JPH051357A - Hot-dip metal coating method - Google Patents

Abstract

PURPOSE:To execute a continuous hot-dip metal coating without developing defect caused by metal dust and dross, to obtain a good hot-dip metal coated product and to keep cleanness in a plating bath to geed condition for long time. CONSTITUTION:In the hot-dip metal coating method for applying the molten metal on a steel strip by bringing a coating roll contacting with a pick-up roll dipping a part thereof into the molten metal bath under non-oxidizing atmosphere into contact with the steel strip, oxygen concn. in non-oxidizing atmosphere is adjusted to 20-100ppm, and also, as the pick-up roll and the coating roll, the one with the surface formed of cobalt-base material, etc., and having <=90 deg.C wetting angle with molten metal, is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot metal plating method, and more particularly to a hot metal plating method for a surface of a metal strip that is continuously threaded.

[0002]

2. Description of the Related Art Various techniques for continuously plating a surface of a continuously moving metal strip with a molten metal bath have been proposed. For example, in Japanese Unexamined Patent Publication (Kokai) No. 54-155128, as shown in FIG. 4, a coating roll 5 is provided in contact with both sides of a moving steel strip 2, and at least one of the coating rolls 5 is provided so as to be in contact with and separated from each other. A device has been proposed. In FIG. 4, 1 is a chamber, 3 is a molten metal container, 4 is a pickup roll, 6 is a roll separating means, 7 is a direction changing roll for passing a metal strip plate, and 8 is a molten metal supply pipe. . The plating metal used includes zinc, lead, tin, aluminum, copper and the like, or alloy metals thereof. This device can perform double-sided plating, single-sided plating of the same metal, or different types of plating, does not need to install a plurality of plating lines, and is excellent in labor saving and process simplification. The plating chamber is kept in a weakly reducing or inert atmosphere to prevent oxidation of the steel strip.

Further, Japanese Unexamined Patent Publication No. 59-208060 discloses a single-sided hot dip galvanizing method in which the front side of the plating inside the plating chamber is a non-oxidizing atmosphere and the rear side of the plating is an oxidizing atmosphere. Proposed (see Figure 5). According to this method, it is possible to prevent the zinc vapor generated from the zinc plating bath from being cooled and deposited in the plating chamber, which adheres to the non-plating surface due to air flow or vibration and deteriorates the appearance and weldability. Is. Specifically, by mixing oxygen gas into the nitrogen gas for controlling the amount of adhesion and controlling the oxygen concentration in the rear of the room to 200 ppm or more, the adhesion of zinc dust can be almost prevented (see FIGS. 6 and 7). ).

Further, in Japanese Patent Laid-Open No. 57-210965, there is shown in FIG.
Corrosion-resistant metal on the surface 10 of the coating roll as shown in
A coating roll 9 for hot dip galvanizing has been proposed in which 11 is coated and dulled, and the surface of the dull 12 is coated with a non-ferrous metal 13. The non-ferrous metal 13 is coated (pre-coated) because, in general, corrosion-resistant metal has poor leaktability with molten metal,
This is to improve this leak property. According to such a roll, the plated metal can be reliably held on the roll surface, and the amount of lifting can be made constant to obtain a uniform amount of adhesion. The basic configuration of the plating apparatus using this roll (plating chamber, roll arrangement, etc.) is the same as that described in JP-A-54-155128.

[0005]

However, among the conventional plating apparatuses described in JP-A-54-155128, the atmosphere in the plating chamber is only a weak reducing or inert atmosphere. However, if the oxygen concentration in the chamber is too low, a large amount of vapor is generated from the molten metal and adheres to the surface of the steel strip as dust, impairing the surface quality, while if the oxygen concentration is too high, a large amount of dross is generated. Occurs, which causes a problem that the cleanliness of the plating bath cannot be maintained. That is, it is necessary to carry out plating within an appropriate oxygen concentration range, but the oxygen concentration is unclear because it is not described.

Further, in the technique described in JP-A-59-208060, zinc dust can be prevented from adhering by setting an oxidizing atmosphere at the back of the plating, but the cleanliness of the plating bath is the same as above. Then it causes a problem.

Further, in the technique described in Japanese Patent Laid-Open No. 57-210965, it is expected that the roll surface will be dull to improve the leak property between the plating bath and the roll, but the dull surface of the roll is It is transferred to a steel plate and causes problems such as deterioration of surface quality and severe change over time.

