JPS63250407A - Method for removing binder from injection-molded metal body - Google Patents

Abstract

PURPOSE:To remove a binder from molded bodies with high temp. controllability without cracking the molded bodies or degenerating the metal of the bodies by embedding the molded bodies obtd. by injection-molding metal powder kneaded with thermoplastic resin in AlN granules and by raising the temp. CONSTITUTION:Powder of a metal such as an Fe-Si alloy is mixed with thermoplastic resin and injection-molded. The molded bodies 3 are embedded in AlN granules 4 of about 5-20 mm average diameter as a filler in a vessel 5 made of Mo or the like. The vessel 5 is positioned in an electric furnace or the like and the temp. is slowly raised under a flow of nitrogen or the like to decompose and remove the thermoplastic resin as a binder. Thus, the binder can be removed without cracking, swelling or collapsing the molded bodies or causing the degeneration of the alloy by gas generated by the decomposition of the binder.

Description

[Detailed Description of the Invention] [Summary] As a method for removing the binder from a molded body obtained by injection molding a mixture of metal powder and thermoplastic resin without causing cracks on the surface, the molded body is placed in aluminum nitride powder. A method of decomposing and removing thermoplastic resin by gradually raising the temperature while it is buried in the plastic.

[Industrial application field]

The present invention relates to a method for removing binder from an injection molded metal body.

The usual way to shape a metal material into a desired shape is to cut it using a lathe or the like, but the material is hard and brittle, making lathe processing difficult in some cases.

For example, magnet bases and motor yokes are made of soft magnetic materials such as iron-silicon (Fe-Si) alloys, and the problem is that the manufacturing yield is low because the materials are hard and brittle. be.

On the other hand, a method for obtaining a metal molded body is to mix metal powder with a thermoplastic resin, then injection mold it into the desired shape, then place it in a furnace and gradually raise the temperature. Lytic process (formerly tec-pro) involves decomposing thermoplastic resin, debinding it, and then sintering it.
This method is suitable for mass production and has a high manufacturing yield.

[Conventional technology]

The problem with the lytic process is that when the binder is removed, the injection molded metal body (hereinafter simply referred to as the molded body) may have minute cracks (5).
Defects generated in this process cannot be repaired even in the high-temperature sintering process because cracks, blisters, and collapses are likely to occur.

Therefore, it is necessary to remove the binder without causing such defects.

This method can be carried out by placing the compact as it is in a furnace, or by placing a metal powder such as copper (Cu) or a ceramic powder such as silicon oxide (5in2) powder or alumina (8l!203) powder. The method used is to place the thermoplastic resin in a furnace and gradually raise the temperature to decompose and remove the thermoplastic resin.

Here, the thermoplastic resin is polystyrene.

Polyethylene or a mixture of the two are used, and after the temperature is raised to near the thermal decomposition temperature, the binder is removed by gradually heating at a rate of several seconds per hour to advance the decomposition. .

However, if the temperature is raised with the molded body exposed, 1 to 2
It is necessary to raise the temperature at a slow rate of 7°C; if it is faster than this, it is inevitable that a considerable temperature gradient will occur between the surface and the inside of the molded product, which will cause problems such as cranking, blistering, and collapse. There is a problem that defects occur.

In addition, when heating by immersing the binder in metal powder or oxide powder, the temperature gradient is alleviated and the heating rate can be increased, but the binder is difficult to remove due to poor air permeability.
Another problem is that reactions with decomposed gas tend to occur.

[Problem that the invention seeks to solve]

As mentioned above, the lytic process is an excellent method for obtaining compacts made of hard and brittle metal, but it is prone to defects and reaction products with decomposed gas during the binder removal process. That's a problem.

[Means for solving problems]

The above problem arises when removing the binder from a molded body obtained by injection molding a mixture of metal powder and thermoplastic resin. This problem can be solved by a method of debinding an injection molded metal body by raising the thermoplastic resin to decompose and remove it.

[Effect]

The problems with the binder removal process are: ■ When the ambient temperature reaches the decomposition temperature of the thermoplastic resin, rapid gas decomposition occurs, causing swelling and collapse.

