JP2012162794A - Electrolytic pickling method for descaling stainless steel strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a current efficiency of 90% or more by appropriately designing the structure of a tank corresponding to the scale of pickling equipment.SOLUTION: A stainless steel strip after annealed is descaled in a neutral salt solution or an acidic aqueous solution by anode electrolyte using indirect energizing method. In such descaling equipment (electrolytic pickling equipment), the electrolytic pickling method satisfies the following formula: L >0.6 DW/I, wherein a distance between anode and cathode is L (mm), current energizing among electrodes is I(A), a substantial width of a pickling tank between the anode and cathode is W (mm), a substantial depth thereof is D (mm), and the substantial width W and substantial depth D are dimensions after the size of insulation substance is subtracted from the actual sizes.

Description

  In the present invention, when an oxide scale formed on the surface of a stainless steel strip by annealing treatment is descaled by anodic electrolysis by an indirect energization method in a neutral salt aqueous solution or an acidic aqueous solution, the energized current flows efficiently to the strip. This relates to the electrolytic pickling method.

  As one of the annealing treatment methods performed on the stainless steel strip after cold rolling, there is an atmospheric annealing method in which heat treatment is performed by burning the fuel in an air atmosphere furnace. In this annealing method, metal oxides are formed on the surface of the stainless steel strip due to oxygen in the atmosphere and water vapor generated by combustion, so that it is removed and annealed to produce a stainless steel strip of good quality. A descaling process is performed after the process.

  The descaling method includes immersion in an acidic aqueous solution, neutral salt aqueous solution or anodic electrolysis in an acidic aqueous solution (hereinafter simply referred to as electrolytic pickling), mixed molten salt of caustic soda and sodium nitrate. There is a method of performing an immersion treatment of these, and the descaling of the stainless steel strip is performed by combining these methods.

  In the electrolytic pickling, an indirect energization method in which cathodes and anodes are alternately arranged in a non-contact manner in the sheet passing direction of the stainless steel strip, and anodic electrolysis and cathode electrolysis are sequentially performed on the stainless steel strip is widely performed. In the indirect energization method, since there is no need to bring the energizing roll into contact with the stainless steel strip, there are no problems such as surface scratches due to contact with the energizing roll. However, since it is not in contact with the stainless steel strip, there is a problem that a part of the current flows directly from the anode to the cathode and the current efficiency flowing to the stainless steel strip is reduced.

  In order to eliminate the inter-electrode current flowing directly from the anode to the cathode, it is most effective to make the tank for performing anodic electrolysis and the tank for performing cathodic electrolysis independent. Such a technique is described in Patent Document 1. However, when the tanks are divided, it is necessary to manage the liquid for each tank, and rolls are required between the tanks, resulting in roll costs, and there is concern about the occurrence of scratches due to contact with the rolls, etc. There are also disadvantages.

JP2004-300541

  In the case where the anode and the cathode are arranged in one tank, it is an effective measure for improving the current efficiency to increase the distance between the anode and the cathode. Although the current efficiency is inferior to dividing the tank, there are significant advantages in consideration of equipment management such as liquid management and rolls.

  Since the overall merit is great, an electrolytic pickling method in which an anode and a cathode are arranged in one tank is widely used. However, a detailed study on the relationship between electrode arrangement and current efficiency has not been conducted, and the distance between the electrodes is too wide and the tank becomes large and the load on the management side becomes large. In some cases, the current efficiency is reduced by reducing the distance between the electrodes. Therefore, it was necessary to study the relationship between the electrode arrangement and the current efficiency and grasp the optimum tank configuration.

  The inventors have found that the decrease in current efficiency occurs when the current flows directly from the anode to the cathode as shown in FIG. 2, and the current efficiency can be increased by increasing the electrical resistance between the anode and the cathode. Based on this idea, various experiments were conducted. As a result, the relationship between the current efficiency and the tank configuration was grasped and the present invention was made.

