JPH0257614A - Degreasing method - Google Patents

Abstract

PURPOSE:To obtain a degreased body free of defects by placing a formed product consisting of metal powder having a specified composition and an org. binder in a low-air-permeability vessel, inserting the vessel into a heating furnace, heating the vessel in a nonoxidizing atmosphere, and uniformly degreasing the formed product. CONSTITUTION:The raw powder consisting essentially of a metallic material and an org. binder are mixed in 50/50-60/40 ratio, heated, and kneaded. The obtained molding material is injection-molded. The formed product is treated in a heated atmosphere to remove a part or the whole of the org. binder, and a degreased body is obtained. In this case, the low-air-permeability vessel contg. the formed product is inserted into a heating furnace filled with a nonoxidizing atmosphere of N2, Ar, etc. The formed product is always covered with an atmosphere saturated with the decomposed gas of the org. binder, and degreased. By this method, the temp. and surface environment around the formed product are uniformized, generation of defects during the degreasing is prevented, and a degreased body free of cracking, etc., is obtained. The degreased body is sintered to obtain a high-quality metallic sintered material.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a sintered metal material, and more particularly to a method for degreasing a metal powder injection molded body.

<Prior Art> A method for manufacturing sintered materials using injection molding is seen as a promising method for manufacturing metal parts with complex shapes.
During the entire process, in the degreasing process, the prior patent (Japanese Patent Laid-Open No. 58
-126901), a sufficient amount of gas is often blown onto the molded body. In extreme cases, a fan was installed in the furnace to remove the gas around the molded product.

<Problems to be Solved by the Invention> However, when the above-mentioned means are used, non-uniformity occurs in temperature and surface environment around the molded article. As a result, there is a high risk that defects will occur in the degreased body.

Therefore, the present invention aims to solve the above problems and provide a degreasing method that reduces the incidence of defects that occur during degreasing of injection molded articles.

Means for Solving the Problems> The present inventors have developed the present invention by conducting detailed experiments regarding the occurrence of defects during degreasing in the production of sintered metal materials using fine powder as a raw material by injection molding, etc. I ended up doing it.

That is, the present invention includes a step of heating and kneading a raw material powder mainly composed of metal powder and an organic binder at a volume ratio of 50:50 to 60:240 to obtain a molding raw material, and injection molding the molding raw material. a step of removing part or all of the organic binder in a heated atmosphere to obtain a degreased body, and a step of sintering the degreased body in a heated atmosphere to obtain a sintered body. This is a method for producing metal sintered materials.

The step of obtaining the degreased body is performed by inserting a container containing the molded body with poor ventilation into a heating furnace with a non-oxidizing atmosphere, and in an atmosphere where the area around the molded body is always saturated with the decomposition gas of the organic binder. To provide a degreasing method characterized by:

The present invention will be explained in detail below.

In the present invention, the degreasing atmosphere is a non-oxidizing atmosphere.

When processing in an oxidizing atmosphere such as air, the oxygen in the air contributes to the decomposition initiation reaction of the organic binder, so the decomposition behavior may be affected by fluctuations in oxygen concentration or changes in part shape and size (changes in oxygen diffusion distance). Change. As the factors that affect the decomposition of the binder increase, manufacturing variations increase and manufacturing control items need to be increased, which is unfavorable in terms of manufacturing. Further, the presence of oxygen also causes an oxidation reaction of the metal powder, which increases production problems similar to the binder decomposition reaction, and is therefore undesirable. Therefore, the degreasing atmosphere needs to be a non-oxidizing atmosphere that does not react in any way with the metal powder and binder constituting the compact.

Further, the molded body must be placed in a container with poor air permeability and inserted into a heating furnace. This is to make the decomposed gas concentration and temperature around the molded body uniform during degreasing. Since both the decomposition gas concentration and temperature are factors that greatly influence the decomposition rate of the binder, if there is non-uniformity in these factors, defects will occur in the degreased body. For example, this occurs when a molded article placed on a support plate or the like is vigorously blown with air. In this case, the gas hits the parts that do not come into contact with the support plate, but the gas does not hit the contact surfaces. In the area that is hit by the blast gas, the temperature rises due to heat transfer with the blast gas, and since the concentration of binder decomposition gas around the area is low, decomposition is promoted. On the other hand, in areas that are not hit by the blast gas, neither heating by the blast gas nor removal of binder decomposition gas components by the blast gas is performed, so decomposition is not promoted. As a result, in each part of the molded body,
Decomposition occurs unevenly, increasing the risk of cracking of the degreased body.