■ A temperature gradient occurs inside and outside the molded object, and cracks occur due to differences in thermal expansion due to the temperature difference.

(2) When heated while buried in a filler made of metal powder or ceramic powder, air permeability is inevitably impaired, resulting in heating in an atmosphere of decomposed gas, which tends to form compounds.

Therefore, the present invention has been proposed as a filler. ■ Excellent breathability.

■High thermal conductivity.

■ Reactions are difficult to occur at the decomposition temperature of the resin.

■Easy to handle.

The filling material is selected based on the necessary conditions such as, and the average particle size is 5.
~2(1*m) aluminum nitride (AlN) powder was chosen.

Here, AffiN is known to have good thermal conductivity and is a thermally and chemically stable material.

The table compares the performance with materials known to have good thermal conductivity.

In the table, the melting points of A I MO3 and SiC are shown in the column of decomposition temperature.

All of these materials are stable materials and do not react chemically during binder removal treatment performed at temperatures up to about 500° C., but AIN is the best in terms of thermal conductivity.

Therefore, the present invention uses AIN powder as a filler, and because of its good thermal conductivity, it is possible to increase and decrease the temperature with good controllability.

Next, the problem when using a filler is that the decomposed gas of the binder is difficult to escape due to poor ventilation, and heating is performed in a decomposed gas atmosphere.

For this purpose, it is necessary to adjust the particle size.

That is, when the particle size is fine, thermal conductivity is good and temperature control is easy, but degassing becomes insufficient.

On the other hand, if the particle size is large, degassing will be sufficient, but thermal conductivity will be insufficient.

Figure 2 explains the reason for this.The particles 1 with good thermal conductivity, such as 8βN, are in contact with each other and filling is performed, but the heat is conducted from the high-temperature area to the low-temperature area. must be carried out through the grain boundaries 2 that are in contact with each other, and as the heat is conducted through repeated condensation and diffusion as shown by the arrows, a considerable spreading resistance is required.For this reason, the larger the grain size, the more
Thermal conductivity becomes insufficient.

The inventors experimentally determined that A with an average particle size of 5 to 20+i+ was used as a condition for maintaining air permeability and effectively utilizing thermal conductivity.
j? N is selected.

〔Example〕

Fe-3i alloy powder with a particle size of 350 mesh or more is mixed with an equal volume of polystyrene and polyethylene mixture and injection molded to form a 611×4 piece as shown in Figure 1.
A rectangular parallelepiped molded body 3 of m×50 mm (length) was made, and four of these molded bodies were embedded in a container 5 made of molybdenum (Mo) using AIN powder 4 having an average particle size of 5 m to 20 mm as a filler.

After positioning in the electric furnace, nitrogen (N2) was added to the
The temperature was raised while flowing at a flow rate of 001/hour, and the temperature was increased to 200
The binder was removed by gradually raising the temperature from ℃ to 500℃ at a rate of 10℃/hour, but the product cracked and blistered.

There was no occurrence of collapse, and no deterioration of the Fe-5t alloy due to binder decomposition gas was observed, proving the advantages of the present invention.

〔Effect of the invention〕

As described above, by carrying out the present invention, it is possible to perform the binder removal treatment of the injection molded article with good temperature controllability and without causing cracks or deterioration, thereby solving the problems of the lytic process. can do.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view for explaining the present invention in detail, and FIG. 2 is a model diagram for explaining heat spread resistance. In the figure, 1 is a grain, 2 is a grain boundary, 3 is a compact,
4 is AIN powder.

Claims (2)

[Claims] (1) When removing the binder from a molded body obtained by injection molding a mixture of metal powder and thermoplastic resin, the molded body is placed in a furnace while being embedded in aluminum nitride powder, and the furnace temperature is 1. A method for removing binder from an injection molded metal body, the method comprising decomposing and removing the thermoplastic resin by increasing the temperature. (2) The average particle size of the aluminum nitride powder is 5 to 20
The method for removing binder from an injection molded metal body according to claim 1, wherein the binder is removed from an injection molded metal body.