JP2002069505A - Granulation of metal powder or ceramic powder, its production method and method for producing sintered material using the granulated powder as raw material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that, in a sintered material used in the process of granulating the fine powder of metal powder, there has been a danger of causing ignition or vaporization, further, there has been no binders having low concentration and exhibiting high viscosity, whereby the formation of a homogeneous slurried viscous liquid with metal powder having remarkably different specific gravity has been impossible, moreover, there has been a need of performing a degreasing stage in the existent binders, additionally, there has been a need of using die steel withstanding high pressure in the conventional powder metallurgy method, and further, the formation of a product having a complicated shape has been impossible. SOLUTION: As a binder, natural high-molecular polysaccharides having sol viscosity of 2% concentration and exhibiting viscosity of >=300 mPa.s are used. As the natural high-molecular polysaccharides, particularly, high viscosity agar is desirable. The granulated body using the above binder has the characteristics of being extremely high in rigidity and further has the characteristics of being enough in workability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a powder metallurgy method for compressing metal powder or ceramic powder to form a compact, and sintering the compact to produce a rigid sintered product. More specifically, a novel granulation method of the raw material powder before molding, a method of compression-molding the granulated powder obtained by the granulation method, and further, by subjecting the molded body to mechanical processing, It relates to obtaining complex shaped sinters.

[0002]

2. Description of the Related Art In a powder metallurgy method for forming a desired part by granulating a metal powder to form a metal granulated powder and performing various steps of compression molding / degreasing / sintering using the granulated powder. Basic technologies have been developed for quite some time and are widely used in industry. On the other hand, a cutting method of cutting a molten metal into a predetermined shape by machining has been widely used from before.

[0003] In a cutting method in which a molten metal is cut into a predetermined shape by machining, a large amount of cutting chips is generated. Generally, these chips are disposed of by landfill or the like without being recycled for economic reasons after the fall in scrap prices. However, recently, from the viewpoint of environmental protection, in particular, as one of the solutions to the problem of treating industrial waste, the generation of cutting chips is extremely small as compared with a cutting method that generates a large amount of cutting chips. The mass use of sintered parts by powder metallurgy with advantages has been seriously considered.

Heretofore, in the powder metallurgy method, a fine powder of a metal powder is granulated by using an organic polymer or an organic solvent as a binder to increase the fluidity of the metal powder, and the thus obtained metal granulated powder is used. Automatic weighing and automatic molding have become possible, which has resulted in a more homogeneous compression molded body. Thereafter, the molded body is degreased and sintered in a sintering furnace to obtain a sintered body. When manufacturing a sintered body having a complicated shape that cannot be obtained by uniaxial molding, a pre-sintering step is provided before the main sintering, and the pre-sintered body obtained by the pre-sintering is machined. By sintering the body, a sintered body with a complicated shape is manufactured.

[0005]

The particle size of the raw material powder used in the powder metallurgy method is as wide as several microns to several tens of microns, but in the case of fine powder having a particle size of several microns, the fluidity of the powder is particularly poor. The density of the molded body varies, which causes uneven sintering shrinkage, and the dimensional accuracy of the sintered body becomes worse than a predetermined value. In order to solve this problem, a metal powder is granulated in advance, and sinter molding is performed using the granulated powder. In the process of granulating the fine metal powder, an organic polymer compound that does not dissolve in water, such as wax, an acrylic resin, or camphor, is dissolved in an organic solvent such as methylene chloride and used as a binder. Excessive residual carbon derived from the organic polymer compound causes inhibition of shrinkage during sintering and lowers the mechanical properties of the sintered body. In order to solve this problem, a degreasing process for removing the organic polymer compounds that do not dissolve in water such as wax, acrylic resin and camphor used as a binder is indispensable, and this process requires special equipment and technology. It emits harmful decomposition gas or generates odor. Further, there is a problem that the organic solvent has a risk of ignition, is easily vaporized and released into the atmosphere, and easily causes air pollution.

One of the features of the powder metallurgy method is that an alloy having specific properties can be easily obtained by mixing a plurality of metal materials at an arbitrary ratio. However, for that purpose, metal powders with extremely different specific gravities in the materials necessary for alloy formation, for example, tungsten and copper,
Even a powder mixture of molybdenum and copper, or even a mixture of tungsten and aluminum, must be uniformly granulated. For example, in order to granulate uniformly by the spray drying method, a slurry-like viscous liquid consisting of a mixture of metal powders having extremely different specific gravities and a binder is sucked up by a pump and supplied to a spraying device rotating at a high speed. Must. In order for such a mixture of metal powders and binder to form a homogeneous slurry-like viscous liquid, there is a problem that a binder having low concentration and high viscosity must be selected.

