steel material are not particularly limited.

The form of the object to be plated is linear (steel wire, etc.),
Two-dimensional shape (steel, plate such as plate, net, etc.),
Various shapes such as a three-dimensional shape (a three-dimensional shape such as a cylindrical shape or a rod shape) can be used. For example, small base materials (for example, bolts, nuts, power transmission fittings) and relatively large base materials (for example, balustrades, main pillars, bridge guard fences, road signs, road guard fences, river fences, Rock fall prevention net etc.) can be used. In the present invention, even an object to be plated having a non-uniform thickness or heat capacity, for example, an object to be plated having a thick portion and a thin portion, can be smoothly melt-plated while preventing the plating layer from falling off.

It should be noted that the object to be plated may be formed with a locking or hooking portion for the hanger, and an attachment member having the locking or hooking portion for the hanger may be detachably attached to the object to be plated. Good. Further, the object to be plated may be generally subjected to a conventional pretreatment prior to the hot dipping, for example, after performing a surface treatment such as a degreasing treatment and an acid cleaning treatment, a surface such as a flux treatment or a shot blast treatment. Processing or the like may be performed. Furthermore, if necessary, the object to be plated may be pre-plated with nickel.

In the method and system of the present invention, the object to be plated is subjected to hot dip plating with the hot dip zinc and the hot dip zinc-aluminum alloy in the state of being hung on the hanger, and normally, hot dipping is performed by the circulating hanger. It uses the circulation circuit of.

[Hot-dip galvanizing, first plating step] In the present invention, the object to be plated is hung on a hanger and hot-dip galvanized in the first plating step. The hot dip galvanizing can be performed using zinc (high-purity zinc or the like) or a zinc alloy. The zinc alloy is, for example, an alloy of zinc and at least one metal selected from tin, magnesium, nickel, copper, titanium, zirconium, sodium (eg, zinc-tin alloy, zinc-magnesium alloy, zinc-nickel). Alloy, etc.). The proportion of metals other than zinc in the zinc alloy is not particularly limited and is, for example, 0.01 to 50% by weight, preferably 0.05 to 30.
%, And more preferably about 0.1 to 10% by weight. In addition, zinc or zinc alloy contains less than 1% by weight of aluminum (for example, 0.
5 wt% or less). Further, zinc or a zinc alloy may contain unavoidable impurities such as iron and cadmium.

The temperature T ₁ of the hot dip galvanizing bath is 430 to 430.
It can be selected from the range of about 500 ° C., but normally 440 to
480 ° C, preferably 450-470 ° C, especially 450-
It is about 460 ° C. The immersion time can be selected from the range of about 60 seconds or more (for example, 60 to 180 seconds),
For example, it is about 100 seconds or more (for example, 100 to 150 seconds, particularly 100 to 130 seconds).

In the first plating step, while being hung on the first hanger, transfer means for transferring the object to be plated to the molten zinc bath controlled to a predetermined temperature along the circulation path, An elevating means for lowering the object to be plated transferred to a predetermined position of the molten zinc bath and lifting it from the molten zinc bath after a predetermined time, and for counting the immersion time of the object to be plated in the molten zinc bath. It can be performed using a timer means. That is, in response to the start signal, the transfer means movably provided along the circulation path (rail or the like) transfers the hanger on which the object to be plated is suspended to a predetermined position of the molten zinc bath. The transfer means is a conventional unit,
For example, a gear train formed on the transport path and a motor having a rotary gear that can mesh with the gear train can be used, or a servomotor or the like may be used. Reaching a predetermined position can be performed using a position sensor such as a contact sensor or a switch, and in response to an arrival signal from the position sensor,
The elevating means lowers the object to be plated together with the hanger to a predetermined immersion height required for immersion, and immerses the object to be plated in the molten zinc bath. In response to reaching the predetermined immersion height, the timer means starts timing, and after a predetermined time elapses, the immersion completion signal is given to the elevating means, and the elevating means together with the hanger raises the object to be plated from the molten zinc bath to a predetermined height. Raise up.

The speed of pulling the object to be plated from the molten zinc bath is, for example, 0.5 to 3 m / min, preferably 1
It is about 2 m / min.

