JP5170390B2 - Iron-based mixed powder for powder metallurgy - Google Patents

Description

  The present invention relates to an iron-based mixed powder suitable for use in powder metallurgy technology.

  The iron-based mixed powder used in the powder metallurgy technique is manufactured by mixing iron powder as a basic component with a metal powder containing an alloy component (hereinafter referred to as alloy powder) and a lubricant. At that time, graphite powder, copper powder, iron phosphide powder or the like is generally used as the alloy powder, and zinc stearate, lithium stearate or the like is used as the lubricant. Further, a machinability improving powder (for example, MnS) may be added as necessary.

  In applying such iron-based mixed powder to powder metallurgy technology, the iron-based mixed powder is filled into a mold, and a molded body manufactured by pressure molding (hereinafter referred to as a green compact) is taken out of the mold. Sinter. However, since iron powder, alloy powder, lubricant, and machinability improving powder have different characteristics (ie, particle size, shape, specific gravity, etc.), the iron-based mixed powder obtained by mixing is transported to the hopper. There was a problem that alloy powder, lubricant, machinability improving powder and the like were segregated in the iron-based mixed powder by charging and discharging from the hopper.

When green compacts are produced from segregated iron-based mixed powders, a uniform distribution of properties (ie, component and density) cannot be obtained with a single green compact, and the properties of multiple green compacts cannot be obtained. Variations occur. Therefore, a sintered body obtained by sintering such a green compact is inevitably reduced in size and strength, and the yield of the sintered body is reduced.
Accordingly, various techniques for preventing segregation of iron powder, alloy powder, lubricant, and machinability improving powder in iron-based mixed powder have been studied. For example, Patent Documents 1 to 3 disclose a technique for preliminarily attaching an alloy powder to the surface of iron powder, and Patent Document 4 discloses a technique for improving the outflow of segregation preventing powder by adding a free lubricant. ing.

Patent Document 5 discloses a technique for producing an iron-based mixed powder using iron powder having a predetermined particle size distribution. This technique prevents variations in the characteristics of the green compact by improving the filling properties when filling the iron-based powder into the mold, and thus prevents the yield of the sintered body from being lowered.
However, it is generally known that when the fluidity of the iron-based mixed powder and the filling property into the mold are enhanced, the pressing force (hereinafter referred to as the unloading power) when the green compact is taken out from the mold is likely to increase. In other words, when iron-based mixed powder with improved fluidity and filling properties is used, the output is increased, resulting in a decrease in productivity due to the long time required to take out the green compact and a decrease in yield due to the occurrence of defects in the green compact. Is often invited.

  In order to reduce the punching power of the green compact, it is effective to use a soft and extensible lubricant at the temperature at which the iron-based mixed powder is pressure-molded. The reason is that the lubricant exudes from the iron-based mixed powder by pressure molding and adheres to the mold surface, reducing the frictional force between the mold and the green compact. However, since such a lubricant has stretchability, it easily adheres to the particles of iron powder and alloy powder, and inhibits the fluidity and filling properties of the iron-based mixed powder.

Therefore, it is difficult to achieve both improvement in fluidity and filling property of the iron-based mixed powder and reduction in the extraction force of the green compact. In order to solve this problem, a two-layered lubricant having a lubricant for reducing the unloading power as a core and a lubricant for improving the fluidity has been studied. However, the manufacturing cost of such a lubricant increases. Moreover, since the particle size of the lubricant increases and it becomes difficult to be crushed by pressure molding, the lubricant particles remain in the green compact and burn or vaporize by sintering to form cavities. The cavities generated in this way are defects in the sintered body, leading to a decrease in the yield of the sintered body.
Japanese Unexamined Patent Publication No. 1-219101 JP-A-2-217403 Japanese Patent Laid-Open No. 3-165502 Japanese Unexamined Patent Publication No. 5-148505 JP 2002-280103 A

  The present invention achieves both improvement of the fluidity and filling property of the iron-based mixed powder and reduction of the punching force of the green compact by inexpensive means, and improves the productivity of the molding process and the sintering process, as well as the green compact and sintering. An object of the present invention is to provide an iron-based mixed powder suitable for use in powder metallurgy technology (hereinafter referred to as an iron-based mixed powder for powder metallurgy) that can achieve improved yield of the bonded body.

