JP3426959B2 - Method for increasing tension of unidirectional electrical steel sheet coating - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for increasing tension when a tension-adding type insulating film is formed on a grain-oriented electrical steel sheet.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are widely used as a magnetic iron core material, and in particular, a material having a low iron loss is required to reduce energy loss. It is generally known that applying a tension to a steel sheet is effective for reducing iron loss. In order to apply tension to the steel sheet, it is effective to form a film made of a material having a smaller coefficient of thermal expansion than the steel sheet at a high temperature. The forsterite film formed by the reaction between the oxide on the surface of the steel sheet and the annealing separator during the finish annealing step can give tension to the steel sheet, and further on the film, colloidal silica, phosphate, The method of forming an insulating film made of chromate has a large effect of applying tension to the steel sheet and is effective in reducing iron loss. Therefore,
A general method for producing a grain-oriented electrical steel sheet is to leave the film produced in the finish annealing step and then apply the above-described tensile insulating film.

On the other hand, according to a study by the inventors, 2.0 kgf / m
It has been found that coating tension up to m ² is effective in reducing iron loss. However, in the current “forsterite coating + phosphate coating containing colloidal silica”, the total coating tension is about 1.0 kgf / mm ² . Therefore, in order to further reduce iron loss, a new oxide film is formed by applying and baking a liquid having a composition containing boric acid and boehmite, which has a large effect of imparting tension per unit amount of adhesion to a conventional phosphate-based film. A forming method is proposed in JP-A-6-65754, etc., and by forming this coating on a grain-oriented electrical steel sheet having a forsterite coating, the total effect of applying tension to the steel sheet is about 1.3 kgf / Increase to about mm ² .

However, when the coating tension is up to 2.0 kgf / mm ² , the iron loss decreases with the improvement of the tensioning effect, but for the production of the low iron loss unidirectional electrical steel sheet, the forsterite coating is used. It is necessary to further improve the tensioning effect of the insulating film formed on the top.

[0005]

In view of the above situation, the present invention enhances the tension imparting effect when a tension-adding type insulating coating is formed on the surface of a grain-oriented electrical steel sheet on which a forsterite coating is formed. It provides a method.

[0006]

Means for Solving the Problem The present invention is to apply a coating solution containing boric acid and boehmite as a main component to a unidirectional electrical steel sheet on which a forsterite coating is formed, followed by continuous annealing to form a coating film, The gist is a method of increasing the tension of a grain-oriented electrical steel sheet coating that is annealed for 0.5 hour or more in a temperature range of 500 to 1000 ° C. Further, the composition ratio of boric acid and boehmite in the coating solution, respectively, in terms of oxide molar ratio, 0.2 ≤ B ₂ O ₃ / Al ₂ O ₃ ≤ 1.0, further,
The gist is the method of increasing the tension of the grain-oriented electrical steel sheet coating after the core is formed by annealing for 0.5 hours or more after the coating is formed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The inventors have set up a steel plate with a forsterite coating.
In order to form an insulating film with excellent force application effect,
The test was conducted. 0.23 mm thick directional electric field containing approximately 3% Si
The magnetic steel sheet was finished until finish annealing. Anneal to this test material
After washing with water to remove the separating agent, boric acid and boehm
Insulating coating liquid containing iron as a main component (molar ratio = 0.5)
Is coated on the surface of the steel sheet with a grooved rubber roll and heated at a temperature of 800 ° C.
It was baked in a continuous annealing furnace for 2 minutes. The film tension at this time
The force is 4.5 g / m on one side. ²Converted to 0.96 kgf / mm²
Met. Batch baking for various times at 500-1000 ℃
After blunting, the film tension was measured.

FIG. 1 shows the relationship between the temperature and time of batch annealing and the amount of increase in tension per normal amount of adhesion. The values in Fig. 1 are the amount of increase in tension (an increase from 0.96 kgf / mm ² ) when the insulating coating was formed at 4.5 g / m ² per side of the steel sheet. From FIG. 1, it can be seen that the film tension is increased by further performing batch annealing after forming the insulating film in the continuous annealing furnace. In particular,
Due to annealing for 30 minutes or more, the improvement margin is large, 0.1 kgf / mm ²
Therefore, the range of the annealing time in the present invention is set to 30 minutes or more.

After forming an insulating film by continuous annealing,
The reason why the film tension increases by performing the batch annealing is considered as follows. The reason why the insulating coating gives tension to the steel sheet is due to the difference in thermal expansion coefficient between the aluminum borate produced in the reaction of boric acid and boehmite and the unidirectional electrical steel sheet. However, since the annealing time in the continuous annealing is short, at most several minutes, it cannot be said that the reaction between boric acid and boehmite in the insulating film is sufficient. Therefore, by carrying out batch annealing for a long time, unreacted boric acid and boehmite react with each other, aluminum borate is produced, and the effect of imparting tension is increased.

In the present invention, the reason why the temperature range of the batch annealing is 500 ° C. or more and 1000 ° C. or less is preferably 500 ° C. or more from the viewpoint of accelerating the reaction between boric acid and boehmite, and 1000 ° C. or less from the viewpoint of economy. Because it is desirable. The grain-oriented electrical steel sheet used as the wound core is subjected to forming called "lacing" and then annealed for the purpose of removing the strain introduced by working. If this annealing is performed under the conditions shown in the present invention,
It is expected that the tension of the insulating film will be increased without increasing the number of steps.