The object to be plated withdrawn from the molten zinc bath removes excess molten zinc, for example, in the air or in an inert gas atmosphere, at a temperature above the melting point of zinc or a zinc alloy, and subjected to centrifugal force or vibration. It is also possible to remove it by acting such as.

The feature of the present invention is that after the first plating step,
The point is that hot-dip plating is performed using a zinc-aluminum alloy in the second plating step without water cooling and hanger replacement. That is, water cooling after the first plating step not only lowers the temperature of the object to be plated but also requires hanger replacement work, which significantly lowers the hot-dip plating efficiency and productivity. Further, when the cooled object to be plated is subjected to hot dip plating in the second bath, the temperature of the second bath is lowered or fluctuated, and it is necessary to raise the temperature of the object to be cold plated for hot dip plating. Greatly reduces the thermal efficiency at. Furthermore, since the thin portion that easily reaches the predetermined temperature by being heated in the second bath is exposed to a high temperature for a long time, the plating layer may drop off, or an oxide film may be generated due to cooling, resulting in zinc-aluminum in the second bath. Form oxide slag in the alloy bath.

On the other hand, in the present invention, since water cooling and hanger exchange are not performed after the first hot dip plating step, the hot dip plating efficiency and productivity can be greatly improved and the thermal efficiency in the second hot plating step can be increased. Can be improved. Furthermore, the second
Since the thin-walled part is not exposed to high temperature in the bath, the thickness of the hot dip galvanized layer in the first bath is maintained as it is in the second bath.
Hot-dip galvanizing with a molten zinc-aluminum alloy can be performed in the bath, and the contamination of the second bath due to the dropping of the plating layer and the formation of an oxide film in the first bath can be greatly suppressed.

According to the present invention, after the first plating step, the object to be plated is not manually cooled to a temperature at which it can be removed from the hanger by water cooling, but is subsequently subjected to hot dip zinc-aluminum alloy plating in the second bath. Good, usually,
The temperature of the object to be plated is 300 ° C or higher (preferably 320 to
While maintaining the temperature at 430 ° C., more preferably about 350 to 400 ° C., hot dip plating is performed in the second molten zinc-aluminum alloy bath. The temperature of the object to be plated may be equal to or higher than the melting point of the zinc or zinc alloy of the first bath or the non-solidifying temperature. The object to be plated that has been subjected to hot dip plating in the first plating step is allowed to cool, and subsequently, in the second bath, molten zinc-
It may be plated with an aluminum alloy.

In order to suppress the cooling of the object to be plated, in the system of the present invention, a non-controlling means for suppressing the cooling of the hot-dip plated object is provided in the circulation path between the molten zinc bath and the molten zinc-aluminum alloy bath. A cooling zone (cooling or heat retaining zone or heating zone) is provided. This non-cooling zone may be a gradual cooling (natural cooling or natural cooling) zone as long as the object to be plated can be kept at a relatively high temperature (particularly a temperature above the melting point of zinc or zinc alloy in the first bath). Good.

The thickness of the primary plating layer formed by the molten zinc bath is
There is no particular limitation as long as it can provide corrosion resistance, and it is usually 20
˜200 μm, preferably 30 to 150 μm, more preferably about 50 to 150 μm.

[Hot-dip zinc-aluminum alloy plating, second plating step] The object plated in the first plating step is subjected to the second plating in a state of being hung on the hanger without being cooled or replaced with a hanger. In the process, hot dip plating is performed with a zinc-aluminum alloy.

The proportion of aluminum in the zinc-aluminum alloy is about 1 to 10% by weight (for example, 2 to 10% by weight), preferably about 3 to 10% by weight (particularly 3 to 7% by weight). By including aluminum in the zinc alloy, it is possible to perform plating with high corrosion resistance.

The zinc-aluminum alloy may further contain magnesium in order to improve the corrosion resistance.
The proportion of magnesium in the alloy is 0.05 to 8% by weight, preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight. The zinc-aluminum alloy may contain metal components such as tin, nickel, copper, titanium, zirconium, and sodium. Further, the zinc-aluminum alloy, unless otherwise specified,
It may contain unavoidable impurities such as iron and cadmium.

