WO2005087411A1 - Iron-based powder mixture for powder metallurgy - Google Patents

Abstract

An iron-based powder mixture for powder metallurgy that excels in fluidity as powder, giving a green compact whose withdrawal from a metal mold is easier than in the prior art, the obtained green compact having a density stabilized and enhanced as compared with that of the prior art. Such an iron-based powder mixture can be produced by a process comprising adding a free lubricant to an iron-based powder and mixing them, wherein the free lubricant has a particle diameter of ≤200 μm and a crush strength, as measured with respect to particles of average diameter, of 0.2 to 2 MPa and wherein the free lubricant is contained in an amount of 0.1 to 1 part by mass per 100 parts by mass of iron-based powder.

Description

 Iron-based powder mixture for powder metallurgy

 The present invention relates to iron-based powder mixtures for powder metallurgy. INDUSTRIAL APPLICABILITY The iron-based powder mixture of the present invention is suitable for use at room temperature without molding lubrication.

, But is not limited to this application.

 Thread

 Field 1

Background art

 Iron-based powder mixture for powder metallurgy (hereinafter abbreviated as iron-based powder mixture or simply mixture) is composed of iron powder (pure iron powder, alloy steel powder, etc.) and auxiliary raw material powder (copper powder, graphite powder, iron phosphide powder). Powder for alloying, etc., and powder for improving machinability such as MnS, if necessary), and further a binder such as zinc stearate / aluminum stearate to mix the powders together. It is a common practice to mix the product (hereinafter referred to as iron-based powder) with a free lubricant. In addition to the free lubricant, there is also a lubricant used by being attached to iron powder. Here, the reason for using the binder is as follows.

 The iron-based powder mixture is a mixture of various powders having different particle sizes, shapes and densities. However, there are various processes from the production of the mixture to the filling into a molding die (hereinafter simply referred to as a die), pressurization (compression) and molding into a molded body (hereinafter referred to as a green compact). Intervenes. For example, there are steps of transporting the mixture, charging the hopper and discharging the hopper, and further filling the mold. Therefore, various powders are not uniformly distributed in the mixture, and segregation is likely to occur.

When the mixture in which such bias has occurred is formed into a green compact, and the green compact is sintered into a final product, the composition varies from product to product. As a result, the size and strength vary greatly, resulting in a large number of defective products. Particularly, alloy powders such as copper powder, graphite powder, and iron phosphide powder mixed with iron-based powder are fine powders each having a smaller particle size than iron powder. In The degree of the variation is further increased.

 As a technique for preventing segregation in the iron-based powder mixture, a technique has been proposed in which a powder for alloy or the like is previously attached to the surface of iron powder using a binder. For example, this technology is disclosed in Japanese Patent Application Laid-Open Nos. Hei 1-291101, Japanese Patent Laid-Open No. 2-217403, Japanese Patent Laid-Open No. Hei 3-162502, and the like. I have. Hereinafter, the above technique using a binder is referred to as segregation prevention treatment. Next, the free lubricant will be described.

 Free lubricant refers to a powdered lubricant that is dispersed free of other particles in the iron-based mixture. Free lubricant is added to the iron-based powder mixture for the purpose of increasing the density of the compact (compact density), reducing the ejection force when removing the compact from the mold, and preventing the mold from being damaged. You.

 However, the iron-based powder mixture that has been subjected to the above-described segregation prevention treatment generally has poor fluidity, and thus it is important to prevent a decrease in fluidity due to the addition of a free lubricant. It is difficult to ensure fluidity while maintaining the above-mentioned lubrication performance. As free lubricants for the purpose of reducing fluidity and ejection force, for example, Japanese Patent Application Laid-Open Nos. 5-148505 and 9-263802 disclose stearic acid and oleic acid. Acid amide, stearic acid amide, molten mixture of stearic acid amide and ethylene bis stearic acid amide (EBS), one or more free powders selected from EBS, and zinc stearate. Disclosed are mixtures of free powder, or even a mixture of free powder of lithium stearate.

However, with the conventional lubricant described above, the density of the green compact formed from the obtained iron-based powder mixture cannot be said to be sufficiently high. In order to solve such problems, methods that respond with molding technology have also been proposed.For example, a method using a combination of mold lubricant and special molding methods such as warm molding, pressure sintering, and twice molding There is known a method of increasing the density of a green compact by a method. However, the use of molding technology leads to an increase in molding costs, and there is a need for an iron-based powder mixture for powder metallurgy that can provide good results without any special measures. On the other hand, as a method of achieving both fluidity, low ejection force, and high density of compacts by devising a lubricant, European Patent Application Publication No. EP 1 346 731 (A 2) Metal stones and their derivatives, such as zinc oxide, potassium stearate, lithium stearate, and lithium hydroxystearate; fatty acids, such as oleic acid and palmitic acid; bisamide stearylate, bisamide sebacate, etc. When adding one or two or more selected from thermoplastic resin powders such as copolymerized products of ethylenediamine and fatty acids or thermoplastic resins such as polyolefin as free lubricants, these lubricant particles (primary particles) are added in advance. A technique using a so-called “granulating type lubricant” has been proposed in which secondary particles are aggregated to increase the particle diameter. Note that a method for producing a powder from which such secondary particles are obtained is generally referred to as a granulation method.

