JP2017177219A - Cold rolling method for electromagnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cold-rolling an electromagnetic steel sheet excellent in sheet thickness accuracy at high efficiency.SOLUTION: There is provided a method for cold-rolling an electromagnetic steel sheet using a tandem rolling machine. In the tandem rolling machine, the work roll surface roughness of a final stand table is 0.03 μmRa or more but 0.08 μmRa or less, and that roughness of the stand table preceding the final one is 0.03 μmRa or more but 0.15 μmRa or less, preferably 0.06 μmRa or more but 0.15 μmRa or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for cold rolling an electrical steel sheet. Furthermore, this invention relates to the method of cold-rolling the magnetic steel plate excellent in plate | board thickness precision with high efficiency.

  Electrical steel sheets are used as iron core materials for electrical equipment such as rotating machines. In recent years, electrical steel sheets with lower iron loss and higher magnetic flux density have been demanded from the viewpoint of energy saving of electrical equipment, and improvement of the magnetic properties of electrical steel sheets has become increasingly important. Moreover, electromagnetic steel sheets are usually used as an iron core by punching them into a predetermined shape and then laminating them. At this time, if the thickness variation of the product is large, the characteristics as an iron core will deteriorate, so electromagnetic steel sheets are required to have high thickness accuracy equivalent to magnetic characteristics, compared to steel sheets for cans and steel sheets for automobiles, The demand for plate thickness accuracy is severe.

  By the way, it has been conventionally known that the magnetic properties of an electrical steel sheet are improved by reducing the plate thickness, and in recent years, the thickness of the electrical steel sheet has been further reduced. For example, when considering cold rolling, if the plate thickness is reduced, the production efficiency is reduced accordingly, so that it is necessary to increase the rolling speed in order to maintain productivity. Further, when the plate thickness is reduced, the number of stacks at the time of stacking is increased, so that the influence of the plate thickness variation on the iron core characteristics is further increased. Specifically, as shown in FIG. 1, it is confirmed that if the plate thickness periodically fluctuates over ± 1.2% of the target plate thickness, an abnormal thickness of the iron core occurs and the characteristics deteriorate. ing.

  As described above, in order to improve the magnetic properties of the electrical steel sheet, it is necessary to cold-roll a thinner object with superior sheet thickness accuracy as compared with the conventional art. At this time, from the viewpoint of productivity, it is necessary to perform rolling at a higher speed, and the technical level required for cold rolling of electrical steel sheets is becoming higher and higher.

  In order to cold-roll a steel sheet with high efficiency, it is preferable to perform rolling using a tandem rolling mill composed of a multi-stand rolling mill. However, it is known that in cold rolling using a tandem rolling mill, when thin materials and hard materials are rolled at high speed, mill vibration called chattering occurs, and a phenomenon in which the plate thickness fluctuates periodically tends to occur. . It has been reported that chattering is often caused by poor lubrication. Therefore, for example, Patent Document 1 and Patent Document 2 disclose a method of controlling the friction coefficient within an appropriate range so that such chattering phenomenon does not occur in steel plates for cans. As a method for controlling the friction coefficient, a method for changing the supply condition of the lubricating oil (rolling oil) has been proposed.

  By the way, in order to respond to increasingly strict product requirements, for example, as disclosed in Patent Document 3, a mill vibrometer that detects chattering is installed in a mill housing of a stand of a tandem rolling mill. By installing the mill vibrometer, it is possible to detect minute plate thickness vibrations, and it is possible to prevent a steel plate with low plate thickness accuracy due to chattering from flowing out into the lower process. In addition, the chattering is detected by the mill vibrometer, and it is possible to avoid the breakage of the steel sheet by taking measures such as reducing the rolling speed before a serious trouble such as the breakage of the steel sheet occurs.

  In reverse cold rolling of stainless steel, as described in Patent Document 4, rolling defects such as chatter are reduced by rolling using a work roll or intermediate roll having a surface roughness of 0.1 μmRa or less. A method is disclosed.

Japanese Examined Patent Publication No. 6-13126 Japanese Patent No. 3368841 JP2015-009261A JP-A-4-356307

  However, electromagnetic steel sheets are required to have high plate thickness accuracy as described above, and the characteristics of the iron core are deteriorated even when minute plate thickness fluctuations that cannot be detected by a mill vibrometer or the like occur.

  For this reason, the method of controlling the chattering by detecting the friction coefficient as in the methods described in Patent Document 1 and Patent Document 2 has room for improvement in order to realize the strict plate thickness accuracy required for the electromagnetic steel sheet. There is.

