JPH0827501A - Powder compacting method - Google Patents

Abstract

PURPOSE:To produce a small-size thin-walled product of complicated shape at a low cost by subjecting pellets, prepared by mixing a binder composed essentially of thermoplastic resin with a metal or ceramic powder, to heating and then to compacting in a die. CONSTITUTION:A sintered compact is produced by compacting a metal powder or a ceramic powder and then sintering the resultant green compact. In the method of producing this sintered compact, a binder composed essentially of thermoplastic resin is mixed with the powder and the resultant mixture is kneaded and pelletized. The resulting pellets are heated in a heating zone 2 using infrared rays and formed into flowable state, and they are then conveyed by means of a conveyor 3 and introduced via an arm 4 into a compacting die 5, where these pellets 1 are compacted into the desired shape. Subsequently, the resultant green compact is cooled and taken out from the die 5 and then degreased and sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding powder in the fields of powder metallurgy and ceramics, and relates to a method for molding a thin and complex molded body which is difficult to manufacture by compression molding of a normal molding method at low cost. .

[0002]

2. Description of the Related Art Usually, in the fields of powder metallurgy and ceramics, products are obtained by the following methods. That is, it is a method of obtaining a metal or ceramic sintered body by adding a small amount of binder to the adjusted raw material powder, compression-molding it into a desired shape using a molding die, and sintering it. It is widely used industrially as the most suitable method for inexpensively mass-producing large-sized sintered bodies. However, the product shape that can be produced by compression molding is limited to a relatively simple shape because it is necessary to fill powder into the compression molding die, and the strength of the resulting molded body is not sufficient, so the strength is maintained. In order to do so, there was a limitation that a certain thickness or more was required. Further, due to the friction between the powder and the inner wall of the mold, the density of each part of the molded body becomes non-uniform, and there is a problem that it is deformed during sintering.

In recent years, a manufacturing method called a powder injection molding method has attracted attention. The powder injection molding method is to add a binder composed of about 10 to 20% by weight of a thermoplastic resin or a plasticizer to a raw material powder, knead the mixture, and then perform injection molding to obtain a molded body, and then perform heating or the like. This is a method of obtaining a metal or ceramic sintered body having a required shape by sintering through a degreasing step of removing the binder. This is an application of an injection molding technique generally used in the field of plastics, and has an advantage that a product having a complicated shape, which is difficult to obtain by general compression molding, can be obtained with high dimensional accuracy and mass productivity. Also, since the molded body contains a large amount of binder as compared with compression molding, the molded body has excellent strength,
The compression molding has an advantage that a product having a thin shape whose shape is difficult to be obtained can be obtained.

However, in injection molding, in addition to the required product parts, a part called a runner or sprue which is a flow path for guiding the kneaded product of the powder and the binder to the product forming part is also molded at the same time. Since the runner and sprue guide the kneaded material to the product-forming portion without delay, it is usually necessary to have a wall thickness of at least 4 mm (gap length of the flow path), which causes the following problems.

[0007] Some parts, such as runners and sprues, which are relatively heavy with respect to the product part, do not become a product, and the yield of the kneaded product decreases, resulting in an increase in cost. In order to eliminate the disadvantage of (1), the runner or sprue is crushed and used again as a raw material for molding. However, the heat history received in the molding machine deteriorates the binder in the kneaded material,
Since the strength of the molded body decreases, the number of times that the runner or sprue can be reused is naturally limited, and this is not a fundamental solution to the problem. Further, in the case of active metal powder, oxidation may proceed due to the heat history of molding, and it may be impossible to reuse the runner and sprue. The molding cycle becomes long and the cost increases. The cost of the molding process is largely determined by the molding cycle. In the case of injection molding, this is determined by the time until the kneaded product is cooled and the strength required for taking out is obtained, so even if the product part of the molded product is thin, it will be necessary to cool the thick runner and sprue. It takes time, and at least 15 seconds or more. On the other hand, the molding cycle of compression molding is several seconds at the maximum, and the cost in the molding process is higher than that of compression molding.

[0006]

SUMMARY OF THE INVENTION An object of the present invention relates to a powder molding method in the fields of powder metallurgy and ceramics, which solves the above-mentioned problems, and particularly, to obtain a product having a small size, a thin thickness, and a complicated shape at a low cost. It is to provide a molding method according to the present invention.

[0007]

According to the present invention, in a method for producing a sintered body by molding and sintering a metal powder or a ceramic powder, a thermoplastic resin is the main component of the powder. Mix and knead the binder to
A molding method characterized in that a molded body is obtained by using granulated pellets and heating the pellets and then compression-molding them in a mold.

[0008]

The present inventor, as a result of extensive studies on the molding method in order to eliminate the above-mentioned drawbacks of the powder injection molding method, has studied a molding method which does not use an injection molding machine while leaving the advantages of the powder injection molding method. As a result, the present invention has been accomplished.

The molding method of the present invention is as follows.
Metal powder or ceramic powder and a binder having an organic polymer as a main component are mixed and kneaded, and a kneaded product is granulated into a size suitable for a desired molded body to prepare pellets. Next, the pellets are heated to make them flowable, placed in a mold, and the kneaded product is filled into a product forming portion in the mold by ordinary compression molding, cooled, and taken out from the mold. .

