JP4523878B2 - Method and apparatus for producing surface-treated steel sheet with excellent appearance - Google Patents

Description

The present invention relates to a method and apparatus for manufacturing a surface-treated steel sheet, and more particularly to a method and apparatus for manufacturing an electroplated steel sheet or chemical conversion-treated steel sheet having excellent appearance and product yield.
Furthermore, the present invention relates to an apparatus for confirming the cleanliness of a steel sheet surface, which can easily and accurately evaluate the surface cleanliness of the steel sheet before the surface treatment, which is a prerequisite for a homogeneous and beautiful appearance quality.

  In recent years, surface treated steel sheets are required to have various performances such as press formability, weldability, and paintability in addition to rust prevention. However, the demand for uniform and beautiful appearance quality without uneven glossiness and color tone has not changed, and the demands from users have become more severe than ever.

In general, the appearance quality of a surface-treated steel sheet is greatly influenced by the surface state of the annealed cold-rolled steel sheet (original sheet). For this reason, in the pre-treatment process of the continuous annealing line, which is the pre-stage equipment of the surface treatment equipment, by performing alkali cleaning treatment, rinsing cleaning treatment, and liquid drainage treatment, the steel plate that is a prerequisite for homogeneous and beautiful appearance quality Ensures surface cleanliness. Moreover, the pickling process which removes the oxide film (scale) which exists in the steel plate surface may be performed between an alkali cleaning process and a rinse cleaning process as needed.
Here, the alkali cleaning treatment refers to a treatment for removing fats and oils such as rust preventive oil and temper rolling oil from the surface of the cold rolled steel sheet before annealing, and generally the cold rolled steel sheet is immersed in a degreasing treatment tank. Washed. The rinse cleaning treatment is a treatment for removing the cleaning liquid used in the alkali cleaning treatment from the surface of the alkali-washed cold-rolled steel plate. Usually, the alkali-washed cold-rolled steel plate is immersed in a cleaning bath (rinsing bath) for cleaning. However, it may be spray cleaned. Furthermore, the liquid draining process refers to a process of removing the rinse cleaning liquid used in the rinse cleaning process from the surface of the rinse-cleaned cold rolled steel sheet. For example, the rinsed cold rolled steel sheet is sandwiched between a pair of ringer rolls. The rinse cleaning liquid adhering to the steel plate surface is squeezed out.

  However, when the coating on the steel sheet surface is thick, such as hot dipping, it is possible to sufficiently ensure the cleanliness of the steel sheet surface by performing such pretreatment, but in the case of electroplating or chemical conversion treatment. Since the film coated on the surface of the steel plate is very thin, the appearance quality is particularly sensitive to the influence of the surface state of the original plate, and appearance defects are likely to occur compared to other surface treatments.

  As one form thereof, a streak-like or band-like pattern (hereinafter referred to as a liquid remaining pattern) appears on the surface of the surface-treated steel sheet due to slight contamination of the rinse cleaning liquid or insufficient drainage. Appearance defects are known (see, for example, Patent Document 1). The liquid remaining pattern is shown in FIG. 1 (a). This is because the rinse cleaning solution for immersing and washing the steel plate that has been subjected to alkali cleaning or pickling treatment is contaminated or if the rinse cleaning solution is insufficiently drained. Specific components contained in the cleaning solution will adhere to the surface of the steel sheet, and if annealing is performed in this state, the water will evaporate and the specific components that adhere will seize unevenly on the surface of the steel sheet. When surface treatment such as the above is performed, uneven adhesion of plating, etc. occurs in the part where the specific component is baked in and the part where it is not, and this appears as a streak-like or strip-like pattern, that is, a liquid residue pattern, and the appearance of the steel sheet This is a phenomenon that greatly impairs quality. When proper cleaning is performed, the liquid residue pattern does not appear as shown in FIG.

The first feature of the liquid residue pattern is that it cannot be easily discriminated by visual observation whether or not the above-mentioned specific component is seized on the surface of the steel sheet after annealing. For this reason, in spite of the specific component being baked on the surface of the steel sheet after annealing, a pickling / electroplating line, etc., which is a subsequent process, is passed through, so that a liquid residue pattern appears after the treatment, and the surface The work itself required for processing was wasted and the product yield was reduced. In addition, since a defective liquid pattern is not noticed until the liquid remaining pattern is developed, not only the original plate but also the work itself required for annealing is wasted, resulting in a decrease in product yield.
And this 2nd characteristic is that once the said specific component is seized on the steel plate surface by annealing, it cannot be easily removed. Even if it can be removed by pickling, the part where the specific component is burned out becomes a state where the surface is roughened due to peracid washing, and the part where the specific component is burned out and removed and the part that is not burned out As a result, uneven adhesion such as plating occurs, and eventually a liquid residue pattern appears.

In addition, although the mechanism by which a liquid residue pattern appears on a steel plate has not been clearly elucidated at present, the present inventor presumes as follows by original research.
The conditions under which the liquid residue pattern appears are as follows: (1) a certain amount of sulfate ions adhere to and dry on the steel sheet, (2) heat-treat the steel sheet, and (3) finally pickle. It has been confirmed by experiments that even if one condition is missing, it does not appear. Therefore, the mechanism of the remaining pattern is that after the rinse water with high sulfate ion concentration adheres to the steel sheet, when the steel sheet is heated in the annealing furnace, Fe-S based complex oxide is generated on the surface of the steel sheet and seizes. It becomes the state. This composite oxide is a substance that cannot be confirmed directly with the naked eye, but is difficult to remove with an acid. Therefore, unevenness occurs in the pickling process on the surface of the steel sheet where it is not generated, and a pattern appears. It is estimated that
As apparent from the above description, in order to prevent the occurrence of the liquid residue pattern and the decrease in product yield due to this, it depends on how the surface cleanliness of the steel sheet before annealing can be ensured.