The temperature of the molten zinc-aluminum alloy bath is
As long as the plating efficiency is not impaired, it can be selected from the range of about 420 to 500 ° C, and usually 420 to 480 ° C (for example, 4
20 to 460 ° C.), preferably about 430 to 450 ° C. (for example, 430 to 440 ° C.). In the second plating step, it is advantageous to carry out the object to be plated at a temperature T ₂ lower than the temperature T ₁ of the first plating step. The difference (Δ (T ₁ −T ₂ )) between the temperature T ₁ of the molten zinc bath and the temperature T ₂ of the molten zinc-aluminum alloy bath is, for example, about 15 to 30 ° C., preferably about 15 to 25 ° C. The immersion time is, for example, 3
It can be selected from the range of about 0 to 150 seconds (for example, 60 to 145 seconds), and is usually 30 to 100 seconds (for example, 45 to 1 seconds).
00 seconds), preferably about 60 to 100 seconds. If the secondary plating is performed under such conditions, even if the thickness or thickness of the object to be plated is not uniform, the thin portion is exposed to the high temperature of the second bath in combination with the secondary plating without cooling. Since it is not exposed to light or for a long time, the plating layer can be effectively prevented from falling off.

In the second plating step, while suspended from the first hanger, the transfer means, the elevating means, and a timer means for immersing an object to be plated in the molten zinc-aluminum alloy bath for a predetermined time. Can be done using. That is, the object to be plated, which is pulled up from the molten zinc bath of the first bath to a predetermined height, is hung on the first hanger by the transfer means provided so as to be movable along the circulation path (rail or the like). Then, it is transferred to a predetermined position in the molten zinc-aluminum alloy bath. In response to the arrival signal from the position sensor to the predetermined position, the elevating means lowers the object to be plated together with the hanger to the predetermined immersion height required for immersion, and immerses the object to be plated in the molten zinc-aluminum alloy bath. . In response to reaching the predetermined immersion height, the timer means starts timing, and after a lapse of a predetermined time, a completion signal is given to the elevating means, and the elevating means works with the hanger to melt the zinc-plated object.
Pull up from the aluminum alloy bath to a specified height.

The withdrawal speed of the plated product from the molten zinc-aluminum alloy bath can be appropriately selected, but if the withdrawing speed is too high, the plated layer is likely to fall off. Second
The rate of withdrawal from the bath can be selected from the range of, for example, about 0.1 to 2 m / min, and is usually about 0.1 to 1 m / min, preferably about 0.2 to 0.8 m / min.

After the immersion, the excess molten zinc-aluminum alloy adhered to the object to be plated is subjected to centrifugal force at a temperature above the melting point of the zinc-aluminum alloy in air or in an inert gas atmosphere, as described above. Alternatively, it may be removed by applying vibration.

The thickness of the secondary plating layer formed by the molten zinc-aluminum alloy bath is not particularly limited as long as it can impart corrosion resistance, and is 20 to 300 μm, preferably 30 to 250 μm.
m, and more preferably about 50 to 200 μm.

[Cooling Step] After the second plating step, the plated product is cooled by a cooling means provided in a circulation path on the downstream side of the molten zinc-aluminum alloy bath and for cooling the molten plated product. It This cooling step can be performed by a conventional method and may be cooled by slow cooling, but usually the plated product is cooled by water cooling in many cases. In cooling the plated product, water as a refrigerant contains various components, for example, a rust inhibitor, a corrosion inhibitor, an antifoaming agent, an antiseptic, alcohols ((poly) ethylene glycol, (poly) propylene glycol, (poly)). ) Water-soluble polyhydric alcohols such as glycerin), organic acids (such as oxalic acid), salts and buffers (such as borate), and bases (such as amines) may be included, but surfactants When the plating layer is immersed in an aqueous solution and cooled, the foaming or swelling of the plating layer can be effectively prevented.

