JP2868589B2 - Neutral salt electrolytic treatment method for stainless steel strip - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a stainless steel strip neutral salt electrolysis method capable of removing scale generated on a stainless steel strip surface by annealing stably and at low cost. is there.

[Conventional technology]

As one of the annealing treatment methods performed on the stainless steel strip after the cold rolling, there is an atmospheric annealing method in which the fuel is burned in a furnace in an atmosphere atmosphere furnace to perform direct flame heat treatment. In this atmospheric annealing, metal oxides (hereinafter, sometimes simply referred to as scales) are formed on the surface of the stainless steel strip by the action of oxygen in the atmosphere. To produce the strip, a descaling treatment is performed after the annealing treatment. Generally, the descaling process of the stainless steel strip is continuously performed in a series of lines together with the annealing process in the preceding process.

There are several methods for descaling conventionally, such as electrolytic treatment in an aqueous solution mainly composed of sodium sulfate (hereinafter referred to as neutral salt electrolytic treatment) or mixed molten salt of caustic soda and sodium nitrate. Pre-treatment such as immersion treatment (hereinafter sometimes simply referred to as salt immersion treatment), and then immersion in nitric hydrofluoric acid (hereinafter sometimes simply referred to as mixed acid immersion) or electrolysis in a nitric acid aqueous solution (Hereinafter, may be simply referred to as nitric acid electrolysis) is widely used.

Of these, the pretreatment typified by the neutral salt electrolytic treatment or the salt immersion treatment is to dissolve and remove the chromium oxide in the poorly soluble scale as chromate ions in the bath, and then perform the mixed acid immersion or nitric acid electrolysis. To facilitate descaling. In particular, this neutral salt electrolytic treatment is described in
This method has been widely adopted since it was disclosed in Japanese Patent No. 162.

This neutral salt electrolysis method will be described with reference to FIG. 2 which is a schematic configuration diagram of an electrolysis apparatus showing a conventional standard electrode arrangement. The electrolytic bath 1 contains an electrolytic bath 2 of an aqueous solution mainly composed of sodium sulfate, and the annealed stainless steel strip S travels in the direction of the arrow to move the inlet and outlet deflector rolls 3 and 3 and the immersion roll 4. , 4 pass through the electrolytic bath 2, during which time electricity is supplied to perform anodic electrolysis of the stainless steel strip S. As an energizing method at the time of anodic electrolytic treatment, a direct energizing method in which a stainless steel strip is used as a positive electrode through a contact roll and a negative electrode arranged in an electrolytic bath is generally used. However, the stainless steel strip after annealing cannot be energized due to the presence of non-conductive scale on the surface, and if you try to forcibly apply electricity, sparks will occur and the stainless steel strip will be damaged. become. For this reason, when descaling a stainless steel strip having a scale on the surface after annealing, a positive electrode 5 is also separately provided in the electrolytic bath 2 to energize the positive electrode 5 and the negative electrode 6 in the electrolytic bath 2. Thus, an indirect energization method of energizing the stainless steel strip S through the electrolytic bath 2 is widely used. As shown in FIG. 2, the arrangement of the electrodes 5 and 6 when the indirect current is applied is usually such that a plurality of positive electrodes 5 and negative electrodes 6 are arranged alternately in opposition to the front and back surfaces of the stainless steel strip S. Thus, an electrode row is formed. When electricity is supplied to the positive electrode 5 and the negative electrode 6 arranged in this way from the DC power source 7 for electrolysis, the positive electrode 5 and the negative electrode 6 are turned on.
The respective portions of the stainless steel strip S facing each other are polarized to a cathode and an anode, respectively, to form a series of electric circuits. As a result, the steel strip portion polarized to the anode is subjected to the anodic electrolytic treatment, and the chromium oxide in the scale is mainly oxidized and dissolved. As a result, descaling is easily performed in the subsequent nitric acid electrolysis or mixed acid immersion. In addition, the steel strip portion polarized to the cathode is subjected to cathodic electrolysis. This cathodic electrolysis converts metal ions dissolved in the electrolytic bath 2 to hydroxide when the pH of the electrolytic bath 2 is high. It has an effect, but is not always necessary.

