JPH0121240B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to continuous plating equipment for steel plates, and in particular, it efficiently performs heat treatment of steel plates, cleaning treatment and activation treatment of steel plate surfaces, and selectively performs electroplating or molten metal plating. This invention relates to continuous plating equipment for steel sheets suitable for plating. [Background of the Invention] Although the continuous plating of steel sheets according to the present invention is not limited to galvanizing, the prior art will be described below using continuous electrogalvanizing as an example. Conventionally, continuous electrolytic galvanizing 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 plate markings with a hydrochloric acid or sulfuric acid aqueous solution, and plating in 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 decrease 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. Thorough pretreatment is therefore necessary. As described in Japanese Patent Application Laid-Open No. 58-87295,
Conventionally, pre-plating treatment, that is, degreasing, cleaning and surface activation treatment of steel sheets, has been performed using a wet method. That is, the steel plate is degreased and cleaned by dipping it in an alkaline aqueous solution or by spraying it.Since it is difficult to completely degrease with this alone, a positive or negative voltage is then applied to the steel plate in an alkaline aqueous solution to perform electrolytic degreasing. 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 an aqueous solution, the processing speed is slow, and at the same time, there is a risk that the oil and fats that have been eluted into the alkaline aqueous solution will re-adhere to the steel sheet during continuous sheet passing, resulting in re-contamination. This requires washing with water, which increases the length of the equipment, which is not preferable. 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 wet degreasing and cleaning treatment in an aqueous solution. Furthermore, cold-rolled steel sheets are usually used for electroplating, but in this case, the conventional method described above requires heat treatment of the steel sheets on a separate line, and it is not possible to perform continuous treatment on the same line. It was not effective in terms of productivity etc. Further, conventional continuous electroplating equipment has not been designed to be able to be used for hot-dipping of steel sheets. [Object of the Invention] The object of the present invention is to efficiently perform cleaning and activation treatment of a steel plate, and to perform an integrated process of heat treatment and electroplating of a steel plate, and to selectively also be used for molten metal plating. Our goal is to provide continuous plating equipment that can. [Summary of the Invention] The continuous plating equipment for steel strip of the present invention includes a preheating furnace, a non-oxidizing furnace that performs degreasing and cleaning treatment by high temperature decomposition in a non-oxidizing atmosphere, and annealing in a reducing atmosphere from the inlet side of the steel strip. A reduction annealing furnace for heat treatment, a cooling room maintained in a reducing atmosphere, a molten metal plating tank, a cooling device, a surface conditioning treatment device that applies a liquid film of acid aqueous solution to the steel strip to dissolve scale on its surface, and water washing. A shape correction device consisting of a 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 are arranged in sequence, and the surface conditioning treatment device and pickling tank are The acid aqueous solution therein can be discharged, the electroplating tank can discharge the plating solution therein, and the molten metal plating tank can freely inject and discharge the molten metal bath therein. , the steel strip is passed through with an acid aqueous solution put into the surface conditioning treatment device and the pickling tank, a plating solution put into the electroplating tank, and a molten metal bath being discharged from the molten metal plating tank. performing continuous electroplating on the steel strip, and discharging the acid aqueous solution from the surface conditioning treatment device and the pickling tank;
Continuous molten metal plating is applied to the steel strip by discharging the plating solution from the electroplating tank and passing the steel strip with the molten metal bath injected into the molten metal plating tank. It is characterized by the following structure. [Embodiments of the Invention] In the present invention, in order to solve the problems associated with conventional wet degreasing described in [Background of the Invention] and to perform the required heat treatment on the same line, degreasing and cleaning treatment is carried out in a non-oxidizing furnace. Do it at the same time. 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 fats and oils that have adhered to it. Here, the surface of the steel sheet is oxidized by heating and scale is generated, which significantly impedes the adhesion of the plating film, so the steel sheet is then kept at a high temperature in a reducing atmosphere consisting of hydrogen and nitrogen gas in a reduction annealing furnace. The scale is reduced and removed, and the steel plate surface becomes an active iron surface. By changing the furnace temperature of this reducing atmosphere, the steel plate can be continuously subjected to any desired annealing heat treatment. The steel sheet is heated by the above vapor phase degreasing treatment and heat treatment, and changes in shape such as warpage in the sheet width direction due to elongation occur, causing inconvenience in plating processing, so the shape is corrected and flattened using a tension leveler 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, less than 1 μm, it is destroyed during light rolling by the skin pass mill and tension leveler, 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 treatment step between the reduction treatment and the shape modification treatment to remove scale from the steel plate and make the surface condition suitable for shape modification. Surface conditioning treatment by scale removal is
