JPH06192706A - Method for degreasing sinterable powder compact - Google Patents

Abstract

PURPOSE:To degrease a sinterable powder compact at low temp. in a short time without oxidizing the powder by heating the compact consisting of a sinterable powder and an org. binder in the oxygen-enriched air to decompose and remove the binder. CONSTITUTION:A composition consisting of a mixture of a sinterable powder consisting of metal powder and/or ceramic powder and org. binder is injection- molded. The obtained compact is heated to decompose and remove the binder from the compact. In this method for degreasing the sinterable powder compact, the binder is preferably decomposed and removed in the oxygne-enriched air contg. 25-50vol.% oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for degreasing a sinterable powder compact.

[0002]

2. Description of the Related Art As a conventional method for producing a molding composition and a sintered body, a mixture of metal powder and / or ceramic powder and an organic binder composed of thermoplastic resin and wax is injection-molded and the molded body is heated. A production method is known in which the organic binder is decomposed and removed by the method described above, and then sintered (JP-A-58-223662, JP-A-2-5470).
No. 3, etc.) The above-mentioned injection molding method is characterized by being capable of molding a three-dimensional complex shape, high precision, mass production, and near net shape without the need for post-processing, and has been put to practical use in recent years. Conventionally, as a degreasing method for decomposing and removing the organic binder by heating the sinterable powder compact, it is carried out in a normal atmospheric atmosphere,
Methods such as performing in an atmosphere of an inert gas such as nitrogen gas or under reduced pressure are generally known.

[0003]

However, in the conventional method, the degreasing time usually requires a long time of 24 hours or more and the degreasing temperature usually requires a high temperature of 400 ° C. or more. The actual situation was that it had caused a great deal of trouble in terms of various performances.

[0004]

In view of the above circumstances, the inventors of the present invention have made extensive studies as to a degreasing method capable of solving the above problems, and as a result, by decomposing and removing the organic binder under oxygen-enriched air, The present invention has been accomplished by finding that not only degreasing can be carried out at a low temperature in a short time, but also there is no concern about oxidation of the sinterable powder.

That is, according to the present invention, a molded body obtained by molding a composition composed of a mixture of a sinterable powder composed of metal powder and / or ceramic powder and an organic binder is heated to convert the organic binder from the molded body. In the degreasing method of decomposing and removing, the degreasing method of a sinterable powder compact is characterized in that the organic binder is decomposed and removed under oxygen-enriched air.

The metal powder of the sinterable powder used in the method of the present invention includes iron (carbonyl iron, atomized iron, reduced iron, etc.), nickel (carbonyl nickel, etc.), cobalt, aluminum, copper, titanium, molybdenum. , Zirconium, chromium, lead, manganese, tungsten, zinc, tin, beryllium, germanium, magnesium and other metal powders and alloy powders containing two or more of these metals (for example, stainless powder, iron-nickel alloy, high speed) Steel powder, superalloys, magnetic materials, bronze, monel metal, iron-silica alloys, iron-boron alloys, cemented carbides, etc.), and two or more of these may be used in appropriate mixture if necessary. You can In addition to these, non-metal powders such as silicon powder and boron powder may be included.

Ceramic powders include oxides (aluminum oxide, silicon oxide, zirconium oxide, beryllium oxide, magnesium oxide, titanium oxide, etc.), silicates (mullite, cordurite, etc.), titanates (barium titanate, etc.). ), Carbides (silicon carbide, boron carbide, aluminum carbide, tungsten carbide, titanium carbide, zirconium carbide, hafnium carbide, chromium carbide,
Vanadium carbide, carbon, etc., nitrides (silicon nitride, aluminum nitride, boron nitride, titanium nitride, etc.), silicides (molybdenum disilicide, etc.), sulfides (cadmium sulfide, zinc sulfide, etc.), etc. and two or more of these A mixture of

These powders are used alone or as a mixture of two or more different kinds or different particle sizes and different forms. It is also used as a mixture of metal powder and ceramic powder. For example, tungsten carbide-cobalt, alumina-aluminum and the like. These mixtures also include blends of metal and ceramic powders and alloys. Moreover, these powders (metal powder and / or
(Or ceramic powder) usually contains several percent of impurities and / or additives. For example, it is a sintering aid, a forming aid, or the like. The average particle size of these powders is
For example, 0.01 to 1 in the case of metal powder or ceramic powder
It is 00 microns. It is preferably 0.1 to 50 microns. In particular, if the diameter is 0.01 micron or less, handling is difficult and moldability is insufficient. Particles over 100 microns have poor sinterability.

