JP2778410B2 - Anti-segregation mixed powder for powder metallurgy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a segregation-preventing mixed powder for powder metallurgy, which has very little segregation and dust generation, has excellent fluidity, and has little change over time in powder characteristics as a mixed powder.

[0002]

2. Description of the Related Art When manufacturing mechanical parts and the like by powder metallurgy, various types of iron powder are used to improve physical properties such as sintering strength, mechanical strength and abrasion resistance, machinability and magnetic properties of products. Compounded with physical property improving component powder or graphite powder for strengthening powder metallurgy products, and also for fluidity as alloy powder, improvement of compression ratio during compression molding, prevention of seizure on molds, etc. It is common to mix and mix a lubricant before molding and sintering. However, in many cases, there is a difference in specific gravity and particle size between the powders to be mixed, so that dusting and segregation occur, which may cause variations in required characteristics such as dimensional accuracy of the obtained sintered product. It has been an issue for many years.

[0003] First, dust generation is mainly caused by the presence of fine powder having a small specific gravity, such as graphite powder.
Not only is the contamination of the working environment when handling powders a problem, but also yields are reduced. Also, segregation occurs when powders with a large difference in specific gravity and particle size are mixed with each other,
For example, it is well known that when the powder mixture is discharged from the hopper, the composition of the alloy components changes at the beginning, middle, and end.

[0004] As means for solving the problems of dust generation and segregation in such mixed powders, the following methods have been broadly classified so far. (1) a method of adding a liquid additive such as tall oil to a powder mixture as disclosed in JP-A-60-502158, (2)
JP-A-63-103001 and JP-A-2-217403 disclose a method in which a solid binder is dissolved in a solvent, added and uniformly mixed, and then the solvent is evaporated. A so-called hot melt method in which a solid binder is melted during a mixing operation as shown in 2064011 and JP-B-63-16441.

As means for preventing the segregation of the added alloy powder, (4) as described in JP-B-54-21803 and JP-A-2-145703, the iron powder for powder metallurgy is provided with desired characteristics. A so-called partial diffusion method in which an alloy powder containing an alloy component is previously mixed, heated in a reducing atmosphere, and then pulverized so that the alloy powder adheres to the surface of the iron powder for powder metallurgy. As shown in 371501, a method of adhering Fe-Mo alloy powder having a specified maximum particle size and alloy powder composition to the surface of an iron-based powder using a binder.

However, these methods are effective in preventing dusting and segregation of fine powders having a low specific gravity such as graphite powder, but are effective in preventing segregation of various alloy powders having a relatively high specific gravity such as copper powder. Was less effective. For example, for parts where copper powder is blended at a particularly high concentration, the segregation of copper powder causes variations in dimensional change and strength, so more stable characteristics are required these days, and each of the above methods is fully satisfactory. The fact was that no good results were obtained.

That is, although the above methods (1) to (3) are certainly effective in preventing segregation of graphite powder and fine powder having a small specific gravity, various methods having a relatively high specific gravity such as copper powder are used. Sufficient effects have not been obtained for preventing segregation of powder and commonly used inexpensive alloy powder of 10 to 75 μm.

The following problems have been pointed out in the conventional method using a liquid binder. That is, when a mineral oil such as a spindle oil is added, the angle of repose of the mixed powder becomes extremely large, and the fluidity is remarkably deteriorated, so that bridging tends to occur at the time of discharge from a hopper or the like, and workability is reduced. Mineral oils are usually volatile, and even vegetable oils change the quality of dry or semi-dry oils, such as tall oil, by reacting with oxygen in the atmosphere. Characteristics (fluidity, apparent density) and green compact characteristics vary greatly.

In the case of the above method (4), for example, in order to obtain Fe-P steel powder as disclosed in Japanese Patent Publication No. 54-21803, it is necessary to use a hydrogen-containing atmosphere at a relatively low temperature of about 500 to 800 ° C. A heat treatment must be performed, and a special heating furnace is required to prevent explosion of hydrogen gas used as an atmosphere gas, and Ni, Cu, Mo is used as disclosed in JP-A-2-145703. In the case of adhesion, etc., the melting point of each alloy element is significantly different, so the diffusion of the specific alloy element excessively progresses, and the compressibility of the obtained steel powder is lowered, or conversely, sufficient adhesion is obtained. The problem that it cannot be done arises.