As the surfactant, for example, nonionic
Surfactant, anionic surfactant, cationic surfactant
Examples include a sex agent and an amphoteric surfactant. Nonionic surface activity
Polyoxyethylene alkyl ether [eg
For example, polyoxyethylene lauryl ether, polyoxy
Polyoxyethylene C such as ethylene cetyl ether
_6-24Alkyl ether (especially polyoxyethylene C
_8-18Alkyl ether), etc.], polyoxyethylene
Rutile phenyl ether [eg polyoxyethylene
Octyl phenyl ether, polyoxyethylene nonyl
Polyoxyethylene C such as phenyl ether_6-18Al
Kill phenyl ether (especially polyoxyethylene C
_6-12Alkyl phenyl ether), etc.], polyoxye
Tylene-polyoxypropylene block copolymer,
Lioxyethylene polyhydric alcohol fatty acid ester [eg
For example, polyoxyethylene glycerin stearate ester
Polyoxyethylene glycerin oleate
Polyoxyethylene glycerin C such as_8-24Fatty acid
Tellur, polyoxyethylene sorbitan stearic acid
Polyoxyethylene sorbitan C such as tell_8-24fatty acid
Ester, polyoxyethylene sucrose C_8-24Fatty acid
Etc.], polyoxyethylene castor oil and polyoxy
Ethylene hydrogenated castor oil, polyhydric alcohol fatty acid ester
[[(Poly) ethylene glycol, (poly) propylene]
Glycol, (poly) glycerin, pentaerythritol
Polyalcohol such as syrup, sorbitan, sorbitol, sucrose
Esters of coal and fatty acids, eg glycerin mono
Glycerin C such as stearic acid ester_8-24Fatty acid
Sucrose, such as steal and sucrose monostearate
C_8-24Fatty acid ester, sorbitan monooleate
Sorbitan C such as tell_8-24Fatty acid esters, etc.]
Lioxyethylene alkyl amines (eg polyoxy
Polyoxyethylene C such as ethylene lauryl amine
_6-24Alkylamine, etc.), polyoxyethylene fatty acid
Amides (eg polyoxyethylene stearate
Polyoxyethylene C such as de_8-24Fatty acid amide
), Fatty acid alkanolamides (eg, N, N-di)
N, N-alkanos such as ethanol stearamide
C_8-24Fatty acid amide) and the like. Nonion
The average addition model of ethylene oxide
The number of moles is 1 to 35 mol, preferably 2 to 30 mol, and
It is preferably about 5 to 20 mol.

Anionic surfactants include carboxylic acid salts [fatty acid soaps (for example, C _8-24 fatty acid metal salts such as sodium laurate)], sulfonic acid salts [alkylbenzene sulfonates (for example, laurylbenzene). C _6-24 alkylbenzene sulfonate such as sodium sulfonate), alkylnaphthalene sulfonate (for example, di C _1-8 alkylnaphthalene sulfonate such as sodium diisopropylnaphthalene sulfonate), sodium α-olefin sulfonate (For example,
C such as sodium 9-octadecenyl sulfonate
_12-18 alkenyl sulfonate, etc.), alkane sulfonate (eg, C _6-24 alkyl sulfonate such as sodium lauryl sulfonate, etc.), sulfate ester salt [sulfated oil, alkyl sulfate ester salt (eg, , C _6-24 alkyl sulfate ester salt such as sodium salt of ester of reducing alcohol of coconut oil and sulfuric acid), etc.] and the like. In the anionic surfactant, examples of salts include salts with ammonia, amines (eg, amines, alkanolamines such as ethanolamine), alkali metals (eg, sodium, potassium, etc.) and the like.

Examples of the cationic surfactant include tetraalkylammonium salts (for example, mono or di C _8-24 alkyl-tri or dimethylammonium salts such as lauryltrimethylammonium chloride and dioctadecyldimethylammonium chloride), trialkylbenzyl. Ammonium salts [eg, C _8-24 alkylbenzyldimethylammonium salts such as cetylbenzyldimethylammonium chloride (benzalkonium chloride, etc.)], benzethonium chloride, alkylpyridinium salts (eg, C such as cetylpyridinium bromide, etc.)
_8-24 alkylpyridinium salt, etc.) and the like.
Examples of the salt include salts with halogen atoms (for example, chlorine atom, bromine atom), perchloric acid and the like.

