Mixed powder for powder metallurgy and green compact using the same

Abstract: A mixed powder for powder metallurgy to be used as a feedstock of a green compact includes an iron powder and/or an iron alloy powder, a component for improving mechanical properties, and a thermosetting resin powder. In the mixed powder, the thermosetting resin powder is composed of at least one resin selected from the group consisting of an epoxy-polyester-based resin, an epoxy-based resin, and an acrylic-based resin. In addition, the average particle diameter of the thermosetting resin powder is 100 μm or less, and the content of the thermosetting resin powder relative to the total amount of the iron powder and/or the iron alloy powder is 0.05 to 1.0 mass percent. (end of abstract)

Agent: Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US
Inventors: Kazuhisa Fujisawa, Takayasu Fujiura, Hironori Suzuki
USPTO Applicaton #: #20060090594 - Class: 075252000 (USPTO)
Related Patent Categories: Specialized Metallurgical Processes, Compositions For Use Therein, Consolidated Metal Powder Compositions, And Loose Metal Particulate Mixtures, Compositions, Loose Particulate Mixture (i.e., Composition) Containing Metal Particles, Mixture Contains Particles Of Nonmetal

Mixed powder for powder metallurgy and green compact using the same description/claims

The Patent Description & Claims data below is from USPTO Patent Application 20060090594, Mixed powder for powder metallurgy and green compact using the same.

Brief Patent Description - Full Patent Description - Patent Application Claims

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a mixed powder for powder metallurgy to be used as a feedstock of a green compact having an adequate density and strength even before the sintering process and having an excellent machinability, and a green compact using the mixed powder as a feedstock.

[0003] 2. Description of the Related Art

[0004] A powder metallurgy is a technology used for producing machine parts and oil-impregnated bearings from a metal powder. Since highly accurate products can be efficiently mass-produced, the powder metallurgy is indispensable particularly in the automobile industry and the like. In this powder metallurgy, in general, a mixed powder including a metal powder is molded by compression and the resultant green compact is then dewaxed. Subsequently, for example, in an iron-based powder metallurgy, the compact is sintered at a temperature of about 1,000.degree. C. to about 1,300.degree. C. In this sintering process, the mixed metal powder forms an alloy, thereby increasing the strength of the compact. A cutting operation is then performed on the resultant sintered compact.

[0005] However, such a sintered compact has an excessively high strength from the viewpoint of a cutting operation. Furthermore, the lifetime of a cutting tool used is shortened because of the high strength of the sintered compact. On the other hand, a green compact cannot be subjected to a cutting operation prior to sintering because the green compact is brittle. Accordingly, a technology is desired by which the strength of a green compact prior to the sintering process is increased, so that the green compact can subsequently be subjected to a cutting operation and finally sintered.

[0006] A document by Tianjun Liu et al. (Funtai oyobi Funmatsu yakin (Journal of the Japan Society of Powder and Powder Metallurgy) Vol. 50, No. 11, pp. 832-836 (2003)) discloses an example of such a technology. According to this technology, a polymer lubricant is added to a mixed powder, which constitutes a feedstock, and a green compact made of the resultant mixed powder is heated at a temperature lower than the sintering temperature. Consequently, the strength of the compact can be increased only by this heat treatment and thus a cutting operation can be performed prior to the sintering process. However, since a polymer lubricant is used as a lubricant, its lubricity during compression molding may be insufficient. In addition, although the temperature is as relatively low as 190.degree. C., it takes about an hour to complete the heat treatment before the cutting operation can be performed. Therefore, this heat treatment decreases the productivity.

[0007] In the powder metallurgy, when a mixed powder is discharged from a storage hopper or when a die is filled with the mixed powder, the fluidity of the mixed powder is one of its important characteristics. Specifically, a low fluidity of a mixed powder causes the following problems. For example, a bulging can occur at the upper part of a discharging hole of a hopper, resulting in a discharge failure. Also, the mixed powder can become clogged in a hose connecting from the hopper to a shoe box. Furthermore, even if a mixed powder having a low fluidity is compulsorily discharged from the hose, the powder may not satisfactorily fill a die, in particular, a die having thin walls. Consequently, a satisfactory compact may not be formed. For these reasons, a raw powder for powder metallurgy having excellent fluidity has been strongly desired.