In the method of the present invention, the amount of the sinterable powder in the entire composition is usually 30 to 70% by volume, preferably 40 to 60% by volume, more preferably 50 to 60% by volume.
% By volume. When the amount of powder exceeds 70% by volume, it becomes difficult to uniformly knead the organic binder and the powder, and molding becomes difficult. If it is less than 30% by volume, the molded product is largely deformed during degreasing.

As the organic binder used in the method of the present invention, all thermoplastic resins conventionally known in the art can be used. The thermoplastic resin is an acrylic resin [poly (meth) acrylic acid ester (polymethylmethacrylate, butylmethacrylate-methylmethacrylate copolymer, etc.)], an olefin resin [hydrocarbon monomer copolymer (olefin and styrene monomer). Copolymer, polyethylene, polypropylene, etc.), olefin copolymer [ethylene copolymer (ethylene-vinyl acetate copolymer, etc.), styrene copolymer (styrene-methyl methacrylate copolymer, etc.)], vinyl ester-based Alternatively, vinyl alcohol resins [polyvinyl acetate, polyvinyl acetal (polyvinyl formal, polyvinyl butyral, etc.)], halogen-containing resins [polyvinyl chloride, etc.], nitrogen-containing resins [poly (meth) acrylonitrile, etc.]. Polyester resin (polyethylene terephthalate, polytetramethylene terephthalate, etc.). Polycarbonate (polyethylene carbonate, polypropylene carbonate, etc.), polyamide (nylon 6,
Nylon 66, nylon 12, etc.), polyimide, aryl acid resin (polyaryl ether, polysulfone,
Such as polyphenylene sulfide). Polyacetal [a homopolymer composed of trioxane, a copolymer of trioxane and one or more comonomers (such as ethylene oxide)]. Examples thereof include celluloses (nitrocellulose, cellulose acetate, ethyl cellulose, etc.) and combinations of two or more of these thermoplastic resins. Among these, the preferable one is that the heat deformation temperature is 130 because it does not easily deform due to its own weight during degreasing.
It is a resin above ℃. Examples thereof include polyacetal, polyphenylene oxide, polysulfone, polycarbonate, polyether and polyamide. In particular, polyacetal has a low melt viscosity and thus has good moldability, and since it has good thermal decomposability, it also has good degreasing properties. Moreover, it is preferably used because it has almost no deformation due to its own weight during degreasing.

The composition used in the method of the invention is
Other ingredients may optionally be included. For example, plasticizers, lubricants, surfactants, various coupling agents (silane coupling agents, etc.), and other materials known in the art can be used.

Examples of the lubricant include polyether [polyethylene glycol (hereinafter abbreviated as PEG), polyethylene oxide and the like], aliphatic hydrocarbon (liquid paraffin, stearic acid and the like), waxes (montane wax and the like) and the like. In particular, when polyacetal is used as the thermoplastic resin, from the viewpoint of compatibility, the molecular weight is 1,
It is desirable to use 000-100,000 PEGs. PE
G further serves to increase the fluidity during injection molding, enhance the deformation preventing effect during degreasing, and accelerate the degreasing speed.

As the plasticizer, phthalic acid esters (dibutyl, dioctyl, butylbenzyl phthalate, etc.),
Examples include aliphatic dibasic acid esters and polyoxyalkylene benzoic acid. As the surfactant, anionic surfactants (dodecylbenzene sulfate, etc.), nonionic surfactants (polyoxyethylene alkylphenyl ether, etc.), cationic surfactants (lauryl trimethyl ammonium chloride, etc.), Examples include amphoteric surfactants (such as stearyldimethylcarboxymethyl-betaine).

