JPH075925B2 - Metal binder and molding composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal binder which is effective when a product is injection-molded from a metal powder as a raw material, and a molding composition containing the metal binder.

[Prior Art] Conventionally, powders of various metals (in this specification, alloys and cemented carbides are sometimes referred to as metals) are molded into powders,
In powder metallurgy in which this molded body is sintered to produce a sintered metal product, the molding is generally performed by a press molding method. However, the press molding method has a drawback in that a complicated shape cannot be molded and a high sintering density and sufficient strength cannot be obtained in the subsequent sintering step.

Therefore, in recent years, the injection molding method has been attracting attention also in the field of molding metal powders, and it has been partially implemented (for example, Japanese Patent Publication Nos. 61-48563, 62-33282 and USP4415).
No. 528, No. 4661315). This injection molding method can be used to mold various products, as well as to mold complicated shapes.
The metal powder and the binder can be kneaded, supplied, and molded in one step, and further, the molding accuracy is high, and the secondary processing is unnecessary or easy.

On the other hand, in powder metallurgy, conventionally, a binder obtained by mixing a polymer material such as ethylene / vinyl acetate copolymer, poly (meth) acrylate, or polypropylene, a plasticizer such as dibutyl phthalate, and a wax such as paraffin wax. Is used. This was also the case when the metal powder was molded by injection molding.

[Problems to be solved] However, conventionally used binders take a long time for degreasing, and cracks or expansions are likely to occur during degreasing, which easily leads to defective molded products. There was a problem that dimensional accuracy could not be obtained.

In addition, a molded product injection-molded using a conventional binder has a problem that the shape cannot be maintained due to softening flow of the molded product unless degreasing and sintering are carried out in a powder.

Therefore, even if the injection molding method is excellent, it is difficult to put the injection molding method into practical use in the field of powder metallurgy as long as the conventional binder is used. Was not available for.

The present invention has been made in view of the above problems, by allowing the binder to be degreased in a single time, while reducing the residual amount of the binder and preventing the occurrence of cracks and expansion during degreasing. The purpose is to provide a metal binder capable of obtaining a good quality sintered product and enabling the practical application of injection molding in the field of powder metallurgy, and a molding composition prepared by mixing the metal binder with a metal powder. And

As a result, it is possible to provide various precision sintered parts at low cost in the field of powder metallurgy.

[Means for Solving Problems] In order to achieve the above object, the metal binder of the present invention is
At least one selected from the group consisting of adamantane, trimethylene norbornane, and cyclododecane is blended with the binder main agent as a binder auxiliary agent.
More specifically, the metal binder of the present invention is selected from the group consisting of a polymer as a binder main component, a plasticizer, a wax, and adamantane, trimethylene norbornane, and cyclododecane made of a sublimable substance as a binder aid. It contains at least one kind of ingredient.

As the polymer of the binder main agent, ethylene / vinyl acetate copolymer, acrylic, polybutylmethacrylate, polyethylene, atactic polypropylene, etc., which maintains the strength of the molded product, is relatively easy to decompose and has a low molecular weight during degreasing, and is easily removed Can be mentioned.

Examples of the plasticizer include phthalic acid plasticizers such as DBP (dibutyl phthalate) that plasticizes the polymer component of the binder.

Further, examples of the wax include paraffin wax, polyethylene wax, liquid paraffin wax and the like.

The blending ratio of the polymer, the plasticizer, and the wax in the binder main agent varies depending on the metal raw material, but usually,
It is preferable that the amount of the polymer is 1.2 to 6.1 parts by weight, the plasticizer is 0.8 to 1.3 parts by weight, and the wax is 1.8 to 4.7 parts by weight with respect to 100 parts by weight of the metal raw material.

More specifically, ethylene-vinyl acetate copolymer 2.
0-3.4 parts by weight, acrylic 1.2-2.7 parts by weight, wax
It is preferable to mix 1.8 to 4.7 parts by weight and 0.8 to 1.3 parts by weight of DBP.

It should be noted that the plasticizer and the wax may be added as needed and are not necessarily required to be blended. Conversely, depending on the type of metal, a plasticizer, an additive other than wax, such as a lubricant, may be added to the binder main component.

In the metal binder of the present invention, at least one selected from the group consisting of adamantane, trimethylene norbornane, and cyclododecane is blended with such a binder main agent as a binder auxiliary agent.

The components of these binder auxiliaries, particularly adamantane, are less toxic than naphthalene, camphor, etc., which have been conventionally used as binder auxiliaries. In addition, since it does not generate a carbonaceous product due to reaction with other materials or self-decomposition, the content of carbon impurities in the final product is reduced, and
Good colorability and sinterability.

