JPH05287308A - Vibration filling method for metal powder - Google Patents

Abstract

(57) [Abstract] [Purpose] In a method for manufacturing a powder metallurgical product, which comprises filling a metal powder into a molding die and sintering the filling together with the molding die,
Workability is improved, and a high-density and high-strength sintered body is obtained. [Structure] When metal particles having different average particle diameters are vibratingly filled into a molding die, the average particle diameter ratio of each is set to 7 or more, and by vibrating and filling in stages sequentially from coarse particles, there is no surface defect. Efficiently manufacture high-density packing. It is desirable to attach the dispersant to the surface of the fine powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a large-sized sintered member such as a mold, and more particularly to a method for vibrating metal powder to obtain a high-density packing.

[0002]

2. Description of the Related Art Large-sized sintered members such as molds have been manufactured by applying the powder metallurgy method. By powder metallurgy,
The inventors of the present invention have found that a member having a complicated shape can be manufactured in a short period of time, as disclosed in JP-A-1-165704 and JP-A-1-165.
It was disclosed in Japanese Patent Publication No. 706. These are a method of vibratingly filling an iron-based metal powder having a predetermined grain size composition into a molding die and sintering together with the molding die to obtain a large-sized member. This is a manufacturing method of infiltrating a copper-based infiltration material to fill voids.

However, in the above method, since the mixed powder having a predetermined particle size is vibratingly packed, the packing density becomes non-uniform, or a nest due to a cross-linking phenomenon of coarse particles occurs.
As a result, defects such as pinholes and sintering strain often occur. As a solution to the problem, the present inventors have proposed in Japanese Patent Application No. 3-50978 a method of vibrating while pressing it with atmospheric pressure through a flexible airtight film.
Although pinholes and the like were drastically reduced by this method, the work was complicated by using a flexible film. Although the packing density is increased and stabilized as compared with the conventional one, it does not reach the tap packing density filled with impact force, and a high packing density molded body for further strengthening has been desired.

[0004]

DISCLOSURE OF THE INVENTION The present invention improves the workability of metal powder filling, which is a problem of the above-mentioned prior art, obtains a high packing density, and obtains a metal powder for obtaining a high-strength sintered body. The vibration filling method of

[0005]

The present inventors have found that the generation of defects such as pinholes during vibration filling is significantly affected by the segregation that occurs during the mixing of the mixed powder to be filled. As a solution, focusing on the fact that it is possible to perform vibration filling in stages without mixing, a high-strength filling body that exceeds conventional filling densities and can be improved in workability compared with the case of using a flexible film. Was found to be a filling method.

That is, according to the present invention, in a method of producing a powder metallurgical product in which a metal powder is filled in a molding die and sintered together with the molding die, a plurality of metal particles having different average particle diameters having a ratio of the average particle diameters of 7 or more to each other is used. A metal characterized by selecting a particle system, vibratingly packing a particle system having the largest average particle size into a molding die, and then gradually vibrating a small particle system into the gap of the packing in order of size. In the powder vibration filling method, it is desirable to loosen the agglomerates by attaching a dispersant to the surface of a metal powder having a small particle size, and then perform vibration filling.

In the present invention, the stepwise vibration filling means that a certain particle system is filled in a molding die under a certain vibration condition, and then another particle system is filled therein under another vibration condition.

[0008]

The function of the present invention will be described in detail below. The type of powder applied to the present invention is not particularly limited, and it is an iron-based powder, a metal powder such as an Al-based powder, and it is preferable to use pure iron powder in terms of cost as the iron-based powder. .. Further, alloy steel powder can be used, and various additives can be added in consideration of filling property and sinterability. As the additive, stearic acid, zinc stearate, graphite powder or the like can be used.

In the present invention, the powder to be filled is divided into a plurality of particle systems having different average particle sizes, and the particles are subjected to vibration filling in a stepwise manner. The number of particle systems to be separately filled is preferably 2-3 particle systems. With 4 particles or more, there is no cost advantage. There is a limit to the improvement of packing density with only one particle system. 2 is also suitable for economically obtaining a high packing density.
It is a particle system or a three-particle system.

First, a two-particle type filling method will be described. First, a powder of a large particle system of the two particle system is filled in a molding die. At this time, the vibration condition cannot be unconditionally limited because it depends on the diameter and shape of the particles, the size of the molding die, and the shape of the molding die, but it is necessary to fill the particles under conditions that do not cause overflow of the particles. Generally, when a particle system is vibrated, a gentle flow occurs or almost no flow occurs. Significantly higher frequencies and amplitudes result in more visible particle flow. This state is called overflow.

