JPH051387A - Formation of insulation coating on grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To advantageously form an insulated coat excellent in tensile force imparting effect and free from powdery oxide film. CONSTITUTION:At the time of coating the surface of a grain-oriented silicon steel sheet finished with finish annealing with a coating treating soln., then heating it to a temp. range exceeding 350 deg.C and forming an insulation coating, the above heating treatment is made to follow the temp. raising stage in which the arrival temp. T( deg.C) after the passage of t(s) from the arrival point of 350 deg.C always satisfies -0.1t<2>+17t+350<T<-0.26t<2>+80t+350, by which the generation of blisters and openings causing powdery oxide film can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating coat on a surface of a grain-oriented silicon steel sheet, which has a high tension-imparting effect and is free of dust.

Generally, in a grain-oriented silicon steel sheet, an insulating coat is applied to the surface of the steel sheet to improve workability, rust prevention, and magnetism by imparting tension, in addition to providing insulation. This insulating coat is usually composed of a forsterite ceramic coating formed at the time of final annealing of grain-oriented silicon steel sheet and a phosphate-based top coating applied thereon. These coatings are required to have characteristics that utilize the difference in the coefficient of thermal expansion from the steel sheet and apply tension to the steel sheet to subdivide the magnetic domains and contribute to the reduction of iron loss. Therefore, it is important to develop a method for obtaining a coating having a high tension imparting effect.

Further, the steel sheet as the final product is cut by a shear after passing through a length measuring roll called a so-called measuring roll. If the steel sheet is dusted, it adheres to the measuring roll. The apparent diameter of the roll changes, and the length cannot be measured accurately. Furthermore, the generation of this powder may worsen the working environment, and the formation of a coating free of powder spray has become an important issue in product manufacturing.

[0004]

2. Description of the Related Art Various proposals have been made for this type of insulating coat. For example, Japanese Patent Publication No. 56-52117 discloses colloidal silica and magnesium phosphate at 82:20.
The improvement of iron loss, magnetostriction, and workability by applying a coating treatment liquid added at a molar ratio of 50% to 50%, and Japanese Patent Publication No. 53-28043 discloses colloidal silica, aluminum phosphate and chromic acid. By applying a coating treatment liquid containing
Regarding obtaining a coating film that contributes to improvement of iron loss and magnetostriction, further, JP-A-2-267276 discloses a method of increasing the tension application effect by increasing the temperature rising rate up to 800 ° C. from 10 to 60 ° C./s. Each is disclosed.

[0005]

However, none of the above methods has a problem in that the generation of powder cannot be prevented. It is an object of the present invention to propose a method for forming a dust-free insulating coat without compromising various coating properties, especially the tensioning effect.

[0006]

Means for Solving the Problems The inventors first investigated the cause of the generation of powder on the coating, and found that the swelling and holes in the coating were one of the major causes of powder ejection. That is, it was found that when a steel sheet having blisters or holes in the coating was passed through a transport roll or a measuring roll, the edges of the blisters or holes were peeled off due to a slight reduction force at the time of passing, and powder was generated. Therefore, as a result of various experiments conducted on methods that prevent the generation of blisters and holes that are the cause of powder spray and do not impair other properties, especially the effect of applying tension, heating after applying the coating solution We have found that it is effective to devise a treatment. That is, the inventors have found that the above object can be achieved by appropriately controlling the relationship between the heating time and the ultimate temperature in the temperature range of 350 ° C. or higher, and completed the present invention.

That is, according to the present invention, when a coating treatment liquid is applied to the surface of a grain-finished grain-oriented silicon steel sheet and then heated to a temperature range exceeding 350 ° C. to form an insulating coat, the heat treatment is In the temperature range of 350 ° C or higher, the reached temperature T after the elapse of t (s) since the temperature reached 350 ° C
(℃) is -0.1t ² + 17t +350 <T <-0.26t ² + 80t
This is a method for forming an insulation coat of grain-oriented silicon steel, which is characterized by following a temperature rising process that always satisfies the relationship of +350. In addition, the heating rate of less than 350 ℃ in heat treatment is 15 ℃
A value of / s or less is advantageous.

