JPH083797A - Cleaning device for steel sheet and method for preventing discoloration using the same - Google Patents

Abstract

PURPOSE:To provide an excellent method for preventing the discoloration of a steel sheet free from problems both in quality and cost effectiveness in an electrolytic cleaning device in which a steel sheet is continuously cleaned. CONSTITUTION:In an electrolytic cleaning device in which a steel sheet 30 is continuously cleaned, a cleaning soln. discharging device 8 is provided closely to the electrode 7 of an electroytic cell 3. In the case of the stop of the steel sheet in the electrolytic cleaning device, the cleaning soln. is discharged toward the surface of the steel sheet from the vicinity of the electrode 7 of the electrolytic cell 3, by which the prevention of the discoloration of the steel sheet is executed. Thus, the discoloration of the steel sheet whose surface is activated can be prevented, the quality and yield are improved, and moreover, the cost effectiveness of a discoloration preventing agent can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic cleaning apparatus which does not cause discoloration on the surface of a steel sheet, and a method for preventing discoloration of a steel sheet after alkaline cleaning or alkaline electrolytic cleaning.

[0002]

2. Description of the Related Art In the process of manufacturing a steel sheet, alkali cleaning, alkaline electrolytic cleaning or the like is performed for the purpose of cleaning the surface of the steel sheet. FIG. 6A shows an example of such a horizontal electrolytic cleaning apparatus for alkaline electrolytic cleaning. In FIG. 6 (a), 3 is an electrolyzer, 4 is an inlet deflector roll, 5 is an inlet dip roll, 6 is an aqueous solution, 7 is an electrode, 11 is an outlet dip roll, 12 is an outlet deflector roll, and 30 is It is a steel strip. In this apparatus, the electrolytic bath 3 is filled with an aqueous solution 6 in which an alkaline cleaning liquid is dissolved, and the steel strip 30 is filled with a deflector roll 4 on the inlet side and a dipping roll 5 on the inlet side.
Is introduced into the electrolytic cell 3. Then, the steel strip 30 is passed between a plurality of pairs of electrodes 7 arranged above and below the pass line of the steel strip 30 close to and facing the pass line. Electrode 7
When electricity is applied, the water in the aqueous solution is electrolyzed and alkaline electrolytic cleaning is performed.

Such a horizontal electrolytic cleaning apparatus may be stopped while the steel sheet is immersed in the electrolytic cleaning apparatus. In such a case, the electrolytic rectifier is turned off to prevent the electrolytic voltage from being applied to the horizontal electrolytic cleaning device. However, in reality, the residual voltage remains between the electrodes, and O ₂ is generated to adhere to the surface of the steel sheet. , The steel plate is discolored.

As a method for preventing such discoloration of the steel sheet, there is a method described in Japanese Patent Publication No. 62-236. This method is a method of preventing discoloration of a steel sheet such as temper color by applying a reverse voltage having the same potential as the residual voltage to the electrodes.

On the other hand, in order to remove impurities adhering to the steel sheet after alkaline cleaning and alkaline electrolytic cleaning,
Although the surface of the steel sheet after alkaline cleaning and alkaline electrolytic cleaning is activated, it is rinsed with cleaning water, so if the line stops due to welding of the coil joint with the next coil, or the steel sheet surface Discoloration may occur on the surface of the steel sheet when the line speed decreases due to inspection, etc. As a method for preventing such discoloration of the steel sheet, a method disclosed in Japanese Patent Laid-Open No. 2-305985 has been proposed. FIG. 6B is a diagram showing an embodiment of such a conventional discoloration prevention method. In FIG. 6 (b),
13 is a scrubber part for polishing the plate surface with a brush roll,
14 is washing water, 31 is a conduit, 32 is a pump, 33 is a water supply pipe, and 34 is a rinse dip tank. The steel sheet 30 is washed in an alkaline electrolytic bath, the surface of the steel plate 30 is washed with a brush roll in the scrubber portion 13, and then rinsed with water in a rinse dip bath 34. The rinse water, to which the discoloration preventing material is added, is continuously supplied to the rinse dip tank 34 from the water supply pipe 33. The cleaning water 14 is continuously discharged from the conduit 31 by the pump 32 when the line is stopped, and the scrubber portion 13,
The steel plate 30 is washed with water in the rinse dip tank 34.

[0006]

However, the above-mentioned prior art has the following problems.

