JPH08199320A - Hot dip coating device for steel strip - Google Patents

Abstract

PURPOSE: To suppress the adhesion of harmful foreign matter suspended on a plating bath surface to steel strip surfaces by providing a coating device for the steel strip with gate-like bodies having plane parts parallel with the surfaces of the steel strip on both sides of the steel strip between a support roll and gas wiping nozzles. CONSTITUTION: The steel strip S is introduced via a snout 2 into the plating bath Z in a plating cell 1 where the plating bath Z is adhered thereon. The steel strip is changed in direction via the sink roll 3 and is pulled upward via a support roll 4. The coating weight is adjusted by the gas wiping nozzles 6. At this time, the coating device is provided with a pair of the gate-like bodies 5 having the plane parts parallel with the steel strip surfaces on both sides of the steel strip S near the bath surface between the support roll 4 and the gas wiping nozzle 6. The top ends of the plane parts of the gate-like bodies 5 are positioned near the bath surface and the bottom ends are positioned deeper by >=100mm than the bath surface. The distances between the plane parts of the gate-like bodies 5 and the steel strip S are set at 5 to 20mm. As a result, the adhesion of the harmful foreign matter, such a dross, to the plating surfaces obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanizing apparatus for steel strips, and more particularly to a hot-dip galvanizing apparatus for steel strips which suppresses adhesion of harmful foreign substances floating near the plating bath surface to the surface of the steel strip. Regarding

[0002]

2. Description of the Related Art Metal plating such as hot-dip galvanizing of steel strip is carried out in a bath provided in the plating tank by advancing the steel strip into a plating tank containing the molten metal to deposit the molten metal on the surface of the steel strip. By changing the traveling direction of the steel strip with a roll and removing the molten metal excessively attached to the surface of the steel strip by a deposit amount adjusting means such as a gas wiping nozzle installed above the plating bath, and adjusting it to the target deposit amount. Has been done.

By the way, in the plating bath, an oxide of the plating metal and a foreign substance called a dross containing a compound with iron as a main component are generated and float mainly in the vicinity of the bath surface and on the surface of the steel strip immediately after plating. The phenomenon of adhesion is observed, and various proposals have been made to prevent or suppress it. JPA
According to 62-185863, it is described that an inert gas such as nitrogen is blown into the plating bath to remove dross floating in the bath. But with this method,
There is a problem that not only the bottom dross accumulated on the bottom is rolled up by excessively stirring the inside of the plating bath, but also the flow of the plating bath becomes violent and the oxidation of the metal on the surface of the plating bath is promoted.

According to Japanese Unexamined Patent Publication No. 4-99258, the plating bath in the plating tank is pumped out and transferred to a sub-pot, the plating bath in the sub-pot is kept at a high temperature, the aluminum concentration is increased, and it is floated as top dross. It is described to be removed. An example of the plating equipment described in this publication will be described with reference to FIG. Fig. 8 is a schematic sectional view of the plating equipment. 91 is a plating tank, 92 is a sub-pot, 93 is a bath roll, 94 is a pumping pipe, 95 is a pumping pump, 96 is a returning pipe, 97 is a returning pump, S is a steel strip. , Z is a plating bath, D ₁ is a bottom dross, and D ₂ is a top dross.

The steel strip S drawn into the plating bath Z from the upper right direction is wound around the bath roll 93 to change its direction, and is pulled vertically upward as indicated by an arrow. On the other hand, a part of the plating bath Z containing the bottom dross D ₁ is transferred by the pumping pump 95 to the sub-pot 92 via the pumping pipe 94, and is kept warm and concentrated in the sub-pot 92 to be top dross D ₂
The clean plating bath from which the dross has been separated and from which the dross has been separated is recovered by the return pump 97 into the plating tank 91 via the return pipe 96.

In this method, the plating bath in the sub-pot has a high concentration, and the composition of the plating bath is different from that of the plating bath in the plating tank. There is a problem that the dross cannot be removed by a general process. In addition, JP-A-4-160141
According to the publication, the plating bath is pumped up, and the dross component is separated and removed by a ceramic filter. However, according to this device, since the ceramic filter is clogged in a short time, it has to be replaced frequently, and since the ceramic filter cannot be reused, enormous cost is required and a serious problem in practicality occurs. is there.

