JP3603534B2 - Black spot flaw prevention device for hot-dip galvanized steel sheet - Google Patents

Description

【００１６】
また、本発明者の実験によれば、１５μｍ未満の微細な塵・埃・酸化鉄・海塩粒子等であれば、鋼板の表面に付着して、トップロール等で鋼板の表面に押し込まれても、製品の品質に影響を及ぼさない。
従って、本発明では、フィルターは粒径が１５μｍ以上の塵・埃・酸化鉄・海塩粒子等を除去できるものを採用することとした。
【００１７】
また、フィルターを通過する冷却ガスの流速は３．０ｍ／ｓより大きくなると、圧力損失が大きくなりすぎてブロワーやファンを必要以上に大きくしなければならなくなるので、本発明では、ブロワーにおける入り側部分のダクト径を大きくして、ブロワーの入り側、特に、フィルターボックス部では、１．０〜３．０ｍ／ｓの流速で冷却ガスが流れるようにした。
【００１８】
また、本発明において、鋼板を冷却する冷却帯のガス吸引部から鋼板への吹付けノズルに至る接ガス部分をステンレス鋼板で製作するのは、以下の理由によるものである。すなわち、前記接ガス部分に、防錆処理剤を塗布した鋼板を使用した場合には、防錆処理剤が剥がれた後は錆が発生する。また、めっき鋼板を使用したとしても、１〜２年も経過すると、めっき鋼板の表面に白錆等が発生する。そして、これらの錆が冷却ガス中に含まれ、鋼板を冷却する時に同時に鋼板に吹き付けられると、黒点疵の発生要因となる。これに対して、ステンレス鋼板を採用した場合には、防錆処理剤を塗布した鋼板は勿論、めっき鋼板よりも耐食性に優れていて、錆や白錆等が発生せず、また、めっき鋼板よりも溶接性が良好であるからである。なお、ステンレス鋼板であれば、特に限定しないが、ＳＵＳ３１６ステンレス鋼のほうが一般的に用いられるＳＵＳ３０４ステンレス鋼よりも耐孔性及び耐食性が良好で、溶接性がすぐれているので、ＳＵＳ３１６ステンレス鋼を採用することが望ましい。
【００１９】
【実施例】
以下、本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を図１及び図２に示す一実施例に基づいて説明する。
図１は本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を適用した合金化溶融亜鉛めっき鋼板製造ラインの概略説明図、図２は本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を構成するフィルターボックスの正面図である。
【００２０】
図面において、１は連続焼鈍炉で前処理された鋼板であり、溶融亜鉛めっき槽２に浸漬された後、シンクロール３を経てガスワイピング装置４でめっき付着量を調整されて、公知の機能であるオフライン退避機能を有する合金化処理装置の加熱帯５で加熱される。
【００２１】
６は加熱帯５の出口に設置されたエアーカーテンであり、加熱帯５で使用された燃焼排ガスがライン外に排出されるのを防止するものである。
加熱帯５で加熱処理された鋼板１は、保持帯の機能と、屋外の大気を吸引し、鋼板１に吹付けて冷却する冷却帯の機能を有する保持帯兼用冷却帯７で冷却保持、または保持された後、Ｎｏ１空冷帯８、Ｎｏ２空冷帯９で冷却され、その後、トップロール１０に至り次工程に移る。なお、１１はシンクロール３からトップロール１０に至るまでに鋼板１がばたつくのを防止するタッチロールである。
【００２２】
ところで、前記保持帯兼用冷却帯７は、冷却帯本体７ａと、保持帯部７ｂと、屋外の大気を吸引するブロワー７ｃと、冷却ガスの風量を調整するサクションダンパー７ｄと、ブロワー７ｃの吸い込み音を消音するサイレンサー７ｅと、ブロワー７ｃに吸引される大気中に含まれる塵・埃・酸化鉄・海塩粒子等を除去するフィルターボックス７ｆ、及びこれらをつなぐダクト７ｇとで構成されている。
【００２３】
また、Ｎｏ１空冷帯８，Ｎｏ２空冷帯９は、屋外の大気を吸引して鋼板１に吹付けて冷却するもので、それぞれ、冷却帯本体８ａ，９ａと、屋外の大気を吸引するブロワー８ｂ，９ｂと、冷却ガスの風量を調整するサクションダンパー８ｃ，９ｃと、ブロワー８ｂ，９ｂの吸い込み音を消音するサイレンサー８ｄ，９ｄと、ブロワー８ｂ，９ｂに吸引される大気中に含まれる塵・埃・酸化鉄・海塩粒子等を除去するフィルターボックス８ｅ，９ｅ、及びこれらをつなぐダクト８ｆ，９ｆとで構成されている。
【００２４】
本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置は、例えば上記したような合金化処理装置に適用して、製造される合金化溶融亜鉛めっき鋼板の黒点疵を防止する装置であり、次のような構成である。
