JPH0551605A - Degreasing furnace and degreasing method - Google Patents

Abstract

(57) [Summary] [Purpose] With regard to degreasing in injection molding sintering, the purpose is to improve the production yield. [Composition] The maximum temperature for heating a molded mixture of a metal powder and an organic binder in a non-oxidizing atmosphere is 1000 ° C, and the maximum temperature for heating at a pressure of less than 10 kg / cm ² is 600 ° C. The degreasing method is characterized in that the molded body is pre-sintered using a degreasing furnace characterized by.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degreasing furnace and a degreasing method capable of degreasing injection-molded powder with a high yield.

It is customary to use a cutting process to obtain a molded product with good dimensional accuracy using metal, but there are molded products that are hard and brittle and difficult to lathe. For example, iron
This includes magnet bases and motor yokes made of soft magnetic materials made of silicon (Fe-Si) alloys and iron-cobalt (Fe-Co) alloys. The production yield is low and not practical.

On the other hand, the metal powder is mixed with an organic binder and then injection-molded into a required shape, which is placed in a furnace,
There is an injection molding sintering method (MIM method) in which the organic binder is decomposed to remove the binder by gradually raising the temperature and the binder is heated to be sintered.

This method is suitable for processing the above-mentioned materials, can be applied to those having complicated shapes, and is characterized by high yield.

[0005]

2. Description of the Related Art The process of sintering an injection-molded product is performed by mixing materials,
It consists of four steps: injection molding, binder removal, and sintering.

The kneading is performed by thoroughly kneading the raw material metal powder having an average particle size of 10 μm or less and an organic binder such as paraffin wax, and then applying a pressure of about 1 ton / cm ² to perform injection molding. Make a body.

Next, the binder is removed from the compact prior to sintering, but this treatment must not be accompanied by deformation of the compact. For this purpose, the binder is decomposed by heating and scattered. There is a method of dissolving and removing the binder by solvent extraction. Generally, a thermal degreasing method is used.

As a method of sintering after heating and degreasing, degreasing and sintering are performed separately, that is, a degreasing furnace and a sintering furnace are used. Degreasing and sintering are continuously performed using one furnace. There are two methods.

In this method, if the binder is completely scattered from the degreasing body, it is liable to collapse when being transferred from the degreasing furnace to the sintering furnace. % Of the binder remained in the sintering furnace.

Then, although heating and sintering are performed, cracks and swelling are likely to occur due to rapid decomposition of the binder, and in order to prevent this, the temperature rising rate is set low, and therefore sintering is performed. There is a problem that the time becomes longer and the cost increases.

Further, there is a problem that the carbon due to the decomposition of the residual binder contaminates the sintering furnace, which deteriorates the characteristics of the sintered body. Further, the method (1) has a problem that the required time is short, but there is a problem that it is difficult to form a sintered body having good characteristics because carbon is generated much due to the decomposition of the binder.

[0012]

In the injection molding sintering method of degreasing by the heating degreasing method and then sintering, as described above, a method of performing degreasing and sintering using different furnaces, There is a method of using one furnace.

However, the former has a problem that the degreased body is likely to collapse, and the latter has a problem that a good quality sintered body cannot be formed due to contamination with carbon, and this problem is to be solved.

[0014]

The above object, according to an aspect of is a heating maximum temperature 1000 ° C. the mixture molded article comprising a metal powder and an organic binder in a non-oxidizing atmosphere, at a pressure of less than 10 Kg / cm ² This can be solved by configuring a degreasing method, which is characterized in that the maximum temperature for heating is 600 ° C., and the compact is pre-sintered using a degreasing furnace.

[0015]

The present invention relates to an improvement in the method of performing degreasing and sintering separately. By improving the structure of the degreasing furnace, 100%
Degreasing.

The problem of the method of performing degreasing and sintering separately is that if degreasing is performed sufficiently, it tends to collapse during transfer to a sintering furnace, and if degreasing is insufficient, it takes a long time for sintering. Therefore, the present invention is to improve the strength of the degreasing furnace and perform the preliminary sintering.