 The use of this granulation type lubricant ensures fluidity due to its relatively large particle size when filled into the mold, and not only efficiently lubricates between the mold and particles during molding, but also partially The particles are broken into fine primary particles, so that they can easily enter gaps between particles, achieving low extraction power and high compact density. Disclosure of the invention

 [Problems to be solved by the invention]

 However, as a result of the investigations by the present inventors, it has been found that even an iron-based powder mixture containing a `` granulated lubricant '' as described in European Patent Application Publication No. EP 1 364 731 It could not be said that the density of the green compact was sufficiently increased, indicating that there is room for further improvement.

In addition, care must be taken that this lubricant does not break secondary particles when mixed with iron-based powder or the like. As a result, it takes more time than necessary to uniformly mix, which has the disadvantage of reducing productivity, and the effect has been somewhat unstable. In view of such circumstances, the present invention has good fluidity as a powder, can be easily extracted from a molding die as a compact, and the density of the obtained compact is more stable than before. To improve and improve iron-based powder mixtures for powder metallurgy. And is aimed at.

[Means for solving the problem]

 The present inventors have found that the above-mentioned problems can be solved by using a free lubricant in which the consolidation strength and the like are appropriately controlled. In addition, the present inventors have found a free lubricant different from the conventional form (primary particles aggregate to form secondary particles) despite being obtained by the granulation method, Was found to be suitable for achieving the above-mentioned consolidation strength. This free lubricant is presumed to be an agglomerate, but since it looks like a single particle, this shape is called `` secondary particles. Granulated particles whose particles cannot be identified. " The present invention is based on these findings. The gist configuration of the present invention is as follows.

 1. Powder metallurgy for powder metallurgy obtained by adding 0.1 to 1 part by mass of a free lubricant to 100 parts by mass of the iron-based powder to an iron-based powder having powder particles adhered to its surface, and mixing. An iron-based powder mixture, wherein the free lubricant has a particle diameter of 200 m or less and a particle having an average particle diameter of 0.2 to 2 MPa, for powder metallurgy. Iron-based powder mixture.

 Here, the powder particles are at least a part of the auxiliary raw material powder, and are mainly alloy powders, but may include machinability improving powders.

 2. The method according to 1 above, wherein the free lubricant is at least one selected from the group consisting of fatty acid monoamides, fatty acid bisamides, polyamides or amide oligomers, metal stones, polyesters, polyols and saccharides. The iron-based powder mixture for powder metallurgy described.

 3. The iron-based powder mixture for powder metallurgy according to the above item 2, wherein the free lubricant is a molten mixture of a fatty acid monoamide and ethylene bisstearic acid amide.

 4. The iron-based powder for powder metallurgy according to the above 3, wherein the fatty acid monoamide is at least one selected from the group consisting of stearic acid amide, oleic acid amide, and erucic acid amide. mixture.

5. The free lubricant is a powder obtained by a granulation method, An iron-based powder mixture for powder metallurgy according to any one of the above.

 6. The iron-based powder mixture for powder metallurgy according to the above item 5, wherein the free lubricant is in the form of particles in which secondary particles cannot be identified.

 7. The composition according to any of the above 1 to 6, wherein zinc stearate is further mixed as a free lubricant, and the total amount of the free lubricant is 0.1 to 1 part by mass with respect to 100 parts by mass of the iron-based powder. An iron-based powder mixture for powder metallurgy according to any one of the above. Brief Description of Drawings

 FIG. 1 is an SEM observation image showing an example of the free lubricant particles (melt mixture of stearic acid amide and EBS: granulated by spray drying) of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, the best embodiments of the present invention will be described, taking into account the circumstances that led to the invention.

 The present inventors arranged the problems of the prior art as follows.

 If the consolidation strength of the lubricant particles becomes unnecessarily high, the density of the green compact does not increase, and the strength of the sintered body thereafter decreases. In addition, if the particle size of the lubricant becomes larger than necessary, defects occur in the sintered body and the strength of the sintered body is reduced. On the other hand, if the particle size of the lubricant is too small, the fluidity is reduced. In order to improve the above-mentioned problems, the present inventors have studied on the effects of the strength and particle size of the lubricant on the density of the compact and the strength of the sintered body. It is known that the intended purpose can be achieved if the particle size distribution of the lubricant mixed with the iron-based powder in a free state is appropriately adjusted and the strength is controlled within a predetermined range. Got.