【００２５】
すなわち、本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置は、鋼板１を冷却または保持する保持帯兼用冷却帯７，Ｎｏ１空冷帯８，Ｎｏ２空冷帯９のガス吸引部から鋼板１への吹付けノズルに至る接ガス部分、すなわち、保持帯兼用冷却帯７では、冷却帯本体７ａ，保持帯部７ｂ，ブロワー７ｃ，サクションダンパー７ｄ，サイレンサー７ｅ，フィルターボックス７ｆ，及びダクト７ｇを、また、Ｎｏ１空冷帯８，Ｎｏ２空冷帯９では、冷却帯本体８ａ，９ａ，ブロワー８ｂ，９ｂ，サクションダンパー８ｃ，９ｃ，サイレンサー８ｄ，９ｄ，フィルターボックス８ｅ，９ｅ，及びダクト８ｆ，９ｆを例えばＳＵＳ３１６ステンレス鋼板で製作するのである。
【００２６】
加えて、本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置では、ブロワー７ｃ，８ｂ，９ｂの入り側における冷却ガスの流速を１．０〜３．０ｍ／ｓとなすべく、例えば図２に示すように、フィルターボックス７ｆ，８ｅ，９ｅのダクト径を大きくし、かつ、この大きくしたダクト部分に１５μｍ以上の塵・埃・酸化鉄・海塩粒子等を除去するフィルター７ｈ，８ｇ，９ｇを配置しているのである。
【００２７】
ところで、フィルターボックス７ｆ，８ｅ，９ｅへのフィルター７ｈ，８ｇ，９ｇの配置手段については、特に限定されるものではないが、例えば枠内にフィルター７ｈ，８ｇ，９ｇを固定したものを、フィルターボックス７ｆ，８ｅ，９ｅの例えば幅方向に固定したレールに沿って摺動させることで配置するようにすれば、フィルター７ｈ，８ｇ，９ｇの取り替えが容易に行えることになる。この時、レールとフィルターボックス７ｆ，８ｅ，９ｅとはシール溶接しておくことは勿論であり、また、フィルター７ｈ，８ｇ，９ｇを固定した枠間、及び枠とフィルターボックス７ｆ，８ｅ，９ｅ間は弾力性部材を介在させて、大気が全てフィルター７ｈ，８ｇ，９ｇを通るようにしておくことは言うまでもない。
【００２８】
上記したような本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を、合金化処理装置に適用した場合には、屋外の大気中に含まれる黒点疵発生の原因となりうる、粒子径が１５μｍ以上の塵・埃・酸化鉄・海塩粒子等を除去できると共に、接ガス部分も錆が発生しなくなるので、合金化溶融亜鉛めっき鋼板の黒点疵発生の割合が、従来は平均１．６件／月であったのが、０件／月になった。
【００２９】
また、合金化処理を行わない溶融亜鉛めっき鋼板（ＧＩ鋼板）を製造する際に、本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を適用した場合にも、溶融亜鉛めっき鋼板の黒点疵発生の割合が、従来は平均０．７件／月であったのが、０件／月になった。
【００３０】
【発明の効果】
以上説明したように、本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置によれば、従来、殆ど除去されずに次の工程に送られていた、黒点疵の原因となりうる微細な塵・埃・酸化鉄・海塩粒子等を除去できると共に、接ガス部分に錆が発生しなくなるので、黒点疵のない高品質な溶融亜鉛めっき鋼板を製造できる。
【図面の簡単な説明】
【図１】本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を適用した合金化溶融亜鉛めっき鋼板製造ラインの概略説明図である。
【図２】本発明に係る溶融亜鉛めっき鋼板の黒点疵防止装置を構成するフィルターボックスの正面図である。
【符号の説明】
１ 鋼板
７ 保持帯兼用冷却帯
７ａ 冷却帯本体
７ｂ 保持帯部
７ｃ ブロワー
７ｄ サクションダンパー
７ｅ サイレンサー
７ｆ フィルターボックス
７ｇ ダクト
７ｈ フィルター
８ Ｎｏ１冷却帯
８ａ 冷却帯本体
８ｂ ブロワー
８ｃ サクションダンパー
８ｄ サイレンサー
８ｅ フィルターボックス
８ｆ ダクト
８ｇ フィルター
９ Ｎｏ２冷却帯
９ａ 冷却帯本体
９ｂ ブロワー
９ｃ サクションダンパー
９ｄ サイレンサー
９ｅ フィルターボックス
９ｆ ダクト
９ｇ フィルター[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for preventing black spots generated on the surface of a hot-dip galvanized steel sheet during the production of the hot-dip galvanized steel sheet.