In the spray drying method, an organic polymer compound which functions as a binder and a wax or a fatty acid are added to a mixture of a metal powder for the purpose of improving the filling property during molding and preventing galling of a mold. Although they are mixed and granulated, there is a problem that when these binders are used, a degreasing step must be performed before sintering.

In the case of using a powder of an iron-based alloy which is easily plastically deformed as a raw material, it is necessary to form the raw metal powder at a high pressure such as a plastic deformation of the raw metal powder, for example, a high pressure of 500 to 700 MPa in order to increase the sintering density. Therefore, when manufacturing a mold, there is a problem that a mold steel material capable of withstanding such a high pressure must be selected.

In the molding operation, the molding is basically performed by applying a pressure from a uniaxial direction. However, recently, efforts have been made to obtain a molded product having a more complicated shape using a mold having a complicated mold structure incorporating a slide mechanism, but there is a limit to that. In order to obtain a more complicated shape, it is conceivable to machine a molded product. However, there is a problem that the strength of the molded product is low, such that the molded product cannot withstand the destructive force caused by the rotation of the cutting tool, or the molded body expands or cracks due to frictional heat of the cutting tool.

[0010] Except for the case where a tungsten-based metal powder is used as a raw material, in order to obtain a product having a complicated shape that cannot be obtained by compression molding, pre-sintering is performed at a temperature lower than a normal sintering temperature before main sintering. The body is obtained and the calcined body is machined. However, there is a problem that the cutting waste generated by this machining is not suitable for recycling and must be landfilled.

[0011]

In order to solve the above-mentioned problems, in the present invention, a sol having a sol viscosity of 2 is used as a binder.
A natural high molecular weight polysaccharide having a viscosity of 300 mPa · s or more at a% concentration is used. In particular, high-viscosity agar which is a kind of natural high molecular polysaccharide is desirable.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. However, it should be understood that the invention is not limited to these embodiments.

Example 1 describes compression molding of raw material powders having extremely different specific gravities.

Embodiment 2 In the second embodiment, compression molding of a tungsten carbide material having a high specific gravity will be described.

[Embodiment 3] In the case of stainless steel SU which is easily plastically deformed
The compression molding using the coarse powder of S316L as a raw material will be described.

[0013]

EXAMPLE 1 Carbonyl nickel and carbonyl iron powder having an average particle size of 2.0 micron were added to tungsten powder having an average particle size of 2.0 micron so as to be 3% by weight and 1.5% by weight, respectively. -Use 2 for wet mixing
After performing for a time, it is dried to obtain a raw material powder. Next, 9.05 kg of this raw material powder had a sol viscosity of 900 mP at a 2% concentration.
1.72 kg of a high-viscosity agar solution having a viscosity of a · s was added, and the mixture was stirred at a temperature of about 60 ° C. while keeping the temperature at around 60 ° C. to form a muddy liquid. This muddy liquid was supplied at 25,000 rpm and the inlet temperature was 1
It was sprayed to a spray dryer at 60 ° C. and an outlet temperature of 78 ° C. to form a spherical granulated powder of 30 to 50 μm. Table 1 shows the compressive strength of compacts using this granulated powder.
It is shown in FIG. Further, for comparison, the compressive strength of a molded body obtained at a molding pressure of 100 MPa and 300 MPa using an acrylic resin and methylene chloride as binders, which has been conventionally used in a normal powder metallurgy method, is also shown.

[Table 1] As is clear from Table 1, 7 of the binder of the present invention was used.
Compressive strength of 0MPa is 300MP of conventional binder
A value higher than the compressive strength of a.

The granulated powder is placed in a mold having a predetermined shape and
After obtaining a molded body by pressure molding at a pressure of 00 MPa, agar was decomposed and removed in a hydrogen atmosphere at 400 ° C. As a result, the residual carbon content of the degassed body was measured.
01 wt%, which was equivalent to the level of tungsten in the starting material.

Next, this degassed body is placed in a hydrogen atmosphere at 14
Sintering was performed in a furnace at 60 ° C. to perform liquid phase sintering in which the nickel-iron bonding layer was melted to obtain a sintered body having a tungsten particle size of 50 μm. The dimensional accuracy of sintered products is ± 0.01mm
A sintered product with extremely high accuracy as shown below was obtained, and the hardness of the sintered product was 330 in Vickers hardness, and it had plastic deformability enough to withstand caulking and was practically usable.