  In addition, as described in Patent Document 3, in a method in which a mill vibrometer is installed in a mill housing and chattering is detected by frequency analysis of the vibration, a steel plate with low plate thickness accuracy due to chattering is used in the lower process. Although it is possible to suppress the outflow, it is difficult to manufacture a steel plate with excellent thickness accuracy.

  In addition, the method of patent document 4 cannot implement | achieve the desired high speed rolling.

  This invention is made | formed in view of the above situation, and proposes the method of cold-rolling the electromagnetic steel plate excellent in plate | board thickness precision with high efficiency.

  As a result of intensive studies to achieve the above object, the present inventors have completed the present invention. The gist of the present invention is as follows.

[1] A method of cold rolling an electrical steel sheet using a tandem rolling mill,
In the tandem rolling mill, the work roll surface roughness of the final stand is 0.03 μmRa or more and 0.08 μmRa or less, and the work roll surface roughness of the stand immediately before the final stand is 0.03 μmRa or more and 0.15 μmRa. A method for cold rolling an electrical steel sheet, which is as follows.
[2] The method for cold rolling an electrical steel sheet according to the above [1], wherein the work roll surface roughness of the stand immediately before the final stand is 0.06 μmRa or more and 0.15 μmRa or less.

  [3] The method for cold rolling an electrical steel sheet according to the above [1] or [2], wherein an oil film thickness h introduced into the roll bite in the final stand obtained from the following formula (1) is 0.050 μm or more.

  In the present invention, the surface roughness Ra of the work roll and the electromagnetic steel sheet is determined based on JIS B 0601 (2013).

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to cold-roll the magnetic steel plate excellent in plate | board thickness precision with high efficiency. Furthermore, it is possible to suppress the occurrence of the slip phenomenon.

FIG. 1 shows a chart of the thickness of an electromagnetic steel sheet measured with a contact-type thickness meter. Minute fluctuations in plate thickness are recorded. FIG. 2 is a diagram showing the influence of the work roll surface roughness of the final stand and the stand immediately preceding it on the plate thickness variation. FIG. 3 is a diagram showing the relationship among the film thickness of the introduced oil, the work roll surface roughness, and the product surface roughness introduced into the roll bites of the final stand.

  Hereinafter, embodiments of the present invention including the best mode will be described.

  As a result of arranging the relationship between the plate thickness variation and the work roll surface roughness when the magnetic steel sheet is cold-rolled with a tandem rolling mill, the present inventors have determined that the work roll surface roughness of the final stand and the final stand 1 Knowing that the work roll surface roughness of the previous stand is within the specified roughness range, it is possible to suppress periodic plate thickness fluctuations to within ± 1.2% of the target plate thickness. The present invention has been completed.

  2. Description of the Related Art Conventionally, as described in, for example, Patent Document 2, a method of suppressing chattering, and consequently thickness variation, by controlling the friction coefficient of a stand where chattering occurs and the upstream or downstream stand of the stand within an appropriate range. As a method for controlling the friction coefficient, a method for changing the supply condition of the lubricating oil (rolling oil) has been proposed.

On the other hand, the present inventor can avoid minute fluctuations in the thickness of the magnetic steel sheet by reducing the friction coefficient of the final stand and the stand immediately before the final stand and reducing the rolling load. Found out. As means for realizing this knowledge, the present inventors have found that it is important to define the work roll surface roughness within a predetermined roughness range, and have completed the present invention.
In general, the stand immediately before the final stand is often applied with a higher rear tension than the final stand. Therefore, when the work roll surface roughness is excessively reduced in the stand immediately before the final stand, there is a high possibility that a slip phenomenon will occur. When the slip phenomenon occurs, the operation is forced to be performed below the generation speed range, and the production efficiency may be reduced. On the other hand, the present inventors suppress both periodic plate thickness fluctuation and slip phenomenon by defining the work roll surface roughness of the stand immediately before the final stand within a predetermined roughness range. It was found that it is possible to realize.

  By the way, the work roll surface roughness of the stand included in the tandem rolling mill, particularly the work roll surface roughness of the final stand, is directly determined by the product surface roughness in many cases because it is directly linked to the product surface roughness of the electromagnetic steel sheet.

  Also in the electromagnetic steel sheet, it is preferable to manage the steel sheet surface roughness after cold rolling to be 0.15 μmRa or more and 0.35 μmRa or less from the viewpoint of, for example, the problem of film coating quality or the welding stability of the product. Based on this, it was preferred that the work roll surface roughness of the final stand be greater than 0.08 μmRa.

