JPS6157918B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrolytic cleaning method before box annealing of a steel strip that has undergone cold rolling, and in particular advantageously prevents the occurrence of scratches that were a concern when unwinding a coil after box annealing, and also This paper attempts to propose an electrolytic cleaning method for cold-rolled steel strips that can effectively reduce contamination on electrode surfaces. 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 in particular electrolytic cleaning is carried out in a sodium silicate-based cleaning bath before box annealing to clean the surface of the steel strip. on the steel strip surface
It is known that depositing SiO ₂ gives good results. By the way, a coil that has been electrolytically cleaned like this,
Normally, after box annealing, skin pass rolling is performed in a skin pass mill, but this has the disadvantage of causing scratches due to misalignment of the steel strips during unwinding. Scratches occur when the gap between the steel strips due to insufficient adhesion occurs when the coil is unrolled in the temper rolling process after annealing, and when it reaches above the mandrel (winding shaft), the coil's own weight This occurs due to the slippage that occurs when it disappears due to In addition, in electrolytic cleaning as described above, the polarity arrangement of the electrodes used is kept constant, but when electrolytic treatment is performed continuously for a long time with the same polarity arrangement, Fe and SiO2 are formed on the cathode surface. ₂ adheres and becomes dirty, increasing the resistance between the cathode surface and the electrolyte.As a result, in order to flow the specified current required for cleaning, the electrolytic voltage needs to increase unnecessarily depending on the degree of contamination on the cathode surface. There were some disadvantages that I had to deal with. This invention advantageously solves the above-mentioned problems, and it goes without saying that it can prevent seizure during box annealing, as well as advantageously prevent the occurrence of scratches during coil unwinding. This paper proposes an electrolytic cleaning method for cold-rolled steel strips that can effectively reduce contamination on electrode surfaces. By the way, in this type of electrolytic cleaning, the number of electrodes used is usually 4 to 8 on each side of the steel strip.
For example, if there are four pieces on one side, the polarity arrangement is as shown in Figure 1 a and b, with the same polarity across the steel strip S and the same polarity in the direction of threading. Two sets of electrode cell pairs having different polarities are arranged in a manner such as +--+, -++- with the adjacent polarities aligned. In addition to the above, there are other polar arrangements of the electrodes.
+-+ and +-+- are conceivable, but such a polar arrangement is rarely used because reactive current tends to flow. Hereinafter, in this specification, the polarity arrays in which the final electrodes end in + and -, as shown in FIGS. 1a and 1b, respectively, will be referred to as positive electrode polarity arrays and reverse electrode polarity arrays, respectively. Now, when electrolytic cleaning is performed for a long time with either the positive or reverse polarity arrangement as listed above,
As described above, the cathode surface is contaminated with Fe, SiO _{2 ,} etc., and the resistance between the cathode surface and the electrolyte increases, resulting in an increase in the electrolytic voltage required to flow a predetermined current. A possible solution to this problem is to switch the polarity arrangement of the electrodes every fixed electrolysis time. FIG. 2 shows the relationship between electrolytic current and voltage when the polarity arrangement is switched, in comparison with a conventional example in which the polarity arrangement is not switched. In the figure, the ○ marks are all conventional examples in which electrolytic cleaning was performed with positive electrode polarity, the ● marks are the cases in which 6 coils were electrolytically cleaned with positive electrode polarity and 1 coil with reverse electrode polarity, and the × marks are the cases in which electrolytic cleaning was performed for each coil. 13%
87% is the reverse electrode polarity, and the remaining 87% is the positive electrode polarity, and the polarity arrangement is changed within a single coil. As is clear from FIG. 2, by switching the polarity arrangement every several coils or within a single coil, it is possible to suppress the increase in electrolytic voltage to a low level. However, as will be explained later, the amount of SiO ₂ deposited varies greatly depending on the switching of the polarity arrangement, so simply switching the polarity arrangement every few coils or within a single coil is not effective from the viewpoint of preventing seizure. This is not desirable. That is, the inventors investigated the electrolytic cleaning ability and the amount of SiO ₂ deposited when using the above two types of polarity arrangement, and found that (1) The cleaning ability is uniquely determined by the supplied current value, and the polarity of the electrode (2) The amount of SiO ₂ deposited on the steel strip surface varies greatly depending on the polarity arrangement, and as shown in Figure 3,
It was found that in the case of positive electrode polarity arrangement a, the amount of SiO ₂ deposited was more than twice as large as in the case of reverse electrode polarity arrangement b. However, according to the inventors' detailed investigation into the occurrence of seizure and scratches, as shown in Figure 6, seizure tends to occur from the center to the outside in the outer winding portion of the coil, that is, the coil wall thickness. On the other hand, it has been newly discovered that scratches occur in the inner winding part of the coil, especially in the wall thickness of 300 mm or more. Therefore, although a certain amount or more of SiO ₂ is required to adhere to the outer winding part of the coil, where seizure is likely to occur, in order to prevent seizure, the inner winding part does not have as much SiO ₂ adhesion as the outer winding part. It is not necessary to reduce the amount to some extent, but it is thought that by reducing the amount to a certain extent, the degree of adhesion of the steel strip at the inner winding portion will increase, which will be more effective in preventing the occurrence of scratches. . Therefore, the inventors developed a method within a single coil.
When adjusting the amount of SiO ₂ deposited by changing the amount of SiO ₂ deposited by changing the polarity arrangement, unexpectedly good results were obtained in achieving the desired purpose. This invention is based on the above-mentioned novel findings. In other words, this invention provides steel strips that have undergone cold rolling.
Prior to box annealing, the steel strip is electrolytically cleaned in a sodium silicate-based washing bath and then wound into a coil.During this winding, the steel strip is sandwiched to make it have the same polarity and to change the polarity in the direction of threading. A plurality of electrolytic cell pairs are arranged in an electrolytic cleaning tank with the adjacent polarities of each cell pair aligned, and the polarity of the electrodes is switched from a reverse electrode polarity arrangement to a positive electrode polarity arrangement. This is a method for electrolytic cleaning of cold rolled steel strip. According to this invention method, electrolysis is performed with opposite electrode polarity at first, and the amount of SiO ₂ deposited on the inner winding part of the coil is somewhat reduced, and by winding it more tightly than before,
The occurrence of scratches that were a concern when unwinding the coil after annealing can be completely prevented, and by switching the polarity to positive electrode polarity and continuing electrolytic cleaning, the occurrence of seizure on the outer winding of the coil can be completely prevented. This can be prevented, and furthermore, by switching the polarity, contamination of the cathode surface can be significantly reduced compared to the conventional method. To change the polarity here, the winding thickness is 200mm.
It is preferable to carry out the process from the time when the wall thickness reaches approximately 300 mm to the time when the wall thickness reaches 50% of the final thickness.
This is because, as shown in the examples below, if the switch is made when the winding thickness reaches approximately 200 mm, scratches will hardly occur. Any time is fine as long as it reaches approximately 200mm, but the 6th
This is because, as shown in the figure, if the winding thickness exceeds 50%, there is a greater risk of seizure occurring. Note that the sodium silicate used in this invention method includes sodium orthosilicate (2Na ₂ O・SiO ₂ ),
Sodium metasilicate (Na ₂ SiO ₃ ), sodium disilicate (Na ₂ Si ₂ O ₅ ), and sodium tetrasilicate (Na ₂ Si ₄ O ₉ ) can all be used, but sodium orthosilicate is particularly useful. suit advantageously. In addition, when switching the polarity, the winding diameter is determined by a coil calculator, and when the winding diameter reaches a predetermined value, a switching signal is sent to the electrolytic current polarity switch, making it easy to switch. I can do it. Examples of the present invention will be described below. FIG. 4 shows an electrolytic cleaning device suitable for carrying out the present invention, where 1 is a payoff reel, 2 is an electrolytic cleaning tank, 3 is a tension reel, 4 is a winding diameter calculator, and 5 is an electrolytic current. The polarity switch 6 is an electrolytic current controller. Now, the various steel strips wound into coils after cold rolling were passed through an electrolytic cleaning tank 2 based on sodium orthosilicate, and the electrolytic current value was kept constant at 3000 ^A x 4. First, electrolytic cleaning was started with reverse electrode polarity. As shown in FIG. A polarity switching signal was sent to the electrode, and the electrolytic cleaning was continued by switching from the reverse electrode polarity to the positive electrode polarity. The outer diameter of each coil after electrolysis is average 2300~maximum
The coil thickness was 2650 mm (coil thickness: 896 to 1071 mm), and the amount of SiO ₂ deposited before and after polarity switching was as shown in FIG. 5b in each coil. Table 1 shows the maximum electrolysis voltage during electrolysis. Furthermore, Table 1 shows the results of investigating the scratch occurrence rate during unwinding after annealing each coil. There was no occurrence of seizure in any of the coils. For comparison, we also investigated the maximum electrolysis voltage and scratch occurrence rate during unwinding when electrolysis was performed according to the conventional method without switching the polarity during electrolysis, and the results are shown in Table 1. Also shown.