Examples of the amphoteric surfactant include alkyl betaines (eg, betaine having a C _8-24 alkyl group such as dimethyllaurylcarboxybetaine) and alkylimidazolium betaines (eg, C _8-24 such as _{laurylimidazolium} betaine). Alkyl imidazolium betaine etc.), alkyl amine oxide (such as lauryl dimethyl amine oxide, etc., amine oxide having a tri C _8-24 alkyl group, etc.) and the like.

These surfactants can be used alone or in combination of two or more. Among these, nonionic surfactants and / or cationic surfactants are preferable.
A more preferable surfactant is composed of at least a nonionic surfactant (particularly, a nonionic surfactant having an oxyethylene chain). When a nonionic surfactant and a cationic surfactant are used in combination, the ratio (weight ratio) of both can be selected from the range of nonionic surfactant / cationic surfactant = 99/1 to 1/99. , Usually 50/50 to 2/98 (particularly 30/70 to 3/9)
It is about 7).

The HLB value of the surfactant is 1 to 30,
It is preferably 2 to 20 (for example, 5 to 20), more preferably about 5 to 15. The HLB value may be adjusted using a plurality of surfactants.

The ratio of the surfactant in the aqueous solution is within the range in which the swelling of the plating layer can be suppressed, for example, 0.1.
It is about 10 to 10% by weight, preferably 0.3 to 5% by weight, and more preferably about 0.5 to 3% by weight.

The aqueous solution containing the surfactant (cooling aqueous solution) is, for example, a rust inhibitor, a corrosion inhibitor, an antifoaming agent, an antiseptic agent, alcohols (monoalcohol such as ethanol or isopropyl alcohol, (poly) ethylene). Contains glycol, (poly) propylene glycol, water-soluble polyhydric alcohols such as (poly) glycerin), organic acids (oxalic acid, etc.), salts and buffers (borate, etc.), bases (amine, etc.) You can leave.

The temperature of the refrigerant (water or aqueous solution) is, for example,
The temperature is 0 to 90 ° C, preferably 10 to 80 ° C, more preferably about 15 to 50 ° C. From the viewpoint of suppressing the occurrence of swelling, the lower the temperature of the aqueous solution is, the more preferable, but the room temperature (15
The occurrence of swelling can be effectively suppressed even at a temperature of about 20 ° C. or higher). Therefore, in the present invention,
Cooling water above room temperature can be used. When the object to be plated is immersed in the refrigerant (the aqueous solution) at the ambient temperature (room temperature), the temperature of the refrigerant rises. Particularly, when the plated product is repeatedly immersed, the temperature of the coolant becomes considerably high. Even in such a case, the temperature of the refrigerant (the aqueous solution) is in a range in which the surfactant is not deactivated, for example, 20 to 80 ° C.
(For example, 30 to 80 ° C.), and usually,
Even at about 40 to 70 ° C., it is possible to effectively prevent the swelling of the plating layer. The immersion time is also not particularly limited, and can be selected from the range of, for example, 1 second or longer, preferably 2 seconds to 10 minutes, more preferably 5 seconds to 5 minutes (particularly 5 seconds to 1 minute).

When the plated product is cooled by immersing it in an aqueous solution containing a surfactant, the zinc-aluminum alloy plated layer is in a high temperature state [for example, 200 ° C. or higher, further 250 ° C. or higher (for example, about 300 to 450 ° C.)]. And even 300 ° C
Above (for example, about 350 to 420 ° C.), particularly in an uncured state (for example, 380 to 420 ° C.)], it is possible to remarkably suppress the occurrence of swelling of the plating layer.

Although the reason why swelling is generated in a zinc alloy containing aluminum is not clear, the eutectic temperature of the zinc-aluminum alloy is about 380 ° C., which is considerably lower than the plating temperature, and therefore the swelling occurs due to boiling of water. It is estimated that the crystal part is lifted and swelling occurs. The plated product hot-dipped using the method described above does not require a slow cooling step of cooling by leaving it in the air, while maintaining a high temperature state,
Can be immediately water cooled. Therefore, the manufacturing process can be simplified, a long cooling time is not required, and the production efficiency and productivity can be greatly improved. Furthermore, since the swelling of the plating layer can be suppressed, the corrosion resistance and the appearance quality can be improved,
Product value can be increased.

