JPH0820803A - Production of sintered compact - Google Patents

Abstract

PURPOSE:To efficiently produce a sintered compact free from defects, such as deformation, cracking, and bulging, by melting and kneading a metal powder and an organic binder consisting of polyacetal of specific thermal deformation temp. and polyalkylene glycols of specific melting point and then subjecting the resulting composition to molding, degreasing, and sintering. CONSTITUTION:A metal powder (iron powder) or a powder mixture of metal powder and ceramic powder (Al2O3 powder, etc.) and an organic binder consisting of polyacetal (homopolymer of trioxane, etc.) A of >=130 deg.C thermal deformation temp. and polyalkylene glycols (polyethylene glycols, etc.) B of 30-100 deg.C melting point are melted and kneaded, by which a composition for molding is prepared. At this time, A:B=(30 to 60):(40 to 70) is satisfied. This composition is injection-molded into a desired shape, arranged on a tray capable of ventilation in a degreasing furnace and heated and degreased under an oxidizing atmosphere, and then sintered under a vacuum of <=10<-3>Torr. By this method, degreasing can be done in a short time without causing thermal deformation, and the superior sintered compact can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered body using a molding composition comprising metal powder or a mixed powder of metal powder and ceramic powder and an organic binder.

[0002]

2. Description of the Related Art As a conventional molding composition comprising a metal powder or ceramic powder and an organic binder, there are used organic binders such as polypropylene, methacrylic acid ester, polystyrene, ethylene-vinyl acetate copolymer and low density polyethylene. Known are plastic resins, or those in which a plasticizer such as paraffin wax, diethyl phthalate, stearic acid or a lubricant is used in combination. A method is also known in which such a composition is injection-molded, an organic binder is removed from the molded body (this is referred to as degreasing), and then sintering is performed to obtain a sintered body (for example, USP 2593943, JP-A-58-22
No. 3662).

[0003]

However, in the conventional composition, the molded body is deformed by its own weight during degreasing,
Since cracks and swelling easily occur due to decomposition gas, the molded body is embedded in ceramic powder or metal powder to prevent deformation, and the amount of decomposition gas generated is usually controlled at a slow heating rate of 1 to 10 ° C / hr. It was necessary to degrease it. Therefore, industrial production has been difficult because a step of removing powder adhering to the surface of the molded body is required before proceeding to sintering, and it takes a long time for degreasing. The present invention was devised in order to eliminate the drawbacks of the prior art as described above, using a composition that can be degreased in a short time without thermal deformation during degreasing, defects such as cracks, swelling, etc. It is an object of the present invention to provide a method for efficiently producing a sintered body free of impurities.

[0004]

According to the present invention, a metal powder or a mixed powder of a metal powder and a ceramic powder, and a heat distortion temperature 1
Polyacetal (A component) of 30 ° C or higher and melting point 30 to 1
An organic binder composed of polyalkylene glycols (component B) at 00 ° C. is melt-kneaded to prepare a molding composition, the composition is molded into a desired shape, and then the organic binder is removed by heating from the molded body. A method for producing a sintered body, which comprises sintering the obtained degreased body. Here, the heat distortion temperature is in accordance with ASTM D648 and the load is 4.
It shall be indicated by the value measured at 6 Kg / cm ² .

As the polyacetal having a heat distortion temperature of 130 ° C. or higher, which is the component A of the binder used in the production method of the present invention, a homopolymer consisting only of trioxane, trioxane and ethylene oxide, dioxolane, substituted dioxolane, and 1,4-dioxane. And the like, and of these, one kind or two or more kinds can be appropriately mixed and used. Of these, those having a heat distortion temperature of 150 ° C. or higher are preferable. Polyacetal has a low melt viscosity, is easy to mold, and has good thermal decomposition.

The polyalkylene glycols having a melting point of 30 to 100 ° C., which is the component B, have a usual molecular weight of 10 such as polyethylene glycol, polytetramethylene glycol, ethylene oxide-propylene oxide copolymer and the like.
There are 000 to 20,000 and the like, and one kind or two or more kinds of them can be appropriately mixed and used.

In contrast to polyacetal as the A component, B
The component polyalkylene glycols have excellent compatibility. Of the polyalkylene glycols, polyethylene glycol is preferred. The molecular weight of polyethylene glycol is usually 1,000 to 20,000, but since it is excellent in moldability and the effect of preventing deformation during degreasing, it has a molecular weight of 1,000 to 1
Thousands are more preferable.