Next, the experimental results leading to the present invention will be described in detail. First, the heat treatment after coating the coating treatment liquid, which affects the surface properties of the coating, was examined. That is, a 0.23 mm thick grain-finished grain-finished annealed steel sheet was used as a sample.
37wt%, primary magnesium phosphate 51wt%, chromic anhydride
A coating treatment liquid containing 12 wt% was applied at 8 g / m ² and baked in the temperature rising pattern shown in Table 1. Table 1 also shows the occurrence of blisters at this time.

From the above experimental results, it has been found that changing the rate of temperature rise in the heat treatment, in particular, increasing the rate of temperature rise is effective in preventing the formation of blisters and holes.

Next, as a sample, a 0.23 mm-thick grain-finished grain-finished annealed steel plate was used. On the surface of the steel plate, colloidal silica: 37 wt%, primary phosphate: 51 wt% and chromic anhydride: 11 wt%. % Coating solution containing 8% / m ²
And apply a temperature rise rate of 10 ℃ / s and then 30 ℃ / s to 800
Annealing was performed by heating to 0 ° C., and the coating was baked to form an insulating coat. This treatment is performed by changing the temperature change rate switching temperature variously, and the result of observing the surface of the obtained insulation coat with a microscope is shown in FIG.

From the figure, it can be seen that the insulating coating obtained by the heat treatment with 350 ° C. as the switching point of the heating rate has the lowest swelling rate. This is considered to be because the dehydration reaction after drying the coating film started at around 350 ° C, and an appropriate heat treatment could be realized by increasing the heating rate from 350 ° C.

Therefore, the heat treatment in the temperature range of 350 ° C. or higher was further examined. That is, the same coating solution was applied at 8 g / m ² on the surface of a steel plate similar to that used in the experiment whose results are shown in FIG. 1, and thereafter, in a temperature range of less than 350 ° C., a heating rate of 10 ° C./s. The insulating coatings obtained by heating at various heating rates in the range of 5 to 80 ° C / s in a temperature range of 350 ° C or higher were observed under a microscope. As shown in FIG. 2 as a result of this observation, the temperature T (° C.) reached at the heating time t (s) starting from 350 ° C. is
= −0.1t ² + 17t +350 The insulation coat obtained by finishing the heat treatment without deviating from the range of the above region I has no swelling, while T = −0.26t ² + 80t +350
The insulating coat obtained by finishing the heat treatment without deviating from the range of the lower region II with respect to the boundary had no hole.
From the results of this experiment, it is possible to obtain an insulating coat having no blisters and holes by terminating the heat treatment without constantly deviating from the region III where the reached temperature T (° C.) overlaps the region I and the region II. It turned out to be obtained.

It is considered that the occurrence of swelling is caused by the dehydration reaction which occurs when the coating film component becomes highly viscous during drying, and in the above-mentioned region I, before the coating film component becomes highly viscous. It is presumed that swelling does not occur because water vapor diffuses into the outer gas phase as dehydration progresses. This blister may reduce the space factor of the product, and the occurrence of blister can be avoided. The present invention is significant. On the other hand, outside the range of the above-mentioned region II, it is considered that the coating film cannot withstand the rapid drying rate, and thus cracks are generated to develop into holes.

As described above, it was found that the heat treatment in the temperature range of 350 ° C. or higher can be avoided by performing the heat treatment in the range of the above range III, but the temperature range of 350 ° C. or lower can be avoided. It was also proved by the following experiment that the heat treatment at 1 is effective in reducing iron loss. That is, after applying the coating solution in the same manner as in the above experiment, heating was performed at various heating rates in a temperature range of less than 350 ° C, and subsequently heating in a temperature range of 350 ° C or higher was within the range III in Fig. 2. The magnetic properties before and after the formation of the insulating coat were examined for the steel sheet on which the insulating coat was formed by performing. The results are shown in Table 2.
Shown in.

[0015]

As can be seen from the table, the effect of reducing iron loss becomes large by setting the rate of temperature rise in the temperature range of less than 350 ° C. to 15 ° C./s or less. This is due to the heat treatment at a temperature rise rate of 15 ° C / s or less in the temperature range of less than 350 ° C.
It is considered that this is because the effect of applying tension to the coating increases.