[0002]
[Prior art]
In a continuous hot-dip galvanizing line, a steel sheet plated in a hot-dip galvanizing bath is made of an alloy consisting of a heating zone, a holding zone, and a cooling zone after the zinc coating amount is adjusted by a coating amount control device. Galvanizing treatment in a chemical treatment furnace to form an alloyed hot-dip galvanized (GA) steel sheet that is interdiffused between the steel substrate and the zinc layer, or (2) the amount of zinc applied was adjusted by the applied amount controller. After that, the steel sheet is cooled as it is to form a regular (normal) spangled steel sheet (GI steel sheet) that produces a beautiful gorgeous pattern, or (3) a large number of steel sheets after plating at a rate faster than the growth rate of zinc crystals. And a minimized (zero) spangled steel sheet that generates fine gorgeous patterns that cannot be discerned by the naked eye.
[0003]
Among them, GA steel sheets are often used for automotive materials and home electric appliances because they have properties such as adhesion of coating films, corrosion resistance after coating, and spot weldability. This GA steel sheet is heated to about 500 to 600 ° C. in the heating zone after the amount of plating is adjusted, and thereafter, is held at a certain temperature in the holding zone, and is provided downstream of the holding zone. After being cooled by gas jet cooling or mist in the cooling zone, and made into GA steel sheet, the traveling direction is changed from vertical to horizontal by the top roll arranged downstream of the cooling zone, sent to the next process, and Done.
[0004]
What is problematic in this series of steps is the fine dust, dust, iron oxide, sea salt particles, etc. contained in the gas or mist sprayed when cooling the steel sheet. That is, when a gas is sucked and blown by a blower in order to cool the steel sheet, these fine dust, dust, iron oxide, sea salt particles, and the like are simultaneously sucked and sprayed on the steel sheet. As a result, fine dust, dust, iron oxide, sea salt particles and the like adhering to the surface of the steel sheet are pushed into the surface of the steel sheet by a top roll or the like, resulting in product flaws (hereinafter referred to as “black spot flaws”).
[0005]
Conversely, when fine dust, dust, iron oxide, sea salt particles, etc. sprayed on the steel sheet are pushed into the roll side, the roll itself is scratched, even if the steel sheet itself has no deposits, Thereafter, flaws are generated on the surface of the steel sheet every rotation cycle of the roll. The black spot flaws formed in this manner cause press spots when pressing a steel sheet. As a result, the quality requirements of the consumer cannot be satisfied.
[0006]
By the way, in the conventional alloying apparatus, for example, in Japanese Patent Application Laid-Open No. 28353/1988, a heat retaining box and a cooling box are exchangeably disposed between a holding band and a cooling zone of the alloying apparatus, And a heat insulation box, a heat insulation box and a cooling box, or a combination of a cooling box and a cooling zone using a bellows which can expand and contract vertically to prevent the invasion of outside air.
[0007]
Further, in Japanese Patent Application Laid-Open No. 5-179415, a cooling zone and a holding zone are provided in parallel on the downstream side of a heating zone constituting an alloying treatment apparatus, and the hot-dip galvanized steel sheet heated in the heating zone is immediately cooled, An alloying treatment system has been proposed that allows selection of whether to keep heat for a certain period of time before cooling.If the heating furnace is a gas heating system, the subsequent cooling zone and tropical heat are affected by the generated high-temperature gas. There is disclosed an apparatus in which a furnace has a sealed structure so that generated hot gas is discharged through a duct.