As an example, in order to efficiently fill a particle system having an average particle size of 500 μm into a container of 50 mmL × 30 mmW × 50 mmH, an acceleration of 1.0 to 3.0 G and an amplitude of both 0.
A range of 01 to 0.1 mm is suitable. At this time, the particles flow gently and a vibration packing density of 95% or more of the tap density can be obtained. Next, the powder having a small particle size is filled into the gaps of the compact already filled with the large particle size. As a method for this, a powder having a small particle size is placed on the large particle size filler and vibrated to fill the gap between the large particle size powders with the small particle size powder.
The vibration condition cannot be unconditionally specified like the vibration condition setting for a large particle size, but as an example, in order to efficiently fill a molded body having an average particle size of 500 μm with a particle system having an average particle size of 50 μm, an acceleration of 1.0 to The amplitude may be set to 5.0 G and both amplitudes may be in the range of 0.01 to 0.1 mm, which was almost the same as the condition for filling the particle system having the average particle size of 500 μm.

Generally, the vibration conditions for filling particle systems having different particle sizes greatly depend on the particle size, and it is necessary to find a vibration condition suitable for each particle size. If conditions are set at least for each particle system, the small particle system can penetrate into the gaps of the large particle system to obtain a high-density filled molded product. The density increases due to such gradual oscillatory filling as compared with the mixed filling, as described above, in the mixed filling, the non-uniformity of the mixture itself hinders the closest packing of the system at the time of filling. It is considered that the non-uniformity can be eliminated by the stepwise filling. Therefore, as described above, it is necessary to optimize the vibration condition, but according to the experience of the present inventors, the suitable vibration condition remarkably depends on the container shape, particle shape, particle diameter, filling weight, etc. Therefore, it cannot be specified unconditionally. However, it is generally known that the condition is suitable when the particle system itself does not visually overflow, and a gentle flow or almost no flow occurs.

Next, the filling of the three-particle system will be described. First, particles of the largest particle size of the three particle sizes are filled in the mold. Next, the medium particle size particle system is filled in the gap of the large particle system packing material while applying vibration in the same manner as in the case of the above-described two-particle system stepwise vibration packing. For the vibration conditions at that time, it is necessary to properly select acceleration, amplitude, and frequency. Next, a small particle size particle system is vibratingly filled into the voids of the already packed material in the same manner as the medium particle size system. The vibration conditions at that time are selected appropriately in the same manner as for the medium particle system.

The method of applying vibration may be any method such as electromagnetic vibration or mechanical vibration. In the present invention, the particle size ratio of the powder used is important. Next, the necessity of the particle size ratio will be described. When using the above-mentioned particle system, the average particle size ratio of each independent particle system needs to be 7 or more. By setting the ratio to 7 or more, the particle system having a small average particle size can penetrate into the gap without expanding the void of the packing material having a large average particle size, and an ideal close packing can be obtained.

When the average particle size ratio is less than 7, particles having a small average particle size penetrate into the gaps between particles having a large average particle size, but the penetration distance is not sufficient. If the vibration conditions are selected so that the particles with a large average particle size can be penetrated, the particles with a small average particle size will penetrate into the spaces with a large average particle size in such a way that the gaps between the particles with a large average particle size will be expanded. Is not obtained,
Insufficient filling such as product nesting. The upper limit of the average particle diameter ratio is not particularly limited, but practically, it is desirable to be about 50 at most. When a three-particle system is selected, an average particle size ratio of about 50 is a practical level. The average particle size of the large particle system is not limited, but a particle size of 10 mm or less is practically desirable.

When iron powder is used as the small grain size,
It is desirable to disperse the agglomerates by adhering a dispersant on the surface thereof before use. This is because when the iron powder is agglomerated, it is difficult for the iron powder to enter the gaps between particles having a large average particle diameter. Next, a method of attaching a dispersant to the surface of iron powder will be described. As a dispersant, a silane-based, titanate-based, or aluminum-based coupling agent is used, and an appropriate amount of this coupling agent is added to a solvent and stirred / dissolved. Iron powder is put into this solution, stirred, and then filtered to dry the iron powder to obtain a powder for filling.

