JP2001152264A - Manufacturing method of high specific gravity sintered body - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a high specific gravity sintered body that can easily obtain a product having a complicated shape by using an injection molding method. SOLUTION: A composition comprising a raw material powder obtained by adding 3% by weight or less of iron and / or copper powder to a tungsten powder and 2 to 6% by weight of nickel powder and a binder containing a dispersant is obtained by injection molding. After demolding the molded body, the molded body is further sintered in a non-oxidizing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high specific gravity sintered body containing tungsten as a main component.

[0002]

2. Description of the Related Art Among typical high specific gravity sintered bodies, a tungsten-nickel-copper alloy material is also called a heavy alloy, and is used as a vibrator, a blocking material, and an electric contact material. In recent years, its use as a material replacing lead has been expanding.

[0003] In order to produce the above-mentioned high specific gravity sintered body, attempts have been made to produce it by powder metallurgy. But,
The ordinary powder metallurgy method is a method in which a raw material powder is charged into a mold and compression-molded by a press, so that it is difficult to obtain a product having a complicated shape. In addition, as a pre-process for performing compression molding, a process of uniformly mixing tungsten powder, nickel powder, and copper powder with a ball mill or the like is required, and thus there has been a problem that work time and man-hours are increased.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high specific gravity sintering method capable of easily obtaining a product having a complicated shape by using an injection molding method. An object of the present invention is to provide a method for producing a body.

[0005]

In order to achieve the above object, the present invention provides a raw material powder comprising a tungsten powder and a nickel powder of 2 to 6% by weight to which 3% by weight or less of iron and / or copper powder is added, and a dispersant. The composition comprising a binder to be contained is injection-molded, the obtained molded body is subjected to a binder removal treatment, and then the molded body is sintered in a non-oxidizing atmosphere.

In the present invention, the binder is contained in an amount of 30 to 70% by volume based on the whole composition,
The dispersant is used in an amount of 2 to 20% by volume per binder, and the non-oxidizing atmosphere is a vacuum atmosphere, or hydrogen, argon, nitrogen or the partial atmosphere. It is assumed that.

[0007]

DETAILED DESCRIPTION OF THE INVENTION (Powder for sintering) Regarding the addition amount of nickel which affects the wettability with tungsten as a starting material, if the addition amount is 2% by weight or less, wetting with tungsten becomes insufficient, and 6% by weight. %, A high specific gravity cannot be obtained, so the content is limited to 2 to 6% by weight. In the present invention, copper or iron or a combination thereof is used as a sintering aid. However, if the added amount exceeds 3% by weight, a high specific gravity cannot be obtained. But 3
% By weight or less. If the average particle size of the raw material powder to be added becomes large, it becomes difficult to densify the raw material powder. Therefore, the particle size of the metal powder used as the raw material is preferably 10 μm or less.

(Binder) The binder in the composition for injection molding is necessary for enabling injection molding of the powder for sintering and for imparting a certain strength to the obtained injection molded article. When the binder content is less than 30% by volume, the fluidity of the composition is reduced, and injection molding becomes difficult. On the other hand, if the content exceeds 70% by volume, surface shrinkage occurs during molding, and the packing density of the sintering powder in the obtained injection-molded product becomes low. Therefore, in the present invention, the content of the binder in the composition for injection molding is set at 30.
７０70% by volume.

The use of a dispersing agent not only suppresses agglomeration of tungsten, nickel, copper or iron powder, but also disperses the powder uniformly, as well as a phase with a resin or wax commonly used as a binder. The solubility and the affinity with the powder for sintering can be improved. Therefore, the dispersant acts as a bridge between the sintering powder and the binder, and as a result, the dispersibility and the releasability from the mold during injection molding are improved.

As the dispersant to be used, fatty acid esters and the like can be considered. Since the dispersibility differs depending on the raw material powder to be used, a dispersant having good dispersibility suitable for the raw material powder to be used is appropriately selected. . If the amount of the dispersing material is less than 2% by volume of the whole binder, the effect of improving dispersibility cannot be sufficiently obtained, while if it exceeds 20% by volume, the strength of the obtained injection molded article decreases, and the molded article becomes brittle. The amount of the dispersant used is preferably 2 to 20% by volume of the whole binder.

(Injection Molding Composition) The injection molding composition according to the present invention is easily prepared by uniformly kneading the sintering powder, the binder and the dispersant in the above-mentioned ratio. This composition is made into a final product through each of the steps of injection molding, degreasing and sintering.