[0016]

EXAMPLE 2 82% of a tungsten carbide powder having an average particle size of 2.5 microns, 8% of a titanium carbide powder, and 10% of a cobalt powder having an average particle size of 2.0 microns were weighed at a ratio of attritor. After performing wet mixing for 50 hours using, is dried to obtain a raw material powder. Next, this raw material powder 7.
To 5 kg, 1.72 kg of a high-viscosity agar solution having a sol viscosity of 2% and a viscosity of 900 mPa · s was added, and the mixture was stirred at a temperature of about 60 ° C. while stirring to form a muddy liquid. This muddy liquid is sprayed onto a spray dryer having a condition of 25000 rpm, an inlet temperature of 160 ° C. and an outlet temperature of 78 ° C.
A 30 micron spherical granulated powder was prepared.

The granulated powder is placed in a mold having a predetermined shape.
After molding under pressure at a pressure of 00 MPa to obtain a molded body, the molded body was passed through a furnace at 400 ° C. in a hydrogen atmosphere to decompose and remove agar and sintered at 1450 ° C. in a vacuum. Thereafter, HIP treatment was performed at 1350 ° C. for 1 hour in argon at 100 MPa to obtain a sintered product. As a result of measuring the transverse rupture strength of this sintered product, it was 3-3.7 GPa, which was equivalent to that of a normal cemented carbide.

[0018]

Example 3 1 kg of SUS316L water atomized powder having an average particle diameter of 66 microns has a sol viscosity of 900 m at a concentration of 2%.
After adding 0.4 kg of a high-viscosity agar solution having a viscosity of Pa · s, sufficiently stirring and solidifying by cooling, the solidified block is pulverized and dried at 60 to 80 ° C. Further, pulverization and sieving were repeated to prepare a granulated powder having a particle size of 297 microns or less. Table 2 shows the results of measuring the compressive strength of a compact obtained by press-molding this SUS316L stainless steel granulated powder at 200 MPa, 400 MPa, and 600 MPa.
Shown in Further, for comparison, the compressive strength of a molded body obtained at a molding pressure of 600 MPa using polyvinyl alcohol and stearic acid as a binder, which has been conventionally used in a normal powder metallurgy method, is shown.

[Table 2] As is clear from Table 2, the compressive strength of the binder of the present invention at 200 to 600 MPa was much higher than the compressive strength of 600 MPa of the conventional binder. Further, the granulated powder obtained by the method of the present invention is 400MP.
The following photograph (1) shows a state where the molded product obtained by compression molding in a is cut at a high speed by an end mill. As shown in this photograph, it is clear that no chipping is observed in the edge portion.

90 g of the granulated powder is placed in a mold having a projection size of 20 × 60 mm, and is pressed under a pressure of 400 MPa to obtain a compact. Then, a two-blade high-speed steel sheet having a diameter of 8 mm is obtained. Using a steel end mill, grooving is performed under the processing conditions of a cutting depth of 4 mm, a rotation speed of the end mill of 2,000 rpm, and a feed of 0.05 mm per tooth, and the sintered product is held at 1350 ° C. for 2 hours in a vacuum. Obtained. A sintered product with a sintering shrinkage of 9.65% and a density of 6.85 g / mm ³ was obtained, which was equivalent to a sintered product by a conventional powder metallurgy method.

[0020]

In the process of granulating the fine metal powder, a degreasing step for removing organic high molecular compounds which are not dissolved in water, such as wax, acrylic resin and camphor, used as a binder is essential. The process requires special equipment and technology, releases harmful decomposition gases, causes odors, and has the danger of ignition of organic solvents and vaporization into the atmosphere The problems of being easily released and causing air pollution can be all solved by using a natural high molecular polysaccharide as a binder. This is because natural high molecular polysaccharides, especially agar, use only water as a solvent, and there is no risk of volatilizing into the atmosphere and polluting the atmosphere without danger of ignition.

The sol has a 2% concentration of 300 mPa.
The use of high-viscosity agar, which is a kind of natural high molecular polysaccharide exhibiting viscosity of s, as a binder makes it possible to obtain a slurry-like viscous mixture of a metal powder having an extremely different specific gravity and a 2% agar solution. The viscosity of the liquid at 70 ° C. is 500 mP
With the help of a stirrer having a high viscosity of not less than a · s and further having a rotation speed of not less than 100 rpm, the above-mentioned metal powders having extremely different specific gravities are unevenly distributed during spray drying and granulated, Can be completely solved.