  On the other hand, when the work roll surface roughness of the final stand is reduced to 0.08 μmRa or less in order to suppress the plate thickness fluctuation, it falls below the preferred range of the steel plate surface roughness after the cold rolling described above. . Therefore, if a desired amount of rolling oil is introduced into the roll bite, the amount of oil pits formed on the surface of the steel sheet increases, and even when the work roll surface roughness of the final stand is reduced, the steel sheet surface roughness is preferably adjusted as described above. The present inventors have found that it can be controlled within the range.

  In this invention, the experimental result which came to limit the work roll surface roughness is described.

  Using a total of 5 tandem rolling mills, magnetic steel sheets with a thickness of 1.8-2.2 mm are cold-rolled to a final thickness of 0.20-0.35 mm at a rolling speed of 500 mpm or more, causing fluctuations in thickness. The situation was investigated.

  At this time, the target surface roughness of the work roll is set as shown in Table 1, and the fourth stand (the stand immediately before the final stand) is set to three levels of 0.05 μmRa, 0.10 μmRa, 0.20 μmRa, Five stands (final stand) were combined at two levels of 0.05 μmRa and 0.10 μmRa, and 13 to 16 coils were cold-rolled under each condition, and the thickness variation was investigated.

  A thickness variation of 500 mm in length is measured with a dial gauge at the center in the longitudinal direction and the center of the sheet width of a cold-rolled steel sheet, and a sheet thickness with a target variation of ± 1.2% or more is regarded as defective. . The results are shown in FIG. In FIG. 2, “●” means that there is no plate thickness defect, and “x” means that there is a plate thickness failure. Further, a case where slip occurs is indicated by Δ. In FIG. 2, the combinations of the work roll surface roughness of the fourth stand and the fifth stand are arranged in six groups, and the positions of ●, x, and Δ are not necessarily accurate.

  As shown in FIG. 2, it can be seen that there is no plate thickness defect under the condition that the work roll surface roughness is small in both the fourth stand and the fifth stand. Furthermore, it can be seen that if the roughness of the fourth stand is too small, a slip phenomenon occurs.

  The smaller the work roll surface roughness of the final stand, the lower the rolling load, which is considered to be effective in suppressing plate thickness fluctuations. Also, the work roll surface roughness of the stand immediately before the final stand is transferred to the steel plate surface to reduce the steel plate surface roughness on the final stand entry side, so that the effect of reducing the rolling load of the final stand is reduced. It is thought that thickness fluctuation is suppressed.

  In addition to the above test, when the work roll surface roughness of the fourth stand and the fifth stand was changed and cold rolling of the magnetic steel sheet was performed, the work roll surface roughness of the fifth stand was 0.08 μmRa or less, the fourth In the stand, the work roll surface roughness was 0.15 μmRa or less, and good results were obtained with respect to suppression of plate thickness variation.

From this experimental result, the work roll surface roughness of the final stand is defined as 0.08 μmRa or less, and the work roll surface roughness of the stand immediately before the final stand is defined as 0.15 μmRa or less. Making the work roll surface roughness of the final stand and the stand immediately before the final stand smaller than 0.03 μmRa increases the polishing load of the work roll and maintains the work roll surface roughness during rolling. This is not preferable because it is difficult to do. Therefore, the work roll surface roughness of the final stand and the stand immediately before the final stand is 0.03 μm Ra or more.
Furthermore, for the purpose of preventing slip, the work roll surface roughness of the stand immediately before the final stand is preferably 0.06 μm Ra or more, more preferably 0.07 μm Ra.
The smaller the work roll surface roughness of the final stand, the lower the rolling load, which is more effective for suppressing plate thickness variation. From this point, the work roll surface roughness of the final stand is preferably 0.07 μmRa or less.
Further, from the viewpoint of achieving both the above-described plate thickness fluctuation suppression and slip suppression, it is preferable that the work roll surface roughness of the final stand and the work roll surface roughness of the stand immediately before the final stand are different.

  The experimental results of the oil film thickness introduced to the roll bite at the final stand will be described. The work roll surface roughness of the fifth stand is set to two levels of 0.05 μmRa and 0.10 μmRa, the rolling oil conditions, the rolling conditions, etc. are changed, the calculated oil film thickness is changed variously, and the cold rolled sheet obtained The surface roughness was investigated.

Here, a method of calculating the introduced oil film thickness (h, unit μm) will be described. The above formula (1) includes the formulas of h, h ₁ , B, and δ. The introduced oil film thickness (h) was calculated using the above formula (1), considering only the plate-out film thickness (h ₁ ) of the steel sheet. The plate-out film thickness (h ₁ ) of the steel sheet was considered to be determined by the supply amount (Q) of rolling oil and the plate-out efficiency (A). As shown in the formula (1), the introduced oil film thickness (h) is the rolling oil properties such as the viscosity (η) of the rolling oil and the pressure viscosity coefficient (α) of the rolling oil, the flat roll radius (R ′) and the roll speed. It varies depending on rolling conditions such as (V ₁ ). The plate-out efficiency (A) is a numerical value measured in advance, and 0.01 is used here.