In the present invention, porous particles having a particle diameter of 1 to 100 μm, which are aggregates of primary fine particles, are one or more selected from inorganic, carbonaceous materials and organic substances having a particle diameter of 1 to 500 nm. It is an iron-based mixed powder for powder metallurgy obtained by impregnating a lubricant and mixing porous particles and iron powder.
In powder metallurgy for iron-based mixed powder of the present invention, it is preferable porous particles have a consolidated and channel structure.

Moreover, it is preferable that the ratio of a lubricant is 20-400 mass parts with respect to 100 mass parts of porous particles. The lubricant is preferably one or more selected from metal soap, bisamide, fatty acid amide, fatty acid, liquid lubricant, and thermoplastic resin.
It inorganic substance used is one of a powder or a mixture of two or more powder selected from SiO _2, TiO _2, Fe ₂ O _3, and _{MgO · Al 2 O 3 · xSiO} 2 · yH 2 O, in the talc Is preferred.

  Moreover, it is preferable that the powder for alloys has adhered to the surface of the iron powder to be used through the organic binder. The organic binder is preferably one or two selected from fatty acid amides and metal soaps.

  According to the present invention, it is possible to achieve both improvement in the fluidity and filling property of the iron-based mixed powder for powder metallurgy and reduction in the extraction force of the green compact by inexpensive means. Therefore, it is possible to improve the productivity and the yield of the green compact and the sintered body, and to manufacture a sintered product having a large and complicated shape.

The iron-based mixed powder for powder metallurgy of the present invention is a mixture of porous particles, iron powder, alloy powder, and lubricant.
First, the porous particles used in the present invention will be described.
The porous particles are those in which voids are included in the particles, and the production method is not particularly limited. However,
(A) porous particles obtained by granulating fine powder (hereinafter referred to as primary fine particles) having a particle diameter of 1 to 500 nm as shown in FIG.
(B) It is preferable to use porous particles having a connected channel structure represented by zeolite as shown in FIG. 2 (b).

Here, the above (A) will be described.
The porous particles are obtained by granulating one kind or two or more kinds of primary fine particles selected from inorganic materials, carbonaceous materials, and organic materials, and are aggregates of primary fine particles. When the particle diameter of the primary fine particles is less than 1 nm (nanometers), the gap between the particles of the primary fine particles becomes minute, so that a sufficient amount of lubricant cannot be retained, and the effect of reducing the unplugging power cannot be obtained. Moreover, clogging occurs during storage and transportation, which not only hinders operation, but extremely fine primary fine particles cause an increase in manufacturing cost. On the other hand, if it exceeds 500 nm, the gap between the primary fine particle particles expands, so that the lubricant easily flows out, a sufficient amount of lubricant cannot be retained, and the effect of reducing the unloading power cannot be obtained. Therefore, the particle diameter of the primary fine particles is preferably in the range of 1 to 500 nm. More preferably, it is 1-20 nm.

The primary fine particles may be granulated to form porous particles. When the particle size of the porous particles is less than 1 μm, when the iron-based mixed powder for powder metallurgy is pressure-molded, the porous particles impregnated with the lubricant segregate in the gaps of the iron-based mixed powder and are not easily crushed, Since the impregnated lubricant is difficult to be released, the effect of reducing the unplugging power cannot be obtained. On the other hand, when the thickness exceeds 100 μm, the porous particles remain in the green compact as they are, resulting in defects in the sintered body obtained by sintering the green compact, causing a reduction in the strength of the sintered body. . Therefore, the particle size of the porous particles is set in the range of 1 to 100 μm. In order to further reduce the above disadvantages, the thickness is preferably in the range of 1 to 40 μm, more preferably in the range of 10 to 25 μm.

