JP5169605B2 - Powder mixture for powder metallurgy and method for producing molded body - Google Patents

Description

  The present invention relates to a powder mixture for powder metallurgy mainly composed of iron-based powder and a method for producing a molded body using the powder mixture.

Since powder metallurgy technology can produce machine parts with complicated shapes with extremely high dimensional accuracy, it is possible to significantly reduce the manufacturing costs of machine parts. Therefore, various machine parts manufactured by applying the powder metallurgy technique are used in various fields. Furthermore, recently, demands for reducing the size and weight of machine parts are increasing, and accordingly, various powders for powder metallurgy for producing machine parts that are small and light and have sufficient strength have been studied. .

For example, in Patent Documents 1 to 3, an alloy powder (eg, copper powder, graphite powder, iron phosphide powder, manganese sulfide powder, etc.) is attached to the surface of an iron-based powder (pure iron powder, alloy steel powder, etc.). Disclosed is a raw powder for powder metallurgy. Usually, a lubricant (for example, zinc stearate, aluminum stearate, etc.) is added to such raw material powder, and this powder mixture is molded and sintered to produce a machine part.

  Recently, for the purpose of increasing the strength of sintered parts, a technique has been developed in which an iron-based powder is molded at a high pressure to increase the density of the molded body. In molding at high pressure, since it is necessary to reduce the frictional force between the iron-based powder and the mold, a method of adding a lubricant to the iron-based powder as described above is generally employed. In addition, a binder that is required for adhering the alloy powder to the surface of the iron-based powder is also required to reduce the frictional force between the particles of the iron-based powder or between the iron-based powder and the mold. On the other hand, since these lubricants and binders have a lower density than iron-based powders, if they are added in large quantities in order to place importance on lubricity, the density of the green compact will be reduced. Therefore, in order to produce a high-density molded body, a lubricant or binder having a low concentration and high lubricity is required.

  For example, in Patent Document 4, a free lubricant containing erucic acid amide and / or oleic acid amide as a lubricant is added to an iron-based powder in which graphite is adhered by an organic binder in a total mixture of 0.05 to 0.00. It is an iron-based powder mixture mixed at a ratio of 2 mass%, and at least 30 mass% of the free lubricant is composed of secondary particles having a particle size of 10 to 200 μm, which are granulated by agglomerating primary particles having a particle size of 1 to 30 μm. Although iron-based powder mixtures for powder metallurgy are disclosed, no particular limitation is imposed on the binder.

JP-A-1-219101 JP-A-2-217403 JP-A-3-162502 JP 2005-264201 A

The organic binder described above is for adhering the alloy powder to the surface of the iron-based powder, but on the other hand, it also has a great effect on the frictional force, adhesion and adhesion between the particles of the iron-based powder. . For example, if a hard organic binder is used in the environment in which it is used, the fluidity of the powder is improved, but on the other hand, the resistance increases during compression, which is disadvantageous for increasing the density of the green compact. In addition, when a soft organic binder is used, the adhesion and adhesion between particles increase, and the fluidity of the powder decreases. Therefore, in the iron-based powder mixture as shown in Patent Document 4, the frictional force between the iron-based powder mixture and the mold may not be sufficiently reduced, particularly in molding at high pressure. Moreover, when a granulated lubricant having a large particle size is added, cavities may remain after sintering, resulting in poor appearance.

Accordingly, an object of the present invention is to form a high-density molded body that can sufficiently reduce the frictional force with the mold in molding at a high pressure without causing mold galling or the like when extracted from the mold. Is to provide a powder mixture for powder metallurgy that can be obtained appropriately. Another object of the present invention is to provide a method for producing a molded body for obtaining a high-density molded body by high-pressure molding such a powder metallurgy powder mixture.

The gist of the present invention for solving the above problems is as follows.
[1] In a powder mixture for powder metallurgy comprising an iron-based powder, an alloy powder attached to the surface of the iron-based powder via an organic binder, and a lubricant released from the iron-based powder,
The penetration of the organic binder and the lubricant at 25 ° C. is 3 to 5 mm , and the total addition amount of the organic binder and the lubricant with respect to the total amount of the iron-based powder and the alloy powder is 0.1 to 0.3 mass. %
A powder mixture for powder metallurgy, characterized in that the organic binder and the lubricant comprise oleic amide .

