JPH02200703A - Manufacture of metal powder sintered body - Google Patents

Abstract

PURPOSE:To manufacture a sintered body having high sintered density and no deformation by heating and degreasing binder under the state of being coated with graphite powder after kneading and forming metal powder for raw material with organic polymer-made binder, and then, executing sintering at the time of manufacturing the sintered body composed of powdery metal or alloy. CONSTITUTION:Mixed material of 86-95wt.% metal or alloy powder and the balance of organic polymer of paraffin wax, polyethylene, etc., as binder, is sufficiently kneaded to manufacture a green compact 7 having complicate shape with method of injection-molding, extrusion-forming, etc. This green compact 7 is laid on a graphite-made boat 8 and circumference of the green compact 7 is covered with the graphite powder 9, and this is charged into a high frequency induction furnace 6 under non-oxidizing atmosphere and heated at 150-600 deg.C to perfectly degrease the binder composed of the organic polymer in the green compact. Successively, this is heated at 1000-1300 deg.C with the high frequency induction furnace 6 under reducing atmosphere of hydrogen, etc., to sinter the green compact composed of the powdery metal. The metal powder sintered body having high sintered density and no deformation with the sintering is manufactured at high yield.

Description

Detailed Description of the Invention A1 Object of the Invention [Field of Industrial Application] The present invention provides a method for sintering a metal powder made of a metal or an alloy to form a sintered body. The present invention relates to a method for producing a metal powder sintered body, in which a Noss molded body is molded using injection molding or extrusion molding, and high-frequency induction heating is used as a method for degreasing and sintering the molded body.

[Conventional technology]

Generally, in a method for manufacturing a sintered body using metal powder made of metal or an alloy, the green body is obtained by compression molding the powder before sintering. When forming a green compact, a mold is usually used and pressure is applied from above and below with a punch, so the shape of the compact obtained is limited to relatively simple shapes such as cylinders or cylinders. In order to obtain products with more complex shapes, it was necessary to process the sintered compacts by cutting, grinding, etc.

In recent years, there have been remarkable developments in metal powder manufacturing technology, as typified by the atomization method.In the manufacturing method of metal powder sintered bodies, metal or alloy powder is mixed with an appropriate amount of organic binder and kneaded. A method of obtaining a complex-shaped molded body by injection molding or extrusion molding after pulverization, and making it into a product through degreasing and sintering steps has begun to be used and is attracting attention.

Injection molding and extrusion molding methods have traditionally been applied to mold plastic materials, but because they allow complex-shaped products to be produced in large quantities with high precision, organic binders are added to metal or alloy powders. The sintered body formed by molding and sintering can be provided to the market at low cost in shapes that were not possible using conventional methods.

The biggest technical problem in manufacturing sintered products using this manufacturing method is that injection molding or extrusion molding requires adding a large amount of organic binder to metal or alloy powder. The question then becomes how to remove this.

The conventional method for removing the organic binder is to decompose the organic binder by applying heat from the periphery of the molded body using resistance heating or the like, and to vaporize and scatter the organic binder.

However, the conventional method of flowing a carrier gas while heating the periphery of the molded object 2 and heating the molded object by resistance heating to remove the binder does not allow for the temperature distribution of the molded object during heating for objects with thin or small shapes. A homogeneous sintered body can be obtained without much difference in temperature, but when removing the binder from a thick or large molded body, the temperature distribution changes significantly, resulting in a temperature difference between the inside and surface of the sample. This causes a difference in the way the binder is removed during the degreasing process. As a result, degreasing becomes uneven, and the degreasing rate differs depending on the location of the sample. Dimensions, especially in thick parts, become out of order. Also, changes such as warping and cracking occur during the subsequent sintering process, making it difficult to obtain a good yield. There was a problem that it was difficult to manufacture the product.

[Problem to be solved by the invention]

In order to eliminate these problems, the present invention uses an induction heating method when heating Blot fat, and by injection molding or extrusion molding in which the metal powder is 95 to 86% by weight and the remainder is an organic polymer as the main component. The molded body is placed in a graphite boat, and the molded body is buried in carbon powder or graphite powder.

By heating the metal powder compact, graphite boat, and carbon powder using high-frequency induction heating as a heat source and thermally decomposing the organic binder, even thick or large shapes can be uniformly degreased to the inside and thickened. The objective is to obtain a binder-free sintered body with uniform dimensions even in a meat-shaped molded body, and also to obtain a sintered body with uniform dimensions in the subsequent sintering process.