The material of the inorganic primary particles that are the material of the porous particles is not particularly limited, but it is preferable to use metal oxide fine powder. Type of metal oxide fine powder, it is preferred to use a fine powder of _{SiO 2, TiO 2, Fe 2} O 3, MgO · Al 2 O 3 · xSiO 2 · yH 2 O. These metal oxide fine powders may be used alone or in combination of two or more.
When granulating inorganic fine powder to produce porous particles, it is preferable to add a lubricant to the inorganic fine powder. The types of lubricants include metal soaps (for example, zinc stearate, manganese stearate, lithium stearate, etc.), bisamides (for example, ethylene bisstearic acid amide), fatty acid amides including monoamides (for example, stearic acid monoamide, erucic acid amide) Etc.), fatty acids (eg oleic acid, stearic acid, etc.), liquid lubricants (eg phosphate esters, polyol esters, mineral oil, polyglycol etc.), thermoplastic resins (eg polyamide, polyethylene, polyacetal etc.) This is preferable because it has the effect of reducing the unplugged output.

  However, a lubricant that becomes liquid at room temperature, such as a fatty acid or a liquid lubricant, causes liquid cross-linking between the particles of the inorganic fine powder, and the particles adhere to each other and aggregate. In addition, wax-based lubricants such as fatty acid amides are solid at room temperature, but have high adhesiveness, so that the particles adhere and aggregate to each other, which may reduce fluidity. The lubricant added when granulating the inorganic fine powder is appropriately selected in consideration of these characteristics. In that case, you may use individually, respectively, and may use 2 or more types together.

  Alternatively, porous particles obtained by granulating inorganic fine powder may be impregnated with a lubricant. The types of lubricants include metal soaps (for example, zinc stearate, manganese stearate, lithium stearate, etc.), bisamides (for example, ethylene bisstearic acid amide), fatty acid amides including monoamides (for example, stearic acid monoamide, erucic acid amide) Etc.), fatty acids (eg oleic acid, stearic acid, etc.), liquid lubricants (eg phosphate esters, polyol esters, mineral oil, polyglycol etc.), thermoplastic resins (eg polyamide, polyethylene, polyacetal etc.) This is preferable because it has the effect of reducing the unplugged output.

Fatty acids and liquid lubricants are preferred because they are easily impregnated into the porous particles. In consideration of these characteristics, the lubricant impregnated into the porous particles obtained by granulating the inorganic fine powder may be used alone or in combination of two or more.
Moreover, you may granulate by adding a lubrication agent to an inorganic fine powder. Even in this case, porous particles impregnated with the lubricant can be obtained.

  If the addition amount (total) of the lubricant is less than 20 parts by mass with respect to 100 parts by mass of the inorganic fine powder, the effect of reducing the extraction force of the green compact cannot be obtained. On the other hand, when the amount exceeds 400 parts by mass, the fine inorganic powder particles or the porous particles agglomerate, which may reduce the fluidity. Therefore, the total content of the lubricant added when granulating the inorganic fine powder and the lubricant impregnated into the porous particles obtained by granulating the inorganic fine powder is 100 parts by mass of the inorganic fine powder. And preferably within the range of 20 to 400 parts by mass.

The carbonaceous material that is a material for the porous particles is not particularly limited as long as it is mainly composed of C. However, it is preferable to use natural graphite powder, artificial graphite powder, coke powder or the like that is inexpensive and easily available. These fine powders may be used alone or in combination of two or more.
The organic material that is the material of the porous particles is not particularly limited, but it is preferable to use cellulose, lactose, polytetrafluoroethylene, polyethylene, acrylic polymer, methacrylic polymer, or the like. These fine powders may be used alone or in combination of two or more.

Here, the above (B) will be described.
As the inorganic porous particles, porous silica, zeolite, and the like obtained by polymerization of silicate sol and secondary aggregation are suitable. As the carbon material porous particles, activated carbon obtained by reacting wood sawdust with gas or chemicals at high temperature is suitable. As the organic porous particles, in addition to cellulose, glucose, starch, carboxymethyl cellulose and the like, methacrylic hollow porous polymer particles obtained by the method described in JP-A-2006-131738 are suitable. .

