JP2691440B2 - Method of manufacturing sintered metal powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECT OF THE INVENTION [Industrial field of use] The present invention utilizes injection molding or extrusion molding of a press-molded body to form a sintered body by pressing and sintering a metal powder composed of a metal or an alloy. The present invention relates to a method for producing a metal powder sintered body, which is formed by molding and uses high-frequency induction heating as a degreasing and sintering method for the molded body.

[Conventional technology]

Generally, in a method for producing a sintered body by using a metal powder made of a metal or an alloy, a green body before sintering obtains a green compact by compression molding the powder. When forming a green compact, a die is usually used and pressure is applied by a punch from the top and bottom, so the shape of the resulting compact is limited to a cylinder or a relatively simple shape such as a cylinder. Therefore, in order to obtain a product having a more complicated shape, it is necessary to perform processing such as cutting and grinding on the sintered body just after sintering to obtain a product.

In recent years, there have been significant developments in the production technology for metal powders, as represented by the atomization method, in the method for producing a metal sintered body, a metal or alloy powder is mixed with an appropriate amount of an organic binder, and kneaded, After crushing, a method of obtaining a molded product having a complicated shape by injection molding or extrusion molding, and performing a degreasing and a sintering process to obtain a product has started to be used and has been drawing attention.

The injection molding method and the extrusion molding method have been conventionally applied to the molding of plastic materials, but since complex shapes can be mass-produced accurately and in large quantities, an organic binder is added to the metal or alloy powder. The sintered body formed by degreasing and sintering after shaping can be provided to the market at a low cost with a shape that cannot be obtained by the conventional method.

And the biggest technical problem in manufacturing a sintered product by such a manufacturing method is that a molded product by injection molding or extrusion molding has a large amount of organic binder added to metal or alloy powder. So, how to remove this? The removal of the organic binder has heretofore been a general method in which the organic binder is decomposed and volatilized and scattered by heating from the periphery of the molded body by resistance heating or the like. However, the conventional method of flowing the carrier gas while heating the periphery of the molded body, and heating the molded body by resistance heating to remove the binder is to reduce the temperature distribution of the molded body at the time of heating in the case of a thin shape or a small shape. Although a uniform sintered body can be obtained without making such a difference, the temperature distribution changes greatly when debinding the thick-walled or large-shaped compact, and there is a difference in temperature between the inside and the surface of the sample. This causes a difference in how the binder is removed during the degreasing process. Therefore, the degreasing becomes non-uniform, the degreasing rate varies depending on the location of the sample, and warpage and cracks also occur in the sintering in the subsequent process, which makes it difficult to manufacture products with high yield. was there.

[Problems to be solved by the invention]

In order to eliminate these problems, the present invention uses an induction heating method during degreasing by heating, so that metal powders of 95 to 86 can be obtained.
Injection molding with the balance being organic polymer as the main component in weight%,
Alternatively, in a molded product formed by extrusion molding, the molded product is placed in a graphite boat, and the molded product is embedded in carbon powder or graphite powder, and the molded product is a metal powder molded product by high frequency induction heating, and a graphite boat and carbon. Heating the powder to a heat source,
By thermally decomposing the organic binder, it is possible to uniformly degrease even thick-walled or large-shaped ones to the inside, and to obtain a uniform sintered body in the subsequent sintering step.

B. Structure of the Invention [Means for Solving the Problems] The present invention provides a molded body made of injection-molded or extrusion-molded metal or alloy powder and an organic binder at 150 ° C. or higher.
Degreasing performed at 00 ° C, and the method by induction heating at the time of subsequent sintering are used. The binder added by the metal powder of metal or alloy powder is 95 to 86% by weight, and the balance is mainly composed of organic polymer. Forming a molded body composed of a binder, and burying the molded body in carbon powder, and by electromagnetic induction by high frequency induction heating of 100 KHZ to several hundred KHZ, metal powder, carbon powder, or graphite powder and graphite in the molded body By generating an eddy current in the boat, Joule heat is generated in the molded body, which is used as a heat source to thermally decompose the binder,
Debinding is performed to enable uniform degreasing even in a molded body having a thick wall and a complicated shape. Further, sintering is performed to obtain a uniform sintered body.

