KR910002894B1 - Insulated agent of a grain oriented electrical steel sheet with a high magnetic flux density - Google Patents

Abstract

An insulated coating agent is composed of at least 5 wt.% zinc diphosphate, magnesium diphosphate, 50-150 wt.% SiO2 and 3-10 wt.% CrO3. The insulated coating agent is used for forming an insulating coated layer on the glass lyer of the directional electrical steel sheet having a high magnetic flux density. The agent has a good liquor stability.

Description

Insulation coating agent for high magnetic flux density oriented electrical steel

The present invention relates to an insulating coating agent for forming an insulating film of a high magnetic flux density oriented electrical steel sheet having excellent liquid stability and excellent surface quality, that is, insulation and adhesion as well as iron loss improvement effect.

High magnetic flux density oriented electrical steel is mainly used as iron core material of electric equipment, transformer, etc. Its magnetic properties, especially iron loss characteristics are very important, and the surface quality of insulating film is also important. The iron core for the transformer is put into a box after the coil is processed in a continuous or short process (cutting)-(wound processing)-(press molding)-(annealing)-(winding), etc., and is manufactured as a final transformer.

In the manufacturing of iron core for transformer, insulation in surface coating is the most important among surface quality characteristics because of high voltage per unit tone and causing interlayer short circuit due to loss of intermediate vortex. In addition, adhesion is important in cutting, press forming and winding process. In relation to the peeling phenomenon of the film, if the film is peeled off, harmful phosphate or silica compound constituting the film scatters, which not only worsens the working environment but also poor insulation of the core portion of the core, which is the main film dropping part, and tension of the steel sheet surface due to simultaneous peeling of the film. Since iron loss increases due to the reduction, transformer characteristics are deteriorated, it has been desired to develop an insulation coating having excellent coating properties such as insulation and adhesion, as well as excellent iron loss and magnetization characteristics of electrical steel sheets.

The grain-oriented electrical steel sheet usually contains 2-4% of silicon, and using the steel to which AlN, MnS, MnSe, BN, etc. is added as a grain growth inhibitor, (hot rolled)-(hot rolled sheet annealing)- (1 or 2 cold rolling)-(Decarbon annealing)-(Annealing separator application)-(Final high temperature annealing)-(Insulation coating treatment), etc. Forsterite film (Mg ₂ SiO ₄ , commonly called glass film) formed by reaction with MgO, an annealing separator, and an oxide layer (SiO ₂ , FeO, etc.) formed on the surface of steel sheet during decarbonization It is formed by the reaction between the phosphate-based coating and the silica coating to improve the magnetostrictive properties. Iron loss characteristics and magnetostrictive characteristics are applied to the directional insulating film formed as described above by applying it to the steel sheet by using a difference in thermal expansion coefficient between the insulating film layer and the steel sheet, that is, attaching a film having a minimum coefficient of thermal expansion. There are a number of techniques for improving this.

For example, according to US Patent No. 3,856,568, a coating film containing colloidal silica, aluminum phosphate, and chromic anhydride or chromate is treated on the surface of the steel sheet after the final high temperature annealing to form an insulating film that can be tensioned by heat treatment. In this way, iron loss and magnetostrictive properties were improved, and US Pat. No. 3,948,786 used colloidal silica, magnesium or aluminum phosphate, and chromic anhydride, chromic acid, dichromate, and US Pat. No. 4,032,366 colloidal silica and phosphoric acid. A method of forming an insulating film using magnesium, chromic acid, etc. has been proposed, and it is recognized that this method has an effect of improving defects and magnetostrictive properties.

As described above, an insulating coating for improving iron loss and magnetostriction characteristics of the grain-oriented electrical steel sheet has been invented, and thus the product characteristic of the grain-oriented electrical steel sheet has been improved by one step.

However, in the liquid itself, the colloidal component by using colloidal silica loses stability and the gelation time is short, so the liquid storage property is poor, so that the coating workability is poor, and the specific gravity of the coating liquid is low, so that the glass film is not very good. Otherwise, the insulation of the film is low, and problems such as powder scattering of the film components due to peeling of the film and deterioration of the transformer characteristics have arisen, and the problem of the film properties itself has been raised in contrast to efforts to satisfy the main purpose of iron loss improvement. Efforts have been made to improve the surface quality and to improve the coating treatment that can be stabilized.

Accordingly, the present invention aims to produce an insulating coating treatment agent for forming an insulating coating of a high magnetic flux density oriented electrical steel sheet having good liquid stability of the treating agent and excellent surface quality, that is, insulation and adhesion as well as improvement in iron loss. In order to achieve the above object, the present inventors have made various studies on the method of forming an insulating film of a grain-oriented electrical steel sheet. MZP) is conventionally insulated by applying a coating material containing colloidal silica and chromic acid or chromate to a surface of a steel sheet in a complex phosphate solution in which a certain amount of magnesium phosphate (MMP) is added to the surface of the steel sheet. Compared to the film, the surface quality such as insulation and adhesion is improved. Become excellent course was found to be also significantly improved core loss properties of the core.

