JPH01215907A - Manufacture of metal sintered compact - Google Patents

Abstract

PURPOSE:To manufacture a sintered alloy product having excellent mechanical characteristic by forming film of Si compound on the surface of raw material metal powder and compacted-sintering kneading material with binder at low temp. and low pressure. CONSTITUTION:At the time of producing the sintered alloy made member by using the metal powder as the raw material with powder metallurgy method, beforehand the metal powder is treated with silane coupling agent having each one or more of Si atom and alkoxy group in one molecule of vinyl triethoxysilane, etc., to form the film of Si compound on the surface of metal powder. By kneading this metal powder with about 5% binder of low density polyethylene, etc., and the other, with lubricant of paraffin wax, etc., and plasticizer of dioctyl phthalate, etc., it is compacted under pressurizing in a die at low pressure. Successively, after degleasing the binder with organic solvent of petroleum, etc., CO2 gas under supercritical condition, etc., it is sintered at low temp. By existence of the Si compound on the surface of metal powder, it is easily sintered and the sintered alloy member having excellent mechanical strength can be manufactured by compacting at low pressure and sintering at low temp. under low cost.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to the production of a sintered body formed through a molding process for obtaining a green molded body from raw material powder, a degreasing process for the green molded body, and a sintering process. It is about the method.

[Conventional technology]

Generally, in the process of manufacturing a metal sintered body, a compact before sintering is obtained as a green compact by compression molding powder. Since this method usually involves applying pressure with a punch from above and below, the shape of the green molded product obtained is limited to relatively simple shapes such as cylinders and cylinders.
To obtain more complex products, the sintered product requires post-processing such as cutting and grinding.

From this point of view, various techniques have been studied to make the shape of the molded object more similar to that of the product. In the field of ceramic products, mainly so-called engineering ceramics, 10 to 20% by weight of a binder mainly composed of organic polymers is added to raw material powder, mixed and kneaded, and then injection molded or extruded molded bodies are produced. A method of obtaining products by degreasing and sintering has been used industrially. Injection molding and extrusion molding are originally molding methods for thermoplastic plastics, but they are suitable for mass production of the final shape of a product without post-processing and with high dimensional accuracy, so they are used as described above. There are some noteworthy solutions to these problems. In recent years, with the development of metal powder manufacturing technology such as the atomization method, attempts have been made to apply injection molding and extrusion molding methods to manufacturing sintered metal products.

The biggest technical problem in the manufacturing process of sintered products as described above is that a large amount of binder is added to the raw material powder, and how to remove this before sintering. The most common method for binder removal, ie, degreasing, is to thermally decompose and volatilize the binder by heating, and in recent years, extraction using carbon dioxide scum in a supercritical state (quasi-liquid state) has also been attempted. In either heating or extraction method, it is desirable to use a binder with as low a molecular weight as possible in consideration of ease of diffusion of pinter in the molded body. For this reason, petroleum-based paraffin wax and the like are often used as binders.

[Invention or problem to be solved]

However, the binder has a low affinity with metal powder, and the mechanical strength of organic polymers generally decreases as the molecular weight decreases, so the molded product itself has insufficient mechanical strength and poses problems in handling. This inevitably leads to a decrease in yield. Moreover, as mentioned above, since the affinity between the binder and the metal powder is low, there is a problem in the dispersibility of the powder in the raw material, which often results in poor molding.

In view of these problems, the present invention improves the dispersibility of the raw material powder by modifying the surface of the raw material powder, and produces a metal sintered body that can improve the mechanical strength of the molded body at low temperature and low pressure. The purpose is to provide a method.

[Means to solve the problem]

According to the present invention, a metal sintered body includes a molding process of mixing and kneading raw materials including metal powder and a binder, compounding, injection molding or extrusion molding to obtain a molded body, a degreasing process, and a sintering process. In the manufacturing method, the metal powder is surface-treated with a silane coupling agent containing one or more silicon atoms and one or more alkoxy groups in one molecule to form a coating of a silicon compound. A method for producing a body is obtained.