The amount of the thermoplastic resin component in the organic binder is usually 5 to 90% by weight, preferably 10 to 80% by weight. If it is more than 90% by weight, the fluidity of the kneaded product is insufficient and molding becomes difficult. If it is less than 5% by weight, the strength of the molded product is insufficient and handling becomes difficult.

In the method of the present invention, the composition is prepared by mixing and / or kneading the components. Mixing is performed with a mixing device such as a V-type mixer, a Henschel mixer, or a ball mill. The kneading is performed by melting using a well-known kneading machine such as a Banbury mixer, a plastomill, a kneader, a pressure kneader, a roll mill and a screw type continuous kneader. The kneading temperature is usually 50 to 400 ° C., preferably 100 to 250 ° C., and the temperature control is performed by constant temperature, temperature increase, temperature decrease, or the like. Kneading time is usually 10 minutes ~
It is preferably from 3 minutes to 20 minutes to 2 hours. The kneading is performed in air or an inert gas. Examples of the kneading method include, but are not particularly limited to, a method of kneading and kneading the whole material at once, a method of kneading a part thereof and then adding the rest, and the like.

In the method of the present invention, the composition is then molded into a sheet or complex shape by injection molding, extrusion molding, press molding, etc., degreased, sintered, and optionally processed to obtain a molded article. . Of these, injection molding is preferred. For injection molding, a normal injection molding machine such as a plunger type or a screw type can be used. Molding conditions differ depending on the shape of the mold and the composition of the composition, but the molding pressure is usually 10
~ 20,000 Kg / cm ² , preferably 100-3.
It is 000 Kg / cm ² . Molding temperature is usually 20-4
The temperature is 00 ° C, preferably 50 to 250 ° C. A composition which is easily thermally decomposed by heating can be molded under reduced pressure or in a non-oxidizing atmosphere (inert gas atmosphere such as nitrogen or argon).

When the molding is completed, a degreasing step for removing the unnecessary organic binder is started. As the degreasing method, heating degreasing, organic solvent or water extraction degreasing, supercritical gas degreasing, photolytic degreasing, etc. have been put to practical use, but the heating degreasing method is widely used in terms of productivity, cost, etc. There is. The degreasing conditions in the thermal degreasing method include atmospheric pressure, reduced pressure, and pressurizing conditions as the degreasing pressure, and an air atmosphere and an inert gas atmosphere (such as nitrogen) are used as the degreasing atmosphere.
A special and expensive degreasing furnace is required to perform degreasing under reduced pressure and pressure conditions as pressure, and when performing degreasing in an inert gas atmosphere, there are problems such as high temperature and long time. From the viewpoint of cost and productivity, it is most common to perform degreasing under atmospheric pressure and atmosphere. However,
Even in this method, the above-mentioned problems remain.

The present inventors have conducted various studies on how to perform degreasing at low temperature and in a short time while keeping the characteristics of degreasing under atmospheric pressure and atmosphere, and as a result, conducted degreasing under oxygen-enriched air. It was found that not only the above problems could be solved, but also the performance of sintered parts could be improved. Normally, it was feared that the use of oxygen-enriched air would cause unnecessary oxidation of the sinterable powder, but since the binder can be decomposed at a low temperature and in a short time, unexpectedly, it would be a normal atmospheric atmosphere. It was found that the oxidation was suppressed more than that performed below. The reason why the decomposition of the organic binder can be performed at low temperature and in a short time is that the oxidative thermal decomposition of the organic binder is promoted by the oxygen-enriched air. It is considered that this was connected to the secondary good result that the oxidation of the sinterable powder was suppressed because it was not exposed.

The oxygen-enriched air used in the method of the present invention is not particularly limited as long as it has a normal atmospheric oxygen concentration of more than 21% by volume, but an oxygen concentration of 25 is preferable.
˜50% by volume. When the oxygen concentration is 25% by volume or less, no significant effect is observed in shortening the degreasing time and lowering the maximum degreasing temperature. When the oxygen concentration is 50% by volume or more, problems may occur in terms of industrial productivity and performance of sintered parts. These degreasing operations can be easily performed by attaching an oxygen cylinder, an oxygen enrichment device, etc. to a commonly used heating degreasing furnace, and blowing and circulating oxygen-enriched air having a constant concentration in the degreasing furnace. Can be implemented.