[0010] Further, Japanese Patent Laid-Open No.
As disclosed in US Pat. No. 3,371,501, in the case of steel powder in which a Fe-Mo alloy powder having a defined maximum particle size and alloy powder composition is adhered to the surface of iron-based powder particles using a binder, a relatively small amount of alloy is used. In the powder addition amount (about 3% by weight or less), although the effect of preventing segregation is slightly recognized with respect to the simple mixed powder (premix powder) of the powder metallurgy steel powder and the alloy powder, it is as large as about 15% by weight. The effect of preventing segregation when the alloy powder of (1) is blended is insufficient, and it is impossible to prevent the powder characteristics (apparent density, fluidity) of the mixed powder from deteriorating or changing over time due to segregation.

An alloy powder as disclosed in Japanese Patent Application Laid-Open No. 4-350101 has a very high product of the calculated quenching multiple of the mixed powder, so that a partially diffused steel powder can be obtained by using the alloy fine powder. Must be cooled very slowly after the heat treatment, which is not suitable for industrial production. In addition, although the publication suggests a description of the effect of preventing segregation by the binder, the prior art as described in the above (1) to (3) prevents the segregation when a large amount of alloy powder is used in combination. Therefore, it is impossible to avoid variations in strength and a decrease in dimensional accuracy due to segregation.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and it is an object of the present invention to provide a powder metallurgy with a powder of a physical property improving component such as an alloy powder, a graphite powder or a lubricant. An object of the present invention is to provide a segregation-preventing powder for powder metallurgy that does not impair dusting, component segregation, and changes over time without impairing properties such as compressibility and fluidity in a mixture of iron powder-based powders.

[0013]

Means for Solving the Problems According to the constitution of the present invention taken to solve the above-mentioned problems, a physical property improving component powder having a maximum particle size of 75 μm or less is used. (1) An iodine value of 15 or less and 100 ° F. (2) Styrene containing 5-75 parts by weight of styrene, butadiene and / or isoprene: 95-25 parts by weight as a monomer component. It has a gist in that it is mixed with an iron powder for powder metallurgy together with a binder for powder metallurgy comprising a copolymer or a hydride thereof to prevent segregation. Preferred physical property improving component powders used herein include metals, alloys or metal oxides such as Ni, Cu, Mo, Cr and Mn, metal oxides thereof, alloys of these alloying elements with iron, Si, P, S and the like. Oxides or alloys thereof with the above-mentioned alloying elements or iron can be mentioned. In the present invention, when a graphite powder and / or a lubricant for powder metallurgy is contained together with these physical property improving component powders However, such segregation can be effectively prevented.

[0014]

[Functions and Examples] In addition to iron powder, one or more powders are used for the purpose of improving various physical properties such as sintered body strength, wear resistance and machinability. (Physical property improving component powder) is generally blended.
Many of these physical property improving component powders have a specific gravity difference and / or a particle size difference from iron powder. Therefore, simply mixing them easily causes the physical property improving component powder to segregate easily. Therefore, as a result of conducting various studies to solve this problem, a physical property improving component powder having a maximum particle diameter of 75 μm or less was used, and (1) an iodine value of 15 or less and a viscosity at 100 ° F. were used as a binder. A liquid fatty acid of 50 cSt or less, or (2) a styrene-based copolymer containing 5 to 75 parts by weight of styrene and 95 to 25 parts by weight of butadiene and / or isoprene as a monomer component, or a hydride thereof. It has been confirmed that the above purpose can be solved satisfactorily if used. Hereinafter, the reasons for the limitation will be described with reference to examples.