  The obtained results are shown in FIG. As shown in FIG. 3, even when the work roll surface roughness of the final stand is 0.05 μmRa, by setting the introduced oil film thickness (h) to 0.050 μm or more, the steel plate (product) surface roughness is in a suitable range ( It was confirmed that the desired target roughness) (0.15 μmRa or more and 0.35 μmRa or less) was entered. As a result, it was found that the surface roughness can be controlled within a desired range while suppressing the thickness variation. Although not shown, even when the work roll surface roughness of the final stand is 0.03 μm Ra, the steel sheet surface roughness is set to a target range (0.15 μm Ra or more by setting the introduced oil film thickness (h) to 0.050 μm or more. 0.35 μmRa or less).

  In addition, it is preferable to apply this invention to the electrical steel sheet whose Si content is 1.5 mass% or more. This is because the rolling load generally decreases when the Si content is low, and a slip phenomenon may occur even when the work roll surface roughness is within a specified range due to excessive reduction of the friction coefficient.

  For the same reason, the present invention is preferably applied when the plate thickness after cold rolling is 0.5 mm or less.

  A tandem rolling mill normally rolls in only one direction and does not perform reverse rolling. In the present invention, the tandem rolling mill is not particularly limited, but a tandem rolling mill having 3 to 6 stands is preferable from the viewpoint of rolling the above-described Si steel sheet to the preferred thickness. The type of stand constituting the tandem rolling mill may be selected as appropriate, and a quadruple rolling mill having two work rolls and two backup rolls is usually used.

  Examples of the present invention will be described below. The technical scope of the present invention is not limited to the following examples.

  The magnetic steel sheet was cold-rolled by a tandem rolling mill equipped with 5 quadruple rolling mills, and the defect occurrence rate of sheet thickness fluctuation and the steel sheet surface roughness after cold rolling were evaluated.

  As shown in Table 2, in the conventional example (Comparative Example 1), the work roll surface roughness of the final stand (fifth stand) is 0.09 to 0.12 μmRa, and under the conditions of the present invention, the work roll surface of the final stand The roughness was set to 0.04 to 0.06 μmRa or 0.07 to 0.08 μmRa. The work roll surface roughness of the fourth stand was changed in the range of 0.03 μmRa to 0.10 μmRa.

  A magnetic steel sheet having a Si content of 3.0% by mass or more and a thickness of 1.8 to 2.2 mm was prepared in 200 coils for each condition, and the sheet thickness was 0.20 to 0.35 mm at a rolling speed (sheet speed) of 600 to 1000 mpm. Finished. From the rolling conditions and rolling oil conditions, the introduced oil film thickness is calculated by the above formula (1) and is shown in Table 2 together. The plate thickness variation was measured by the same method as described above, and a plate having a periodic variation of the target plate thickness of ± 1.2% or more was regarded as a defective plate thickness.

  Table 2 shows the results. In the conventional example, the defect rate of the plate thickness variation is 7.0%, whereas in the example of the present invention, the defect rate can be reduced to 1.5% or less. Moreover, in the present invention example in which the introduced oil film thickness is 0.050 μm or more, the surface roughness of the electromagnetic steel sheet, which is a preferable management range, can be achieved from 0.15 μmRa to 0.35 μmRa. Furthermore, the occurrence of slip is suppressed by setting the work roll surface roughness of the last stand (fourth stand) to 0.06 μmRa or more.

  As described above, by applying the present invention and appropriately setting the work roll surface roughness and the introduced oil film thickness, the steel sheet surface roughness is within the target range, and the electromagnetic steel sheet particularly excellent in sheet thickness accuracy is highly efficient. Can be cold rolled.

Claims (3)

A method for cold rolling an electrical steel sheet using a tandem rolling mill,
In the tandem rolling mill, the work roll surface roughness of the final stand is 0.03 μmRa or more and 0.08 μmRa or less, and the work roll surface roughness of the stand immediately before the final stand is 0.03 μmRa or more and 0.15 μmRa. A method for cold rolling an electrical steel sheet, which is as follows.   The method for cold rolling an electrical steel sheet according to claim 1, wherein the work roll surface roughness of the stand immediately before the last stand is 0.06 µmRa or more and 0.15 µmRa or less. The method for cold rolling an electrical steel sheet according to claim 1 or 2, wherein an oil film thickness h introduced into the roll bite in the final stand obtained from the following formula (1) is 0.050 µm or more.

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