In the present invention, as compared with ordinary compression molding,
The fluidity of the raw material powder in the mold is excellent, so a compact shaped body can be obtained, and since a large amount of binder is added to the powder compared to compression molding, the strength of the shaped body is improved. An excellent thin molded body can be obtained and the advantages of the powder injection molding method described above can be obtained. Further, in the present invention, the runner and sprue necessary for the powder injection molding method are not required, so that the problem that the cost is higher than that of the compression molding, which is a drawback of the powder injection molding method, is solved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

(Example 1) FIG. 1 is a schematic view of a molding apparatus used in Examples 1 and 2 and Comparative Examples 1 and 2. FIG.
As shown in (1), the pellets 1 kneaded and granulated are heated by the heating unit 2 using infrared rays, and moved by the conveyor 3. An arm 4 is provided for putting the pellets into a compression molding die 5. Figure 2
In the perspective views of the molded products molded in Examples 1 and 2 and Comparative Example 2, the thickness is 0.2 mm and the outside has a box-like shape of 15 × 15 × 10 mm.

Alumina powder having an average particle diameter of 1.2 μm was prepared as a raw material powder, and 7% by weight of low-density polyethylene, 6% by weight of paraffin wax and 1% by weight of dioctyl phthalate were used as a binder for 86% by weight of alumina powder for diffusion. Were mixed with a mixer having a rotary blade of No. 5 and kneaded, extruded and cut at 100 ° C. with an extruder equipped with a φ5 mm die and a cutting mechanism to obtain pellets of φ5 mm × 8.2 mm.

Using this pellet, the pellet shown in FIG. 2 was obtained by heating the pellet to 80 ° C. using the apparatus shown in FIG.

(Comparative Example 1) Using the powder used in Example 1, 3 wt% of a 10 wt% aqueous solution of polyvinyl alcohol was added as a binder to the powder and mixed in an automatic mortar to obtain a molding powder. This powder was examined for compression molding using the compression molding die 5 of FIG. 1, but the shape retention was difficult due to the low strength of the molded body, and a molded body of the desired shape could not be obtained.

From Example 1 and Comparative Example 1, it can be seen that the present invention makes it possible to form a shape that cannot be subjected to ordinary compression molding.

(Example 2) As a raw material powder, an average particle size of 10
Titanium powder of μm was prepared, and 13% by weight of paraffin wax as a binder was mixed with 87% by weight of titanium powder with a mixer having a rotary blade for diffusion, and the extruder was equipped with a φ5 mm die and a cutting mechanism. By kneading, extruding and cutting at 100 ° C., pellets of φ5 mm × 8.2 mm were obtained.

Using the pellets, the pellets were heated to 80 ° C. by using the apparatus shown in FIG. 1 and compression-molded with a mold 5 which gives a molded article as shown in FIG. 2 to obtain a molded article.

The temperature of this molded body was raised at 50 ° C./hr to 30
Degreasing by holding at 0 ℃ for 2 hours, then 1100
Sintered at ° C. Degreasing and sintering were performed in vacuum. When the oxygen analysis of the obtained sintered body was performed, it was 700 ppm.

Comparative Example 2 Molding powder was obtained by mixing 2 wt% of liquid paraffin with 98 wt% of titanium powder used in Example 2 in an automatic mortar. This powder was examined for compression molding using the compression molding die 5 of FIG. 1, but the shape retention was difficult due to the low strength of the molded body, and a molded body of the desired shape could not be obtained.

Next, the pellets produced in Example 2 were injection-molded at 120 ° C. by using an injection-molding die which can obtain the molded body shown in FIG. The sprue and runner of the obtained molded product were disintegrated and injection molded again under the same conditions. The box-shaped product portion of the obtained molded body was degreased and sintered in the same manner as in Example 2 to obtain a sintered body. When the oxygen analysis of the obtained sintered body was performed, it was 2000 ppm.

From Example 2 and Comparative Example 2, it can be seen that the present invention makes it possible to form a shape that cannot be subjected to ordinary compression molding. Further, when the powder injection molding method is applied to the active metal powder, it is difficult to reuse the runner and the sprue, and it can be seen that the cost such as the raw material powder cost is significantly increased as compared with the present invention.

Although alumina powder and Ti powder were used as the raw material powders in this embodiment, it is clear that other ceramic powders or metal powders can also be applied.

Various kinds of thermoplastic resins, which are the main components of the binder, can be applied. For example, various polyolefins and various acrylic resins can be applied, and waxes and plasticizers can be used as required. Is.

With respect to the amount of binder added in the present invention, if the amount is small, the fluidity required for filling the mold cannot be obtained, or the required molded body strength cannot be obtained. At the same time, a large amount of binder decomposition gas is generated, which causes a defective appearance such as swelling in the sintered body. The amount of the binder added varies depending on the particle size of the powder used, the particle size distribution, and the shape, and is about 20 to 55% by volume of the powder, preferably 30 to 5%.
It is about 0% by volume.

[0026]

As described above in detail, according to the present invention, it is possible to obtain a thin molded article having a complicated shape which is difficult to manufacture by the compression molding of the ordinary molding method, and the molding cost thereof is powder injection molding. Much lower than the conventional method, the molding according to the present invention has a great effect of high added value and cost reduction by increasing the degree of freedom of the product shape as compared with the conventional method, and is extremely important industrially.

[Brief description of drawings]

FIG. 1 is a schematic view of a molding apparatus according to Examples 1 and 2 and Comparative Examples 1 and 2.

FIG. 2 is a perspective view of molded bodies molded in Examples 1 and 2 and Comparative Examples 1 and 2.

[Explanation of reference symbols] 1 pellet 2 heating unit 3 conveyor 4 arm 5 (compression molding) mold

Claims (1)

[Claims] 1. Molding metal powder or ceramic powder,
In a manufacturing method for obtaining a sintered body by sintering,
Mixing a binder containing a thermoplastic resin as a main component with respect to the powder, kneading, and heating pellets produced by granulation,
A method for molding powder, comprising compression molding in a mold.