JPH0474439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic cleaning method before box annealing of a cold-rolled steel strip that has undergone cold rolling, and is particularly advantageous in preventing seizure between sheet surfaces, which was a concern that might occur during the box annealing. This is what we try to avoid.

Steel strips wound into coils after cold rolling often suffer from seizures between the sheet surfaces during subsequent box annealing. For this reason, various measures have been taken to prevent such seizure, and one particularly effective method is to perform electrolytic cleaning in a sodium silicate-based cleaning bath prior to box annealing.
The surface of the steel strip is cleaned and SiO ₂ is added to the surface of the steel strip.
is known to attach.

However, in the above anti-seize method,
When the amount of SiO ₂ deposited on the steel strip surface becomes too large,
Produces a milky white temper color during annealing. Since this temper color impairs the appearance of the product after painting, it is desirable to suppress its occurrence as much as possible. If the amount of SiO ₂ deposited is too small, no anti-seizure effect can be expected.

It was also confirmed from the SiO ₂ amount analysis results by glow discharge analysis shown in FIG. 1a that temper color occurs when a large amount of SiO ₂ is deposited.
The analysis results shown in Figure a show that the amount of SiO ₂ deposited was measured by glow discharge at locations A, B, and C where temper color did not occur, and at locations D and E where temper color occurred, as shown in Figure b. The analysis revealed that the amount of SiO ₂ deposited was approximately 20% higher in areas where temper color occurred than in areas where temper color did not occur.

Therefore, in order to prevent both seizure and temper color from occurring at the same time, it is necessary to adjust the amount of SiO ₂ deposited within a predetermined appropriate range. It was difficult to deposit an appropriate amount of SiO ₂ .

In order to solve the above problem, the inventors conducted various studies on electrolytic cleaning methods for cold-rolled steel strips before annealing, and as a result, they succeeded in reducing the amount of SiO ₂ deposited on one side of the steel strip. By depositing the excess amount on the other side, it was discovered that seizure could be completely prevented on at least one side of the steel strip without the risk of temper color, leading to the completion of this invention.

In other words, this invention provides steel strips that have undergone cold rolling.
When performing electrolytic cleaning in a sodium silicate-based cleaning bath prior to box annealing, the polarity of the final electrode in the electrolytic cleaning bath is reversed from one side of the steel strip to the other side. This is a method for electrolytic cleaning of cold rolled steel strip.

Hereinafter, this invention will be specifically explained according to the experimental results that led to its origin.

Normally, in this type of electrolytic cleaning, the number of electrodes used is 4 to 8 on each side of the steel strip, and their polar arrangement is, for example, 4 on each side, as shown in Figures 2a and b. As shown in FIG. They are arranged as follows. Other polar arrangements include −＋−＋
, +-+-, etc., but such a polar arrangement is rarely used because reactive current tends to flow.

By the way, in the two types of polar arrangement as mentioned above, when the polar arrangement of the final electrode is + such as "+--+", the amount of SiO ₂ deposited is smaller than when the polarity of the final electrode is -. However, in either case, the amount of adhesion varies greatly; for example, even when the same charge density is applied as shown in FIG. 3, there is a variation of 0.5 to 1.0 mg per m ² .

Figure 4 shows the results of investigating the appropriate amount of SiO ₂ to adhere from the viewpoint of preventing seizure. The figure shows SiO ₂ between the steel strips.
This study investigated the relationship between adhesion amount and adhesion strength, and if the adhesion strength is 60 kg/cm ² or less, it can be considered that no seizure has occurred.

From the results in the same figure, to prevent burn-in, 1.0
It can be seen that a SiO ₂ adhesion amount of mg/m ² or more is required.

On the other hand, from the perspective of preventing temper color, SiO ₂
When examining the appropriate adhesion amount of SiO 2, it was found that the adhesion amount of SiO ₂ was 2
It has been shown that concentrations exceeding mg/m ² are dangerous.

Therefore, the adhesion amount X of SiO ₂ is 1≦X≦2 (mg/
m ² ) is desirable.

However, it was extremely difficult to control the amount of SiO ₂ within the above range, as is clear from the results shown in FIG. 3 above. In other words, if the electrode polarity arrangement is +--+ on both sides of the steel strip, the variation will be too large, and on the other hand, it will be -++-+.
-, there is a great possibility that the amount of SiO ₂ deposited will be 1 mg/m ² or less, and in any case, it is doubtful that seizure and occurrence of temper color can be effectively prevented.

