JP3385945B2 - Hot-dip metal plating equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot dip metal plating apparatus for batch hot dip metal plating of metal materials, and particularly to hot dip galvanizing suitable for performing a batch hot dip Al-Zn plating process using a wet flux. Regarding the device.

[0002]

2. Description of the Related Art Steel materials are widely used in structures in the form of rods, plates, pipes and other forms, or a combination thereof, but they are inherently susceptible to corrosion and are therefore used in various types of rust prevention. Means have been used. As such a rust preventive means, coating of a different kind of paint, metal, etc. on the surface of the steel material used as a structural material is performed, and as one kind of the metal coating, hot metal plating (hereinafter, simply (Also sometimes referred to as "hot dip plating"), especially hot dip galvanization is a relatively economical method of rust prevention, and it is very wide-ranging from small parts such as screws and bolts to large structural members such as H-shaped steel. Has been used. However, since the galvanized coating is inferior in corrosion resistance to salt corrosion in the vicinity of the coast, a corrosion-resistant coating having higher corrosion resistance has been demanded.

In such a background, it has been found that hot-dip Al-Zn alloy plating has significantly better corrosion resistance than hot-dip galvanizing. In particular, hot-dip Al-Zn alloy plating consisting of 55 wt% Al, 1.5 wt% Si, and the balance Zn not only excels in the corrosion resistance of the plating coating layer itself, but also achieves both sacrificial corrosion resistance for steel materials. It has been confirmed that it is the most excellent in that it is possible to achieve the above, and now it has reached a considerable industrial production in the corrosion-resistant thin steel sheet.

By the way, in the case of a continuous material having a constant shape such as a thin steel plate, generally, the hot-dip galvanizing can be performed continuously, and a hot-dip galvanizing bath is arranged on the outlet side of the continuous annealing equipment. It is performed in hot dip equipment. In a typical continuous hot-dip galvanizing equipment, the steel sheet is first cleaned by heating it in a weakly oxidizing non-oxidizing furnace, and then introduced into a reducing furnace connected to the non-oxidizing furnace to reduce and reduce it in an atmosphere containing hydrogen. Annealing is performed, and then it is immersed in a hot dip bath without being exposed to the atmosphere to perform hot dip plating.
The steel sheet is shielded from the atmosphere from the time of cleaning to the time of infiltration of the plating, during which degreasing and reduction of oxides are carried out, and the steel sheet infiltrates into the molten metal plating tank under the condition that the molten metal easily wets.

Such continuous hot dip metal plating equipment was developed for zinc plating, but is also used for aluminum plating and Al-Zn alloy plating. That is,
The hot-dip Al-Zn alloy plating can be operated by utilizing the hot-dip galvanizing equipment and method only by changing the composition of the plating bath and the operating conditions.

On the other hand, in the case of steel materials such as structural members and various parts, hot-dip galvanizing has been performed by a batch method by immersing the steel material in a hot-dip galvanizing bath in the atmosphere. In this case, even if the steel material is degreased and pickled in advance, it is inevitable to oxidize before the bath is infiltrated. Therefore, it is inevitably formed by using a flux consisting of salt, which is generally called flux. Means for melting oxides on the surface of steel and promoting wetting by molten metal have been used.

[0007] As a matter of introduction, there are a dry method and a wet method as the method of treatment with this flux, but the Al content is 45-
In the case of 60% by weight hot dip Al-Zn alloy plating treatment, the wet method, which is capable of fully exhibiting the flux function, is effective and is being industrially put into practical use.

Although the specification of the molten Al-Zn alloy plating bath is not mentioned in the prior art, in general,
For the material of the inner wall of the plating tank, a steel material that is highly corrosive due to molten Al-Zn alloy is not used, but refractory or graphite with weak corrosiveness is used. It is used after being shaped into a shape.

By the way, when such a hot-dip plated product is manufactured by a batch method, if it is not manufactured for a long time, Al
− Once the Zn alloy plating bath is solidified, the Al
-Repeat solidification-melting to dissolve the Zn alloy plating bath. However, by repeating such solidification-melting of the plating bath, cracks or cracks occur in the inner wall of the molten Al-Zn alloy plating bath, which not only significantly shortens the life of the plating bath, but also It was experienced that it could be very dangerous as it could leak from cracks and cracks.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to develop a technique for preventing the occurrence of cracks or cracks on the inner wall of a molten metal plating tank used when performing batch type molten metal plating.

A more specific object of the present invention is hot-dip Al-Zn alloy plating for preventing cracks and cracks on the inner wall of a hot-dip galvanizing bath used in a batch hot-dip Al-Zn plating method using a wet flux. Is to provide a tank.

[0012]

In order to solve the above-mentioned problems, the present inventors have decided on the hot-dip plating conditions, the heating conditions, the supply form of the material to be plated, and the inner wall shape of the hot-dip plating tank. Diligently studied. As a result, focusing on the importance of the inner wall structure of the hot dip bath, the conventional mechanism of inner wall cracking and cracking was grasped as follows.