[2] A powder mixture for powder metallurgy according to the above [1], which is a powder mixture for high pressure molding with a molding pressure of 686 MPa or more.
[3] A method for producing a molded body, wherein the powder mixture for powder metallurgy according to [1] is molded at a molding pressure of 686 MPa or more.

The powder mixture for powder metallurgy according to the present invention can sufficiently reduce the frictional force with the mold in molding at a high pressure, does not cause mold galling or the like when extracted from the mold, and has a high density. It is possible to appropriately obtain the molded body.

A powder mixture for powder metallurgy according to the present invention (hereinafter simply referred to as “powder mixture”) includes an iron-based powder, an alloy powder attached to the surface of the iron-based powder via an organic binder, and the iron-based powder. Contains free lubricant.
Examples of the iron-based powder constituting the powder mixture of the present invention include pure iron powder and alloy steel powder, and one or more of these can be used. Examples of the alloy steel powder include those previously alloyed by adding an alloy component at the molten steel stage, and those obtained by partially diffusing and adhering the alloy component to the iron powder surface.

Examples of the alloy powder (auxiliary material) include copper powder, graphite powder, iron phosphide powder, and manganese sulfide, and one or more of these can be used. The content of the alloy powder in the powder mixture is usually about 0.1 to 10 mass%.
In the powder mixture of the present invention, the alloy powder and the organic binder are added to the iron-based powder, mixed while heating to a temperature equal to or higher than the melting point of the organic binder, and then cooled to solidify the organic binder. It can be obtained by adding a lubricant and mixing.

  Conventionally, during compression molding of a powder mixture mainly composed of iron-based powder, as the molding pressure increases (that is, the density of the molded body increases), the frictional force with the side surface of the mold increases, and the molded body is It was thought that the extraction force when extracting from the mold increased. Recently, it has become possible to mold at a molding pressure of 686 MPa or more due to improvements in molding technology. When molding at such a high molding pressure, the extraction force decreases at a certain level of molding pressure or higher. It has become clear that there is. The cause of the decrease in the extraction force under such high-pressure molding is that the organic binder or lubricant contained in the powder mixture decreases from the inside of the molded body to the outside, that is, the mold as the void inside the molded body becomes smaller during molding. It is thought that this is because a lubricating film is formed on the mold surface by being extruded to the surface. From this, it is considered that the organic binder and lubricant blended in the powder mixture should be easily deformed.

  As a result of examining the optimum conditions of the organic binder and the lubricant from the above viewpoint, the inventors have found that the penetration at 25 ° C. is 0.3 mm or more, preferably 0.8 mm or more, more preferably 3 mm or more. It has been found that by using a certain organic binder and lubricant, the extraction force can be reduced when molding at a high molding pressure (generally 686 MPa or more). Here, the penetration is known as an index for evaluating the hardness of wax, asphalt, etc., and the measurement method is defined in JIS-K-2207 (usually measured at room temperature of 25 ° C.). .

On the other hand, when the hardness of the organic binder or lubricant is unnecessarily low, that is, when the penetration is too high, the adhesion and adhesion between the particles increase and the fluidity as a powder decreases. For this reason, it has been found that the penetration of the organic binder and the lubricant at 25 ° is 10 mm or less, preferably 8 mm or less, more preferably 5 mm or less.
Therefore, in the powder mixture of the present invention, the penetration of the organic binder and lubricant at 25 ° C. is 0.3 to 10 mm, preferably 0.8 to 8 mm, and more preferably 3 to 5 mm.

Examples of organic binders and lubricants having the above penetration include fatty acid monoamides, fatty acid bisamides, and metal soaps, and one or more selected from these can be used. In addition, when using 2 or more types of components, the case where they are used in the state of melt-mixing is also included.
Examples of fatty acid monoamides include stearic acid amide, erucic acid amide, oleic acid amide, palmitylamide, mistylamide, and lauryl amide, and fatty acid bisamides include ethylene bisstearamide, ethylene bislauric acid amide, and ethylene bisoleic acid. Examples of the metal soap include amide, ethylene bisbehenic acid amide, and methylene bis stearic acid amide, and examples of the metal soap include zinc stearate, manganese stearate, lithium stearate, calcium stearate, and magnesium stearate. Further, some thermoplastic resins such as polyethylene, polypropylene, and polyamide can be used.

