JPH02156054A - Method for preventing dross penetration to hot dip coated steel sheet - Google Patents

Abstract

PURPOSE:To prevent the dross penetration to the hot dip metal coating surfaces of the steel sheet and to produce the hot dip metal coated steel sheet having high quality by providing headers of a specific shape for ejecting a hot dip coating bath in front of a sink roll and snap rolls in the hot dip coating bath at the time of subjecting the surfaces of the steel sheet to hot dip metal coating. CONSTITUTION:The steel sheet 14 to be plated is admitted through a snout 17 into the hot dip coating bath of molten Zn, etc., and after the hot dip metal coating layers are formed on the surfaces thereof, the steel sheet is pulled up from the hot dip coating bath by the sink roll 12 and the snap rolls 13. The headers 15 which has plural blow ports 18 disposed to an inverted V shape with respect to the progressing direction of the steel sheet 14 and are used to blow the hot dip coating bath are disposed in the positions a, b before the sink roll 12 and the snap rolls 13 in this case to remove the dross sticking to the surfaces of the steel sheet by blowing the hot dip coating bath to the steel sheet surfaces. The hot dip coating bath contg. the dross is sucked from suction headers 16 and is filtered of the dross by a filter 20 and is again supplied as the clean hot dip coating bath to the headers 15.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to a method of floating on the surface of a plated steel plate by a roll in a plating bath in order to stably produce a sound product through continuous hot-dip coating of steel plates. The present invention relates to a method for preventing dross from being pushed in.

<Conventional technology and its problems> “
"Dross" not only adheres to the surface of plated steel sheets and causes a significant deterioration in quality, but countermeasures have become an extremely important problem, such as necessitating a reduction in production speed in order to alleviate this problem.

For example, during continuous hot-dip galvanizing of steel sheets, Fe leached from the surface of the steel sheet to be plated is used as a core to form M in the plating bath.
Or Zn reacts and Fe-Aj! in the bath! A system alloy (intermetallic compound) and a Fe-Zn system alloy (intermetallic compound) are generated. These two types of intermetallic compounds are mixed to form dross, but the difference in mixing ratio causes a difference in specific gravity and different behavior, so bottom dross (Fe) deposits at the bottom of the plating bath pot. - Zn-based intermetallic compounds), top dross floating on the bath surface (Fe-All
(mainly intermetallic compounds).

and floating dross (there is no significant difference in the mixing ratio between the Fe-AE-based gold intermetallic compound and the Fe-Zn-based intermetallic compound) floating in the bath.

Of these, "floating dross" is a particular problem, and because its specific gravity is almost equal to that of molten zinc, it is drawn into the flow of the plating bath caused by the rolls in the bath (sink rolls and snap rolls) or the steel plate during threading, and the steel plate It is attracted to the surface and pushed into the steel plate plating layer by the rolls in the bath, forming dross defects. As described above, these dross defects not only impair the appearance of the plated surface, but also deteriorate the chemical conversion treatment properties, thereby adversely affecting the corrosion resistance.

Therefore, as a measure to prevent dross defects during continuous hot-dip galvanizing, a method has been proposed in which molten zinc purified by filtration is sprayed onto the surface of the steel plate immediately after it emerges from the plating bath surface ( JP-A-62-151553
issue). However, this method is not sufficient to remove floating dross that is deeply pushed into the steel sheet plating layer by the rolls in the bath, and there is currently a need for a more reliable measure to prevent dross defects.

Based on these circumstances, the purpose of the present invention is to
To provide a means for effectively preventing dross intrusion during continuous hot-dip plating treatment and stably producing plated steel sheets with sufficiently excellent appearance and other surface properties.

Means for Solving the Problem> In order to achieve the above object, the present inventors first used a water model as shown in FIG. A basic investigation on the behavior of floating dross was conducted by floating resin powder 3 and passing it through a steel plate 4, and the following was clarified.

(a) The movement of floating dross is largely influenced by the movement of the steel plate to be treated that has entered the bath through the snout 7 rather than the rolls in the bath (sink roll 5 or snap roll 6), and the movement of the steel plate to be treated in the bath is It becomes concentrated near the surface of the steel plate as if being drawn into the movement of
(see arrow in the figure), and in this state it gets caught in the bath roll.

