JPH0770610A - Method for sintering injection-molded product - Google Patents

Abstract

PURPOSE:To maintain shape retentivity and to enhance the quality of a sintered product by carrying out temporary sintering after satisfactory dewaxing when a sinterable injection-molded product is sintered. CONSTITUTION:When an injection-molded product based on sinterable powder of a metal, ceramic, etc., is sintered, the green body is satisfactorily dewaxed at >=95% dewaxing rate and temporarily sintered in an atmosphere at a temp. between the dewaxing temp. and sintering temp. Satisfactory shape retentivity for sintering work can be maintained, pores and defects are eliminated by the satisfactory dewaxing and sintering not producing high pressure of gas is enabled. A high quality sintered product is obtd. and the contamination of a furnace can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a sinterable powder such as metal or ceramic as a material, and injection-molds the powder to obtain a green body, which is then sintered to form a molded product such as a sintered part. To densify and improve the strength of the sintered body by sintering, prevent pore defects, improve the target chemical composition and properties, and prevent contamination of the sintering furnace. With the goal.

[0002]

2. Description of the Related Art As a manufacturing process of a sintered product using powders of metal, ceramics, etc., generally, a raw material powder that can be sintered is mixed with approximately the same amount of a binder, and the mixture is heated and kneaded. → Granulation → Pellet → Injection molding → Green body → Degreasing → Degreasing body → Firing → Product order. That is, when a green body is manufactured by the injection molding method, the raw material powder is wrapped in a binder having substantially the same volume as that of the green body powder to impart fluidity, and then injected into each molding die.

The green body obtained by the above process is then subjected to a binder degreasing step, but at that time, the green body (degreased body) becomes brittle and easily broken, and a sintering operation in a later step is performed. Therefore, the following degreasing method is known as a method for controlling the degreasing conditions to leave a small amount of binder in the green body in order to keep the strength of the green body constant.

That is, one of them is the "heat degreasing method" which utilizes the heat decomposition property of the binder. This is a method in which about 5 to 13% of the binder remains in the green body by gradually heating and holding the green body to the decomposition evaporation temperature, and the remaining binder is removed from the molded body. The other is known as a "solvent extraction method" which has a lower temperature and an extremely shorter degreasing time than the heat degreasing method. This is because the binder is degreased by being decomposed by the organic solvent in an organic solvent such as methylene chloride or in vapor, and in this case as well, about 5 to 13% of the binder remains in the green body.

[0005]

However, in the case of the above-described conventional degreasing method, it is necessary to reinforce the brittleness of the green body and maintain a certain shape retention property for sintering, but the residual If the amount of binder is too large, in the sintering process, firstly, gas is generated by the binder, and pore defects remain in the sintered body, and secondly, sintering becomes impossible due to a large gas pressure, resulting in a dense It is difficult to obtain a sintered body.

Thirdly, the elements (particularly carbon) in the binder are partly solid-dissolved or compounds such as carbides are formed, and as a result, they are unavoidably removed from the components or deteriorated in quality. Fourthly, there is a problem that the sintering furnace is contaminated by the evaporative gas and the function of the furnace is deteriorated.

[0007]

Therefore, the present invention solves the above-mentioned various problems in the prior art, maintains sufficient shape retention so as not to lose the shape when the green body is sintered, and It is intended to eliminate porosity defects, obtain dense and high-quality products, and prevent contamination and deterioration of function of the sintering furnace. In the case of sintering an injection molded product whose main material is a sinterable powder, the injection molded green body is sufficiently degreased with a degreasing rate of 95% or more before sintering, and then this is continuously degreased at a temperature of not less than Further, the present invention relates to a method for sintering an injection-molded article, characterized in that the particles are bonded together by pre-sintering in an atmosphere at a temperature not higher than the sintering temperature to maintain sufficient shape retention of the green body.

[0008]

[Function] After the green body is sufficiently degreased, the green particles are subsequently pre-sintered in an atmosphere at a temperature not lower than the degreasing temperature and not higher than the sintering temperature, whereby mutual adhesion between the powder particles occurs, Sufficient shape retention can be maintained without a binder.

[0009]

EXAMPLES The concrete contents of the present invention will be explained below. First, as an injection molded article, sinterable powder of various metals such as ordinary carbon steel or ceramics is used as a main material, This is kneaded with a binder in an atmosphere of a temperature of 140 to 150 degrees Celsius. In this case, the binder is usually a mixture of acrylic resin and wax in a ratio of 1: 1 and is usually powder 90-97.
The kneading ratio is about 10 to 3 (weight) percent of binder with respect to (weight) percent.

