JPH04323307A - Production of tungsten heavy metal product - Google Patents

Abstract

PURPOSE:To produce a tungsten heavy metal product high in dimensional precision, having an intricate shape, low in residual carbon and excellent in strength with good productivity by the powder metallurgy using injection molding. CONSTITUTION:The powders of W, Ni, Fe or Cu are mixed, the mixed powder is kneaded with an org. binder and injection-molded, the molded body is embedded in a W powder or in a powder having the same or nearly the same composition as that of the mixed powder and heated to the final temp. of 600-750 deg.C in a nonoxidizing gas to remove the binder, and the molded body is then brought out of the powder and sintered in hydrogen gas.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention manufactures tungsten heavy alloy products with complex shapes and high strength by kneading raw material powder of tungsten heavy alloy with an organic binder and sintering the injection molded compact. Regarding the method.

0002

[Prior Art] Tungsten heavy alloys consist of about 80% by weight or more of tungsten and nickel, iron, or copper. Particularly, those with a tungsten content of more than about 90% by weight are called tungsten superheavy alloys. Automobile flyweights and computer HDDs that require a large amount of weight
In addition to applications such as commercial weights and VTR heads, it is also being used in applications requiring mechanical strength such as quills, shanks, and boring bars.

[0003] Since tungsten heavy alloys including such tungsten superheavy alloys contain tungsten with a high melting point,
Conventionally, it has been manufactured by powder metallurgy. In addition, recently, when mixed powder with a predetermined composition is molded using normal pressure molding methods such as press molding or CIP molding, the shape of the product that can be manufactured is limited and the dimensional accuracy is limited. A method of kneading an organic binder, obtaining a molded body similar to the desired final product by injection molding, and then sintering this molded body has been studied. This method of sintering a molded body obtained by injection molding can accommodate complex three-dimensional shapes and achieves high dimensional accuracy, so it has the advantage that a final product can be obtained without machining.

[0004] In general, the technology for sintering molded bodies obtained by injection molding is already well known, as disclosed in Japanese Patent Publication No. 42682/1982 and Japanese Patent Application Laid-open No. 250102/1982. There is. Regarding the organic binder to be kneaded into the powder, for example, lubricants such as atactic polypropylene, wax, and paraffin described in Japanese Patent Publication No. 51-29170, or Japanese Patent Application Laid-Open No. 57-26105
Various types of materials are known, such as polyethylene, polystyrene, and beeswax described in the above publication. Furthermore, since the molded body obtained by injection molding contains an organic binder, it is necessary to heat the molded body to remove the binder before sintering. Conventionally, methods include increasing the strength by slightly oxidizing the material, and removing the binder from the molded product while it is embedded in alumina powder.

However, it has been difficult to directly apply powder metallurgy technology using injection molding to tungsten heavy alloys. In other words, since the powder that makes up the component system of tungsten heavy alloy has a high specific gravity, there is a problem that the molded body deforms due to its own weight during the debinding treatment in which the molded body obtained by injection molding is heated before sintering. Even with the conventional method of embedding a molded body in alumina powder, it was not possible to completely suppress the deformation.

[0006] Furthermore, carbon tends to remain in tungsten heavy alloys even after binder removal treatment, and for this reason, about 0.1% by weight of carbon usually remains in the product after sintering. This residual carbon significantly reduced the strength and toughness of the product, resulting in a product that was inferior in strength and toughness to products manufactured by the usual powder metallurgy method using pressure molding. Moreover, in the conventional debinding process,
In order to prevent the formation of cracks and deformation in the molded product, only an extremely slow heating rate of 20°C/hour or less can be achieved, and therefore the entire debinding process takes 30 to 40°C.
It took a lot of time and a very long time.

[0007]

[Problems to be Solved by the Invention] In view of the above-mentioned conventional circumstances, the present invention improves the binder removal treatment after injection molding, thereby achieving a complex shape with high dimensional accuracy, low residual carbon, and excellent strength. The purpose of the present invention is to provide a method for manufacturing tungsten heavy alloy products with high productivity.

[0008]

[Means for Solving the Problems] In order to achieve the above object, in the method for manufacturing a tungsten heavy alloy product of the present invention, tungsten powder and nickel powder, iron powder or copper powder are mixed to a predetermined composition, After kneading an organic binder into this mixed powder and injection molding it into a predetermined shape, embedding the molded body in tungsten powder or in a powder containing at least tungsten powder with the same composition as the mixed powder or a composition close to the mixed powder, It is characterized in that the organic binder is removed from the molded body by heating it to a final temperature of 600 to 750°C in a non-oxidizing gas, and then the molded body taken out from the powder is sintered in hydrogen gas.