Specifically, an iron-based powder obtained by adding an auxiliary material such as copper powder and graphite powder to iron powder, adding a binder thereto, and binding the iron powder and the auxiliary material powder, is further added. Add a lubricant that does not bind to iron-based powder (free lubricant) to make an iron-based powder mixture. That is, the iron-based powder mixture of the present application includes powder particles to which the iron-based powder is bonded and particles of a lubricant that does not bond to the iron-based powder, but particularly a lubricant that does not bond to the iron-based powder. A certain limit was imposed on the particles. Hereinafter, a free lubricant whose crushing strength is controlled will be described first, and then, other raw materials, preferable manufacturing conditions, and the like will be described in a process order. A free lubricant that can be further added in addition to the free lubricant whose consolidation strength is controlled will be described later.

<Free lubricant with controlled consolidation strength>

 The particle size of the free lubricant whose consolidation strength is controlled shall be 200 m or less. The particle size of other free lubricants should be 200 μm or less.

 When an iron-based powder mixture containing a free lubricant having a large diameter of more than 200 / im is compression-molded, the free lubricant remains in the compact as a mass without being crushed, and it becomes large voids after sintering. As a result, the sintered body becomes defective and reduces the strength of the sintered body. Therefore, in the present invention, the upper limit of the particle size of the free lubricant is set to 200 m. The easiest way to reduce the particle size to 200 m or less is to pass through a sieve having a mesh size of 200 m or less. In addition, it is preferable that there is no particle having a particle diameter of more than 200 Am, but less than about 0.5% by mass is not a problem. Also, if there are many particles smaller than 10 m in the free lubricant particles with controlled crushing strength, the number of particles increases, the interparticle force increases, and the flow of the iron-based powder mixture containing the free lubricant increases. Is reduced. For this reason, in the case of the loose lubricant having a controlled pulverized strength, particles having a size of 10 μm or less are preferably limited to less than 30% by mass of the whole free lubricant. Naturally, the average particle size of the free lubricant is preferably 10 μm or more. In producing free lubricant particles having such upper and lower limits, the average particle size is 20 to 180 m, so this range is set to the range of the average particle size of the iron-based powder mixture according to the present invention. It is preferable to manage as. A more preferred range is from 20 to 100 / zm.

In particular, in the method for producing free lubricant particles (granulation method) described later, if the average particle diameter is set to 40 to 120 mm, the production can be performed without special management. A more preferred range is 30 to 80 μπι. The average particle size is measured using a laser diffraction type particle size distribution measuring device, and the average value based on mass is taken. Further, regarding the strength of the free lubricant particles, the particles are not broken down to 10 m or less during mixing at the time of producing the iron-based powder mixture, that is, at the time of mixing the free lubricant with the iron powder or the like. It is preferable to do so. When a small amount of iron-based powder mixture is prepared, this mixing may be performed manually without using a mixing device. On the other hand, in order to produce a practical-scale volume, a mechanical mixing stirrer is generally used. As the mixing stirrer, a device (and operating conditions) that does not exert excessive force on the powder during mixing, such as a V-type mixer and a Nauta mixer, is selected. On the other hand, since a Henschel mixer or the like exerts a relatively large force on particles, it is preferable to use lighter stirring than the standard (such as lowering the stirring speed) when using such an apparatus.

 In any case, when a mixing stirrer of a practical scale is used, since the equipment is relatively large and the amount of powder to be handled is large, a force is generated due to the weight of the powder. As a result, each free lubricant particle must have a pulverulent strength that can withstand these forces. According to the study of the present inventors, the consolidation strength is 0.2 MPa or more, preferably 0.5 MPa or more in the temperature range in which the iron-based powder mixture is produced. all right.

 Further, when the consolidation strength exceeds 2 MPa, even if the iron-based powder mixture containing the same is compression-molded, as described above, the free lubricant remains in the compact as a lump without being crushed. After sintering, large voids are formed after the sintering, resulting in defects of the sintered body, and the ejection force of the green compact becomes excessive. Therefore, in the present invention, the upper limit of the pummel strength is set to 2 MPa. Preferably it is 1 MPa or less.

In carrying out the present invention, the crushing strength of the free lubricant particles was measured by a micro compression testing machine (Shimadzu Corporation), which is a compression testing machine for fine single particles. . Note that if the particles to be measured include a wide range of particle sizes, the error is large. Therefore, the consolidation strength of the particles having the average particle size was determined. Specifically, it is necessary to extract particles of (average particle size ± 15 μm), perform the operation with 20 or more particles, and determine the average. did.