Example 1 (Reason for Limiting the Iodine Value of Liquid Fatty Acid to 15 or Less) To an iron powder for powder metallurgy (a particle size of 180 μm or less), a graphite powder (average particle size of 3 μm) was added at 0.8% with respect to the total amount of the mixed powder. Copper powder (Atomized copper powder: Average particle size)
30 μm) was mixed at 2.0% with respect to the total amount of the mixed powder, and mixed at 100 rpm for 5 minutes using a rotary blade mixer.
Viscosity is constant (viscosity at 100 ° F. is 30 cSt) and iodine value is 2 (sample name A), 7 (same B), 12 (same C), 17 (same D), 50 (same E), 100 The same fatty acid as in (F) was added so as to be 0.08% with respect to the total amount of the mixed powder, and the mixture was further mixed at 100 rpm for 6 minutes. At this time, primary sampling was performed to obtain a test powder for an airflow method described below.

Next, a lubricant (zinc stearate: average particle size)
30 μm) was added so as to be 0.75% with respect to the total amount of the mixed powder, and the mixture was mixed at 100 rpm for 2 minutes. At this time, secondary sampling was performed to obtain a test powder for investigating the degree of segregation of copper powder and graphite powder and the powder characteristics.

First, the degree of carbon adhesion was measured by a gas flow method using the primary sampled test powder. Figure 2 for measurement
New crypore filter 1 as shown in (mesh 12μm)
Funnel-shaped glass tube 2 with inner diameter (inner diameter 16 mm, height 106 mm)
The sample powder P (25 g) was put thereinto, nitrogen gas was flowed from the bottom at a rate of 0.8 liter / min for 20 minutes, and the graphite adhesion rate was determined by the following equation. Graphite adhesion rate (%) = [Amount of carbon after nitrogen gas flow / Amount of carbon before nitrogen gas flow] x 100 (%)

Next, the powder characteristics and the degree of segregation of the components were measured using the test powder sampled secondarily. The apparent density was measured according to JIS-Z2504, and the fluidity was measured according to JIS-Z2502. Regarding the degree of graphite segregation and the degree of segregation of copper powder, when 500 kg of each mixed powder was formed by continuous pressing, samples formed in one hopper were extracted at equal intervals at 10 points, and these formed body samples were analyzed. It was defined as the difference between the maximum and minimum values for graphite and copper. Table 1 shows the results. As a comparative powder, an example was added in which a premix without the addition of fatty acid (each sample G) and spindle oil (the same H) or tall oil (the same I) were added instead of the fatty acid.

[0019]

[Table 1]

From Table 1, it can be seen that the mixed powder to which the fatty acid was added showed an improvement in the graphite adhesion rate and an improvement in the prevention of component segregation as compared with the case where no fatty acid was added. In addition, those to which spindle oil or tall oil is added are effective in improving graphite adhesion rate and preventing segregation of components, but are not preferred because of poor fluidity. Next, the apparent density and the fluidity were measured by changing the number of days elapsed after the production in order to check the change over time in the powder characteristics. The results are shown in Tables 2 and 3.

[0021]

[Table 2]

[0022]

[Table 3]

From Tables 2 and 3, it can be seen that the iodine value of the fatty acid and the change with time of the powder properties are closely related. When the iodine value is 15 or less, the changes over time in the apparent density and the fluidity for two months are small, but when the iodine value exceeds 15, the apparent density decreases and the fluidity deteriorates remarkably.

The definition of the iodine value is a value obtained by converting the amount of halogen absorbed when a halogen is applied to a sample into the amount of iodine and expressing it in percentage with respect to the sample. In the case of a fatty acid, it is proportional to the amount of unsaturated bonds. When there are many unsaturated bonds, fatty acids are liable to undergo oxidative deterioration because they react with oxygen at the portion and easily polymerize. Therefore, the higher the iodine value, the lower the apparent density of the mixture due to oxidative deterioration and the lower the fluidity. Therefore, in the present invention, the iodine value of the fatty acid is limited to 15 or less.

Example 2 (Reason for Limiting the Viscosity of Liquid Fatty Acid at 100 ° F. to 50 cSt or Less) A powdery iron powder (particle size of 180 μm or less) and graphite powder (average particle size of 3 μm) were mixed with the total amount of the mixed powder. 0.8% (weight ratio: same hereafter) copper powder (atomized copper powder: average particle size
30 μm) was mixed at 2.0% with respect to the total amount of the mixed powder, and mixed at 100 rpm for 5 minutes with a rotary blade mixer.
The iodination is constant at 2 and the viscosity at 100 ° F. is 3 cSt (sample name J), 7 cSt (same K), 18 cS, respectively.
t (the same K), 30 cSt (the same M), 55 cSt (the same N), and 80 cSt (the same O) fatty acids are added so that each becomes 0.08% with respect to the total amount of the mixed powder.
Mixing was performed for minutes. At this point, primary sampling was performed to obtain a test powder for the air flow method.