(Injection molding / degreasing) Injection molding can be carried out using a usual injection molding machine used for plastic injection molding. Degreasing is generally performed by subjecting the injection molded body to heat treatment. However, when a metal that is easily oxidized is used as the sintered powder, the heat treatment is performed under an inert gas atmosphere or a reducing atmosphere. It is preferable to perform the above.

(Sintering) When sintering a debindered compact, it is necessary to sinter in a non-oxidizing atmosphere. This non-oxidizing atmosphere is a vacuum atmosphere or hydrogen,
It is necessary to perform sintering in argon, nitrogen or the above partial atmosphere. By sintering in the non-oxidizing atmosphere, a high density sintered body can be obtained.

[0014]

EXAMPLES Example 1 Average particle size of 4 μm as raw material powder
To the tungsten powder, 3.3% by weight of nickel powder having an average particle diameter of 5 μm, 1.7% by weight of iron powder having an average particle diameter of 5 μm, and 47% of a wax-based binder containing 10% by volume of a dispersant per binder. After adding volume% and kneading at 150 ° C., the mixture was granulated into pellets. The pellets were injection molded using an injection molding machine under the conditions of an injection pressure of 800 kg / cm ² .

[0015] The obtained compact (width 8 mm, length 40 m)
m, 4 mm thick rectangular parallelepiped) is heated to 300 ° C.
After holding for 1 minute, the wax-based binder was removed. Thereafter, the debindered molded body was sintered in a vacuum at 1460 ° C. for 2 hours. The appearance and sintered density of the sintered product thus obtained were examined. At this time, the external appearance was visually observed and evaluated, and the sintered density was measured and evaluated using a hydrometer. Table 1 shows the results.

Example 2 A sample was prepared in the same manner as in Example 1 except that 5.0% by weight of nickel powder having an average particle size of 5 μm and 2.5% by weight of iron powder having an average particle size of 5 μm were added. It was evaluated similarly. Table 1 shows the test results.

Example 3 An average particle size of 4 μm was used as a raw material powder.
To a tungsten powder having an average particle size of 3.0% by weight of nickel powder having an average particle size of 5 μm and 1.5% by weight of a copper powder having an average particle size of 9 μm, and a wax-based binder to which a dispersant is added at 8% by volume per binder. After adding 45% by volume and kneading at 150 ° C., the mixture was granulated into pellets. These pellets were injection-molded into a mold under an injection pressure of 750 kg / cm ² using an injection molding machine.

The obtained molded product (width 8 mm, length 40 m)
m, a 4 mm thick rectangular parallelepiped) was heated to 300 ° C. and held for 60 minutes to remove the wax-based binder. Thereafter, the molded body subjected to the binder removal treatment is treated in a hydrogen atmosphere up to 1100 ° C., and then at 1350 ° C. for 2 hours.
Sintering was performed in an argon partial atmosphere. The sintered body thus obtained was evaluated in the same manner as in Example 1. Table 1 shows the test results.

Comparative Example 1 A sample was prepared and evaluated in the same manner as in Example 1 except that no dispersant was added to the binder component. Table 1 shows the test results. Due to the poor dispersion state of the powder, the sintered body was deformed.

Comparative Example 2 A sample was prepared and evaluated in the same manner as in Example 3 except that no dispersant was added to the binder component. Table 1 shows the test results. Due to the poor dispersion state of the powder, the sintered body was deformed.

[0021]

[0022]

According to the manufacturing method of the present invention, a sintered body having a high density and excellent appearance can be easily and stably manufactured, and the injection molding method is used. Even a product having a shape can be easily manufactured.

Claims (3)

[Claims] 1. A binder containing 2 to 6% by weight of nickel powder, 3% by weight or less of at least one metal powder of iron or copper, and the balance being tungsten powder, and a binder containing a dispersant. Injection molding a composition consisting of
A method for producing a high specific gravity sintered body, comprising debinding the obtained molded body and sintering the molded body in a non-oxidizing atmosphere. 2. The composition according to claim 1, wherein the binder is used in an amount of 30 to 30%.
The method for producing a high specific gravity sintered body according to claim 1, wherein the content is 70% by volume, and the dispersant is used in an amount of 2 to 20% by volume per binder. 3. The non-oxidizing atmosphere is vacuum or hydrogen,
The method for producing a high specific gravity sintered body according to claim 1 or 2, wherein the atmosphere is argon, nitrogen, or the partial atmosphere.