Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2002-02-13
2004-06-15
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C164S463000
Reexamination Certificate
active
06749700
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing an amorphous alloy ribbon having excellent surface conditions and shape in edge portions, and a method for producing a nano-crystalline alloy ribbon using such an amorphous alloy ribbon.
PRIOR ART
Liquid-quenching methods are widely known as methods for producing amorphous alloy ribbons for use in magnetic cores, magnetic shields, etc. The liquid-quenching methods include a single roll method, a double roll method, a centrifugal method, etc., and preferable among them from the aspect of productivity and the maintenance of an apparatus is a single roll method in which a molten metal is supplied onto a cooling roll rotating at a high speed and rapidly quenched to form an alloy ribbon.
FIG. 1
shows one example of apparatuses for carrying out the single roll method. An alloy ingot in a crucible
1
is melted by a high-frequency coil
2
, and the resultant alloy melt
3
is ejected through a nozzle
4
onto a cooling roll
5
rotating at a high speed and rapidly quenched to form an amorphous alloy ribbon
6
. As shown in
FIG. 1
, for instance, a high-pressure gas such as nitrogen, a compressed air, etc. is supplied from a peeling-gas nozzle
7
in an opposite direction to the rotation direction of the cooling roll
5
immediately after the casting, thereby forcedly peeling the amorphous alloy ribbon
6
from the cooling roll
5
.
The amorphous alloy ribbon
6
produced by the above method tends to be provided with small dents called “air pockets” on a side in contact with the cooling roll
5
. This is because a gas is entrained into a boundary between a melt pool portion
10
(hereinafter referred to as “paddle”) and the cooling roll
5
by the rotation of the cooling roll
5
, so that it expands in the paddle
10
until the melt is solidified. Because the formation of such air pockets leads to the roughing of a surface of the ribbon
6
, the air pockets should be as few as possible.
Proposed by German Patent DD266046A1, Japanese Patent Laid-Open No. 6-292950, etc. to suppress the formation of air pockets is a method in which a CO
2
gas is supplied to the paddle in various directions. This method is advantageous in that it can suppress the formation of air pockets to reduce the surface roughness of a ribbon on a side in contact with the cooling roll.
Alternatively, Japanese Patent Laid-Open No. 59-209457, Japanese Patent Publication No. 1-501924, etc. propose a method for producing an amorphous alloy ribbon in vacuum or in a He atmosphere, a method for producing an amorphous alloy ribbon while flowing a gas having a lower density than the air at normal temperature, such as a heated CO gas, a He gas at normal temperature etc., to the paddle from rearward. Why the formation of air pockets can be suppressed by these methods seems to be the fact that a gas entrained by the rotation of the cooling roll has a reduced density, resulting in decrease in the kinetic pressure of the gas impinging on the paddle, thereby suppressing the vibration of the paddle.
Among the above methods, the method of flowing a CO
2
gas to the paddle from rearward (from a side opposite to the side on which the ribbon is formed) is suitable for the mass production of amorphous alloy ribbons from the aspect of production cost and safety.
The total length of an amorphous alloy ribbon continuously produced in one casting lot by a liquid-quenching method generally exceeds 3,000 m. When the resultant amorphous alloy ribbon is wound around a reel after the completion of casting, the ribbon is likely to be twisted. Accordingly, the quenched ribbon should continuously be wound immediately after peeling from the cooling roll.
For instance, Japanese Patent Laid-Open Nos. 8-318352 and 11-188458 disclose a method in which a magnetized reel rotating in an opposite direction to a cooling roll is positioned near the cooling roll to magnetically attract the peeled ribbon, which is continuously wound around the reel.
It is also known that the heat treatment of an amorphous alloy ribbon produced by the above-described methods at a temperature equal to or higher than the crystallization temperature of the alloy can provide a nano-crystalline alloy ribbon having an average particle size of 100 nm or less. Typical alloys capable of forming nano-crystalline alloy ribbons are Fe—Si—B—(Nb, Ti, Hf, Mo, W, Ta)—Cu alloys, Fe—(Co, Ni)—Cu—Si—B—(Nb, W, Ta, Zr, Hf, Ti, Mo) alloys, Fe—(Hf, Nb, Zr)—B alloys, Fe—Cu—(Hf, Nb, Zr)—B alloys, etc. described in Japanese Patent Publication Nos. 4-4393 and 7-74419, Japanese Patent 2,812,574, etc.
The nano-crystalline alloys are not only substantially free from thermal instability unlike the amorphous alloy, but also are subjected to less change with time and have lower magnetostriction and higher permeability than the amorphous alloys, they are used for common-mode choke coils, pulse transformers, leakage breakers, etc.
As a result of experiment to produce an amorphous alloy ribbon
6
using a laboratory-scale apparatus whose casting time is less than 30 seconds while flowing a CO
2
gas, the resultant ribbon had excellent surface conditions. However, in a production experiment using a mass-production-scale apparatus, it was found that as the casting time passed, there arose the problems of embrittlement and crystallization in the formed amorphous alloy ribbon that were not observed in the short casting process, though the surface conditions of the amorphous alloy ribbon was improved by the supply of a CO
2
gas. In addition to these problems, it has also be found that a new problem of serrated irregular shapes in their edge portions takes place. This phenomenon never occurs even in the long casting process of an amorphous alloy ribbon unless a CO
2
gas is supplied.
Because the total length of an amorphous alloy ribbon continuously produced in one casting step by a mass-production apparatus exceeds 3,000 m, the amorphous alloy ribbon is continuously wound around a large reel during the casting from the aspect of efficiency. The ribbon is then divided to proper length that can easily be handled to produce wound cores, etc., and wound around a large number of small reels. At this time, if the ribbon had a serrated irregular shape in its edge portions, the edge portion of the ribbon engages a reel, resulting in extreme difficulty in handling.
The irregular shape of the ribbon in its edge portions also poses inconveniences in the production of a wound core. In the continuous production of a wound core from a ribbon, the winding of the ribbon is often carried out with the edge portions of the ribbon abutting against a plate to make the resultant wound core have a constant height. In this case, too, if the ribbon had a serrated irregular shape in its edge portions, the ribbon engages the abutting plate, thereby making the production of a wound core difficult.
If the ribbon were brittle, breakage, cracking, etc. would be likely to occur in the production of wound cores and laminated cores. In addition, if the ribbon contains coarse crystals, it would have large crystal magnetic anisotropy, resulting in the deterioration of its soft magnetic properties. Further, if an amorphous alloy ribbon having coarse crystals were heat-treated at a temperature equal to or higher than the crystallization temperature of the alloy, the resultant nano-crystalline alloy ribbon would have deteriorated soft magnetic properties.
OBJECTS OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for continuously producing an amorphous alloy ribbon having improved surface conditions on a side in contact with a cooling roll and excellent edge shapes, free from embrittlement and crystallization.
Another object of the present invention is to provide a method for producing a nano-crystalline alloy ribbon by heat-treating such an amorphous alloy ribbon.
DISCLOSURE OF THE INVENTION
As a result of investigating problems such as irregular edge shapes, embrittlement and crystallization occurring as the amount of a ribbon cast increa
Bizen Yoshio
Nagao Michihiro
Sunakawa Jun
Hitachi Metals Ltd.
Sughrue & Mion, PLLC
Wyszomierski George
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