In the spray drying method, when granulation was performed using a binder mixed with an organic polymer compound, wax, fatty acid, etc., a degreasing step had to be performed before sintering. The inventor has already known that the degreasing step can be omitted completely by using agar as a binder as described above (Japanese Patent Publication No. Hei 7-68566).
issue).

When using a powder of an iron-based alloy that is easily deformed by plastics as a raw material, a mold steel material that can withstand high pressure had to be selected in order to increase the sintering density. As a result, such a selection became unnecessary. As is clear from the above Table 1, the 70 MPa compressive strength of the binder of the present invention is higher than the 300 MPa compressive strength of the conventional binder.

Further, using a natural polymer polysaccharide as a binder, 1 kg of SUS316L water atomized powder having an average particle size of 66 microns has a sol viscosity of 900 mPa · s at a 2% concentration.
After adding 0.4 kg of a high-viscosity agar solution having a viscosity of s and sufficiently stirring and cooling and solidifying, the solidified block is pulverized and dried at 60 to 80 ° C., and the pulverization and sieving are repeated. A granulated powder having a particle size of 297 microns or less is prepared.
By forming a molded body under pressure at Pa, 400 MPa and 600 MPa, as shown in Table 2 above,
It has become possible to produce a molded article having a value much higher than the compressive strength of a molded article using a conventional binder. Therefore, according to the present invention, in order to obtain a more complicated shape,
Even when a compact having high compression strength is machined, it is possible to obtain a machined body that does not cause swelling or cracking.

Further, as disclosed in the present invention,
SUS3 using natural polymer polysaccharides, especially agar as binder
Chips generated when 16L stainless steel granulated powder is pressed at 400MPa with an end mill at a high speed are cut in a weakly sintering state such as temporary sintering and have completely different form from the original raw material powder. Since it is not lost, it can be reused as granulated powder for compression molding by collecting it as it is, or can be returned to the granulation process and mixed with new raw material powder for reuse. Therefore, the problem of environmental pollution caused by landfill disposal of cutting chips can be surely solved as before.

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[Procedure amendment]

[Submission date] August 28, 2000 (2008.2.
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

Example 3 1 kg of SUS316L water atomized powder having an average particle diameter of 66 microns has a sol viscosity of 900 m at a concentration of 2%.
After adding 0.4 kg of a high-viscosity agar solution having a viscosity of Pa · s, sufficiently stirring and solidifying by cooling, the solidified block is pulverized and dried at 60 to 80 ° C. Further, pulverization and sieving were repeated to prepare a granulated powder having a particle size of 297 microns or less. Table 2 shows the results of measuring the compressive strength of a compact obtained by press-molding this SUS316L stainless steel granulated powder at 200 MPa, 400 MPa, and 600 MPa.
Shown in Further, for comparison, the compressive strength of a molded body obtained at a molding pressure of 600 MPa using polyvinyl alcohol and stearic acid as a binder, which has been conventionally used in a normal powder metallurgy method, is shown. As is clear from Table 2, the compressive strength of the binder of the present invention at 200 to 600 MPa was much higher than the compressive strength of 600 MPa of the conventional binder. Further, the granulated powder obtained by the method of the present invention is 400MP.
The following photograph (1) shows a state where the molded product obtained by compression molding in a is cut at a high speed by an end mill. As shown in this photograph, it is clear that no chipping is observed in the edge portion.

Continued on the front page (72) Inventor Yoshinari Amano 2-1-1, Ohama, Sakata-shi, Yamagata F-term (reference) in Sakata Office, Tokyo Tungsten Co., Ltd. 4G030 GA01 GA05 GA14 4K018 BA09 BA11 BA13 BC11 CA07

Claims (7)

[Claims] 1. A granulated powder comprising a metal powder or a ceramic powder for use as a sintering material, characterized by being granulated using a natural polymer polysaccharide as a binder. 2. A granulated powder molding method for molding the granulated powder according to claim 1, wherein a natural polymer polysaccharide is used as a binder. 3. The granulated powder molding method according to claim 2, wherein the natural high molecular polysaccharide is agar. 4. The granulated powder molding method according to claim 2, wherein the granulation is performed using a spray drying method. 5. The granulation according to claim 3, wherein an agar aqueous solution is added to the metal powder or the ceramic powder, and the mixture is stirred until they are homogeneously mixed, and then dried and pulverized to perform granulation. Powder molding method. 6. A production method for producing a sintered material by a compression molding method and / or a sintering method from the granulated powder molded by the method according to claim 2. 7. A method for producing a final sintered material by subjecting a compact formed by the production method according to claim 6 to a cutting process, processing a shape which cannot be obtained only by compression molding, and further sintering. Method.