JPH01247504A - Method for degreasing green compact - Google Patents

Abstract

PURPOSE:To prevent the adsorption of gas generated by the decomposition of an org. binder on a green compact and to uniformly remove the org. binder by embedding the green compact in activated carbon powder and degreasing the compact by heating. CONSTITUTION:A mixture consisting of 5-15wt.% binder based on a thermoplastic polymer and the balance metal power, alloy powder, ceramic powder, etc., is kneaded, pulverized and injection-molded or extrusion-molded. The resulting green compact is embedded in activated carbon powder and degreased by heating in an atmosphere of gaseous Ar, etc. Since gas generated by the decomposition of the binder is adsorbed on the activated carbon powder and the compact is held in the powder, the compact can be degreased without deforming even when it has a complex shape.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a green body using injection molding or extrusion molding to obtain a sintered body of metal or ceramics, and particularly relates to a method for manufacturing a green body by using injection molding or extrusion molding. This invention relates to a method of degreasing before binding.

[Conventional technology]

Generally, in the process of manufacturing a sintered body of metal or ceramics, a green compact before sintering is obtained as a green compact by compression molding powder. Since this method usually involves applying pressure with a punch from above and below, the shape of the molded product obtained is limited to relatively simple shapes such as 2 cylinders and 1 cylinder, and it is not possible to produce products with more complex shapes. To obtain this, it is necessary to perform post-processing such as cutting and grinding on the sintered product.

On the other hand, in the field of ceramic products centered on so-called engineering ceramics, green powders with complex shapes are produced by adding raw powder KIO to 20% by weight of an organic binder, mixing and kneading, and then injection molding or extrusion molding. Obtain a molded body and degrease it.

The production of sintered products through a sintering process has begun to be carried out industrially and is attracting attention.

In addition, as typified by the atomization method in recent years.

Significant progress has been made in the development of metal powder molding technology.

Attempts have been made to apply the manufacturing method described above to metals as well.

Injection molding and extrusion molding are methods that have traditionally been applied to mold plastic materials, but because they can produce complex shapes in large quantities with high precision, they can be used to produce metal-ceramic sintered bodies that are impossible with conventional techniques. It has the potential to be able to offer products with the same shape to the market at low cost.

The biggest technical challenge in producing sintered products using this process is the addition of a large amount of organic binder to the powder as mentioned above, so how can this be removed? The question is whether to do so. The most common method for binder removal, ie, degreasing, is to decompose and volatilize the organic binder by heating. When degreasing is carried out by heating, it is necessary to quickly remove the decomposed gas that has volatilized from the green molded object so that it does not adsorb to the surface of the molded object again, so a carrier gas is always flowed around the molded object. There is usually one.

The rate at which the decomposed gas volatilized from the green molded body is adsorbed onto the surface of the molded body again depends on the concentration of decomposed gas around the molded body (tx).
The carrier gas flow rate is set so that the decomposed gas concentration is as low as possible. Therefore, as the number of molded bodies processed increases, the flow rate of the carrier gas increases and the arrangement of the molded bodies also becomes complicated. This is because it is necessary to circulate the carrier gas in such a way that the decomposed gas concentration is sufficiently low at any location between the selvedge molded bodies.

[Problem to be solved by the invention]

However, it is difficult to perform the treatment under substantially uniform conditions, and as a result, the degreasing rate varies greatly among the degreased molded bodies.

In one compact, carbon deposits occur partially due to adsorption of decomposition gas, and the subsequent sintering process can cause deformation such as cracks and defects (yield rate) and product quality. It has become difficult to manufacture.

Therefore, one technical problem of the present invention is to solve the following problems:
It is an object of the present invention to provide a method for degreasing a green molded body, which eliminates the adsorption of the decomposed gas of the organic binder to the green molded body in the degreasing process and uniformly removes the organic binder from the green molded body.

[Means to solve the problem]

According to the present invention, a mixture in which 5 to 15 parts by weight of a binder mainly composed of a thermoplastic polymer is mixed with a metal powder, an alloy powder, or a ceramic powder is kneaded and pulverized, and then injection molded or extruded. After producing a green molded body, in the degreasing method step for a green molded body, the green molded body is completely heated and degreased, the green body is embedded in activated carbon powder, and heat degreased. A degreasing method is obtained.