Further, by adding the sublimable substance, in the initial stage of the degreasing process, the sublimable substance is removed and other binder components are eliminated so that a escape route is created in advance, which facilitates degreasing and shortens the degreasing time. .

When adamantane and trimethylene norbornane are blended together, the ratio of both is 1: 9 or more, preferably 1: 9 to.
Set to 4: 1.

In addition, the mixing ratio of the binder main agent and the binder auxiliary varies depending on the type of metal raw material, but in general,
With respect to 100 parts by weight of the metal raw material, the binder aid is 05
To 5.0 parts by weight, preferably 1.0 to 2.0 parts by weight.

Such metal binders can be used to obtain sintered products by using metal powders of iron, nickel, copper, stainless steel, etc., alloy powders of ferrite etc. or cemented carbide (WC, TiC, TaC / Co, Ni etc.) powders as raw materials. Used in case. The metal powder includes an alloy or a cemented carbide in which ceramics are partially mixed.

Next, steps for obtaining a sintered product from metal powder using the metal binder of the present invention will be described with reference to FIG.

An adamantane composition comprising a metal powder pulverized by a mechanical method or a plasma method or the like, a binder main agent to which a plasticizer and a wax are added if necessary, and a binder auxiliary is kneaded in a mixer (step 101). The kneading conditions include, for example, 80 to 150 ° C., preferably 100 to 120 ° C. and 0.5 to
It is 3 hours, preferably 0.5 to 1 hour.

The kneading can be performed using, for example, a Henschel mixer, a ladle machine, or a kneading machine such as a blast mill, a heating kneader, and a cokneader that applies a shearing force simultaneously with heating.

In addition, as a compounding procedure, the metal binder and the metal powder may be compounded after sufficiently mixing the binder main agent and the binder auxiliary agent to obtain a metal binder, or the metal powder, the binder main agent and the binder auxiliary agent may be mixed. You may mix | blend with an agent simultaneously or sequentially.

Next, the kneaded product is formed into pellets as a molding material by granulation with a roll or a pelletizer (step 102).

The molding materials obtained in this way are the mud casting method (slip casting method), the pressure casting method, the press molding method,
Mechanical wheel method, extrusion molding method, rubber press method (CI
P), tamping method, high temperature pressure molding method, injection molding method, doctor blade method (sheet molding), roller machine method, etc.

Among these various molding methods, the injection molding method is particularly preferable. That is, the composition containing the metal binder of the present invention can favorably perform the injection even when the injection molding pressure and the injection temperature are low, and can shorten the time required for degreasing after the injection molding. is there.

When molding by injection molding method,
It is supplied to an injection molding machine such as a plunger method, a pre-plastic type or a screw in-line type, and injection-molded to obtain a primary molded product (step 103). Injection molding is, for example, 120 to 20
It can be carried out at 0 to 300 to 1500 kg / cm ² . It is also possible to supply the kneaded product of the metal powder, the binder main agent and the binder auxiliary agent to the injection molding machine as the kneaded product without once pelletizing.

Next, the primary molded article is degreased to remove the metal binder (step 104). At this time, the molded product does not need to be embedded in the powder, and only needs to be placed on the table. The degreasing treatment is carried out by heating at 20 to 600 ° C. for 20 to 120 hours, preferably 50 to 100 hours. The sublimable substance of the binder aid is removed at the initial stage of the degreasing treatment, and the binder components thereafter are easily and uniformly removed. The metal binder according to the present invention is removed in a much shorter time than the conventional metal binder, and the residual amount thereof is extremely small.

After the degreasing treatment, the primary molded product is fired to obtain a sintered product (step 105).

The degreasing step (104) and the firing step (105) described above
Can be performed continuously.

Next, the molding composition of the present invention will be described.

In order to achieve the above-mentioned object, the molding composition of the present invention comprises a metal powder mixed with a binder main agent and at least one selected from the group consisting of adamantane, trimethylene norbornane, and cyclododecane as an auxiliary agent. is there. And, preferably, the metal powder in this molding composition contains a metal of Group 8 element such as iron, nickel,
Powders of metal such as cobalt or alloys containing them (for example, Cr-Ni-C, Fe-Ni) are used.

Further, as the binder main agent and the binder auxiliary agent of this molding composition, the same ones as those constituting the above metal binder are used. That is, a polymer, a plasticizer, a wax or the like is used as the binder main agent, and at least one selected from the group consisting of adamantane, trimethylene norbornane, and cyclododecane is used as the binder aid composed of a sublimable substance.

Among these, examples of the polymer as the binder main agent include ethylene / vinyl acetate copolymer, acrylic, polybutyl methacrylate, polyethylene, atactic polypropylene and the like.