In that case, one of the causes of the residual liquid pattern is a harmful component contained in the rinse solution, particularly sulfate ions, so it is very natural to try to solve the problem drastically by eliminating the expression factor itself. It is a way of thinking.
One of them is a method of using pure water as a rinse cleaning solution. Pure water has a very low concentration of harmful sulfate ions, and even if the drainage is insufficient, the amount of sulfate ions adhering to the steel sheet surface is very small, so the use of pure water can completely solve the problem. It should be.
However, a large amount of rinse cleaning liquid is required in the rinse cleaning process, and pure water is expensive, so it is not cost-effective and cannot be used in large quantities at the manufacturing site.

For this reason, many manufacturing sites have conventionally responded by using industrial water which is advantageous in terms of cost, and still respond by this method.
However, since industrial water is basically water drawn from reservoirs and rivers, the water quality varies greatly depending on the external environment such as weather conditions. For example, although the sulfate ion concentration in industrial water is low during the rainy season, the sulfate ion concentration increases in the summer when the sunny day continues.
Therefore, the method of using a large amount of industrial water to prevent contamination of the rinsing cleaning liquid can exert a certain effect if the sulfate ion concentration is low and the liquid draining is properly performed. Since the water quality fluctuates greatly depending on the actual environment, there was a fact that it was necessary to rely on the experience and know-how of skilled workers in determining the amount of water used. In addition, although it is industrial water that is cost-effective, the amount of water to be used is to be suppressed as much as possible. As described above, it is not uncommon to perform excessive cleaning with an emphasis on product quality. There was an aspect that could not be said to be a method.
In addition, the biggest problem in using industrial water is that industrial water contains sulfate ions, which are one of the harmful components, so unlike pure water, even if used in large quantities. In other words, the appearance of the liquid residue pattern may not be prevented.

Furthermore, even if the sulfate ion concentration is low, there is a problem that a liquid residue pattern appears if the subsequent draining is insufficient. That is, for example, in Patent Document 1, the cleaning liquid adhering to the steel sheet surface is drained with a ringer roll, then water vapor is sprayed onto the steel sheet surface for cleaning, and further draining is performed with a ringer roll disposed at a later stage. Although the method is disclosed, since the ringer roll is generally made of rubber, it is easy to get a streak-like scratch at the sharp edge of the steel sheet, and when the degree of the scratch progresses (deteriorates), the appearance of the liquid residue pattern It becomes one of the factors.
Specifically, when scratches occur in the ringer roll that presses the rinse cleaning liquid adhered to the steel sheet surface by pressing the pair of rolls onto the steel sheet surface, the rinse cleaning liquid concentrates on the scratched portion and passes through the ringer roll. The rinse cleaning liquid remains in the form of streaks or strips on the surface of the steel sheet. Therefore, when annealing is performed in this state, moisture is evaporated and the adhering harmful components are streaked or banded on the surface of the steel sheet, and when surface treatment such as electroplating is performed on the surface, this is striped or banded. That is, it appears as a liquid residue pattern, which greatly deteriorates the appearance quality of the steel sheet. This is a mechanism that even if the concentration of sulfate ions contained in the rinsing cleaning liquid is low, a residual liquid pattern appears when the liquid drainage becomes insufficient due to damage of the ringer roll or the like.

Therefore, as another approach, measure the amount of harmful components adhering to the surface of the steel sheet using a component analyzer, and confirm (control) that the amount of adhesion is less than the specified value before annealing and surface treatment. An application method is disclosed (for example, see Patent Document 1).
However, the data obtained by chemical analyzers, X-ray spectroscopic analyzers, etc. is only one point on the surface of the steel sheet, that is, point data at the measurement point, so the distribution and form of the deposits can be accurately grasped. Can not. For this reason, even if the adhesion amount is less than the specified value, a liquid residue pattern may appear after the surface treatment.
That is, as an aesthetics required for the surface-treated steel sheet, the entire surface of the surface-treated steel sheet is observed planarly (two-dimensionally) continuously, and whether or not the steel sheet surface is uniformly treated is determined. It is evaluated from the viewpoint of whether or not it has been processed, or whether the glossiness and color tone are uneven. Depending on the method, the distribution and form of the deposits can be grasped in a plane. For example, even if the sulfuric acid component is streaked or band-like and adheres to the surface of the steel sheet, it is not possible to grasp what range is distributed or whether the distribution is uneven. For this reason, when it was confirmed that the adhesion amount was not more than the specified value and annealing and surface treatment were performed, the liquid remaining pattern that appeared as a streak-like or band-like pattern could not be completely prevented.
Moreover, in order to make it possible to grasp the distribution and form of the deposits in a planar (two-dimensional) manner, an improvement measure for increasing the number of measurement points is conceivable. However, the above-described component analyzer generally has a small unit area that can be measured. Moreover, since the data on the amount of adhesion obtained is only an average value in the unit area, the distribution of the deposit on the steel sheet surface could not be accurately grasped.

