JP2000045016A - Stress relieving annealing method for core for coiled iron core excellent in expanding operability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the adhesion between steel sheets and to easily execute a core expanding operation by executing the annealing that removes working strains generated at the time of forming a grain oriented silicon steel sheet in such a manner that the concn. of oxygen in the atmosphere is controlled to a specified one. SOLUTION: At the time of subjecting the one obtd. by coiling a grain oriented silicon steel sheet into a cylindrical shape (core) to bending and forming it into a prescribed form, mechanical strains in the steel sheet caused by the bending are removed by annealing in the atmosphere in which the concn. of oxygen is <1.0%. At this time, among the atmospheric gases, as to the gas seeds excluding an oxidizing gas, all kinds of gas can be used if only it is the inert one, but, argon, helium or the like is particularly preferable, and, moreover, the atmosphere may be incorporated with hydrogen. Furthermore, in the case the annealing atmosphere contains water vapor, by controlling the concn. of water vapor in the atmosphere to >=+1 deg.C to <+30 deg.C expressed in terms of the dew point, the core easy to expand can be obtd., and, moreover, the discoloration of a film does not occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for manufacturing a wound iron core in which a unidirectional silicon steel sheet is formed into a predetermined shape and then annealed in order to remove a processing distortion during forming.

[0002]

2. Description of the Related Art A grain-oriented silicon steel sheet is mainly used as a core material of a transformer. There are two main types of transformer core manufacturing methods. One is a stacked iron core method of manufacturing an iron core by laminating unidirectional silicon steel sheets of a predetermined shape and size, and the other is a cylindrical method of manufacturing a unidirectional silicon steel sheet of a predetermined shape and size. It is a wound iron core method in which the core is wound up.

[0003] Among them, the latter wound iron core method involves the following steps. First, the unidirectional silicon steel sheet is sheared to a predetermined size. Next, it is wound into a cylindrical shape, and further, the material wound into the cylindrical shape (hereinafter, referred to as a core) is subjected to a bending process to be formed into a predetermined form. At this time, a mechanical strain is introduced into the steel sheet by the bending. Since the introduced strain deteriorates the core properties, the core is annealed to remove the strain.

[0004] The annealed core is once expanded. The developed annealed steel sheet is inserted between copper wires and the like to form a transformer. This series of work of unfolding the core and winding it around the copper wire is called a racing work.

[0005]

The operation of unwinding an annealed core and incorporating it between copper wires and the like is an important step that affects the productivity of a transformer. In this operation, if it takes time to develop the core, the productivity is reduced. Therefore, it is desired that the annealed core be easily developed. However, sometimes the annealed steel plates may cause a kind of adhesion phenomenon. When the steel sheets are bonded to each other, a great deal of labor and time are required for core development, and the productivity is greatly reduced. Therefore, various means for preventing adhesion have been proposed. For example, Japanese Patent Application Laid-Open No. 3-39484 discloses a method in which colloidal silica having a relatively large particle diameter is contained in a coating solution containing phosphate and chromic acid as main components. In addition, Japanese Patent Application Laid-Open No. H4-165082 discloses a method in which a non-colloidal solid is contained in a coating solution containing phosphate and chromic acid as main components. These techniques have some effect. However, even if these techniques are applied, the problem that the steel sheets sometimes adhere to each other has not yet been solved.

[0006]

Means for Solving the Problems The inventors of the present invention have studied and studied techniques for preventing adhesion, and have found that the prior art is directed to a unidirectional silicon steel sheet, particularly to an improvement in its insulating film. I noticed that it was limited. Then, as a result of considering an approach different from the film improvement, it was found that the atmosphere at the time of annealing the core, particularly, the oxidizing gas concentration had an influence. That is, the present invention provides a method for manufacturing a wound iron core in which a unidirectional silicon steel sheet is formed into a predetermined shape and then annealed to remove working strain during forming, wherein the oxygen concentration in the atmosphere during the working strain removal annealing is set to 1%. 0.0% or less, and the atmospheric water vapor concentration in the above-mentioned annealing for processing strain removal is set to + 1 ° C. or more and less than + 30 ° C. in terms of dew point. Is the way.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors annealed the core in various atmospheres and examined the degree of adhesion between steel sheets. The survey was conducted in the following manner. First, a large number of samples having a short side of 3 cm and a long side of 4 cm were cut out from a unidirectional silicon steel sheet having an insulating film formed thereon. Next, these samples were stacked such that the short side and the long side were alternated. When laminated in this way, the samples come into contact with each other at just 3 cm square. Therefore, the contact area is 9 cm ² . A load of 60 kg / cm ² was applied to the laminated product and fixed with bolts. Next, this is at a temperature of 800
Annealing was performed at 2 ° C. for 2 hours. At this time, the annealing atmosphere was adjusted using nitrogen gas having different oxygen concentrations. After cooling to room temperature, the sheet was peeled off one by one, and the peeling force at that time was determined. Fifteen samples were prepared, and the average value of their peeling forces was determined. It is considered that the peel force obtained by such a test method reflects the ease of deployment in actual core deployment. Table 1 shows the results. Table 1 also shows an overview of the film after annealing.

[0008]

[Table 1]

According to Table 1, the oxygen concentration in the annealing atmosphere is 1000
Under the condition of less than 1 ppm, the peeling force is 400 g or less, whereas under the condition of oxygen concentration of 10000 ppm, that is, 1%, the peeling force is as large as 1000 g or more. From this result, it was found that the core can be easily developed by setting the atmosphere oxygen concentration during the core annealing to less than 1%.
In this oxygen concentration range, there was no difference in the appearance of the film.