[0009]

[Operation] The method of the present invention is to manufacture tungsten heavy alloy products by a powder metallurgy method using injection molding, and tungsten heavy alloy products include 80% by weight or more of W and Ni.
It is an alloy consisting of Fe or Cu, and includes a tungsten super-heavy alloy with a W content of 90% by weight or more. The raw material powder is at least one of W powder, Ni powder, Fe powder, and Cu powder, and these are mixed with alcohol and the like using a ball mill, attritor, etc., and simultaneously pulverized to obtain a mixed powder. These raw material powders preferably have a particle size of 20 μm or less in order to obtain good sinterability. In particular, if mixing and pulverization are insufficient, sinterability will be inhibited and a sintered body with close to true density will not be obtained. The particle size of the mixed powder after mixing and pulverization is preferably 5 μm or less.

[0010] After the mixed powder is kneaded with an organic binder, it is molded into a molded body similar to the final product by injection molding as usual, and then the molded body is subjected to a binder removal treatment. The present inventors investigated how to prevent the deformation of the compact during the binder removal process, and found that the conventional method of embedding the compact in alumina powder is too light compared to tungsten heavy alloy. Therefore, it was determined that deformation would occur in the tungsten heavy alloy powder compact, and the idea was to embed the compact in powder with a high specific gravity such as iron or copper. However, powders such as iron and copper easily react with the components of the compact at high temperatures, and iron powder adhering to the surface of the compact may affect the sintering process, making it difficult to obtain a normal tungsten heavy alloy. It was difficult.

[0011] From these points of view, the powder used to embed the molded body during the binder removal process should have approximately the same specific gravity as the mixed powder of each raw material powder constituting the molded body, and should not easily react with the molded body and affect sintering. After various studies, we decided to use tungsten powder, a powder with the same composition as the mixed powder forming the compact, or a powder with a composition close to that of the mixed powder and containing at least tungsten powder. It was found that deformation of the molded body can be prevented by this method. Further, the treatment atmosphere is sufficient as long as it can suppress oxidation of the compact, and therefore the treatment is carried out in a non-oxidizing gas such as hydrogen gas, nitrogen gas, or an inert gas such as argon. Note that the organic binder may be one that has been commonly used in the past, and for example, paraffin, polyethylene, wax, etc. can be used alone or in combination.

According to the method of the present invention, if a molded body is embedded in the powder and subjected to binder removal treatment, the molded body will hardly deform and will almost completely maintain its shape during injection molding, and moreover, the shape of the molded body will be maintained almost completely. Since no deformation occurs, it is possible to increase the temperature increase rate by heating to 20 to 50° C./hour, which is almost double that of the conventional method, and therefore, the entire debinding treatment time can be significantly shortened to 10 to 30 hours. In addition, the amount of residual carbon in the molded product is reduced to 0 due to the binder treatment described above.
．． Since the amount is 0.2% by weight or less, a tungsten heavy alloy product with high strength and excellent properties can be obtained by sintering.

[0013] In the above-described binder removal treatment, the final temperature by heating must be controlled to 600 to 750°C. If the final temperature is less than 600°C, the strength of the compact will be weak and it will be difficult to handle, and if it exceeds 750°C, the powder embedded in the compact will tend to start reacting with the compact, making it difficult to separate the compact and powder later. It is from.

[0014] The molded body subjected to the binder removal treatment is then sintered in hydrogen gas. The sintering temperature usually ranges from the melting point of the nickel, iron or copper binder phase to +50°C, preferably from +30°C to +40°C above the melting point. Although sintering at a temperature below the melting point of the binder phase can result in densification, the growth of tungsten grains is small and sufficient toughness cannot be obtained. On the other hand, if the melting point of the binder phase exceeds +50°C, the tungsten heavy alloy will be severely deformed by gravity, making it impossible to obtain a product with excellent dimensional accuracy.

The tungsten heavy alloy produced by the method of the present invention has excellent properties such as strength equivalent to that produced by ordinary powder metallurgy because the final amount of residual carbon is extremely small. Because it has excellent dimensional accuracy that could not be achieved with metallurgical methods, it can be used as a variety of products without any machining such as cutting after sintering. Particularly recently, in the medical field, radioactive substances with short half-lives are injected into the human body for examination of affected areas and radiation therapy, but tungsten heavy alloys also have excellent radiation shielding effects, so ,062,3
It can also be used as a radiation shielding cover for protecting doctors and nurses from radiation exposure by being attached to the outer periphery of a radioactive substance syringe as described in the specification of No. 53.