In addition, except for the method described in Patent Document 1, a sample plate is similarly collected from a steel plate before annealing, and surface treatment such as annealing and electroplating is performed on the sample plate, and a liquid residue pattern appears on the sample plate. A method of annealing and surface treatment on the steel sheet to be subjected to surface treatment after confirming that it does not occur is also unthinkable.
According to this method, if the sulfuric acid component is in the form of a streak or strip and adheres to the surface of the steel plate, a liquid residue pattern appears on the surface of the sample plate, and this can be easily confirmed visually. The expression of the liquid residue pattern can be predicted more reliably than the method described in 1. In other words, if a liquid residue pattern does not appear on the surface of the sample plate, annealing and surface treatment can be performed with peace of mind. On the other hand, if a liquid residue pattern appears on the surface of the sample plate, the cleaning process in the pretreatment process can be performed quickly. It can correspond to.
However, it is necessary to newly provide an annealing facility and a surface treatment facility for the sample plate, which is not a practical method in terms of facilities and cost.
Japanese Patent Laid-Open No. 10-317180

In other words, in order to drastically resolve the appearance of the liquid residue pattern, it depends on how harmful components contained in the rinse cleaning solution are reduced. Therefore, it is necessary to use industrial water that contains sulfate ions, and the concentration of which varies greatly depending on the external environment such as weather conditions.
In addition, even if blessed with the external environment such as weather conditions, even if the sulfate ion concentration is low, if the drainage is not performed properly due to damage or wear of the ringer roll, a liquid residue pattern will appear. Sometimes it ends up. And since the rubber ringer roll is easily scratched at the sharp end of the steel plate, the liquid remaining pattern is more likely to appear.

On the other hand, if you have to use industrial water or rubber ringer rolls that easily get scratched, if there is a means to at least confirm that the liquid residue pattern will appear after the surface treatment Measures such as increasing the amount of water used, forcibly lowering the sulfate ion concentration, or replacing the ringer roll were not possible, but there was no means that was realistic in terms of equipment and cost. For this reason, the response is delayed until a liquid residue pattern appears on the surface of the steel plate after the surface treatment, and as a result, not only the original plate but also the work itself required for the surface treatment is wasted.
Furthermore, even if cleaning is performed only with industrial water without using pure water, it has a certain effect in preventing the appearance of residual liquid patterns when conditions are met. If there was a means to obtain the product, rinse cleaning and surface treatment could be performed with peace of mind, but there was no means that could be said to be realistic in terms of equipment and cost, so excessive cleaning, etc. I had to rely on it.

The problem to be solved by the present invention is that an electroplated steel sheet or a chemical conversion treatment that prevents the appearance of a liquid residue pattern and is excellent in appearance and product yield while using industrial water as a rinse cleaning liquid under such a background. It is providing the method and apparatus which can manufacture a steel plate.
Furthermore, the present invention provides an apparatus for confirming the cleanliness of a steel sheet surface, in which there is no means that can be said to be realistic in terms of equipment and costs, and whether or not a liquid residue pattern can be easily confirmed visually. It is.

The present inventor, how to prevent the appearance of the liquid residue pattern under the restriction that industrial water containing sulfate ions and whose concentration greatly varies depending on the external environment such as weather conditions must be used. As a result of various experimental studies on whether or not the above can be achieved, the following findings were obtained.
(A) Industrial water contains sulfate ions, which are harmful components, and its concentration varies greatly depending on the external environment such as weather conditions. Have an effect. In particular, when a sulfate ion concentration is 10 ppm or less, a predetermined effect is exhibited.
(B) However, even if the sulfate ion concentration in industrial water is low, a liquid residue pattern may appear if the drainage is insufficient due to damage of the Ringer roll, etc. It is necessary to confirm the cleanliness of the steel sheet surface by doing. In other words, it should be able to detect an increase in sulfate ion concentration, ringer roll damage, and the like.

From the above, even when the industrial water is used as the rinsing cleaning liquid, the present inventor performs sufficient drainage and easily confirms the distribution and form of sulfate ions seized on the steel sheet surface in the annealing furnace. If it can be done, it came to the knowledge that expression of a liquid residue pattern can be prevented. Therefore, the present inventor has obtained the following new knowledge as a result of conducting numerous theoretical and experimental studies in order to develop the new means.
(C) An electrolytic degreasing treatment and an electrolytic acid under predetermined conditions for an annealed plate in which sulfate ions are baked into stripes or strips on the surface, in other words, an annealed plate in which a liquid residue pattern appears if the surface treatment is performed as it is. When the washing process is sequentially performed, a pattern (hereinafter referred to as a pseudo pattern) very similar to the liquid remaining pattern appears on the surface of the annealed plate. That is, by using the new means, it is possible to detect the presence or absence of a liquid residue pattern and to detect an increase in sulfate ion concentration or ringer roll damage in the stage before the surface treatment after annealing.

  Based on the above knowledge, the present inventor is able to produce an electroplated steel sheet or a chemical conversion treated steel sheet having excellent appearance and product yield by preventing the appearance of a liquid residue pattern while using industrial water as a rinse cleaning liquid. And its apparatus, and a device for confirming the cleanliness of the surface of a steel sheet, in which there is no means that can be said to be realistic in terms of equipment and cost, and whether or not a liquid residue pattern can be easily observed visually. I came up with it. The gist is as follows.