These porous particles are impregnated with a lubricant as in (A). Since the lubricant used and the impregnation technique are the same as those in (A), description thereof is omitted.
Next, the iron powder used in the present invention will be described.
The iron powder is preferably one in which an alloy powder or a machinability improving powder is attached to the surface of the iron powder via an organic binder (hereinafter referred to as alloy component exterior iron powder). By attaching the alloy powder or the machinability improving powder to the surface of the iron powder, segregation of the alloy powder or the machinability improving powder is prevented. The characteristics of the iron powder to be used are not limited, and are appropriately selected according to the specifications required for the sintered product obtained by sintering the green compact.

The organic binder is preferably a fatty acid amide or a metal soap. These organic binders may be used alone or in combination of two kinds.
When the addition amount of the organic binder is less than 0.05% by mass, the alloy powder and the machinability improving powder cannot be uniformly and sufficiently adhered to the surface of the iron powder. On the other hand, if it exceeds 0.6% by mass, the iron powder adheres and agglomerates, which may reduce the fluidity. Therefore, the amount of organic binder added is preferably in the range of 0.05 to 0.6% by mass. In addition, the addition amount (mass%) of an organic binder points out the ratio of the organic binder to the mass of the iron-base powder for powder metallurgy.

Graphite powder, copper powder, and Ni powder are used for the alloy powder, and MnS powder or the like is used for the machinability improving powder. These alloy powders or machinability improving powders may be used alone or in combination of two kinds.
Furthermore, when a free lubricant is added, the fluidity of the iron-based mixed powder for powder metallurgy can be improved. The free lubricant is added separately from the lubricant encapsulated in the porous particles, and the amount added is preferably in the range of 0.05 to 0.5% by mass as a proportion of the mass of the iron-based mixed powder for powder metallurgy. The types of free lubricants include metal soaps (for example, zinc stearate, manganese stearate, lithium stearate, etc.), bisamides (for example, ethylene bisstearic acid amide), fatty acid amides including monoamides (for example, stearic acid monoamide, erucic acid amide) Etc.), fatty acids (for example, oleic acid, stearic acid, etc.), and thermoplastic resins (for example, polyamide, polyethylene, polyacetal, etc.) are preferred because they have the effect of reducing the output of the green compact.

  The porous particles obtained as described above, the alloy component-coated iron powder, the free lubricant and the like are mixed to obtain an iron-based mixed powder for powder metallurgy. As the mixing apparatus, conventionally known stirring blade type mixers (for example, Henschel mixer) and container rotation type mixers (for example, V type mixer, double cone mixer, etc.) can be used. This iron-based mixed powder for powder metallurgy has excellent fluidity and filling properties, and can reduce the output of the green compact. Moreover, an iron-based mixed powder for powder metallurgy can be produced using an inexpensive material.

  The powder for alloy was made to adhere to the surface of the iron powder through an organic binder to obtain an alloy component exterior iron powder. The organic binder used and the amount added are as shown in Table 1. In addition, the addition amount (mass%) of an organic binder points out the ratio of the organic binder to the mass of the iron group mixed powder for powder metallurgy. As the alloy powder, copper powder and graphite powder are used, and the addition amounts thereof are Cu: 2 mass% and C: 0.8 mass%, respectively. In addition, the addition amount (mass%) of Cu and C points out the ratio of Cu and C to the mass of the iron-based mixed powder for powder metallurgy.

Moreover, the metal oxide fine powder shown in Table 2 was granulated to form porous particles. Table 2 shows the types and amounts of lubricant added during granulation. In addition, the addition amount (mass%) of the lubricant added at the time of granulation indicates the ratio of the lubricant to the mass of the iron-based mixed powder for powder metallurgy.
The particle size of the obtained porous particles is as shown in Table 2. A free lubricant was used separately from the lubricant impregnated in the porous particles. Table 2 shows the types of free lubricants and the amounts added. In addition, the addition amount (mass%) of a free lubricant points out the ratio of the lubricant to the mass of the iron group mixed powder for powder metallurgy.