In addition to the components A and B, a third component (component C) may be added to the organic binder in order to improve moldability. Examples of such C component include polycarbonate, polyphenylene oxide, polyphenylene sulfide, polyvinylidene fluoride, polyamide (for example, nylon 6, 11, 12, 66 or copolymers thereof).
Polyester (eg polyethylene terephthalate, polybutylene terephthalate), polyaryl sulfone, polyaryl ether, polyether sulfone, polyether ether ketone, waxes (petroleum wax, natural wax, synthetic ax, etc.), various low-temperature solids at room temperature Molecular weight compound (metal soap such as stearic acid,
Aliphatic amines such as distearylamine, various surfactants), polyethylene, polypropylene, poly-4-methylpentene-1, polystyrene, poly-α-methylstyrene, ethylene-vinyl acetate copolymer, polymethacrylic acid ester, Examples include polyethylene oxide. Polyethylene oxide is preferable from the viewpoint of compatibility. The organic binder further contains a plasticizer (diethyl phthalate, dibutyl phthalate, etc.) which is liquid at room temperature, a surfactant for improving the wettability of the binder with respect to the metal powder, various coupling agents, etc. within the range usually used. May be.

The polyacetal (component A) having a heat distortion temperature of 130 ° C. or higher in the organic binder serves to impart fluidity to the composition and to prevent deformation during degreasing. If the heat distortion temperature is lower than 130 ° C, the deformation preventing effect becomes insufficient. The amount of component A in the binder is usually 20 to 60
%, Preferably 30 to 60% by weight. When the amount of the component A is less than 20% by weight, the strength of the molded product is insufficient and handling becomes difficult. The polyalkylene glycol (component B) having a melting point of 30 to 100 ° C. serves to increase the fluidity of the composition, facilitate injection molding, further enhance the deformation preventing effect during degreasing, and accelerate the degreasing speed. . When the melting point is 30 ° C. or lower, the strength of the molded article becomes weak, and when it exceeds 100 ° C., the deformation preventing effect becomes insufficient.
The amount of component B in the binder is usually 40 to 80% by weight,
It is preferably 40 to 70% by weight. The amount of B component is 80
If the content is more than wt%, the strength of the molded product will be insufficient. The amount of C component in the binder is usually 0 to 60% by weight, preferably 0 to 30% by weight. If the amount of C component exceeds 60%, the molded body is likely to be deformed during degreasing.

The metal powder used in the production method of the present invention includes metal powders of iron, aluminum, copper, titanium, molybdenum, zirconium, cobalt, nickel, chromium and alloy powders containing these metals as main components (for example, Stainless powder, high-speed steel powder, cemented carbide powder, magnetic material powder, etc.), and one or more of these may be appropriately mixed and used as necessary. Ceramic powder may be added to these metal powders in the range of 0 to 95% by weight. Such ceramic powders include oxides (aluminum oxide, silicon oxide, zirconia oxide, titanium oxide, mullite, cordierite, etc.), carbides (silicon carbide, boron carbide, zirconia carbide, etc.), nitrides (silicon nitride, aluminum nitride, boron nitride). , Titanium nitride, etc.) and other powders. In addition to the powders, sintering aids, molding aids, other powders for improving the physical properties, and the like can be appropriately added to these powders in advance. The addition method may be simple mixing or coating on the surface of the powder.

The average particle size of the metal powder and the ceramic powder is usually 0.01 μm to 50 μm, preferably 0.1 μm.
It is m-20 micrometers. When the particle size is smaller than 0.01 μm, the sinterability is improved, but the bulkiness is high and the handleability is poor, and the moldability is poor. Particle size is 50
If it exceeds μm, the sinterability becomes poor. The amount of the powder used in the production method of the present invention in the whole composition is usually 40.
˜70% by volume, preferably 50-60% by volume. If the powder amount exceeds 70% by volume, it becomes difficult to uniformly knead the powder and the binder, and it becomes difficult to perform injection molding. Further, if it is less than 40% by volume, the deformation of the molded body during degreasing becomes large.