 When the consolidation strength was measured for particles having a particle size outside this range, the consolidation strength tended to decrease as the particle size increased. For this reason, when the measurement was performed without classification by the particle size, the measured values varied as described above. However, even in this case, the value obtained by averaging a large number of measurement results did not differ from the above average value. From this, it was confirmed that the consolidation strength measured for the particles of the above (average particle size soil 15 m) was representative of the whole. The temperature at which the measurement is performed is preferably the temperature at which the free lubricant is mixed during production. The temperature during mixing is from 10 to 100 ° C, preferably from 10 to 50 ° C, unless the temperature is particularly raised.

 In the present invention, the evaluation is based on the measured value at 25 ° C. as a guide. Next, the material of the free lubricant having controlled crushing strength according to the present invention includes fatty acid monoamides such as monoamide stearate and monoamide erucate, fatty acid bisamides such as ethylene bisstearate amide, and polyamides. Metal or amidoligomers, zinc stearate, calcium stearate, lithium stearate, polyesters, polyols, sugars and the like. These materials can be used alone or in a mixture. However, it is easier to adjust the average particle consolidation strength to a predetermined value by using two or more of the above compounds. · '

 In particular, a combination of a fatty acid monoamide and ethylene bisstearic acid amide is preferable, and among them, a combination of at least one selected from the group consisting of stearic acid amide, oleic acid amide, and pereric acid amide is preferred. More preferably, one of them is combined with ethylenebisstearic acid amide. The method for adjusting the pulverized strength of the free lubricant to the range of 0.2 to 2 MPa, preferably 0.5 to IMPa is not particularly limited, but the following method is particularly preferred.

Normally, free lubricant powder is produced by pulverizing a mass-produced lubricant. However, it is difficult to reduce the crushing strength to less than 2 MPa by this method. Therefore, it is preferable to use a so-called “granulation type lubricant” as described above.

 As a granulation method, first, primary particles obtained by a pulverization method described in European Patent Application Publication No. EP 1 364 731 1 are bound or aggregated with a marmellaizer or the like to form secondary particles. Can be applied. However, in this method, it is relatively difficult to stabilize the piling strength to 0.2 MPa or more or 0.5 MPa or more. On the other hand, a suitable granulation method includes a spray drying method.

 The form of the particles obtained by this method may be in the form of secondary particles as described above, or in the form of primary particles (primary-part icle-like) in which secondary particles cannot be identified. Particles of the latter form (granulated particles in which secondary particles cannot be distinguished) are easier to stabilize the compaction strength within a suitable range.

 In particular, when the melt mixture of the above fatty acid monoamide, ethylene bisstearic acid amide, and the melt is granulated by a spray drying method, the latter form is easily obtained. In the spray-dry method, a liquid obtained by mixing and melting both raw materials is sprayed into a cooling gas for granulation. Fatty acid monoamides are considered to have a suitable molecular weight, especially when at least one member selected from the group consisting of stearic acid amide, oleic acid amide and erlic acid amide is used. The results are good. The above composition (a molten mixture of at least one selected from the group consisting of amides of stearic acid, oleic acid and erucic acid and ethylenebisstearic acid) is particularly preferred. The reason for the suitability is not known in detail, but may be due to the following reasons.

As an example, Fig. 1 shows lubricant particles (scanning electron microscopic image) of a 2: 1 (mass ratio) molten mixture of stearate amide and ethylenebisstearate amide. As shown in Fig. 1, the melt mixture of these fatty acid monoamides and ethylene bisstearic acid amide was granulated by the spray drying method. It has no cohesive strength and becomes granulated particles that cannot be distinguished from individual secondary particles when used. However, these granulated particles The crushing strength of each of the primary particles obtained by the pulverization method, which is similar in appearance, is lower each time, and the crushing strength range of the present invention is just achieved. For this reason, the present inventors believe that the granulated particles that cannot distinguish individual secondary particles themselves are substantially aggregates of fine particles.

 That is, the lubricant particles (granulated particles for which secondary particles cannot be identified) obtained by the above method are easily crushed (crushed) at the time of compression molding, and are disaggregated to form fine small pieces. It is thought to be. It is considered that the small pieces enter between the iron-based powder particles and the like and exert a lubricating action. The function of this small piece is similar to the function of primary particles in a conventional granulation type lubricant (granulation type forming secondary particles), but it is more refined in terms of shape, size, softness, etc. Therefore, it is thought that it works more effectively to improve the density of green compacts than before. In the above composition, it is considered that small pieces containing a large amount of ethylenebisstearic acid are particularly effective after compaction.

 On the other hand, the above-mentioned lubricant particles are less likely to be decomposed than the secondary particles of the conventional granulated lubricant, and the fluidity and low extraction of the iron-based powder mixture are stable even after each step up to filling the mold. It is considered that each effect of output and green density improvement is maintained.