  Table 2 shows the total amount of the lubricant added during granulation and the free lubricant in a ratio with respect to 100 parts by mass of the metal oxide fine powder.

These alloy component-coated iron powder, porous particles, and free lubricant were mixed to obtain an iron-based mixed powder for powder metallurgy, and the filling property was investigated with a filling tester shown in FIG.
In conducting the filling test of the iron-based mixed powder for powder metallurgy, the powder box 2 containing the iron-based mixed powder 1 for powder metallurgy is moved at a speed of 200 mm / second as shown in FIG. , 40 mm deep, 0.5 mm wide) for 0.5 seconds and filled in cavity 3 with iron-based mixed powder 1 for powder metallurgy. In addition, the arrow X in FIG. 1 shows the moving direction of the powder box 2.

  Next, the mass of the iron-based mixed powder 1 for powder metallurgy in the cavity 3 was measured, and the packing density of the iron-based mixed powder 1 for powder metallurgy was calculated from the volume of the cavity 3. The filling density is converted into a ratio (hereinafter referred to as filling factor) to the apparent density (value measured in accordance with JIS standard Z2504) of the iron-based mixed powder 1 for powder metallurgy before filling and shown in Table 3. The filling rate in Table 3 is an average value of 10 filling tests. The variation of filling rate is also shown with standard deviation. The larger the filling rate, the better the filling property, and 100% means that the filling is complete.

As is apparent from Table 3, the inventive example had a higher filling rate and a smaller variation than the comparative example.
Next, the iron-based mixed powder 1 for powder metallurgy was filled in a mold (outer diameter 11 mm, height 11 mm), and pressure-molded by applying a pressure of 588 MPa at room temperature to obtain a cylindrical green compact. The punching power when the green compact was removed from the mold was measured. The results are shown in Table 3. Further, the density of the obtained green compact was measured. The results are also shown in Table 3.

  As is clear from Table 3, the invention example had a lower output than the comparative example.

It is a perspective view which shows the principal part of a filling test machine. It is sectional drawing which shows the example of a porous particle typically.

Explanation of symbols

1 Iron-based mixed powder for powder metallurgy 2 Powder box 3 Cavity
11 Porous particles
12 Lubricant
13 Primary particles
14 Connected channel structure

Claims (7)

One kind or two or more kinds selected from inorganic substances, carbonaceous materials and organic substances having a particle diameter of 1 to 500 nm are used as primary fine particles, and porous particles having a particle diameter of 1 to 100 μm, which are aggregates of the primary fine particles, are impregnated with a lubricant. And an iron-based mixed powder for powder metallurgy, wherein the porous particles and iron powder are mixed.   The iron-based powder for powder metallurgy according to claim 1, wherein the porous particles have a connected channel structure. The iron-based mixed powder for powder metallurgy according to claim 1 or 2 , wherein a ratio of the lubricant is 20 to 400 parts by mass with respect to 100 parts by mass of the porous particles. The said lubricant is 1 type, or 2 or more types chosen from metal soap, bisamide, fatty acid amide, a fatty acid, a liquid lubricant, and a thermoplastic resin, The any one of Claims 1-3 characterized by the above-mentioned. The iron-based mixed powder for powder metallurgy described in 1. The inorganic _{material, SiO 2, TiO 2, Fe} 2 O 3 , and _{MgO · Al 2 O 3 · xSiO} 2 · yH 2 O, that is a kind of powder or a mixture of two or more powders selected from among talc The iron-based mixed powder for powder metallurgy according to any one of claims 1 to 4 . The iron-based powder for powder metallurgy according to any one of claims 1 to 5 , wherein the iron powder is made by adhering a powder for an alloy to the surface of the iron powder via an organic binder. The iron-based powder for powder metallurgy according to any one of claims 1 to 6 , further comprising a free lubricant.

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