That is, the cracking mechanism of the inner wall of the plating bath based on such knowledge is schematically shown in FIGS. 1 (a) to 1 (d). Although a wet flux is used in the illustrated example, the present invention relates to the structure of the batch type molten metal plating tank, and is not limited by the presence or absence of the flux and the type.

First, FIG. 1 (a) shows the melting of the plating bath 2 in the molten Al--Zn alloy plating tank 1. As shown in the figure, the material of the molten Al--Zn alloy plating tank 1 is refractory ( If the shape is a box, the wet flux is used in the surface activation treatment in the previous step, and therefore the flux 3 is brought into the molten Al-Zn alloy plating bath 2. See Figure 1 (b). Since the flux and the molten Al-Zn alloy do not react with each other, the flux 3 is likely to collect on the upper portion of the molten Al-Zn alloy plating bath and the inner wall portion. In the figure,
Shown in black. Then, when the plating bath is solidified, as shown in FIG. 1 (c), thermal contraction is observed in the plating bath 2, so that the flux 3 is present in the gap between the plating bath 1 and the plating bath 2.

Then, as shown in FIG. 1 (d), once the solidified plating bath is redissolved, the amount of thermal expansion of the plating bath 2 in the solid state is the refractory in the plating tank 1 via the flux. Is stressed, and cracks or cracks 4 are generated particularly in stress concentration portions such as corner portions.

Based on such knowledge, when the inner wall shape of at least the main part of the hot dipping bath is composed of a semi-spherical or semi-elliptical continuous inclined surface, when the solidified plating bath is redissolved, plating is performed. It was found that the amount of thermal expansion when the bath 2 is in the solid state can be released to the upper part, the stress applied to the inner wall portion via the flux 3 can be relaxed, and the cracking of the inner wall of the plating tank 1 can be suppressed, and the present invention Came to.

The present invention is as follows. (1) Comprising a molten metal plating bath containing a molten metal plating bath, characterized in that the inner wall cross-sectional shape of at least the main part of the molten metal plating bath is constituted by a continuous inclined surface, for batch type molten metal plating Hot metal plating equipment.

(2) The molten metal plating apparatus according to the above (1), wherein the inner wall of the molten metal plating tank is axisymmetric with respect to the central axis of the furnace bottom. (3) The molten metal plating apparatus according to (1) or (2) above, wherein the continuous inclined surface is a semicircular surface, an elliptical surface, or a tapered surface or a curved surface including a plurality of surfaces having an intersection angle of more than 90 degrees.

(4) The composition of the plating bath contained in the molten metal plating bath is Al: 45 to 60% by weight, Si: 0.5 to 2% by weight,
The hot-dip galvanizing apparatus according to any one of (1) to (3) above, which is aluminum-zinc (Al-Zn) alloy plating with the balance being Zn. (5) The molten metal plating apparatus according to (4) above, which performs batch type molten metal plating using a wet flux.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail with reference to the accompanying drawings, taking molten Al-Zn alloy plating using a wet flux as an example. The mechanism for preventing cracks on the inner wall of the plating tank in the present invention will be described with reference to the accompanying drawings. The same elements as those in FIG. 1 are designated by the same reference numerals.

First, FIG. 2 (a) shows a state in which the plating bath 2 is melted in the molten Al-Zn alloy plating tank 1, and the inner wall of the molten Al-Zn alloy plating tank 1 is composed of a continuous inclined surface 5 in cross section. ing. The material of the molten Al—Zn alloy plating tank 1 may be appropriately composed of a refractory material as in the conventional example.

As already mentioned, since the wet flux is used in the surface activation treatment in the previous step, during the plating treatment, as shown in FIG. 2 (b), the molten Al--Zn alloy plating bath 2 is used. Flux 3 is brought in. But,
Since the flux 3 and the molten Al-Zn alloy do not react with each other, the flux 3 gathers on the upper portion of the molten Al-Zn alloy plating bath and the inner wall portion, as shown by the black portion in the figure. However, in the case of the present invention, the inner wall of the plating tank forms the continuous inclined surface 5, and in particular, in the illustrated example, it has a semicircular or elliptical shape. Even if the flux 3 intervenes in the gap with the plating bath 2, as shown in FIG. 2 (c), the thermal contraction of the flux differs from the plating, and the depth of the plating bath only becomes shallow. No thermal distortion remains.

As shown in FIG. 1 (d), even when the plating bath is redissolved, according to the present invention, the inner wall of the plating tank 1 is composed of the continuous inclined surface 5, so that it is once solidified. Even if the plating bath is heated to expand its volume in the solid phase state, the stress generated therewith acts to push up the plating bath 2 and not to destroy the inner wall. In the illustrated example, since the continuous inclined surface 5 has a semicircular shape or an elliptical shape, the force due to the expansion of the plating bath acts as a slip on the inner wall and does not apply pressure. Therefore, according to the present invention, even if the plating bath is thermally expanded in the solid state, it does not press the inner wall of the plating tank and cracks or cracks do not occur. Such an effect is exhibited by making the main part of the plating tank a continuous inclined surface .