Since the degreasing conditions vary greatly depending on the shape and the atmosphere during composition degreasing of the composition, general quantification is difficult, but the maximum degreasing temperature can be lowered by using the oxygen-enriched air of the present invention. Not only that, the temperature rising rate at the time of degreasing can be increased, so that the total degreasing cycle can be significantly reduced. Incidentally, according to the method of using the oxygen-enriched air of the present invention, cracking of the degreased body is less likely to occur as compared with the conventional method, but in order to obtain a more sound degreased body, various setters or jigs are used for molding. It is necessary to devise it at the time of installation so that oxygen-enriched air can be sufficiently ventilated over the entire body.

The final product is obtained by sintering the degreased body. Sintering is usually performed under reduced pressure, normal pressure or increased pressure in an oxidizing, reducing or inert gas atmosphere, and the degreased body is usually 0.1 to 1,000 ° C./hr, preferably 10 to 800.
C./hr at a temperature raising rate of usually 600 to 2,500.degree. C., preferably 600 to 2,200.degree. C., more preferably 80.
The temperature is raised to 0 to 2,000 ° C, and at that temperature usually 10 minutes to
It is carried out by holding for 10 hours, preferably 30 minutes to 3 hours. When sintering in vacuum, the degree of vacuum is 10
^{It is −2} Torr or more, preferably 10 ⁻³ Torr or more.

[0022]

The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited to these. Parts in the examples and comparative examples are parts by weight.

Preparation of Molded Body 1 Stainless powder (PF-20 made by Taiheiyo Metal Co., Ltd.) 100.0 parts Polyacetal (F40-03 made by Mitsubishi Gas Chemical Co., Ltd.) 5.0 parts PEG1000 (PEG1000 made by Sanyo Chemical Industries) 5.0 parts Using a pressure kneader, the temperature was gradually lowered to 200 ° C. at the time of charging and 170 ° C. after the start of kneading, and kneading was performed for about 60 minutes. Then, the kneaded composition was injection-molded into a mold under the conditions of a molding temperature of 165 ° C. and an injection pressure of 900 kg / cm ² by using an injection molding machine (100 mm × 10 mm × 4 m).
m) was obtained. Manufacture of molded product 2 Molded by the same method as in the manufacture of molded product 1, except that the binder was changed to 4.0 parts of EVA, 3.0 parts of polybutyl methacrylate, 4.0 parts of paraffin wax, and 1.5 parts of dibutyl phthalate. I got body 2. Manufacture of molded body 3 WC / Co powder (manufactured by Toho Metal Co., Ltd.) 100.0 parts Polyacetal (F40-03 manufactured by Mitsubishi Gas Chemical Co., Ltd.) 5.0 parts PEG1000 (PEG1000 manufactured by Sanyo Chemical Industries) 3.0 parts Ionet YB400 (Sanyo Chemical Co., Ltd.) Molded product) was used to obtain a molded product 3 in the same manner as in the production of the molded product 1.

Examples 1 to 3 and Comparative Examples 1 to 5 Molded bodies 1 to 3 were degreased under the following conditions. Molded article 1 Under oxygen-enriched air atmosphere with oxygen concentration of 37% (Example 1) Molded article 1 Under normal atmospheric atmosphere (Comparative example 1) Molded article 1 Under nitrogen atmosphere (Comparative example 2) Molded article 2 Oxygen concentration 40% Under an oxygen-enriched air atmosphere of (Example 2) Molded body 2 Under normal air atmosphere (Comparative example 3) Molded body 2 Under nitrogen atmosphere (Comparative example 4) Molded body 3 Under oxygen-enriched air atmosphere of 37% oxygen concentration (Example 3) Molded article 3 Under normal atmosphere (Comparative example 5) (Facilities used) Air-circulating heating degreasing furnace manufactured by Peng Seisakusho (Degreasing condition) Maximum degreasing temperature: Necessary for reaching a degreasing rate of 95% Maximum heating temperature Degreasing rate: (Molded body weight-Degreased body weight) / Binder weight in molded body x 100 (%) Degreasing heating rate: Maximum heating heating rate that does not cause degreasing defects Next, in sintering furnace under vacuum atmosphere (10 ^-3 Torr or more), example 1 2, Comparative Examples 1 to 4 1300 ° C. × 2h
Example 3 and Comparative Example 5 were 1700 ° C. × 2 h under the condition of rs.
Sintering was carried out under the condition of rs. The sintered densities are summarized in Table 1. The definitions of terms appearing in the table are as follows. Degreasing time: (Maximum degreasing temperature-Degreasing start temperature) / Degreasing heating rate Sintering density: Sintered body density / True density of raw material powder × 100
(%)