Next, a lubricant (zinc stearate: average particle size)
30 μm) was added so as to be 0.75% with respect to the total amount of the mixed powder, and the mixture was mixed at 100 rpm for 2 minutes. At this time, a secondary sampling was performed to obtain a test powder for investigating the degree of segregation of copper powder and graphite powder and powder characteristics. Table 4 shows the results of the carbon adhesion rate and the powder characteristics.

[0027]

[Table 4]

From the above results, it can be seen that even if the viscosity is changed, the effect of improving the carbon adhesion rate and preventing the segregation of the components is almost the same. For Samples (J), (N) and (O), poor flowability was observed.
Was limited to 50 cSt or less.

Reference Example 1 (Reasons for Determining Copolymer Composition of Styrene-Based Copolymer) In this experiment, iron powder for powder metallurgy (particle size of 180 μm or less) and graphite powder (average particle size of 2 μm) were used as base powders.
m), which were mixed at a ratio of 99 parts by weight of the former to 1 part by weight of the latter.

As shown in FIG. 2 (flow diagram), these powdery raw materials were stirred at a high speed by a rotary blade type mixer, and a toluene solution of a binder composed of a styrene copolymer having a copolymer composition shown in Table 5 was obtained. Is dropped or sprayed, and the mixture is stirred vigorously for about 5 minutes, then switched to gentle stirring and dried for a predetermined time to remove the solvent. When a lubricant is used in combination, the graphite powder and the lubricant may be simultaneously attached to the iron powder for powder metallurgy using a binder. Then, a part of the dried powder is extracted and used as a sample for measuring the graphite scattering rate. To the remaining dry powder, 0.75% by weight of zinc stearate powder as a lubricant is added and stirred to prepare a sample for flowability measurement. Table 5 shows the results.

[0031]

[Table 5]

As is clear from Table 5, when the copolymerization ratio of styrene is less than 5 parts (parts by weight, the same applies hereinafter), the graphite scattering rate is suppressed, but the fluidity of the mixed powder becomes poor. A problem arises in the compactibility. On the other hand, when the copolymerization ratio of styrene exceeds 75 parts, the graphite scattering rate cannot be sufficiently reduced, and the function as a binder cannot be sufficiently exhibited. Therefore, in order to simultaneously satisfy the graphite scattering rate and the fluidity, the copolymerization ratio of styrene and butadiene should be 5 to 75%.
Parts: The latter must be set in the range of 95 to 25 parts. This tendency can be obtained by using isoprene as a monomer component to be copolymerized with styrene, or by using butadiene and isoprene together, or by using these hydrides.

Reference Example 2 Next, Table 6 shows that butyl acrylate: methyl methacrylate: acrylic acid = 57 as typical examples of other organic binders.
38: 5 (weight ratio) terpolymer (comparator: weight average molecular weight about 50,000) was selected, and the binder (styrene: butadiene = 35: 65 weight ratio copolymer: weight) according to the present invention. (The average molecular weight is about 100,000) (the experimental method is the same as above). As is clear from this table, the binder according to the present invention is different from other organic binders. It can be seen from the comparison that both the graphite scattering rate and the fluidity are excellent.

[0034]

[Table 6]

REFERENCE EXAMPLE 3 As described above, the preferable copolymer composition of the styrene copolymer used in the present invention is as described above. It must be spread evenly, and the surface of the iron powder must be uniformly coated with no excess or shortage to bind well with the physical property improving component powder and lubricant powder,
For that purpose, it is considered that the concentration and the amount of the binder added to the raw material powder are also important. Therefore, a binary copolymer of styrene: butadiene = 35: 65 (weight average molecular weight:
Experiments were conducted to clarify the effects of the concentration of the binder, the amount added, and the like in the toluene solution on the graphite scattering rate. In this experiment, the drying time ratio affecting the productivity (the concentration of the binder in the toluene solution was 5%, and the amount of the binder relative to the raw material powder was 0.1% in terms of the solid content, but the drying time was 1.00. Time ratio). Table 7 shows the results.