As the material of the electrode in such a neutral salt electrolysis treatment, there was no long-life and relatively inexpensive material,
For the positive electrode 5, a common steel base material and a lead-antimony alloy lining or build-up welding on the surface thereof (hereinafter, may be simply referred to as a lead electrode) have been used for a long time. However, this lead electrode was cracked or peeled off the lining with use, and its life was about 6 months. This is presumed to be due to the fact that the lead-antimony alloy elongates with the passage of current, resulting in a difference in the amount of elongation with the base material. Furthermore, this lead electrode was heavy, and the work load required for electrode replacement was heavy. In addition, since the applied voltage is high, the cost of electrolyzing power is increased, and furthermore, the lead-antimony alloy dissolves to a considerable extent, thus causing a problem of bath contamination. Since the negative electrode 6 does not require high corrosion resistance, inexpensive SUS410 has been used,
Although it was not possible to replace it, some corrosion had occurred.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the drawbacks of the above-mentioned prior art and to be able to carry out the neutral salt electrolytic treatment of a stainless steel strip after annealing at a high efficiency and economically with almost no breakage of the positive electrode.

[Means for solving the problem]

As a result of various studies, the present inventor has found that iridium oxide used when performing a surface treatment such as formation of an oxide film and electrolytic etching by electrolytically treating a metal such as aluminum in a solution containing an organic acid or a salt thereof. Using an insoluble electrode having a main electrode coating (hereinafter referred to as an iridium-based insoluble electrode) as a positive electrode and an electrode made of stainless steel or titanium as a negative electrode to form a specially arranged electrode row. As a result, it has been found that the above-mentioned object can be achieved, and the present invention has been completed.

Hereinafter, the neutral salt electrolytic treatment method of the stainless steel strip according to the present invention will be described in detail with reference to FIG. 1 which is a schematic configuration diagram of an electrolytic apparatus showing an example of electrode arrangement.

In the method of the present invention, the positive electrode 5 is used as JP-B-63-3099.
An iridium-based insoluble electrode having an electrode coating composed of iridium oxide and an oxide of a metal selected from titanium, tantalum, niobium, cobalt and manganese is used, as described in Japanese Patent Publication No. 6 (1994). As described above, the iridium-based insoluble electrode is subjected to a surface treatment such as formation of an oxide film and electrolytic etching by oxidizing a metal such as aluminum in a solution containing an organic acid or a salt thereof by an indirect energization method. Although it has been developed as a positive electrode that can withstand long-term stable use in the case, the present inventor has found that the electrolysis of the stainless steel strip S in an aqueous solution mainly composed of sodium sulfate is sufficiently effective. is there.

In the present invention, stainless steel or titanium is used as the negative electrode 6. Stainless steel is preferably SUS30
4, selected from SUS316, SUS430, SUS420, SUS410, etc., and titanium is selected from the first, second and third types specified in JISH4600. These have not only a sufficient function as a cathode in an electrolytic bath 2 of an aqueous solution mainly composed of sodium sulfate, but also have a light weight, strong strength and considerable corrosion resistance, and are relatively inexpensive materials because they are mass-produced and widely used. It is.

The electrolytic device of the present invention has a structure in which a positive electrode 5 and a negative electrode 6 are arranged in one electrolytic cell 1 in which an aqueous solution mainly composed of sodium sulfate is bathed as an electrolytic solution 2 as shown in FIG. As a major feature of the present invention, the number of cathodes 6 is larger than the number of cathodes 5, which is not a difference of about one or two, but is substantially in a ratio of, for example, 1: 4 to 8 and The arrangement of the positive electrode 5 and the negative electrode 6 in the upstream region and the downstream region (the upstream and downstream in the present invention are based on the running direction of the stainless steel strip S) from the central part of the electrolysis apparatus is symmetric. The positive electrode 5 and the negative electrode 6 are connected to a DC power source 7 for electrolysis. Then, as shown in FIG. 1, all the positive electrodes 5 are sequentially arranged, that is, the adjacent positive electrodes 5,5 are arranged.
The positive electrode group formed side by side without the intervening negative electrode 6 is arranged at the center of the electrode row. The reason for disposing the positive electrode 5 and the negative electrode 6 so that they are symmetrical in the upstream area and the downstream area from the center of the electrolyzer is that the stainless steel strip S in the upstream area and the downstream area has a potential difference. If the positive electrode 5 or the negative electrode 6 is arranged in the electrolytic apparatus in a biased manner, a large potential difference occurs between the stainless steel strip S in the upstream region and the downstream region, and as a result, annealing and pickling are performed. Unless a series of lines including processing and the like are electrically insulated, a spark is generated in a portion having a low electric resistance, which causes damage to the equipment and flaws on the stainless steel strip S. Further, the positive electrodes 5 are sequentially arranged, that is, the adjacent positive electrodes 5,
All positive electrodes 5 without a negative electrode 6 interposed between them
The reason for arranging the positive electrode group formed by sequentially arranging the electrodes in the center of the electrode row is that the position where the positive electrode 5 and the negative electrode 6 are adjacent to each other is reduced so that the stainless steel flowing from the adjacent positive electrode 5 to the negative electrode 6 is reduced. This is to minimize a reactive current that does not contribute to electrolytic pickling of the steel strip S. When it is necessary to perform the neutral salt electrolysis at a high current density or the neutral salt electrolysis for a long electrolysis time, the negative electrode 6 or the positive electrode 5 having a large electrode area is required. When it is difficult to manufacture an electrode having an electrode area, an electrode group in which electrodes having the same polarity are often arranged may be used. It is on the street.