Note that the lubricant particles tend to be hollow as can be seen from FIG. The force S, which may have contributed to the above effects, is also unknown. Based on the above findings, the use of free lubricants with granulated particles that cannot distinguish the secondary particles obtained by granulation from two or more types of raw materials is the most important in terms of the power S, the optimization of the compaction strength, and the effect. preferable. Also, it is preferable that at least one of the raw materials is a substance having particularly good lubricating performance, for example, ethylene bisstearic acid amide. Suitable consolidation strength can be obtained by adjusting the composition and spray conditions (in the case of the spray-drying method). As described above, stearic acid amide, oleic acid amide and erucic acid amide are used. A combination of at least one selected from the group consisting of and a molten mixture of ethylenebisstearic acid amide is preferred. The composition ratio of the above fatty acid monoamide and ethylene bisstearic acid amide is preferably about 1.2: 1 to 3: 1 by mass. The tendency obtained from many experiments is that the use of stearic acid amide has slightly better fluidity and low ejection force, while the use of oleic acid amide has a slight increase in high-pressure powder density in absolute value. Get higher. L-acid acid amide has an intermediate characteristic between the two. Ethylene bisoleic acid amide is ethylene bisstearic acid amide.

It is similar to (EBS) in structure, physical properties, molecular weight, etc., and especially similar in lubricity. Therefore, similar good results can be expected when used in the above-mentioned free lubricant together with or instead of EBS.

 In addition, behenic acid amide and palmitic acid amide are similar in structure, physical properties, molecular weight, and the like to stearic acid amide, oleic acid amide, and erlic acid amide. Accordingly, the fatty acid monoamide may be used together with or instead of at least one selected from the group consisting of stearic acid amide, oleic acid amide and erlic acid amide. Similar good results can be expected even when oxamine or palmitic acid amide is used as the free lubricant. It is to be noted that the above granulation operation for producing the free lubricant can be freely combined with a pulverization operation, a sieving operation and the like.

<Other free lubricants>

 In addition, when zinc stearate is mixed as a free lubricant in addition to the above-mentioned lubricant having controlled pulverized strength, fluidity is particularly improved. The ratio (mass ratio) of the lubricant and the zinc stearate whose consolidation strength is controlled is preferably about 4: 1 to 2: 3. The particle size of zinc stearate is not particularly limited, but is preferably about 1 to 20 μm.

In addition, lithium stearate and manganese stearate, which are substances similar to zinc stearate, have similar effects. Polyethylene, mannitol, etc. also have good effects as free lubricants. Therefore, at least one selected from the group consisting of zinc stearate and these substances added may be mixed in the above ratio in total. The preferred particle size range for these materials is also The same applies to the case of zincate.

 The method for producing powder particles of zinc stearate and the like described above is not particularly limited, and the conventional pulverization method is sufficient in view of cost. The crushing strength does not need to be particularly controlled, and there is no problem if it is larger than 2 MPa.

 The addition of free lubricants other than those described above is generally less preferred. Amount of free lubricant added>

 The free lubricant is added in a total amount of 0.1 to 1 part by mass with respect to 100 parts by mass of the iron-based powder. If the ratio of the free lubricant is less than 0.1 part by mass, a sufficient lubricating effect cannot be obtained, while if it exceeds 1 part by mass, a high green compact density cannot be obtained.

<Other raw materials and production conditions>

 Known iron-based powders such as pure iron powder and alloy steel powder can be used as the iron powder as a raw material of the iron-based powder mixture according to the present invention, and there is no particular limitation. Further, a part of the alloy powder may be bonded to pure iron powder or the like by partial diffusion bonding.

 The auxiliary raw material powder is mainly a so-called alloy powder added to improve the strength and other properties of the sintered product. Alloy powders include graphite powders and powders mainly composed of various metals (Cu, Mo, Ni, Cr, etc.). In addition, powder for improving machinability (eg, powder of MnS) can be added as an auxiliary material. Known auxiliary raw material powders other than those described above can also be used without problems. In the present invention, the auxiliary raw material powder is bonded to the iron powder using a binder (segregation prevention treatment), but any known binder can be applied without any problem. The following organic binders are particularly suitable.

 (1) Metal stone (eg, zinc stearate, lithium stearate, calcium stearate)

 (2) Eutectic mixture of metal lithology and fatty acids (stearic acid, oleic acid, etc.)

(3) Fatty acid amides (such as stearyl acid amide and ethylene bis stearamide) (4) Eutectic mixture of metal lithology and fatty acid amide

 (5) Thermoplastic resins (polyolefins containing polyethylene, polypropylene, polyamides, polystyrenes, etc.)