The composition used in the production method of the present invention can be produced by melt-kneading the respective components, cooling and pulverizing (coarse crushing) or pelletizing. In the above, the kneading can be carried out using an ordinary kneader such as a Banbury mixer, a plastomill, a kneader, a pressure kneader, a roll mill, a screw type extruder. The kneading temperature is usually 150 to 350 ° C., preferably 150 to 250 ° C., and the kneading time is usually 20 minutes to 2 hours, preferably 30 minutes to 1 hour. If necessary, each component or mixture may be dried before kneading. As a kneading method, there are a method in which all components are charged at once and kneaded, a binder component alone is first added and kneaded, and then ceramic powder or metal powder is added and kneaded, and a binder component is added later.

When injection molding is performed using the composition, an ordinary plunger type or screw type injection molding machine can be used. Molding conditions differ depending on the shape of the mold and the composition for injection molding, but the molding pressure is usually 100 to 3000.
Kg / cm ² , preferably 200 to 2000 Kg / c
m ² , the molding temperature is usually 150 to 350 ° C., preferably 1
It is 50 to 250 ° C. In addition, extrusion molding, press molding and the like can be performed. For compositions that are easily thermally decomposed by heating, kneading under reduced pressure or in an inert atmosphere,
A molding method may be adopted.

Degreasing is carried out in an oxidizing, reducing or inert gas atmosphere under reduced pressure, normal pressure or increased pressure, usually at 1 to 60 ° C. /
hr, preferably 25 at a temperature rising rate of 10 to 40 ° C./hr
The temperature is raised to about 0 to 500 ° C, preferably 250 to 350 ° C, and the temperature is usually 0 to 10 hours, preferably 1
Hold for ~ 5 hours. The molded body in the manufacturing method of the present invention does not need to be embedded in the powder or supported by a jig in order to maintain the shape, and can be arranged and degreased on the shelf plate in the degreasing furnace as it is. Here, it is possible to shorten the degreasing time by using a shelf plate on which the molded body is placed and having a structure that allows ventilation, and by applying a flow of atmospheric gas to the lower surface of the molded body. As such a shelf plate, a wire mesh made of stainless steel or the like, a ceramic formed in a lattice shape, or the like is used.

Sintering is usually performed at 600 to 2 in an oxidizing, reducing or inert gas atmosphere under vacuum, atmospheric pressure or pressure.
The temperature is raised to about 000 ° C. The heating rate is usually 50-
The temperature is 1000 ° C./hr, and the maximum temperature is maintained for 10 minutes to 10 hours. When sintering in vacuum, the degree of vacuum is usually 10
^-2 torr or higher vacuum, preferably 10 ^-3 t
Orr or higher vacuum. In the conventional method in which degreasing is embedded in the powder, it is necessary to remove the powder adhering to the surface of the degreasing body before proceeding to sintering, and it is difficult to continuously perform from degreasing to sintering. However, by using the composition of the present invention, such a step is unnecessary, and it is possible to continuously perform sintering in the same heating furnace.

[0016]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

[Production of Composition] Production Examples 1 to 3 Metal powders having the composition ratios shown in Table 1 and an organic binder are kneaded at 150 to 180 ° C. for 45 minutes using a pressure kneader and crushed while cooling. An injection molding composition was obtained.

Comparative Production Examples 1 and 2 Metal powders having the composition ratios shown in Table 1 and an organic binder were kneaded with a pressure kneader at 150 ° C. for 45 minutes and crushed while cooling to obtain an injection molding composition. It was

[0019]

[Table 1]

Symbols in the table FEN-8: Mixed powder of 92% by weight of iron powder having an average particle size of 4 μm and 8% by weight of nickel powder having an average particle size of about 10 μm SUS304: Stainless powder having an average particle size of 10 μm POM: Polyacetal homopolymer (Heat deformation temperature 17
0 ° C.) CO-POM: polyacetal copolymer (heat distortion temperature 158 ° C.) PP: polypropylene (heat distortion temperature 110 ° C.) PEG-4000: polyethylene glycol (average molecular weight 4000, melting point 56 ° C.) PW: paraffin wax (melting point 58 ° C.)

[Production of Degreased Body] The compositions of Production Examples 1 to 3 were heated using an injection molding machine at a heating cylinder temperature of 150 to 170.
° C, mold temperature: 50 ° C, injection pressure: 1500 Kg / cm
^Under the condition of ^2, the test piece as shown in FIG. 1 (100 mm × 10
mm × 4 mm). Observation of the obtained moldings revealed that they all had a good appearance. Then, the above-mentioned molded body was placed on a support rod installed at a constant distance L (1, 2, and 3 cm) as shown in FIG. 2, and heated at a temperature rising rate of 20 ° C./hr in a circulating air oven at 350 ° C. Degreasing was performed by raising the temperature to 0 ° C and holding at that temperature for 2 hours. After degreasing, the deformation amount (h) was evaluated as shown in FIG. The degreasing rate and the amount of deformation are shown in Table 2.

