JPH04154948A - Molten zinc bath cell - Google Patents

Abstract

PURPOSE:To prevent the generation of a galvanized sheet having the defective plating surface arising from the sticking of dross by constituting a galvanizing device of a plating bath cell having a specific shape and a dross settling cell adjacent thereto, gathering the formed dross to the settling cell and removing the dross. CONSTITUTION:A steel strip 15 to be plated is introduced into a plating cell 10 contg. a galvanizing bath 11 and is pulled up perpendicularly by a sink roll 14 in the galvanizing bath 11. The amt. of the molten Zn sticking to the steel strip 15 is adjusted by wiping nozzles 16 above the plating bath surface. The spacings between the inlet side wall surface 11b, side wall surface 11c and base 11a of the plating bath cell 10 and the sink roll 14 are reduced, by which the plating bath is moved at a high speed in an arrow direction on progression of the steel strip 15 and is put over a shallow flow passage 17 into the adjacent settling cell 12 where the dross in the plating bath 11 settles to the bottom in the settling cell 12 and deposits by forming a dross layer 20. Since the dross does not exist in the plating bath cell, the contamination of the galvanized steel strip 15 with the dross and the contamination of the plated surface do not arise.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a hot-dip zinc bath in a hot-dip galvanizing line, and more specifically, to a hot-dip galvanizing bath for preventing deterioration in the quality of galvanized steel sheets due to foreign matter deposited in the hot-dip galvanizing bath. Concerning the shape of zinc bathtubs.

<Prior art> Conventionally, when continuously hot-dip galvanizing a strip-shaped thin steel sheet, the steel sheet 1 to be plated is first drawn into a hot-dip zinc bath 2 and then placed therein, as shown in FIG. The molten zinc is pulled up vertically by the roll 3 in the bath, and the excess molten zinc that adheres to the surface of the molten zinc is removed by a pair of opposing wiping devices installed on the molten zinc bath 2. Equipment is used that uses the force of the airflow jetted from the nozzle 4 to blow off the plating to a desired thickness.

In such hot-dip galvanizing manufacturing equipment, foreign matter (hereinafter referred to as dross) is generated by chemical reactions between molten zinc and oxygen in the atmosphere, aluminum added to the molten zinc, and iron leached from the steel sheet to be plated. )
It is inevitable that dross will more or less accumulate on the bottom surface of the molten zinc bath 2, and this accumulated dross often causes very serious problems that impair the quality of the steel sheet I to be plated.

The dross deposited on the bottom of the molten zinc bathtub 2 remains deposited on the bottom as long as there is no flow of molten zinc and the situation is quiet, but this dross has almost no difference in specific gravity from the molten zinc. Moreover, since the molten zinc is violently agitated by the running of the steel plate 1 to be plated and the rotational movement of the rolls 3 in the bath, it often winds up and adheres to the steel plate 1 to be plated, resulting in a significant deterioration of the plating quality. It will be damaged.

Conventionally, in order to alleviate such inconveniences, the accumulated dross was frequently removed using a ladle, a large amount of aluminum was added to float the dross, and then the dross was scooped out. A structure is adopted in which the molten zinc bath 2 is deepened and the distance between the bottom surface of the bath 2 and the roll 3 in the bath is increased to increase the allowable amount of dross deposited and reduce the amount of rolling up. However, all of these operations are not easy, and it is extremely difficult to perform them while maintaining stable operations.

In addition, such a method has the drawback of not only reducing productivity but also increasing labor costs, equipment costs, etc., which is a major problem.

In order to deal with such problems,
Publication No. 34 discloses that a hot-dip galvanizing bath is divided into a plating tank and a reaction tank by a partition wall with an open bottom, and while plating is performed in the plating tank, a stirrer installed in the reaction tank The bath in the tank is forcibly stirred to promote the reaction between the bottom dross flowing into the reaction tank along the gentle slope of the bottom of the plating tank and the AI put into the bath in the reaction tank. U. By circulating the balanced bath through convection within the plating tank, an increase in bottom dross can be prevented, resulting in a low A
A hot-dip galvanizing method and apparatus capable of performing I-concentration operations have been proposed.

However, in this cited example, basically, after the bottom dross is deposited at the bottom of the plating waste, in order to let it flow down naturally into the reaction tank, the bottom end of the zinc roll and the bottom of the plating tank are The distance can be reduced only by the conventional allowable bottom dross deposition height, and it is not possible to drastically reduce the depth of the plating waste or reduce the capacity.

In addition, the angle of repose for the bottom dross to flow down is relatively large, so the bottom slope of the plating waste is at least 3
0' or more, and as a result, the depth of the plating waste and reaction tank becomes considerably deep.