 It goes without saying that these may be used alone or in combination. The addition amount may be appropriately determined by referring to a known technique, but generally about 0.1 to 1.0 parts by mass is added to 100 parts by mass of the iron powder.

 Note that it is not necessary to bind all the auxiliary raw material powders, and it is only necessary to preferentially bind auxiliary raw material powders that tend to cause segregation, such as graphite powder. Further, a powdery lubricant may be similarly bonded to the iron-based powder. As the lubricant added for the purpose of binding, those disclosed in known technical literatures can be used without any problem.

 The average particle size of the iron powder, the auxiliary material, and the lubricant powder to be combined is preferably in the range of about 0.1 to 250 μm. The total content of the auxiliary raw material powder is generally about 0.05 to 10 parts by mass with respect to 100 parts by mass of the iron powder. When mixing the free lubricant with the iron-based powder, there is a risk of consolidation, although the method has been improved, and it is preferable to avoid the conditions of the apparatus which exerts considerable force on the powder as described above. As such a mixer, a mixer having a small shearing force applied to the mixed powder, such as a container rotating type, a mechanical stirring type, a flow stirring type, and a non-stirring type, is preferable. In the container rotary mixer, a horizontal cylindrical type, an inclined cylindrical type, a V type, a double conical type and a continuous V type are preferable, and a mixer having a built-in stirring blade can also be suitably used. In the mechanical stirring type mixer, a ripon type, a screw type, a multi-axis paddle type, a conical screw type and a rotating disk type are preferable. The fluidized stirring type mixer is preferably a fluidized bed type, a swirling flow type, or a jet pump type.

The operating conditions for mixing are determined appropriately according to the pressure strength, and also depend on the dimensions of the mixing vessel. For example, when using a 1-ton class V-type container rotary mixer for industrial production, it is preferable to operate the container at a rotational speed of 5 to 10 rpm for about 5 minutes, but 1.6 liters. With a small V-shaped container rotary mixer Is about 25 'rpm and about 15 minutes is suitable (about 60 minutes is no problem). Note that this example is merely a guide, and the upper limit of the appropriate mixing time and mixing intensity (the number of rotations of the container or the stirring device, etc.) may be set while appropriately examining the mixing result. Investigation into whether the mixing conditions were appropriate can be confirmed by confirming that the characteristics of the obtained iron-based powder mixture are compatible. Alternatively, whether or not the granulated particles are sufficiently maintained after mixing may be directly measured. This can be confirmed by removing the other powder from the iron-based powder mixture after mixing by means such as magnetic separation, and then measuring the particle size distribution of the free lubricant. For reference, in the case of a conventional granulated type free lubricant having a pulverized strength of less than 0.2 MPa, a certain amount of granulated particles can be obtained by mixing for 5 minutes in the 1-ton class V-type container rotary mixer. In order to maintain it, the rotation speed of the vessel must be less than 8 rpm.

<Molding method of green compact>

 As a molding method in compression molding, any known method is suitable. For example, a method in which the iron-based powder mixture is brought to room temperature and the mold is heated to 50 to 70 ° C (preheating) is preferable because the powder can be easily handled and the green compact density is further improved.

 Although a warm forming method may be used, the cost increases. When a molten mixture of stearic acid amide and EBS is used, the melting point of the free lubricant is so low that the fluidity of the iron-based powder mixture may deteriorate due to heating. Not suitable.

 Further, a lubricant may be separately applied or electrostatically attached to the mold (mold lubrication). However, since the present invention has an advantage in cost that such a lubricant can be omitted, it is preferable to omit mold lubrication.

A publicly known method may be used for the sintering heat treatment after the green compact is formed. In addition, the obtained sintered body can be subjected to treatment such as carburizing and quenching (CQT) to control the material. 〔Example〕

 (Invention Example 1)

 0.2 parts by mass of a mixture of 2.0 parts by mass of copper (symbol: Cu) powder and 0.8 parts by mass of graphite powder per 100 parts by mass of pure iron powder equivalent to a commercial product The stearate amide was added as an organic binder, and heated and mixed (segregation preventing treatment) to obtain an iron-based powder.

 In addition, after melting stearic acid amide and ethylenebisstearic acid amide at a mass ratio of 2: 1, granulation was performed by spray drying to obtain a particle diameter of 10 μm or more. The melting point of this granulated product was about 11 ° C. This granulate (particle size 1

Lubricant of 50 μm or less and an average particle diameter of 70 μm) was added to 100 parts by mass of the iron-based powder, and 0.2 parts by mass was mixed with a V-type mixer at 25 ° C. Thus, an iron-based powder mixture was obtained. The V-type mixer used had a capacity of 1.6 liters, the rotation speed was 24 rpm, and the mixing time was 60 minutes.

