JP3392889B2 - Raw material composition for sintering and method for producing sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw material composition for sintering which is a mixture of fine metal particles and a thermoplastic binder, and a method for producing a sintered body using the raw material composition for sintering. is there.

[0002]

2. Description of the Related Art Conventional methods for sintering a metal powder to obtain a sintered body having a desired shape can be roughly classified into the following two methods. One is a method that has been practiced for a long time, and is a method in which a powder raw material is pressure-molded and then sintered. The other one is a relatively new technique, in which a thermoplastic raw material composition obtained by mixing a thermoplastic binder with fine particles of the main raw material is molded,
This is a method of sintering after removing the binder from the molded body.

In the latter method, in order to improve the sinterability and increase the sintering density, the main raw material to be mixed with the thermoplastic binder to form the raw material composition for sintering has a particle size of about 4 μm. It is required that the particles be fine particles. By molding the raw material composition for sintering using the main raw material thus finely divided, removing the binder, and then sintering by a known method, a sintered body having high tensile strength and elongation can be obtained. Has been.

[0004]

However, when the main raw material is made into fine particles to a size of about 4 μm, it takes a great deal of cost to make the fine particles itself, and the pressure-molded body of the powder raw material is obtained without performing the above-mentioned fine particles. Compared with the old method of sintering, the production cost of the sintered body increases significantly.

Therefore, there has been a problem that it can be used only for a special purpose which is allowed to increase in cost.

Further, when the thermoplastic binder is mixed with the fine particles of the main raw material and pressure molding is performed, selection of the thermoplastic binder is also an important point related to productivity and production cost.
That is, the thermoplastic binder acts as a factor for exerting a pressing force and a heating temperature required for pressure molding, and also as a factor for facilitating mold release after molding. In the molding process, the higher the required pressurization value and heating temperature, the more costly it is to maintain the environment, and the deterioration of the mold release leads to a decrease in product yield, resulting in a decrease in productivity and production cost. Leading to higher prices.

Therefore, as a thermoplastic binder to be mixed with the fine particles of the main raw material, the pressurizing value and the heating temperature at the time of molding can be kept low, and the mold releasing property is good, and it is easy to perform after molding. It is required to be removable, and it is required to develop a thermoplastic raw material composition based on these.

The present invention has been made in view of the above circumstances, and it is possible to reduce the cost of raw materials and the like, and also to improve the formability and to obtain a sintered body with excellent performance at low cost. An object is to provide a raw material composition for use and a method for producing a sintered body.

[0009]

The raw material composition for sintering according to claim 1 is formed by injection molding the raw material composition for sintering.
Is formed, and the molded body is sintered to obtain a desired shape.
A raw material composition for sintering used for manufacturing a sintered body.
Liquid gallium is added to a mixture of carbonyl iron having a particle size of 5 to 20 μm or less and a thermoplastic binder in an amount of 800 to 50 μm.
It is characterized by containing 00 ppm.

The method for producing a sintered body according to claim 2 is the method for producing a sintered body using the raw material composition for sintering according to claim 1, which comprises the following first step, second step By performing the step and the third step, a sintered body is obtained.

In the first step, a raw material composition for sintering is prepared by adding 800 to 5000 ppm of liquid gallium to a mixture of carbonyl iron, which is a fine metal particle having a particle size of 5 to 20 μm or less, and a thermoplastic binder. Then, injection molding is performed by heating and pressurizing to obtain a molded product having a desired shape.

The second step is a step of removing the thermoplastic binder from the molded body obtained in the first step.

The third step is a step of firing the molded body which has been subjected to the second step in a reducing atmosphere to obtain a sintered body having a desired shape.

[0014]

The raw material composition for sintering according to claim 1 uses inexpensive carbonyl iron particles as fine metal particles, and the particle size of the carbonyl iron particles may be relatively large, so that it is about 4 μm. It becomes possible to provide the raw material composition for sintering at a low cost, as compared with the conventional case using the metal fine particles described above.

Moreover, gallium is a low melting point metal, and liquid gallium added to the raw material composition for sintering improves the fluidity at the time of molding, keeps the pressure value at the time of molding low, and lowers the heating temperature. It produces the effect of suppressing, enables injection molding at low temperature, and facilitates high-quality molding.