1. Structure of the invention [Means for solving the problem] The present invention is a method of degreasing and sintering a molded body made of injection molded or extruded metal or alloy powder and an organic binder at 150°C or higher and 600°C. In some cases, a method using induction heating is used, and a molded body is formed of a binder to which metal powder of metal or alloy powder is added and the binder is 95 to 86% by weight and the remainder is an organic polymer as the main component,
The compact is immersed in carbon powder, and an eddy current is generated in the metal powder, carbon powder, or graphite powder in the compact and in the graphite boat by electromagnetic induction by high-frequency induction heating of 100KH2 to several hundred KH2. This method generates Joule heat in the molded body, uses it as a heat source to thermally decompose the binder, removes the binder, and obtains a binder-free sintered body with uniform dimensions even in thick and complex shaped molded bodies. be.

That is, in the present invention, an injection molded body or an extrusion molded body made of a binder containing 95 to 86% by weight of metal powder and the balance mainly composed of an organic polymer is placed in a graphite boat, and the molded body is surrounded by carbon powder or Metal powder covered with graphite powder and heated and degreased by high-frequency induction heating at a temperature of 150°C or more and 600°C in a non-oxidizing atmosphere, and then sintered at a temperature of 1000°C or more and 1300°C in a reducing atmosphere. This is a method for manufacturing a sintered body.

[Effect]

The present invention adds an organic polymer binder comprising paraffin wax, polyethylene, or dioctyl phthalate to a metal powder of a metal or an alloy without requiring complicated machining to obtain a metal molded body with a complicated shape. A molded body is made by kneading, crushing, injection molding, or extrusion molding, and after debinding, debinding and sintering, high-temperature sintering is performed to obtain a metal molded body with a complex shape at 150°C. Above 6
Degreasing and sintering performed at 00°C is performed using a sintering method using high frequency induction.

Conventionally, resin sintering for removing binder was performed using resistance heating, but in the case of thick samples, the removal of binder at the center and surface in the thickness direction was not uniform, resulting in warping and bending of the sintered finished product. In addition, there were problems such as a height in the center of the thickness.

In the present invention, a molded body of an organic polymer and metal powder is placed in a graphite boat, the molded body is covered with carbon powder or graphite powder, and the entire molded body is heated uniformly, especially from the inside, by high-frequency induction heating to remove the molded body. It is used as a binder.

In the present invention, the mixing ratio of the organic polymer of the binder and the metal powder is 95% by weight to 86% by weight based on the specific gravity ratio of the metal powder.
Weight percent is preferred. In this case, the mixing cost of metal powder is 95
When it is more than 86% by weight, injection molding work becomes difficult, and when it is less than 86% by weight, defects occur frequently in the shape after degreasing and sintering, making it impractical. Therefore, the mixing ratio of metal powder is 95% by weight. to 86% by weight. When performing high frequency induction heating, the diameter of the embodiment of the present invention is 30 mmφ and the thickness is 20 mm.
For the mnx sample, the output is 5KvJ and the excitation frequency is 100K.
Although a H2 high frequency induction heating oscillator was used, the excitation frequency can be selected in the range of 50KH2 to several hundred KH2 for practical use. In addition, debinding is carried out by slowly increasing the temperature by about 10°C per hour.
2 at a final temperature of 600°C for metal powder containing 50% by weight of C0.
However, the holding temperature must be higher than the recrystallization temperature of the metal powder, and therefore, the holding temperature during degreasing and sintering differs depending on the type of metal. Fe in this example
For a molded body of alloy powder containing 50% by weight and 50% by weight of Co, the temperature may be at most 600°C, and the temperature was limited to 600°C. The starting temperature for degreasing was approximately 150°C, and the lower limit temperature during degreasing and sintering was 150°C.

In the examples of the present invention, high-temperature sintering was carried out at 1250°C in a high-purity hydrogen gas atmosphere, but vacuum annealing may also be used.The high-temperature sintering temperature varies depending on the required magnetic properties and mechanical strength, but it can be performed at a temperature of 1000°C or higher. All you need is a maximum temperature of 130
0°C is sufficient. However, the sintering temperature varies depending on the sintering temperature of the metal powder, and when sintering a metal powder with a low melting point, it is natural that a lower sintering temperature condition than in the embodiments of the present invention is sufficient.

〔Example〕

F with an average particle size of 10 μm produced by water atomization method
An alloy powder having a composition of 50% by weight of e and 50% by weight of cobalt was mixed into the composition shown in Table 1 and cross-milled to obtain a raw material for injection molding.

