JPS61147900A - Method and installation for continuous electroplating of steel strip - Google Patents

Abstract

PURPOSE:To execute efficient continuous electroplating of a steel plate at a high speed and high productivity by executing simultaneously a high-temp. electrolytic cleaning treatment and annealing heat treatment of the steel strip in a gaseous phase and pickling and activating the steel strip after descaling and shape correction then subjecting the steel strip to electroplating. CONSTITUTION:The steel strip 1 is passed through an oxygen free furnace 9 via an inlet side installation 2 and a preheating furnace 8 of weak oxidizing property and is heated to the prescribed temp. The heated steel strip is degreased and cleaned by pyrolysis. The steel strip 1 is then passed through a reduction annealing furnace 10 in which a gaseous mixture atmosphere composed of N2 and H2 is maintained. The scale of the steel strip is reduced away and annealed in said furnace. Such strip is cooled to some extent in a cooling chamber 11 and is then passed through a zinc hot dipping cell 12 from which the strip is drawn into the atmosphere and is cooled by a forced air cooler 13. The strip 1 after cooling is treated with an aq. acid soln. in a surface treatment device 14, by which the strip is descaled. The descaled strip is subjected to washing 15 and drying 16, then to shape correction by a skin pass mill 17 and a tension leveler 18. The strip 1 is thereafter subjected to the surface activation by about 10% aq. sulfuric acid soln. in a pickling tank 19 and is continuously electroplated in a galvanizing tank 21 after washing 20.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to continuous electroplating of steel plates, and in particular to continuous electroplating of steel plates suitable for efficiently performing heat treatment of steel plates, cleaning treatment of steel plate surfaces, and activation treatment. Regarding electroplating methods and equipment.

[Background of the invention]

Although the continuous electroplating of steel sheets according to the present invention is not limited to galvanization, the conventional technology will be explained below by taking continuous electrogalvanization as an example.

Conventionally, continuous electrogalvanizing of steel sheets has generally been carried out by a series of wet processes including degreasing with an alkaline aqueous solution, activation of the steel sheet surface with a hydrochloric acid or sulfuric acid aqueous solution, and plating from a zinc sulfate bath.

It goes without saying that the performance of electroplated steel sheets is affected by the plating conditions, but pre-treatments such as degreasing, cleaning, and surface activation of the steel sheet also have a large effect.

Inadequate pretreatment particularly causes a decline in the uniformity and adhesion of the plating film, which significantly impairs the decorative properties and corrosion resistance that are the original objectives of plating. Therefore, thorough pretreatment is necessary.

As described in JP-A No. 58-87295, pre-plating treatment, that is, degreasing and cleaning of steel sheets, and surface activation treatment have conventionally been wet methods. In other words, the steel plate is degreased and cleaned by immersing it in an alkaline water bath or by spraying it.Since complete degreasing is difficult with this alone, electrolytic degreasing is performed by applying a positive or negative voltage to the steel plate in an alkaline aqueous solution. . Thereafter, the steel plate is washed with water, immersed in an aqueous acid solution such as hydrochloric acid or sulfuric acid to remove oxides on the surface and activated, and after washing with water, electroplating is performed.

However, since this method involves wet degreasing in a water bath, the processing speed is slow, and at the same time, there is a risk that the nine oils and fats that have been eluted into the alkaline water bath may re-adhere to the steel sheet during continuous sheet passing, resulting in recontamination. Therefore, sufficient washing with water is required, which is undesirable because the length of the equipment becomes long. Furthermore, since iron is eluted into the alkaline aqueous solution during electrolytic degreasing, a process for removing it is also required.

These problems inevitably occur in any wet degreasing and cleaning process in an aqueous solution.

In addition, cold-rolled steel sheets are usually used for electroplating, but in this case, in the conventional method described above, the steel sheets must be heat treated on a separate line, and it is not possible to heat-treat the steel sheets on a separate line. Therefore, it was not effective in terms of productivity. Further, conventional continuous electroplating equipment has not been designed to be able to be used for hot-dip plating of steel sheets.

[Purpose of the invention]

The object of the present invention is to provide a continuous electroplating method that can efficiently perform cleaning and activation treatment of steel sheets, as well as perform integrated processing of heat treatment and electroplating of steel sheets, and can also be selectively used for hot-dip plating. and provide facilities.

[Summary of the invention]

The continuous electroplating method of the steel strip of the present invention includes a step of simultaneously subjecting the steel strip to degreasing and cleaning treatment by high-temperature decomposition and annealing heat treatment in a gas phase, a surface conditioning treatment step of removing scale on the surface of the steel strip, and then a step of a surface conditioning treatment step of removing scale on the surface of the steel strip. Shape correction process to correct warpage,
It is characterized in that the main steps are a surface activation treatment step and an electroplating treatment step, which are combined in this order.