Therefore, as described in claim 2, the thermoplastic binder is removed after the raw material composition for sintering according to claim 1 is molded and fired, so that it is baked at low cost with excellent performance. It becomes possible to obtain a union.

[0017]

EXAMPLES First, an example of a sintering raw material composition according to the present invention will be described, and then a method for producing a sintered body using the sintering raw material composition of that example will be described. To do.

The raw material composition for sintering of one example was obtained by adding 1000 ppm of liquid gallium to a mixture of carbonyl iron powder having an average particle size of 10 to 15 μm and a thermoplastic binder.

The thermoplastic binder is a mixture of acrylopolymer and wax in a volume ratio of 60:40. The thermoplastic binder and carbonyl iron are double armed at a volume ratio of 40:60.
Knead in a dispersion type mixer. Then, during the kneading process of this thermoplastic binder and carbonyl iron, 1000 ppm of the above-mentioned liquid gallium was added,
By continuing the kneading treatment at a temperature of 0 to 150 ° C. for 2 hours, a uniformly mixed raw material composition for sintering is obtained.

Next, with reference to FIG. 1, a method for producing a sintered body using the raw material composition for sintering of one example will be described.

First, the first step of heating and pressing the raw material composition for sintering of the above-described embodiment into a rod-shaped compact (green body) by an injection molding machine is performed (step 10).
1).

The molding conditions at the time of injection molding are a pressure value of 116 to 117 Kgf and a heating temperature of 150 ° C., and both the pressure value and the heating temperature are relatively low values, and good molding is possible.

Next, the absorber made of ashless paper is placed in the oven, the green body obtained in the first step is placed thereon, and the temperature of the oven is slowly raised to 200 ° C. Performing a second step of removing the thermoplastic binder from the green body by maintaining the temperature for 3 hours thereafter (step 102).

Then, the green body which has been subjected to the second step is put into a furnace, and the dew point is -59.4 ° C at 1 atm in the furnace.
A reducing atmosphere is created by introducing the hydrogen gas. And, in this reducing atmosphere, the temperature inside the furnace is 750 ° C.
After the temperature is raised to 3 ° C and held for 3 hours, the third step of cooling to room temperature to obtain a rod-shaped sintered body is performed (Step 1
03).

The raw material composition for sintering of the above-mentioned embodiment uses inexpensive carbonyl iron particles as the metal fine particles, and the particle size of the carbonyl iron particles may be relatively large, so that it is up to about 4 μm. It becomes possible to provide the raw material composition for sintering at a low cost as compared with the conventional case using the metal fine particles.

Further, gallium is a low melting point metal, and liquid gallium added to the raw material composition for sintering improves the fluidity at the time of molding, keeps the pressure value at the time of molding low, and lowers the heating temperature. It produces the effect of suppressing, enables injection molding at low temperature, and facilitates high-quality molding.

Since the thermoplastic binder made of acrylopolymer and wax can be easily removed by heating at about 200 °, it becomes possible to obtain a sintered body with excellent performance at low cost.

The inventor of the present invention variously changes the particle size of carbonyl iron, the addition amount of liquid gallium, the mixing ratio of carbonyl iron and the thermoplastic binder, and the like, under various conditions of the above-described embodiment. Then, the production of the raw material composition for sintering and the production of the sintered body were repeatedly tested, and the results were evaluated.

As a result, the following was found.

As the carbonyl iron particles, it is preferable to use particles which are as uniform as possible, but the particle diameter is 5 to 20.
When the thickness was in the range of μm, it was possible to confirm the same action and effect as in the example.

Further, generally, as the particle size of the raw material composition becomes smaller, the total free energy per unit volume derived from the interfacial energy between the metal fine particles and the thermoplastic binder increases. However, on the other hand, as the particle size decreases, the amount (capacity) of particles that can be contained in the raw material composition decreases, and the degree is determined by the value of the total free energy described above. Until now, it has been said that the mixing ratio of the fine metal particles and the thermoplastic binder in the raw material composition is preferably about 45:55 by volume.