In addition, a clean molten metal is jetted from a slit nozzle having an outlet parallel to the steel strip to the steel strip near the bath surface to prevent harmful foreign matter from approaching or foreign matter that has already adhered. There is also a way to wash away.
However, in this method, not only the slit nozzle is easily clogged with foreign matter, but also the tip of the nozzle is easily damaged or melted, so that the jet flow of the molten metal becomes unstable and the objective of foreign matter removal cannot often be achieved completely.

[0008]

DISCLOSURE OF THE INVENTION The present invention realizes a molten metal plating apparatus which solves the above-mentioned problems in the prior art, is free from problems such as melting loss and clogging, and economically prevents foreign matter from adhering. The purpose is to do.

[0009]

A molten metal plating apparatus for a steel strip according to the present invention includes a bath roll provided in the plating tank to change the traveling direction of the steel strip, and an adhesion amount adjusting means provided above the plating tank. In a steel strip plating apparatus for removing excessive molten metal adhered to the steel strip surface by means of a flat portion parallel to the steel strip surface on both sides of the steel strip between the in-bath roll and the deposit amount adjusting means. It is preferable that the upper end of the flat part of the weir is located near the bath surface, and the lower end of the flat part of the weir is at least 100 mm deeper than the bath surface. , And the distance between the steel strip and the plane of the weir is 5
A molten metal plating apparatus for the above steel strip having a thickness of up to 20 mm, and more preferably, for melting the above steel strip characterized by having a height adjusting mechanism for causing the height of the weir-like body to follow the bath surface. It is a metal plating device.

[0010]

[Operation] According to the present invention, since a pair of weir-like bodies are provided with a steel strip sandwiched between the in-bath roll of the plating tank and the gas wiping nozzle, that is, near the bath surface of the plating bath, It prevents the dross floating on the surface from contacting the steel strip surface, and the dross in the gap between the weir and the steel strip is drawn toward the weir and returned to the plating bath together with the excessively adhered molten metal. Therefore, there is no dross attached to the surface of the steel strip, and a plated steel strip with excellent quality can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view around a plating tank in a hot dip galvanizing facility, 1 is a plating tank, 2 is a snout provided at the exit end of the pretreatment facility, 3 is a bath roll, 4 is a support roll, 5 Is a weir, 6 is a gas wiping nozzle that is an adhesion amount adjusting means, S is a steel strip, Z is a plating bath, and D is a harmful foreign substance such as dross.

After the steel strip S is subjected to pretreatment such as cleaning and annealing, it enters the plating bath Z in the plating tank 1 in the atmosphere of the pretreatment equipment through the snout 2 and melts on the surface of the steel strip S. Zinc adheres. The traveling direction is changed by an in-bath roll (also referred to as a sink roll) 3 provided in the plating bath Z, positioned by a pair of support rolls 4 and pulled up, and on the way, on the bath surface of the plating bath Z. The excessively adhering molten zinc is removed by the gas wiping nozzle 6, and an appropriate amount of adhering zinc is removed, and the molten zinc is transferred to a downstream process such as cooling.

Between the support roll 4 and the gas wiping nozzle 6, that is, on both sides of the steel strip S near the bath surface, a pair of weir-like bodies 5 having flat portions parallel to the steel strip surface are provided. In this embodiment, the support roll 4 is provided at this position for the purpose of preventing the vibration of the steel strip S and fixing the pass line. However, there is a case where the support roll 4 is not provided. The body 5 is provided between the in-bath roll 3 and the adhesion amount adjusting means 6.

The weir-like body 5 may have any structure on the back side as long as the flat portion is formed on the side facing the steel strip S. It is preferable that the upper end be chamfered obliquely as shown in FIG. 2 because the flow downward of the surplus plating bath will be smooth. Weir 5
As for the flat portion, since it is necessary to avoid melting, thermal deformation, breakage, etc. due to molten metal, it is preferable to use a ceramic material having a small coefficient of thermal expansion and excellent melting resistance, such as a smooth plate of high-purity alumina. . Also for other portions such as the portion supporting the flat portion, it is necessary to use an iron base material, for example, a chromium-containing heat-resistant steel or the like to suppress the adverse effects such as melting and thermal deformation. In addition, in order to avoid deformation and destruction due to differences in the members used, it is important to devise a mechanism such that the difference in thermal strain is released by a sliding mechanism or the like.

