JPH04247861A - Continuous galvanizing method and device - Google Patents

Abstract

PURPOSE:To produce the galvanized steel sheet having excellent surface characteristics by controlling the accompanying flow generated by the viscosity of a plating bath and the bath flow derived therefrom. CONSTITUTION:A strip 1 is introduced to the plating bath in a molten zinc pot 3. While the progressing direction of the strip is changed by a sink roll 4 in the plating bath, the strip is continuously plated to produce the steel sheet. The accompanying flow generated by the viscosity of the plating bath and the bath flow derived therefrom as the strip 1 in the plating bath travels and the sink roll 4 revolves are controlled by a flow regulating device 5 having A, B, C parts and D, E parts. The flow regulating device 5 is provided between the sink roll 4 and the base of the pot 3. The galvanized steel sheet which is substantially free from dross flaws is easily obtd. in this way.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot-dip metal plating method and apparatus for suppressing the adhesion of dross to steel plates.

0002

[Prior Art] In the Sendzimer type, which is the mainstream of current hot-dip galvanizing methods, in which the strip is immersed in a zinc bath pot, compounds of FeZn7, Fe2Al5, and Fe/Al/Zn are mainly caused by the elution of Fe from the strip. Although the occurrence of inclusions (dross) such as these can be controlled to some extent by adjusting the Al concentration in the bath, etc., they are essentially unavoidable. Such dross adheres to the strip while the strip is being passed through the plating bath, and has a very adverse effect on the surface quality of the steel sheet. Therefore, several measures have been proposed to eliminate or suppress the negative effects of this dross. For example, ■methods based on removing dross from the bath using a ceramic filter (JP-A-62-151553, JP-A-63-140070, JP-A-63-50454;
(No. 1) Directly eliminating the adhesion of dross to the steel plate (Japanese Unexamined Patent Publications No. 151553/1982, 11747/1999) ■ Preventing the adhesion of dross to the steel plate using ultrasonic waves Method (Japanese Unexamined Patent Publication No. 2-125850) ■ Method of separating dross components by adjusting aluminum concentration by introducing a part of the bath outside the system (Japanese Unexamined Patent Publication No. 2-34761) ■ Preventing dross adhesion by adjusting plating bath components Law (Unexamined Japanese Patent Publication 1983)
(Japanese Unexamined Patent Publication No. 2-11744). However, these methods cannot be said to be industrially effective because they cannot completely eliminate the adhesion of dross and are economically difficult.

0003

Generally, the tendency of dross to adhere increases as the strip passing speed increases. In order to obtain the required plating performance, it is sufficient to stir the plating bath in an amount sufficient to uniformize the components and temperature of the plating bath, but by increasing the strip running speed, it is possible to improve the strip running and the rotation of the pot roll. As a result, the bath flow caused by mutual interference between the accompanying flow with the strip caused by the viscosity of the plating bath and the flow derived from interference with the inner wall of the plating bath pot becomes intense. As a result, the dross is rolled up and rolled in more violently, and the dross is more likely to adhere to the strip. This tendency is particularly remarkable when iron-zinc-based dross, called bottom dross, is present. In addition, the conventional Sendzimer type is also a device and method characterized by high productivity, but from the viewpoint of reducing manufacturing costs, securing product quantities that match demand, and improving productivity, it is possible to achieve strip threading without sacrificing quality. Improvements that can speed up the process are desired. Therefore, the present invention does not directly remove dross from the system, but does not disturb the bath flow in the molten zinc pot even when the strip passing speed increases, suppresses the adhesion of dross, and increases the The present invention provides a high-quality, high-productivity continuous hot-dip galvanizing method and apparatus.

