JPH08319502A - Method for dewaxing metal powder injection-molded body - Google Patents

Abstract

PURPOSE: To shorten the degreasing time and to facilitate degreasing at the time of degreasing a metal powder injection-molded body consisting of metal powder and org. binder by embedding the body in a metal oxide powder not reacting with the body to degrease the body. CONSTITUTION: The mixture of a metal powder (stainless steel powder having about 10μm average grain diameter, etc.) and an org. binder (PE wax, etc.) is injection-molded to prepare a metal powder injection-molded body G (green body). A metal oxide powder A (activated alumina having >=80m<2> /g specific surface) not reacting with the green body G is filled in a closed dewaxing furnace, and the green body G is completely embedded in the powder. Gaseous N2 is then supplied into the dewaxing furnace from a suction pipe 3 and discharged from an exhaust pipe 2, the furnace is heated to about 400 deg.C by a heater H, and the green body is dewaxed with 40-98% efficiency. Consequently, the treating time is shortened, and dewaxing is carried out with an inexpensive equipment and simple operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing method for removing an organic binder from a metal powder injection molded body for obtaining a metal sintered body.

[0002]

2. Description of the Related Art Conventionally, in order to obtain a sintered metal body, metal powder is mixed with an organic binder made of paraffin wax or acrylic resin, and the mixture is injected by a method similar to the well-known plastic injection molding. A metal powder injection molded body, a so-called green body (hereinafter, the metal powder injection molded body is referred to as a green body) is formed by forming the metal powder injection molded body. Then, prior to the sintering treatment of the green body, a degreasing treatment for removing the organic binder is performed.

As the degreasing method, the green body is placed in a vacuum and further heated to remove the organic binder, the green body is heated to evaporate and remove the organic binder, and the organic binder is used as a solvent. There is a method of extracting and removing, a method of decomposing the organic binder with ultraviolet rays, and the like, and these methods are used alone or in combination.

[0004]

However, in any of the conventional degreasing methods for the above-mentioned green body, one to several days are required for degreasing without causing defects such as deformation and cracking of the green body. In addition to requiring a long time, there are drawbacks such as requiring a complicated temperature rising pattern, expensive equipment when operating under vacuum, and a complicated combination of organic binders. It was

Therefore, the present invention has been made in order to solve the above-mentioned drawbacks, and the purpose thereof is to shorten the processing time, to use a simple organic binder composition, and to use inexpensive equipment. Another object of the present invention is to provide a method for degreasing a green body that enables degreasing of the green body with a simple operation.

[0006]

In order to achieve the above object, a degreasing method for a green body according to the present invention is a degreasing furnace for degreasing a green body obtained by injection molding a mixed material of metal powder and an organic binder. In the method of degreasing a green body, the degreasing process is performed by embedding the green body in a metal oxide powder that does not react with the green body.

As the above-mentioned metal powder, any metal powder that is commonly used as a material for sintered metal can be used, and for example, stainless steel powder having an average particle diameter of 10 μm can be used. You can

As the above-mentioned organic binder, any of those commonly used as a binder for molding a green body can be adopted. For example, paraffin wax,
A material made of polypropylene, stearic acid, an acrylic resin, or the like can be used alone or in combination.

As the metal oxide powder which does not react with the green body, activated alumina powder can be used. As this activated alumina powder, it is possible to use activated alumina powder which is generally commercially available for adsorption purification used in the chemical industry or for chromatography.
The specific surface area of the activated alumina powder is 80-18.
It is 0 m ² / g. When the specific surface area is less than 80 m ² / g, the ability to adsorb the organic binder is low, and the activated alumina powder is likely to adhere to the periphery of the green body in the form of clothes. Further, if the specific surface area exceeds 180 m ² / g, the number of commercially available products will decrease, and it will be necessary to specially manufacture it, which may be expensive. When the specific surface area of the activated alumina powder is 80 to 180 m ² / g, the ability to adsorb the organic binder is high, and not only the degreasing treatment time can be shortened, but also
The temperature rising pattern can also be simplified. In addition, since it is not necessary to perform degreasing treatment under vacuum, vacuum equipment is not required and the process can be performed at low cost.

The degreasing treatment of the green body is carried out in a degreasing furnace composed of a well-known electric furnace so as to be completely embedded in the above-mentioned activated alumina powder. Then, like a well-known degreasing furnace, it is operated to suck and exhaust an inert gas to prevent the oxidation of the metal powder and to promote the diffusion or evaporation of the decomposition gas of the organic binder from the activated alumina powder. . The heating temperature of the degreasing furnace is not uniform depending on the type of organic binder used, but at least,
This is the temperature at which the organic binder used is melted. Further, it is not necessary to pay particular attention to the heating rate as in the conventional case.
In addition, if the heating temperature is about 400 ° C., it can be applied to various organic binders currently used.

The inert gas is used to create an atmosphere for preventing the oxidation of the metal powder and also to serve as a carrier gas for promoting the diffusion and evaporation of the decomposition gas of the organic binder from the activated alumina powder. . Therefore, the amount of the inert gas may be as small as a level of rectification in the furnace. Further, it is more effective to stir the inert gas with a fan or the like built in the degreasing furnace in order to keep the temperature inside the furnace uniform.