Since the weir-like body 5 of the present invention is basically a plate-like member, its function is not impaired by complicated failures such as melting damage and clogging, and it can be replaced when it is consumed. , Very economical. The operating conditions in this example are as follows.・ Material of steel strip: Niobium-titanium added ultra low carbon aluminum killed steel cold-rolled steel ・ Dimensions of steel strip: Strip thickness 0.8mm x strip width 1219mm ・ Line speed: 90m / min ・ Plating bath temperature: 470 ℃ ・ Plating bath composition : Al 0.19%, Fe 0.04%, balance Zn ・ Target amount of adhesion: 90 g / m ² per side Fig. 2 is a partially enlarged view of the vicinity of the weir-like body 5 in Fig. 1,
Only the left side of the weir 5 is shown, and the right side is omitted.

The preferred range was examined by variously changing the distance between the flat surface portion of the weir-shaped body 5 and the steel strip S and the height with respect to the bath surface. First, by changing the distance A between the flat surface portion of the weir 5 and the steel strip S, the harmful foreign matter D attached to the surface of the steel strip S after plating
Were counted. The harmful foreign matter D is generally called dross, and the size thereof ranges from extremely fine to a maximum major axis of about 2 mm. Here, the number of particles having a major axis of 100 μm or more was counted. The results are shown in Fig. 3.

Generally, the number of harmful foreign substances deposited is 20 / 100d
It is recognized that if it is more than m ^2, the appearance of the plating surface will be significantly impaired, and the commercial value will decrease accordingly.
When the number of adhering substances is 20/100 dm ² or more, generally, the ratio of enormous harmful foreign substances having a major axis of 1 mm or more tends to increase rapidly.
With 20 pieces / 100 dm ² , the proper range of the distance A is 25 mm or less.

Consider this result with reference to FIG. According to experiments by the inventors of the present invention, such as a water model, the foreign matter present in the gap between the flat surface of the weir 5 and the steel strip S remains stationary as the steel strip S moves upward as indicated by the arrow a. Weir 5
The phenomenon of approaching to the flat part is recognized. The foreign matter then rides on the downward flow of the surplus plating bath due to gas wiping and returns into the plating bath Z as shown by the arrow b, but when the distance A exceeds 25 mm, it is shown by the arrow a. Since the approaching tendency is weak and the steel sheet S remains near the steel strip S and moves upward, it adheres to the steel strip surface. If the distance A is 5 mm or less, the steel strip S is brought into contact with the flat portion of the dam-like body 5 due to vibration or the like, and scratches are generated on the surface of the steel strip, which is not preferable in terms of quality.

Next, the height B of the upper end of the plane portion of the weir-like body 5
Was changed up and down with respect to the bath surface as a reference, and the same measurement was performed. FIG. 4 shows the results. The proper range of the height B of the upper end is -20 to +20 mm. Considering this result, since a large amount of foreign matter floats near the bath surface, the weir-like member 5 is extremely effective near the bath surface as a shield that does not allow it to directly contact the steel strip S. If the upper end is higher than the bath surface, the downward flow generated by the gas wiping does not flow to the back side of the weir 5, but flows back into the gap between the flat portion and the steel strip, increasing the adhesion of foreign matter. It seems to be. Also, if the upper end of the flat surface is too lower than the bath surface, a large amount of foreign matter floating near the bath surface
It is considered that not only the metal directly comes into contact with the metal but also turbulence occurs due to the flow of the plating bath at the upper end portion of the flat portion below the bath surface, and the adhesion of foreign matter increases.

Further, the depth C at the lower end of the plane portion of the weir-shaped body 5 is
Was changed in the vertical direction and the same measurement was performed. Results are shown in FIG. As a proper range of the depth C at the lower end, it is sufficient if the lower side is negative with respect to the bath surface and −100 mm or more. Considering this result with reference to FIG. 2, when the depth C at the lower end is less than −100 mm, the phenomenon that the harmful foreign matter D approaches the plane portion of the weir 5 as shown by the arrow a sufficiently occurs. Moreover, the effect as a weir that does not allow the harmful foreign matter D floating near the bath surface to contact the steel strip S is considered insufficient. That is, the flow of the plating bath containing many foreign substances as shown in FIG.
It is estimated that it extends to about 00 mm.