0004

[Means for Solving the Problems] The continuous hot-dip galvanizing method and apparatus according to the present invention are characterized in that (1) a strip is guided into a plating bath in a hot-dip galvanizing pot, and the strip is guided in a plating bath while changing its traveling direction by a sink roll in the plating bath; In the manufacturing method of steel plate, in which strips are continuously plated, a rectifier is used to
A continuous hot-dip galvanizing method that controls the accompanying flow caused by the viscosity of the plating bath and the resulting bath flow as the strip travels in the plating bath and the sink roll rotates.
and (2) In a steel plate manufacturing equipment in which the strip is guided into a plating bath in a molten zinc pot and the strip is continuously plated while changing its traveling direction by a sink roll in the plating bath, the strip travels in the plating bath and sinks. Continuous hot-dip galvanizing equipment, characterized in that a rectifier is provided between the sink roll and the bottom of the pot to control the accompaniment flow caused by the viscosity of the plating bath and the bath flow derived therefrom as the roll rotates. Consisting of In other words, the flow of the plating bath that accompanies the strip threading is complex, but its elemental flow can be roughly divided into two types: - diagonal downward flow caused by the strip running from the front of the strip threading towards the sink roll; Horizontal flow caused by the running of the bottom surface that changes the flow. ■Upward flow caused by the strip running upward from the bottom of the sink roll.
■Rotational flow at the end face of the sink roll as the sink roll rotates.■Flow caused by the blowing out of the bath near the point where the longitudinal surface of the sink roll and the inner surface of the strip begin to come into contact, and the present invention controls these flows. This is what is intended. Compared to the specific gravity of the bath (bulk), dross can be roughly divided into those that are heavier than the bath (iron-zinc-based dross) and those that are lighter than the bath (iron-aluminum-based dross). Although they tend to float in the plating bath, those that have grown to a size of several tens of microns or more tend to float to the top of the plating bath or sink to the bottom if the bath flow is sufficiently small. The dross particle size that affects the surface quality of the steel plate is mainly several tens of microns or more, and it is highly effective to suppress the agitation of the entire bath caused by the above-mentioned flow, or to suppress it locally.

[0005]

[Operation] The continuous hot-dip galvanizing method and apparatus according to the present invention will be explained with reference to the examples shown in the drawings. FIG. 1 shows an example of an apparatus used in the method of the present invention, in which a is a schematic sectional view of a plating bath pot, and b is a schematic plan view. strip 1
is guided from a snout 2 on the outlet side of a reduction annealing furnace (not shown) into a plating bath pot 3 containing molten zinc-aluminum alloy, and progresses by a sink roll 4 provided in the pot 3. After changing direction and exiting the plating bath system, the amount of plating deposited is adjusted by gas wiping, etc., and then passed through an alloying furnace, a cooling device, etc., and the required plating is applied. In FIGS. 1(a) and 1(b), the flow of the bath that occurs before the strip 1 that has entered the plating bath from the snout 2 is changed in running direction by the sink roll 4 is rectified by the A part of the rectifier 5. damped and rectified by the section. In addition, the almost horizontal flow of the bath caused by the running of the lower surface portion of the strip 1 whose direction is changed by the sink roll 4 is rectified by the B section of the rectifying device 5 and mechanically shielded from the downward direction, and diagonally upward by the C section. It is rectified and released. That is, the bath flow caused by the running of the strip 1 in the plating bath is locally confined above the rectifier 5 by the rectifier 5. The rotational flow at the end face of the sink roll 4 as the sink roll 4 rotates and the flow caused by the blowing of the bath in the vicinity where the longitudinal surface of the sink roll 4 and the strip 1 begin to come into contact are shown in the D and E parts of the rectifying plate. It is controlled by the parts projecting from both ends of the sink roll 1. Although not shown in the diagram,
It is also effective to make these portions D and E into a weir shape. Strip 1 and sink roll 4 lower surface and rectifier 5
It is necessary that the distance between the rectifying device 5 and the rectifying device 5 is such that the rectifying effect of the bath is achieved and that dross does not accumulate on the upper surface of the rectifying device 5. This interval is preferably in the range of 10 mm to 500 mm. 10m
The reason why the width is greater than m is that if it is less than 10 mm, there will be a region where the bath flow cannot be fully controlled, and in actual operation, there is a risk of mechanical contact between the strip 1 and the rectifying device 5. In addition, the basis for 500mm or less is 500mm
Above is the normal strip running speed range (50-200
m/min), the rectification effect is reduced, and
This is because the space created by the rectifier 5 becomes a small pot in the plating bath pot 3, and there is a possibility that dross with a heavy specific gravity will begin to accumulate on the upper surface of the rectifier 5. A of rectifier 5
The angles formed by the portions and the B portions, and between the B portions and the C portions are not particularly limited, but are preferably from 110 degrees to 160 degrees.