Furthermore, since the bath surface between the plating waste and the reaction tank is separated by a partition wall, floating dross must be disposed of in the plating tank, and no improvements can be made in this regard. It has not been.

Therefore, there is no suitable technology capable of dealing with the above-mentioned problems, and no fundamental solution has been adopted.The present invention has been made to solve the above-mentioned problems.

The device of the present invention is disclosed in the above-mentioned Japanese Patent Publication No. 57-58434.
Unlike the method in the publication, the main aim is to prevent any bottom dross from settling and accumulating at the bottom of the molten zinc bath, making it possible to significantly reduce the depth of the bath, and to remove floating dross from the settling bath. Since it can be removed on the side, it is clearly easy to use in terms of workability.

While the apparatus of the present invention circulates the entire plating solution between the plating bath and the precipitation bath by the flow of the plating solution along with the movement of the steel plate, Japanese Patent Publication No. 57-58434 discloses that The major difference is that the plating solution in the entry area does not circulate as much.

<Means for Solving the Problems> The present invention provides a hot-dip galvanizing bath in a hot-dip galvanizing line, along with a steel plate to be plated wound around a roll in the bath.
and a plating bath formed by a bottom part that maintains a distance of 300 mm or less between the bottom face and the roll body circumference in the bath, and a side wall connected to the bottom part and forming an inclination greater than the angle of repose of the dross, and a shallow flow in the plating bath. It is composed of a precipitation bath connected via a channel and a pump installed in the precipitation bath, and prevents the precipitation of dross in the plating bath by the stirring action caused by the movement of the rolls in the bath and the steel strip to be plated. In addition, the generated dross is actively deposited in the precipitation bath, and the clean molten zinc from which the dross has been separated is transferred from the precipitation bath to the vicinity of the penetration position of the steel plate to be plated in the plating bath by a pump. This is a characteristic molten zinc bathtub.

Effects and Examples> The operation and embodiments of the present invention will be explained based on the drawings.

FIG. 1 is a diagram showing the structure of an embodiment of the apparatus of the present invention, and is a side sectional view seen from the side of a conveying line for a steel plate to be plated.

In FIG. 1, reference numeral 10 indicates a molten zinc bath according to the present invention, which consists of the main components of a plating bath 11, a settling bath 12, and a pump 13.

A bath roll 14 is disposed in the plating bath 11, and the steel plate 15 to be plated, which has been drawn in from the left, is turned vertically upward, and at this time, the surface of the steel plate 15 to be plated is coated with molten metal. Zinc adheres.

Steel plate 15 to be plated is pulled up from the plating bath 11
Further, the molten zinc passes between a pair of wiping nozzles 16 which are arranged above the plating bath 11 to face each other. It is blown away by the force of the airflow jetted from the plate and finished to the required amount of coating, that is, the thickness of the plating film.

The plating bath 11 has a bottom portion 11a having a curved surface.
The position of the center of this radius of curvature almost coincides with the position of the axis of the roll in the bath 14, and the radius of curvature is about lO~300 mm between the circumference of the body of the roll in the bath 14 and the bottom part 11a. The value is chosen to ensure a gap of .

The entrance side (wall surface 11b on the left in the figure) extending upward from the bottom 11a of the plating bath 11 is sloped at a gentler slope than the slope of the steel plate to be plated 15 entering, and this slope angle is set to prevent dross from accumulating. The angle of repose is greater than the angle of repose of the dross, and the slope is as steep as possible so as not to come into contact with the plated steel plate 15.

Furthermore, the wall surface lIC on the exit side (right side in the figure) of the plating bath 11 can be considered in the same way, but it is practically vertical.

Plating bath 11 and precipitation bath 1 placed in front of it
2 and 2 are connected to each other by a shallow channel 17, and the main purpose of this channel 17 is to gently guide molten zinc from the plating bath 11 to the precipitation bath 12 without any drop, and the bottom position of this channel is In order to prevent floating dross from getting caught here, it is usually designed to be at least 10 m deeper than the surface 18 of the molten zinc.

The settling bath 12 is for settling and separating the dross mixed in the molten zinc, and is designed to minimize the movement of the molten zinc in the bath in order to make it easier for the dross to settle and accumulate on the bottom surface. It has sufficient surface area and depth.

Another purpose of the precipitation bath 12 is to dissolve the zinc supplied here and maintain it at a required temperature, and the heating method here is to heat the wall surface of this bath from the outside with a gas burner or an electric heater. Alternatively, a method using a heating device attached to the wall surface of this device that generates heat from an induced eddy current is applied (not shown).

However, heating of the molten zinc may be carried out on the plating bath 11 side, or may be heated on both the plating bath 11 and the precipitation bath 12, depending on the case.

The pump 13 is for sending clean molten zinc from which dross has been separated in the precipitation bath 12 back to the plating bath 11, and the molten zinc that is pumped from this is sent to the piping 1
9 into the inlet side of the plating bath 11.