[0008]
[Problems to be solved by the invention]
However, the above-mentioned inventions are all aimed at providing an apparatus capable of producing a good GA steel sheet, and at the time of alloying treatment, a fine dust, dust, or the like contained in a gas or mist for cooling the steel sheet. No measures have been taken to prevent black spots caused by iron oxide, sea salt particles and the like.
[0009]
In other words, in Japanese Patent Application Laid-Open No. 64-28353, the holding zone, heat insulation box, cooling box, and cooling zone have a structure in which bellows are used to prevent invasion of outside air. No measures have been taken on the obi side. Therefore, fine dust, dust, iron oxide, sea salt particles and the like are directly sprayed on the steel sheet. The same applies to Japanese Patent Application Laid-Open No. 5-179415.
[0010]
The present invention has been made in view of the above-mentioned conventional problems, and has been made in a continuous hot-dip galvanizing line, and is provided with an alloyed hot-dip galvanized steel sheet and other hot-dip galvanized steel sheets (GI steel sheets and minimized (zero) spangle steel sheets). ) Does not directly spray fine dust, dust, iron oxide, sea salt particles, etc. on the steel sheet surface, and as a result, does not cause black spots on the manufactured alloyed hot-dip galvanized steel sheet. It is intended to provide a device.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a device for preventing black spots on a hot-dip galvanized steel sheet, in which a gas contact portion from a gas suction part of a cooling zone for cooling the steel sheet to a spray nozzle for the steel sheet is made of a stainless steel sheet. At the same time, the duct diameter of the inlet side portion of the blower is increased so that the flow rate of the cooling gas at the inlet side of the blower is 1.0 to 3.0 m / s, and dust having a diameter of 15 μm or more The filter which removes is arranged. By doing so, rust does not occur in the gas contact portion, and rust does not adhere to the surface of the steel sheet. Also, fine dust, dust, iron oxide, sea salt particles and the like having a size of 15 μm or more are removed by the filter and do not adhere to the surface of the steel sheet.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The apparatus for preventing black spots on a hot-dip galvanized steel sheet according to the present invention, after subjecting the steel sheet to hot-dip galvanizing, adjusts the zinc adhesion amount with an adhesion amount control device, and heats / holds / cools, or heats / heats in an alloying furnace. Black spots generated on the surface of a galvannealed steel sheet manufactured by cooling or a hot-dip galvanized steel sheet manufactured by cooling and manufacturing, after applying hot-dip galvanizing to the steel sheet and then adjusting the zinc adhesion amount with a coating amount control device A device for preventing flaws, in which a gas contact portion from a gas suction portion of a cooling zone for cooling a steel plate to a nozzle for spraying the steel plate is made of a stainless steel plate, and a cooling gas flow rate on the inlet side of the blower is 1 The diameter of the duct on the entrance side of the blower is increased so as to be 0.0 to 3.0 m / s, and a filter for removing dust of 15 μm or more is disposed in the enlarged duct.
[0013]
That is, in the present invention, in the process of manufacturing a GA steel sheet or other hot-dip galvanized steel sheet, after applying a hot-dip galvanizing method to the steel sheet, the amount of zinc coating is adjusted by a coating amount control device, and then heated and heated in an alloying furnace. When holding and cooling, heating or cooling, or after adjusting the amount of zinc deposited, when cooling, fine dust and dust that are included in the gas blown to cool the steel sheet and cause black spots・ In order to remove iron oxide and sea salt particles, a filter is installed on the inlet side of the blower in the cooling zone.
[0014]
Then, the present inventor collected fine dust, dust, iron oxide, sea salt particles and the like contained in the cooling gas, and as a result of inspection, found that sand, iron oxide, sea salt particles, abrasive grains contained in the cooling gas. Was as shown in Table 1 below.
[0015]
[Table 1]

[0016]
According to the experiment of the present inventor, fine dust, dust, iron oxide, sea salt particles and the like having a size of less than 15 μm adhere to the surface of the steel sheet and are pushed into the surface of the steel sheet by a top roll or the like. Also does not affect the quality of the product.
Therefore, in the present invention, a filter capable of removing dust, dust, iron oxide, sea salt particles and the like having a particle size of 15 μm or more is adopted.
[0017]
If the flow rate of the cooling gas passing through the filter is higher than 3.0 m / s, the pressure loss becomes too large and the blower and the fan must be made larger than necessary. The duct diameter of the portion was increased so that the cooling gas flowed at a flow rate of 1.0 to 3.0 m / s on the inlet side of the blower, particularly on the filter box.