(1) A cleaning treatment for either one or both of alkaline cleaning and pickling on a cold-rolled steel sheet, a rinsing cleaning process for removing the cleaning liquid adhering to the cleaning process from the steel sheet surface, and a rinsing cleaning liquid adhering to the rinsing cleaning process Either a pretreatment step of a continuous annealing line for performing a liquid draining treatment to be removed from the steel plate surface, an annealing step of continuously annealing the pretreated cold-rolled steel plate, and electroplating and chemical conversion treatment on the annealed steel plate or In the method of manufacturing a surface-treated steel sheet having a surface treatment process for performing both surface treatments, a sample is taken from the steel sheet before the surface treatment between the annealing process and the surface treatment process, and the sample is subjected to electrolytic degreasing treatment and electrolysis. Excellent in appearance, characterized by further comprising a cleanliness evaluation step that evaluates the cleanliness of the surface of the steel sheet depending on whether a predetermined pattern appears on the sample surface by sequentially performing pickling treatment A method for producing a surface-treated steel sheet.

(2) When the predetermined pattern is developed in the cleanliness evaluation step, either or both of the rinse cleaning ability and the liquid draining ability in the pretreatment step of the continuous annealing line are strengthened. The manufacturing method of the surface treatment steel plate excellent in the external appearance as described in 1).
(3) The method for producing a surface-treated steel sheet having excellent appearance according to (2) above, wherein the rinse cleaning ability is enhanced by using a rinse cleaning solution having a sulfate ion concentration of 10 ppm or less.

(4) The surface excellent in appearance according to any one of (1) to (3), wherein the electrolytic degreasing treatment and the electrolytic pickling treatment are performed at a coulomb amount of 30 to 240 C / dm ^2. A method for producing a treated steel sheet.
(5) The surface-treated steel sheet having excellent appearance according to any one of (1) to (4), wherein the electrolytic degreasing treatment and the electrolytic pickling treatment are performed at a temperature of 10 to 35 ° C. Production method.
(6) The electrolytic degreasing treatment is performed using an electrolytic degreasing solution having a NaOH concentration of 5 to 50 g / L, and the appearance according to any one of (1) to (5) is excellent. Manufacturing method of surface-treated steel sheet.
(7) The electrolytic pickling treatment is performed using an electrolytic pickling solution having an H ₂ SO ₄ concentration of 30 to 50 g / L, according to any one of (1) to (5), For producing a surface-treated steel sheet having an excellent appearance.

(8) An apparatus for visually confirming the surface cleanliness of a steel plate before electroplating or chemical conversion treatment, an electrolytic degreasing bath for electrolytically degreasing a sample taken from the steel plate, and electrolysis for electrolytic pickling of the sample Between a pickling bath, a sample immersed in an electrolytic degreasing solution housed in the electrolytic degreasing bath or an electrolytic pickling bath housed in the electrolytic pickling bath, and an electrode included in each processing bath A device for confirming the cleanliness of the surface of a steel sheet, comprising a power source for applying a DC voltage.
(9) Furthermore, means for holding the sample perpendicular to the surface of the electrolytic degreasing solution or electrolytic pickling solution, means for moving the held sample in a horizontal direction, and means for moving the held sample up and down The apparatus for confirming the cleanliness of the surface of a steel sheet according to (8), characterized by comprising:

(10) The cleanliness of the steel sheet surface as described in (8) or (9) above, wherein the electrolytic treatment in the electrolytic degreasing treatment tank and the electrolytic pickling treatment tank is performed at a Coulomb amount of 30 to 240 C / dm ² . Confirmation device.
(11) The apparatus for confirming the cleanliness of the steel sheet surface according to any one of (8) to (10), wherein the temperature of the electrolytic degreasing solution and the electrolytic pickling solution is 10 to 35 ° C.
(12) NaOH concentration of the electrolytic degreasing solution is 5 to 50 g / L, the steel sheet surface cleanliness confirmation device according to any one of (8) to (11) above.
(13) The apparatus for confirming the cleanliness of the steel sheet surface according to any one of (8) to (11), wherein the electrolytic pickling solution has a H ₂ SO ₄ concentration of 30 to 50 g / L. .
(14) A surface-treated steel sheet excellent in appearance, wherein the apparatus for confirming the cleanliness of the steel sheet surface according to any one of (8) to (13) is disposed on the exit side of the continuous annealing line. Manufacturing equipment.

According to the method and apparatus for producing a surface-treated steel sheet according to the present invention in which a steel sheet surface cleanliness evaluation process is newly provided between the annealing process and the surface treatment process, even if industrial water or a ringer roll is used. In addition, since it is possible to reliably and easily predict whether or not the liquid residue pattern will appear in the stage after the surface treatment after annealing, it is possible to stably produce an electroplated steel plate or a chemical conversion treated steel plate excellent in appearance and product yield.
Specifically, when the result that the liquid residue pattern appears in the stage after the surface treatment after annealing, the surface treatment work can be stopped quickly, and wasteful work that had to be performed by the conventional technology Can be prevented in advance. In addition, it is possible to quickly take measures to prevent recurrence such as increasing the industrial water used in the rinsing cleaning process, which is the upper process, and replacing the ringer roll. Yield can be improved.
On the other hand, when the result that the liquid residue pattern does not appear is obtained, the surface treatment as the next process can be performed with confidence, and the surface-treated steel sheet having an excellent appearance without the liquid residue pattern is obtained stably. be able to. In addition, the result that the pattern does not appear confirms that the cleaning performance in the rinsing cleaning process is normal, so it is possible for an inexperienced worker to rely on the experience and know-how of a skilled worker. Even if it exists, it can be operated under appropriate cleaning conditions, and the operation can be stabilized and the cost of rinse water can be reduced.
This contributes to the long-term stable operation of continuous annealing lines and electroplating or chemical conversion treatment lines, and to the homogeneous and beautiful appearance quality that has been increasingly demanded by users in recent years. Since the surface-treated steel sheet can be manufactured stably, the influence on the manufacturing quality and the economic effect are extremely large, and the industrial utility as well as the steel industry is extremely large.

