JPH06172808A - Production of metal powder injection-molded article - Google Patents

Abstract

PURPOSE:To obtain a sintered compact in which a metal powder is uniformly distributed and having higher dimensional precision. CONSTITUTION:A mixture of metal powder and binder is injection-molded, debindered and then sintered to produce a metallic product. In this case, a mixture of the depolymerizable polymer and random-decomposable polymer having a small m.p. difference is used as the main component of the binder, the depolymerizable polymer is firstly decomposed in an org. solvent and extracted, then the random-decomposable polymer is heated in an inert gas or nitrogen atmosphere, and the molded body is debindered. Polybutylene terephthalate is used as the depolymerizable polymer and PP as the random- decomposable polymer. Since the polybutylene terephthalate is depolymerized with ethylene glycol and simultaneously extracted, it is optimally used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal powder injection-molded article, and more specifically, to devise a composition of a binder to be used.

[0002]

2. Description of the Related Art A conventional metal powder injection-molded article is one in which 40 to 50% by volume of a binder is added to a metal powder, and the binder is swollen or cracked in a binder removing step. For the purpose of preventing the occurrence of defects, for example, a mixture of a wax having a melting point of 40 ° C to 60 ° C and a resin having a melting point of 140 ° C to 160 ° C was used.

[0003]

However, since the binder is a raw material having a very large melting point difference with a melting point difference of 100 ° C. to 120 ° C., it is heated and has fluidity during injection molding. The kneaded product is filled in the mold while being cooled and solidified, but there is a difference in solidification speed between the high melting point component and the low melting point component. For this reason, the kneaded material to be replenished at the holding pressure stage has a particularly large amount of binder having a low melting point component, and has a composition having a small amount of high melting point component and metal powder. Therefore, as a result of the small amount of metal powder in the vicinity of the gate portion as shown in FIG. 1, there is a difference in the content ratio of metal powder in each part of the molded body. The shaped body in which the metal powder is unevenly distributed in this way becomes a sintered body that is deformed when the binder is removed and sintered.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to obtain a sintered body having a desired shape by equalizing the metal powder content in each part of the molded body. It is intended.

According to the present invention, when a mixture of a metal powder and a binder is injection molded, debindered, and then sintered to produce a metal product, a depolymerization type polymer and a random polymer having a relatively small melting point difference are used. Using a mixture with a decomposable polymer as the main component of the binder, in the binder removal step, the depolymerization type polymer is first extracted while decomposing it in an organic solvent, and then the random decomposition type polymer is placed in an inert gas or nitrogen atmosphere. It is characterized in that the binder is removed by extracting while being heated at.

As the binder used in the present invention, polybutylene terephthalate can be used for the depolymerization type polymer, and polypropylene can be used for the random decomposition type polymer. Polybutylene terephthalate can be depolymerized with ethylene glycol at the same time. It is optimal because it can be extracted.

[0007]

When the kneaded body is press-fitted into the mold by using an injection molding machine, the outside of the kneaded body is filled while being cooled by the mold. If the cooling is further continued, the inside is also cooled and the volume shrinks, but since the injection pressure is constantly applied to the kneading body, the shrinkage can be replenished from the gate portion. At this time, since the difference in melting temperature between the depolymerization type polymer, which is the main component of the binder, and the random decomposition type polymer is relatively small, the kneaded body to be replenished has a composition almost equal to that of the initial stage of press-fitting even in the latter stage of press-fitting Is.

The sufficiently cooled kneaded body is taken out of the mold to obtain a molded body. The molded body is a depolymerized polymer which is a component of the binder, and becomes a porous molded body when decomposed and extracted in an organic solvent, but the random decomposed polymer is
Since it exists without reacting with the organic solvent, it is possible to handle while maintaining the retention.

The porous molded body decomposed and extracted is heated in an inert gas or a nitrogen atmosphere to prevent the remaining powder of the random decomposition type from being debindered in order to prevent oxidation of the metal powder. Since the temperature rising rate at this time is a large number of pores penetrating the molded body, even if the temperature is raised at a rate of 60 degrees Celsius per hour, defects such as cracks and swelling do not occur. is there.