According to the technique disclosed in Japanese Patent Publication No. 62-236, when a line is stopped, a reverse voltage having the same potential as the residual voltage is applied to the electrodes as a countermeasure against the temper color due to the electrolytic residual voltage. Although it is effective to prevent discoloration, there is a problem in that it is difficult to prevent discoloration of the steel sheet due to the attachment of stains in the liquid.

The technique disclosed in Japanese Patent Laid-Open No. 2-305985 has the following problems. It is difficult to keep the concentration of the rinse dip tank constant. In order to prevent discoloration of the steel sheet when the line is stopped, the cleaning water in the rinse dip tank is used from the scrubber part and the rinse dip tank inlet / outlet part, so the cleaning level in the rinse dip tank is significantly reduced. For this reason, it is necessary to replenish water supply for the lowered level, but it is also necessary to replenish the discoloration preventive agent with the water supply replenishment, which increases the running cost. If the rinse dip tank is used continuously for a long time, the solution of the discoloration inhibitor is contaminated, which affects the surface properties of the steel sheet and causes a problem in chemical conversion treatment. Since the rinse dip tank is used, the discoloration preventive agent must be applied to the steel sheet that does not require the discoloration preventive agent, which increases the running cost.

The present invention has been made in view of the above situation, and an object of the present invention is to provide an excellent method for preventing discoloration of a steel sheet which has no problems in quality and cost.

[0010]

The above-mentioned problems can be solved by the following means. What is claimed is: 1. An electrolytic cleaning device for continuously cleaning a steel sheet, comprising a cleaning liquid discharging device provided near an electrode of an electrolytic bath. A method for preventing discoloration of a steel sheet in an electrolytic cleaning apparatus, which comprises discharging a cleaning liquid toward the surface of the steel sheet from the vicinity of an electrode of an electrolytic bath when the steel sheet is stopped.

[0011]

According to the present invention, in the electrolytic cleaning device for continuously cleaning the steel sheet by providing the steel plate passage between the electrodes immersed in the cleaning liquid, the cleaning liquid ejecting device is arranged close to the electrode of the steel plate passage. When the steel plate stops, the cleaning liquid is discharged from the cleaning liquid discharging device to the surface of the steel plate to wash away O ₂ that tends to adhere to the surface of the steel plate and other substances that cause discoloration. Therefore, discoloration does not occur on the steel sheet.

[0012]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a view showing an embodiment of the present invention. An electrolytic tank which constitutes a main part of an electrolytic cleaning device, a discoloration preventing device for preventing discoloration of a steel sheet generated in the subsequent steps, and the discoloration thereof. The application method and timing of the inhibitor are shown. In the following figures, the same parts as those in FIG. In FIG. 1, 1 is a coil before electrolytic cleaning, 2 is an alkaline cleaning tank, 8 is a cleaning liquid discharge device, and 9
Is a cleaning liquid discharge pump, 10 is a pipe, 15 is cleaning water to be supplied, 16 is a discoloration inhibitor pump, 17 is a discoloration inhibitor stock solution tank, 18 is a static mixer, 19 is a cleaning water supply automatic opening / closing valve, and 20 is An automatic opening / closing valve for the discoloration preventing agent, and 21 is an overflow valve.

In FIG. 1, an alkaline cleaning solution (sodium orthosulfate 2Na ₂ OSiO ₂ ,
Or it is filled with an aqueous solution of caustic soda (NaOH). The steel plate 30 is introduced into the electrolytic tank 3 by the entrance deflector roll 4 and the entrance dip roll 5. Then, it passes through a plurality of pairs of electrodes 7 arranged above and below the pass line of the steel plate 30 in close proximity to and facing the pass line, and is carried out to the scrubber portion 13 via the outlet dipping roll 11 and the outlet deflector roll 12. . In this electrolytic tank 3, a plurality of cleaning liquid ejecting devices 8 are arranged close to the electrodes 7 of the steel plate passage. Then, the cleaning liquid is supplied from the electrolysis tank from the pump 9 to the cleaning and discharging device through the pipe 10.

Next, with respect to the surface of the steel sheet carried out to the scrubber section 13, a constant-solution metering pump 16 for the discoloration-preventing agent was used.
A fixed amount of stock solution is supplied. Study mixer 18
Discoloration inhibitor and wash water are mixed. Rinsing water supply automatic opening / closing valve 19 is for rinse water rinse dip tank 3
4 is automatically opened / closed, and the automatic anti-discoloration valve 20 for the anti-discoloration agent is automatically opened / closed to supply the anti-discoloration agent to the wash water. The overflow valve 21 keeps the liquid level of the washing water in the rinse dip tank constant.