[0008] Although the object is different from that of the present invention, the following technology for producing a bonded magnet is known: A thermosetting resin is added to a magnetic powder or the like, and a heat treatment is then performed. Thus, a compact is cured without sintering while the magnetic properties of the compact are ensured. The resultant compact is used without further treatment. Accordingly, this manufacturing technology of a bonded magnet may be applied to the powder metallurgy. However, known manufacturing technologies of bonded magnets cannot be applied to the powder metallurgy as they are.

[0009] For example, Japanese Unexamined Patent Application Publication Nos. 4-284602 (paragraph No. 0007, and Examples), 6-112022 (paragraph Nos. 0015 and 0016, and Examples), 6-188137 (paragraph Nos. 0015 and 0020, and Examples), and 8-31677 (paragraph Nos. 0031 and 0033, and Examples) disclose methods for producing a bonded magnet in which a mixture of an alloy powder and a thermosetting resin (binder) is used as a feedstock. However, the type and the particle diameter of the thermosetting resin are not studied in detail because these technologies relate to a bonded magnet and their objects are different from the object of the present invention. In addition, the content of thermosetting resin is relatively large from the viewpoint of application to the powder metallurgy. For example, according to Japanese Unexamined Patent Application Publication No. 4-284602, the content of a thermosetting resin binder is 0.5 to 4 mass percent base on an alloy. According to Japanese Unexamined Patent Application Publication No. 6-112022, 0.5 to 5 parts by weight (in particular, 1 to 3 parts by weight) of a thermosetting resin is added to 100 parts by weight of a magnetic powder. However, in Examples in these patent documents, the amount of a thermosetting resin relative to the total amount of an alloy powder is 2 mass percent or more. According to investigations made by the inventors of the present invention, when a thermosetting resin is excessively added to a mixed powder for powder metallurgy, the fluidity of the powder and the density of the green compact are decreased.

[0010] According to Japanese Unexamined Patent Application Publication No. 10-303009 (Claims), an epoxy resin powder having an average particle diameter of 50 .mu.m or less, which is used as a resin binder, is mixed with a magnetic powder to mold a bonded magnet. The compounding ratio of the epoxy resin powder to the magnetic powder is 0.1 to 0.5 mass percent. An inorganic additive is added to the mixed powder in order to suppress the abrasion with a die during molding. However, in this mixed powder, a component that improves the strength or machinability of the compact is not considered. In addition, the content of this inorganic additive is very small (20 to 40 mass percent of the total amount of the resin binder, 0.02 to 0.2 mass percent of the total amount of the magnetic powder). Therefore, even if the inorganic additive has a function of enhancing the strength of the compact or the like, the function may not be fulfilled in such a small content.

SUMMARY OF THE INVENTION

[0011] In view of the above-described situation, it is an object of the present invention to provide a mixed powder for powder metallurgy to be used as a feedstock of a green compact. Because of its excellent fluidity, the mixed powder provides a high productivity. Furthermore, a green compact using the mixed powder as a feedstock has an adequate density and strength, and is excellent in terms of machinability. Therefore, a cutting operation can be performed prior to the sintering process, and in addition, the lifetime of a cutting tool used can be extended. Also, it is an object of the present invention to provide a green compact using this mixed powder as a feedstock for powder metallurgy, the green compact having an excellent strength and the like even before sintering.

[0012] To solve the above-described problems, the inventors of the present invention have extensively studied, in particular, the composition of a mixed powder for powder metallurgy and found the following: When a component for improving mechanical properties and a thermosetting resin powder are added to a base powder, and in addition, an appropriate thermosetting resin powder is used, a green compact having an adequate density and strength can be produced. The present invention has been made on the basis of this finding.

