JP2000199001A - Powder and method for manufacturing high density sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably manufacture a sintered parts of high sintering density by a pressing method by granulating powder small in mean grain size (fine powder) into granulated powder, setting the mean grain size to be approximately on the same level as that of the powder large in mean grain size (general powder), and mixing the granulated powder with the general powder to be formed and sintered. SOLUTION: Raw fine powder and raw general powder are metallic powders formed of iron, iron alloy, nickel, etc. The fine powder is preferably 1-100 μm in mean grain size. The fine powder is fed to a granulating device, a binder such as polyvinyl alcohol and polyvinyl pyrolidone is added thereto, and mixed therein to be granulated. A mixing granulating method is preferably of a rolling type in which a rotary pan, a rotary cylinder or a rotary cone is used. The binder is removed simultaneously with a lubricant in a degreasing process after the mixed powder is formed. A parts of the sintering density of >=93% can be easily and inexpensively manufactured by the pressing method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powder for a sintered body by a powder metallurgy method and a method for producing the sintered body.

[0002]

2. Description of the Related Art Sintered parts manufactured by the powder metallurgy method are characterized in that there is no restriction on the shape of the parts and that small and complicated parts can be manufactured with high precision without machining. For this reason, sintered parts manufactured by the powder metallurgy method have recently attracted attention as parts used for machines, automobiles, home electric appliances and the like. Such a sintered component is manufactured by, for example, injection molding or press molding a stainless steel powder to form a molded body having a predetermined shape, and sintering the molded body.

[0003] In the production of such sintered parts,
Recently, it has been required to maintain a high sintering density and a high mechanical strength. For example, sintered parts made of stainless steel powder have been widely used as parts in the exhaust gas system of automobiles. It is required to have a high density, no open pores, a strength to withstand the stress caused by the vibration of an automobile, a resistance to oxidation and corrosion by gas and the like.

Among these, the relative density, which is the ratio of the measured density to the true density, is used as a standard for the sintered density, and is required to be at least 93%, preferably 95% or more. It is said that if the sintered part has a relative density of 93% or more than 95%, there are no open pores, that is, pores that penetrate the entire thickness of the sintered part.

Several methods have been proposed for producing sintered parts having such a high sintered density. For example, in JP-A-7-316603, "the average particle size is 11
a high-density and high-strength sintered powder characterized in that the abundance of powder having a particle size of 21 μm or more contained in the powder having a particle size of 21 μm or less is less than 17.5 wt%. Discloses that "a sintered body having a relative density of 95% or more can be obtained and high mechanical properties can be stably obtained."

[0006]

However, as a method of manufacturing a sintered part having a high sintered density, Japanese Patent Laid-Open No.
Attempts to use the method disclosed in US Pat. No. 6,603,009 have the following problems. That is, (1) Since the average particle diameter of the powder is too small, when a sintered part is manufactured by a press molding method using such a powder, the fluidity of the powder is extremely reduced, and the Since the powder does not flow, a sintered part having a normal shape cannot be obtained. Also in the embodiment of JP-A-7-316603, parts are manufactured only by the injection molding method. (2) Since powders having a small average particle size are generally expensive, it is not economical to produce a sintered component using only such powders.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a powder for stably producing a sintered part having a high sintering density by a press molding method, and to provide a method for the same. And

Conventionally, powders typified by -100 mesh products have been used as raw materials in the production of sintered parts by press molding, and their relative densities have been only as low as about 85%. An object of the present invention is to provide a powder capable of easily and inexpensively producing a sintered part having a sintered density of 93% or more by a press molding method and a method thereof.

[0009]

Means for Solving the Problems The present inventors have conducted various studies in order to solve the above-mentioned problems, and as a result, have produced “powder having a small average particle size” (hereinafter referred to as “fine powder”). After the granulated powder is made into a granulated powder, and the average particle size of the granulated powder is set to substantially the same level as the powder having a large average particle size (hereinafter, referred to as “general powder”), Have been found to be able to solve the above problems and produce a sintered part having a high sintering density by mixing and forming a mixed powder.