As the electrolytic bath 2, an aqueous solution mainly composed of sodium sulfate is conventionally used, but the following concentrations and liquid temperatures are preferable in order to maintain the activity of the iridium-based insoluble electrode for a long time. The concentration of sodium sulfate is 50-300 g / l, more preferably 100-200 g / l, and the liquid temperature is 40-80 ° C., more preferably 55-6.
5 ° C.

[Operation] As shown in FIG. 1, the positive electrode 5, the negative electrode 6 and the electrode array of the electrolytic cell 1 are constituted as described above, and the electrolytic bath 2 is made of an aqueous electrolytic solution mainly composed of sodium sulfate. ,
While the stainless steel strip S is passed through, indirect energization is performed. In this case, since the iridium-based insoluble electrode is used as the positive electrode 5, even if the current is applied at a higher current density than the lead-antimony alloy positive electrode 5 used in the prior art, there is less damage, and thus the positive electrode 5 Electric current can be supplied to more negative electrodes 6 while maintaining the current density in a normal state.
Therefore, the number of cathode electrodes 6 can be increased even if the total number of electrodes is the same as in the prior art, and the number of cathode electrodes 6 can be increased if the number of anode electrodes 5 is the same. Therefore, for example, even when the existing electrolytic cell 1 is used, by changing the number and arrangement of the positive and negative electrodes 5 and 6 and configuring the electrode row as described above, the stainless steel strip S can pass through the electrolytic bath 2. When the vehicle travels, the time for passing through the position facing the increased negative electrode 6, that is, the time for receiving the anodic electrolysis, becomes longer, and a sufficient electrolytic treatment is performed.

Then, the positive electrodes 5 are sequentially arranged, that is, the adjacent positive electrodes 5,
All positive electrodes 5 without a negative electrode 6 interposed between them
Are arranged in the center of the electrode row, so that there are only two places where the positive electrode 5 and the negative electrode 6 are adjacent to each other. The reactive current that does not contribute to electrolytic pickling of the stainless steel strip S flowing to 6 is very small, and the power efficiency is very good.

Furthermore, in order to prevent a decrease in the surface activity of the positive electrode 5 due to the formation of a battery between the positive electrode 5 and the negative electrode 6 during non-electrolysis, a voltage of 2 volts or more is applied between the positive electrode 5 and the negative electrode 6 during non-electrolysis. Or the electrolytic bath 2 is transferred to another tank and the electrolytic tank 1 is emptied.

〔Example〕

Example 1, Comparative Example 1 Annealed stainless steel strip S (SUS304, thickness 1.0 mm, width 1)
030 mm) was passed through a plate under the conditions described below and electrolytic pickling was continued for 6 months. That is, in the first embodiment, the positive electrode 5
As the iridium-based insoluble electrode, and as the negative electrode 6
First electrodes made of SUS304 stainless steel material
An electrolytic device (electrode area of each electrode was 26 dm ² ) in which an electrode array was formed in the same manner as in the drawing was used in combination, and an aqueous sodium sulfate solution having a concentration of 150 g / l was used as the electrolytic bath 2. The electrolysis conditions depend on the full load current.
The temperature was 5,000 A, and the bath temperature was 60 ° C.

In Comparative Example 1, an electrolysis device was used in which an electrode made of a lead-antimony alloy was used as the positive electrode 5 and an electrode made of SUS410 was used as the negative electrode 6 in the same manner as in FIG. Except for the above, it was the same as Example 1.