[0013] Specifically, a mixed powder for powder metallurgy of the present invention is used as a feedstock of a green compact, and the mixed powder includes an iron powder and/or an iron alloy powder, a component for improving mechanical properties, and a thermosetting resin powder. In the mixed powder, the thermosetting resin powder is composed of at least one resin selected from the group consisting of an epoxy-polyester-based resin, an epoxy-based resin, and an acrylic-based resin. In addition, the average particle diameter of the thermosetting resin powder is 100 .mu.m or less, and the content of the thermosetting resin powder relative to the total amount of the iron powder and/or the iron alloy powder is 0.05 to 1.0 mass percent.

[0014] The mixed powder for powder metallurgy preferably further includes a lubricant. This is because the lubricant can decrease the coefficient of friction between the green compact and a die. As a result, the generation of die galling and damage of the die can be suppressed. The lubricant is preferably at least one compound selected from the group consisting of ethylenebisstearamide, stearamide, zinc stearate, and lithium stearate. This is because these compounds are excellent as an additional component of the mixed powder for powder metallurgy.

[0015] The component for improving mechanical properties is preferably at least one substance selected from the group consisting of copper, nickel, chromium, molybdenum, graphite, and manganese sulfide. This is because these substances are diffused into the iron powder or the like during the sintering process. Consequently, the hardness or the toughness of the compact can be improved or the machinability of the compact can be improved.

[0016] Furthermore, a green compact of the present invention is made of the above-described mixed powder for powder metallurgy.

[0017] The mixed powder for powder metallurgy of the present invention has excellent fluidity and the like and provides an excellent productivity. Furthermore, since a green compact using this mixed powder as a feedstock has an adequate density and strength even before sintering, the green compact can be subjected to a cutting operation. In addition, since the green compact does not have an excessively high strength, the lifetime of a cutting tool used can be extended. Accordingly, the mixed powder for powder metallurgy of the present invention and the green compact using the mixed powder as a feedstock are excellent for industrial application from the viewpoint that the productivity of powder metallurgy can be improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A mixed powder for powder metallurgy of the present invention includes an iron powder and/or an iron alloy powder, a component for improving mechanical properties, and a thermosetting resin powder. The thermosetting resin powder is composed of at least one resin selected from the group consisting of an epoxy-polyester-based resin, an epoxy-based resin, and an acrylic-based resin; the average particle diameter of the thermosetting resin powder is 100 .mu.m or less; and the content of the thermosetting resin powder relative to the total amount of the iron powder and/or the iron alloy powder is 0.05 to 1.0 mass percent.

[0019] For example, commercially available normal iron powders and/or iron alloy powders used for a material for metallurgy can be used in the present invention.

[0020] The component for improving mechanical properties is added in order to improve the mechanical properties such as the hardness and the toughness of a compact or to improve the machinability of the compact by diffusing into a base iron powder or the like during the sintering process. Examples of the component for improving mechanical properties include metal powders used for alloys such as copper, nickel, chromium, and molybdenum powders; and inorganic powders such as graphite and manganese sulfide powders. These components may be used alone or in combinations of two or more powders. The component for improving mechanical properties may be mixed with an iron powder or the like when used. Alternatively, for example, graphite may be uniformly adhered to an iron powder or the like with a binder therebetween when used.

[0021] The content of metal powder used for alloys serving as a component for improving mechanical properties is 0.1 to 4 mass percent (hereinafter, unless otherwise stated, the "mass percent" is simply represented by "%") relative to the total amount of a base iron powder or the like. At a content of less than 0.1%, a satisfactory improvement of mechanical properties may not be achieved because of a small amount of diffusion in the base powder. On the other hand, at a content exceeding 4%, the improvement of mechanical properties is also decreased. In addition, at such an excessively high content, a green compact having a satisfactory density may not be produced because the compressibility is impaired. The content of inorganic powder such as graphite is 0.1% to 1% relative to the total amount of a base iron powder or the like. At a content of less than 0.1%, the improvement may not be satisfactory. At a content exceeding 1%, the mechanical properties may be impaired.

Brief Patent Description - Full Patent Description - Patent Application Claims
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