JP2001192703A - Metal power as feedstock suitable for metal injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the variability in quality characteristics of a metal powder as a feedstock suitable for injection molding. SOLUTION: The metal powder as a feedstock suitable for metal injection molding has 0.320-0.400 spheroidizing index (SI) represented by the following equation: SI=CS÷ρ0÷SA (wherein, CS is specific surface area (m2/cm3) expressed in terms of sphere by means of microtrack by the laser scattering method; ρ0 is the true density (g/cm3) of the metal powder to be measured wit a pycnometer; and SA is the specific surface area (m2/g) of the powder by the BET(Brunauer-Emmett-Teller) method).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw metal powder having a shape particularly suitable for metal injection molding.

[0002]

2. Description of the Related Art Raw metal powder used for metal injection molding is classified into gas atomized powder, water atomized powder,
Milling, carbonyl powder, etc. are the main ones. However, each powder has advantages and disadvantages in terms of quality and cost.For example, gas atomized powder is a spherical powder, so injection molding is good, but it has drawbacks such as weak degreased body strength and high cost. . Although water atomized powder is inexpensive, it has disadvantages such as poor injection moldability because it is a powder of irregular shape. In recent years, this water atomized powder has been subjected to mechanical spheroidizing treatment, and some products that are inexpensive and have good injection moldability have been supplied.

[0003]

As the raw material powder for metal injection molding, it is important to select a product that satisfies the required qualities such as injection moldability and degreased body strength and is highly economical. The quality characteristics of the metal powder alone or the mixture described above include the tap density of the powder used, the average particle size of the powder,
The particle size distribution, specific surface area, and the like could not be controlled, and large variations occurred between powder production lots. This is because the shape state of each particle which affects the injection moldability and the degreased body strength could not be grasped. The tap density that appears to embody the shape of the powder at first glance is greatly affected not only by the particle shape but also by the particle size distribution. Therefore, it is an issue to eliminate the variation in the quality characteristics.

[0004]

According to the present invention, there is provided a raw metal powder suitable for metal injection molding, characterized in that the spheroidization index (SI) shown in the following formula has a numerical value of 0.320 to 0.400. is there.

SI = CS ÷ ρ ₀ ÷ SA Where, CS: sphere converted specific surface area (m ² / cm ³ ) by laser scattering method.

Ρ ₀ : true density of the metal powder to be measured (g / c)
m ³ ): By pycnometer. SA: Specific surface area of powder by BET method (m ² / g) The above-mentioned spheroidization index (SI) indicates how close the shape of a metal powder constituting a measurement sample is to a perfect sphere by measuring the shape state of each powder particle. , Which can be relatively grasped as an aggregate of powder. It has been found that the SI value in the range of 0.320 to 0.400 is optimal as a raw metal powder for injection molding. That is, by using the metal powder having the specified SI value for injection molding, quality variation between raw material powder lots can be suppressed, and a product of stable quality can be manufactured under certain injection conditions. That is, as long as the SI value is managed, the quality characteristics required for metal injection molding, such as injection moldability and degreased body strength, can be centrally controlled.

[0007] As a method for stabilizing the state of the particle shape of the powder, a method has been proposed in which the powder is imaged in a state in which the powder is separated one by one, and the image is analyzed to quantify the spheroidized state. That is, there has been proposed a method of calculating the ratio of the circumference of each of the irregular shaped powders in the image to the circumference when the projected area is converted into a circle. However, these methods take an extremely long time for analysis, and are not industrial methods such that reliability cannot be obtained unless the number of analysis fields is considerably increased. Thus, the present invention has been achieved.

In the present invention, when the SI value is less than 0.32, the injection moldability is poor, and there is a possibility that poor filling of the mold may occur. On the other hand, when the SI value exceeds 0.40, the strength of the degreased body is reduced. Insufficient results have been confirmed by a number of tests. That is, the present invention has found that a raw metal powder having an SI value between 0.320 and 0.400 is most suitable for injection molding.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a raw metal powder, SUS31
6 L, Kovar, 17-4 PH, and 410 L gas atomized powder, water atomized powder, and mechanical atomized powder of water atomized powder of water atomized powder having three different particle sizes were prepared.

As shown in Table 1, powder materials having various particle sizes and tap densities were prepared by appropriately mixing these powders. A mixture of these raw metal powders and a polyethylene copolymer as a binder in an amount of 8.0 wt% was formed into a plate shape of 10 mm × 15 mm × 7 mm by an injection molding machine, and then the binder was removed by a known binder removal method. Was removed by heating to prepare a degreased body sample. The percentage of the damaged product when this degreased sample was transported 2 m by a roller conveyor was defined as the degreased body strength. Similarly, a mixture of the raw material powder and 8.0 wt% binder was applied to a flow tester, and the flow rate was measured at 160 ° C. in a heated state. Here, the minimum flow rate required to obtain a complex-shaped product by injection molding is 0.2
0 cm ³ / min. The test results are also shown in Table 1.
In the table, the water atomized powder and the gas atomized powder are abbreviated as water and gas, respectively. Water spheroidization means a powder obtained by spheroidizing a water atomized powder.

[0011]

[Table 1]

[0012]

[Table 2]

As shown in Table 1, the injection molding properties depend only on the spheroidization index (SI). When the SI value is less than 0.320, the injection moldability is poor and poor filling into the mold occurs. easy. If the SI value exceeds 0.400, the degreased body strength is insufficient.

[0014]

According to the present invention, a method for producing a raw material powder,
Irrespective of the constituents of the powder, simply controlling the numerical value of the sphering index (SI) makes it possible to easily and industrially control the injection moldability.

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[Procedure amendment]

[Submission date] December 22, 1999 (1999.12.
22)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

As shown in Table 1, powder materials having various particle sizes and tap densities were prepared by appropriately mixing these powders. A mixture of these raw metal powders and a polyethylene copolymer as a binder in an amount of 8.0 wt% was formed into a plate shape of 10 mm × 15 mm × 7 mm by an injection molding machine, and then the binder was removed by a known binder removal method. Was removed by heating to prepare a degreased body sample. The percentage of the damaged product when this degreased sample was transported 2 m by a roller conveyor was defined as the degreased body strength. A flow tester is also used in which 8.0 wt% binder is blended with the raw material powder.
(Die diameter φ1.0 mm, pressure 10 kgf / cm ² ) , and the flow rate was measured at 160 ° C. in a heated state. Where moldability
Determination is minimum required to obtain a complicated shape articles by injection molding <br/> flow amount 0. 20 cm ³ / min or more was regarded as good . The test results are also shown in Table 1. In the tables, the water atomized powder and the gas atomized powder are abbreviated as water and gas, respectively. Water spheroidization means a powder obtained by spheroidizing a water atomized powder.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

[Table 1]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012]

[Table 2]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shigeyoshi Muto F-term (reference) 4K018 BA17BB01

Claims (1)

[Claims] 1. A spheroidizing index (SI) represented by the following formula:
A raw metal powder suitable for metal injection molding, having a numerical value of 0.320 to 0.400. SI = CS ÷ ρ ₀ ÷ SA Here, CS: spherical equivalent specific surface area (m ² / cm ³ ) by laser scattering method. ρ ₀ : true density of the metal powder to be measured (g / cm ³ ): by a pycnometer. SA: Specific surface area of powder by BET method (m ² / g)