Hereinafter, the best mode for carrying out the present invention will be described with reference to FIGS.
FIG. 2 is a flowchart showing one embodiment of a method for producing a surface-treated steel sheet according to the present invention, a pretreatment process of a continuous annealing line, an annealing process, and a cleanliness evaluation process that is the greatest feature of the present invention, and the surface And processing steps.

The pre-treatment process of the continuous annealing line consists of alkali cleaning treatment to remove oils and fats such as rust preventive oil and temper rolling oil from the steel sheet surface, and inorganic dirt existing on the steel sheet surface such as rust and oxide film (scale ), Pickling treatment for removing smut, etc., rinsing washing treatment for removing the washing liquid used in these washing treatments from the steel plate surface, and further a rinsing treatment for removing the rinsing washing liquid adhering to the rinsing washing treatment from the steel plate surface Consists of
In addition, as shown in FIG. 2, in the manufacturing method of the surface treatment steel plate which concerns on this invention, the case where a pickling process is not included is also included.

The alkali salt of the cleaning solution used in the alkali cleaning treatment is not particularly limited, and any one of sodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate, sodium cyanide, sodium borate and the like or Mixtures of these can be used.
If necessary, the detergency can be improved by adding an anionic surfactant or a nonionic surfactant to the alkaline cleaning liquid.
Also, the cleaning method is not particularly limited, and any one of immersion cleaning, brush cleaning, electrolytic cleaning, spray cleaning and the like can be used in combination.

The cleaning liquid used in the pickling treatment is not particularly limited, and any one of hydrochloric acid, sulfuric acid, nitric acid, or a mixture thereof can be used.
In addition, by adding a pickling inhibitor (inhibitor) as necessary, the surface of the steel sheet can be prevented from roughening and relatively uniform derusting and descaling can be performed. Moreover, the wettability of the steel plate surface can be improved by adding a pickling accelerator.
The cleaning method is not particularly limited, and any one of immersion cleaning, electrolytic cleaning, mechanical method, or the like can be used in combination.

As the rinse cleaning liquid used in the rinse cleaning treatment, as described above, not only pure water but also industrial water, ion-exchanged water, and the like can be used.
As a matter of course, it is effective to reduce the sulfate ion concentration of the rinse cleaning solution in order to suppress the appearance of the remaining liquid pattern, and it is preferable to set the sulfate ion concentration to 10 ppm or less.
This is a knowledge that has been clarified for the first time as a result of numerous experiments and analyzes by the present inventor, and the contents thereof are as follows.

As described above, the expression factor of the remaining liquid pattern is liquid drainage failure due to damage of sulfate ion and Ringer roll contained in the rinse liquid, but the present inventor has said that liquid draining is performed properly, The following experiment was conducted to investigate the limit value of the sulfate ion concentration at which the liquid residue pattern does not appear. FIG. 3 is a schematic diagram showing the investigation method.
First, a cold rolled steel sheet having a plate size of t0.2 mm × W900 mm was subjected to electrolytic degreasing and electrolytic pickling under the following conditions, and the cleaning liquid used in these treatments was completely removed using pure water.
[Electrolytic degreasing conditions]
NaOH: 20 g / L, liquid temperature: 55 ° C., current density: 20 A / dm ² , energization for 1.3 seconds [electrolytic pickling conditions]
H ₂ SO ₄ : 20 g / L, liquid temperature: 25 ° C., current density: 20 A / dm ² , energization for 1.3 seconds

Thereafter, a rinse solution having a sulfate ion concentration of 5, 10, 25, and 50 ppm was attached to the steel sheet at 5 g / m ² per side as shown in FIG. 3, and then 5% H ₂ residual N ₂ , dew point: − The plate temperature was raised to 650 ° C. in 30 seconds in an atmosphere of 40 ° C., and then maintained at 650 ° C. for 30 seconds. Subsequently, it cooled to 80 degreeC and de-furnaceed.
Thereafter, 3 g / L of Sn plating was applied to one surface of the annealed annealed plate under the following plating conditions, and it was observed whether or not a liquid residue pattern was developed.
[Plating conditions]
Sn ion concentration: 20 g / L, liquid temperature: 50 ° C., current density: 5 A / dm ² , energization for 11 seconds

  As a result, there was no problem in the appearance quality for the steel plate having a sulfate ion concentration of 10 ppm or less, but a liquid residue pattern was developed for the steel plate using the rinse solution having a sulfate ion concentration of 25 ppm and 50 ppm. Appearance quality was greatly impaired.