From this fact, it seems that the larger the depth C at the lower end of the flat portion of the weir-like body 5, the better. However, there is a flow containing precipitated foreign matter also at the bottom of the plating tank, and the weir-like shape. Since there are difficulties in terms of equipment such as putting in and out of the body 5, there are naturally limits depending on the line, but in general the numerical values cannot be limited. As discussed above, the relative position of the dam 5 with respect to the bath surface is important, and it is not preferable to fix it to the plating tank itself. Therefore, it is important that the height be adjusted by following some height adjusting mechanism to the liquid surface. An example of the height adjusting mechanism is shown in FIG. A float 7 and a link mechanism 8 float the float 7 in the plating bath Z in the plating tank 1 and support the dam 5 through the link mechanism 8. The link mechanism 8 may be omitted, and the dam 5 may be directly supported by the float 7.

Another example of the height adjusting mechanism is shown in FIG. A liquid level gauge 9 and an electric lifting mechanism 10 detect the liquid level by the liquid level meter 9, and the electric lifting mechanism 10 moves the weir-like body 5 up and down by the lifting mechanism. A known linear movement mechanism such as a screw nut system or a rack and pinion system can be adopted as the electric lifting mechanism 10, and instead of the electric lifting mechanism 10, a hydraulic cylinder or the like may be used.

[0023]

EFFECTS OF THE INVENTION According to the present invention, since a weir having a simple structure which does not cause problems such as melting loss and clogging is installed in the plating tank, maintenance is simple and equipment cost is low, and It has an excellent effect that a high-quality plated steel strip can be produced without adhesion of harmful foreign matter such as dross.

[Brief description of drawings]

FIG. 1 is a sectional view around a plating tank showing an embodiment of the present invention.

FIG. 2 is a partially enlarged view in which a part of FIG. 1 is enlarged.

FIG. 3 is a graph showing effects in the example.

FIG. 4 is a graph showing the effect of the same example.

FIG. 5 is a graph showing an effect of the same example.

FIG. 6 is a cross-sectional view around a plating tank showing an example of a height adjusting mechanism.

FIG. 7 is a cross-sectional view around a plating tank showing another example of the height adjusting mechanism.

FIG. 8 is a schematic sectional view of a plating facility showing a conventional technique.

[Explanation of symbols]

 1 Plating Tank 2 Snout 3 Roll in Bath 4 Support Roll 5 Weir 6 Gas Wiping Nozzle 7 Float 8 Link Mechanism 9 Liquid Level Gauge 10 Electric Lifting Mechanism S Steel Strip Z Plating Bath D Hazardous Foreign Material

Claims (5)

[Claims] 1. A plating tank (1) in which the traveling direction of the steel strip is changed by a bath roll (3) provided in the plating tank (1).
In a steel strip plating device for removing molten metal excessively attached to the surface of a steel strip (S) by an attachment amount adjustment means (6) provided above, the in-bath roll (3) and the attachment amount adjustment means ( An apparatus for hot-dip metal plating of steel strip, wherein weirs (5) having flat portions parallel to the surface of the steel strip are installed on both sides of the steel strip (S) between 6). 2. The hot-dip galvanizing apparatus for steel strip according to claim 1, wherein the upper end of the flat portion of the weir (5) is near the bath surface. 3. The hot-dip galvanizing apparatus for steel strips according to claim 1, wherein the lower end of the plane portion of the weir (5) is at a position deeper than 100 mm deeper than the bath surface. 4. The apparatus for hot-dip metal plating of steel strip according to claim 1, wherein the distance between the steel strip (S) and the flat surface of the dam-like body (5) is 5 to 20 mm. 5. The height adjusting means (7, 8, 9, 10) for causing the height of the weir (5) to follow the bath surface, according to any one of claims 1 to 4. Steel strip hot-dip metal plating equipment.