This is achieved by chemical dissolution using an acid aqueous solution. The acid aqueous solution used in the chemical dissolution method for this surface conditioning treatment 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. Therefore, it is best to use it as an aqueous solution at an appropriate concentration. 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 order to perform surface conditioning treatment using this chemical dissolution method, it is most convenient and practical to set up a pickling tank filled with an acid aqueous solution and continuously immerse the steel plate. Therefore, in the present invention, the surface conditioning treatment is performed by the following means other than immersion in a pickling bath. In other words, the temperature of the steel plate after the above-mentioned reduction treatment process is usually about 450°C, and it is reduced to about 150°C in about 30 seconds by natural cooling and forced air cooling in the atmosphere.
cooled down to below. However, the oxidation of steel plate is approximately
At temperatures below 250°C, it is extremely slow, so the thickness of the scale is almost determined by the time it is cooled to approximately 450-250°C, and it is relatively thin at approximately 1000-3000Å, depending on the thickness of the steel plate. thin. For this reason, in the present invention, in order to remove scale, an effective method other than dipping the steel plate in a pickling bath is to form a liquid film of an acid aqueous solution on the surface of the steel plate, thereby dissolving the scale. do. Roll coating, as illustrated in FIG. 2, is an effective means for forming a liquid film. That is, as shown in FIG. 2, the acid aqueous solution 2 is lifted up by the pick-up roll 3, a thin film of the acid aqueous solution is formed on the applicator roll 4 that is in pressure contact with this, and the acid aqueous solution is transferred from the applicator roll 4 to the surface of the steel plate 1. death,
Dissolve scales with a thickness of 1000-3000 Å. It is preferable that the roll be a rubber-wrapped roll so that it is not eroded by the acid aqueous solution. If a rubber-wrapped 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 wiper 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 fiber or sponge can be used. In this way, the use of a roll coater or a wiper to form a liquid film of an aqueous acid solution has the advantage of making the apparatus more compact and increasing the 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. In addition, Figures 2 and 3
The surface conditioning treatment device shown in the figure is designed to allow the acid aqueous solution contained therein to be expelled to the outside. 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 degreasing and cleaning treatment and heat treatment described above. For shape modification, general methods such as light rolling using a skin pass mill, tension leveler, etc., and applying tensile elongation are used. In order to impart surface activity suitable for electroplating, the steel sheet after shape modification is pickled in a pickling tank, which is a common method for continuous electroplating, and after washing with water, the required plating thickness is determined in the electroplating tank. will be processed. Note that the acid aqueous solution in the pickling tank and the plating solution in the electroplating tank can be discharged. 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 manufactured. In the present invention, a hot-dip galvanizing tank is provided between the reduction annealing heat treatment step after the degreasing and cleaning treatment and the surface conditioning treatment step, and the steel strip passes through this tank. The hot-dip galvanizing tank is adapted to allow a hot-dip zinc bath to be filled or emptied into it. When carrying out the electroplating described above, this molten zinc bath is left empty. In addition, a molten zinc bath is poured into this tank, and the acid aqueous solution in the surface conditioning treatment device, the acid aqueous solution in the pickling tank, and the plating solution in the electroplating tank are discharged to operate the equipment of the present invention. In operation, hot-dip galvanized steel strip can be produced instead of electrogalvanized steel strip. As described above, by using the equipment of the present invention, it is possible to achieve a process in which electrogalvanized steel sheets and hot-dip galvanized steel sheets can be selectively manufactured as necessary within the same plating line very easily. Although the above explanation has been made with reference to galvanizing steel strips, the present invention is not necessarily limited to the production of galvanized steel sheets, and can be applied to general plating such as tin plating. It is applicable. 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 according to the present invention. In FIG. 1, the 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. The steel strip 1 is heated to about 450°C in a preheating furnace 8, and then transferred to a non-oxidizing furnace 9 in which the atmosphere is maintained at a weakly oxidizing to neutral atmosphere.
