JPH0520132B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for homogenizing powders such as metal powders and ceramic powders used as raw materials for various mechanical parts.

BACKGROUND OF THE INVENTION As is well known, ceramic products have recently been used as strong and functional parts, and sintered forged products have been increasingly used for parts that require mass production. Ceramic powder and metal powder, which are the raw materials for these ceramic products and sintered forged products, must be thoroughly and uniformly mixed before use in order to homogenize the final product. A wet mixing method using a liquid such as lower alcohol or water as a dispersion medium is known. In other words, in the conventional wet mixing method, the raw material powder and the dispersion medium are mixed by stirring in a ball mill, for example, and then heated with a spray dryer or other suitable dryer to remove the dispersion medium and dry the mixture. ,
Alternatively, after stirring and mixing are completed, the mixture is frozen and placed in a vacuum atmosphere, thereby scattering and removing the dispersion medium and drying.

Problems to be Solved by the Invention However, although the above-mentioned conventional method can achieve uniform mixing, the raw material powder may change in quality in the process of removing the dispersion medium, or it may require large and complicated equipment. There was a problem. In other words, in the method of heating and drying using a spray dryer or other dryer, the raw material powder is extremely fine and has a large specific surface area, and the drying is performed in an oxidizing atmosphere. However, metal powders such as iron powders are oxidized, and all types of powders have the problem of bonding between particles. On the other hand, the freeze-vacuum drying method not only consumes a large amount of energy for freezing, but also requires special and expensive containers and equipment to maintain the vacuum state, which increases not only running costs but also equipment costs. There was a problem.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a powder mixing method that prevents deterioration of the powder and can be easily carried out.

Means for Solving the Problems In order to achieve the above object, the present invention is characterized in that a liquefied gas that becomes a gas at normal temperature and normal pressure is used as a dispersion medium. The method is characterized in that liquefied gas that has been liquefied by pressurizing above normal pressure is mixed with powder such as metal powder or ceramic powder as a dispersion medium, and after completion of stirring and mixing, the pressure is reduced to normal pressure to vaporize and separate the liquefied gas. It's a method.

DETAILED DESCRIPTION OF THE INVENTION The powders targeted by this invention are not particularly limited, but include ceramic powders such as silicon carbide, silicon nitride, and boron nitride, especially carbides and nitrides thereof, and metal powders. It is effective if applied to reduced iron powder, etc.

In addition, the liquefied gas used as the dispersion medium can be liquefied petroleum gas, liquefied natural gas, or liquefied fluorocarbon, but when reusing it, it should be easily liquefied, non-toxic, easy to handle, and safe. It is preferable to use one that has excellent properties.

Further, stirring and mixing is performed in a pressurized atmosphere to keep the dispersion medium in a liquid state, and such mixing operation can be performed using a ball mill or a vibration mill.

Examples Examples of the present invention will be described below together with comparative examples.

Example 1 100 g of commercially available β-type silicon carbide powder, 1.0 g of amorphous boron powder, and 1.0 g of carbon black were placed together with nylon balls in a pressure-resistant steel ball mill lined with nylon resin, and a liquid volume was added as a dispersion medium. 250ml of liquefied petroleum gas (No. 1 propane)
is press-fitted into the pressure-resistant ball mill, and in that state it is heated for 20
The mixing process was carried out by rotating the ball mill for hours. Immediately after the mixing was completed, the contents of the pressure ball mill were discharged through its lower spout. In that case, since the inside of the pressure-resistant ball mill was under high pressure, the contents spouted out, and the liquefied petroleum gas, which was the dispersion medium, was vaporized and separated, and the mixed powder became dry. Particle size 40~
It had a spherical shape of 100 μm.

In order to examine the quality of the obtained mixed powder, a sintered body was created using the mixed powder. That is,
First, the mixed powder was pressed using a metal mold for 150 m
After preliminary molding at a pressure of Kg/cm ² , hydrostatic pressure was applied at a pressure of 3.0 ton/cm ² . The density of the obtained compact is
It was 1.86g/ ^cm3 . Next, the obtained molded body was heated in a Tammann furnace in an argon gas stream for 2100 min.
Baked at ℃ for 30 minutes. The density of the obtained sintered body is
3.12g/ ^cm3 , and the bending strength by three-point bending is:
The average strength was 65.0Kg/ ^cm2 .

Comparative Example 1 Made by conventional mixing method. That is, the powder shown in Example 1 above was mixed in a ball mill using alcohol as a dispersion medium, and after the mixing was completed, the contents were taken out and dried at a temperature of 100°C in an ordinary dryer. Summer. The obtained dried product was in the form of nodules.

In order to examine the quality of the dried product, it was ground into powder, then molded and fired in the same manner as in Example 1. The density of the obtained sintered body was 2.85 g/cm ³ . The average three-point bending strength was 35.4 Kg/cm ² .

From the results of Example 1 and Comparison 1 above, it was recognized that the quality of the ceramic mixed powder produced by the method of the present invention was excellent.

Example 2 Pure iron powder was mixed in the same manner as in Example 1 to homogenize it. In other words, pure iron powder with an average particle size of 35 μm was placed together with nylon balls in a pressure-resistant steel ball mill lined with nylon resin, and liquefied petroleum gas (No. 1 propane) was then pressurized, and the mill was rotated in that state for 20 hours. Mixed. Immediately after the mixing was completed, the lower nozzle of the pressure-resistant ball mill was opened and the mixture was discharged while being spray-dried.

The oxygen concentration in the obtained dry powder was 0.02wt%.

Comparative Example 2 Pure iron powder (average particle size 35 μm) was mixed in the same manner as in Example 2 using alcohol as a dispersion medium.

The oxygen concentration in the obtained dry powder was 0.38 wt%.

From the results of Example 2 and Comparative Example 2, it was confirmed that the method of the present invention is effective in preventing oxidation.

Effects of the invention As is clear from the above explanation, according to the mixing method of the present invention, a liquefied gas that becomes a gas at room temperature and pressure is used as a dispersion medium, so special treatment such as heating is not required simply by returning it to normal pressure. To be able to separate and remove the dispersion medium without having to mix, and therefore to obtain a dry mixed powder in a uniformly dispersed state even in wet mixing, and to prevent deterioration due to oxidation, etc., and to obtain a homogeneous and high-quality powder material. I can do it. In addition, since the drying process can be carried out by returning the pressure to normal pressure, the operations and equipment need only be as simple as those normally used.Furthermore, if a liquefied gas that liquefies at a relatively low pressure at room temperature is used, The dispersion medium can be easily recovered and running costs can be reduced.

Claims (1)

[Claims] 1 Liquefied gas, which is a gas at room temperature and pressure, is liquefied under pressure and mixed with powder such as metal powder or ceramic powder as a dispersion medium, and after stirring and mixing is completed, the pressure is reduced to normal pressure to vaporize the liquefied gas. A method of mixing powders characterized by separation.