Further, the continuous electroplating equipment for steel strip of the present invention includes a preheating furnace, a non-oxidation furnace, a reduction annealing furnace, a cooling chamber kept in a reducing atmosphere, a cooling device, and an acid aqueous solution brought into contact with the steel strip from the steel strip inlet side. It consists of a rest adjustment device for removing scale on the surface, a shape modification device consisting of a water washing tank, a dryer, a skin pass mill, and a tension leveler, a surface activation device consisting of a pickling tank, a water washing tank, and an electroplating tank. It is characterized by the fact that

[Embodiments of the invention]

In the present invention, in order to solve the problems associated with the conventional wet degreasing described in [Background of the Invention] and to perform the necessary heat treatment on the same line, the degreasing and cleaning treatment is performed in a gas phase. Degreasing and cleaning treatment in the gas phase can be carried out simply and at a high processing speed by heating the steel plate to a high temperature and incinerating the attached oil needles. Here, the surface of the steel sheet is heated and oxidized to form scale, which significantly impedes the adhesion of the plating film, so it is then kept at high temperature in a furnace with a reducing atmosphere consisting of hydrogen and nitrogen. is reduced and removed, making the steel plate surface an active iron surface.

By changing the temperature in the reducing atmosphere 6 furnace during this vapor phase degreasing step, the steel plate can be continuously subjected to any desired annealing heat treatment.

The steel sheet is heated during the vapor phase degreasing treatment and heat treatment, and changes in shape such as warping in the sheet width direction due to elongation occur, which causes problems in plating processing, so the shape is corrected and flattened using a tension repeller or the like. However, when a steel plate that has been subjected to reduction treatment at a high temperature is supplied to a shape modification device, the high-temperature steel plate is oxidized in the atmosphere and scale is generated on the surface. Although this scale is thin, 1 μm or less, it is destroyed during light rolling using a skin pass mill and tension repeller, which are shape modifying devices, and the destroyed fine scale is pushed into the steel plate, causing surface damage and property deterioration. This problem can be solved by inserting a surface conditioning step between the reduction treatment and the shape modification treatment to remove scale from the steel plate and make it suitable for shape modification. Surface conditioning by removing scale can be achieved by gas phase methods such as glazma discharge or glow discharge in a room maintained in a reducing atmosphere, mechanical methods such as brushing with an abrasive brush roll, or chemical dissolution using an acid aqueous solution. The goal can be achieved by any method, including law.

Among these surface conditioning methods, a simple and practical method is a chemical dissolution method using an acid aqueous solution. The acid aqueous solution used in this method is preferably one or a mixture of two or more of inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as citric acid, oxalic acid, and tartaric acid, and is used as an aqueous solution of an appropriate concentration. It's good.

Further, it is practical to add an inhibitor to the acid aqueous solution in order to prevent loss of steel sheet base iron. The inhibitor to be added is preferably an organic compound rather than an inorganic compound, and amine compounds, sulfur compounds, triazole compounds, etc. are practical.

In the chemical dissolution method, the method of contact between the acid aqueous solution and the steel plate is important. A pickling tank filled with acid aqueous solution is installed,
Continuously immersing the steel plate is the simplest and most practical method. However, this is the amount of acid aqueous solution used);
Since the amount of water is also large, methods other than the pickling tank can also be used. That is, the temperature of the steel plate after the reduction treatment step is usually about 450°C, and is cooled down to about 150°C or less in about 30 seconds by natural cooling and forced air cooling in the atmosphere.

However, the oxidation of steel plates is extremely slow at temperatures below about 250°C, so the scale thickness is approximately 450°C to 250°C.
It is almost determined by the time the steel plate is cooled to 500X, and is relatively thin at approximately 1000 to 3000X, although it also depends on the thickness K of the steel plate. For this reason, there are effective methods for removing scale other than immersing the steel plate in a pickling tank. One method is to form a liquid film of an aqueous acid solution on the surface of the steel plate, and dissolve the scale using K. Roll coating is an effective method for forming a liquid film, as illustrated in FIG. That is, as shown in FIG. 2, the aqueous acid solution 2 is lifted up by the big aragroll 3, a thin film of the aqueous acid solution is formed on the africator roll 4 that is in pressure contact with the aqueous acid solution, and the aqueous acid solution is applied from the applicator roll 4 to the surface of the steel plate 1. Transcribe, 100
Dissolve scales from 0 to 3000X thickness. It is preferable that the roll be a rubber-wrapped roll so that it will not be corroded by the acid aqueous solution.