The present invention has been made in view of such circumstances, and an object thereof is to solve the problems of the above-mentioned prior art and to reduce the surface property due to the adhesion of metal dust to the steel strip surface. Also, it is possible to prevent the deterioration of the cleanliness of the plating bath due to dross, and further it is possible to prevent the deterioration of the surface quality due to the transfer of the roll surface shape to the steel sheet, and to manufacture a hot-dip galvanized steel strip with good surface quality. It is an object of the present invention to provide a hot-dip galvanizing method that can be performed.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have conducted extensive studies, and as a result, when performing hot metal plating in a non-oxidizing atmosphere, the oxygen concentration in the non-oxidizing atmosphere (ie, Oxygen concentration in the plating chamber)
Moreover, they have found that the properties and materials of the surface of the plating roll have a great influence on the finish of the plated surface, and have completed the present invention. That is, the present invention is a molten metal plating for coating a steel strip with a molten metal by bringing a coating roll, which is brought into contact with a pick-up roll partially immersed in a molten metal bath in a non-oxidizing atmosphere, into contact with the steel strip. In the method, the oxygen concentration in the non-oxidizing atmosphere is adjusted to 20 to 100 ppm, and the leak angle with the molten metal on the surface of the pickup roll and the coating roll is 90 ° or less. The main point is the plating method.

[0010]

The structure and operation of the present invention will be described. The present invention is based on the findings obtained as a result of repeated studies as described above, and the details are as follows.

That is, by controlling the oxygen concentration in the non-oxidizing atmosphere in the plating chamber in the range of 20 to 100 ppm, it is possible to suppress vapor generation of molten metal and dross generation,
Therefore, it is possible to prevent the deterioration of the surface property due to the adhesion of metal dust to the steel strip surface, and the deterioration of the cleanliness of the plating bath due to dross. On the other hand, when the oxygen concentration in the atmosphere is less than 20 ppm, zinc vapor, etc. A large amount of metal vapor is generated and condenses, resulting in the deposition of metal dust such as zinc dust on the plate surface to be plated. Conversely, when it exceeds 100 ppm, metal dross such as zinc dross is generated in the hot dip bath. It was found that the amount increased and the cleanliness of the hot dip bath decreased. Therefore, the present invention, as described above, to adjust the oxygen concentration in the non-oxidizing atmosphere to 20 to 100 ppm, thereby reducing the surface texture due to the adhesion of the metal dust to the steel strip surface, and
It prevents the deterioration of the cleanliness of the plating bath due to dross.

Further, when the oxygen concentration is adjusted to 20 to 100 ppm as described above and the leak angle with the molten metal on the surfaces of the pickup roll and the coating roll is set to 90 ° or less, the amount of molten metal picked up and the steel It was found that the amount of transfer to the band is stable, transfer of the roll surface shape to the steel plate is less likely to occur, and such an effect cannot be obtained when the leak angle exceeds 90 °. Therefore, the present invention provides
As described above, the leak angle with the molten metal on the roll surface should be 90 ° or less, thereby stabilizing the transfer amount of the molten metal to the steel strip and making the plating thickness uniform, and to the steel plate with the roll surface shape. It becomes possible to prevent the deterioration of the surface properties due to the transfer of the.

When the surfaces of the pickup roll and the coating roll are kept in a bright finish state with an average surface roughness Ra of 1 μm or less, transfer of the roll surface shape to the steel sheet can be prevented more reliably and good surface properties can be obtained. It becomes possible to obtain the product of. Further, the transfer amount does not change with time, and stable operation can be continued. Therefore, it is desirable to use those having a surface roughness Ra of 1 μm or less as the pickup roll and the coating roll.

[0014]

EXAMPLE FIG. 1 shows the overall structure of a molten metal plating apparatus according to an example of the present invention. The overall structure is similar to that of a normal continuous hot-dip galvanizing equipment for steel sheets, and the plating apparatus 25 is installed in connection with a continuous annealing furnace 80. 14 in the figure is a coil,
15 is a shearing machine, 16 is a welding machine, 17 is a louver, 18 is an alloying treatment furnace, 19 is a cooling device, 20 is a skin pass, 21 is a tension leveler, 22 is a chemical conversion treatment device, 23 is an oiler, and 24 is a coiler. ing.