(b) However, if the new bath solution is supplied from the width direction of the steel plate to be treated, the floating dross that gets caught up in the flow caused by the movement of the steel plate and concentrates on the surface of the steel plate will be removed from the new solution supply port. It is effectively blown away from the surface of the steel plate.

(C) In this case, a header having a plurality of spray holes arranged in an inverted V-shape facing the traveling direction of the steel plate is placed in front of the roll in the bath, and the spray is passed through the holes to the center of the width of the steel plate. If you supply new liquid from the edge toward the edge,
Unlike when fresh liquid is supplied from only one side of the steel plate edge, the dross floating in the bath is not drawn in from the other side of the steel plate edge, and the steel plate remains clean without dross adhesion. However, the dross passes through the rolls in the bath, and no dross is pushed in.

(d) Furthermore, by arranging the bath suction/recovery port to face the fresh liquid supply flow and carrying out plate threading while sucking the bath, floating dross can be collected and removed extremely effectively. This makes it possible to more reliably prevent the harmful effects of floating dross.

(e) Even when the bath in the treatment tank is directly blown out from the inverted V-shaped bottom groove instead of the new solution, it is found to be highly effective in preventing dross intrusion.

The present invention was completed after confirming that the above-mentioned findings apply directly to actual continuous hot-dip plating processing, and by adding various studies and ideas. As shown in FIG. 1, in front of the sink roll 2 in the hot-dip plating bath 11 (the position indicated by the symbol A) and in front of the snap roll 13 (the position indicated by the symbol A), there are respectively opposed in the advancing direction of the steel plate to be plated 14. A header 15 for hot-dip plating metal spraying having a plurality of spray holes arranged in an inverted V shape is arranged, and the steel plate is passed through the bath while being sprayed from the header 15 onto the surface of the steel plate to be plated. Alternatively, for hot-dip plating metal spraying, a header 16 for suction of hot-dip plated metal is also arranged at the edge position of the steel plate path opposite to the header 15 for hot-dip plating, and the hot-dip plating metal is sprayed from the header 15 for blowing molten metal onto the surface of the steel plate to be plated. By spraying plated metal and passing the plate through the bath while sucking the flow of the hot-dip plated metal with the hot-dip plated metal suction header 16, it is possible to effectively prevent dross from being forced into the continuous hot-dip plated steel plate. It is characterized by the ability to stably manufacture sound plated steel sheets.

(Function) That is, during continuous hot-dip plating of a steel plate, at the positions indicated by the symbols A and 1 in FIG. 1 (just before the sink roll 12 and just before the snap roll 13, 13), as shown in FIG. A header 15 for hot-dip plating metal spraying having a plurality of spraying nozzles 18 arranged in an inverted V shape facing the direction of movement of the steel plate 14 to be plated which has passed through the snout 17 and entered the bath. When the plated steel plate 14 is passed through the plated steel plate 14 while spraying molten plated metal onto the plated steel plate surface from this header 15, the plated steel plate 14 gets caught in the fast flow generated by the movement of the plated steel plate 14 during the threading. The dross concentrated on the surface of the steel plate (floating dross and some toppled dross) is smoothly and reliably blown away from the center of the width of the steel plate toward both edges, and the dross concentrated on the surface of the steel plate is blown away smoothly and reliably, and the dross concentrated on the surface of the steel plate is blown away smoothly and reliably from the center of the width of the steel plate toward both edges. Almost no dross exists on the surface of the steel plate 14, and therefore, the sink roll 12 and the snap roll 13 do not cause indentation (ie, "dross defect #") due to dross entrainment.

In this case, as shown in FIG. 1 and FIG.
A suction header 16 is also arranged to suck the plating bath flow generated by the blowout from the header 15.
If the steel plate 14 to be plated is passed through the plated steel plate 14, the dross that is blown away after concentrating on the surface of the steel plate is effectively captured, the plating bath is purified, and the effect of preventing dross from being pushed in is further improved.

The "molten metal containing a large amount of floating dross" sucked in by the hot-dip plated metal suction header 16 is
As shown in FIG. 2, it is preferable to perform a cleaning process using filters 20, 21, etc. in the subbot 19 and then circulate it to the main pot. Thereby, it is possible to more reliably prevent dross from being pushed in.