In addition, the same experiment was performed on the annealed plate when zinc plating was applied to one side of 5 g / m ² by an electrogalvanization line or when chromium plating was applied to one side of 100 mg / m ² by a tin-free steel line. However, there was no problem in appearance quality for the steel sheet having a sulfate ion concentration of 10 ppm or less, but a liquid residue pattern was developed in the steel sheet using the rinse solution having a sulfate ion concentration of 25 ppm and 50 ppm, and the appearance of the surface-treated steel sheet. Quality was greatly impaired.
Similarly, when the same treatment was performed on the annealed plate when phosphoric acid treatment was performed on one side of 8 mg / m ² or chromate treatment was performed on one side of 8 mg / m ² , Sn plating or the like was performed. The result was similar to the case.

Therefore, it is preferable to set the sulfate ion concentration to 10 ppm or less as the rinse cleaning liquid used in the rinse cleaning process.
In addition, although it does not specifically limit as a method to reduce a sulfate ion density | concentration, 2 pairs or more of ringer rolls are installed in the rinse tank exit side of the pretreatment process of a continuous annealing line, and in the lower stage of the final ringer roll By spraying pure water with a nozzle in the sheet width direction on the steel sheet, the sulfate ion concentration of the rinse cleaning liquid adhering to the steel sheet can be reduced.

The liquid draining process is not particularly limited, and liquid draining may be performed with a rubber ringer roll that is generally used. As described above, liquid draining is enhanced by increasing the number of ringer rolls installed. It is also possible to plan.
Further, as described above, regardless of the upper and lower stages of the ringer roll, the rinse cleaning ability can be supplementarily enhanced by performing spray cleaning with pure water or the like.

  An annealing furnace or annealing conditions are not particularly limited, and a continuous annealing line used in a manufacturing process of a general cold-rolled steel sheet or surface-treated steel sheet can be used.

Next, the cleanliness evaluation process, which is the greatest feature of the method for producing a surface-treated steel sheet according to the present invention, will be described.
In this process, a sample is collected from the steel sheet after annealing and before surface treatment, and the sample is subjected to electrolytic degreasing treatment and electrolytic pickling treatment in sequence, and a pattern very similar to the liquid residue pattern, that is, a pseudo pattern, appears on the sample surface. Confirm whether or not to do.
This is also the result of numerous experiments and analyzes by the inventor. As a result, an annealed plate in which sulfate ions are burned in the form of stripes or strips on the surface, in other words, an annealed plate in which a liquid residue pattern appears if surface treatment is performed as it is On the other hand, this is based on the first finding that a pseudo pattern appears on the surface of the annealed plate when electrolytic degreasing treatment and electrolytic pickling treatment are sequentially performed under the following conditions.

Tables 1 to 3 show the results of the experiment. On the ringer roll exit side, the sulfate ion concentration is intentionally 0 to 50 ppm so as to be symmetrical when viewed from the longitudinal direction. Spray the rinsing cleaning solution, and divide the coil into two in the longitudinal direction on the exit side of the annealing furnace, and apply plating to one coil (hereinafter referred to as this coil) with the electric Sn plating line, and the other The coils (hereinafter referred to as evaluation coils) are subjected to electrolytic degreasing treatment and electrolytic pickling treatment under the conditions shown in Tables 1 to 3, and then both coils are arranged so as to be in the form before division. This is an experiment on whether or not the liquid remaining pattern and the pseudo pattern appear symmetrically in the comparative observation.
The electrolytic degreasing conditions, the electrolytic pickling conditions in the pretreatment process, and the cleaning solution used in these treatments using pure water were completely removed, and the annealing conditions and Sn plating conditions for this coil were as described above. The conditions are the same as those used in the limit value investigation of the sulfate ion concentration at which the liquid residue pattern does not appear.
Furthermore, after the experiment, when the same experiment was performed using an electrogalvanizing line, a tin-free steel line, a phosphoric acid treatment line, and a chromate treatment line, the result was the same as that of the electric Sn plating line. It substitutes in Tables 1-3.
However, in the limit value investigation of the sulfate ion concentration at which the liquid residue pattern does not appear, liquid drainage failure, which is one of the causes of the liquid residue pattern, was removed from the experimental conditions for the purpose of investigation, but in this experiment In order to investigate the influence of liquid drainage failure, a flaw is intentionally provided on the ringer roll so that when the steel plate is viewed from the longitudinal direction, the lines are symmetrically formed.

The electrolytic degreasing treatment and the electrolytic pickling treatment are desirably performed at a Coulomb amount (current density × electrolysis time) of 30 to 240 C / dm ² .
As shown in the experimental results of Table 1, the degreasing / pickling ability is low at less than 30 C / dm ² , and the liquid remaining pattern appears in this coil, but the pseudo pattern does not appear in the evaluation coil. If it exceeds 240 C / dm ² , it becomes per-acid pickling, and even the pseudo pattern that appears is pickled and cannot be visually confirmed.
The electrolytic degreasing treatment and the electrolytic pickling treatment are desirably performed with the same amount of coulomb. If the electrolytic conditions for degreasing and pickling are changed, the control becomes complicated, and two sets of power sources for electrolysis are required, which increases the scale of the apparatus.

The electrolytic degreasing treatment and the electrolytic pickling treatment are desirably performed at 10 to 35 ° C. That is, the electrolytic degreasing solution and the electrolytic pickling solution are desirably 10 to 35 ° C.
As shown in the experimental results in Table 1, the degreasing / pickling ability is low at less than 10 ° C., and the liquid remaining pattern appears in this coil, but the pseudo pattern does not appear in the evaluation coil. Even if the temperature exceeds 35 ° C., a pseudo pattern appears, but a temperature raising device is required and it is not worth the cost.