Next, the inventors examined the effect of the moisture concentration in the annealing atmosphere. The investigation method followed the method of examining the effect of oxygen concentration. The moisture concentration in the atmosphere was determined based on the dew point. Table 2 shows the results.

[0011]

[Table 2]

From Table 2, the peeling force is 400 g or less when the dew point of the annealing atmosphere is + 15 ° C. or less, whereas the peeling force is extremely large at 1000 g or more when the dew point is + 60 ° C. From this result, it was found that the core can be easily developed by setting the atmospheric moisture concentration during core annealing to less than + 30 ° C. in terms of dew point. On the other hand, regarding the appearance of the film after annealing, it was found that the appearance of the film was good when the atmosphere dew point was within a certain range. That is, under the condition where the atmosphere dew point is 0 ° C. or less, or + 30 ° C. or more,
Although the film was discolored, under the condition where the atmospheric dew point was 1 ° C. or more and less than + 30 ° C., no discoloration of the film occurred and the film was good.

Therefore, considering both the core expandability and the film appearance, when the annealing atmosphere contains water vapor,
It was found that the case where the atmospheric water vapor concentration was 1 ° C. or more and less than + 30 ° C. in terms of dew point was desirable. The reason why the adhesion between steel sheets during core annealing can be reduced by reducing the concentration of oxidizing gas species such as oxygen and water in the annealing atmosphere to a certain concentration or less has not been completely elucidated. It is thought that the films were denatured by the oxidizing gas and the films were fused together.

The present invention is applicable regardless of the type of the coating.
For example, the present invention can be applied to a unidirectional silicon steel sheet or the like in which a film is formed by baking a coating liquid containing colloidal silica mainly containing a phosphate such as aluminum phosphate or magnesium phosphate and chromic acid. Further, the gas species other than the oxidizing gas in the atmosphere gas during the core annealing may be any type of gas as long as it is inert to the steel sheet. For example, nitrogen, argon, helium and the like are preferable. Further, hydrogen may be contained in the atmosphere.

[0015]

Example 1 First, a 0.30 mm-thick unidirectional silicon steel sheet provided with an insulating film was sheared to a predetermined size. Next, it was wound into a cylindrical shape. Then, the cylindrically wound product (core) was subjected to a bending process and formed into a predetermined form. At this time, a mechanical strain was introduced into the steel sheet by the bending, and thus annealing was performed in a nitrogen atmosphere to remove the strain. At this time, the oxygen concentration in the annealing atmosphere was adjusted. After cooling to room temperature, the annealed core was deployed. Table 3 also shows the results of evaluating the deployment workability at this time.

[0016]

[Table 3]

According to Table 3, the atmospheric oxygen concentration was 15,000 pp.
m (comparative example: condition number), the developing operation was difficult, but the oxygen concentration in the atmosphere was 10 ppm to 5000.
When it was as low as ppm (Example: condition number), the developing operation was easy and excellent. Example 2 First, a unidirectional silicon steel sheet with an insulating film having a thickness of 0.23 mm was sheared to a predetermined size. Next, it was wound into a cylindrical shape. Then, the cylindrically wound product (core) was subjected to a bending process and formed into a predetermined form. At this time, a mechanical strain was introduced into the steel sheet by the bending, and thus annealing was performed in a nitrogen atmosphere to remove the strain. At this time, the dew point (water vapor concentration) of the annealing atmosphere was adjusted. After cooling to room temperature, the annealed core was deployed. Table 4 shows the results of evaluating the deployment workability at this time as well.

[0018]

[Table 4]

From Table 4, when the atmospheric dew point was as high as 30 ° C. (Comparative Example: Condition No.), the developing operation was difficult.
When the atmospheric oxygen concentration is as low as 0 ° C. to 25 ° C. (Example:
(Condition number) was easy to develop and excellent.

[0020]

By setting the oxidizing gas in the annealing atmosphere of the core in a certain concentration range, the adhesion between the steel sheets can be reduced, and the core development work can be facilitated.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Osamu Tanaka Inside Nippon Steel Plant Design Co., Ltd., 46-46 Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture (72) Koji Yamazaki Inventor Koji Yamazaki1- 1 Inside Nippon Steel Corporation Yawata Works (72) Inventor Kimihiko Sugiyama 1-1 Yawata-machi, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Inventor Tomoji Kumano Fukuoka F-term (reference) in Nippon Steel Corporation Yawata Works 1-1 Kitabi-cho, Tobata-ku, Kitakyushu-shi

Claims (2)

[Claims] In a method for manufacturing a wound iron core in which a unidirectional silicon steel sheet is formed into a predetermined shape and then annealed to remove working strain during forming, the oxygen concentration in the atmosphere for removing the working strain is set to 1. A strain relief annealing method for a core for wound iron core, which is excellent in deployment workability, characterized by being less than 0%. 2. A method for manufacturing a wound iron core in which a unidirectional silicon steel sheet is formed into a predetermined shape and then annealed to remove processing strain during forming, the dew point conversion of the atmospheric water vapor concentration in the processing strain removal annealing. A strain relief annealing method for a core for a wound iron core, which is excellent in workability of development, wherein the temperature is set to + 1 ° C. or more and less than + 30 ° C.