Generally, as a method for surface modification of inorganic powder, (1) a surfactant such as an olefinic acid derivative is uniformly adsorbed on the surface. (2) While the powder is dispersed in a suitable dispersion medium, a monomer capable of polymerization reaction and a catalyst are added and reacted to coat the powder surface with the polymer. (3) Coating the surface with a thermoplastic or thermosetting polymer. (4) The surface is coated with an organometallic compound having an alkoxy group, that is, a coupling agent. Although (1) is effective in improving the dispersibility of the powder, the mechanical strength of the green molded product tends to decrease, and surfactant powder = 6
− The bond with the rice surface is not strong. For (2), the catalyst used is of course a highly viscous chemical like peroxide, so it often does not soak the metal surface.
3) becomes more difficult to process as it becomes finer, making it less practical. Therefore, the present inventors focused on (4), and as a result of investigation, found that silicon atoms and alkoxy groups are each included in one molecule. The silane coupling agent having one or more of these can improve the dispersibility of the metal powder and the mechanical strength of the compact, and also contribute to improving the sinterability during sintering by surface treatment with the above-mentioned compound. This discovery led to the present invention.

In the method according to the present invention, a chemical bond is formed between the powder surface and the compound by the alkoxy group, a film is formed that is strongly bonded to the surface, and the affinity of the powder with the binder is increased, thereby improving the dispersibility of the powder. It is thought that this contributes to improving the mechanical strength of the molded article.

In the present invention, examples of the silane coupling agent for treating metal powder include vinyltriethoxysilane, vinyl-tris(2-methoxy(·xy)silane), γ-methacryloxypropyltrimethoxy-silane, and γ-aminopropyltrimethoxysilane. Methoxysilane, β-(3,4-epoxy-cyclohexyl)ethyl-1-rimethoxysilane,
Examples include, but are not limited to, silane coupling agents such as γ4katopropyltrimethoxysilane.

In the present invention, the surface treatment method for the metal powder may be a simple method in which the above-mentioned silane cup link additive is dissolved as it is in a suitable solvent such as ethanol, mixed with the powder, and left as it is; In order to quickly remove the solvent and promote the reaction, heating may be used, or in that case, it is preferable to conduct the reaction in an inert gas to suppress oxidation of the surface of the metal powder. In the present invention, it is possible to remove only the paint particles and leave a silicon-containing film on the surface of the metal powder in the degreasing process by heating or organic solvent extraction, and in the sintering process, it is possible to remove the silicon-containing film on the surface of the metal powder. If there is a component that forms a compound with silicon, it is understood that the reaction between that component and silicon contributes to the promotion of sintering. Furthermore, during the sintering process silicon can diffuse into the metal powder particle phase in the green compact to obtain a solid solution.

In the present invention, the organic thermal spraying for extraction is an organic solvent that can dissolve the binder, such as aromatic solvents such as petroleum, benzene, toluene, and xylene, and chlorinated organic solvents such as carbon tetrachloride trichloride. but not limited to.

The present invention will be explained in detail by way of examples below.

〔Example〕

Table 1 shows green molded bodies and sintered bodies obtained by the metal sintered body manufacturing method according to the example of the present invention. For comparison, a clean molded body and a sintered body obtained by a conventional metal sintered body manufacturing method are also shown.

From this table, it can be seen that -10 = green molded bodies according to examples obtained with metal powders surface-treated with a silane coupling agent also have an injection temperature of 40°C and an injection pressure of 50°C. Despite its small size, the bending strength is 2.
It can be seen that the sintered body has a high density and an excellent yield.

A metal sintered body according to an example of the present invention was manufactured as follows. Table 2 shows the chemical composition of the raw material powder for the metal sintered body according to the example of the present invention. As shown in this table, the raw material powder is
Metal powder 91 surface-treated with a coupling agent
．． 0 wt%, 5.0% low density polyethylene as binders, organic polymers, lubricants, and plasticizers, 2.5 wt% paraffin wax with a melting point of 63°C, and 1.5 wt% dioctyl phthalate.

Table 2 The metal powder according to this example was subjected to surface treatment as follows.

