JPH077323Y2 - Bottom dross roll-up suppression device - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a device for suppressing the winding of bottom dross in hot dip galvanizing, especially hot dip galvanizing.

[Conventional technology]

Currently, in North America and Canada, road salt is sprayed to prevent freezing of roads in order to prevent automobile slip accidents caused by freezing of the road surface in winter. By the way, due to the rock salt spraying, the car body is exposed to a severe corrosive environment. Therefore, in terms of car body materials, surface-treated steel sheets with high corrosion resistance, especially exterior steel sheets, have weldability and workability similar to those of cold-rolled steel sheets, and alloyed hot-dip galvanized steel sheets with excellent corrosion resistance have attracted attention. Has been done.

The alloyed hot-dip galvanized steel sheet as a steel sheet for automobile exteriors is required to have extremely strict specifications such as sharpness after painting. However, in a hot-dip galvanizing line that produces alloyed hot-dip galvanized steel sheets, Fe in the strip elutes and reacts with Zn in the plating bath to reduce FeZn ₇ in order to keep the Al concentration in the plating bath low. Dross, which is the main component, is easy to generate, and it is very difficult to meet strict finishing specifications.

FIG. 2 is an explanatory diagram of a dross generation state during hot dip galvanizing.

The strip 1 sent to the plating tank 3 through the snout 2 goes around the sink roll 4 and collects.
5, After being plated through the stabilizing roll 6, it is taken out from the plating tank 3 and is wiped by the wiping nozzle 7.
It is sent to the next step after the Zn adhesion amount is adjusted. that time,
By reacting Fe eluted from the strip 1 with Zn in the plating bath, FeZn ₇ (dross) is formed and floats in the plating bath. A part of the floating dross 9 is combined with Al in the plating bath and floats as a top dross 10 on the bath top, and gradually accumulates on the bottom of the plating tank to form a bottom dross 8. Bottom dross 8 accumulated at the bottom of the plating tank
Is adhered to the surface of the strip 1 by being wound up in the plating bath by the accompanying flow 11 of the plating bath generated along with the movement of the strip 1 near the lower part of the sink roll 4.

When the bottom dross 8 is adhered to the strip 1 as described above, a surface non-uniform portion called a press spot occurs during pressing, which not only impairs the sharpness of the coated steel sheet, but also a non-uniform portion called a dross spot. The result formed,
It forms a local battery, causes surface defects that reduce the corrosion resistance of the product, and causes quality defects in the plated steel sheet. As described above, at the present time when the required quality and specifications for plated steel sheets have become strict, the occurrence of such surface defects on the steel sheet is a very serious problem, and its solution is strongly desired.

Therefore, various methods for preventing the dross from adhering to the strip have been conventionally considered. The general method is, for example, as disclosed in JP-A-47-38630 or JP-A-55-128564, by enriching the Al content in the plating bath and dross of Fe ₂ Al ₅ As a top dross, it is a method of floating on the surface of the plating bath and collecting it.

However, since Al has the effect of suppressing alloying of the plating film, the target of production is limited to the smallest possible amount in the case of alloyed steel sheet, which promotes generation of top dross and promotion of levitation. Therefore, when a large amount of Al is added, a part of the Al remains in the plating bath, causing poor alloying and causing a fatal problem of quality deterioration. Therefore, recently, countermeasures have been considered in the direction of preventing dross adhesion without relying on addition of Al. As such a countermeasure, a ceramic sheet is continuously supplied to the bottom of the plating bath to take out the bottom dross. No. 61-190055), an inert gas is bubbled in the plating bath to float as a floating dross together with air bubbles (JP-A-62-185863), Zn in the bath is circulated by an electromagnetic pump, It is known to remove dross with a dross filter (Japanese Utility Model Publication No. 57-52563).

However, there is a problem that the cost is high due to the use of a large number of ceramic sheets, and so far it has not been put to practical use. In addition, the measure (1) has a problem that the bottom dross removing effect is insufficient, and the bottom dross diffuses into the bath together with bubbles, which cannot be easily implemented. further,
However, there is a problem that the dross filter may be clogged in a short time, which is not practical.