On the other hand, in the present invention, since atmospheric gas is not actively introduced into the container, there is no non-uniformity depending on the region in the molded body as described above.

Further, since the decomposed gas components saturated in the container gradually escape to the outside of the container, decomposition proceeds in an amount corresponding to the escaped gas components. In this way, the reaction proceeds while maintaining an equilibrium state, so the risk of degreasing defects occurring is low.

Furthermore, as the temperature rises, the saturated vapor pressure increases, so there is no fear that the decomposition reaction will stop.

In other words, the decomposition reaction is simply shifted to the higher temperature side, and the degreasing rate does not drop significantly.

Only by doing the above can degreasing be performed with fewer degreasing defects.

Examples of ways to reduce air permeability include using a metal container with a porous ventilation hole in a part of the container, or filling the opening of the container with inert powder such as Al1,05. This can be done by using bricks or the like.

Regarding the production of metal sintered materials using the degreasing method of the present invention,
Conventional known methods can be used for the steps before and after degreasing.

First, the powder used in the present invention is an alloy or a single metal obtained by an atomization method, a reduction method, a carbonyl method, or a pulverization method, and if necessary, these powders are classified,
It can be prepared by mixing. However, reduction method,
Since the powder composition produced by the carbonyl method and the pulverization method is quite limited, the atomization method has a wide range of applications.

Further, the average particle diameter of these powders can be 20 μm or less, and powders of about 7 to 14 μm are preferred because they have the advantage of providing excellent sintered properties such as high density.

Applicable composition systems include stainless steel, pure iron, Fe-Ni,
It can be applied to a wide range of materials such as structural materials such as Fe-5i and Fe-Co, and magnetic materials.

To produce a molded object by injection molding, the injection molding powder of the present invention, preferably having an average particle size of 20 μm or less, is first mixed and kneaded with a binder as a molding aid to prepare an injection molding compound. do.

Applicable binders include thermoplastic resins, waxes,
Alternatively, any known binder containing a mixture thereof may be used, and a plasticizer, lubricant, degreasing accelerator, etc. may be added as necessary.

Thermoplastic resins include acrylic and Bolier.

One type of tyrene type, polypropylene type, polystyrene type, etc., or a mixture of two or more types can be used.

As waxes, one or a mixture of two or more of natural waxes such as beeswax, wood wax, and montan wax, and synthetic waxes such as low-molecular polyethylene, microcrystalline wax, and paraffin wax can be used. may be selected as appropriate depending on the main components of the binder, such as di-2-ethylhexyl phthalate (DOP), diethyl phthalate (DEP), di-n-butyl phthalate (DH
P) etc. can be exemplified.

As the lubricant, higher fatty acids, fatty acid amides, fatty acid esters, etc. can be used, and in some cases, waxes may also be used as the lubricant.

Further, if necessary, a sublimable substance such as camphor may be added as a degreasing accelerator.

The mixing ratio of such binder and raw material powder is usually about 50:50 to 40:60 vol.

The method of kneading the raw material powder and the binder is not particularly limited, and various kneaders such as a pressure kneader, a Panberry mixer twin-screw extruder, etc. may be used.

The injection molding compound thus prepared may be granulated using a pelletizer, a pulverizer, etc., if necessary, to form pellets.

Next, the obtained injection molding compound is injection molded to produce a molded article.

Injection molding may be carried out using an injection molding machine used for normal injection molding, such as a normal injection molding machine 5 for plastics or an injection molding machine for ceramics or metal powder that has recently become commercially available.

At this time, the injection pressure is usually 500 to 2500 k
gf/c+n', and the temperature is 100 to 180°C.

Finally, the obtained molded body is subjected to a degreasing treatment.

In the method for producing a metal sintered body of the present invention, the degreasing treatment is performed in a non-oxidizing atmosphere, preferably a nitrogen atmosphere, an argon atmosphere, or a mixed atmosphere thereof. N
Reducing scum such as No. 2 can also be used, but it is inferior in that it is explosive, requires careful handling, and increases the cost of the heating furnace. It is also known that the atmospheric pressure may be increased or decreased as necessary.

