JPH11302859A - Tension increasing method of grain-oriented silicon steel sheet coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the tension imparting effect of a tension addition type insulating film formed on the surface of a steel sheet having no forsterite coating film by applying a coating solution consisting essentially of boric acid and boehmite, continuously annealing to form a coating film and annealing at a specific temp. for a specific time. SOLUTION: The annealing is applied at 500-1000 deg.C for >=0.5 hr. The composition ratio of boric acid to boehmite in the coating solution is preferably controlled to 0.2<=B2 O3 /Al2 O3 <=1.0 respectively expressed in terms of oxide by mol. And the annealing after the formation of coating film is preferably carried out after an iron core is formed. The difference of the coefficient of thermal expansion between aluminum borate generated by the reaction of boric acid with boehmite and the steel sheet causes the insulating film to impart tension to the steel sheet. In the continuous annealing, the reaction of boric acid with boehmite is insufficient in the insulating film because of the short annealing time and then, the tension imparting effect is increased by applying batch annealing for a long time to carry out the reaction to generate aluminum borate.

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 A grain-oriented electrical steel sheet is widely used as a magnetic iron core material. In particular, a material having a small iron loss is required to reduce energy loss. In general, it is known that reducing iron loss is effective by applying tension to a steel sheet. In order to impart tension to a 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 steel sheet surface 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 a steel sheet and is effective in reducing iron loss. Therefore,
It is a general method for manufacturing a grain-oriented electrical steel sheet to apply a tensile insulating film as described above while leaving the film generated in the finish annealing step.

On the other hand, according to studies by the inventors, 2.0 kgf / m
It has been found that application of a coating tension up to m ² is effective in reducing iron loss. However, in the current “forsterite film + phosphate film containing colloidal silica”, the total film 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 containing a composition containing boric acid and boehmite, which has a large effect of imparting tension per unit amount to a conventional phosphate-based film. A forming method is proposed in Japanese Patent Application Laid-Open No. 6-65754 and the like. By forming this coating on a grain-oriented electrical steel sheet having a forsterite coating, the total effect of imparting tension to the steel sheet is about 1.3 kgf / to increase up to about mm ^2.

[0004] However, up to a coating tension of 2.0 kgf / mm ² , iron loss is reduced due to the improvement in the effect of imparting tension. However, for the production of a unidirectional electrical steel sheet having a low iron loss, a forsterite coating is required. It is necessary to further improve the effect of imparting tension to the insulating film formed thereon.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention enhances the effect of applying a tension when a tension-adding type insulating film is formed on the surface of a grain-oriented electrical steel sheet on which a forsterite film is formed. It provides a method.

[0006]

Means for Solving the Problems The present invention applies a coating solution containing boric acid and boehmite as a main component to a grain-oriented electrical steel sheet on which a forsterite coating is formed, and forms a coating by continuous annealing. The gist of the present invention is a method for increasing the tension of a coating of a grain-oriented electrical steel sheet, which is annealed at a temperature in a range of 500 to 1000 ° C. for 0.5 hours or more. Further, the composition ratio of boric acid and boehmite in the coating solution is, in terms of oxide molar ratio, 0.2 ≦ B ₂ O ₃ / Al ₂ O ₃ ≦ 1.0, and further,
The gist of the present invention is a method for increasing the tension of a coating of a unidirectional electromagnetic steel sheet, in which the above-described annealing for 0.5 hour or more after the formation of the coating is performed after the iron core is formed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The inventors have drawn up a steel plate with a forsterite coating.
To form an insulating film with excellent force-imparting effect,
The test was performed. 0.23mm thick directional electrode containing about 3% Si
The magnetic steel sheet was finished until finish annealing. This test material is annealed
After washing with water to remove the separating agent, boric acid and
Insulating coating liquid containing silica as main component (molar ratio = 0.5)
With a grooved rubber roll on the steel plate surface,
And baked in a continuous annealing furnace for 2 minutes. The film tension at this time
The force is 4.5 g / m of coating amount on one side ^Two0.96kgf / mm in conversion^Two
Met. Batch baking at 500-1000 ° C for various times
The film was blunted and 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 numerical values in FIG. 1 are the amount of increase in tension (increase from 0.96 kgf / mm ² ) when the insulating film is formed at 4.5 g / m ² per one surface of the steel sheet. From FIG. 1, it is found that the film tension is increased by further performing batch annealing after forming the insulating film in the continuous annealing furnace. Especially,
The improvement is large with annealing for 30 minutes or more, 0.1 kgf / mm ²
Accordingly, 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 coating tension is increased by performing the batch annealing is considered as follows. The reason why the present insulating coating imparts tension to the steel sheet is due to the difference in the thermal expansion coefficient between the aluminum borate generated in the reaction between boric acid and boehmite and the grain-oriented electrical steel sheet. However, since the annealing time in continuous annealing is short, at most several minutes, it is difficult to say that the reaction between boric acid and boehmite in the insulating film is sufficient. Therefore, by performing long-time batch annealing, unreacted boric acid and boehmite react with each other to produce aluminum borate, 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 promoting the reaction between boric acid and boehmite, and 1000 ° C. or less from the viewpoint of economy. This is because it is desirable. A grain-oriented electrical steel sheet used as a wound iron core is subjected to forming called lacing, and then annealed to remove distortion introduced by processing. If this annealing is performed under the conditions shown in the present invention,
An increase in the tension of the insulating film can be expected without increasing the number of steps.