Therefore, the applicant of the present application, by Japanese Patent Application No. 1-150832, rectifies the accompanying flow of the plating bath accompanying the progress of the strip below the sink roll immersed in the plating bath in the plating bath in the molten metal plating apparatus. We have proposed a bottom dross roll-up suppression device with a straightening plate.

FIG. 3 is a schematic side view showing an example of a bottom dross roll-up suppressing device proposed by the applicant, and FIG. 4 is a perspective view of a current plate used for this.

A current plate arranged on the bottom of the plating tank below the sink roll 5
Reference numeral 20 denotes a horizontal plate 21 located immediately below the sink roll 5, and a first inclined portion whose lower end is connected to the strip-entry side end of the horizontal portion 21.
22 and a second inclined portion 23 whose upper end is connected to the strip outlet side end of the horizontal portion 21, and below the horizontal portion 21 and the second inclined portion 23 are a vertical front wall portion 24 and a pair of side wall portions 25. It has been blocked. The width of the baffle plate 20 is equal to or longer than the total length of the sink roll 5.

According to such a bottom dross roll-up suppressing device, since the accompanying flow of the plating bath accompanying the progress of the strip 1 is rectified above the straightening vane 20 and the flow velocity is increased, the straightening vane 20
The bottom dross 8 is prevented from accumulating on the upper surface of
The bottom dross 8 accumulated on the bottom of the rectifying plate 20 due to the relative decrease in the flow velocity on the strip entrance side and the strip exit side.
By suppressing the winding of the dross, the dross adhesion to the strip 1 can be easily and reliably suppressed by the hydrodynamic means without depending on the addition of Al. Among the current plate, the current plate 20 of the type shown in FIG. 3 and FIG.
For example, the effect of winding up the bottom dross, which is far superior to the arc-shaped straightening plate that surrounds the lower portion of the sink roll 5, is shown.

[Problems to be solved by the device]

However, it has been found that such a bottom dross roll-up suppressing device has a difficulty in the durability of the current plate. That is, the material is highly durable against the plating bath.
Even if the current plate is made of a metal material such as SUS316L, it will be eroded after only a few months of use, and there will be holes on the surface that will obstruct the current function, or take the current plate out of the plating bath. It causes the bad effect that it becomes impossible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bottom dross roll-up suppressing device which does not deteriorate the excellent function of the above-mentioned type of current plate, but rather enhances the function thereof and extends the life thereof.

[Means for Solving the Problems]

The apparatus of the present invention has a straightening plate for rectifying the accompanying flow of the plating bath accompanying the progress of the strip below the sink roll immersed in the plating bath in the plating tank of the molten metal plating apparatus. A restraint device,
An upper surface of the straightening vane is located directly below the sink roll, a first inclined surface extending obliquely upward from a strip entrance side end of the horizontal surface, and an oblique downward direction extending from a strip exit side end of the horizontal plane. It is characterized in that it is composed of the projected second inclined surface and that the material surface constituting the second inclined surface is coated with a highly corrosion-resistant substance having low wettability with respect to the plating bath.

[Action]

The horizontal surface located immediately below the sink roll, the first inclined surface extending obliquely upward from the strip entrance end of the horizontal surface, and the second inclined surface extending obliquely downward from the strip exit end of the horizontal surface provide the upper surface. The constituted rectifying plate has a particularly excellent rectifying function. By coating the surface of the material forming the straightening vane with a highly corrosion-resistant substance having low wettability with respect to the plating bath, corrosion of the material forming the straightening vane is prevented and the plating bath on the upper surface of the straightening vane is prevented. The resistance to the accompanying flow is reduced, and the excellent rectifying function of the rectifying plate is further improved.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical side view showing an example of a current plate used in the device of the present invention.

The current plate 20 shown here includes a horizontal plate 21, a first inclined portion 22,
It has the 2nd slope part 23, the front wall part 24, and the side wall part 25 (4th.
See figure). Each part has a three-layer structure in which both sides of a plate-shaped main body 20a made of a metal material such as SUS316L are coated with a highly corrosion resistant substance 20b.