Inside, the steel strip 1 is heated to about 700°C, and cold rolling oil and the like adhering to the surface of the steel strip 1 are incinerated and degreased. Next, the steel strip 1 is placed in a reduction annealing furnace 10 in which the atmosphere is maintained in a reducing atmosphere consisting of a mixed gas of N ₂ and H ₂ .
It is heated to 750 to 800°C, and the scale generated in the preheating furnace 8 to the non-oxidation furnace 9 is reduced to obtain a clean iron surface. At the same time, the steel strip 1 is subjected to necessary heat treatment in the reduction annealing furnace 10. Next, the steel strip 1 is heated in a cooling chamber 11 maintained in the same atmosphere as the reduction annealing furnace 10.
It is cooled to 450°C, passed through an empty hot-dip galvanizing tank 12 containing no molten zinc, and drawn out into the atmosphere, where it is cooled to below 150°C 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 is reduced to 5wt%.
An acid aqueous solution prepared by adding 1wt% hexamethylenetetramine to sulfuric acid is applied to both sides of the steel strip 1 to dissolve it, and then the remaining acid aqueous solution is washed away in a water washing tank 15 and used for light rolling during shape correction in the next process. The surface is adjusted to suit. Then steel strip 1
is dried in a dryer 16, and then a shape correcting device consisting of a skin pass mill 17 and a tension leveler 18 corrects the warping of the plate caused during degreasing, cleaning and heat treatment, and flattens it. Then steel strip 1
The surface is activated with a 10wt% sulfuric acid aqueous solution in the pickling tank 19, and the acid aqueous solution remaining on the surface is washed away in the water washing tank 20, and then electrogalvanized with a zinc sulfate bath in the electrogalvanizing tank 21. will be administered. Table 1 shows the characteristics of the electrogalvanized steel sheet obtained in this example and the electrogalvanized steel sheet obtained as a comparative example in the process shown in FIG. 1, which did not include the surface conditioning step.

[Table] Example 2 An electrogalvanized steel sheet was manufactured in the same process as in Example 1 using the surface conditioning treatment apparatus 14 shown in FIG. 3. Surface conditioning treatment device 14
Then, an acid aqueous solution prepared by adding 1 wt % hexamethylenetetramine to 10 wt % hydrochloric acid was applied to the surface of the steel strip 1 to remove scale. As in Example 1,
The properties of the electrogalvanized steel sheet obtained were extremely satisfactory. Example 3 In the continuous galvanizing equipment shown in Fig. 1,
The hot-dip galvanizing tank 12 is filled with a 450°C molten zinc bath, the acid aqueous solution in the surface conditioning treatment device 14 and the acid aqueous solution in the pickling tank 19 are removed, and then the electrolytic galvanizing tank 21 is coated with zinc sulfate. The liquid was drained and emptied, and the steel strip 1 was continuously passed in the same manner as in Example 1 to obtain a beautiful hot-dip galvanized steel sheet. [Effects of the Invention] In the continuous plating equipment of the present invention, since fats and oils are decomposed at high temperature in a non-oxidizing atmosphere in a non-oxidizing furnace, degreasing can be performed without promoting oxidation of the steel sheet surface. Furthermore, in the next step, the reduction annealing furnace, annealing heat treatment is performed in a reducing atmosphere.
Since it is necessary to reduce only the extremely thin oxide layer formed on the surface of the cold-rolled steel strip, the annealing temperature can be adjusted to suit the steel type without raising the furnace temperature unnecessarily. Unnecessary softening of the material can be prevented. Furthermore, in pickling to activate the surface before electroplating, since scale has already been removed, an extremely short pickling time is sufficient. Since it can be done in a much shorter time than it would take to use electroplating equipment, it is possible to speed up electroplating equipment. In addition, degreasing, cleaning and heat treatment of steel strips are carried out on the same line.