When the temperature is further raised and sintered after the binder removal is completed, there is almost no difference in the content ratio of the metal powder in each part of the molded body at the time of molding, so that the sintered body is not deformed and the dimensional accuracy is improved. An excellent sintered body can be obtained.

[0011]

Example: Carbonyl iron powder having an average particle diameter of 4.8 microns was used as 100 parts by weight, polybutylene terephthalate (melting point 225 degrees Celsius) was used as 6 parts by weight, and polypropylene (melting point 170 degrees Celsius) was used as 2 parts by weight as a main binder. Using 0.3 part by weight of stearic acid as a lubricant, kneading was performed for 30 minutes with a pressure kneader heated to a kneading temperature of 240 degrees Celsius. The obtained kneaded body was cooled and then pulverized to a size of about 5 mm to prepare pellets. The obtained pellets were put into an injection molding machine at an injection temperature of 250 degrees Celsius and an injection pressure of 1300 kilograms / square centimeter to obtain 90 degrees Celsius.
It was pressed into a mold which was kept warm, cooled sufficiently, and taken out to obtain a molded product having a shape as shown in FIG.

The molded body was immersed in ethylene glycol heated to 100 degrees Celsius for 8 hours to complete primary degreasing of polybutylene terephthalate while successively performing depolymerization and extraction. At this time, the molded body was obtained by extracting 66% by weight of all binders.

The primary degreased compact was heated to 4 degrees Celsius for 3 hours in a nitrogen atmosphere of 50 Torr using a degreasing and sintering furnace.
The temperature was raised to 50 ° C., and the temperature was kept at 450 ° C. for 2 hours to complete the secondary degreasing of polypropylene. After that, while maintaining a vacuum inside the furnace, the temperature is 135 degrees Celsius at a rate of 200 degrees Celsius per hour.
The temperature was raised to 0 ° C., held for 2 hours, and then cooled to obtain a sintered body.

The dimensions of the obtained sintered body were the same in both the portion 4 near the gate and the portion 5 apart from the gate shown in FIG.

[0015]

The present invention has the following remarkable effects. 1) Since the main component of the binder is a resin polymer, the strength of the molded body is very high and the handling is easy. 2) The depolymerized polymer is decomposed and extracted in an organic solvent to make the molded body porous, so that the heating and degreasing step is completed in a very short time. 3) Since degreasing is performed in two steps: degreasing in an organic solvent and degreasing in an inert gas or nitrogen atmosphere, the metal powder is completed without oxidation, and there is no need for reduction in a dangerous hydrogen atmosphere during sintering. 4) It is possible to prevent uneven distribution of metal powder in various parts of the molded body in the injection molding process, and to manufacture a metal powder injection molded product with high dimensional accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing uneven distribution of metal powder in a conventional technique.

[Fig.2] Outline drawing of the test piece for dimension measurement

[Explanation of symbols]

 1-Gate 2-Burr 3-Metallic powder 4-Dimensions near the gate 5-Dimensions away from the gate

Claims (4)

[Claims] 1. A depolymerizable polymer and a random decomposition type polymer having a relatively small melting point difference when a metal product is manufactured by injection-molding a mixture of a metal powder and a binder, debindering the mixture, and then sintering the mixture. Using a mixture with a polymer as the main component of the binder, in the binder removal step, the depolymerization type polymer is first extracted while being decomposed in an organic solvent, and then the random decomposition type polymer is added in an inert gas or nitrogen atmosphere. A method for producing a metal powder injection-molded article, in which extraction is performed while heating to remove the binder. 2. The method for producing a metal powder injection-molded article according to claim 1, wherein the depolymerization type polymer is polybutylene terephthalate. 3. The method for producing a metal powder injection-molded article according to claim 1, wherein the random decomposition type polymer is polypropylene. 4. The method for producing a metal powder injection-molded article according to claim 1, wherein the means for decomposing and extracting in the organic solvent causes depolymerization with ethylene glycol and extraction at the same time.