[0018]
Further, in the present invention, the gas contact portion from the gas suction portion of the cooling zone for cooling the steel plate to the spray nozzle for the steel plate is made of a stainless steel plate for the following reason. That is, when a steel plate coated with a rust preventive agent is used in the gas contact portion, rust is generated after the rust preventive agent is peeled off. Further, even if a plated steel sheet is used, white rust or the like is generated on the surface of the plated steel sheet after a lapse of one to two years. If these rusts are contained in the cooling gas and are sprayed on the steel sheet at the same time as the steel sheet is cooled, it causes black spots. On the other hand, when a stainless steel plate is used, not only steel plates coated with a rust preventive agent, but also have better corrosion resistance than plated steel plates, and do not generate rust or white rust, etc. This is because the weldability is also good. As long as it is a stainless steel plate, there is no particular limitation. However, SUS316 stainless steel is used because it has better porosity and corrosion resistance than SUS304 stainless steel, which is generally used, and has excellent weldability. It is desirable to do.
[0019]
【Example】
Hereinafter, an apparatus for preventing black spots on a hot-dip galvanized steel sheet according to the present invention will be described based on an embodiment shown in FIGS. 1 and 2.
FIG. 1 is a schematic explanatory view of a production line for an alloyed hot-dip galvanized steel sheet to which the apparatus for preventing black spots of a hot-dip galvanized steel sheet according to the present invention is applied, and FIG. It is a front view of the filter box which performs.
[0020]
In the drawing, reference numeral 1 denotes a steel sheet which has been pretreated in a continuous annealing furnace, and after being immersed in a hot-dip galvanizing bath 2, the amount of plating applied is adjusted by a gas wiping device 4 via a sink roll 3, and a known function is used. It is heated in a heating zone 5 of an alloying apparatus having an off-line retreat function.
[0021]
Reference numeral 6 denotes an air curtain installed at the outlet of the heating zone 5 for preventing the combustion exhaust gas used in the heating zone 5 from being discharged out of the line.
The steel sheet 1 that has been heat-treated in the heating zone 5 is cooled and held in the holding band / combination cooling zone 7 having the function of a holding zone and the function of a cooling zone that sucks outdoor air and sprays and cools the steel sheet 1, or After being held, it is cooled in the No. 1 air cooling zone 8 and the No. 2 air cooling zone 9, and then reaches the top roll 10 and moves to the next step. Reference numeral 11 denotes a touch roll for preventing the steel plate 1 from fluttering from the sink roll 3 to the top roll 10.
[0022]
The holding band / cooling band 7 includes a cooling band main body 7a, a holding band portion 7b, a blower 7c for sucking outdoor air, a suction damper 7d for adjusting a flow rate of cooling gas, and a suction sound of the blower 7c. , A filter box 7f for removing dust, dust, iron oxide, sea salt particles and the like contained in the air sucked by the blower 7c, and a duct 7g connecting these.
[0023]
The No. 1 air-cooling zone 8 and the No. 2 air-cooling zone 9 are for sucking outdoor air and spraying the steel sheet 1 to cool them. The cooling zone main bodies 8a and 9a, and the blowers 8b and 9b for sucking outdoor air, respectively. 9b, suction dampers 8c, 9c for adjusting the air volume of the cooling gas, silencers 8d, 9d for silencing the suction sound of the blowers 8b, 9b, and dust contained in the air sucked by the blowers 8b, 9b. It comprises filter boxes 8e, 9e for removing iron oxide / sea salt particles and the like, and ducts 8f, 9f connecting these.
[0024]
The apparatus for preventing black spots on a hot-dip galvanized steel sheet according to the present invention is, for example, an apparatus for applying the above-described alloying treatment apparatus to prevent black spots on a manufactured hot-dip galvanized steel sheet. It is such a configuration.
[0025]
That is, the apparatus for preventing black spots on the hot-dip galvanized steel sheet according to the present invention blows the steel sheet 1 from the gas suction part of the holding and cooling zone 7, the No. 1 air cooling zone 8, and the No. 2 air cooling zone 9 for cooling or holding the steel sheet 1. In the gas contact portion reaching the mounting nozzle, that is, in the holding band / cooling band 7, the cooling band main body 7a, the holding band portion 7b, the blower 7c, the suction damper 7d, the silencer 7e, the filter box 7f, and the duct 7g are provided. In the air cooling zone 8 and the No. 2 air cooling zone 9, the cooling zone main bodies 8a and 9a, the blowers 8b and 9b, the suction dampers 8c and 9c, the silencers 8d and 9d, the filter boxes 8e and 9e, and the ducts 8f and 9f are made of, for example, SUS316 stainless steel plate. Make it.