The powder used as a raw material in the present invention is a fine powder and a general powder, both of which are metal powders. The present invention relates to iron and iron alloys (for example, stainless steel, silicon steel, structural steel, tool steel, Speed steel, Alnico alloy, Sendust alloy, Permendur alloy, Permalloy alloy, etc.), nickel, nickel alloy (Permalloy, etc.), chromium, chromium alloy, cobalt, cobalt alloy, titanium, titanium alloy, etc. It is.

The fine powder used in the present invention includes:
A metal powder having an average particle size of 1 to 100 μm is preferred.
If a metal powder having an average particle size of 1 μm or less is to be granulated, the required amount of the binder increases, and it takes a long time to remove the binder, resulting in a large cost burden. Also, when the average particle size of the raw metal powder exceeds 100 μm, the packing density of the sintered part formed by molding the granulated powder produced from this powder is low, and the density does not increase even after sintering, Further, the dimensional accuracy is also deteriorated. Therefore, the upper limit of the average particle size of the fine powder of the raw material is 100 μm. In consideration of the production conditions and economics of the fine powder of the raw material, the average particle size of the metal powder as the preferable raw material is 2 μm to 60 μm.

Next, in order to granulate the raw material fine powder, the fine powder is supplied to a granulator, a binder is added, and the mixture is granulated. Granulation methods include mixed granulation, forced granulation,
Any of the heat-based granulation methods may be used, but preferably, a rolling-type mixed granulation method using a rotating plate, a rotating cylinder, or a rotating cone is used. As the binder, polyvinyl alcohol, polyvinyl pyrrolidone, wax,
Use an organic substance such as agar, or a mixture of water and an organic substance.

The binder such as polyvinyl alcohol added at the time of producing the granulated powder does not need to be particularly provided with a removing step, and is removed simultaneously with the lubricant in the degreasing step performed after molding the mixed powder. When the properties of the binder to be added in the granulation process and the lubricant to be added in the molding process are different and the binder is difficult to remove compared to the lubricant, degreasing conditions such as extending the degreasing time or increasing the degreasing temperature are used. It is necessary to adjust.

Further, the granulated powder and the general powder are mixed to form a mixed powder, and the mixed powder is molded and sintered under the sintering conditions generally used in a hydrogen atmosphere. Known sintering conditions such as sintering under an inert atmosphere such as nitrogen, argon, etc., sintering under reduced pressure, vacuum or oxidizing atmosphere may be used.

[0015]

The gist of the present invention will be described below in more detail with reference to examples.

[0016]

Example 1 As a fine powder, stainless steel (S) having a particle size distribution shown in Table 1 and obtained by a water atomization method was used.
US316L) 50 kg of powder is supplied to a tumbling fluidized-granulation device (manufactured by Powrex Co., Ltd.), and a 5% solution of PVP (polyvinylpyrrolidone) using methyl alcohol as a binder is continuously supplied while rotating a rotating disk. And granulated. The air supply at this time is about 8.5 m ³
/ Hr, the supply air temperature is 70 ° C., the number of revolutions of the rotating disk part is about 205 rpm, the temperature of the granulated powder is about 35 ° C., the supply amount of the binder is about 110 g / min, the granulation time is 180 minutes,
The drying time was about 10 minutes.

[0017]

[Table 1] By this granulation, a granulated powder having a particle size distribution shown in Table 2 was obtained.

[0018]

[Table 2] Next, the granulated powder shown in Table 2 was mixed with a stainless steel (SUS316L) powder obtained by a water atomizing method having a particle size distribution shown in Table 3 as a general powder to prepare a mixed powder. Usually, it is a so-called -100 mesh powder.) In preparing this mixed powder, the mixing ratio between the granulated powder and the general powder was variously changed.