Although the passing speed was the same in Example 1 and Comparative Example 1, the current density in Comparative Example 1 was 24 A / dm ² , The electrode 6 has a current density of 16 A / dm ² , and the total electrolysis time is 4 seconds for the positive electrode 5 and 6 seconds for the negative electrode 6, whereas in Example 1, the current density is 48 A / dm ^{2 for the} positive electrode 5, 12 A / dm ^{2 for} electrode 6
The total electrolysis time is 2 seconds for the positive electrode 5 and 6 seconds for the negative electrode 6.
It was 8 seconds. That is, the load of the anodic electrolysis on the stainless steel strip S was the same as 96 coulombs / dm ² in both cases.

In each of Example 1 and Comparative Example 1, each electrode was new at the start of use of the electrolysis apparatus, and was used as it was during the entire period. Further, the electrolytic bath 2 was occasionally updated as usual.

In this way, the electrolytic pickling of the annealed stainless steel strip S was performed for 6 months, and the descaled state and the broken state of each electrode were observed. Table 1 shows the results at the start of pickling and after 6 months. The results shown in the table are all obtained immediately after the bathing, and the descaling state was obtained by immersion treatment in a mixed acid bath in which the conditions did not change significantly.

According to Table 1, in Examples, the positive and negative electrodes 5, 6 did not break even after 6 months of use, and the descaling was good.

〔The invention's effect〕

As described in detail above, the neutral salt electrolysis treatment method for a stainless steel strip according to the present invention is specially arranged using an iridium-based insoluble electrode as a positive electrode and a stainless steel or titanium electrode as a negative electrode. By using the electrolysis apparatus, it is possible to reduce the damage to the positive electrode, increase the number of negative electrodes, and efficiently perform anodic electrolysis of the stainless steel strip, and obtain the following effects. .

Since the frequency of replacement of the positive electrode is reduced, the production capacity is improved and the manufacturing cost is reduced.

The positive electrode group is formed by sequentially arranging the positive electrodes, that is, all the positive electrodes are sequentially arranged without interposing the negative electrode between the adjacent positive electrodes, and the positive electrode group is arranged at the center of the electrode row. Since only two locations are adjacent to each other, the reactive current that does not contribute to electrolytic pickling of the stainless steel strip flowing from the adjacent positive electrode to the negative electrode is very small, and the power efficiency is very good.

The iridium-based insoluble electrode used as the positive electrode is
Since the applied voltage is lower than the conventional lead-antimony alloy and the electrolytic treatment can be performed at a relatively low electrolytic voltage, the cost of the electrolytic power can be reduced.

Because it became possible to increase the number of negative electrodes,
When the total load current is the same, the current density per cathode decreases, and the life of the cathode is extended.

Stainless steel used as negative electrode, 1st class, 2nd class
Since the seed and the third kind titanium are lightweight and inexpensive, the weight of the electrode is reduced, the labor required for electrode replacement is reduced, and the cost of the negative electrode is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an electrolytic apparatus showing an example of electrode arrangement in a method for electrolytic pickling of a stainless steel strip according to the present invention.
The figure is a schematic configuration diagram of an electrolysis apparatus showing a conventional standard electrode arrangement. In the drawings: 1 ... Electrolyzer 2 ... Electrolysis bath 3 ... Deflector roll 4 ... Immersion roll 5 ... Positive electrode 6 ... Negative electrode 7 ... DC power supply for electrolysis S ... Stainless steel strip

Claims (1)

(57) [Claims] 1. A plurality of positive electrodes and a plurality of negative electrodes connected to the positive electrode via a DC power supply for electrolysis are arranged in one electrolytic cell so as to face a running surface of a stainless steel strip. In carrying out the neutral salt electrolysis by the indirect energization method while running the annealed stainless steel strip in an aqueous solution mainly composed of sodium sulfate using an electrolysis apparatus equipped with an electrode row,
An insoluble electrode having an electrode coating composed of iridium oxide and an oxide of a metal selected from titanium, tantalum, niobium, cobalt and manganese is used as the positive electrode, and stainless steel and the first, second and third types are used as the negative electrode. Using a metal electrode selected from each of the third types of titanium, the number of cathodes is greater than the number of cathodes, and the arrangement of cathodes and cathodes in the upstream and downstream regions from the center of the electrolyzer. Wherein a positive electrode group formed by sequentially arranging all the positive electrodes is arranged at the center of an electrode row to perform electrolysis.