However, as in the present invention, when the thermoplastic binder composed of acrylopolymer and wax is mixed with carbonyl iron, the mixing ratio of carbonyl iron is 5 by volume.
It can be in the range of 5 to 65% by volume, and removal of the thermoplastic binder after molding can be facilitated as much as the mixing ratio of the thermoplastic binder is reduced.

Although the amount of liquid gallium added was 1000 ppm in the above-mentioned embodiment, the effect of suppressing the pressure value and heating temperature during injection molding is 8
Good confirmation was possible even in the range of 00 to 5000 ppm.

For reference, the experimental data are as follows. When gallium is not added, the pressure value is 140 Kgf and the heating temperature is 1
Although the temperature was 50 ° C, the amount of gallium added was 3000
In the case of ppm, the pressurization value is 71 to 99 Kgf, the heating temperature is 143 to 145 ° C., and the addition amount of gallium is 5
In the case of 000 ppm, the pressurization value was 79 to 85 kgf and the heating temperature was 148 ° C. at 148 ° C. When the amount of gallium added is less than 800 ppm, the effect of fluidity at the time of molding disappears, and when it is more than 5000 ppm, there is no difference in effect compared with the case of addition of 4000 to 5000 ppm. However, the increase in raw material cost due to the increase in the amount of added gallium is a burden.

Therefore, the amount of gallium added is 800 to 5
It is considered appropriate to set it to 000 ppm.

FIG. 2 compares the fluidity of the sintering raw material composition containing 3000 ppm of gallium and the sintering raw material composition containing no gallium. In the figure, the vertical axis represents the flow value (ml / sec) showing the fluidity, the horizontal axis represents the heating temperature (° C), and the solid curve F1 represents gallium 30.
The flow characteristics of the sintering raw material composition when adding 00 ppm, and the broken line curve F2 shows the flow characteristics of the sintering raw material composition without addition of gallium.

Further, in the above-mentioned one embodiment, a mixture of acrylopolymer and wax in a volume ratio of 60:40 was used as the thermoplastic binder, but the thermoplastic binder is one of the embodiments. It is not limited to the one disclosed in the above, and a known thermoplastic binder may be used.

[0038]

The raw material composition for sintering according to claim 1 is
Since inexpensive carbonyl iron particles are used as the metal fine particles, and the particle size of the carbonyl iron particles may be relatively large, it can be used for sintering as compared with the conventional case of using the metal fine particles up to about 4 μm. The raw material composition can be provided at low cost.

Moreover, gallium is a low melting point metal, and the liquid gallium added to the raw material composition for sintering improves the fluidity at the time of molding, keeps the pressure value at the time of molding low, and lowers the heating temperature. It produces the effect of suppressing, enables injection molding at low temperature, and facilitates high-quality molding.

Therefore, as described in claim 2, by removing the thermoplastic binder after molding the sintering raw material composition according to claim 1 and firing, the firing is performed at a low cost and with excellent performance. It becomes possible to obtain a union.

[Brief description of drawings]

FIG. 1 is a process explanatory view of an example of the present invention.

FIG. 2 is an explanatory diagram of flow characteristics depending on whether gallium is added to the raw material composition for sintering.

[Explanation of symbols]

101 First step 102 Second step 103 Third step

Claims (2)

(57) [Claims] 1. A molding is produced by injection molding a raw material composition for sintering.
Formed and sintered this molded body to obtain the desired shape
A raw material composition for sintering, which is used for producing a bonded body.
Then , liquid gallium is added to a mixture of carbonyl iron having a particle size of 5 to 20 μm or less and a thermoplastic binder at 800 to 5000 pp.
A raw material composition for sintering, characterized by containing m. 2. The method for producing a sintered body using the raw material composition for sintering according to claim 1, wherein the particle size of the fine metal particles is 5
˜20 μm or less of carbonyl iron and a thermoplastic binder, the raw material composition for sintering containing 800 to 5000 ppm of liquid gallium is injection- molded by heating and pressurizing to obtain the desired composition. A first step of obtaining a molded article in the shape of, a second step of removing the thermoplastic binder from the molded article obtained by the first step, and a molded article that has undergone the second step are fired in a reducing atmosphere. And a third step of forming a sintered body having a desired shape.