Compositions – Magnetic – With wax – bitumen – resin – or gum
Reexamination Certificate
2000-08-23
2002-07-09
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
With wax, bitumen, resin, or gum
C252S062560, C252S062570, C252S062580, C252S062590, C252S062600, C252S062610, C252S062620, C252S062630, C252S062640
Reexamination Certificate
active
06416681
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to ferrite sintered product obtained by forming a ferrite body using ferrite-forming granules and sintering the ferrite body, a producing method thereof and granules for forming the ferrite body. Particularly, the invention relates to granules enabling to produce ferrite formed bodies having excellent work ability and the ferrite sintered product with reduced loss of magnetic core and the method of producing the same as well as the ferrite-forming granule enabling to bring about a formed body of high density prior to the sintering.
Ferrite is broadly used to electronic parts, and the ferrite is formed with ferrite material and is obtained by baking the formed body. As methods of producing the ferrite bodies, conventionally there are employed various methods, and among them, a drying pressure forming method is generally employed. That is, the granules are effected under pressure to produce ferrite formed bodies. The granules are made as follow. For example, a water slurry is prepared with powder of ferrite raw material, a binder and a water, and the mixed material is dried by a spray dryer to make granules. Otherwise, the powder of ferrite raw material and the binder solution are agitated to mix them, and the drying and an oscillating extrusion granulation are repeated to make granules. Then, the formed bodies are baked to turn out sintered ones. Herein, the oscillating extrusion granulation method is defined as a method in that grains are granulated to be grain diameter of, for example, several mm, and crushed on meshes of a net to be fine powder, and this operation is performed in several steps of making net meshes gradually smaller, whereby particles of smaller than predetermined particle size are available.
In the pressure forming process for obtaining the formed body before the sintering, it is important to use such ferrite-forming granules of good fluidity, filling property into a mold and easy fragility with small pressure from the viewpoint of making excellent quality of ferrite sintered products and increasing productivity.
As the methods of producing granules of good fluidity and easy fragility with small pressure, JP-A-5-159918 and JP-B-7-17460 disclose methods that a slurry is prepared with a dispersing agent into granulation. Further JP-B-3-31660 and JP-A-10-59776 disclose methods that segregation of the binder is controlled for granulation.
However, the methods described in these publications are technologies to be applied to a spray-dry granulating method generally using a spray dryer, and if applying to an oscillating extrusion granulating method, desired effects could not be exhibited and have narrow usage.
In the methods in the above publications, although the fluidity and the easy fragility of granules are improved, satisfied effects could not be realized in strength of the formed body and electro-magnetic properties of the sintered product, in particular loss of magnetic cores.
[A0003]
When making complicated shapes such as coiling drum like cores or when requiring highly dimensional precision, since desired parts cannot be produced by only baking the formed bodies, therefore machining procedures such as cutting, grinding, and polishing are required. In general, by which stage of producing the ferrite products, the machining procedure is disposed, there are following methods.
(1) a method of machining a closely baked ferrite body in a predetermined dimensions or shapes,
(2) a method of machining a ferrite formed body under a semi-sintered condition by baking the ferrite at lower temperature by 100 to 500° C. than temperature of making the ferrite close, that is, by baking at neighborhood temperature of starting the sintering, and
(3) a method of not baking, but directly machining the ferrite formed body.
In the method (1) of machining the sintered body, since the ferrite has very high hardness in itself, the dimensional precision of the processed product is lowered, and further shocks while machining are large and pitching is easily generated.
In the method (2) of machining the half-sintered body, since the ferrite has not been made perfectly close, the hardness and anti-abrasion are low, while the workability is heightened, but since a ground of the half sintered body is still on the way of shrinkage and if a rest sintering is started after the machining is carried out under the shrinkage condition, the baking at the temperature brought under the half-sintered condition largely changes sizes. Besides, when the ferrite formed body is baked under the half-sintered condition, temperature distribution in a furnace is largely varied by disposing the places or the number of the ferrite formed bodies within the furnace, so that the dimensional precision of the ferrite formed bodies is reduced under the half-sintered condition on the way of shrinkage.
For such reasons, in general the method (3), that is, machining under not sintered condition after forming is employed for machining the ferrite formed bodies, excepting especial cases.
When the ferrite formed body is machined by the method (3), since the mechanical strength of the formed body is weaker than that of the sintered or half-sintered ferrite formed body, defects as cracks or breakage are easy to occur. Therefore, the prior art depends on such methods of rendering the ferrite formed body to be high density or drying the formed body for heightening the mechanical strength, followed by processing. However, in the ferrite formed body whose mechanical strength is heightened by such as drying, the hardness of the surface is made high, so that abrasion of a grinding disc as a diamond wheel becomes large and failures in processing are easy to happen such as defects or lowering in the precision of the faces which have been processed in a short period of time, resulting in easily generating inferior products and decreasing yield. For increasing the yield, cleanings must be frequently carried out to processing tools such as the diamond wheel, and thus problems requiring complicated maintenance are involved with the prior art.
SUMMARY OF THE INVENTION
In view of the above mentioned problems, it is accordingly object of the invention to provide granule for forming ferrite with which such ferrite formed body may be produced, making less abrasion of tools for machining the formed body and generating neither defects of the formed body nor reduction of precision in the processed face which are created by shock of the tools during processing as well as ferrite formed body therewith.
Further, it is an object of the invention to provide a molding granule enabling to bring ferrite sintered products of reduced loss of magnetic core and a method of producing the same.
The granule for forming ferrite formed body according to a first aspect of the invention is provided by mixing, for granulation, powders of ferrite raw material, polyvinyl alcohol as a binder and polyethylene glycol added as plasticizer and having molecular weight being 1000 to 6000.
The granule for forming ferrite according to a second aspect of the invention is characterized by adding 5 weight parts to 50 weight parts of polyethylene glycol with respect to 100 weight parts of polyvinyl alcohol.
The ferrite formed body according to a third aspect of the invention is provided by using granules for forming ferrite of the first aspect or the second aspect, and is characterized in that when the Vickers hardness of the formed body is Y and the density thereof is X (g·cm
−3
), the relation between Y and X is
Y=
19
X−A,
and satisfies X=3.0 to 3.9 g·cm
−3
and A=44 to 56.
A ferrite sintered product of a first aspect of the invention is characterized by sintering molded body of ferrite-forming granule composed by mixing, for granulation, powder of ferrite raw material, polyvinyl alcohol as a binder and polyethylene glycol added as a plasticizer and having molecular weight being 1000 to 6000, the ferrite sintered product being 0.2 wt % or lower in coefficient of water absorpt
Koslow C. Melissa
TDK Corporation
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