Next, the structure and operating condition of the plating apparatus 25 will be described. As shown in FIG. 2, a plating chamber 27 formed by a chamber 26 controlled to a non-oxidizing atmosphere.
A diverting roll 28 is provided below. Steel plate 29
Is subjected to heat treatment in a continuous annealing furnace 80 so as to have optimum conditions for hot dip coating, and then converted from a horizontal direction to a vertical direction by a direction change roll 28.

A coating roll 30 is arranged in the plating chamber 27 so as to sandwich the steel plate 29. The component-adjusted plating agent (molten metal) 31 is supplied from a molten metal container 32 to a coating pot 34 in a plating chamber controlled to a non-oxidizing atmosphere by a pump 33 through a supply pipe 35. The molten metal in the coating pot 34 is transferred to the steel plate 29 via the pickup roll 36 and the coating roll 30. The coating amount is controlled by coating roll 30
This is performed by the adhesion amount control device 37 provided on the upper part.
Further, the molten metal container 32 is separately replenished with the molten metal from a replenishment line 38 according to the consumption amount of the molten metal 31.

The amount of molten metal supplied to the coating pot 34 is automatically adjusted by the process computer according to the line speed, the plate width, the target plating thickness and the like. In order to clean the metal supplied to the coating pot 34, an impurity removing device 39 is provided in the molten metal container 32. The impurity removing device 39 is composed of, for example, a ceramics filter. The molten metal supply pipe 35, the chamber 26, the coating pot 34, and the rolls 30 and 36 have a heating / heat insulating structure.

The steel plate 29 introduced into the plating chamber 27 comes into contact with the molten metal picked up on the surface of the coating roll 30 and is transferred onto the surface of the steel plate. After that, the amount of adhesion is controlled by adjusting the gas injection pressure from the gas wiping device 37 and adjusting the distance between the steel plate and the nozzle. The non-oxidizing atmosphere in the chamber 26 is performed by supplying a non-oxidizing gas from the gas jet into the chamber 26. At this time, if the gas is appropriately heated and supplied, the temperature decrease in the plating chamber may be further prevented.

The basic structure of the plating apparatus according to the embodiment of the present invention is as described above. Below, with respect to the process conditions (atmosphere in the plating chamber, each roll surface material, each roll surface texture) for producing a hot-dip plated steel sheet having a good surface texture and stably, based on an example in which zinc alloy plating was performed Explained.

Influence of atmosphere in plating chamber ---- FIG. 3 shows the relationship between the oxygen concentration in the plating chamber 27 and the amount of zinc vapor and dross produced. The minimum amount of zinc vapor and dross is shown when the oxygen concentration in the plating chamber is in the range of 20 to 100 ppm. That is, when the oxygen concentration exceeds 100 ppm, the dross (Z
nO) production increases, the cleanliness of the plated metal decreases, and the properties of the product surface deteriorate. On the other hand, the oxygen concentration is 2
When it is 0 ppm or less, a large amount of zinc vapor is generated, which adheres to and contaminates the product surface before and after plating, causes an unplated portion, and deteriorates the product surface property, which causes a serious problem. The bath composition in this example is 0.15% Al-Zn alloy system, and the bath temperature is 460 ° C.
It is controlled to be constant. Although the evaporation rate of zinc changes depending on the bath temperature, it shows a drastic change at 20 ppm in the temperature control range in actual operation.

Roll surface material ---- Table 1 shows the results of a basic investigation of the leak property between various roll surface materials and the plating agent (molten zinc alloy) in the range of suitable oxygen concentration.

[0022]

[Table 1]

As can be seen from Table 1, when the surface material of the roll is made of oxide (ceramic), chromium carbide or graphite, the leak angle with molten metal is poor in the measured oxygen concentration range, and the leak angle is θ. Indicates a value of 100 ° or more. On the other hand, the metal-based alloy had good leakability with the zinc alloy in any oxygen concentration range. However, in the case of the zinc alloy plating of this example, it is necessary to select an appropriate roll surface material from the viewpoint of corrosion resistance and abrasion resistance. For example, in stainless steel (No. 11 to 13) and carbon steel (No. 14), elution into the bath progresses due to contact with the zinc alloy bath, not only wear of the roll but also elution of roll surface material Will change the bath composition.

Based on the basic data obtained here, the validity was examined by incorporating it in an actual device, and a sample N
Good results were obtained with the cobalt-based materials of o. 1, 7, 8, and 10. In addition, stable plating could be performed even during long-term operation. Therefore, it can be said that it is desirable that at least the surface layer of the pickup roll and the coating roll is made of a cobalt-based material.