Table 1 Next, using this raw material, injection molding was performed at a temperature of 160°C, and the outer diameter was 3011 and the thickness was 2I1m, 10am, 20! A cylindrical molded body of Im was produced. These samples were heated to a thickness of 10 Ia using the high frequency induction heating sintering apparatus shown in Figure 1.
11 graphite boat 8, its surroundings were covered with activated carbon powder 9, and argon gas was flowed from the carrier gas inlet 2 to the carrier gas outlet 3 at a rate of 2 liters/min, with an output of 5 KW. Using a high-frequency induction heating device with an excitation frequency of 100 KH2, temperature control was performed while sensing the temperature with an optical thermometer 4 through a temperature observation window 5 so that the temperature rose from room temperature at a rate of 10°C per hour until it reached 600°C. After heating and holding at 600° C. for 2 hours, the mixture was cooled to room temperature to prepare a binder-free sample. For comparison, a sample was prepared in which the binder was removed under the same conditions using resistance heating.

Next, each sample created using the induction heating method and the resistance heating method was heated from room temperature to 1250 °C at a rate of 100 °C per hour in high-purity hydrogen gas, and held for 10 hours to perform sintering. Furnace cooled.

Table 2 shows the results of impurity analysis after degreasing based on differences in the dimensions of each molded product.

Table 2 below shows that when a heat source is used, the center of the sample is clearly more difficult to remove.

Table 3 shows the relative density after sintering in hydrogen gas at 1250°C.

Looking at Table 3, it can be seen that there is no difference in the impurity content due to the difference in thickness for the samples degreased using the induction heating method according to the present invention, but when using the resistance heating method of the comparative example It is clear that the content of impurities increases as the thickness increases. In addition, 30mmφX is shown in Figure 2.
A 20++i+a thick molded body was degreased using high-frequency induction heating and resistance heating, and the sample was divided into three parts in the thickness direction, and impurity analysis was performed.The results are shown below. According to this, when using the induction heating method, there was no difference in local impurity content, but when using the conventional method, resistance heating
: Good Δ: Slight deformation or cracking ×: Deformation, cracking In Table 3, the examples of the present invention were degreased and sintered by induction heating, and the comparative examples were degreased and sintered by resistance heating. As the sample becomes rougher, the relative density tends to decrease slightly, but when comparing the present invention and the comparative example, the comparative example has a higher thickness dependence, and the relative density is also 2 or 2. 3% lower. Also, regarding the appearance of the sintered body.

As shown in Table 3, according to the present invention, no deformation cracks were observed in the sintered body, but in the comparative example, deformation such as warpage was observed in the center of the sample, and the wall thickness increased. Indeed, the degree of deformation has increased. In 1), by using the induction heating method for degreasing, the metal constituting the molded body itself,
Alternatively, it is conceivable that the alloy powder serves as a heat source and can be uniformly degreased, thereby increasing the relative density of the sintered body, resulting in a good product with almost no deformation. In addition, in the present invention, if the weight ratio of the organic polymer binder added to the Kinno-14 powder and the alloy powder is less than 5% by weight, injection molding or extrusion molding is difficult;
If it exceeds 5% by weight, the shape formed during binder removal sintering at 600°C will collapse and a normal sintered body will not be obtained. shall be. Further, the frequency of the high-frequency induction heating device may be selected between several tens of KH7 to several hundred KH2, and in the embodiment, a high-frequency oscillator with an output of 5 KW and an excitation frequency of 100 KH2 was used.

As described above, according to the present invention, the center of the graphite boat, graphite powder, and carbon powder in which the molded body is embedded is heated by using the high frequency induction heating method for thermal degreasing. Since binder removal is performed in such a way that the metal of the compact or the alloy powder itself serves as a heat source, degreasing is performed uniformly. the result,
When the degreased molded body is sintered in hydrogen gas at 1250°C,
The sintered density is improved, and warping, deformation, etc. can be almost eliminated. Therefore, it has become possible to provide a sintered body with high sintered density and no deformation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a degreasing and sintering furnace using induction heating according to the present invention. FIG. 2 is a diagram showing gas analysis values at a position in the thickness direction of a sample having a shape of 30 mmφX 20 m++Jf:. 1. High frequency oscillator with power controller, 2.
...Gear gas inflow, 3.Carrier gas outlet, 4.Light thermometer, 5.Temperature observation window, 6..
Furnace body, 7...Test 8...Graphite boat, 9...Carbon powder or graphite powder. Figure 1

Claims (1)

[Claims] 1. An injection-molded or extrusion-molded body made of a binder containing 95 to 86% by weight of metal powder and an organic polymer as the main component is placed in a graphite boat, and the periphery of the molded body is surrounded by carbon powder or graphite powder. After covering and degreasing by high frequency induction heating at a temperature of 150°C or higher and 600°C or lower in a non-oxidizing atmosphere, it is heated at a temperature of 1000°C or higher in a reducing atmosphere
A method for producing a metal powder sintered body, characterized by sintering at a temperature of 300°C.