[0017]

Next, the reasons for limitation in the method of the present invention will be described. First, the steel sheet on which the insulating coat according to the present invention is formed is a grain-oriented silicon steel sheet, which is usually a steel sheet that has undergone a series of steps of hot rolling, cold rolling, decarburization annealing and finish annealing.

The coating treatment liquid for forming the insulating coat contains colloidal silica in an amount of 30 to 50 wt%, Mg, A
20-60 wt% of one or more primary phosphates selected from l, Ca, Sr and Mn and 3-10 wt% of chromic anhydride
Those containing are preferable. That is, if the colloidal silica is less than 30 wt% or the primary phosphate exceeds 60 wt%, the effect of imparting tension cannot be expected, while the colloidal silica exceeds 50 wt% or the primary phosphate is less than 20 wt%. When it is, the coating film is not uniform, and thus the adhesiveness is deteriorated. And since chromic anhydride decreases hygroscopicity, 3-10 wt%
It is preferable to add in the range of. As other components, if silica powder or alumina powder is added in an amount of 0.1 wt% or more, the sticking resistance (resistance to film fusion during stress relief annealing) can be improved, but if it exceeds 1 wt%, the surface properties deteriorate. Therefore, it is preferable to add it in the range of 0.1 to 1 wt%. The basis weight is preferably adjusted within the range of 4 to 15 g / m ² . If it is less than 4 g / m ² , the insulating property becomes a problem, while if it exceeds 15 g / m ² , the space factor is lowered, which is not preferable.

Next, after applying the coating treatment liquid,
First, increase the heating rate in the temperature range below 350 ° C to 15 ° C.
By carrying out the heat treatment at a temperature of / s or less and subsequently performing the heat treatment in the temperature range of 350 ° C. or higher within the range of the region III of FIG. 2 described above, the generation of blisters and holes is avoided. Note that baking is performed at 700 to 950 to obtain a film with good film quality.
It is preferable to hold the temperature in the temperature range of ℃ for 10 seconds or more.

[0020]

[Example] After removing the unreacted separating agent of the final finish annealed plate (0.23 mm thickness) of the grain-oriented silicon steel obtained through a normal process, and then performing strain relief annealing and phosphoric acid pickling, Various coating liquids were applied, heated to 350 ° C. at a temperature rising rate of 10 ° C./s, and then heat-treated according to A to E shown in FIG. As shown in Table 3 as a result of examining various characteristics of the thus-obtained insulating coat, the method of the present invention is excellent in the powder spray resistance and the effect of imparting tension, and other coating characteristics are also superior to those of the conventional one. Was not inferior.

[0021]

[Table 3]

[0022]

EFFECTS OF THE INVENTION According to the present invention, an insulating coat having good dust-spraying resistance can be formed without impairing various coating characteristics, particularly the effect of imparting tension, and a product suitable as an iron core material for transformers and generators. Can be provided with high dimensional accuracy.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a swelling occurrence rate and a temperature rising pattern switching temperature.

FIG. 2 is a graph showing the relationship between the elapsed time and the reached temperature in the temperature range of 350 ° C. or higher.

FIG. 3 is a graph showing a temperature rising pattern in a temperature range of 350 ° C. or higher.

Claims (2)

[Claims] 1. A method of applying a coating treatment liquid to the surface of a grain-finished grain-oriented silicon steel sheet and then heating it to a temperature range exceeding 350 ° C. to form an insulating coat, wherein the heat treatment is 350 ° C. or more. In the temperature range of, the temperature reached T (℃) after the elapse of t (s) from the point of 350 ℃ always follows the temperature rising process that satisfies the relationship of −0.1t ² + 17t +350 <T <−0.26t ² + 80t +350. A method for forming an insulating coat of a grain-oriented silicon steel sheet, comprising: 2. The method for forming an insulation coat of a grain-oriented silicon steel sheet according to claim 1, wherein the rate of temperature increase below 350 ° C. in the heat treatment is 15 ° C./s or less.