An alloy having a chemical composition of 50% Fe and 50% Co in atomic percent was obtained by high frequency heating in an argon gas atmosphere, and an alloy powder with an average particle size of 10 μm was obtained by water atomization. Weighed 10k (] of the alloy powder, and the inner volume was 10.1i.
was added to the super mixer. The stirring blades of the mixer were rotated at 200 r, p, m, and a solution of 50 g of γ-aminopropyltrimethoxysilane dissolved in 250 cc of ethyl alcohol was added dropwise and stirred for 10 minutes. This alloy powder was heated at 120℃ for 3 hours in a drying oven flushed with nitrogen gas.
The metal sintered body according to the example of the present invention was then heated for 0 minutes and was manufactured as follows. The mixture was mixed, kneaded, and pulverized according to the composition shown in Table 2 to obtain raw materials for injection molding.

Next, using this raw material, a clean molded body having an outer diameter of 50 mm, an inner diameter of 35 mm, and a thickness of 5 marks was produced by injection molding. This green molded body is hydrogen = 70% arurgone 3 in volume ratio.
The temperature was raised from room temperature to 600°C at a rate of 10°C/Hr in a 0% air flow, maintained for 2 hours, and then cooled to room temperature. Next, the pressure was reduced to 2XIO-'Torr in the furnace, and the temperature was raised from room temperature to 1200°C at 200°C Hr.
After holding for 0 hours, it was rapidly cooled to obtain a sintered body. Analyze the grain interfaces of this sintered body using EDX. As a result, silicon could not be detected. Further, measurements were made using the green molded sintered bodies shown in Table 1.

Further, for comparison, a metal sintered body according to a conventional example was manufactured as follows. A sintered body was manufactured by the same manufacturing method as in the example except that the powder was not surface-treated with γ-aminopropyltrimethoxysilane. 1st
The bending strength of the green molded body, the relative density of the sintered body, and the elemental analysis results of the sintered body listed in the table were measured from the green molded body and the sintered body obtained at this time.

〔Effect of the invention〕

As described in detail above, according to the present invention, the mechanical strength of an injection-molded green molded body and the relative density of a sintered body can be improved at low cost. Further, according to the present invention, the injection molding conditions can be set to low temperature and low pressure. As is well known, the generation of scraps such as sprue and runners is unavoidable in injection molding, but recycling scraps can help reduce costs, especially for materials that contain expensive metal powder, as in this case. . Therefore, it is important to keep the molding temperature as low as possible in order to prevent thermal deterioration of the material. As in this case, when using a material containing metal powder, the mold wears more significantly than when using ordinary plastic, but lowering the molding pressure is important in extending the life of the mold.

As described above, the effect of the present invention greatly contributes to cost reduction, and is extremely important industrially.

= 14- Procedural amendment (voluntary) March 2, 1986

Claims (1)

[Claims] 1. A metal sintering process comprising a molding process of mixing and kneading raw materials containing metal powder and a binder, compounding, and injection molding or extrusion molding to obtain a molded body, a degreasing process, and a sintering process. In the method for producing a compact, the metal powder is surface-treated with a silane coupling agent containing one or more silicon atoms and one or more alkoxy groups in one molecule to form a film of a silicon compound. A method for manufacturing a metal sintered body. 2. The degreasing step is a step in which the binder is decomposed and volatilized by heating the molded body to leave a silicon compound covering the surface of the metal powder, and the sintering step is a step in which the binder is decomposed and volatilized by heating the compact, leaving a silicon compound covering the surface of the metal powder. 2. The method for producing a metal sintered body according to claim 1, characterized in that sintering is promoted. 3. The degreasing step is a step in which the molded body is eluted with the binder extraction solvent to leave a silicon compound covering the surface of the metal powder, and the sintering step is a step in which sintering is promoted by the silicon compound. A method for producing a metal sintered body according to claim 1, characterized in that: 4. The method for manufacturing a metal sintered body according to claim 3, wherein the degreasing step uses a liquid-phase organic solvent as an extraction solvent. 5. The method for manufacturing a metal sintered body according to claim 4, wherein the degreasing step uses a fluid in a supercritical state as an extraction solvent. 6. The sintering step includes a step of diffusing silicon atoms in the silicon compound coating the surface of the metal powder into the metal powder to form a solid solution. A method for producing a metal sintered body according to any one of the above.