[0026]
In addition, in the apparatus for preventing black spots on a hot-dip galvanized steel sheet according to the present invention, the flow rate of the cooling gas on the entry side of the blowers 7c, 8b, 9b is set to 1.0 to 3.0 m / s, for example, as shown in FIG. As shown, the duct diameters of the filter boxes 7f, 8e, 9e are increased, and filters 7h, 8g, 9g for removing dust, dust, iron oxide, sea salt particles, etc. of 15 μm or more are provided in the enlarged duct portion. It is arranged.
[0027]
By the way, the means for arranging the filters 7h, 8g, 9g in the filter boxes 7f, 8e, 9e is not particularly limited. For example, a filter in which the filters 7h, 8g, 9g are fixed in a frame is replaced with a filter box. If the filters 7h, 8e, and 9e are arranged by sliding along, for example, rails fixed in the width direction, the filters 7h, 8g, and 9g can be easily replaced. At this time, the rails and the filter boxes 7f, 8e, 9e are, of course, sealed and welded, and between the frames to which the filters 7h, 8g, 9g are fixed, and between the frames and the filter boxes 7f, 8e, 9e. Needless to say, the elastic member is interposed so that the atmosphere can pass through the filters 7h, 8g, and 9g.
[0028]
When the apparatus for preventing black spots of a hot-dip galvanized steel sheet according to the present invention as described above is applied to an alloying treatment apparatus, the particle diameter may be 15 μm or more, which may cause black spots included in outdoor air. Dust, dust, iron oxide, sea salt particles, etc. can be removed, and rust does not occur in the gas contact area. The month was reduced to 0 cases / month.
[0029]
In addition, when manufacturing the hot-dip galvanized steel sheet (GI steel sheet) without performing the alloying treatment, the black spot flaw of the hot-dip galvanized steel sheet is generated even when the hot spot galvanized steel sheet black spot prevention apparatus according to the present invention is applied. Was 0.7 cases / month on average, but 0 cases / month.
[0030]
【The invention's effect】
As described above, according to the apparatus for preventing black spots on a hot-dip galvanized steel sheet according to the present invention, fine dust and dust that can be a cause of black spots that have been conventionally sent to the next step without being removed. -Since iron oxide, sea salt particles, etc. can be removed, and rust does not occur in the gas contact portion, a high quality hot-dip galvanized steel sheet without black spots can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a production line for an alloyed hot-dip galvanized steel sheet to which a device for preventing black spots on a hot-dip galvanized steel sheet according to the present invention is applied.
FIG. 2 is a front view of a filter box included in the apparatus for preventing black spots on a galvanized steel sheet according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steel plate 7 Holding band combined cooling band 7a Cooling band main body 7b Holding band part 7c Blower 7d Suction damper 7e Silencer 7f Filter box 7g Duct 7h Filter 8 No1 cooling band 8a Cooling band main body 8b Blower 8c Suction damper 8d Silencer 8e Filter box 8f Duct 8g Filter 9 No2 cooling zone 9a Cooling zone main body 9b Blower 9c Suction damper 9d Silencer 9e Filter box 9f Duct 9g Filter

Claims (1)

After hot-dip galvanizing the steel sheet, adjust the zinc coating amount with the coating amount control device, and heat, hold and cool in an alloying furnace, or heat and cool to produce an alloyed hot-dip galvanized steel sheet, After applying hot-dip galvanizing to the surface of the hot-dip galvanized steel sheet, the amount of zinc is adjusted by a coating amount control device to prevent black spots on the surface of the hot-dip galvanized steel sheet. The gas contact part from the gas suction part of the belt to the spray nozzle to the steel plate is made of stainless steel plate, and the flow rate of the cooling gas on the inlet side of the blower is set to 1.0 to 3.0 m / s. An apparatus for preventing black spots on a hot-dip galvanized steel sheet, wherein a duct diameter of an entrance side portion is increased, and a filter for removing dust of 15 μm or more is disposed in the enlarged duct portion.

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