The steel sheet 30 is subjected to alkali cleaning in the alkali cleaning tank 2, then to alkaline electrolytic cleaning in the alkaline electrolytic cleaning tank 3, and then spray cleaned with cleaning water 15 in the scrubber portion 13. Here, when the line speed exceeds 50 m / min, the wash water 15 does not contain a discoloration inhibitor.

When the line stops due to welding of coil joints of steel plates, or the line speed is 50 m /
When it is less than min, discoloration occurs in the steel plate. In this case, the washing water supply automatic opening / closing valve 19 is automatically closed, and the discoloration preventing agent automatic opening / closing valve 20 is opened to mix the discoloration preventing agent with the washing water 15 by the stationary mixer 18, and the scrubber portion 13 Apply the tarnish inhibitor to the steel plate with the header nozzle. In addition, when the line is stopped 1
By stopping the spray of the discoloration preventive agent after a lapse of more than a minute, the cost reduction effect of the discoloration preventive agent can be achieved.

When the line is stopped or the line speed is 50 m /
If the steel plate 30 continues to be immersed in the cleaning water 15 in the rinse dip tank 34 in the case of min or less, discoloration occurs in the steel plate 30 because the cleaning water 15 contains no discoloration inhibitor. Therefore, the position of the overflow valve 21 is set below the steel plate passage position so that the steel plate 30 is not submerged in the cleaning water 15. As described above, in the present invention, the cleaning water 15 and the discoloration preventive agent are automatically switched even when the steel plate 30 is interrupted during cleaning and the line is stopped, or in the case of surface inspection at a line speed of 50 m / min or less during cleaning of the steel plate. As a result, discoloration of the steel plate 30 can be prevented.

Since the cleaning apparatus of FIG. 1 is also used as a conventional product manufacturing line, it can be used as a shared facility by lowering the water in the rinse dip tank 34 in advance. In this case, in order to have both the cleaning effect and the discoloration prevention effect, the flow rate of the cleaning water is preferably 15 to 40 m ³ / h. If it is less than 15m ³ / h, there is little discoloration prevention effect, and 40m ³
If it exceeds / h, it is economically disadvantageous.

FIG. 2 is a view showing an embodiment of an apparatus in which the scrubber portion also serves as rinse hot water cleaning. In the figure below,
The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.
In Fig. 2, if the line speed exceeds 50m / min, it is spray-washed from the cleaning water 15. If the line speed is 50m / min or less, the scrubber is cleaned as it is at 15 and the discoloration inhibitor is applied only to the rinse part. To do. Further, when the line is stopped, the cleaning water 15 is automatically stopped, and the discoloration preventive agent is automatically applied to the scrubber part and the rinse part by the discoloration prevention coating device of a system different from this cleaning water system. Automatically spray anti-tarnish agent or anti-tarnish agent mixed in wash water. In this case, it is preferable that the spray method is 1 to 10 L / min in the form of a spray. If it is less than 1 L / min, the effect of preventing discoloration is small, and if it exceeds 10 L / min, it is economically disadvantageous. In the case of a dedicated line, the discoloration preventive agent may be sprayed only with the scrubber portion 13 or only with a simple spray rinse tank without a brush.

Since the cleaning apparatus shown in FIGS. 1 and 2 is also used as a conventional product manufacturing line, it is possible to lower the cleaning water in the rinse dip tank 34 in advance.
In the case of a dedicated line, it is not possible to lower the washing water in the rinse dip tank 34 in advance, but the circulation spray pump to the scrubber of the rinse dip is automatically stopped and this washing is performed. Discoloration-preventing device that is separate from water and automatically sprays discoloration-preventing agent.
Spray 1 to 10 L / min on the steel sheet in contact with air. FIG. 3 shows an example of such a dedicated line. Here, if the line speed is less than 50m / min, the scrubber is directly sprayed with cleaning water,
The rinse water 15 to the rinse is stopped. At this time, the valve 31 is closed, and the discoloration preventive agent is sprayed on the steel plate in contact with the air other than the rinse dip tank of the rinse tank, and the discoloration of the steel plate can be prevented.

In an unannealed material or a re-tempered material that is temper-rolled without passing through the annealing step according to the present invention, discoloration prevention during cleaning is indispensable. It is suitable for preventing discoloration of steel sheets that have undergone such processes. The tarnish inhibitor used in the present invention is not particularly limited as long as it is a water-soluble tarnish inhibitor used for ordinary steel sheets. In addition, the washing water mixed with the discoloration preventive agent is usually 10 to 90 ° C, preferably 40 to 80 ° C. The concentration of the discoloration preventing agent is preferably 1000 to 2000 mg / l. If it is less than 1000 mg / l, the effect of preventing discoloration is small, and 2000
It is economically disadvantageous if it exceeds mg / l.