For the electrolytic degreasing treatment, it is desirable to use an electrolytic degreasing solution having a NaOH concentration of 5 to 50 g / L.
As shown in the experimental results of Table 2, the degreasing capacity is low at less than 5 g / L, and the liquid remaining pattern appears in this coil, but the pseudo pattern does not appear in the evaluation coil. When it exceeds 50 g / L, foaming becomes intense and bubbles adhere to the surface of the sample. Even though the liquid remaining pattern does not appear in this coil, a pseudo pattern appears in the evaluation coil.

For the electrolytic pickling treatment, it is desirable to use an electrolytic pickling solution having a H ₂ SO ₄ concentration of 30 to 50 g / L.
As shown in the experimental results of Table 3, the pickling ability is low at less than 30 g / L, and the liquid remaining pattern appears in this coil, but the pseudo pattern does not appear in the evaluation coil. When it exceeds 50 g / L, it becomes per-acid wash, and even the pseudo pattern which expressed will be pickled, and it cannot confirm visually.

FIG. 4 is a schematic diagram of a steel sheet surface cleanliness confirmation apparatus 2 according to the present invention, and an electrolytic degreasing bath 3 for electrolytically degreasing a sample 1 collected from a steel plate before electroplating or before chemical conversion treatment, and an electrolytic degreasing solution. A washing tank 4 for washing the sample, an electrolytic pickling treatment tank 5 for electrolytic pickling of the sample, and a washing tank 6 for washing the electrolytic pickling solution.
Moreover, since the said cleanliness confirmation apparatus is equipped with the power supply 8, between the sample 1 immersed in the electrolytic degreasing liquid accommodated in the said electrolytic degreasing treatment tank 3, and the electrode 7 which the electrolytic degreasing treatment tank 3 comprises A direct-current voltage can be applied, whereby an electrolytic degreasing treatment for confirming the cleanliness of the steel sheet surface can be easily performed. Similarly, a DC voltage can be applied between the sample 1 immersed in the electrolytic pickling solution accommodated in the electrolytic pickling treatment tank 5 and the electrode 7 included in the electrolytic pickling treatment tank 5. Thus, the electrolytic pickling treatment for confirming the cleanliness of the steel sheet surface can be easily performed.

The cleanliness confirmation device 2 has means for holding the sample perpendicular to the surface of the electrolytic degreasing solution or electrolytic pickling solution, means for moving the held sample in a horizontal direction, and raising and lowering the held sample. It is desirable to provide means. Thereby, no matter how many people use the apparatus, the cleanliness of the steel sheet surface can be confirmed with good reproducibility.
That is, according to the cleanliness confirmation apparatus 2 for the steel sheet surface according to the present invention, even if the state of industrial water or ringer roll to be used is unknown, the liquid residue can be reliably and easily obtained at the stage before the surface treatment after annealing. Since it is possible to predict whether or not the pattern will appear, it is possible to stably produce an electroplated steel plate or a chemical conversion treated steel plate that is excellent in appearance and product yield.

Therefore, as shown in FIG. 2, the cleanliness confirmation device is desirably arranged on the exit side of the continuous annealing line. As a result, it is possible to perform surface treatment such as electroplating after confirming the cleanliness of the steel plate surface that has the most significant impact on the appearance quality of the surface treated steel plate in advance, so that plating defects etc. can be completely prevented Can do.
In addition, when a pseudo pattern appears, the surface treatment operation can be stopped promptly, preventing unnecessary work that had to be performed by the conventional technology, and rinsing cleaning ability and liquid in the pretreatment process of the continuous annealing line. It is possible to quickly take measures to prevent a recurrence such as strengthening one or both of the cutting capabilities, and to improve the appearance quality and product yield of the surface-treated steel sheet.
In addition, as the strengthening of the rinse cleaning ability, measures such as increasing industrial water used in the rinse cleaning process or reducing the sulfate ion concentration of the rinse cleaning liquid to 10 ppm or less, replacement of the rinse cleaning liquid, increase in the rinse cleaning tank, Alternatively, it is possible to take measures such as adding auxiliary cleaning such as spray cleaning with pure water or brush cleaning.
In addition, for enhancing the liquid draining ability, it is possible to take measures such as repair and replacement of the ringer roll, increase in the number of installed units, adjustment of the pressing pressure, or addition of a liquid absorbing ringer roll.

  On the other hand, when the pseudo pattern does not appear, the surface treatment as the next step can be performed with confidence, and a surface-treated steel sheet having an excellent appearance that does not exhibit the liquid residue pattern can be stably obtained. In addition, the result that the pseudo pattern does not appear confirms that the cleaning processing capability in the rinse cleaning process is normal, so that it is possible for an inexperienced worker to rely on the experience and know-how of a skilled worker. Even if it exists, it can be operated under appropriate cleaning conditions, and it is possible to stabilize the operation and reduce the cost of rinse water.

  Finally, the surface treatment process will be described. The surface treatment in the process is sufficient if the annealing plate is subjected to either or both of electroplating and chemical conversion treatment, and a general electric Sn plating line. Electrogalvanization line, tin-free steel line, phosphate treatment line, and chromate treatment line can be used, and the surface treatment conditions were also used in the investigation of the limit value of sulfate ion concentration where the liquid residue pattern does not appear. It is sufficient if the conditions can be implemented.