Namely, the present inventors found that when a green molded body was heated and degreased in a carrier gas, the surface of the brown body discolored unevenly, and this discoloration was largely due to the carbon layer generated by adsorption of decomposition gas. When sintering in this state, it can be seen that the part to which the carbon layer is attached progresses to sintering more than other parts, and as the shrinkage progresses unevenly as a whole, deformation such as cracking occurs. I discovered that this occurs. Therefore, in order to prevent the decomposed gas volatilized from the green molded body from adhering to the surface of the green molded body, we investigated a method for quickly absorbing the decomposed gas. As a result, by heating and degreasing in activated carbon, there is little discoloration on the surface of the brown body, and even in the post-process sintering, the entire sample shrinks uniformly, eliminating deformation such as warping and cracking. This invention is based on the following headings. The amount of activated carbon is not particularly limited, but may be 10 to 11 of the binder amount as long as it is sufficient to absorb the decomposition gas of the binder.
It is preferable to fill the container so that a specific surface area of 105 m2 is obtained. In addition, not all of the decomposition gas that volatilized from the green molded body is adsorbed.

Some of it will emit through the activated carbon, so if it is not removed, the concentration of cracked gas in the furnace will increase.

Therefore, in order to remove this, it is preferable to flow a carrier gas. Although the flow rate of the carrier gas depends on the degreasing rate, it may be relatively small, and may be 5 t/min or less in the case of a furnace with an internal volume of 120 t.

Further, according to the degreasing method of the present invention, adsorption of decomposed gas and holding of the molded body can be performed at the same time, so that even complex-shaped molded bodies can be degreased without deforming them.

〔Example〕

Examples of the present invention will be given below and explained in detail.

An alloy having a composition of Fe 50 wt% - Co 50 wt96 was melted by high frequency heating in an argon gas atmosphere.

A powder with an average particle size of 10 μm was produced by a water atomization method. When the oxygen concentration was analyzed, it was approximately 5.200 ppm.
Met.

Next, the mixture was mixed according to the composition shown in Table 1.

The raw material for injection molding was obtained by kneading and pulverizing.

Below is the margin: Table 1 Next, using this raw material, the temperature was 190℃ and the dirge pressure was 100℃.
Under the condition of 9/crn2, the outer diameter is 50m+ and the thickness is 1■.

Green molded bodies of 2m, 5ms+, and 10+m were produced by injection molding.

These molded bodies were made of activated carbon 1Sgr with a grain size of 350 mesh under and a specific surface area of 1000 m2/, li'.
After embedding in the chamber, an atmosphere was created in which argon gas was flowed at 2 t/min, and the temperature was raised from room temperature to 600°C at a temperature increase rate of 10°C per hour. After being held at 600°C for 2 hours, it was cooled to room temperature. Next, it is placed in a vacuum furnace and heated from room temperature to 200℃ per hour.
The temperature was increased to 1200'C at a temperature increase rate of 1,200'C, held for 10 hours, and then rapidly cooled.

For comparison, a green molded body was placed on an alumina plate, argon gas k 10 L/min was flowed, and heat degreasing and sintering were performed under the same conditions. Table 2 shows the shape of the sintered body and the sintered density at this time.

Below, the shapes of the blank sintered bodies are compared in terms of proportions. As shown in Figure 1, the ratio of the maximum value to the thickness of the sample is expressed as a percentage.

From the results in Table 2, it can be seen that the thinner the thickness, the greater the distortion. However, according to the method of the present invention, the degreasing ratio is 1/1 compared to the conventional heating degreasing in a carrier gas.
You can see that it is 0.

It can be seen that a sintered body with very small deformation can be obtained by the method of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, a sintered body with very small deformation can be obtained by heating and degreasing in activated carbon.

[Brief explanation of the drawing]

FIG. 1 shows measurement positions and calculation formulas for dimensions used to express the proportion of sintered bodies. Figure 1 Shape of sintered body (warpage ratio)

Claims (1)

[Claims] 1) Binder whose main component is a thermoplastic polymer: 5-
A green molded body is produced by kneading and pulverizing a mixture of 15% by weight and the balance being metal powder, alloy powder, or ceramic powder, injection molding or extrusion molding to produce a green molded body, and then heating and degreasing the green molded body. A method for degreasing a green body, characterized in that in the degreasing method step, the green body is embedded in activated carbon powder and degreased by heating.