FIG. 4 is a diagram showing an electrolytic cleaning method for preventing discoloration of a steel plate by using a cleaning liquid discharging device of the electrolytic cleaning device. In FIG. 4, 22 is a motor, 23 is a power supply, 24 is a switch, 25 is a drive motor, 26 is a pulse generator, 27 is a polarity change switch, 28 is a bridle roll speed adjuster, and 29 is a rectifier. A signal from a pulse generator 26 directly connected to a drive motor 25 of the bridle roll is constantly sent to a switch 24 that turns on and off the supply of electricity from a power source 23 of a motor 22 of the pump 9. When the signal from the pulse generator 26 becomes 0, that is, when the line is stopped, the switch 24 is turned on and the pump 9
Is driven and the cleaning liquid is sent from the electrolytic tank 3 to the cleaning liquid discharge device 8 through the pipe 10, and the cleaning liquid is discharged toward the surface of the steel plate 30 and adheres to the surface of the steel plate 30 to cause discoloration O ₂ Etc. are washed out. When the signal from the bridle roll drive motor 25 becomes larger than 0 revolutions, the switch 24 is turned off and the pump 9 is stopped.
When the line is stopped, the polarity of the electrode 7 is switched by the polarity switch 27, but the switching command for the polarity switch 27 is also issued in synchronization with the signal from the pulse generator 26.

FIG. 5 is a view showing a cleaning liquid discharge device. Here, the nozzle gap is preferably 3 to 10 mm. 3m
If it is smaller than m, it may come into contact with the steel plate, and if it is larger than 10 mm, the cleaning effect is deteriorated. The nozzle angle is 15 ~
45 ° C is preferred. If it is lower than 15 ° C or higher than 45 ° C, the cleaning effect decreases. The discharge velocity is 0.3 to 1.2 m / s.
ec is enough. If it is less than 0.3 m / sec, the cleaning effect is reduced, and if it is more than 1.2 m / sec, it is economically disadvantageous.

Table 1 shows the case where the cleaning liquid discharge device is used by switching the polarity (8 poles) every time the line is stopped according to the present invention (Example) and the conventional cleaning liquid device is not provided (Comparative example).
It is the result of comparing the discoloration and the discoloration of the steel sheet by the following criteria.

[0026]

[Table 1]

◎ ── Extremely excellent (no rusting or discoloration at all) ○ ── Excellent (no rusting or discoloration) × ── Inferior (prominent rusting or discoloration .)

Here, the test piece is a cold rolled steel sheet (JIS-G3141-SPCC,
It is 1200mm wide x 0.8mm thick) and the base material of the plank is dull finish. Further, in this investigation, the discharge conditions of the cleaning liquid are as follows. Nozzle gap 3mm Nozzle angle 15 ° Flow velocity 1.2m / sec The nozzle is sprayed in the opposite direction to the steel sheet spray direction Alkaline liquid (sodium orthosulfate) Electrode voltage 40V Electrode, current density 10.9A / dm ²

In each of the examples and comparative examples, the visual evaluation of the discoloration occurrence state of the steel sheet is performed as a standard. From Table 1, it can be seen that the present invention prevents discoloration of the steel sheet. still,
In the present invention, it has been confirmed that the effect of the cleaning liquid ejecting device is not reduced depending on the type of alkaline liquid (sodium orthosulfate, sodium hydroxide, etc.), the combination pattern of the polarities of the electrodes, or the current density of the electrodes. There is.

FIG. 7 shows the results of investigating the flow velocity of the alkaline liquid convection between the electrodes due to the nozzle gap of the discharge device. Here, the test piece is a cold rolled steel sheet (JIS-G3141-SPCC, 1800 mm width x 1.0 mm thickness), and the base material of the thick plate is a dull finish. In addition, the size of the electrode (grid) is 2200mm for both the top and bottom.
The width x 1300 mm length is used.

In FIG. 7, Examples A to C are those in which the nozzle gap of the discharge device is 3 to 10 mm and the nozzle angle is 15 °, and Comparative Example D is 12 mm in the nozzle gap and nozzle angle is 15 °. This is the case. Here, in the evaluation of Examples and Comparative Examples, the flow velocity was measured from a certain place from the entrance to the exit of the electrode, and the convection state was evaluated according to the following criteria. ◎ ── Very good ○ ── Good △ ── Slightly inferior × ── Inferior (insufficient convection)

From FIG. 7, the nozzle gap according to the present invention is
It can be seen that 3 to 10 mm (more preferably 3 to 5 mm) is good.