Of course, when spraying hot-dip plated metal, it is preferable that the molten metal blown out from the nozzle 18 attached to the header 15 be filtered, but it is also possible to use hot-dip plated metal without filtration. As mentioned above, it has the effect of reducing dross defects.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> First, using the existing continuous hot-dip galvanizing equipment,
Positions A, B, and C shown in the figure (positions immediately before the sink roll and immediately before the snap roll) are arranged as shown in Figure 4 for the A position (position immediately before the sink roll), and positions B and C (positions immediately before the snap roll) are arranged as shown in Figure 4. For the position immediately before the roll), there is a header for hot-dip plating metal spraying which has a plurality of nozzles arranged in an inverted V-shape facing the advancing direction of the steel plate 14, each having the same shape as shown in Fig. 5. 15, and a hot-dip plated metal suction header 16 opposed thereto. In addition, at the position immediately before the sink roll (position A), only the surface side of the steel plate to be plated 14 is applied, and at the position immediately before the snap roll, the surface side of the steel plate to be plated 140 (position C)
As shown in FIG. 3, the headers are arranged on both sides of the back side (position B).

Next, using such continuous hot-dip galvanizing equipment, A
i' Contains 70.25% by weight and the remainder is substantially Z
A steel plate to be plated is placed in a hot-dip plating bath having a composition of
In addition to continuous immersion at a speed of m/Iwin, the hot-dip plating bath is sprayed onto the surface of the steel plate from the header 15 for hot-dip plating, and the hot-dip plating bath flow is applied to the hot-dip plating metal suction header 16. Manufacture of hot-dip galvanized steel sheets was carried out under suction.

The dross-rich molten plating bath sucked by the molten plating metal suction header 16 is collected in the sub-bond 19 and the dross is separated, as shown in FIG. It was circulated to the main pot.

When the quality of the hot-dip galvanized steel sheet manufactured by the method according to the present invention was compared with that obtained by the conventional method, the results were shown in Table 1 below. It was confirmed that the plating was reduced to 0, and the number of dross attached to the plated steel sheet was drastically reduced.

Furthermore, it has been found that when the method of the present invention is applied, the amount of bottom dross generated in the main pot is reduced to 1/3 to 1/4.

Summary of Effects> As explained above, according to the present invention, dross on the surface of a continuous hot-dip coated steel sheet is accurately removed in a bath in front of a roll in the bath to prevent dross from being pushed into the bath. This brings about extremely useful effects industrially, such as making it possible to stably mass-produce high-quality hot-dip plated steel sheets with excellent properties.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for preventing dross intrusion according to the present invention. FIG. 2 is a detailed explanatory diagram of part A in FIG. 1. 3 to 6 are explanatory diagrams of the hot-dip galvanizing equipment used in the examples. FIG. 7 is an explanatory diagram of a water model used to investigate the behavior of dross in a hot-dip plating bath. In the drawings: 1...Aquarium, 2...Water. 3... Resin powder, 4... Steel plate. 5.12... Think roll. 6.13...Snap roll. 7.17...Snout, 11...Hot-dip plating bath. 14... Steel plate to be plated. 15...Header for hot dip plated metal spraying 16...
Hot-dip plated metal suction header 18... Spraying is done through the mouth (
Nozzle), 19...Sub pot. 20, 21...filter.

Claims (2)

[Claims] (1) In the continuous hot-dip plating process of steel plates, a plurality of spray ports are arranged in an inverted V-shape in front of the sink roll and in front of the snap roll in the hot-dip plating bath, respectively, facing the advancing direction of the steel plate to be plated. A method for preventing dross intrusion into a continuous hot-dip plated steel plate, characterized by arranging a header for spraying hot-dip plated metal having the following properties, and passing the plate through the bath while spraying hot-dip plated metal from the header onto the surface of the steel plate to be plated. . (2) In the continuous hot-dip plating process of steel plates, a plurality of spray ports are arranged in an inverted V-shape in front of the sink roll and in front of the snap roll in the hot-dip plating bath, respectively, facing the advancing direction of the steel plate to be plated. A header for spraying hot-dip plated metal is arranged, and a header for suction of hot-dip plated metal is placed at the edge of the passageway of the steel plate to be plated opposite to this, and the header for spraying hot-dip plated metal is placed on the surface of the steel plate to be plated. A method for preventing dross from being forced into a continuous hot-dip plated steel plate, which comprises spraying plated metal and passing the plate through a bath while sucking the flow of the hot-dip plated metal using a hot-dip plated metal suction header.