In the cooling step, the plated product pulled up from the molten zinc-aluminum alloy bath by the elevating means is hung on the first hanger and transferred to a predetermined position in the cooling tank by the transfer means. In response to the arrival signal from the position sensor to the predetermined position, the elevating means lowers the plated object together with the hanger to a predetermined height and immerses the plated object in the aqueous solution in the cooling tank. In response to reaching the predetermined immersion height, the timer means starts timing, and after a lapse of a predetermined time, gives a completion signal to the elevating means, and the elevating means raises the plated product from the cooling tank to the predetermined height together with the hanger.

The total thickness of the hot-dip plated layer is in a range where corrosion resistance can be imparted, for example, 30 to 500 μm, preferably 4
It may be 0 to 300 μm, and more preferably about 50 to 250 μm.

[Exchange Step] In the present invention, after the cooling step,
In the exchanging step, the first hanger (with a plated object if necessary) is replaced with a new second hanger (with a new object to be plated if necessary) and provided for the first plating step. . Therefore, in the hot dip coating system of the present invention, an exchange area for exchanging the hanger used for the hot dip plating treatment with a new second hanger is provided in the circulation path on the downstream side of the hot dip zinc-aluminum alloy bath. Has been.

In the exchanging step, the plated product is circulated along with the hanger from the molten zinc-aluminum alloy bath as the second bath to the molten zinc bath as the first bath (that is, the exchange area). It may be removed and replaced with a second hanger together with a new object to be plated. First, the first hanger used for hot dip plating is replaced with a new second hanger, and then a molten zinc bath as the first bath. A new object to be plated may be hung on the second hanger during the period up to (exchange area).

The exchange process may be performed automatically using a robot system or may be performed manually. After the exchange process, the transfer means is
A new hanger is transferred to the molten zinc bath as the first bath.

After being subjected to the second plating step, deposits (zinc or zinc alloy) were removed or separated from the first hanger removed from the circulation path in the exchange step, and then subjected to hot dipping. The first hanger can be reused as a new hanger (second hanger). Zinc or zinc alloy that adheres to the hanger may be mechanically separated or removed. It is heated to a temperature above the melting point of the adhered substance (zinc or zinc alloy) and then mechanically operated with a scrubber or centrifugal separation or vibration. It may be separated or removed by a method utilizing. Furthermore, since the deposit separated or removed from the hanger contains active ingredients such as zinc and aluminum, zinc and aluminum are separated and purified from the deposit, and the zinc component of the molten zinc bath and the aluminum of the molten zinc-aluminum alloy bath are removed. It may be reused as an ingredient. Further, since the deposit includes aluminum, the deposit separated or removed from the hanger is
It may be reused as a zinc-aluminum alloy component in the plating step.

In the present invention, the hanger may have not only a single hook portion but also a plurality of hook portions.
Further, not only a single object to be plated but also a plurality of objects to be plated may be removably hung on the hanger or the hook portion of the hanger.

Although the method and system of the present invention may be performed non-automatically in a discontinuous process or in manual operation, in a continuous process or automatic operation, a circuit (circulation rail or closed loop) and a single operation in an exchange zone are used. By using the hanger replacement described above, the object to be plated can be continuously subjected to two-bath hot dip plating, and the plating efficiency can be improved. Therefore, the present invention is useful as a continuous hot dip plating method or a continuous hot dip plating system.

[0058]

According to the present invention, the object to be plated is hot dip galvanized and hot-dipped with a zinc-aluminum alloy without water cooling. Therefore, the time required for cooling and the heating time and heat of the object to be plated in the second bath can be improved. Energy can be significantly reduced.
Moreover, since the hanger is replaced after hot-dip galvanizing with a zinc-aluminum alloy and cooled, it is possible to replace the hanger with one operation.
It can be done only once. Therefore, a continuous process can be constructed, and even if hot dip plating is performed using two baths, the hot dip plating can be performed efficiently, and the plated product can be manufactured with high productivity and thermal efficiency. Further, it is possible to effectively suppress the contamination of the hot-dip plating bath and the dropping of the plating layer.