Although the solvent varies depending on the type of powder and coupling agent, water, ethanol, methanol or the like can be used. By performing the stepwise vibration filling in this way, compared with the filling method using a flexible film or the like, it is possible to perform high-density filling excellent in workability without requiring facility improvement.

The mold may be of any type as long as it has sufficient strength up to the temperature at which the powder transfers the shape of the mold correctly and does not impair the shape of the mold due to a significant reaction with the powder. Uses a ceramic type or graphite type that can maintain strength up to. An infiltrant is placed on the upper surface of the powder-filled layer and the powder-filled layer of the molding die that have been filled by vibration, and sintering / infiltration is performed in a non-oxidizing atmosphere or under vacuum or reduced pressure. Sintering and infiltration may be performed in one heat cycle, and the effects obtained even if sintering and infiltration are performed in different heat cycles do not change.

According to the manufacturing method of the present invention, it is possible to easily obtain a uniformly packed high-density packing, and it is possible to remarkably suppress the occurrence of defects such as pinholes when sintered.

[0020]

EXAMPLES Examples will be described below. [Example 1] Iron-based powder having an average particle size of 500 μm, 25
Atomized pure iron powders of 0 μm, 58 μm, 35 μm and 6 μm were prepared. The atomized iron powder of 6 μm is produced by the high pressure water atomizing method.

300 mm L x 200 mm W x 300 mm
Using a ceramic mold of H, the particle system with the large average particle size shown in Table 1 was vibrated and packed first, and then the particle system with the small average particle size was loaded on the packing and vibrated. By virtue of this, stepwise vibration filling was performed. In the case of a three-particle system, coarse particles, medium particles, and fine particles shown in Table 2 were filled in this order. The vibration at the time of filling was performed using an electromagnetic shaker under the condition that the powder was uniformly filled without causing overflow. When almost no filling was carried out under the condition that the superfluidity did not occur, the superfluidity was intentionally caused and mixing was attempted. The filler was placed on the upper surface of the packed layer with a copper-based infiltration material, heated at 1010 ° C. for 70 minutes in a nitrogen gas atmosphere to sinter the filler, and then heated to 1120 ° C. over 2 hours to infiltrate. The material was melted and the infiltration proceeded. The holding time at 1120 ° C. was 100 minutes, and then the furnace was cooled. After cooling, the sintered body was taken out of the molding die, and the surface of the sintered body which was in contact with the bottom surface of the molding die was visually observed to examine the state of pinholes and coarse grain segregation. The vibration packing density when filling was also compared with the conventional method.

As shown in Table 1, the stepwise vibration filling method according to the present invention increases the packing density as compared with the conventional mixing vibration method. Further, as shown in Comparative Example 4, the particle size ratio is 7
If it is smaller than the above range, in the case of stepwise vibration filling, filling due to overflow is necessary, resulting in pinholes or segregation. Table 2 summarizes the results for the three particle system. If the particle size ratio does not reach 7, filling by superfluidity is required even in the stepwise vibration filling method, resulting in pinholes and segregation. Further, the packing density is increased by using the stepwise vibration packing method as compared with the conventional mixed packing method.

Example 2 Methanol was used as a solvent, and a titanate coupling agent was added as a dispersant thereto, and the mixture was stirred and dissolved to obtain a solution having a concentration of 3 wt%. Carbonyl iron powder was added to this solution and further stirred.
Then, it was filtered off and the carbonyl iron powder was dried. Carbonyl iron powder thus obtained (average particle size 6 μm)
And using atomized pure iron powders having average particle diameters of 58 μm and 500 μm, the same procedure as in Example 1 was performed.

As shown in Table 3, when the carbonyl iron powder is subjected to the above dispersion treatment, the packing density is further increased in the stepwise vibration packing method.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

According to the present invention, it is possible to obtain a uniform and high-density filler with good workability and a high-strength sintered body without surface defects.

Claims (2)

[Claims] 1. A method for producing a powder metallurgical product, comprising filling a metal mold with a molding die and sintering the filling together with the molding die, wherein a plurality of metal particles having different average particle diameters having an average particle diameter ratio of 7 or more. A metal characterized by selecting a particle system, vibratingly packing a particle system having the largest average particle size into a molding die, and then gradually vibrating a small particle system into the gap of the packing in order of size. Powder vibration filling method. 2. The vibration filling method for a metal powder according to claim 1, wherein the metal powder having a small particle size is subjected to vibration filling after the dispersant is attached to the surface to loosen the agglomeration.