That is, the present invention, the metal powder is 95 to 86% by weight, the remainder is an injection molded body consisting of a binder containing an organic polymer as a main component, or an extrusion molded body is installed in a graphite boat, carbon powder around the molded body, or Metal powder characterized by being covered with graphite powder, degreased by heating at a temperature of 150 ° C to 600 ° C in a non-oxidizing atmosphere by high frequency induction heating, and then sintered at a temperature of 1000 ° C to 1300 ° C in a reducing atmosphere. It is a method for manufacturing a sintered body.

[Action]

The present invention adds an organic polymer binder consisting of paraffin wax, polyethylene, dioctyl phthalate to metal powder of metal or alloy without requiring complicated machining to obtain a metal sintered body having a complicated shape. , Kneading, crushing and injection molding or extrusion molding to make a molded body,
After degreasing, sintering is performed to obtain a metal sintered body having a complicated shape. Degreasing is performed at 150 ° C to 600 ° C and subsequent sintering is performed by using high frequency induction heating.

Conventionally, degreasing was performed by resistance heating, but in thick samples, the binder is not uniform between the center and the surface in the thickness direction, causing warpage and bending of the sintered body, and swelling in the center of the thickness. Therefore, there were problems such as middle and high school.

The present invention, a molded body of an organic polymer and a metal powder is installed in a graphite boat, the molded body is covered with carbon powder, or graphite powder, the entire molded body is uniformly heated by high frequency induction heating,
Degreasing is performed, and thereafter, sintering is similarly performed.

In the present invention, the mixing ratio of the organic polymer of the binder and the metal powder is preferably 95% by weight to 86% by weight in terms of the specific gravity ratio of the metal powder. In this case, when the mixing ratio of the metal powder is 95% by weight or more, injection molding becomes difficult, and when it is 86% by weight or less, the shape after degreasing often has defects, which makes it unpractical. The mixing ratio of 95% by weight or
86% by weight. When performing high-frequency induction heating, the diameter of 30 mmφ of the embodiment of the present invention, the output of 5 KW for the sample with a thickness of 20 mm,
I used a transmitter for high frequency induction heating with an excitation frequency of 100 KHZ, but I chose the excitation frequency in the range of 50 KHZ to several hundred KHZ.
Can be put to practical use. Degreasing is performed by a slow temperature rise of about 10 ° C / hour. Since the thermal decomposition of the organic binder is almost completed at around 600 ℃, it was limited to 600 ℃. The degreasing start temperature was around 150 ° C, and the lower limit temperature during degreasing sintering was 150 ° C. Sintering was carried out at 1250 ° C. in a high-purity hydrogen gas atmosphere in the examples of the present invention, but vacuum sintering may also be used, and depending on the required magnetic properties and mechanical strength, the sintering temperature may be 1000 ° C. or higher. Good, maximum temperature is 13
00 ° C is enough. However, the sintering temperature varies depending on the sintering temperature of the metal powder, and when sintering the metal powder having a low melting point, it is natural that the sintering temperature is lower than that of the embodiments of the present invention.

〔Example〕

Fe with an average particle size of 10 μm produced by the water atomization method
An alloy powder having a composition of 50% by weight and 50% by weight of Co was mixed with the composition shown in Table 1, kneaded and pulverized to obtain a raw material for injection molding.

Next, using this raw material, injection molding was performed at a temperature of 160 ° C. to produce cylindrical molded bodies having an outer diameter of 30 mm and thicknesses of 2 mm, 10 mm, and 20 mm. These samples were placed on the graphite boat 8 having a thickness of 10 mm by the high frequency induction heating device shown in FIG.
The surrounding area is covered with activated carbon powder 9, and argon gas is caused to flow from the carrier gas inlet port 2 to the carrier gas outlet port 3 at a rate of 2 liters / minute, and a high frequency induction heating device with an output of 5 KW and an excitation frequency of 100 KHZ is installed. Use from room temperature to every hour
The temperature is controlled through the temperature observation window 5 while sensing the temperature from the optical thermometer 4 so that the temperature rise rate is 10 ° C.
The temperature was raised to 600 ° C., the temperature was maintained at 600 ° C. for 2 hours, and then cooled to room temperature to prepare a binder-free sample. For comparison, a sample was prepared by debinding under the same conditions using resistance heating. Then, each sample prepared using the induction heating method and the resistance heating method was heated in a high-purity hydrogen gas from room temperature to 1250 ° C. at a heating rate of 100 ° C./hour and sintered for 10 hours. The furnace was cooled.

