Dust core and method for producing the same

• US 20040061582A1
• Filed: 07/18/2003
• Published: 04/01/2004
• Est. Priority Date: 01/19/2001
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Toyota Motor Corporation), Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Hattori, Takeshi, Tajima, Shin, Okajima, Hiroshi, Kondo, Mikio, Awano, Yoji
• Granted Patent: US 6,903,641 B2
• Time in Patent Office: Days
• US Class Current: 336/83
• CPC Class Codes: B22F 1/10 Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
• CPC Class Codes: B22F 1/102 Metallic powder coated with organic material
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: H01F 1/14783 with insulating coating
• CPC Class Codes: H01F 1/24 the particles being insulated
• CPC Class Codes: H01F 3/08 made from powder powder coatings on sheets H01F3/02; on strips or ribbons H01F3/04; on wires H01F3/06
• CPC Class Codes: H01F 41/0246 Manufacturing of magnetic circuits by moulding or by pressing powder magnetic cores made by moulding or by pressing powder H01F27/255; soft magnetic particles H01F1/20, H01F1/36
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor
• CPC Class Codes: Y10T 29/49071 by winding or coiling
• CPC Class Codes: Y10T 29/49073 by assembling coil and core

Abstract

The present invention is characterized in that, in a powder magnetic core obtained by compaction of an iron-based magnetic powder covered with an insulation film, a saturation magnetization Ms is Ms≧1.9 T in a 1.6 MA/m magnetic field; a specific resistance ρ is ρ≧1.5 μΩm; a magnetic flux density B_2k is B₂k≧1.1 T in a 2 kA/m magnetic field; and a magnetic flux density B_10k is B_10k≧1.6 T in a 10 kA/m magnetic field. In accordance with the present invention, it has been possible to industrially carry out compacting iron-based magnetic powders under remarkably high compacting pressures. As a result, high-performance powder magnetic cores are obtained which have a high density, and which are good in terms of the specific resistance and magnetic permeability.

Claims

1. A powder magnetic core obtained by compacting an iron-based magnetic powder covered with an insulation film, wherein:

a saturation magnetization Ms is Ms≧

1.9 T in a 1.6 MA/m magnetic field;

a specific resistance ρ

is ρ

≧

1.5 μ

Ω

m;

a magnetic flux density B_2k is B_2k1.1 T in a 2 kA/m magnetic field; and

a magnetic flux density B_10k is B_10k≧

1.6 T in a 10 kA/m magnetic field.

2. The powder magnetic core set forth in claim 1, wherein a density d is d≧

7.4×

10³ kg/m³.

3. The powder magnetic core set forth in claim 1, wherein said specific resistance ρ

is ρ

≧

7 μ

Ω

m.

4. The powder magnetic core set forth in claim 3, wherein said specific resistance ρ

is ρ

≧

10 μ

Ω

m.

5. The powder magnetic core set forth in claim 1, wherein said magnetic flux density B_2k is B_2k≧

1.3 T.

6. The powder magnetic core set forth in claim 1, wherein said magnetic flux density B_10k is B_10k≧

1.7 T.

7. The powder magnetic core set forth in claim 1 whose 4-point bending strength σ

is σ

≧

50 MPa.

8. The powder magnetic core set forth in claim 1, wherein said iron-based magnetic powder is an iron powder composed of pure iron with a purity of 99.8% or more.

9. The powder magnetic core set forth in claim 1, where said iron-based magnetic powder is an iron alloy powder including cobalt (Co) in an amount of 30% by mass or less.

10. The powder magnetic core set forth in claim 1, where said iron-based magnetic powder is an iron alloy powder including silicon (Si) in an amount of 2% by mass or less.

11. The powder magnetic core set forth in claim 1, wherein said iron-based magnetic powder is such that particle diameters fall in a range of from 20 to 300 μ

m.

12. The powder magnetic core set forth in claim 1, wherein said insulation film is a phosphate coating or an oxidized coating.

13. A process for producing a powder magnetic core comprising:

a coating step of coating an insulation film on a surface of an iron-based magnetic powder;

an applying step of applying a higher fatty acid-based lubricant to an inner surface of a die;

a filling step of filling the iron-based magnetic powder with the insulation film coated into the die with the higher fatty acid-based lubricant applied; and

a forming step of warm pressure compacting the iron-based magnetic powder filled in the die.