Table 2 shows the results of a test in which the effect of the concentration of the anti-discoloration agent on the anti-discoloration effect was examined when the anti-discoloration agent was stopped 1 minute after the line was stopped according to the present invention. The test piece is a cold rolled steel plate (JIS-G3141-SPCC, 1200mm width x 1.0mm thickness)
Then, the base material of the original plate is a dull finish. In Examples Nos. 1 to 3 in the table, the concentration of the tarnish preventive agent is changed, and in Comparative Example No. 4, only the wash water containing no tarnish preventive agent is used. For the examples and comparative examples, the visual observation of the occurrence of discoloration was evaluated according to the following criteria. ◎ ── Very good (no rusting or discoloration at all) ○ ── Excellent (no rusting or discoloration at all) △ ── Slightly inferior (some rusting or discoloration at all) × ── Inferior (prominent rusting and discoloration)

[0034]

[Table 2]

Table 2 shows that the present invention prevents discoloration of the steel sheet. According to the present invention, when the line is stopped or when the line speed is 50 m / min or less, when the discoloration agent is applied from the scrubber part, the discoloration preventive agent is used as a final agent in order to stop the cleaning with the cleaning water in the rinse dip tank. Also serves as a rinse. Table 3 shows the results of a test for investigating the effect of the steel sheet on the chemical conversion treatability in this case. The test piece is a cold-rolled steel sheet (JIS-G3141-SPCC, 1200 mm width × 1.0 m
m thickness), and the base material of the original plate is a dull finish.
In Examples Nos. 1 to 3 in the table, the concentration of the tarnish preventive agent is changed, and in Comparative Example No. 4, only the wash water containing no tarnish preventive agent is used. Here, the chemical conversion treatment conditions are as follows. Degreasing: Fine Cleaner 4826TA (trade name) was used and treated at 50 ° C. for 18 minutes at 18 g / l. Surface adjustment: PL-ZMS (trade name), 1g / l at 20 ℃
It was processed for 20 seconds. Phosphate treatment: Using PB-3030M (trade name) at 51 ℃
Immersion treatment was performed at 50 g / l for 2 minutes.

The chemical conversion treatability of Examples and Comparative Examples was evaluated by the following method. The adhered amount of the chemical conversion film was obtained by a gravimetric method, and the chemical conversion treatability was represented by the P adhered amount (the amount of metal adhered to the steel sheet), and judged according to the following criteria. ◎ ── Very good (P adhesion amount 2.5 to 3.2 g / m ² ) ○ ──Good (P adhesion amount 1.1 to 2.4 g / m ² ) × ── Poor (P adhesion amount 1.0 g / m ² or less or 3.3) g / m ²
that's all)

[0037]

[Table 3]

It can be seen from Table 3 that the present invention has good chemical conversion treatability.

[0039]

As described above, according to the present invention, it is possible to prevent discoloration of a steel sheet which has been caused by alkali cleaning or alkaline electrolytic cleaning, and to further perform a rinse cleaning on the steel sheet thereafter.
By a method of effectively applying a discoloration preventive agent to a target material, it is possible to prevent discoloration of a steel plate whose surface has been activated, improve product quality and yield, and improve the discoloration preventive agent. Economic efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a system diagram showing an embodiment different from FIG. 1 of the present invention.

FIG. 3 is a system diagram showing an embodiment different from FIGS. 1 and 2 of the present invention.

FIG. 4 is a system diagram showing a cleaning liquid discharge device of the present invention.

FIG. 5 is a diagram showing a positional relationship between nozzles and electrodes of an alkaline cleaning and discharging device.

FIG. 6 is a diagram showing a cleaning process of a conventional discoloration prevention method.

FIG. 7 is a diagram showing a flow velocity state of an alkaline liquid due to a nozzle gap of a discharge device.

[Explanation of symbols]

 3 Electrolyzer 7 Electrode 8 Cleaning Liquid Discharge Device 30 Steel Plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Yamamoto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. An electrolytic cleaning device for continuously cleaning a steel sheet, wherein an electrolytic cleaning device is provided in the vicinity of an electrode of an electrolytic cell, and a cleaning liquid discharging device is provided. 2. A method for preventing discoloration of a steel sheet in an electrolytic cleaning apparatus, which comprises discharging a cleaning liquid toward the surface of the steel sheet from the vicinity of the electrode of the electrolytic bath when the steel sheet is stopped.