| (19) |
 |
|
(11) |
EP 0 619 584 A3 |
| (12) |
EUROPEAN PATENT APPLICATION |
| (88) |
Date of publication A3: |
|
26.10.1994 Bulletin 1994/43 |
| (43) |
Date of publication A2: |
|
12.10.1994 Bulletin 1994/41 |
| (22) |
Date of filing: 21.03.1994 |
|
|
| (84) |
Designated Contracting States: |
|
DE FR GB |
| (30) |
Priority: |
09.04.1993 US 44421
|
| (71) |
Applicant: GENERAL MOTORS CORPORATION |
|
Detroit
Michigan 48202 (US) |
|
| (72) |
Inventor: |
|
- Gay, David Earl
Noblesville,
Indiana 46060 (US)
|
| (74) |
Representative: Denton, Michael John et al |
|
Patent Section
1st Floor
Gideon House
28 Chapel Street
Luton
Bedfordshire LU1 2SE
Luton
Bedfordshire LU1 2SE (GB) |
|
| |
|
| (54) |
Magnetic body formed from encapsulated ferromagnetic particles and method for the
manufacture thereof |
(57) A method for stress-relieving a compression-moulded magnetic body is provided for
purposes of enhancing the magnetic permeability of the magnetic body. The method involves
encapsulating ferromagnetic particles with a preferred polymeric coating material,
comprising either a polybenzimidazole or a polyimide derived from either 3-4' oxydianiline
or polymethylene dianiline. The preferred coating materials are capable of withstanding
elevated temperatures for a duration which is sufficient to anneal the magnetic body
formed from the coated metal particles. As a result, the stresses induced in the magnetic
core by the compression-moulding process can be relieved without detriment to the
mechanical properties and magnetic characteristics of the magnetic core.