If a 9-round roll is used, the roll surface is flexible, so it can follow the surface shape of the steel plate. Alternatively, as illustrated in FIG. 3, the thin scale layer can be dissolved and removed by continuously applying the acid aqueous solution to the surface of the steel plate 1 using a soft wiper 6 impregnated with the acid aqueous solution. The material is preferably porous and highly elastic so that it does not damage the surface of the steel plate and can retain a large amount of acid aqueous solution, and glass fibers or sponge can be used. In this way, by using a roll coater or Wainohira to form a liquid film of an acid aqueous solution, the device can be made more compact.
Moreover, it has the advantage of increasing processing speed.

In addition to the above, the formation of a liquid film of the acid aqueous solution can also be achieved by spraying the acid aqueous solution or the like.

After the scale has been dissolved, the steel plate is washed with water to remove residual acid aqueous solution, and after drying, it is sent to the next shape correction device to correct shape changes such as warping in the width direction of the steel plate due to the heat treatment performed at the same time as the degreasing and cleaning described above. .

For shape modification, general methods such as light rolling using a skin repeller, tension repeller, etc., and applying tensile elongation are used.

After shape correction, the steel sheet is subjected to pickling, which is a common method for continuous electroplating, in order to give it surface activity suitable for electroplating, and after washing with water, it is plated in an electroplating bath to the required plating thickness. .

Through the above-mentioned series of processes, the process of degreasing and cleaning the steel plate, heat treatment, surface conditioning by removing scale, and correction of shape changes such as plate warping that occur during heat treatment can be carried out efficiently and consistently on the same line, resulting in high productivity. Electrogalvanized steel sheets are produced.

Furthermore, as shown in Example 3 below, if a hot-dip galvanizing bath is placed between the degreasing and cleaning process and the general surface conditioning process, it will be extremely easy to coat electrogalvanized steel sheets and hot-dip galvanized steel sheets in the same plating line. Steel plates can be manufactured selectively as required.

Although the above explanation was given for galvanizing steel strip,
The present invention is not necessarily limited to the production of galvanized steel sheets, but can be applied to general plating such as tin plating.

Examples of the present invention will be specifically described below.

Example 1 FIG. 1 shows an example of equipment for continuous electrogalvanizing of steel strips based on the present invention.

In FIG. 1, a steel strip 1 is a payoff reel.

It is continuously supplied by an inlet equipment 7 consisting of main equipment such as a cutting shear and a welder, and then enters a preheating furnace 8 which is isolated from the surrounding atmosphere and whose atmosphere is adjusted to be slightly oxidizing. Steel strip 1 is heated to approximately 450°C in preheating furnace 8.
The steel strip 1 is then heated to about 700°C in a non-oxidizing furnace 9 where the atmosphere is maintained at a slightly oxidizing to neutral atmosphere to incinerate cold rolling oil etc. adhering straight to the steel strip 1 and degrease it. be done. Next, the steel strip 1 was placed in an atmosphere of N2. ) A mixture of I2 is heated to 750 to 800°C in a reduction annealing furnace 10 (2) maintained at a reducing property consisting of S, and the scale generated in the preheating furnace 8 or non-oxidation furnace 9 is reduced to produce clean iron. It's a shame. At the same time, the steel strip 1 is subjected to necessary heat treatment in a reduction annealing furnace 10.Then, the steel strip 1 is cooled to about 450 c in a cooling chamber 11 maintained in the same atmosphere as the reduction annealing furnace 10.
It passes through an empty hot-dip galvanizing tank 12 containing no molten zinc, is drawn out into the atmosphere, and is cooled to 150° C. or lower by a forced air cooling device 13. Next, the steel strip 1 is introduced into the surface conditioning treatment device 14 shown in FIG.
The scale generated during the cooling process by 150'cK was
An acid aqueous solution prepared by adding 1 vt % hexamethylenetetramine to wt % sulfuric acid is dissolved by applying it to both sides of the steel strip 10, and then the remaining acid aqueous solution is washed away in a water washing tank 15 to be used for shape correction in the next process. The surface is adjusted to make it suitable for light rolling. The steel strip 1 is then dried in a dryer 16 and then in a skin mill 17. A shape correction device consisting of a tension leveler 18 corrects the warp of the board that occurred during the first degreasing and cleaning and heat treatment, and flattens it. Next, the surface of the steel strip 1 is activated with a 10vt% sulfuric acid aqueous solution in a pickling tank 19, and after washing and removing residual acid water on the surface in a water washing tank 20, zinc sulfate is applied in an electrogalvanizing tank 21. Electrogalvanized by bath.