As the plasticizer, a phthalic acid-based plasticizer such as DBP can be used.
(Dibutyl phthalate) and the like.

Further, examples of the wax include paraffin wax, polyethylene wax, liquid paraffin wax and the like.

The blending ratio of the polymer, the plasticizer, and the wax in the binder main agent varies depending on the metal raw material, but usually,
It is preferable that about 1.2 to 6.1 parts by weight of the polymer, 0.8 to 1.3 parts by weight of the plasticizer, and 1.8 to 4.7 parts by weight of the wax relative to 100 parts by weight of the metal raw material, more specifically, ethylene-vinyl acetate copolymer is used. 2.0-3.4 parts by weight, acrylic 1.2-
2.7 parts by weight, wax 1.8 to 4.7 parts by weight, DBP 0.8 to 1.3
It is preferable to blend in parts by weight.

On the other hand, the mixing ratio of the binder main agent and the binder auxiliary varies depending on the type of the metal raw material, but generally, with respect to 100 parts by weight of the metal raw material, the binder auxiliary is 0.5 to 5.0.
Parts by weight, preferably 1.0 to 2.0 parts by weight.

When blending with adamantane and trimethylene norbornane, the ratio of both should be 1: 9 or more, especially 1: 9.
It is preferably set to 4: 1.

[Examples] Next, the present invention will be specifically described by comparison with Examples in which injection molding was performed using a metal powder mixed with the metal binder of the present invention as a raw material, and Comparative Examples.

Table 1 is a table showing the composition of the metal powder and the binder main agent and the binder auxiliary agent, Table 2 is a table showing each condition of molding, degreasing and sintering, and Table 3 is an evaluation of the sintered body. It is a table.

Binder main agent and binder auxiliary agent in the types and blending amounts shown in Table 1 using a lab blast mill, 100 ± 10
Kneading was performed at 30 ° C. for 30 minutes (the torque at this time was 150 kg · cm).

Then, the kneaded product was crushed by a manual press and further squeezed to obtain a lump of 5 to 7 mmΦ.

This lump was molded with an injection molding machine [Yamashiro Seiki Co., Ltd., vertical plunger type] under the molding conditions shown in Table 2.

This molded product was degreased under the degreasing conditions shown in Table 2 and then fired under the sintering conditions shown in Table 2 to obtain a sintered metal product.

Table 3 shows the evaluation of the appearance, density and residual carbon content of the sintered metal product (sintered body).

In addition to the results shown in the above table, the following was found.

When an internal crack of the sintered metal product was inspected by an X-ray photograph, no crack was found in the example, but a crack was found in the comparative example.

When at least one selected from the group consisting of adamantane, trimethylene norbornane and micrododecane was used as the binder aid, the toxicity was extremely low as a sublimation substance.

In addition, also in the case of the molding composition of the present invention obtained by mixing a metal powder with a metal binder, the same results as in the above-mentioned examples were obtained.

[Effects of the Invention] As described above, according to the metal binder of the present invention and the molding composition of the present invention in which the metal binder is mixed with the metal powder, the degreasing time can be shortened. At the same time, cracks and expansion do not occur during degreasing, and high sintered density and high dimensional accuracy can be obtained, so that product quality can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of steps until a sintered product is obtained using the metal binder of the present invention. 101: Kneading process, 102: Pelletizing process 103: Injection molding process, 104: Degreasing process 105: Firing process

Claims (7)

[Claims] 1. A metal binder characterized in that at least one selected from the group consisting of adamantane, trimethylene norbornane, and cyclododecane is mixed as a binder auxiliary agent in the binder main agent. 2. The binder main agent is a polymer 1.2 to 6.1.
1 part by weight, 1.8 to 4.7 parts by weight of wax, and 0.8 to 1.3 parts by weight of DBP.
The metal binder according to the item. 3. The metal binder according to claim 1 or 2, wherein the binder aid is blended in an amount of 0.5 to 5.0 parts by weight. 4. A molding composition comprising a metal powder and a binder main agent, and at least one selected from the group consisting of adamantane, trimethylene norbornane and cyclododecane as a binder auxiliary agent. 5. The molding composition according to claim 4, wherein the metal powder is made of a metal of Group 8 element or an alloy containing these metals. 6. The main binder is 2.0 to 3.4 parts by weight of an ethylene-vinyl acetate copolymer, based on 100 metal raw materials,
The molding composition according to claim 4 or 5, wherein 1.2 to 2.7 parts by weight of acrylic resin, 1.8 to 4.7 parts by weight of wax and 0.8 to 1.3 parts by weight of DBP are blended. . 7. The molding composition according to claim 4, wherein the binder aid is blended in an amount of 0.5 to 5.0 parts by weight based on 100 parts of the metal raw material. .