[0019]

[Table 3] After adding 0.5% by mass of commercially available ACRAWAX (manufactured by Lonza Japan Co., Ltd.) as a lubricant to this mixed powder, a test piece was formed using a press machine at a molding pressure of 6 to 8 t / cm ² . After sintering at 1200 ° C. for 1 hour in a sintering furnace in a hydrogen atmosphere, the sintered density was measured.

The results show that, as shown in Table 4, there is a possibility that a sintered part having a relative density of 93% or more can be manufactured by changing the mixing ratio of the general powder and the granulated powder and the molding pressure.

[0021]

[Table 4]

[0022]

EXAMPLE 2 Next, a test piece molded under the same conditions as in Example 1 was sintered at 1300 ° C. × 1 hour in a sintering furnace in a hydrogen atmosphere in order to investigate the influence of the sintering temperature. The sintering density was measured.

As shown in Table 5, the results show that increasing the sintering temperature broadens the range in which sintered parts having a relative density of 93% or more can be manufactured.

[0024]

[Table 5]

[0025]

Example 3 Next, using the same fine powder as in Example 1, a granulated powder having a smaller particle size than that in Example 1 was obtained in the same manner as in Example 1.

[0026]

[Table 6] Next, the granulated powder shown in Table 6 was mixed with a stainless steel (SUS316L) powder obtained by a water atomizing method having a particle size distribution shown in Table 7 as a general powder to prepare a mixed powder.

[0027]

[Table 7] After adding 0.5% by mass of commercially available ACRAWAX (manufactured by Lonza Japan Co., Ltd.) as a lubricant to this mixed powder, a test piece was formed using a press machine at a molding pressure of 6 to 8 t / cm ² . After sintering at 1300 ° C. × 1 hour in a sintering furnace in a hydrogen atmosphere, the sintered density was measured.

As shown in Table 8, the results are as follows.
It was confirmed that by making the particle diameters of the general powder and the granulated powder smaller, a sintered part having a relative density of 93% or more can be stably manufactured.

[0029]

[Table 8]

[0030]

Example 4 A similar experiment was performed on stainless steel (SUS410L) obtained by a water atomizing method. The particle size distribution of the fine powder, granulated powder and general powder used was almost the same as in Example 1. The granulation conditions and sintering conditions were the same as in Example 1.

As shown in Table 9, the sintering temperature was 1200 for SUS410L even for the same stainless steel.
It is understood that a sintered body having a relative density of 93% or more can be stably obtained even at ℃.

[0032]

[Table 9] As described above, the particle size of fine powder, granulated powder, general powder,
By appropriately selecting the conditions such as the mixing ratio of the granulated powder and the general powder, the molding pressure, the sintering temperature, etc., a sintered component having a sintered density of 93% or more can be stably manufactured.
The selection of the mixing ratio between the granulated powder and the general powder is particularly important, but after securing a relative density of 93% or more, further considering the necessary relative density, cost and other conditions, the optimum mixing ratio is determined. You have to choose.

[0033]

According to the present invention, a powder having a small average particle size is granulated into a granulated powder, a mixed powder of the granulated powder and a powder having a large average particle size is produced, and the mixed powder is formed and sintered. By tying, a sintered part having a high sintered density can be manufactured, and the effect is extremely large.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kinyuki Kato 1-6-1 Otemachi, Chiyoda-ku, Tokyo F-term (reference) 4K018 BB04 BC11 BC12

Claims (2)

[Claims] 1. A high-density sintered body characterized in that a granulated powder produced by granulating a powder having a small average particle diameter and a powder having a large average particle diameter are mixed to form a mixed powder. Manufacturing powder. 2. A method of mixing a granulated powder produced by granulating a powder having a small average particle diameter with a powder having a large average particle diameter to form a mixed powder, and molding and sintering the mixed powder. A method for producing a high-density sintered body characterized by the following.