  When the organic binder and the lubricant as described above are used, the organic binder and the lubricant are easily extruded onto the surface of the molded body at the time of molding at a high pressure. For this reason, it is possible to reduce the frictional force with the mold by using a relatively small amount of the organic binder and the lubricant. For this reason, the powder mixture of the present invention has a total amount of organic binder and lubricant added to the total amount of iron-base powder and alloy powder (= organic binder and lubricant for a total of 100 parts by weight of iron-base powder and alloy powder). The total mass part of the agent) is 0.1 to 0.8 mass%, preferably 0.1 to 0.5 mass%. When the total addition amount of the organic binder and the lubricant exceeds 0.8 mass% with respect to the total amount of the iron-based powder and the alloy powder, the density of the molded body is difficult to increase. On the other hand, when it is less than 0.1 mass%, the mold A sufficient lubricating film cannot be formed on the surface. The addition amount of the organic binder with respect to the total amount of the iron-base powder and the alloy powder is preferably 0.05 to 0.6 mass%, and the addition amount of the lubricant is preferably about 0.05 to 0.6 mass%. .

  In addition, the powder mixture of the present invention is mainly composed of iron-based powder, to which an alloy powder, an organic binder and a lubricant are added, and if necessary, for improving machinability such as MnS. Powder etc. can be added. These are either in the form of adhering to the iron-based powder with an organic binder as in the case of the alloy powder, or in the form of being released from the iron-based powder like a lubricant (for example, for improving machinability such as MnS) The powder is contained in the powder mixture in the former form).

  As described above, the powder mixture of the present invention exhibits the function of reducing the frictional force with the mold when molded at a high molding pressure, and in particular, a molding pressure of 686 MPa or more (more preferably 785 MPa). The above is a powder mixture suitable for high pressure molding. That is, in this case, the powder mixture of the present invention is filled in a mold and compression-molded at a molding pressure of 686 MPa or more to obtain a compact (compact). This molded body is sintered to form a sintered body, and then heat-treated to obtain a product (mechanical part).

After adding copper powder, graphite powder and organic binder to iron powder at the blending ratio shown in Table 1 and Table 2, mixing with heating to a temperature above the melting point of the organic binder with a Henschel type high speed mixer, 60 ° C The powder was cooled to the following (the powder at this stage is referred to as “segregation prevention treated powder”). Next, a lubricant was added and mixed to produce a powder mixture for powder metallurgy. The powder mixture for powder metallurgy was examined for graphite powder adhesion rate, fluidity, and green compact properties as follows. The results are shown in Table 3.

(1) Graphite powder adhesion rate In order to evaluate the adhesion state of the graphite powder by the organic binder, the graphite powder adhesion rate was measured by the following method. First, C analysis of the segregation prevention treated powder as a whole was performed, and then the segregation prevention treated powder was classified with a sieve to obtain classified products on a 200 mesh sieve and a 100 mesh sieve. This classification product was subjected to C analysis, and the ratio of the ratio to the C analysis value of the entire segregation prevention treated powder as a percentage was defined as the graphite powder adhesion rate.

(2) Fluidity The fluidity of the segregation preventing powder was measured by a method based on JIS-Z-2502. (3) Green compact characteristics Powder metallurgy powder mixtures were molded at molding pressures of 686 MPa, 980 MPa, and 1472 MPa, respectively, to form tablet-shaped compacts having a diameter of 11 mm and a height of 11 mm. Under the present circumstances, the extraction force when extracting a molded object from a metal mold | die, and the density of the obtained molded object were measured.

Claims (3)

In a powder mixture for powder metallurgy comprising an iron-based powder, a powder for an alloy attached to the surface of the iron-based powder via an organic binder, and a lubricant released from the iron-based powder,
The penetration of the organic binder and the lubricant at 25 ° C. is 3 to 5 mm , and the total addition amount of the organic binder and the lubricant with respect to the total amount of the iron-based powder and the alloy powder is 0.1 to 0.3 mass. %
A powder mixture for powder metallurgy, characterized in that the organic binder and the lubricant comprise oleic amide . 2. The powder mixture for powder metallurgy according to claim 1, wherein the powder mixture is used for high pressure molding at a molding pressure of 686 MPa or more. A method for producing a molded body, comprising molding the powder mixture for powder metallurgy according to claim 1 at a molding pressure of 686 MPa or more.