That is, in general, degreasing is performed by pressurizing and heating in an atmosphere of non-oxidizing gas such as argon (Ar), nitrogen (N ₂ ) or by depressurizing to atmospheric pressure or less. Has been done.

The reason for pressurizing or depressurizing is that the results are superior to normal pressure, and pressure degreasing is generally performed. As the degreasing furnace, an electric furnace capable of pressurizing up to 9.9 Kg / cm ² and heating up to about 400 ° C is used for degreasing.

Here, the value of 9.9 Kg / cm ² is the upper limit of the standard value of the second class pressure vessel. Therefore, as a method of solving this problem, the inventor increased the strength of the degreasing furnace to increase the mechanical strength to 60%.
It was improved so that heating up to 0 ° C was possible with a pressure of less than 10 kg / cm ² .

The reason why the temperature is set to 600 ° C. is that the sintering starting temperature of most of the metals used in the injection molding sintering method (MIM method) is 600 ° C. or less. That is, according to the present invention, after the binder is completely scattered, the metal powder is heated to a degree that the mutual sintering of the metal powders slightly progresses (temporary sintering) to perform degreasing.
Degreasing is performed using a degreasing furnace that can raise the temperature to 600 ° C at a pressure value corresponding to the type 2 pressure vessel.

In this way, although the metal powder is a small amount, it does not collapse due to vibration during transfer because it is sintered, and since the binder is completely removed, it has good characteristics. You can get a body.

[0022]

[Example] Fe-50% Co alloy powder was kneaded with a binder containing polyethylene as a main component, and a molded body having four protrusions 2 having different heights was injected into a frame body 1 as shown in FIG. It was molded into a sample.

If the temperature is 600 ° C. or less in a non-oxidizing atmosphere,
A degreasing furnace capable of pressurizing up to 9.9 Kg / cm ² and capable of heating up to 1000 ° C was prepared. Then, supplying N ₂ gas, 4 Kg / c
While applying a pressure of m ^2, the temperature was raised to 600 ° C. to degrease and perform temporary sintering.

As a result of analysis of this sample, no binder was found at all. Next, for comparison, the same molded body was used, and a pressure of 4 kg / cm ² was applied using a conventional degreasing furnace.
Degreasing was performed by raising the temperature to 450 ° C.

As a result of analysis, this sample contained about 10% binder.
It remained. In order to compare the handling properties of the two, the height at which the sample was damaged when dropped on a wooden bench was measured. Broken at height.

Next, the two kinds of samples were transferred to a sintering furnace, heated to 1400 ° C. in an H ₂ atmosphere, and held at this temperature for 1 hour for sintering. As a result of analysis, the residual carbon content in the sintered body was 0.007% in the former, while 0.01% in the latter.
8%, and carbon adhered to the inside of the sintering furnace.

[0027]

EFFECT OF THE INVENTION Using the degreasing furnace according to the present invention, heating to a temperature at which pre-sintering occurs and degreasing and then sintering is carried out. You can get a unity.

[Brief description of drawings]

FIG. 1 is a plan view (A) and a side view (B) of a molded body used in an example.

[Explanation of symbols]

 1 frame 2 protrusion

Claims (3)

[Claims] 1. A mixed compact comprising a metal powder and an organic binder can be positioned and heated in a non-oxidizing atmosphere while applying pressure to degrease and pre-sinter the compact. Degreasing furnace. 2. The maximum heating temperature in the non-oxidizing atmosphere according to the preceding paragraph is 1000 ° C., and the maximum heating temperature at a pressure of less than 10 kg / cm ² is 600 ° C. Degreasing furnace as described. 3. A degreasing furnace according to claim 1, wherein a mixed compact composed of a metal powder and an organic binder is positioned, and degreasing and pre-sintering are performed while applying pressure in a non-oxidizing atmosphere. Characterizing degreasing method.