Roll surface properties ---- Table 2 shows the results of investigating the transfer condition to the strip by changing the roll surface roughness for the material having good leakability with the molten zinc alloy. The oxygen concentration in the plating chamber is constantly controlled at 20 ppm. If the surface roughness Ra is more than 1 μm to 3 μm, the pick-up amount varies in the roll width direction, or the pick-up amount is not picked up. there were. On the other hand, when the surface roughness Ra is 1 μm or less, the pickup amount from the coating pot is stable in all cases, and good transfer is performed to the strip via the coating roll. That is, the pickup roll,
By controlling the surface roughness Ra of the coating roll to 1 μm or less, stable (that is, uniform plating thickness and good surface properties) hot-dip plating could be stably performed. Moreover, the problem of transfer of the roll surface shape to the strip could be solved.

[0026]

[Table 2]

A specific operation example of the present invention will be described. Width 1200
mm, thickness 0.7 mm cold rolled steel sheet 17, line speed 100 m
It was soft annealed at 800 ° C. for 30 seconds in a heat treatment furnace at a speed of 1 minute / minute and passed through a plating apparatus 25. Coating roll has a diameter of 4
The surface material is Co type (No.8) at 00mmφ and the surface roughness is 0.3.
μm. The plating bath is 0.15% Al-Zn alloy and the temperature is
It was 460 ° C. Oxygen concentration in the plating equipment is 20 ppm
It is a nitrogen atmosphere. Under these conditions, a 10 μm thick plating was applied to obtain a zinc alloy-plated steel sheet. The surface of this plated steel sheet was smooth and no surface defects were observed.

[0028]

EFFECTS OF THE INVENTION Since the present invention has the above-described structure and functions, continuous hot-dip metal plating can be carried out without causing defects due to metal dust or dross.
Good molten metal plating products can be obtained, the cleanliness of the plating bath can be maintained in a good state for a long time, and the roll life is long and efficient operation is possible. It is a big place to do.

[Brief description of drawings]

FIG. 1 is a perspective view of an entire molten metal plating apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of a molten metal plating apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an oxygen concentration in a plating chamber and a generation rate of metal dust and dross according to an example of the present invention.

FIG. 4 is a cross-sectional view showing an example of a conventionally proposed hot metal plating apparatus.

FIG. 5 is a cross-sectional view showing another example of a conventionally proposed molten metal plating apparatus.

FIG. 6 is a diagram showing the relationship between the amount of mixed oxygen and the amount of zinc dust adhering to a conventional apparatus when nitrogen gas is being ejected.

FIG. 7 is a diagram showing a relationship between an air blowing amount and the number of zinc dust adhered in a conventional device.

FIG. 8 is a diagram showing an outline of a conventionally proposed improved hot-dip galvanizing roll.

[Explanation of symbols]

1--chamber, 3--molten metal container, 4--pickup roll, 7--direction roll, 8--supply pipe, 9--coating roll, 10--roll constituent metal, 11--corrosion resistant metal, 12--Dal, 13--Nonferrous metal, 14--Coil, 15--Shearing machine, 16--Welding machine, 17--Looper, 18--Alloying furnace, 19--
Refrigerator, 20--Skin Pass, 21--Tension Leveler, 22
--Chemical conversion equipment, 23--oiler, 24--coiler, 25--plating equipment, 26--chamber, 27--plating chamber, 28--direction changing roll, 29--steel plate, 30--coating roll , 31--molten metal, 32--molten metal container, 33--metal pump, 34--coating pot, 35--supply pipe, 36--pickup roll, 37--adhesion control device, 38--replenishment Line, 39--impurity remover, 80--continuous annealing furnace.

Claims (3)

[Claims] 1. A molten metal plating method for coating a steel strip with a molten metal by bringing a steel strip into contact with a coating roll which is brought into contact with a pickup roll partially immersed in a molten metal bath in a non-oxidizing atmosphere. In, while adjusting the oxygen concentration in the non-oxidizing atmosphere to 20 ~ 100 ppm, the leak angle with the molten metal of the surface of the pickup roll and the coating roll is 90 ° or less molten metal plating Method. 2. The hot-dip metal plating method according to claim 1, wherein the surfaces of the pickup roll and the coating roll have an average surface roughness Ra of 1 μm or less. 3. The hot-dip metal plating method according to claim 1, wherein at least the surface layers of the pickup roll and the coating roll are made of a cobalt-based material.