Since plating processing can be performed, productivity is improved. Moreover, in the present invention, after the heat treatment in the reduction annealing furnace and before the electroplating treatment, a surface conditioning treatment suitable for correcting the change in shape of the steel strip due to the heat treatment is performed, so that the steel strip has a beautiful surface without any defects. An electroplated steel sheet can be obtained. Moreover, according to the equipment arrangement of the present invention, this surface conditioning treatment only requires dissolving and removing relatively thin scale, so it is not necessary to use large equipment such as immersion in a pickling tank, and to apply a film of acid aqueous solution to the steel. It has the advantage that a compact surface conditioning treatment device that applies it to the strip and dissolves scale on its surface is sufficient. Furthermore, according to the steel strip continuous plating equipment of the present invention,
By placing a molten metal plating tank in front of the surface conditioning treatment equipment, where the molten metal bath can be freely injected and discharged, electroplating and molten metal plating can be used on the same line, meeting the demand for thinner plating. It has the advantage that it is possible to economically manufacture tempered steel sheets depending on the purpose, such as electroplating for the needs of thicker plates and molten metal plating for the needs of thicker plates. In addition, electroplating has the feature that it is possible to obtain various types of plated steel sheets extremely easily by simply replacing the plating solution (aqueous solution) in the plating tank, and that multi-purpose plated steel sheets can be obtained. Although molten metal plating can only be applied to certain limited types of metals, it is extremely advantageous for mass production and is suitable for mass production of small numbers of products.The continuous plating equipment of the present invention has the characteristics of both. can be used separately on the same line, which has an extremely large industrial effect.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a plating process according to an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing an embodiment of a surface conditioning treatment apparatus used in the present invention. 1... Steel strip, 2... Aqueous acid solution, 3... Pick-up roll, 4... Applicator roll, 6...
Wiper, 7...Inlet equipment, 8...Preheating furnace, 9...
... Non-oxidation furnace, 10 ... Reduction annealing furnace, 11 ... Cooling room, 12 ... Melt plating tank, 13 ... Forced air cooling device, 14 ... Surface conditioning treatment device, 15 ... Water washing tank, 16 ... ... Dryer, 17 ... Skin pass mill, 18 ... Tension leveler, 19 ... Pickling tank, 20 ... Water washing tank, 21 ... Electrogalvanizing tank.

Claims (1)

[Claims] 1. A preheating furnace from the inlet side of the steel strip, a non-oxidizing furnace that performs degreasing and cleaning treatment by high temperature decomposition in a non-oxidizing atmosphere,
A reduction annealing furnace that performs annealing heat treatment in a reducing atmosphere;
A cooling room maintained in a reducing atmosphere, a molten metal plating tank, a cooling device, a surface conditioning treatment device that applies a liquid film of acid aqueous solution to the steel strip to dissolve scale on its surface, a water washing tank, a dryer, a skin pass mill, and A shape correction device consisting of a tension leveler, a surface activation device consisting of a pickling tank, a water washing tank, and an electroplating tank are arranged in sequence, and the surface conditioning treatment device and the pickling tank discharge the acid aqueous solution therein. The electroplating tank is capable of discharging the plating liquid therein, the molten metal plating tank is capable of freely injecting and discharging the molten metal bath therein, and the surface conditioning treatment device and A steel strip is formed by pouring an acid aqueous solution into a pickling tank, pouring a plating solution into the electroplating tank, and passing the steel strip in a state in which the molten metal bath is discharged from the molten metal plating tank. Continuous electroplating is applied, and
The acid aqueous solution is discharged from the surface conditioning treatment device and the pickling tank, the plating solution is discharged from the electroplating tank, and the molten metal bath is poured into the molten metal plating tank, and then the steel strip is passed through. 1. Continuous plating equipment for steel strips, characterized in that the equipment is configured to continuously apply molten metal plating to steel strips.