This pump 13 has its suction port at a moderate depth and as far away from the plating N11 as possible so as not to suck in the dross 20 deposited on the bottom of the settling bath 12 or the dross floating on the surface 18 of the molten zinc bath. It is installed so that it is in the correct position.

The function of the molten zinc bathtub 10 according to the present invention configured as described above will be described below.

The steel sheet 15 to be plated that entered the molten zinc from the inlet side of the plating bath 11 is changed direction by the rolls 14 in the bath and is conveyed vertically upward, and the rolls 14 in the bath follow the movement of the steel plate work 5 to be plated. It is pulled and rotates passively.

At this time, the bottom 11a of the plating bath 11 and the steel plate 1 to be plated are
5 or in the gap between the roll 14 in the bath and the molten zinc, which is stirred by frictional force, creates a strong flow in the direction of the solid arrow.

The present invention was carried out by focusing on the fact that dross cannot be precipitated and deposited on the bottom 11a of the plating bath 11 due to this flow.

The strength of this flow varies depending on the speed of the steel to be plated Fi11 or the width of the gap between the bottom 11a of the plating bath 11 and the steel plate to be plated 15 or the roll in the bath, but in actual operation it is 40 to 200 m. It has been found that in the speed range of /min, if the width of the gap is about 300 mm or less, dross cannot be precipitated and deposited on the bottom portion 11a.

Of course, since the inclination angles of the wall surfaces 11b and Ilc are more inclined than the angle of repose of the dross, it is natural that dross cannot be deposited on these surfaces.

In the embodiment, the gap between the bottom 11a of the plating bath 11 and the steel plate I5 to be plated or the roll 14 in the bath is
1 so that the steel plate 15 to be plated does not come into contact with the bottom part 11a and the speed of molten zinc flowing through this gap is as fast as possible.
00mm was selected.

In the plating bath 11 having this shape, there is always fast movement of molten zinc in any part, and dross cannot be deposited anywhere in the plating bath 11, so the dross that had been precipitated suddenly rolls up. It is impossible for this to impair the quality of the plated surface.

The dross generated in the plating bath 11 flows out through the channel 17 toward the precipitation bath 12 together with the molten zinc, and settles in the precipitation bath 12 with a gentle flow, leaving the dross 20 at the bottom. It accumulates as a result.

Clean molten zinc from which dross has been separated in the settling bath 12 is injected into the inlet side of the plating bath 11 via a pipe 19 by a pump 13.

Basically, the injection point into the plating bath 11 can be anywhere, but in order to eliminate the stagnation of molten zinc in the plating bath 11 and to ensure that the circulation with the precipitation bath 12 is as efficient as possible, there are certain points in the figure. This position as shown in is the most suitable.

The dross 20 accumulated in the settling bath 12 can be discharged automatically using a suction pump (not shown) or manually using a ladle, but in either case, this can be easily carried out during operation. can.

<Effects of the Invention> As described above, the hot-dip galvanizing tank according to the present invention not only solves the problems of settling dross being rolled up and making it difficult to discharge dross during operation, but also eliminates the problem of settling dross. It can demonstrate its features in various aspects, such as the ability to easily apply techniques such as lowering the temperature of molten zinc in the bath to accelerate the production and separation of dross.
The industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an embodiment of the apparatus of the present invention, and is a side sectional view seen from the side of a conveying line for a steel plate to be plated. FIG. 2 is an explanatory diagram of a conventional continuous hot-dip galvanizing apparatus for steel strips. 1... Steel plate to be plated, 2... Molten zinc bath, 3...
...Roll in the bath, 4...Wiping nozzle,
10... Molten zinc bath, 1]... Plating bath, H
a'--bottom, Ilb, 1lc-wall surface, 1
2... Sedimentation bath, 13... Pump, 14...
... Roll in bath, 15 ... Steel plate to be plated, 16
... Wiping nozzle, 17... Channel, 18...
Surface of molten zinc bath, 19...piping. 20...dross. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] In a hot-dip galvanizing bath on a hot-dip galvanizing line, there is a bottom part that runs along the steel plate to be plated wrapped around the roll in the bath and maintains a distance of 300 mm or less between the bottom surface and the circumference of the roll in the bath, and a dross connected to the bottom part. It consists of a plating bath formed by a side wall that is inclined at an angle of repose greater than The stirring action of the steel strip to be plated prevents the precipitation and accumulation of dross in the plating bath, and the generated dross is actively deposited in the precipitation bath, and clean molten zinc from which the dross has been separated is produced. A molten zinc bathtub characterized in that a pump is used to transport the steel plate from the precipitation bath to the plating bath near the entry point of the steel plate to be plated.