JPH04170357A - Dewaxable molded body of magnetic powder and method for dewaxing same - Google Patents

Abstract

PURPOSE:To obtain a dewaxed molded body having superior dimensional accu racy by using magnetic powder and a binder composed of org. high molecular compds. soluble and insoluble in various solvents. CONSTITUTION:A mixture of magnetic powder with solvents such as toluene and CO2 and a binder composed of org. high molecular compds. soluble and insoluble in the solvents is injection- or extrusion-molded. The binder in the resulting molded body is dissolved and extracted with an org. solvent or a solvent having a supercritical phase and the molded body is dewaxed and sintered to obtain a powder metallurgical product.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a sintered body of a magnetic material with excellent degreasing properties and a method for degreasing the same. In the process.

A magnetic powder compact that can be degreased after injection molding or extrusion molding of a mixture of a compact to be subjected to sintering with a binder mainly composed of magnetic powder and an organic polymer compound, cross-wire, and pelletizing. The present invention relates to a degreasing method.

[Prior art and its problems] In general, in the process of manufacturing magnetic material products by powder metallurgy, 11
The compact to be subjected to compaction is obtained as a green compact by compression molding raw material powder.

This is because the method usually involves punching the raw material powder filled into the mold from above and below.

The shapes of the resulting molded bodies are limited to relatively simple shapes such as two cylinders and one cylinder; to obtain products with more complex shapes, post-processes such as cutting and grinding are performed on the sintered products. There is a need.

In order to solve these problems, various techniques are being studied to obtain molded bodies with complex shapes that cannot be obtained using conventional methods.However, in the field of ceramic products, mainly engineering ceramics, raw material powder A method of obtaining a product by adding a binder mainly composed of 10 to 20% by weight of an organic polymer compound, mixing, kneading, injection molding or extrusion molding, and degreasing and sintering the molded product has begun to be used. There is. Injection molding is an organic polymer compound.

In other words, it has been developed as a plastic molding method, and it is suitable for mass production of products with high dimensional accuracy without post-processing, so it is attracting attention as a solution to the problems mentioned above. There is something to do. Supported by the recent development of metal powder manufacturing technology and binder compounding technology, typified by the atomization method, this manufacturing method is now being accepted for application to metal sintered products.

The difference between this method of using injection molded or extrusion molded bodies for sintering and the conventional method of sintering compression molded bodies is that the molding method is different, but in the former, the molded body contains a large amount of binder. , it is necessary to remove the binder, that is, degrease before sintering. Incidentally, in the latter example, the molded body does not contain a total heat binder, or even if it does contain it, it is only in a very small amount, so that it can be directly sintered. and.

The conventional and common degreasing method is to gradually heat the molded body and volatilize the binder as pyrolysis gas, but if the rate of temperature increase at this time is too high, pyrolysis gas will be generated. If the temperature is too rapid, the molded product may become blistered or
Therefore, assuming that the temperature is raised from room temperature to 600℃, the time required for the degreasing process is approximately 40 to 1.20 hours.
, which ends up being a long time. Also.

Particularly when the raw material powder is metal, if the atmosphere during the degreasing process is oxidizing, the metal will be oxidized.

The product will no longer be able to exhibit its original characteristics. For this reason, the atmosphere in the degreasing process needs to be inert or reducing, which is a major factor that hinders the reduction in manufacturing costs as well as the required time.

Furthermore, there is another important technical issue.

When the organic polymer compound that is the main component of the binder is thermoplastic, the cause of the deformation of the molded product during the degreasing process is
A phenomenon of thermal deformation occurs due to its characteristics, and this problem becomes more pronounced when the molded product has a shape that has hollow portions or protrusions in the horizontal direction.

[Means for Solving the Problems] The present invention was made in order to deal with the problem of deformation in the degreasing process caused by the thermoplastic property of organic polymer compounds, and it provides a degreased molded article and a degreased product with excellent one-dimensional accuracy. The purpose is to provide a method.

In order to achieve such an object, the present invention (1) involves degreasing and sintering a molded body obtained by injection molding or extrusion molding of a mixture of magnetic powder and a binder whose main component is an organic polymer compound. in the process of obtaining powder metallurgy products.

