Metal treatment – Stock – Magnetic
Patent
1989-04-14
1991-11-26
Sheehan, John P.
Metal treatment
Stock
Magnetic
148306, 148308, 148313, 148315, 420 9, 420 99, 420117, 420120, 420435, 420581, H01F 104
Patent
active
050679937
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a magnetic core material made of Fe-Co base alloy for use at high frequencies, and which has excellent high-frequency alternating magnetic properties. The core material is used in a head core and a plunger yoke of a dot impact printer, and further in a stator and a rotor of a pulse motor.
Such a magnetic core material for use at high frequencies with high frequency signals usually should have a characteristic that a magnetic flux induced due to an applied current rises, and eddy current losses due to an excess current are reduced by making a current resistance ratio of the magnetic core large. Therefore, most magnetic core materials are made of an Fe base casting alloy and have a relatively large current resistance ratio, and excellent magnetic properties. The materials have a composition of 2-3.5% by weight Si and the remainder of Fe and unavoidable impurities. Throughout the following, all percentages refer to weight percentages.
Recently, a word processor, for example, needs to be small-sized and to have high-performance. Therefore, a material of high saturated magnetic flux density should be utilized for a head core of a dot impact printer in order to form a compact head core. In order to meet these requirements, attempts were made to use an alloy of high magnetic flux density, e.g. 50% Fe-50% Co casting alloy, instead of said Fe-Si casting alloy mentioned above (See "Preliminary Lecture Paper of the 23rd autumn Meeting", Japan Electric Material Technique Association). However, such an alloy of high magnetic flux density has lower high-frequency magnetic properties than one expects, partly because of a small current resistance. A magnetic core material made of said Fe-Co alloy has a poor magnetic flux rise because of a large eddy current loss. Therefore, the magnetic core material made of the Fe-Co alloy cannot meet the requirements of high-speed printing operations and clarity of printing which are needed in a word processor.
SUMMARY OF THE INVENTION
An object of the present invention is to produce a magnetic core material for use at high frequencies, and which has excellent high-frequency alternating magnetic properties.
According to the present invention, a magnetic core material for use with high frequency signals is made of a Fe-Co base alloy, whose composition is 45-53% of Co, 0.3-3%, preferably 0.5-1.5% of C, 0.1-2% of one or both of Mn and Si, 0.01-0.2% of at least one of Mg, Ca, and Ce as needed, and the remainder of Fe and unavoidable impurities, the structure of the alloy comprising a ferrite matrix containing graphite in an amount of from 1-20% by volume dispersed therein.
The magnetic core material of the present invention has better high-frequency alternating magnetic properties than the conventional magnetic core made of Fe-Co casting alloy, suffers little eddy current loss, and gives improved magnetic flux rising. Therefore, the magnetic core material of the present invention readily meets the requirements of machines of high-speed, small-size and high-performance.
The present invention was developed based on the above findings. Below are descriptions as to the reasons for including ingredients in the Fe-Co base alloy which forms a magnetic core material for high frequency us according to the present invention, for limiting ranges of ratios of the compositions included, and for limiting the ratio of graphite as stated above. (a) Co
The reason for including Co as an ingredient is that Co together with Fe in the specified amounts provides a solid solution of a phase resulting in prominently high magnetic flux density. Also, the reason for limiting the ratio of Co is that a desired high magnetic flux density cannot be ensured when the ratio of Co is less than 45% or more than 53%. Consequently, the amount of Co is determined to be 45-53% in the present invention.
(b) C
The reason for including C as an ingredient is that most of the C ingredient forms graphite which is dispersed in the ferrite matrix, resulting in improvements in hig
REFERENCES:
patent: 3891475 (1975-06-01), Tomita et al.
patent: 4116727 (1978-09-01), Major
Wakita Saburo
Yamaguchi Kiyoshi
Yanagisawa Norio
Mitsubishi Materials Corporation
Sheehan John P.
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