JP3279701B2 - Molding method of ferrite raw material powder - 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 forming a calcined ferrite powder for use in a power transformer or the like.

[0002]

2. Description of the Related Art Mn-Zn ferrites are used as power transformer materials for switching power supplies and the like. In recent years, these devices have been required to be smaller and lighter. Therefore, the driving frequency has been increased from the conventional 100 kHz to the present 500 kHz.
It is expanding to a high frequency region of kHz or more, and application in a MHz region is considered in the future. However,
The eddy current loss, which is particularly problematic in the high frequency region of the power loss, is proportional to the square of the driving frequency. Therefore, the power loss increases with an increase in the frequency, and the heat generation becomes a considerable size.

To solve such a problem, it is effective to reduce the crystal grain size of the sintered body. For example, using fine powder produced by hydrothermal synthesis as a raw material,
There is also reported an example in which a fine sintered body having a crystal grain size of 2 μm is manufactured by sintering by the HIP method to improve power loss (Nikkei Materials & Technology, January 1993,
p. 24).

[0004] As described above, in order to produce a sintered body having ultra-fine crystal grains of 2 µm or less, the calcined raw material has a particle size of 1%.
It is required to be a fine powder having a level of 000 ° or less. However, when such fine powder is formed by a normal uniaxial press, the friction between the powders is large,
This causes a reduction in molding density, an increase in molding pressure, and the occurrence of lamination. In addition, sound molding cannot be performed, for example, powder enters into the gaps between the molds to significantly reduce the life of the molds. Therefore, it is necessary to form such fine powder by using CIP, or by firing under pressure by HIP or hot pressing. However, the use of CIP and HIP has many problems in terms of mass productivity and manufacturing cost.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a fine calcined ferrite powder having an average primary particle size of 1000 ° or less by a usual uniaxial press.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention focuses on the fact that fine raw material powders are liable to agglomerate in water, and attempts to improve the formability by utilizing the aggregability. Thus, the present invention has been completed. The present invention is as follows. A ferrite raw material powder having an average primary particle size of 1000 ° or less is dispersed in water in the form of a slurry, dried until the water content becomes 4 to 10% by weight, a binder is added, granulation is performed, and press molding is performed. And a method for molding ferrite fine raw material powder.

[0007]

According to the above description, the first slurrying operation causes the fine powder to agglomerate and exhibit the same behavior as particles having a relatively large particle size. Molding becomes possible. As a result, a sintered body having an extremely fine particle size can be easily obtained, and this is effective for manufacturing a core in which power loss in the MHz region is significantly improved.

[0008] The water content after drying of the present invention is 4 to 10
When the amount is set to less than 4% by weight, agglomeration of the fine powder is dissolved when the amount is less than 4% by weight, so that the density of the compact does not increase and lamination occurs. This range is set because the adhered material is adhered and the shape of the molded body is lost. The calcined powder used in the present invention may be any powder produced by a spray roasting method or powder obtained by a wet method such as a hydrothermal synthesis method as long as the particle size is 1000 ° or less.

[0009]

Next, embodiments of the present invention will be described. The calcined Mn-Zn ferrite powder having a particle size of about 400 ° obtained by the spray roasting method was dispersed in water to be dispersed in a slurry having a powder amount of 30%. Dry until the water content reaches a predetermined value in a dryer, and use PVA as a binder.
Was added and the mixture was granulated with a grinder. The granulated powder was uniaxially pressed at a pressure of 2 ton / cm ³ to form a ring having an outer diameter of about 29 mm, an inner diameter of about 18 mm, and a height of about 7 mm. The compact density was measured from the dimensions. Table 1 shows the results.

[0010]

[Table 1]

[0011]

As described above, according to the present invention, extremely fine ferrite calcined powder, which has conventionally been difficult to mold, can be easily produced by a normal uniaxial press. As a result, a ferrite core of fine crystal grains excellent in power loss in a high frequency, especially in a MHz region, can be manufactured at a low cost, which is extremely effective for miniaturization of a high frequency transformer.

Continued on the front page (72) Inventor Fumihiko Hasegawa 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa New Nippon Steel Corporation Advanced Technology Research Laboratories (72) Inventor Yoshitaka Yamana 2-6-3 Otemachi, Chiyoda-ku, Tokyo (56) References JP-A-2-289430 (JP, A) JP-A-59-21527 (JP, A) JP-A-60-77164 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01F 1/12-1/375

Claims (1)

(57) [Claims] 1. A fine ferrite raw material powder having an average primary particle size of 1000 ° or less is dispersed in water in a slurry state.
A method for forming a ferrite raw material powder, comprising drying until the water content becomes 4 to 10% by weight of the whole, adding a binder, performing granulation, and pressing.