(2) In the degreasing step, the binder is dissolved and extracted using a liquid phase or supercritical phase solvent.

(3) Thereafter, the molded body is subjected to a degreasing process while being magnetically absorbed by the support.

Conventionally, a method of embedding a molded body in powder has been used as a method to deal with the problem of thermal deformation in the above-mentioned degreasing process. However, although this method aims to support the weight of the molded body with powder, the inventor of the present invention is limited to cases where the powder used is a magnetic material, and by magnetically adsorbing the molded body, deformation due to its own weight is prevented. We focused on preventing However, as is well known, magnetic materials have one of their temperature-related properties, the Curie temperature, above which magnetic properties are completely lost. In other words, a magnetic material having a Curie temperature lower than the degreasing temperature cannot be absorbed by the support base. By the way,
Looking at the Curie temperature of Panki's magnetic materials, as an example of hard materials, the Sm-Co type is approximately 850 degrees Celsius.
, about 450°C for Sr-ferrite, about 230°C for permalloy as an example of a soft material, and about 120°C for Mn-Zn ferrite. Therefore, if a binder composition and a degreasing method that can be degreased at 120° C. are adopted, the present invention can be applied to most magnetic materials.

From this point of view, the present inventor investigated a method of degreasing at a low temperature of 120° C. or lower.

(I) This may be possible if a component soluble in a liquid phase or supercritical phase solvent is used as a binder and degreasing is performed by extraction.

(n) Even if the degreasing rate is not 100%, there is no problem with the sintering process; in fact, it is better to leave a certain amount of binder in the molded product to improve shape retention. Because you can get it.

Organic polymer compounds other than those mentioned above may also be added as binder components.

<m> The higher the temperature, the higher the extraction speed.

In addition, during extraction, the binder swells with the solvent and the molded body becomes soft, so the above purpose was achieved by using a support that forms a magnetic closed circuit with the molded body to prevent deformation. It can be done.

Therefore, the substances that can be used as the binder component of the magnetic powder compact used in the method of the present invention include a combination of substances soluble and insoluble in various solvents, and specifically, acrylic polymers, benzene, Styrenic polymers are soluble.

Since polyolefins such as polyethylene are insoluble, such a combination is given as an example.

However, it goes without saying that it is not limited to this. Examples of usable solvents include, but are not limited to, various organic solvents in the liquid phase, and carbon dioxide in the supercritical phase for ease of handling. Examples include carbon and a mixture of carbon dioxide and an organic solvent such as toluene.

(First Example) Paraffin wax with a melting point of 60° C. was added to 90% by weight of Ni-Zn ferrite calcined powder with an average particle size of 0.5 μl.
4.5% by weight of polybutyl methacrylate with an average molecular weight of about 120.000, 1.5% by weight of ethylene-vinyl acetate copolymer with a vinyl acetate content of 11% and an average molecular weight of about 120.000. % was weighed and kneaded for 20 minutes using a pressure kneader. This mixture was processed into a diameter of approximately 410 mm using an extruder equipped with a rotating blade. The length of the pellet was 5■■.

This raw material was extruded using an extrusion molding machine into a cross-sectional shape as shown in FIG. 1, and a molded product having a length of 30 cm was obtained through a cutting process.

Next, with the upper side of this molded body adsorbed to an Sr ferrite magnet, it was immersed in benzene and degreased under the conditions of holding at 70° C. for 8 hours. When the weight change of the molded body before and after degreasing at this time was measured, a weight loss of 8.1% was observed, and 81% of the binder was extracted. The remaining 19% is considered to be ethylene-vinyl acetate copolymer, which is unnecessary for benzene. At this time, the Sr ferrite magnet was adsorbed through a porous alumina plate in consideration of the convenience of removing it later.

This degreased body was sintered at a temperature of 1,150° C. for 2 hours to obtain a sintered body. The dimensions of this sintered body are shown in Table 1.

In addition, in Comparative Example 1, a sintered body was obtained by degreasing and sintering in the same manner as in Example 1, except that the adsorption magnet was not used for the molded body produced in the same manner as in Example 1. It is something.