[Table] As is clear from Table 1, the occurrence of scratches in the examples was significantly reduced compared to the conventional example, and the increase in electrolytic voltage was also significantly reduced. As described above, according to the method of the present invention, it goes without saying that it is possible to prevent seizure during box annealing, and it is also possible to significantly reduce scratches that may occur during unwinding after box annealing. It is possible to effectively reduce contamination of the cathode surface and suppress the increase in electrolytic voltage to a low level.

[Brief explanation of the drawing]

Figures 1a and b are arrangement diagrams of positive electrode polarity and reverse electrode polarity, respectively. Figure 2 is a graph showing the relationship between electrolytic current and voltage. Figure 3 is the amount of SiO ₂ deposited depending on the difference in electrode polarity arrangement. 4 is a layout diagram of an electrolytic cleaning device suitable for implementing the present invention, FIG. 5 a is a graph showing the timing of electrode polarity switching, and FIG. 5 b is a graph showing the timing before and after polarity switching FIG. 6 is a graph showing the change in the SiO ₂ adhesion amount, and FIG. 6 is a graph showing the relationship between the coil thickness ratio and the scratch occurrence rate and seizure occurrence rate.

Claims (1)

[Claims] 1. When a cold-rolled steel strip is electrolytically cleaned in a sodium silicate-based washing bath prior to box annealing and then wound into a coil, during this winding,
Regarding the polarity arrangement of electrodes, in which a plurality of electrolytic cell pairs having the same polarity across a steel strip and having different polarities in the direction of threading are arranged in an electrolytic cleaning tank with the adjacent polarities of each of the cell pairs aligned, A method for electrolytic cleaning of cold rolled steel strip, characterized by switching the polarity from a reverse electrode polarity arrangement to a positive electrode polarity arrangement.