Hereinafter, the present invention will be described.

By weight ratio, C: 0.05%, Si: 3.15%, Mn: 0.068%, S: 0.024%, and the remainder of the hot slab of the oriented electrical steel sheet composed of Fe in two known cold rolling processes including hot rolling and annealing. As a result, the thickness of the final steel sheet was 0.27 mm. Subsequently, after decarbonization annealing in an absorption atmosphere, MgO-based annealing separator was applied and the final high temperature annealing was performed to form secondary recrystallization and a glass film.

Subsequently, the excess annealing separator on the surface of the steel sheet was removed by pickling treatment, and then the coating agent of the present invention was applied thereto, followed by baking for 30 seconds at 850 ° C., resulting in a significant improvement in surface quality characteristics and improved iron loss. The coating agent applied for forming the insulating coating of the present invention is a colloidal coating based on 100 g of the mixed phosphate to a mixed phosphate composed of at least 5 wt% zinc phosphate (hereinafter referred to as%) and the rest of which is magnesium phosphate. 50-150% of silica as SiO ₂ and 3-10% of chromic acid as CrO _{3 are} added to the insulating coating agent.

Here, in order to compare the liquid characteristics of the phosphate system underlying the present invention, a solution of 60% aqueous solution of known magnesium phosphate (MMP) and aluminum phosphate (MAP) and the first zinc phosphate (MZP) of the present invention The characteristics were compared and shown in Table 1.

TABLE 1

* Note: molar ratio = H ₃ PO ₄ / Mg, Al, Zn (25% excess phosphoric acid added)

In Table 1, the specific liquidity and viscosity of three aqueous solutions to which 25% of free phosphoric acid (phosphoric acid added in excess of the reaction was added) were added. The specific gravity and viscosity of the MZP solution were higher than those of MMP and MAP. It is relatively high, and it is easy to improve or control the adhesion during the application process and compare the long-term storage stability (liquid stability) at the same molar ratio (25% excess phosphoric acid). It is not only stable but also MMP and MAP contain more than 25% of phosphoric acid, so that it can be stabilized without sedimentation production. It can be seen that the wet resistance due to the excess phosphoric acid also can be relatively excellent, it can be seen that the phosphate composed of MZP is the most excellent in the liquidity. Next, the reason for limiting the component properties and composition of the coating agent in the present invention will be described.

Phosphate acts as a binder (collder) of colloidal silica, which is the basic component of the coating material for high magnetic density grade oriented electrical steel sheet, and plays a role in stabilizing the formation of the silica film. In other words, if the insulation is poor, the most preferred is zinc phosphate. In general, zinc phosphate and magnesium phosphate are similarly mixed, and if it is extremely good, it is advantageous to add more magnesium phosphate to obtain excellent surface quality. In addition, a product having excellent magnetic properties, that is, low iron loss can be obtained.

The purpose of adding the first zinc phosphate is to improve the adhesion between the insulating film and the base material compared to the use of the first magnesium phosphate.The reason is that the first zinc zinc phosphate, which is the object of phosphate treatment on steel materials before painting (painting), is well known Due to the strong adhesion and flexibility, the demand is high enough to withstand bending during processing, so even if it acts as a binder of colloidal silica, which is a component of the insulating film, its properties are retained. do.

In addition, the reason that the iron loss improvement effect is increased is that the tension imparted to the material is increased by the effect of filling the zinc phosphate with the smallest defects such as microcracks in the case of the first magnesium phosphate to form a dense film free of defects. do. In fact, the insulation film formed by adding zinc phosphate first has a very beautiful gloss in appearance as compared to the first addition of magnesium phosphate alone. At this time, the most suitable amount of zinc phosphate should be added if the insulation of the glass film is bad, and more than 5% should be added even if it is extremely excellent. As shown in Table 1, it is easy to control the coating workability due to its high specific gravity and viscosity. This is because it is easy to obtain the above-mentioned adhesion and iron loss improvement effect. Since colloidal silica forms an amorphous, dense coating that can reduce the thermal expansion rate of the coating, it is important to improve magnetic properties, that is, to improve iron loss in high magnetic flux oriented electrical steel sheets. the iron loss improvement effect also decreases as they become cracks of the coating rather much tension applying effect a reduction in the 50-150% SiO ₂ with good conditions to less than 50% of the iron loss improvement effect is weak, and 150% or more by a given film tension do.

Chromic acid has the effect of inhibiting moisture absorption (tacky property, sticky adhesion to the film) due to water absorption in the air when the film is left in the air for a long time, and improving the coating workability. This is because the chromium compound is stabilized by combining with the excess phosphoric acid contained in the phosphate among the coating components, and the spreadability between the liquids is good. 3-10% of CrO ₃ is good for 100 g of phosphate. And at least 10% of the chromium is present in excess, which results in a white pattern on the exterior, which is undesirable because of poor appearance.