Below is the chord β (Second Example) Fe-
50Co powder was kneaded with a binder in the same manner as in the first example to obtain a pellet-shaped raw material. This raw material was molded into the shape shown in FIG. 2 using an injection molding machine. This molded body was placed on a support stand as shown in Fig. 3 (the shaded area is a magnet for attraction), and degreased under the same conditions as in the first example.
Subsequently, sintering was performed at 1,200°C for 3 hours. The dimensions of this sintered body are shown in Table 2.

In Comparative Example 2, a sintered body was obtained by degreasing and sintering in the same manner as in Example 2, except that no support was used for the molded body produced in the same manner as in Example 2. be.

Hereinafter (Third Example): 90% by weight of Ni-Zn ferrite calcined powder with an average particle size of 0.5 μm and 1.5% Ni of dibutyl phthalate.
2.5% by weight of paraffin wax with a melting point of 60°C
, average molecular weight of about 120; ooo polybutyl methacrylate 4.5% by weight, average molecular weight of about 180,000
1.0% by weight of high-density polyethylene and 0.5% by weight of ethylene-vinyl acetate copolymer with a vinyl acetate content of 11% and an average molecular weight of about 120,000 were weighed, and they were mixed in a pressure kneader. The mixture was kneaded for 20 minutes. This mixture was made into pellets with a diameter of about 4 as and a length of 5 cm by extrusion equipped with a rotating field. This raw material was made into an extrusion molded product in the same manner as in the first example.

This compact was adsorbed to an Sr ferrite magnet in the same manner as in the first example, and was charged into an extraction tank (inner volume: 800 cc) 9 of an extraction device as shown in FIG. This extraction tank 9
The temperature was raised to 60° C., and the extraction tank 9 was filled with carbon dioxide using the pump 7. Then, the pressure inside the extraction tank 9 is set to 200 kg.
The valve on the outlet side was opened and carbon dioxide was adjusted to flow at 2001/hr while maintaining the temperature at /c-. Immediately thereafter, the pump 3 was activated to flow toluene into the tank 9 at a flow rate of 300 cc/Hr. After 2 hours, the pump was stopped, and only carbon dioxide was allowed to flow for another 2 hours to replace toluene in tank 9 with carbon dioxide. Then, the pressure inside the tank 9 was reduced to atmospheric pressure, and the molded body was taken out.

As a result of measuring the weight change of the molded body before and after, the weight loss was 8.3%, and 83% of the binder was extracted and removed.

This degreased molded body was sintered in the same manner as in the first example.

A sintered body was obtained. The dimensions of this sintered body are shown in Table 3.

In Comparative Example 3, a sintered body was obtained by degreasing and sintering the molded body produced in the same manner as in Example 1, but not using an adsorption magnet, in the same manner as in Example 3. It is.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain magnetic material products with complex shapes without deformation by powder metallurgy, and this invention greatly contributes to expanding the use of magnetic materials in industrial applications. Extremely useful.

[Brief explanation of the drawing]

FIG. 1: An explanatory diagram showing the cross-sectional shape of the extrusion molded body in the first example. FIG. 2 is an explanatory diagram showing the shape of the injection molded article in the second embodiment. FIG. 3: An explanatory diagram showing the shape of the support base in the second embodiment. FIG. 4: An explanatory diagram showing an outline of the extraction device in the third embodiment. 1... Carbon dioxide cylinder, 2... Solvent tank, 3...
...Solvent pump, 4,5...Pressure valve, 6...Heat exchanger, 7...Carbon dioxide pump, 8...Heat exchanger, 9
...Extraction tank. 10... Extraction separation tank, 11... Solvent recovery tank, 12.
...Pressure gauge, 13... Integral flow meter. Procedural amendment (voluntary) January 7, 1991

Claims (2)

[Claims] (1) A degreasable magnetic powder compact comprising a binder whose main components are magnetic powder and an organic polymer compound, the binder containing a component that is insoluble in a liquid phase or supercritical phase solvent. (2) In the process of obtaining a powder metallurgy product by degreasing and sintering a compact formed by injection molding or extrusion molding of a mixture consisting of magnetic powder and a binder whose main components are an organic polymer compound, the degreasing process removes the binder. Magnetic powder molding is performed by dissolving and extracting with a liquid phase or supercritical phase solvent, and is characterized in that the molded product is subjected to a degreasing process while being magnetically adsorbed to a support. How to degrease your body.