[0059]

The present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these examples.

Comparative Example 1 A hot-rolled steel sheet (SPHC, thickness 3 mm, length 75 mm × width 150 mm) was degreased and acid-washed with hydrochloric acid, and then zinc chloride 50 g / L, ammonium chloride 150 g /
It was dipped in an aqueous solution flux containing L, taken out, and then dried.

The pretreated steel sheet was immersed in a molten zinc bath at 450 ° C. for 120 seconds, then pulled out of the molten zinc bath and water-cooled, and molten zinc-aluminum at 430 ° C. containing 5% by weight of aluminum and 1% by weight of magnesium. 6 for alloy bath
Immersion was carried out for 0 seconds, and after withdrawing from the bath, immediately (within 10 seconds), water cooling was performed to form a zinc-aluminum alloy plating film. The weight of the zinc-aluminum alloy in the molten zinc-aluminum alloy bath is 30 kg. The time for producing one plated product in one cycle was 220 seconds, the temperature of the zinc-aluminum alloy bath fluctuated by 4.6 ° C., and the energy of 14 kcal was required to hold at 430 ° C.

Example 1 A steel sheet pretreated in the same manner as in Comparative Example 1 was immersed in a molten zinc bath at 450 ° C. for 120 seconds, then withdrawn from the molten zinc bath and allowed to cool in air for 60 seconds without water cooling. Meanwhile, the molten zinc-aluminum alloy bath of Comparative Example 1 was immersed for 60 seconds, pulled out of the bath, and then cooled with water to form a zinc-aluminum alloy plating film. The time for producing one plated product in one cycle is 250 seconds, the temperature of the zinc-aluminum alloy bath varies by 0.4 ° C, and 430
Energy of 1.2 kcal was required to hold at ℃.

Example 2 Immediately after withdrawing from the molten zinc-aluminum alloy bath, immersion cooling was performed with an aqueous solution containing 1% by weight of a nonionic surfactant (polyoxyethylene nonylphenyl ether) and having a temperature of 60 ° C. A zinc-aluminum alloy plating film was formed in the same manner as in Example 1. The time for producing one plated product in one cycle, the temperature fluctuation of the zinc-aluminum alloy bath, and the amount of energy required for maintaining the temperature of the second bath are the same as in Example 1.

Example 3 A hot-rolled steel sheet (SPHC, thickness 3 mm, length 75 mm × width 150 mm) was degreased and acid-washed with hydrochloric acid, and then zinc chloride 50 g / L and ammonium chloride 150 g /
It was dipped in an aqueous solution flux containing L, taken out, and then dried.

The pretreated steel sheet was immersed in a molten zinc bath at 450 ° C. for 120 seconds and then cooled to 430 ° C. while keeping the temperature of the object to be plated at 350 ° C. or higher without water cooling.
Immersed in the molten zinc-aluminum alloy bath for 60 seconds and then withdrawn from the molten zinc-aluminum alloy bath, immediately containing 1 wt% of a nonionic surfactant (polyoxyethylene nonylphenyl ether), and at a temperature of 60 ° C. It was immersed and cooled in an aqueous solution to form a zinc-aluminum alloy plating film.

When the above operation was carried out in a continuous process, the time for producing one plated product was 200 seconds, and the fluctuation range of the temperature of the zinc-aluminum alloy bath was 0.
It was 1 ° C and required 0.4 kcal of energy to keep the second bath at a temperature of 430 ° C.

Example 4 The pretreated steel sheet was immersed in a molten zinc bath at 460 ° C. for 100 seconds, and then the temperature of the object to be plated was kept at 370 ° C. or higher without being cooled with water, while the molten zinc at a temperature of 440 ° C. −
Immersion in an aluminum alloy bath for 60 seconds and then withdrawing from the molten zinc-aluminum alloy bath, immediately followed by immersion cooling with an aqueous solution containing 1% by weight of a nonionic surfactant (polyoxyethylene nonylphenyl ether) and a temperature of 20 ° C. Then, a molten zinc-aluminum alloy plating film was formed.