The high corrosion resistance substance 20b itself is a substance having excellent corrosion resistance to the plating bath, and a low wettability to the plating bath, and specifically, for example, a metal material such as WC-12Co and Mo,
Metal oxide ceramics such as Al ₂ O ₃ —TiO ₂ and CaO—SiO ₂ —ZrO ₂ can be mentioned.

The coating of the highly corrosion resistant substance 20b on the surface of the main body 20a is usually performed by thermal spraying.

The coating thickness of the highly corrosion resistant substance 20b is preferably 100 μm or more.

According to the bottom dross roll-up suppressing device using such a flow straightening plate 20, the accompanying flow of the plating bath accompanying the progress of strips guided by the peripheral surface of the sink roll above the flow straightening plate 20 is the upper surface of the straightening plate 20. Is rectified by and the flow velocity increases. As a result, the accumulation of bottom dross on the upper surface of the straightening vane 20 is prevented, and the relative lowering of the flow velocity on the strip inlet side and the stripping side of the straightening vane 20 suppresses the rolling up of the bottom dross accumulated on these portions. It Therefore, dross adhesion to the strip is suppressed.

At this time, since the surface of the main body 20a of the rectifying plate 20 is coated with the highly corrosion-resistant substance 20b having low wettability with respect to the plating bath, the rectifying effect with respect to the accompanying flow of the plating bath is high, and the dross adhesion to the strip is more effective. Be restrained by.

Further, since the body 20a of the current plate 20 is prevented from being corroded, an excellent dross adhesion preventing effect can be stably obtained for a long period of time. When the rectifying plate 20 is only the main body 20a, erosion holes were formed on the upper surface after about 6 months of use, but when the surface of the main body 20a is coated with a highly corrosion resistant substance 20b made of, for example, WC-12Co to a thickness of 100 to 150 μm No erosion holes were formed even after 1 year from the start of use, and the straightening plate 20 could be smoothly pulled up from the plating bath.

Acrylic powder that assumes bottom dross (true specific gravity 1.2, particle size 2
(50 ± 100 μm), and the acrylic powder concentration was measured just above the strip just before the sink roll to investigate the effect of suppressing bottom dross winding. When the concentration when the straightening vane was not installed was 100, the arc-shaped straightening vane surrounding the lower part of the sink roll could reduce the concentration to about 50, but the straightening vane shown in FIG. The concentration can be further reduced to a lower concentration of about 15, and in actual operation, the effect of improving rectification by the highly corrosion-resistant substance coated on the upper surface can be expected, so the effect of suppressing bottom dross winding is remarkable. By the way, the straightening plate in which the tilting directions of the first slanting portion and the second slanting portion were reversed was not so different from the arc-shaped straightening plate.

[Effect of device]

As is clear from the above explanation, the bottom dross roll-up suppressing device of the present invention can suppress the dross adhesion to the strip without depending on the Al concentration by the excellent hydrodynamic action of the flow straightening plate, and further, Has excellent corrosion resistance. Furthermore, a rectifying effect of a highly corrosion-resistant substance that enhances corrosion resistance can be expected, and the quality of plated products is further improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing an example of a current plate used in the device of the present invention, FIG. 2 is an explanatory view of a dross generation state during hot dip galvanizing, and FIG. 3 is a bottom dross proposed by the present applicant. Fourth schematic side view showing an example of the winding suppression device,
The figure is a perspective view of the current plate. 1: Strip, 3: Plating tank, 4: Sink roll, 8: Bottom dross, 20: Rectifier plate, 20a: Main body, 20b: High corrosion resistant substance.

Claims (1)

[Scope of utility model registration request] 1. A bottom dross roll-up control in which a straightening plate is arranged below a sink roll immersed in a plating bath in a plating bath in a molten metal plating apparatus to straighten the accompanying flow of the plating bath as the strip advances. In the device, an upper surface of the straightening vane is located directly below the sink roll, a first inclined surface extending obliquely upward from a strip entry side end of the horizontal plane, and a strip exit side end of the horizontal plane. Suppression of bottom dross winding, characterized in that it is composed of a second inclined surface that extends obliquely downward and that the surface of the material that forms the current plate is covered with a highly corrosion-resistant substance that has low wettability with respect to the plating bath. apparatus.