14. The process for producing a powder magnetic core set forth in claim 13, wherein said coating step is a step in which a phosphoric acid is contacted with the iron-based magnetic powder to form a phosphate film on a surface of the iron-based magnetic powder.

15. The process for producing a powder magnetic core set forth in claim 13, wherein said applying step is a step in the higher fatty acid-based lubricant dispersed in water or an aqueous solution is sprayed into said die which is heated.

16. The process for producing a powder magnetic core set forth in claim 13, wherein said filling step is a step in which said iron-based magnetic powder which is heated is filled into said die which is heated.

17. The process for producing a powder magnetic core set forth in claim 13, wherein said forming step is a step in which a compacting temperature is from 100 to 220°

C.

18. The process for producing a powder magnetic core set forth in claim 13, wherein said forming step is a step in which a compacting pressure is 700 MPa or more.

19. The process for producing a powder magnetic core set forth in claim 13, wherein said higher fatty acid-based lubricant is a metallic salt of higher fatty acids.

20. The process for producing a powder magnetic core set forth in claim 19, wherein said higher fatty acid-based lubricant is one or more members selected from the group consisting of lithium stearate, calcium stearate and zinc stearate.

21. The process for producing a powder magnetic core set forth in claim 13, wherein said higher fatty acid-based lubricant is such that a maximum particle diameter is less than 30 μ

m.

22. The process for producing a powder magnetic core set forth in claim 13, wherein an annealing step is further carried out in which a green compact obtained after said forming step is heated and is thereafter cooled gradually.

23. The process for producing a powder magnetic core set forth in claim 22, wherein said annealing step comprises a heating step in which a heating temperature is from 300 to 600°

C. and a heating time is from 1 to 30 minutes.

24. A process for producing a powder magnetic core comprising:

a coating step of coating an insulation film on a surface of an iron-based magnetic powder;

an applying step of applying a higher fatty acid-based lubricant to an inner surface of a die;

a filling step of filling the iron-based magnetic powder with the insulation film coated into the die with the higher fatty acid-based lubricant applied; and

a forming step of warm compacting the iron-based magnetic powder filled in the die;

whereby a powder magnetic core obtained is that;

the saturation magnetization Ms is Ms≧

1.9 T in a 1.6 MA/m magnetic field;

the specific resistance ρ

is ρ

≧

1.5 μ

Ω

m;

the magnetic flux density B_2k is B_2k≧

1.1 T in a 2 kA/m magnetic field; and

the magnetic flux density B_10k is B_10k≧

1.6 T in a 10 kA/m magnetic field.

25. A powder magnetic core obtained by:

a coating step in which an insulation film containing Fe is coated on a surface of an iron-based magnetic powder;

an applying step of applying a higher fatty acid-based lubricant to an inner surface of a die;

a filling step of filling the iron-based magnetic powder with the insulation film coated into the die with the higher fatty acid-based lubricant applied; and

a forming step of warm compaction of the iron-based magnetic powder filled in the die so that a metallic soap film is formed by a reaction between Fe in the insulation film and the higher fatty acid-based lubricant, wherein;

a saturation magnetization Ms is Ms≧

1.9 T in a 1.6 MA/m magnetic field;

a specific resistance ρ

is ρ

≧

1.5 μ

Ω

m;

a magnetic flux density B_2k is B_2k≧

1.1 T in a 2 kA/m magnetic field; and

a magnetic flux density B_10k is B_10k≧

1.6 T in a 10 kA/m magnetic field.

26. A process for producing a powder magnetic core comprising:

a coating step in which an insulation film containing Fe is coated on a surface of an iron-based magnetic powder;

an applying step of applying a higher fatty acid-based lubricant to an inner surface of a die;

a filling step of filling the iron-based magnetic powder with the insulation film coated into the die with the higher fatty acid-based lubricant applied; and

a forming step of warm compaction of the iron-based magnetic powder filled in the die so that a metallic soap film is formed by a reaction between Fe in the insulation film and the higher fatty acid-based lubricant.