The invention described in claim 1 relates to equipment for descaling the annealed stainless steel strip in a neutral salt aqueous solution or an acidic aqueous solution by anodic electrolysis using an indirect current method (hereinafter simply referred to as electrolytic pickling equipment). The distance between the anode and the cathode is L (mm), the current passing between the electrodes is I (A), the actual width of the pickling tank between the anode and the cathode is W (mm), and the actual depth is D (mm) Is an electrolytic pickling method that satisfies the following formula.
L> 0.6DW / I (1)
Here, the substantial width W and the substantial depth D refer to dimensions obtained by subtracting a portion where an insulator is installed from actual dimensions.
Invention of Claim 2 is the electrolytic pickling method of Claim 1 which makes the distance between a stainless steel strip and an electrode 20 mm or more and 150 mm or less.
The invention according to claim 3 uses an aqueous solution containing 100 to 250 g / l Na ₂ SO ₄ as a neutral salt electrolysis aqueous solution, and an aqueous solution containing 50 to 200 g / l H ₂ SO ₄ or HNO ₃ as an acidic aqueous solution. It is the electrolytic pickling method of Claim 1 or 2 characterized by the above-mentioned.

  According to the present invention, an appropriate tank configuration corresponding to the scale of the pickling facility can be designed, and a current efficiency of 90% or more can be obtained.

Schematic configuration diagram of descaling equipment according to an embodiment of the present invention Diagram showing current circuit in indirect energization method Examples of descaling equipment according to embodiments of the present invention Diagram showing the relationship between the structure of the pickling tank and the current efficiency

  A descaling facility according to an embodiment of the present invention is shown in FIG. An anode and a cathode are arranged above and below the stainless steel strip to be passed through at a certain distance from the steel strip. Considering the electrolytic voltage and cost, it is preferable to use an electrode coated with a platinum group metal or a white metal oxide for the anode and an iron-based alloy such as stainless steel for the cathode. At this time, the closest distance between the anode and the cathode is defined as an interelectrode distance L. From the viewpoint of current efficiency, the closer the distance between the steel strip and the electrode is, the better. The following is preferable.

  Two or more sets of electrode arrangements as shown in FIG. 1 may be installed in one tank. An electrode coated with a platinum group metal or white metal oxide can be used as the anode, and an iron-based alloy such as stainless steel can be used as the cathode.

As the pickling solution, a general pickling solution used for descaling stainless steel can be used. In the present invention, an aqueous solution containing 100 to 250 g / l Na ₂ SO ₄ is assumed as the neutral salt aqueous solution, and an aqueous solution containing 50 to 200 g / l H ₂ SO ₄ or HNO ₃ is assumed as the acidic aqueous solution.

The total energization amount is determined according to the scale of the pickling facility, and the current and the electrode shape may be adjusted so that the current density on the electrode surface is 100 to 5000 A / m ² .

SUS304 was descaled using a neutral salt solution, a sulfuric acid solution, and a nitric acid solution shown in Table 1. During descaling measuring current I _d flowing through the steel strip, the ratio of applied current 1000A and current efficiency. As shown in FIG. 3, the current efficiency was obtained when the distance between the electrodes was changed or when the actual width and depth of the pickling tank were changed by installing an insulator in the tank.

FIG. 4 summarizes the current efficiency under each condition. By designing the shape and electrode arrangement of the pickling tank within the scope of the present invention, a current efficiency of 90% or more could be obtained regardless of the type of pickling solution.

Claims (3)

For the equipment for descaling the annealed stainless steel strip in a neutral salt aqueous solution or acidic aqueous solution by anodic electrolysis using the indirect current method (hereinafter simply referred to as electrolytic pickling equipment), the distance between the anode and the cathode is L (Mm), where the current flowing between the electrodes is I (A), the substantial width of the pickling tank between the anode and the cathode is W (mm), and the substantial depth is D (mm), the following equation is satisfied: Electrolytic pickling method.
L> 0.6DW / I (1)
Here, the substantial width W and the substantial depth D refer to dimensions obtained by subtracting a portion where an insulator is installed from actual dimensions.   The electrolytic pickling method according to claim 1, wherein a distance between the stainless steel strip and the electrode is 20 mm or more and 150 mm or less. The aqueous solution containing 100 to 250 g / l Na ₂ SO ₄ as the neutral salt electrolysis aqueous solution and the aqueous solution containing 50 to 200 g / l H ₂ SO ₄ or HNO ₃ as the acidic aqueous solution are used. Or the electrolytic pickling method of 2.

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