 Note that the crushing strength of the mixed lubricant particles is 0.

It was 6 MPa. The flowability of the iron-based powder mixture was measured with a 2.63 mm funnel, and showed a good flowability of 21 sec Z 50 g. Subsequently, the iron-based powder mixture was filled in a mold, and compressed at a pressure of 686 MPa according to the standards of the Japan Powder Metallurgy Association (JPMA P09, JPMA P13). The compact was formed into a compact having a diameter of 11.3 mm and a length of 11 mm.

When the density of the obtained green compact and the pulling force from the molding die were measured, they were 7.27 Mg / m ³ and 16 MPa, respectively. In this method, when the extraction power is 2 OMPa or more, so-called mold galling occurs, and the surface of the green compact is apt to be scratched. It was compressed at a pressure of 686 MPa to form a ring with an outer diameter of 38 ηιιηφ and an outer diameter of 25 mm φ. Atsu 7

(Invention Example 2)

To 100 parts by mass of the same iron-based powder as in Example 1, oleic acid amide and ethylene A mixture of stearic acid amide and a 2: 1 mass ratio of a granulated material with a particle size of 10 m or more (lubricant with a particle size of 150 m or less and an average particle size of 70 μm) was melted in a mass ratio of 2: 1. .2 parts by mass were added and mixed at 25 ° C. with a V-type mixer to obtain an iron-based powder mixture. Note that when the pressurized strength of the lubricant particles was measured, it was 0.3 MPa for the particles at 25 ° C and 70111. Further, the fluidity of the iron-based powder mixture was measured with a funnel having a diameter of 2.63 mm and found to be as good as 25 g _C 50 g.

Subsequently, the obtained iron-based powder mixture was filled in a mold, and compressed at a pressure of 686 MPa according to the standards of the Japan Powder Metallurgy Association (JPMAP09, JPMAP13). A green compact having a diameter of 11.3 mm and a height of 11 mm was produced. When the density of the green compact thus obtained and the pulling force from the molding die were examined, it was 7.29 Mg / m ³ , and the pulling force was 14 MPa.

(Invention Example 3)

 To 100 parts by mass of the same iron-based powder as in Example 1, the same lubricant as in Example 1 was added in the same amount as in Example 1, and heated and mixed at 70 ° C with a Henschel mixer (blade). The number of revolutions was 500 rpm, the mixing time was 1 minute), and an iron-based powder mixture was obtained. The fluidity of this iron-based powder mixture was measured with a funnel having a diameter of 2.63 mm, and showed a good fluidity of 21 sec / 50 g.

This iron-based powder mixture is filled in a mold, and compressed at a pressure of 686 MPa according to the standards of the Japan Powder Metallurgy Association (JPMA P09, JP MA P13). A green compact of 1 1.3 mm, height: 11 mm was produced. When the density of the obtained green compact and the pulling force from the molding die were examined, it was 7.27 Mg / m ³ , and the drawing power was 16 MPa.

 As described above, the iron-based powder mixture according to the present invention is obtained by mixing iron powder or the like and a lubricant by vigorous stirring. However, since the lubricant maintains an appropriate particle size distribution, it is preferable. Showed fluidity.

(Comparative Example 1)

To 100 parts by mass of the same iron-based powder as in Example 1, ethylene bisstearic acid amide (lubricant) having a particle size of 150 / im or less and an average particle size of 15 _m was mixed with another lubricant. Without using it, 0.2 part by mass of a single substance was added and mixed at room temperature with a V-type mixer.

 When the crushing strength of the lubricant particles was measured, it was as strong as 2.5 MPa for the particles at room temperature and 70 / xm.

The obtained iron-based powder mixture was filled in a mold, and compressed at a pressure of 686 MPa according to the standards of the Japan Powder Metallurgy Association (JP MA P09, J JMAΡ13). A green compact having a diameter of 11.3 mm and a height of 11 mm was produced. When the density of the obtained green compact and the pulling force from the molding die were examined, it was found to be 7.20 Mg / m ³ , and the pulling power was 23 MPa. That is, the density of the green compact and the pulling force from the molding die were not satisfactory values.

(Comparative Example 2)

 Oleic acid amide and ethylene bisstearic acid amide were melted in the same iron-based powder as in Example 1 at a mass ratio of 2: 1. 2 parts by mass were added and mixed at room temperature with a V-type mixer to obtain an iron-based powder mixture. Needless to say, this free lubricant contains more than 50% by mass of particles having a particle size of 10 m or less. The flowability of the iron tomb powder mixture could not be measured using a 2.63 mm φ funnel because no flow occurred.

A mold is filled with the iron-based powder mixture, and compressed at a pressure of 686 MPa according to the standards of the Japan Powder Metallurgy Association (JPMAP09, JPMAP13). A compact of 3 mm and a height of 11 mm was prepared. When the density and the molding force of the obtained green compact were examined, they were found to be 7.29 MgZm ³ and 14 MPa, respectively.