The processing temperature of the degreasing treatment is max. about 450 to 650°C, and the holding time is about 0 to 6 hr. Note that if the heating rate at this time is too high, cracks or blisters will occur in the obtained molded body, so it is preferable to raise the temperature at a constant rate of about 5° C./hr to 20° C./hr.

In the present invention, a metal sintered body is manufactured by sintering the degreased molded body thus obtained by injection molding.

After the degreasing, if the metal powder is stainless steel, 1
0-'~10-'T o r r, 1050~130
After holding at 0°C for 0.5 to 4 hours, inert gas such as argon or nitrogen was introduced, and the temperature was maintained at 1200 to 1370°C for 0.5 to 2 hours.
It is best to hold it for a while and sinter it. In addition, other Fe, Fe
- When using only low oxidizing metals such as Ni-based or Fe-C0-based, 800 to 1
Sintering is preferably carried out at 300°C for 0.5 to 4 hours.

When sintering a highly oxidizable metal such as Fe-3i, it is sintered in the same manner as stainless steel.

By going through these steps, the present invention can obtain an excellent metal sintered body.

<Example> Hereinafter, the present invention will be specifically explained based on Examples.

(Example 1) Powders shown in Table 1 were prepared. The average particle size is added to the same table. A binder was added to each of these powders, kneaded using a pressure kneader, and then ground to prepare an injection molding compound. By injection molding machine, 4
A rectangular parallelepiped test piece measuring 0x10x2 mm was molded. Injection molded bodies were heated at +5°C in nitrogen or argon as shown in Table 1.
The temperature was raised to 650° C. at a rate of 300° C./h, and the temperature was maintained for 30 minutes to perform a degreasing treatment. Regarding sintering, Q about stainless steel.
After holding at 1150°C for 90 minutes in 0OITorr, 1
The test was carried out by introducing Ar gas at atmospheric pressure and maintaining the temperature at 1350° C. for 2 hours. In addition, for Fa-Ni, 1 in hydrogen
The temperature was maintained at 250°C for 2 hours.

In addition, in the above degreasing, the following (a), (b), (C)
This was done using the method.

The degreasing process of invention example (a) is shown in FIG.

Figure 1 shows a molded body 1 to be degreased and sintered.
The container 3 is placed in a container 3 made of No. 04, and then placed together with the container 3 in a furnace tube 4. Then, Ar or N2 gas is constantly fed into the furnace core tube 4.

At this time, the container 3 is opened so that the molded body 1 does not come into direct contact with the blast of Ar or N2 gas 6, and the atmosphere around the molded body 1 is always saturated with the decomposed gas of the organic binder. Fill the section with alumina powder 7.

Then, in this state, using the heater 5, the temperature was raised and degreased using the method described above.

In addition, for comparative example (b), as shown in FIG.
Said 5US304'#! 5US304 instead of container 3
Degreasing was performed using board 2.

As for comparative example (C), as shown in Fig. 3,
Degreasing was carried out in the same manner as described above, using the 5US304 plate 2 and stirring the atmosphere inside the furnace core tube 4 using the blower fan 8.

For each level of degreasing, 10 molded products were used, and the presence or absence of defects was visually inspected.

The degreasing defect rate and sintered body properties are added in Table 1.

From Table 1, the defect occurrence rate during degreasing is the lowest in the present invention.

Furthermore, the properties of the obtained sintered body were also sound in terms of density ratio and C10 content.

<Effects of the Invention> According to the present invention, it has become possible to reduce the incidence of defects during degreasing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the degreasing method according to the present invention. FIGS. 2 and 3 are schematic diagrams showing an example of a conventional degreasing method as a comparative example. 5...Heater, 6...Ar or N2 7...Alumina powder, 8...Blower fan, -...Gas flow direction

Claims (1)

[Claims] (1) A step of heating and kneading a raw material powder mainly consisting of metal powder and an organic binder at a volume ratio of 50:50 to 60:40 to obtain a molding raw material, and injection molding the molding raw material. A metal comprising the following steps: obtaining a molded body, removing part or all of the organic binder in a heated atmosphere to obtain a degreased body, and sintering the degreased body in a heated atmosphere to obtain a sintered body. A method for producing a sintered material, wherein the step of obtaining the degreased body is performed by inserting a container with poor air permeability containing the molded body into a heating furnace filled with a non-oxidizing atmosphere, and removing air around the molded body. A degreasing method characterized in that this is always carried out in an atmosphere saturated with decomposition gas of an organic binder.