FIG. 2 shows the second part of the apparatus used in the method of the present invention.
This is an example and shows a schematic cross-sectional view of a plating bath pot. This uses an arc-shaped rectifier, but the basic operation is the same as the example shown in FIG. 1. Moreover, FIG. 3 is a third example of the apparatus used in the method of the present invention, and shows a schematic cross-sectional view of a plating bath pot. This is used as a rectifier,
The simplest one, compared to the example of FIG. 1 and the example of FIG. Although the flow is damped and rectified by the method, the rectification is poor at the part where the flow is released, but compared to a plating method without a rectifier, it has a greater bath flow control effect. The distance between the lower surface of the sink roll 4 and the rectifier 5 is the same as the example in FIG. 1 . Also,
The effect when weirs are provided in portions D and E of the rectifier 5 is also similar to the example of FIG. 1. In addition, since the distance F between the bottom of the rectifier 5 and the bottom of the pot is required to be at least 50 mm for storing bottom dross, the present invention is implemented in a pot where the distance between the lowest surface of the sink roll 4 and the bottom of the pot 3 is less than 550 mm. In this case, when setting the upper limit of the distance between the lower part of the sink roll 4 and the rectifying device 5, priority is given to securing the distance F of 50 mm or more.

[0007]

EXAMPLES FIG. 4 shows the attained sheet passing speeds at which no dross defects are detected for three examples (FIGS. 1 to 3) used to implement the method of the present invention using an actual hot-dip plating line. The implementation conditions for this result are the plating bath temperature of 450 to 452°C.
, the aluminum concentration is 0.13 to 0.14%, the distance between the bottom of the plating bath pot and the lower end of the sink roll is 750 mm, and the distance between the lower end of the sink roll and the upper surface of the bottom of the rectifier is 200 mm. Note that the achieved plate passing speeds in the embodiment shown in FIG. 1 and the embodiment shown in FIG. 2 are speeds limited for other reasons, and these two speeds are not limited due to dross defects.

[0008]

According to the present invention, hot-dip galvanized steel sheets having excellent surface properties with almost no dross defects can be easily obtained at a very wide range of sheet threading speeds.

[0009]

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus showing an embodiment of the present invention (
(a is a schematic cross-sectional view, b is a schematic plan view)

FIG. 2 is a schematic sectional view of a device showing another embodiment of the present invention;

FIG. 3 is a schematic cross-sectional view of a device showing still another embodiment of the present invention;

FIG. 4 is a comparison between the embodiment of the present invention and the conventional method regarding the attained sheet passing speed at which no dross defects are detected.

[Explanation of symbols]

1 Strip 2 Snout 3. Plating bath pot 4. Think roll 5　Rectifier

Claims (2)

[Claims] Claim 1. A method for producing a steel plate in which a strip is guided into a plating bath in a molten zinc pot, and the strip is continuously plated while changing its traveling direction by a sink roll in the plating bath. A continuous hot-dip galvanizing method characterized by controlling the accompanying flow caused by the viscosity of the plating bath and the bath flow derived therefrom as the strip travels and the sink roll rotates. 2. A steel plate manufacturing apparatus in which a strip is guided into a plating bath in a molten zinc pot and is continuously plated on the strip while changing its traveling direction by a sink roll in the plating bath, in which the strip is guided into a plating bath in a molten zinc pot, and the strip is continuously plated while changing its traveling direction by a sink roll in the plating bath. Continuous hot-dip galvanizing, characterized in that a rectifier is provided between the sink roll and the bottom of the pot to control the accompanying flow caused by the viscosity of the plating bath and the bath flow derived therefrom as the sink roll rotates. Device.