[0022]

[Figure 1]

[0023]

FIG. 2

[0024]

FIG. 3

The compositions of Comparative Examples 1 and 2 were heated at a heating cylinder temperature of an injection molding machine of 150 ° C. and an injection pressure of 1000 Kg / g.
Molding and degreasing were performed in the same manner as in Example 1 except that the size was changed to cm ² . The degreasing rate and the amount of deformation are shown in Table 2.

[0026]

[Table 2]

Production Example 1 used in the production method of the present invention
The degreased bodies of the compositions Nos. 3 to 3 were not deformed at all as shown in Table 2, the degreasing rate was about 98% by weight, and the appearances of the molded articles were all good. On the other hand, the degreased bodies of the compositions of Comparative Production Examples 1 and 2 had a degreasing rate of about 85% by weight as shown in Table 2, and the deformation amount was slightly deformed even when the distance between the supporting rods was as narrow as 1 cm. And was deformed significantly at 2 cm or more.

Example 1 The degreased body obtained in Production Example 3 was sintered at 1250 ° C. for 2 hours in a vacuum higher than 10 ⁻³ torr to obtain a sintered body having a relative density of 95%. Example 2 A degreased body obtained in the same manner as in Production Example 3 except that stainless steel powder having an average particle diameter of 4.7 μm was used was used.
Sintering was performed in the same manner as above to obtain a sintered body having a relative density of 98%.

As can be seen from Production Examples 1 to 3 and Comparative Production Examples 1 and 2, when the organic binder is polypropylene and wax, deformation due to its own weight is likely to occur during degreasing. On the other hand, according to the composition used in the production method of the present invention, a polyacetal having a heat distortion temperature of 130 ° C. or more and easily thermally decomposed as a binder component, and a melting point of 30 to 1 are used.
Use of polyalkylene glycols that are easily decomposed by heat at 00 ° C to obtain a good degreased body that does not deform even if the distance between the supporting rods is wide (that is, the molded product is large). Moreover, degreasing could be performed at a relatively low temperature in a short time. In addition, in the above Production Examples and Comparative Production Examples, only the results obtained by performing the metal powder are shown. However, the results of the deformation of the degreased body being smaller than those of the conventional composition are obtained for the mixture of the metal powder and the ceramic powder.

[0030]

The manufacturing method of the present invention has the following effects. Since it is prevented from being deformed by its own weight during degreasing,
It eliminates the need for embedding into powder and jigs for shape retention, which were required for degreasing, and improves productivity and product accuracy. Degreasing that does not deform, even if it is difficult to embed in powder or retain shape by a jig, such as complicated shaped products or large molded products, and that easily deforms during degreasing, such as molded products using stainless steel powder You can get the body. Since the step of removing the degreased body from the powder is unnecessary, continuous production from degreasing to sintering becomes possible.
Productivity can be increased. The temperature rising rate can be increased as compared with the conventional composition, and the degreasing time can be shortened.

[0031]

[Brief description of drawings]

FIG. 1 is a perspective view of a test piece, FIG. 2 is a view showing a method for measuring the deformation of the test piece, and FIG. 3 is an explanatory view of the amount of deformation.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C04B 35/64 301

Claims (4)

[Claims] 1. An organic binder comprising a metal powder or a mixed powder of a metal powder and a ceramic powder, a polyacetal (A component) having a heat distortion temperature of 130 ° C. or more, and a polyalkylene glycol (B component) having a melting point of 30 to 100 ° C. Melt kneading to prepare a molding composition, molding the composition into a desired shape, heating and removing the organic binder from the molded body, and sintering the obtained degreased body. A method for producing a bound body. 2. The method according to claim 1, wherein the component B accounts for 40 to 70% by weight of the organic binder. 3. The method according to claim 1, wherein the removal of the organic binder is carried out by placing the molded body on a shelf plate through which the molded body can be ventilated, and applying a flow of atmospheric gas to the lower surface of the molded body. 4. Stainless steel powder is used as the metal powder, the organic binder is removed in an oxidizing atmosphere, and sintering is performed at 10
^The method according to any one of claims 1 to 4, which is performed under a vacuum of ^-3 torr or less.