Table 1 shows the characteristics of the electrogalvanized steel sheet obtained in this example and the electrogalvanized steel sheet obtained as a comparative example when the six adjustment steps of the steps shown in FIG. 1 were not included.

Example 2 An electrogalvanized steel sheet was manufactured in the same process as in Example 1 using the surface conditioning treatment apparatus shown in FIG. 3. In the mass processing adjustment processing equipment, 10V is applied to the surface of the steel strip l.
An acid aqueous solution prepared by adding 1 wt % hexamethylenetetramine to rt % hydrochloric acid was applied to remove scale. Implementation row 1
As in the case of , the properties of the electrogalvanized steel sheet obtained were extremely satisfactory.

Example 3 In the continuous galvanizing process shown in FIG. Then, remove the zinc sulfate plating solution in the electrogalvanizing tank 21, empty KL, and steel strip 1 in the same way as in LPJ1.
By continuous threading, we obtained more beautiful hot-dip galvanized steel sheets.

〔Effect of the invention〕

According to the continuous electroplating method of the present invention, the steel sheet is degreased by high-temperature decomposition in a gas phase, and the steel sheet is heat treated at the same time as the degreasing and cleaning, and the surface is adjusted to be suitable for correcting changes in the shape of the steel sheet due to heat treatment. As a result, beautiful electroplated steel sheets with no surface defects can be obtained. Furthermore, since heat treatment and electroplating of steel sheets can be performed within the same plating line, productivity is improved.

Furthermore, according to the continuous steel strip plating equipment of the present invention, by inserting a hot-dip plating tank in which the molten metal bath can be freely injected and discharged before the surface conditioning treatment device, electrolytic galvanizing and hot-dip galvanizing can be performed in the same manner. Can be used selectively on the line; electrogalvanizing is used for thinner coatings, and K for thicker coatings.
It has the advantage of being able to economically produce 11t hot-dip galvanized steel plates as needed for different purposes.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the plating process of one embodiment of the present invention, Fig. 2
3 are diagrams showing an embodiment of the surface conditioning treatment apparatus used in the present invention. 1... Steel strip, 2... Aqueous acid solution, 3...
・Pickup roll, 4... Applicator roll, 6... Wiper, 7... Entry side equipment, 8...
・Preheating furnace, 9... Non-oxidation furnace, 10... Reduction annealing furnace, 11... Cooling chamber, 12... Melting galvanizing tank, 13... Forced air cooling device, 14... Surface Adjustment processing device, 15...Washing tank, 16...Dryer, 1
7... Skin arm sumil 18... Te/shi, Nrepeller 19... Pickling tank, 20... Water washing tank,
21...Electrogalvanized tank. Figure 2 Diagram 3

Claims (1)

[Claims] 1. A step of simultaneously subjecting a steel strip to degreasing and cleaning treatment by high-temperature decomposition and annealing heat treatment in a gas phase, a surface conditioning treatment step of removing scale on the surface of the steel strip, and then correcting warpage of the steel strip. 1. A method for continuous electroplating of steel strip, characterized by sequentially combining a shape modification process, a surface activation process, and an electroplating process as main processes. 2. The method for continuous electroplating of a steel strip according to claim 1, wherein the degreasing and cleaning treatment of the steel strip is carried out in a heated atmosphere with adjusted oxidizing properties and in a heated reducing atmosphere. 3. The method for continuous electroplating of a steel strip according to claim 1, wherein the surface conditioning treatment of the steel strip is performed by immersion in an acid aqueous solution or by coating a liquid film with an acid aqueous solution. 4. From the inlet side of the steel strip, the preheating furnace, non-oxidation furnace, reduction annealing furnace,
A cooling room maintained in a reducing atmosphere, a cooling device, a surface conditioning treatment device that brings an acid aqueous solution into contact with the steel strip to remove scale from its surface, a shape modification device consisting of a water washing tank, a dryer, a skin pass mill, and a tension leveler, and an acid 1. Continuous electroplating equipment for steel strips, characterized in that a surface activation device consisting of a washing tank, a washing tank, and an electroplating tank are sequentially combined. 5. The surface conditioning treatment device and the pickling tank can discharge the acid aqueous solution therein, the electroplating tank can discharge the plating solution therein, and there is a space between the cooling chamber and the cooling device. 5. The continuous electroplating equipment for steel strips according to claim 4, wherein a hot-dip plating bath capable of freely injecting and discharging a molten metal bath is inserted.