Plastic and nonmetallic article shaping or treating: processes – Recycling of reclaimed or purified process material
Reexamination Certificate
2000-10-26
2003-07-29
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Recycling of reclaimed or purified process material
C264S109000, C264S115000, C252S062590
Reexamination Certificate
active
06599450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to materials-recovery-type recycling of bonded magnets which are excellent in dimensional accuracy and workability, therefore, widely used as an industrial material.
2. Related Art of the Invention
Hard magnetic material of any type is generally hard and brittle; moreover, its manufacturing process usually includes casting, sintering, heat treatment, and grinding finishing as a last step so as to produce a prescribed dimension. As a result, the processing cost becomes high for applications where close dimensional tolerance is required, which leads to a remarkable increase in the cost of product. In addition, with this material, intricate shapes and thin products are hard to make.
The hard magnetic material having been improved in the above disadvantages in processability and workability and having come into use is a bonded magnet. The bonded magnet is a magnet produced by mixing hard magnetic material powder with a binder, such as plastic and rubber, and subjecting the mixture to molding forming, and it is characterized in that it has a high dimensional accuracy, it is workable into an intricate shape and into a thin product, it is free from fear of cracking and chipping, and that it has a light weight.
The magnetic properties of the bonded magnets are inferior to those of cast magnets and sintered magnets since they contain 2 to 15 wt % binder of non-magnetic material (25 to 50% by volume); however, after powerful powders of magnetic materials such as rare earth permanent magnet were obtained, their properties have been rapidly improved and they have wider applications.
The particle size of the magnetic powder of, for example, rare earth permanent magnet is made uniform, the uniform powder is mixed with a binder, and the mixture is subjected to molding forming by the compression molding, injection molding, etc. In cases where the binder is a thermosetting resin, the molded form is subjected to thermosetting subsequently. In the bonded magnets, the density and the void largely affect the magnetic properties; accordingly, the particle size of the magnetic powder and the mixing ratio of the binder to the magnetic powder are important factors in improvement in the magnetic properties thereof.
On the other hand, since the bonded magnet is a mixture of a binder and magnetic material powder, it becomes much more difficult to decompose and recycle the used bonded magnets or bonded magnets rejected as defectives. In particular, in cases where the binder is a thermosetting resin, the bonded magnets are allowed to have a three-dimensional network structure by the setting reaction and generally to become insoluble and non-fusible solids; accordingly, these resin-set bonded magnets have been hard to decompose, and therefore, considered to be unfit for recovering and reusing.
Considering that the waste disposal problem is becoming more serious and the effective use of the resources is important, however, the development of volume reduction technology and of treatment technology for reusing is an urgent problem for the bonded magnets including those having been used as well as those having been rejected as defectives during the processes. In particular, the bonded magnets are composed of metals, metal oxides, etc., and metals are valuables which are more costly than resins which are used as a binder; accordingly, the fact that the possibility of recovering and reusing such costly valuables is limited becomes a bigger issue. In cases where the bonded magnets are composed of rare earth metals such as cobalt and neodymium, the issue becomes much bigger.
Thus, several investigations have been carried out of recycling the bonded magnets; however, for the bonded magnets using thermosetting resins such as epoxy resin as a binder, it is completely impossible to separate and decompose them. Therefore, the only approach taken for resources recovery has been to crush the bonded magnets, mix a small amount of crushed magnets with a virgin magnet powder, add a binder to the mixture, and subjecting the mixture to molding forming.
In the conventional method as above in which the bonded magnets are crushed, the magnet powder and the binder are not satisfactorily separated; therefore, if the mixing ratio of the recycled material to the virgin magnet powder is increased, the density of the bonded magnet, that is, the magnet powder content is decreased, which means that the bonded magnet having the same density as the conventional one cannot be obtained. This means the deterioration of magnetic properties.
In addition, the properties of the magnet powder tend to deteriorate when further pulverizing the raw material. In accordance with the conventional crushing method, since the pulverization of the magnet powder itself is inevitable, the magnetic properties of the bonded permanents magnets produced deteriorate.
Further, due to the pressure applied during the molding forming of the bonded magnets, the particle diameter of the magnet powder becomes smaller. In the conventional method, however, the binder and the magnet powder cannot be separated from each other, and the magnet powder is mixed and reused with its particle size remaining small, which also results in the deterioration of magnetic properties.
After all, the present situation is that the reclamation and resource recovery of the bonded magnets cannot be fully achieved by the conventional method.
SUMMARY OF THE INVENTION
Accordingly, in light of the problems described above, the object of the present invention is to provide a method of recycling bonded magnets having the same properties as the currently used one by separating magnetic materials from any type of bonded magnets.
One aspect of the present invention of the present invention is a recycling method of producing magnetic material powder from bonded magnets which are produced by mixing magnetic material powder, as raw material powder, with a binder and subjecting a mixture to molding forming, comprising at least the steps of:
(a) separating and collecting the magnetic material powder from the bonded magnets by removing all or a prescribed percentage of the binder contained in the magnets;
(b) removing all or a prescribed percentage of the particles of diameter smaller than a prescribed particle diameter from the separated and collected magnetic material powder; and
(c) mixing the magnetic material powder, from which the particles of diameter smaller than the prescribed one are removed, with a virgin magnetic material powder in a prescribed mixing ratio, so as to produce a new raw material powder.
Another aspect of the present invention is a method of recycling bonded magnets produced by mixing magnetic material powder, as raw material powder, with a binder and subjecting a mixture to molding forming, comprising the steps. of:
(a) separating and collecting the magnetic material powder from the bonded magnets by removing all or a prescribed percentage of the binder contained in the magnets;
(b) removing all or a prescribed percentage of the particles of diameter smaller than a prescribed particle diameter from the separated and collected magnetic material powder;
(c) mixing the magnetic material powder, from which the particles of diameter smaller than the prescribed one are removed, with a virgin magnetic material powder in a prescribed mixing ratio, so as to produce a new raw material powder; and
(d) mixing the newly produced raw material powder with a prescribed percentage of a binder and subjecting the mixture to molding forming.
Still another aspect of the present invention is the recycling method, wherein the prescribed percentage of the binder to be removed in the step (a) is determined in terms of the prescribed mixing ratio in the step (c).
Yet another aspect of the present invention is the recycling method, wherein the prescribed particle diameter in the step (b) is determined in terms of the prescribed mixing ratio in the step (c).
A further aspect of the present invention is the recycling method, whe
Onishi Hiroshi
Terada Takahiko
Yamagata Yoshikazu
Yamashita Fumitoshi
Lechert Jr. Stephen J.
Matsushita Electric - Industrial Co., Ltd.
RatnerPrestia
LandOfFree
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