The degreasing treatment in the degreasing furnace has a degreasing rate of 4
It is performed until it becomes 0 to 98%. The higher this degreasing rate,
It is possible to obtain a high quality sintered metal product with less residual carbon in the sintered metal, and it is possible to shorten the removal time of the organic binder remaining in the sintering furnace. However, if the degreasing rate exceeds 98%, it becomes difficult to maintain the shape in the process such as transferring the green body.
It is necessary that at least about 2% of the organic binder remains. Further, if the degreasing rate is less than 40%, there is a drawback that the removal treatment time of the residual organic binder during the sintering treatment in the sintering furnace becomes long. In any case, as described above, when the green body is embedded in the activated alumina powder in the degreasing furnace and a series of degreasing treatment operations are performed, the deformation due to the conventional degreasing treatment does not occur, and the original green body is not deformed. It can be degreased while maintaining its shape.

[0013]

The degreasing of the green body according to the present invention is carried out in the metal oxide powder. Therefore, first, the organic binder eluted from the green body is diffused and adsorbed in the metal oxide powder. At this stage, a large part of the organic binder in the green body is adsorbed by the metal oxide powder,
Voids are generated in the place where the organic binder of the green body was present, and swelling and cracking due to the generation of gas due to the decomposition of the remaining organic binder is less likely to occur.

[0014]

Embodiments of the present invention will be described below.

[Embodiment 1] As shown in FIG. 1, in a hermetic degreasing furnace 1 heated by a heater H, a specific surface area of 15
An activated alumina powder A having an average particle size of 50 μ and 0 m ² / g is filled. In the present invention, the size of the particle size of the activated alumina powder is not an important factor, and there is no problem as long as it is commercially available for adsorption purification or chromatogram.

In activated alumina powder A, an average particle size of 10 μm
A material obtained by kneading 90 parts by weight of stainless steel powder of m and 10 parts by weight of an organic binder containing polyethylene wax having a melting point of about 120 ° C. as a main component was injected with an injection molding machine to obtain a thickness of 5 mm. , A green body test piece G having a width of 10 mm and a length of 50 mm was completely embedded.

Thereafter, N ₂ gas was supplied into the degreasing furnace 1 from the intake pipe 3 at a rate of about 10 liters / minute, and was simultaneously discharged from the exhaust pipe 2.

While supplying and discharging the above-mentioned inert gas,
After the temperature was raised to 370 ° C. in 6 hours, heat treatment was performed at that temperature for 2 hours to perform degreasing treatment.

After the degreasing treatment, the test piece G was taken out from the activated alumina A, and the degreasing rate was 80%, and the test piece G had no defect such as deformation. Also, activated alumina powder A
The activated alumina powder A adhering to the surface of the test piece G taken out from the inside could be removed very easily.

The degreased test piece G was placed in a sintering furnace (not shown), evacuated, and then discharged from room temperature to 60 at a temperature rising rate of 200 ° C./hr while supplying and discharging an inert gas at 10 l / min.
Heated linearly to 0 ° C and held for 10 minutes. afterwards,
Heat to 1200 ° C. at a heating rate of 100 ° C./hr, and
It hold | maintained for 0 minute and the sintering process was performed.

The carbon content of the sintered test piece G was 0.
It was confirmed that the degreasing treatment was completely performed at a content of 01% or less.

Example 2 The average particle size of the activated alumina powder A used in Example 1 was changed from 50 μ to 150 μ,
The other conditions were exactly the same as in Example 1 above. As a result, the carbon amount of the sintered test piece G was 0.
The degreasing treatment was completely performed at 01% or less. Therefore, it was confirmed that the particle size of the activated alumina powder was not an important factor.

COMPARATIVE EXAMPLE The same green body test piece as in the above example was used, except that α alumina powder (specific surface area 2 m ² / g, average particle size 47 μ) was used instead of activated alumina powder. Degreasing treatment was performed under the conditions.

The test piece after the degreasing treatment showed discoloration, and when taken out from the α-alumina powder, a coat of the α-alumina powder adhered around the test piece, so
The alumina powder could not be easily removed. The degreasing rate of this test piece was 60%.

When the test piece after the degreasing treatment was sintered under the same conditions as in the above-mentioned examples, the carbon content was 0.04%, and it was confirmed that the degreasing treatment was incomplete.

[0026]

The degreasing method for a green body according to the present invention allows the green body to be embedded in a metal oxide powder for degreasing treatment, so that the degreasing time can be shortened and can be easily and Degreasing treatment can be performed at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a degreasing furnace when performing a method according to an embodiment of the present invention.

[Explanation of symbols]

 1 Degreasing furnace 2 Exhaust pipe 3 Air supply pipe H Heater A Activated alumina powder G Green body (test piece)

Claims (4)

[Claims] 1. A degreasing method for a metal powder injection molded article, which comprises degreasing a metal powder injection molded article obtained by injection molding a mixed material of metal powder and an organic binder, wherein the metal powder injection molding is performed. A method for degreasing a metal powder injection-molded article, which comprises burying the body in a metal oxide powder that does not react with the metal powder injection-molded article and performing a degreasing treatment. 2. The degreasing method for a metal powder injection-molded article according to claim 1, wherein the metal oxide powder is an activated alumina powder. 3. The specific surface area of activated alumina powder is 80 m ^2.
/ G or more, The degreasing method of a metal powder injection-molded article according to claim 2, characterized in that. 4. The degreasing method for a metal powder injection-molded article according to claim 1, wherein the degreasing treatment is performed until the degreasing rate becomes 40% or more and 98% or less.