The kneaded product of the powder and the binder is pulverized and granulated into pellets having a diameter of 5.0 mm or less, and further the above-mentioned kneading temperature (1 degree Celsius) is measured by an injection molding machine.
An injection-molded article is obtained at a temperature of about 40 to 150 degrees. As the degreasing step, known degreasing means such as a heat degreasing method or a solvent extraction method may be used, and a method of embedding an injection molded product in alumina powder at an ambient temperature of 300 to 350 degrees Celsius may be considered. The conditions such as degreasing time are not uniform depending on which of the above-mentioned degreasing means is adopted, but it is necessary to set the degreasing rate for the green body to be 95% or more. In the degreased green body, as shown in FIG. 1, all the binders are removed except for the portions where the powder particles are substantially in close contact with each other.

Next, the pre-sintering is carried out after the above-mentioned degreasing step is completed. The calcination is generally performed in a nitrogen gas or a vacuum atmosphere, and the temperature condition of the calcination is, in the case of metal powder, the degreasing temperature (300 degrees Celsius) or higher and the sintering temperature (1 degree Celsius).
It is carried out in an atmosphere having a temperature of 300 ° C. or less.
In this case, as a result of experiments, it became clear that the temperature range of 800 to 900 degrees Celsius is the best calcination temperature. Further, it is sufficient for the pre-sintering time to the extent that sufficient shape retention can be provided so as not to lose the shape before starting the sintering operation in the subsequent step, and usually about 15 to 30 minutes (mi
n). As shown in FIG. 1, only the surfaces of the powder particles are diffused and fixed in the structure of the green body that has been pre-sintered, and the shape is maintained to such an extent that it can withstand the final sintering operation.

Then, the green body that has been pre-sintered is finally sintered. A known sintering furnace can be used for the sintering, and the sintering condition is about 90 to 150 minutes (min) at an ambient temperature of 1300 to 1380 degrees Celsius, and the sintering is completed and the temperature is naturally cooled to room temperature. Completed as a product.

[Experimental Example] Steel type: Stainless steel (SUS304 / C: <0.
08% / Ni: 8.0% / Cr: 18%) Powder: Gas atomized powder, average particle size: 11 microns Molded product: Thrust ring height: 12.7 mm Outer diameter: 60 ^φ Wall thickness: 3.7 mm Specimen plate thickness: 4.1 mm Parallel part width: 8.
0mm Total length: 110mm

Process: Kneading (powder 93.0 (W)%, binder 7.0 (W)%) (140 to 150 degrees Celsius) binder = acrylic resin + wax (1: 1) ↓ pulverization granulation (5.0 mm or less) → Pellet ↓ Injection molding (140 to 150 degrees Celsius) ↓ Degreasing (sample embedded in alumina powder in air) 300 to 350 degrees Celsius 60 to 180 minutes (min) ↓

Temporary sintering (in nitrogen gas or vacuum) 800 to 900 degrees Celsius In this case, the test piece does not move in a degreased state. Temporary sintering time 20-30 minutes (min) ↓

Baking (in vacuum) 1300 to 1330 degrees Celsius Sintering time 120 minutes (min)

[Experimental Results] The results of inspecting the materials of the products obtained based on the above experimental examples are shown below. Tensile strength: 530 N / square millimeter Elongation: 43% Density: 7.83 g / cubic centimeter Relative density: 98% (Melting material density: 8.0 g / cubic centimeter) Shrinkage dimension: Height direction 16% Length / width direction Each 15% dimensional accuracy: ± 0.5% or less

From the above results, it was confirmed that all of the tensile properties, density and dimensional accuracy of the product sufficiently satisfied the targets.

[0019]

As described above, according to the present invention, in the case of sintering an injection molded product whose main material is a sinterable powder such as metal or ceramic, the green body injection-molded before sintering is degreased. Since it is designed to be sufficiently degreased at 95% or more, there is no risk of gas generation by the binder in the sintering process, and no pore defects remain in the sintered body. It becomes possible to obtain a dense sintered body by carrying out the sintering without occurrence of

Further, since the elements (particularly carbon) in the binder are not partly solid-dissolved or compounds such as carbides are not formed, there is no separation of components or deterioration of quality, and moreover, due to vaporized gas. It does not cause contamination of the sintering furnace or deterioration of the function of the furnace. Further, after degreasing, since the preliminary sintering is performed in an atmosphere at a temperature not less than the degreasing temperature and not more than the sintering temperature, the brittleness of the green body before sintering is sufficiently reinforced and the firing is performed. It is possible to maintain a certain degree of shape retention for binding, and it is possible to obtain a high quality sintered product.

[Brief description of drawings]

FIG. 1 is a partially enlarged view of a structure showing a sintering process of an injection molded article according to the present invention.

Claims (1)

[Claims] 1. A green body injection-molded before sintering is sufficiently degreased with a degreasing rate of 95% or more when sintering an injection-molded product mainly made of a sinterable powder such as metal or ceramics. After that, the method for sintering an injection-molded article is characterized by subjecting it to preliminary sintering in an atmosphere at a temperature not lower than the degreasing temperature and not higher than the sintering temperature.