[0025]

[Table 1] ------------------ Degreasing, Degreasing, Degreasing time, High sintering density Temperature Temperature rate (° C) (° C / hr) (hr) (%) -------------------------------------------------------------------------------------------------------------------------- --- Example 1 185 15 5 97.5 --------------------------------------- 2 320 12 20 97.0 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Example 3 180 15 599 . 6 ------------------------------------------- Comparative Example 1 250 10 15 94.0 --- −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example 2 45 7 50 94.4 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example 3 400 10 32 93.2 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example 4 550 8 59 95.0 −−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example 5 250 8 17 99.0 −−−−−−−−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−

According to the method of the present invention, in order to obtain a degreased body having a degreasing rate of 95% and no degreasing defects at all, in Example 1, the degreasing maximum temperature is 185 ° C. and the degreasing temperature rising rate is 15 ° C./h.
r, degreasing time of 5.7 hrs is possible, and Comparative Example 1 (normal air atmosphere) is 250 ° C., 10 ° C./hr,
15 hours, Comparative Example 2 (nitrogen atmosphere) 450 ℃, 7 ℃
/ Hr and 50 hrs, it can be seen that degreasing can be performed at low temperature in a short time. In the case of this example, there was no cracking, swelling, pores or the like inside or outside the degreased body, and no deformation due to its own weight was observed. Also, the surface of the degreased body was hardly oxidized. Then, when the degreased body was sintered,
A fairly high relative density could be achieved in this example. The reason for this is that the oxidative decomposition by heating of the organic binder is promoted by oxygen, so that the degreasing rate becomes faster, the degreasing time can be shortened, and the maximum degreasing temperature can be lowered. As a result, the oxidation of the metal powder is suppressed, and the sintering easily proceeds. Since the decomposition of the organic binder is promoted and the binder is decomposed almost completely, unnecessary carbon does not remain during sintering.
It is presumed to be the cause. From these results, according to the method of the present invention, not only the degreasing time can be shortened, the degreasing maximum temperature can be lowered, but also the sintering density can be improved, which is a great effect in improving the performance of various sintered parts. Turned out to be. Further, similar effects were observed in the comparison between Example 2 and Comparative Examples 3 to 4 and the comparison between Example 3 and Comparative Example 5.

[0027]

The degreasing method using oxygen-enriched air of the present invention has the following effects. Since the oxygen-enriched air accelerates the thermal oxidative decomposition of the organic binder, it is possible to reduce the degreasing time and the maximum degreasing temperature, which leads to an improvement in productivity and a reduction in cost. Since degreasing can be performed under atmospheric pressure at low temperature for a short time, a degreasing furnace with simple specifications can be used. Unwanted oxidation of the metal powder can be suppressed. Since the decomposition of the organic binder is performed with high efficiency, the amount of residual carbon can be significantly reduced. As a result, it is possible to obtain a sintered part having various characteristics such as density, hardness, strength, corrosion resistance, magnetism and structure. Therefore, according to the method of the present invention, not only the productivity of the sintered part can be improved and the cost can be reduced, but also the sintered part having high superiority in various performances can be provided.

Claims (2)

[Claims] 1. A molded body obtained by molding a composition comprising a mixture of a sinterable powder composed of metal powder and / or ceramic powder and an organic binder is heated to decompose and remove the organic binder from the molded body. A method for degreasing a sinterable powder compact, which comprises decomposing and removing an organic binder under oxygen-enriched air. 2. The degreasing method according to claim 1, wherein the oxygen-enriched air has an oxygen concentration of 25 to 50% by volume.