When the composition of the insulating film coating liquid contains boric acid and boehmite as the main components, it is necessary that the molar ratio in terms of the respective oxides is 0.2 ≦ B ₂ O ₃ / Al ₂ O ₃ ≦ 1.0. is there. This is because, if the composition ratio is less B ₂ O ₃ exceeds this range, sufficient iron loss improvement effect for the film tension is reduced can not be obtained, whereas, if the B ₂ O ₃ is too large, stoichiometry This is because an excessive amount from the theoretical composition remains as an unreacted material, resulting in deterioration of water resistance and corrosion resistance and deterioration of heat resistance and sticking resistance.

As a means for applying the coating liquid to the surface of the steel sheet, any conventionally known method such as dipping method, spraying, or electrophoresis method can be used in addition to the above-mentioned grooved rubber roll (roll coater). Can be adopted.

[0013]

[Example] (Example 1) The test material contains about 3% Si.
A 23 mm thick unidirectional electrical steel sheet that had been subjected to finish annealing was used. An insulating coating solution containing boric acid and boehmite as the main components (oxide conversion molar ratio B ₂ O ₃ / A
l ₂ O ₃ = 0.5) is applied to the steel plate surface with a roll coater,
It was baked at a temperature of 800 ° C for 120 seconds. As a result, iron loss W
_17/50 was 0.825 W / kg (B ₈ = 1.920 T), and the coating tension was 0.94 kgf / m ² in terms of the coating amount per one surface of 4.5 g / m ² .

Further, batch annealing was carried out at 850 ° C. for various times. Table 1 shows the _amount of improvement in coating tension and iron loss W _17/50 at that time. It can be seen that when the annealing time is 0.5 hours or more, the film tension is significantly improved and the iron loss reduction effect is also increased.

[0015]

[Table 1]

(Example 2) The test material contains about 3% Si.
A grain-oriented electrical steel sheet having a thickness of 0.23 mm, which had been subjected to finish annealing, was used. An insulating coating solution containing boric acid and boehmite as the main components (oxide conversion molar ratio B ₂ O ₃ / A
l ₂ O ₃ = 0.5) is applied to the steel plate surface with a roll coater,
It was baked at a temperature of 850 ° C for 120 seconds. As a result, iron loss W
_17/50 was 0.835 W / kg (B ₈ = 1.910T), and the coating tension was 0.95 kgf / m ² in terms of the coating amount per one surface of 4.5 g / m ² .

Further, batch annealing was carried out at 850 ° C. for various times. Table 2 shows the improvement in coating tension and iron loss W _17/50 at that time. It can be seen that the coating tension is remarkably improved when the annealing time is 0.5 hours or more, and the iron loss reducing effect is great.

[0018]

[Table 2]

(Example 3) The test material contains approximately 3% Si.
A grain-oriented electrical steel sheet having a thickness of 0.23 mm, which had been subjected to finish annealing, was used. An insulating coating solution containing boric acid and boehmite as the main components (oxide conversion molar ratio B ₂ O ₃ / A
l ₂ O ₃ = 0.5) is applied to the surface of the steel plate with a grooved rubber roll,
It was baked at a temperature of 800 ° C for 120 seconds. As a result, iron loss W
_17/50 was 0.831 W / kg (B ₈ = 1.915T), and the coating tension was 0.93 kgf / m ² in terms of the coating amount per one surface of 4.5 g / m ² .

Further, batch annealing was carried out at 900 ° C. for various times. Table 3 shows the improvement in coating tension and iron loss W _17/50 at that time. It can be seen that the coating tension is remarkably improved when the annealing time is 0.5 hours or more, and the iron loss reducing effect is great.

[0021]

[Table 3]

[0022]

INDUSTRIAL APPLICABILITY The present invention enhances the tension imparting effect of the insulating coating when the tension-adding type insulating coating is formed on the surface of the grain-oriented electrical steel sheet on which the forsterite coating is formed. It is possible to manufacture a grain-oriented electrical steel sheet that can maximize the iron loss reduction effect of the addition.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between batch annealing temperature and time, and the amount of increase in tension of a coating film per 4.5 g / m ² attached amount.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-5-279746 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/00 C21D 9/46 501 H01F 1 / 18

Claims (3)

(57) [Claims] 1. A coating solution containing boric acid and boehmite as a main component is applied to the surface of a grain-oriented electrical steel sheet on which a forsterite coating has been formed, and the film is formed by continuous annealing, and then in a temperature range of 500 to 1000 ° C. Then, the method for increasing the tension of the grain-oriented electrical steel sheet coating is characterized by performing annealing for 0.5 hour or more. 2. The composition ratio of boric acid and boehmite in the coating liquid is 0.
2. It is set that 2 ≦ B ₂ O ₃ / Al ₂ O ₃ ≦ 1.0.
A method for increasing the tension of the unidirectional electrical steel sheet coating described. 3. The method for increasing the tension of a unidirectional electrical steel sheet coating according to claim 1, wherein the annealing after the coating formation is performed after the iron core is formed.