When the composition of the insulating coating solution is mainly composed of boric acid and boehmite, it is necessary to satisfy 0.2 ≦ B ₂ O ₃ / Al ₂ O ₃ ≦ 1.0 in terms of the molar ratio of each oxide. 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 The excess from the stoichiometric composition is left as an unreacted substance, which causes a reduction in water resistance and corrosion resistance, and a deterioration in heat resistance and sticking resistance.

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

[0013]

EXAMPLES (Example 1) The test material contains about 3% Si.
A 23-mm-thick unidirectional electromagnetic steel sheet which had been finished until finish annealing was used. An insulating coating solution containing boric acid and boehmite as the main components (molar ratio in terms of oxide: B ₂ O ₃ / A
l ₂ O ₃ = 0.5) on the surface of the steel plate with a roll coater,
Bake at 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 side of 4.5 g / m ² .

Further, batch annealing was performed at 850 ° C. for various times. Table 1 shows the improvement in the film tension and the 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 reducing 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 that had been finished up to finish annealing was used. An insulating coating solution containing boric acid and boehmite as the main components (molar ratio in terms of oxide: B ₂ O ₃ / A
l ₂ O ₃ = 0.5) on the surface of the steel plate with a roll coater,
Baking at a temperature of 850 ° C. for 120 seconds. As a result, iron loss W
_17/50 was 0.835 W / kg (B ₈ = 1.910 T), and the coating tension was 0.95 kgf / m ² in terms of the coating amount per side of 4.5 g / m ² .

Furthermore, batch annealing was performed at 850 ° C. for various times. Table 2 shows the improvement in the film tension and the iron loss W _17/50 at that time. It can be seen that the film tension is significantly improved when the annealing time is 0.5 hours or more, and the effect of reducing iron loss is large.

[0018]

[Table 2]

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

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

[0021]

[Table 3]

[0022]

According to the present invention, the tension imparting effect by the insulating coating when the tension applying type insulating coating is formed on the surface of the unidirectional electrical steel sheet having the forsterite coating formed thereon is enhanced. It is possible to manufacture a grain-oriented electrical steel sheet that can maximize the effect of reducing iron loss.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the batch annealing temperature and time and the amount of increase in the film tension per 4.5 g / m ^{2 applied} amount.

Claims (3)

[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 is formed, and the coating is formed by continuous annealing. A method for increasing the tension of a coating of a grain-oriented electrical steel sheet, wherein annealing is performed for 0.5 hour or more. 2. The composition ratio of boric acid and boehmite in the coating solution is 0.1% in terms of molar ratio in terms of oxide.
2. The structure according to claim 1, wherein 2 ≦ B ₂ O ₃ / Al ₂ O ₃ ≦ 1.0.
The method for enhancing the tension of a coating of a unidirectional electromagnetic steel sheet according to the above. 3. The method for increasing the tension of a coating of a grain-oriented electrical steel sheet according to claim 1, wherein the annealing after the formation of the coating is performed after the iron core is formed.