Table 2 shows the result of the impurity analysis after degreasing due to the difference in the size of each molded body.

Looking at this, regarding the sample degreased using the induction heating method according to the present invention, in the impurity content due to the difference in thickness,
Although no difference is observed, it can be seen that when the resistance heating method of the comparative example is used, the content of impurities increases as the thickness obviously increases. Also, as shown in Fig. 2, 30 mmφ x 20 mm
The thickness of the molded body was degreased by the degreasing method using high frequency induction heating and resistance heating, and the sample was divided into three parts in the thickness direction, and the results of impurity analysis were shown. According to this, when the induction heating method was used, a partial difference in the impurity content was not shown, but when the resistance heating method by the conventional method was used, the central portion of the sample was clearly removed. It has been shown to be bad.

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

In Table 3, examples of the invention are degreasing by induction heating,
The sintered product and the comparative example were degreased and sintered by resistance heating. As the sample becomes thicker, the relative density tends to be slightly smaller, but when the present invention and the comparative example are compared, the comparative example has a higher thickness dependency, and
The relative density was also reduced by 2-3%. Also, in the appearance of the sintered body, according to the present invention, as shown in Table 3, no deformation cracks were found in the sintered body, but in the comparative example, the center portion of the sample had a moderately high warp. Deformation was observed, and the thicker the wall, the greater the degree of deformation. Therefore, by using the induction heating method for degreasing, the metal or alloy powder constituting the molded body itself serves as a heat source and can be uniformly degreased,
It is considered that, as a result, the relative density of the sintered body increased and a good sintered body with almost no deformation was obtained. In the present invention, the weight ratio of the organic polymer binder added to the metal powder and the alloy powder is 5 times the organic polymer binder.
If it is less than 10% by weight, injection molding or extrusion molding is difficult,
If the amount exceeds 14% by weight, the shape formed during degreasing will collapse and a normal degreased product will not be obtained, and the amount of the binder containing an organic polymer as a main component is 5 to 14% by weight.
Moreover, the frequency of the high frequency induction heating device is several tens of KHZ or several hundreds of K.
It suffices to select between frequencies between HZ and output in the embodiment.
A high-frequency oscillator with 5KW and an excitation frequency of 100KHZ was used.

C. Effects of the Invention As described above, according to the present invention, the graphite boat in which the compact is embedded by using the high-frequency induction heating method for heating and degreasing, the graphite powder, the carbon powder center is heated, and the metal of the compact, Alternatively, debinding is performed so that the alloy powder itself serves as a heat source, so that degreasing is performed uniformly. After that, when the degreased body is similarly sintered at 1250 ° C. in hydrogen gas, the sintered density is improved, and warpage and deformation can be almost eliminated. Therefore, it is possible to provide a sintered body having a high sintering density and no deformation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a degreasing and sintering furnace by 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 shape of 30 mmφ × 20 mm thickness. 1 ... High-frequency oscillator with power controller, 2 ... Carrier gas inlet, 3 ... Carrier gas outlet, 4 ...
Light thermometer, 5 ... Temperature observation window, 6 ... Furnace body, 7 ... Sample, 8 ... Graphite boat, 9 ... Carbon powder or graphite powder.

Claims (1)

(57) [Claims] 1. An injection-molded body or an extrusion-molded body comprising 95% to 86% by weight of metal powder with the balance being a binder containing an organic polymer as a main component is placed in a graphite boat, and the periphery of the molded body is carbon powder, or After covering with graphite powder and degreasing by heating at a temperature of 150 ℃ to 600 ℃ in a non-oxidizing atmosphere by high frequency induction heating, 1000 ℃ to 1300 ℃ in a reducing atmosphere.
A method for producing a metal powder sintered body, which comprises sintering at a temperature of.