(Examples 4 to 20, Comparative Examples 3 to 7)

 Table 3 shows the results of producing the iron-based powder mixtures shown in Tables 1 and 2 and measuring the properties. Manufacturing conditions and methods for investigating characteristics other than those described in Tables 1 and 2 are the same as those of Invention Example 1. '

The iron-based powder B was 0.6 parts by mass of graphite with respect to 100 parts by mass of iron powder (partially diffused alloy powder) obtained by partially diffusing and joining 2 mass% of Ni powder and 1 mass% of Mo powder. The powder was mixed and segregated in the same manner as in Example 1 with 0.2 parts by mass of stearic acid amide. Prevention treatment was applied. The addition amounts of Ni and Mo are mass fractions based on the partially diffused alloy powder.

 In addition, when zinc stearate is further added as a free lubricant, it is mixed with a granulated lubricant in advance and then added (Inventive Examples 11 to 13, 15, 16, 18, and 19). The method of mixing with the iron-based powder together with the granulation type lubricant (Inventive Examples 4 to 10 and 17) was appropriately used.

Comparative Examples 4 to 7 are examples of conventional secondary particle granulation type free lubricants, in which primary particles having a particle size of about 1 μm are aggregated to form secondary particles. In these comparative examples, when the mixing was performed under the condition that the shear force applied to the powder was relatively large (Comparative Examples 4 and 5), the fluidity was significantly reduced. In addition, even when the powder was mixed with reduced power, the fluidity was not sufficiently improved when the raw material of the free lubricant was a soft substance (Comparative Example 6), and when the raw lubricant was a hard substance (Comparative Example 6). 7) indicates that the density of the green compact is not sufficiently improved.

table 1

* 2: Mass percentage with respect to total free lubricant * 3: Mass part with respect to 100 parts by weight of iron-based powder * 4: Mixing granulated by mixing thiomethacrylate with adhesive Table 2

 * 1: A = pure iron powder +0.8 mass% black +2. Omass% Gu powder (bonded with 0.2 mass% Xamido thearate Y)

 B = 2mass% N i -1 massttlo Partially diffused alloy powder + 0.6mass% graphite powder (bonded with 0.2mass% X ammonium terate) * 2: Percentage by mass based on total free lubricant

* 3: Parts by mass based on 100 parts by weight of iron-based powder Table 3

 * 2: Die is preheated to 60 ° C during compression molding

Industrial potential

 ADVANTAGE OF THE INVENTION According to the present invention, not only the fluidity as a powder is good, and it is possible not only to reduce the extraction force of a green compact when molded, but also to increase the density compared to the conventional one, and to stabilize and improve the strength of a sintered body. Thus, an iron-based powder mixture for powder metallurgy is obtained.

Claims

The scope of the claims 1. For powder metallurgy obtained by adding 0.1 to 1 part by mass of a free lubricant to 100 parts by mass of the iron-based powder to an iron-based powder having powder particles adhered to its surface, and mixing. An iron-based powder mixture,  An iron-based powder mixture for powder metallurgy, wherein the free lubricant has a particle diameter of 200 / zm or less and a particle having an average particle diameter of 0.2 to 2 MPa. 2. The free lubricant is at least one selected from the group consisting of fatty acid monoamides, fatty acid bisamides, polyamides or amide oligomers, metal stones, polyesters, polyols and saccharides. The iron-based powder mixture for powder metallurgy according to 1. 3. The iron-based powder mixture for powder metallurgy according to claim 2, wherein the free lubricant is a molten mixture of a fatty acid monoamide and ethylene bisstearic acid amide. 4. The iron base for powder metallurgy according to claim 3, wherein the fatty acid monoamide is at least one selected from the group consisting of stearic acid amide, oleic acid amide, and erucic acid amide. Powder mixture. 5. The iron-based powder mixture for powder metallurgy according to any one of claims 1 to 4, wherein the free lubricant is a powder obtained by a granulation method. 6. The iron-based powder mixture for powder metallurgy according to claim 5, wherein the free lubricant is in the form of particles in which secondary particles cannot be identified. 7. The composition according to claim 1, wherein zinc stearate is further mixed as a free lubricant, and the total amount of the free lubricant is 0.1 to 1 part by mass with respect to 100 parts by mass of the iron-based powder. An iron-based powder mixture for powder metallurgy according to any one of the above. 8. The method according to claim 6, wherein zinc stearate is further mixed as a free lubricant, and the total amount of the free lubricant is 0.1 to 1 part by mass with respect to 100 parts by mass of the iron-based powder. Iron-based powder mixture for powder metallurgy.