(A) is a figure in the case where a liquid residue pattern is developed by performing annealing / pickling after washing under improper conditions, and (b) is a liquid after washing under proper conditions, annealing / pickling. It is a figure when the remaining pattern does not express. It is a flowchart which shows 1 aspect of the manufacturing method of the surface treatment steel plate which concerns on this invention. It is a schematic diagram which shows the limit value investigation method of the sulfate ion concentration which does not express a liquid residue pattern. It is a schematic diagram of the cleanliness confirmation apparatus of the steel plate surface concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample 2 Cleanliness confirmation apparatus 3 Electrolytic degreasing processing tank 4 Water washing tank which wash | cleans electrolytic degreasing liquid 5 Electrolytic pickling processing tank 6 Water washing tank 7 which wash | cleans electrolytic pickling liquid 8 Power supply 9 Sample side wiring 10 Processing tank side electrode wiring

Claims (14)

Either or both of alkaline cleaning and pickling on the cold rolled steel sheet, a rinse cleaning process for removing the cleaning liquid adhering to the cleaning process from the steel sheet surface, and a rinse cleaning liquid adhering to the cold cleaning steel sheet from the steel sheet surface A pre-treatment step of a continuous annealing line for performing liquid draining treatment to be removed;
An annealing process for continuously annealing the pre-treated cold-rolled steel sheet;
In the manufacturing method of the surface treatment steel plate provided with the surface treatment process which performs the surface treatment of either or both of electroplating and chemical conversion treatment to the annealed steel plate,
Between the annealing process and the surface treatment process,
A cleanliness evaluation process in which a sample is taken from the steel plate before the surface treatment, the sample is subjected to electrolytic degreasing treatment and electrolytic pickling treatment in order, and the cleanliness of the steel plate surface is evaluated by whether or not a predetermined pattern appears on the sample surface. A method for producing a surface-treated steel sheet having excellent appearance, further comprising:
2. The method according to claim 1, wherein when a predetermined pattern is developed in the cleanliness evaluation step, either or both of the rinse cleaning ability and the liquid draining ability in the pretreatment step of the continuous annealing line are enhanced. For producing a surface-treated steel sheet having an excellent appearance.
The method for producing a surface-treated steel sheet having excellent appearance according to claim 2, wherein the rinsing cleaning performance is enhanced by rinsing using a rinsing cleaning solution having a sulfate ion concentration of 10 ppm or less.
Method for producing a high surface-treated steel sheet appearance according to any one of claims 1 to 3, characterized in that the electrolytic degreasing and electrolytic pickling in coulombs of 30~240C / dm ^2.
The method for producing a surface-treated steel sheet having excellent appearance according to any one of claims 1 to 4, wherein the electrolytic degreasing treatment and the electrolytic pickling treatment are performed at a temperature of 10 to 35 ° C.
The method for producing a surface-treated steel sheet having excellent appearance according to any one of claims 1 to 5, wherein the electrolytic degreasing treatment is performed using an electrolytic degreasing solution having a NaOH concentration of 5 to 50 g / L. .
Wherein the electrolytic pickling process, excellent in appearance according to any one of claims 1 to 5, H ₂ SO ₄ concentration and performing using an electrolytic pickling solutions 30 to 50 g / L surface A method for producing a treated steel sheet.
An apparatus for visually confirming the surface cleanliness of a steel plate before electroplating or chemical conversion treatment, an electrolytic degreasing bath for electrolytically degreasing a sample taken from the steel plate, and an electrolytic pickling treatment for electrolytically pickling the sample DC voltage between a bath, a sample immersed in an electrolytic degreasing solution contained in the electrolytic degreasing treatment bath or an electrolytic pickling solution contained in the electrolytic pickling treatment bath, and an electrode included in each treatment bath An apparatus for confirming the cleanliness of the surface of a steel sheet, comprising a power source for applying a pressure.
Furthermore, a means for holding the sample perpendicular to the surface of the electrolytic degreasing solution or the electrolytic pickling solution, a means for moving the held sample in a horizontal direction, and a means for raising and lowering the held sample were provided. The cleanliness confirmation apparatus of the steel plate surface of Claim 8 characterized by these.
The electrolytic degreasing treatment vessel and purifier verification apparatus of the steel sheet surface according to electrolytic treatment in the electrolytic pickling bath in claim 8 or 9, characterized in that in coulombs of 30~240C / dm ^2.
The temperature of the said electrolytic degreasing liquid and an electrolytic pickling liquid is 10-35 degreeC, The cleanliness confirmation apparatus of the steel plate surface of any one of Claims 8-10 characterized by the above-mentioned.
The NaOH concentration of the said electrolytic degreasing liquid is 5-50 g / L, The cleanliness confirmation apparatus of the steel plate surface of any one of Claims 8-11 characterized by the above-mentioned.
Cleanliness checking apparatus of the steel sheet surface according to any one of claims 8 _to 11 _H 2 SO ₄ concentration of the electrolyte pickling solution characterized in that it is a 30 to 50 g / L.
An apparatus for producing a surface-treated steel sheet excellent in appearance, wherein the apparatus for confirming the cleanliness of the steel sheet surface according to any one of claims 8 to 13 is arranged on the exit side of the continuous annealing line.

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