The following will supplement the shape and material of the inner wall of the hot dip bath. That is, regarding the inner wall shape of the molten metal plating tank, the cross-sectional shape is a continuous inclined surface, specifically, a semicircular shape, an elliptical shape, or a tapered surface or a curved surface including a plurality of surfaces with an intersection angle of more than 90 degrees. However, the effect is not limited as long as it can absorb the thermal expansion amount of the once solidified plating bath in the solid state.

Also, in the case of hot-dip metal plating of a long material, for example, the plating tank body may be formed in a gutter shape, and both ends thereof may be formed in a spherical shape or an elliptical shape, in which case the crossing angle with the longitudinal surface is 90. When the temperature is above the limit, it is possible to absorb the amount of thermal expansion as described above.

FIGS. 3 (a) to 3 (d) exemplify a hemisphere 6, an ellipsoid 7, a paraboloid 8, a rectangular prism 9 and the like, and the shape of the inner wall of the molten metal plating tank according to the present invention. . In any of the shapes, by letting the thermal expansion of the plating bath in the solid phase escape to the upper part, the stress applied to the inner wall portion can be relaxed, and in the present invention as a shape that exerts such an action effect, "continuous It is referred to as an "inclined surface", and it may be formed by combining a plurality of tapered surfaces, that is, a straight surface or a curved surface if the intersection angle α shown in FIG. 3 (d) is more than 90 degrees.

In any of the forms, the shape of the inner wall is preferably axially symmetrical with respect to the furnace central axis. More preferably, its planar shape is also composed of continuous curves. The material of the hot dip bath is not particularly limited. In general, the material is not particularly limited as long as it is a material that does not substantially react with the molten Al-Zn alloy such as refractory, ceramics and graphite.

The inner wall structure itself of the hot dipping bath may be the same as the conventional one, including the material thereof as described above, but by adopting the present invention, the cross-sectional shape of the inner wall is a continuous inclined surface. Depending on the type of material such as refractory, ceramics and graphite, it may be preferable to form the inner wall by integral molding or block formation, and such an aspect is also within the scope of the present invention.

[0029]

EXAMPLES Examples of the present invention will be described below. When the solidification and dissolution of the plating bath were repeated under the following test conditions, the results of crack evaluation of the refractory in the inner wall shape of the refractory (graphite) 30 mm thickness on the iron shell thickness of 20 mm are shown in Table 1. Shown in.

As can be seen from Table 1, when the coagulation-dissolution of the plating bath is repeated according to the present invention, cracks on the inner wall of the plating tank are more likely to be cracked in the hemispherical shape or the elliptical shape according to the present invention.
Compared with the case of the box shape of the prior art, the result of the present invention was favorable.

[0031]

[Table 1]

Test conditions: Plating bath condition: Zn-55% Al-1.6% Si Temperature condition of plating tank: 620 ℃ → Repeated normal temperature Flux component: Cryolite + NaCl + KCl

[0033]

According to the present invention, in the batch type molten Al-Zn plating method using a wet flux, the shape of the molten metal plating bath is made hemispherical or elliptical,
It is possible to prevent cracks and breaks on the inner wall of the molten metal plating tank and prolong the life of the molten metal plating tank.

[Brief description of drawings]

1 (a) to 1 (d) are explanatory views showing a crack generation mechanism of an inner wall of a molten metal plating tank by repeating solidification-melting of a plating bath in a conventional technique.

2 (a) to 2 (d) are explanatory views showing a mechanism for preventing cracks on an inner wall of a molten metal plating tank by repeating solidification / melting of a plating bath in the present invention.

3 (a) to 3 (d) are schematic explanatory views showing an example of the shape of the inner wall of the molten metal plating tank according to the present invention.

[Explanation of symbols]

1: Molten Al-Zn alloy plating tank according to conventional technology 2: Molten Al-Zn alloy 3: Flux 4: Cracks on the inner wall of the plating tank 5: Hot dip Al-Zn alloy plating tank according to the present invention

Continuation of the front page (56) References JP-A-50-15826 (JP, A) JP-A-50-57050 (JP, A) JP-B 39-24022 (JP, B1) (58) Fields investigated (Int .Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (5)

(57) [Claims] 1. A molten metal plating bath containing a molten metal plating bath, the expansion of the plating bath of the molten metal plating bath.
A molten metal plating apparatus for batch type molten metal plating, characterized in that the inner wall cross-sectional shape of the inner wall on which the force is applied is constituted by a continuous inclined surface. 2. The hot-dip galvanizing apparatus according to claim 1, wherein an inner wall of the hot-dip galvanizing bath is axisymmetric with respect to a central axis of the furnace bottom. 3. The continuous inclined surface is a semicircular surface, an elliptical surface,
3. The molten metal plating apparatus according to claim 1, which is a tapered surface or a curved surface including a plurality of surfaces having a crossing angle of more than 90 degrees. 4. The composition of the plating bath housed in the molten metal plating bath is Al: 45-60 wt%, Si: 0.5-2 wt%, and the balance Zn being an aluminum-zinc (Al-Zn) alloy plating. The molten metal plating apparatus according to any one of claims 1 to 3. 5. The molten metal plating apparatus according to claim 4, which performs batch type molten metal plating using a wet flux.