Therefore, the inventors focused on the fact that the amount of SiO ₂ deposited varies depending on the polarity arrangement of the electrodes during electrolytic cleaning, and as shown in Fig. When electrolysis was performed on the other side with the reverse arrangement, the cleaning ability did not deteriorate at all, and it was found that during subsequent box annealing, the occurrence of seizure could be completely prevented on at least one side without producing any temper color. He completed this invention.

Figure 6 shows the polarity arrangement of the upper electrode as "-++-",
The lower part is set as "+--+", and the results of investigating the amount of SiO ₂ deposited on each of the front and back surfaces are shown when electrolysis is performed at the same current value.

The amount of adhesion on the front side is about 88% compared to the back side.

By performing electrolysis on one side of the steel strip in a reverse arrangement on the other side, SiO ₂ is deposited on one side to an extent that there is no risk of temper color, while the other side is coated with a slightly higher amount of SiO 2. By attaching SiO ₂ to the surface, the occurrence of seizure could be completely prevented.

In order to obtain particularly good results in this invention, it is desirable that the supplied electricity density be approximately 4±1C/dm ² , and with the above supplied electricity density, the amount of SiO ₂ deposited will fall within an appropriate range. , and a sufficiently satisfactory result was obtained with a difference of about 0.3 mg/m ² between the front and back surfaces, and even if there was variation in the amount of adhesion on the back side, the surface The occurrence of burn-in was completely prevented without the occurrence of temper color.

Next, the degreasing and SiO ₂ adhesion mechanism when electrolytic cleaning is performed according to the present invention will be explained with reference to FIG.

The surface of the steel strip S is degreased by water electrolysis before the final electrode, and then SiO ₂
is attached. At this time, the polarity of the final electrode is on the + side.
The amount of SiO ₂ deposited is large and decreases on the - side, but as mentioned above, the cleaning power depends on the current value regardless of the polarity _.
There is no change in cleanliness, only the amount of adhesion changes.

Examples of the present invention will be described below.

As shown in Figure 5 above, the polarity arrangement of the electrodes is "-++-" at the top of the steel strip and "+--" at the bottom.
+'', electrolytic cleaning was performed at an electrolytic amount of electricity of 4 C/dm ² and wound into a coil. This coil was then subjected to box annealing, and the occurrence of seizure and temper color at that time was investigated.

As a result, there was no occurrence of burn-in, and no temper color was generated on the surface.
On the back side, some traces of this were also visible at about 50 mm from the edge (the edge in the width direction of the board).

As described above, according to the present invention, in electrolytic cleaning of a cold rolled steel strip before box annealing, the coil after box annealing can be cleaned without reducing the cleaning ability.
At least on one side, seizure can be completely prevented without any temper coloring occurring.

[Brief explanation of the drawing]

Figure 1a is a graph showing the relationship between the occurrence of temper color and the amount of SiO ₂ deposited, Figure 1b is a plan view of the steel strip showing the state of occurrence of temper color, Figure 2a,
b is a polar arrangement diagram of electrodes according to the conventional method, Fig. 3 is a graph showing the relationship between charge density and SiO ₂ adhesion amount, and Fig. 4 is a graph showing the relationship between SiO ₂ adhesion amount and adhesion strength. Figure 5 is a graph showing the polar arrangement of the electrode according to the present invention, Figure 6 is a graph showing the difference in the amount of SiO ₂ deposited on the front and back surfaces, and Figure 7 is a graph showing the polarity arrangement of the electrode according to the present invention on the front and back surfaces. FIG. 8 is a graph showing the relationship between the electric charge density and the amount of SiO ₂ deposited in the case of degreasing and SiO ₂ deposition in this invention.
It is an explanatory view of an adhesion mechanism.

Claims (1)

[Claims] 1. When electrolytically cleaning a cold-rolled steel strip in a sodium silicate-based cleaning bath prior to box annealing, the polarity of the final electrode in the electrolytic cleaning bath is changed from one side of the steel strip to another. A method for electrolytic cleaning of cold-rolled steel strip, characterized by electrolyzing in a reverse arrangement on the surface.