Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
2001-05-30
2004-12-14
Sheehan, John P. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C164S423000, C164S463000, C075S331000, C075S334000
Reexamination Certificate
active
06830633
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic material manufacturing method, ribbon-shaped magnetic materials, powdered magnetic materials and bonded magnets. More specifically, the present invention relates to a magnetic material manufacturing method, a ribbon-shaped magnetic material manufactured by the method, a powdered magnetic material formed from the ribbon-shaped magnetic material and a bonded magnet manufactured using the powdered magnetic material.
2. Description of the Prior Art
Rare-earth magnetic materials formed from alloys containing rare-earth elements have high magnetic properties. Therefore, when they are used for magnetic materials for motors, for example, the motors can exhibit high performance.
Such magnetic materials are manufactured by the quenching method using a melt spinning apparatus, for example. Hereinbelow, explanation will be made with regard to the manufacturing method using the melt spinning apparatus.
FIG. 19
is a sectional side view which shows the situation caused at or around a colliding section of a molten alloy with a cooling roll in the conventional melt spinning apparatus which manufactures a ribbon-shaped magnetic material by means of a single roll method.
As shown in this figure, in the conventional method, a magnetic material made of a predetermined alloy composition (hereinafter, referred to as “alloy”) is melt and such a molten alloy
60
is injected from a nozzle (not shown in the drawing) so as to be collided with a circumferential surface
530
of a cooling roll
500
which is rotating relative to the nozzle in the direction indicated by the arrow A in FIG.
19
. The alloy which is collided with the circumferential surface
530
is quenched (cooled) and then solidified, thereby producing a ribbon-shaped alloy in a continuous manner. This ribbon-shaped alloy is called as a melt spun ribbon. Since the melt spun ribbon was quenched in a rapid cooling rate, its microstructure has a structure composed of an amorphous phase or a microcrystalline phase, so that it can exhibit excellent magnetic properties as it is or by subjecting it to a heat treatment. In this regard, it is to be noted that the dotted line in
FIG. 19
indicates a solidification interface
710
of the molten alloy
60
.
The rare-earth elements are liable to oxidize. When they are oxidized, the magnetic properties thereof tend to be lowered. Therefore, normally, the manufacturing of the melt spun ribbon
80
is carried out under an inert gas atmosphere.
However, this causes the case that gas enters between the circumferential surface
530
and the puddle
70
of the molten alloy
60
, which results in formation of dimples (depressions)
9
in the roll contact surface
810
of the melt spun ribbon
80
(that is, the surface of the melt spun ribbon which is in contact with the circumferential surface
530
of the cooling roll
500
). This tendency becomes prominent as the peripheral velocity of the cooling roll
500
becomes large, and in such a case the area of the formed dimples becomes also larger.
In the case where such dimples
9
(especially, huge dimples) are formed, the molten alloy
60
can not sufficiently contact with the circumferential surface
530
of the cooling roll
500
at the locations of the dimples due to the existence of the entered gas, so that the cooling rate is lowered to prevent rapid solidification. As a result, at portions of the melt spun ribbon where such dimples are formed, the crystal grain size of the alloy becomes coarse, which results in lowered magnetic properties.
Magnetic powder obtained by milling such a melt spun ribbon having the portions of the lowered magnetic properties has larger dispersion or variation in its magnetic properties. Therefore, bonded magnets formed from such magnetic powder can have only poor magnetic properties, and corrosion resistance thereof is also low.
SUMMARY OF THE INVENTION
In view of the above problem involved in the prior art, it is an object of the present invention to provide a magnetic materials manufacturing method which can manufacture magnets having excellent magnetic properties and reliability, as well as a ribbon-shaped magnetic material manufactured by the method, a powdered magnetic material formed from the magnetic material and a bonded magnet manufactured using the magnetic powder.
In order to achieve the above object, the present invention is directed to a magnetic material manufacturing method for manufacturing a ribbon-shaped magnetic material by colliding a molten alloy to a circumferential surface of the cooling roll so as to cool and then solidify it, the ribbon-shaped magnetic material having an alloy composition represented by the formula of R
x
(Fe
1-y
Co
y
)
100-x-y
B
z
(where R is at least one rare-earth element, x is 10-15 at %, y is 0-0.30 and z is 4-10 at %), wherein the circumferential surface of the cooling roll has dimple correcting means for dividing dimples to be produced on a roll contact surface of the ribbon-shaped magnetic material which is in contact with the circumferential surface of the cooling roll.
According to the above structure, it becomes possible to provide a magnetic material manufacturing method which can manufacture magnets having excellent magnetic properties and excellent reliability.
In this invention, it is preferred that the cooling roll includes a roll base and an outer surface layer provided on an outer peripheral portion of the roll base, and the outer surface layer has said dimple correcting means. This arrangement makes it possible to provide magnets having especially excellent magnetic properties.
In this case, it is preferred that the outer surface layer of the cooling roll is formed of a material having a heat conductivity lower than the heat conductivity of the structural material of the roll base at or around a room temperature. This makes it possible to quench the molten alloy of the magnetic material with an appropriate cooling rate, thereby enabling to provide magnets having especially excellent magnetic properties.
Further, the outer surface layer of the cooling roll is preferably formed of a ceramics. This also makes it possible to quench the molten alloy of the magnetic material with an appropriate cooling rate, thereby enabling to provide magnets having especially excellent magnetic properties. Further, the durability of the cooling roll is also improved.
Further, in the present invention, it is preferred that the outer surface layer of the cooling roll is formed of a material having a heat conductivity equal to or less than 80 W·m
−1
·K
−1
at or around a room temperature. This also makes it possible to quench the molten alloy of the magnetic material with an appropriate cooling rate, so that it is possible to provide magnets having especially excellent magnetic properties.
Furthermore, it is also preferred that the outer surface layer of the cooling roll is formed of a material having a coefficient of thermal expansion in the range of 3.5-18[×10
−6
K
−1
] at or around a room temperature. According to this, the surface layer is firmly secured to the base roll of the cooling roll, so that peeling off of the surface layer can be effectively prevented.
In the present invention, it is also preferred that the average thickness of the outer surface layer of the cooling roll is 0.5 to 50 &mgr;m. This also makes it possible to quench the molten alloy of the magnetic material with an appropriate cooling rate, so that it is possible to provide magnets having especially excellent magnetic properties.
Moreover, it is also preferred that the outer surface layer of the cooling roll is manufactured without experience of machining process. By using such a cooling roll, the surface roughness Ra of the circumferential surface of the cooling roll can be made small without machining process such as grinding or polishing.
In the present invention, it is preferred that the dimple correcting means includes at least one ridge formed on the circumferential sur
Arai Akira
Kato Hiroshi
Seiko Epson Corporation
Sheehan John P.
LandOfFree
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