Metallurgical apparatus – Means for holding or supporting work
Reexamination Certificate
2000-03-02
2002-10-15
Jenkins, Daniel J. (Department: 1742)
Metallurgical apparatus
Means for holding or supporting work
C419S038000
Reexamination Certificate
active
06464931
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a case for use in a sintering process to produce a rare-earth magnet and to a method for producing a rare-earth magnet by a sintering process using the case.
2. Description of the Related Art
A rare-earth magnet is produced by pulverizing a magnetic alloy into powder, pressing or compacting the alloy powder in a magnetic field and then subjecting the pressed compact to a sintering process and an aging treatment. Two types of rare-earth magnets, namely, samarium-cobalt magnets and neodymium-iron-boron magnets, have found a broad variety of applications today. In this specification, a rare-earth magnet of the latter type will be referred to as an “R—T—(M)—B magnet”, where R is a rare-earth element including Y, T is Fe or a Fe—Co compound, M is an additive and B is boron. The R—T—(M)—B magnet is often applied to many kinds of electronic devices, because the maximum energy product thereof is higher than any other kind of magnet and yet the cost thereof is relatively low. However, a rare-earth element such as neodymium is oxidized very easily, and therefore great care should be taken to minimize oxidation during the production process thereof.
In the prior art process, a green compact (or as-pressed compact) obtained by compacting R—Fe—B magnetic alloy powder is sintered within a furnace after the compact has been packed into a hermetically sealable container (sintering pack
100
) such as that shown in FIG.
1
. This is because the sintered compact would absorb too much impurity existing inside the furnace and be deformed if the compact was laid bare inside the furnace. The sintering pack
100
includes a body
101
of the size 250 mm.~300 mm.~50 mm., for example, and a cover
102
. Inside the pack
100
, multiple green compacts
80
are stacked one upon the other on a sintering plate that has been raised to a predetermined height by spacers (not shown). The sintering pack
100
may be made of SUS304, a type of stainless steel, for example, which is strongly resistant to elevated temperatures.
As shown in
FIG. 2
, multiple sintering packs
100
are stacked on a rack
201
with spacers
202
interposed therebetween. Then, the rack
201
is loaded into a sintering furnace in its entirety and subjected to a sintering process. After the sintering process is finished, the cover
102
is removed from each of these sintering packs
100
and the sintered compact is unloaded from the pack
100
and then transferred to another container for use in an aging treatment.
According to the conventional process, however, while the sintering pack
100
, in which the green compacts
80
are packed, is being transported to the rack
201
, the green compacts
80
might fall apart due to vibration or might have their edges chipped, thus adversely decreasing the production yield. A green compact for an R—Fe—B magnet, in particular, has usually been compacted with lower pressure compared to a ferrite magnet so that the particle orientation thereof in a magnetic field is improved. Thus, the strength of the green compact is extremely low, and great care should be taken in handling the compact.
Also, since the sintering pack
100
is provided with the cover
102
, the green compacts
80
should be loaded and unloaded into/from the pack
100
manually. This is because it is difficult to load or unload them automatically. Thus, according to the conventional technique, productivity is hard to improve.
Moreover, although SUS304, the material for the sintering pack
100
, is capable of withstanding an elevated temperature of 1000° C. or more, the mechanical strength of the material at that high temperature is not so high. Due to the effect of elevated temperature on the mechanical strength of the material, if the pack
100
is continuously used in the heat for a long time, then the cover
102
might be deformed thermally or a chemical reaction might be caused between Ni contained in SUS304 and Nd contained in the green compacts
80
to erode the container. That is to say, the material is not sufficiently durable. Additionally, its lack of dimensional precision means that SUS304 is inadequate to use with automated processes.
Another problem with the use of SUS304 for sintering cases is that its thermal conductivity is relatively low. To obtain a sufficiently high heat conduction through the walls of sintering pack made of SUS304, the walls of the pack must be of a thin construction, which undesirably decreases their strength. Increasing the thickness of the walls of the pack to increase their strength results in poor conduction of heat, which increases the amount of required time required for the sintering process.
SUMMARY OF THE INVENTION
An object of the present invention is providing a highly durable sintering case which exhibits excellent thermal conductivity and resistance to thermal deformation, and which will not react with rare earth elements.
Another object of the present invention is providing a sintering case, which is easily transportable and effectively applicable to an automated sintering furnace system and yet excels in shock resistance, mechanical strength and heat dissipation and absorption.
Still another object of the present invention is providing a method for producing a rare-earth magnet by performing sintering and associated processes using the inventive sintering case.
A case according to the present invention is used in a sintering process to produce a rare-earth magnet. The case includes: a body with an opening; a door for opening or closing the opening of the body; and supporting means for horizontally sliding a sintering plate, on which green compacts of rare-earth magnetic alloy powder are placed. The supporting means is secured inside the body. At least the body and the door are made of molybdenum.
In one embodiment of the present invention, the body consists of: a bottom plate; a pair of side plates connected to the bottom plate; and a top plate connected to the pair of side plates so as to face the bottom plate. The door is slidable vertically to the bottom plate by being guided along a pair of guide members. The guide members are provided at one end of the side plates. In this particular embodiment, the upper end of the door is preferably folded to come into contact with the upper surface of the top plate when the door is closed.
In another embodiment of the present invention, the case may further include a plurality of reinforcing members that are attached to the body to increase the strength of the body. Each said reinforcing member includes: a first part in contact with the body; and a second part protruding outward from the first part. In this particular embodiment, the reinforcing members are preferably made of molybdenum.
In still another embodiment, the supporting means preferably includes multiple rods that are supported by the pair of side plates, and each said rod is preferably made of molybdenum.
Another case according to the present invention is used in a sintering process to produce a rare-earth magnet and is made of molybdenum.
Still another case according to the present invention is used in a sintering process to produce a rare-earth magnet and is made of molybdenum containing at least one of: 0.01 to 2.0 percent by weight of La or an oxide thereof; and 0.01 to 1.0 percent by weight of Ce or an oxide thereof.
Yet another case according to the present invention is used in a sintering process to produce a rare-earth magnet and contains 0.1 percent by weight or less of carbon and at least one of: 0.01 to 1.0 percent by weight of Ti; 0.01 to 0.15 percent by weight of Zr; and 0.01 to 0.15 percent by weight of Hf. The balance of the case is made of molybdenum.
Yet another case according to the present invention is used in a sintering process to produce a rare-earth magnet. The case includes: a casing including platelike members; and means for supporting a sintering plate, on which green compacts of rare-earth magnetic alloy powder are placed. The supporting means is provided inside the
Okayama Katsumi
Oota Akiyasu
Wada Tsuyoshi
Costellia Jeffrey
Jenkins Daniel J.
Nixon & Peabody LLP
Sumitomo Special Metals Co. Ltd.
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