The coating material of the composition described above is formed by applying to a directional electric wave having a glass film after the final high temperature annealing and performing a baking treatment at 700-900 ° C., the liquid coating of the initial coating material is also good and the insulating film formed It is possible to manufacture a grain-oriented electrical steel sheet having excellent surface quality and magnetic properties.

Hereinafter, the present invention will be described in detail through examples.

Example 1

By weight, C: 0.042, Si: 3.08, Mn: 0.069, S: 0.024 and the rest are inevitably mixed with impurity and Fe for directional electrical steel sheet for high magnetic flux density by hot rolling to cold rolling by a known method. The final thickness was 0.275 mm. After the cold rolled sheet was annealed at 830 ° C. for 3 minutes in a decarburizing atmosphere, an annealing separator was applied to perform final high temperature annealing at 1200 ° C. for 20 hours. After the hot-annealed process, the glass plate with the glass coating was cut into 3cm wide and 10cm long specimens to remove excess annealing separator remaining on the surface by pickling, and after 3 hours hot calibration at 850 ° C. The insulation and magnetic properties of the film were measured and used as the "test specimen". At this time, the iron loss value of the specimen was W17 / 50, which was 1.01-1.05 Tesla, and the formation state of the glass film was extremely poor. The addition ratio of MZP and MMP in the coating agent was changed by classifying 0.95-0.85Amp., Normal, insulating 0.65-0.55Amp., And extremely good, insulating 0.35-0.25Amp. 100g of phosphate was coated with 125g of colloidal silica and 5g of chromic anhydride to adjust the insulation thickness to 5.00-5.5g / m, followed by baking at 860 ° C for 15 seconds. After the treatment, the specimens were treated as "post-treatment specimens." The MZP and MMP addition amounts of the coating agent and the characteristics of the coating film before and after the treatment were measured and shown in Table 2.

TABLE 2

[Exam conditions]

l. Insulation: Storage current Amp. When current of 0.5V, 1.0Amp is input under 300psi pressure.

2. Adhesiveness: Area% peeled off at 180 ° bend in 20mm diameter rod

3. Iron loss rate:% of iron loss rate measured in W17 / 50 by specimen measuring device before and after treatment.

In Table 2, specimens Nos. 1, 7, and 13, which are comparative materials, show poor insulation and adhesion as well as magnetic improvement of magnetic properties, and are particularly poor in glass coating, irrespective of whether the initial glass coating has insulation or not. The condition is 0.95-0.85 Amp. At the level, the difference is remarkable. Therefore, by adding 5% or more of MZP as a phosphate which is a condition of the present invention, it is possible to form an insulating film which can improve not only the surface quality of the product but also the magnetic properties.

Example 2

In the specimen of the hot annealing plate treated in the same manner as in Example 1, take a specimen of insulating 0.65-0.55Amp., Which is usually formed on the glass film, and add colo to MZP 50g + MMP 50g phosphate based on 100g of phosphate. After this month, an insulating coating was formed by coating and baking a coating prepared by changing the addition amount of silica and chromic anhydride, and the characteristics of the specimens after treatment were shown in Table 3 below.

TABLE 3

As can be seen in Table 3, in the specimen in which the addition amount of colloidal silica was changed to 0-200g, the insulation and adhesion were slightly inferior, but the main iron improvement of colloidal silica addition was 50g or less (Comparative Example). It is weak in 1-2), but it is more than 4%, and in the comparative example 7, which is 200 g, the improvement degree is weakened by the micro crack which arises in the surface, and is excluded from the scope of the present invention. In addition, the surface quality and magnetic properties did not change in the specimens in which the addition amount of chromic acid was changed to 0-15 g, but as described above, in 3g or less (Comparative Examples 8 and 9), wettability and coating workability were poor and 10g or more (comparative). In Example 13), appearance defects of white streaks appear in the appearance of the formed film, and thus are excluded from the scope of the present invention. Therefore, when the insulating coating agent added with colloidal silica 50-150g chromic acid 3-10g to 100g of the phosphate condition of the present invention is treated, the insulating film of the grain-oriented electrical steel sheet having excellent surface quality, that is, insulation and adhesion as well as tension tension is excellent. Can be formed.

Claims (1)

In an insulating coating agent for forming an insulating coating on a glass coating of a high magnetic flux density oriented electrical steel sheet, a mixed phosphate composed of zinc phosphate of not less than 5wt% and the balance of magnesium phosphate based on 100 g of phosphate Insulation coating agent of high magnetic flux density oriented electrical steel sheet characterized by adding 50-150wt% silica as SiO _{2 and} 3-10wt% chromic acid as CrO _{3 this} month.