[0016]

[Example 1] W powder, carbonyl Ni powder, carbonyl Fe powder, and electrolytic Cu powder (all particle sizes 2 to 3 μm) were prepared as raw material powders, and each powder had a composition of 95% by weight.
．． 0%W-3.0%Cu-1.6%Ni-0.4%Fe
The mixture was pulverized and mixed using an attritor for 6 hours, and then sieved through a 150 mesh sieve. 300 g of polyethylene and 600 g of wax were added as an organic binder to 30 kg of the mixed powder that had passed through the sieve, and the mixture was kneaded in a kneader for 3 hours. This kneaded product was injection molded using an injection molding machine with a mold clamping force of 20 tons, with a mold for two products measuring 20 mm long x 10 mm wide x 5 mm high maintained at a temperature of 40°C. The obtained compact was embedded in W powder, heated in nitrogen gas to 300°C at a heating rate of 30°C/hour, held at that temperature for 5 hours, and then heated to 700°C at a heating rate of 50°C/hour. The binder was removed by heating to . Thereafter, the binder-removed molded body was sintered at 1400° C. in a hydrogen gas atmosphere.

The obtained sintered body has a density of 18.10 g/
cm3, it has a structure similar to that of one sintered after normal press forming, and there are no cavities or patches even when observed under a 100x optical microscope, indicating that it is a normal W-Ni-Cu-Fe based super-heavy alloy. This was confirmed. In addition, the hardness of this W super-heavy alloy is HV 310, and the tensile strength is 60 kg/mm2.
Therefore, it was found that the material had mechanical properties on the same level as those obtained by sintering after normal press forming. Furthermore, it was found from the dimensional measurements of the obtained sintered body that the distortion during debinding of the molded body was suppressed to 0.05 mm or less.

[0018]

[Example 2] Raw material powders include W powder, carbonyl Ni powder, and carbonyl Fe powder (all particle sizes 2 to 3 μm)
were prepared, and the composition of each powder was 97.0% W-2.
The mixture was mixed to become 0% Ni-1.0% Fe, pulverized and mixed with an attritor for 6 hours, and sieved with a 150 mesh sieve. 1000 g of paraffin was added as an organic binder to 30 kg of the mixed powder that had passed through the sieve, and the mixture was kneaded in a kneader for 2 hours. Using the same injection molding machine as in Example 1, this kneaded material was molded into 15 mm diameter x 60 mm length x 1.5 mm thickness.
The mold for one pipe-shaped product is maintained at a temperature of 40℃,
Injection molded. The obtained molded body had the same composition as the above mixed powder (97.0%W-2.0%Ni-1) as a raw material.
．． 0% Fe) powder and heated to 700° C. at a heating rate of 30° C./hour in 0.1 atm nitrogen gas to perform binder removal treatment. Next, the binder-removed molded body was sintered at 1450° C. in a hydrogen gas atmosphere.

The obtained sintered body has a density of 18.50 g/
cm3, it has a structure similar to that of one sintered after normal press forming, and there are no cavities or patches even when observed under a 100x optical microscope, indicating that it is a normal W-Ni-Fe based super-heavy alloy. confirmed. Moreover, the hardness of this W super-heavy alloy is H
Since the V was 330 and the tensile strength was 65 kg/mm2, it was found that it had mechanical properties at the same level as those obtained by sintering after normal press forming. It was also found from the dimensional measurements of the obtained sintered body that the distortion during debinding of the molded body was suppressed to 0.1 mm or less.

[0020]

[Effects of the Invention] According to the present invention, by improving the binder removal treatment of a molded article by injection molding, it is possible to almost completely remove the organic binder in a short time while suppressing the deformation of the molded article. It is possible to manufacture tungsten heavy alloy products with high precision and complex shapes and excellent strength at low cost and with good productivity.

Claims (2)

[Claims] Claim 1: Mix tungsten powder and nickel powder, iron powder, or copper powder to a predetermined composition, knead an organic binder to this mixed powder, injection mold it into a predetermined shape, and then mold the molded body into tungsten powder. The organic binder is removed from the molded body by embedding it in a powder containing at least tungsten powder with the same composition as the mixed powder or a composition close to the mixed powder, and heating it to a final temperature of 600 to 750°C in a non-oxidizing gas. A method for manufacturing a tungsten heavy alloy product, which comprises: sintering the compact taken out of the powder in hydrogen gas. 2. The method for producing a tungsten heavy alloy product according to claim 1, wherein the heating rate of the compact embedded in the powder is 20 to 50° C./hour.