When the above operation was carried out in a continuous process, the time for producing one plated product was 180 seconds, and the fluctuation range of the temperature of the zinc-aluminum alloy bath was 0.
It was 2 ° C and required 0.6 kcal energy to keep the second bath at a temperature of 440 ° C.

Table 1 shows the results of visual observation of the states of the plating films obtained in Examples and Comparative Examples.

[0070]

[Table 1]

As is clear from Table 1, the plated layers of the plated products obtained in the examples had no drop and had a uniform thickness.

Continued front page    F-term (reference) 4K027 AA05 AA06 AA07 AA08 AA12                       AA22 AB05 AB26 AB42 AB43                       AB44 AC32 AC47 AC55 AC72                       AD05 AD13 AD26 AE02 AE03                       AE12

Claims (9)

[Claims] 1. A method of suspending an object to be plated on a hanger, hot dip galvanizing, and then hot-dip galvanizing with a zinc-aluminum alloy, wherein the object to be plated hung on a first hanger is hot dip galvanized. A first plating step, a second plating step after the first plating step of hot dip plating with a zinc-aluminum alloy without water cooling, and a step of cooling the plated object after the second plating step. After the cooling step, the first plating hanger is replaced with a new second hanger, and the hot-dip plating method is used for the first plating step. 2. The hot dip plating method according to claim 1, wherein the object to be hot dip plated in the first plating step is hot dip plated with a zinc-aluminum alloy while maintaining the temperature at 300 ° C. or higher. 3. The hot dip plating method according to claim 1, wherein after being subjected to the second plating step, deposits are removed from the first hanger and reused as the second hanger. 4. In the first plating step, the object to be plated is immersed in a molten zinc bath having a temperature of T ₁ 440 to 480 ° C. for 100 seconds or more to perform hot dip plating, and in the second plating step, the object to be plated is 30 to _{1 in} a molten zinc-aluminum alloy bath at a temperature T ₂ which is 15 to 30 ° C. lower than the temperature T ₁ of the first plating step.
The hot dip plating method according to claim 1, wherein the hot dip plating is performed by immersing the steel for 00 seconds. 5. The hot dip plating method according to claim 1, wherein the zinc-aluminum alloy contains 1 to 10% by weight of aluminum. 6. The hot dip plating method according to claim 1, wherein the zinc-aluminum alloy further contains magnesium. 7. After hot-dip plating in the second plating step,
The hot dip plating method according to claim 1, wherein the plated product is immersed in an aqueous solution containing a surfactant and cooled. 8. An object to be plated is hot dip galvanized along a circulation path, hot-dipped with a zinc-aluminum alloy without water cooling, and then the object is cooled, and a first hanger is newly added. The hot dip plating method according to claim 1, wherein the work of replacing with a hanger and continuously performing the hot dip galvanizing is performed. 9. A hot-dip galvanizing system provided with a circulation path for sequentially performing hot-dip galvanizing and hot-dip zinc-aluminum alloy plating on an object to be plated in a state of being hung on a hanger, which is hung on a first hanger. In such a state, the object to be plated is transferred along the circulation path to a molten zinc bath controlled to a predetermined temperature and a molten zinc-aluminum alloy bath controlled to a predetermined temperature one after another for circulation. And means for lowering the objects to be plated transferred to the molten zinc bath and the molten zinc-aluminum alloy bath respectively, and raising and lowering for raising from the molten zinc bath and the molten zinc-aluminum alloy bath after a predetermined time elapses. Means, a timer means for counting the immersion time of the object to be plated in the molten zinc bath and the molten zinc-aluminum alloy bath, and the molten zinc bath A non-cooling zone provided between the hot dip zinc-aluminum alloy bath and for suppressing cooling of the hot-dip galvanized product, and a circulation passage on the downstream side of the hot-dip zinc-aluminum alloy bath, and the hot-dip galvanized product Cooling means for cooling the molten zinc-
A hot dip plating system in which a circulation passage on the downstream side of an aluminum alloy bath is provided with an exchange area for exchanging a hanger used for hot dip treatment with a new second hanger.