[0036]

[Table 7]

As is evident from Table 7, when using the styrene copolymer as the binder, not only the solution concentration of the binder and the amount of solids added to the raw material powder, but also the amount of The addition amount of the styrene-based copolymer solution should also be considered.If this value is too low, the binder solution becomes difficult to spread over the entire surface of the iron powder, resulting in insufficient bonding, and it is difficult to sufficiently suppress segregation and graphite scattering. Become. On the other hand, if this value is too high, segregation of the binder solution itself occurs in the mixed system, causing uneven mixing, and a part of the bonding force is insufficient, so that the intended purpose is hardly achieved.

Therefore, when adding the styrene copolymer, the amount of the styrene copolymer to be added as a solution is preferably adjusted within a range of 1 to 3% based on the raw material powder. However, if the absolute amount of the binder as a solid content is insufficient, the bonding strength after drying is insufficient, while if too large, the mixed powder is partially agglomerated and needs to be reground, so that the solid content is low. Is 0.1
It is better to be within the range of 0.2%.

The preferred concentration of the solution cannot be specified uniformly since it varies depending on the molecular weight (degree of polymerization) of the styrenic copolymer and the accompanying solution viscosity, but it is usually 5 to 15%. , More preferably 5 to 10%
Are used. The preferred molecular weight of the styrene copolymer is 10,000 to 1,000,000 in weight average molecular weight,
More preferably, the molecular weight is in the range of 30,000 to 500,000. When the molecular weight is too small, the action as a binder tends to be insufficient as a whole, while when the molecular weight is too large, mixing unevenness occurs, and the segregation preventing effect is satisfactory. It is difficult to be displayed.

Reference Example 4 Next, Table 8 shows that the styrene: butadiene = 35: 65 copolymer (weight average molecular weight: about 100,000) was used as a binder and the solution concentration of the binder was based on the above method. And the agglomeration of graphite (Sieve 250
μm), and the fluidity and compressibility when 0.75% zinc stearate powder is additionally added thereto (sample size: diameter 11.3 mm × 10 height mm, molding pressure: 5 ton /
cm ² ) is shown. In this table, an example without a binder is also shown for comparison.

[0041]

[Table 8]

As is clear from Table 8, the graphite scatter rate in the case where no binder was added was extremely large, while the graphite scatter rate was significantly suppressed by adding an appropriate amount of a styrene copolymer as a binder. Can be In the above experimental example, a case where graphite powder and a lubricant were mixed with iron powder was described as an example.However, in a case where iron powder or steel powder is modified by adding another alloy element, manganese sulfide, phosphorus, sulfur, etc. The optimum addition amount can be changed according to the specific gravity, shape, particle size, wettability, and further addition amount of the added physical property improving component powder, graphite powder, lubricant powder, etc. Therefore, it is desired to adjust the addition amount each time.

Reference Example 5 Next, Table 9 shows that an iron powder for powder metallurgy (having a particle diameter of 180 μm or less) was used as a base metal powder, and a graphite powder (having an average particle diameter of 3 μm) was used.
m) A mixed powder comprising 0.8% by weight, 2.0% by weight of copper powder (average particle size: 30 μm) and 0.75% by weight of zinc stearate powder was used, and the following method was the same as that employed in Example 3 above. 5 shows the results of examining the graphite scattering rate and fluidity in FIG. However, as the binder, styrene:
A copolymer having a butadiene = 35: 65 weight ratio (weight average molecular weight: about 100,000) was added as a toluene solution having a binder concentration of 10% to the raw material powder in an amount of 0.2% by weight in terms of solid content and uniformly mixed.

[0044]

[Table 9]

As is clear from these results, the use of a styrene copolymer as a binder does not impair the flowability (moldability) for powder metallurgy, and is extremely light and easily segregated. It can be seen that segregation and scattering of the improving component powder (such as graphite) and the lubricant powder can be effectively prevented.

Incidentally, the first and second embodiments are
The effect when a liquid fatty acid having an iodine value of 15 or less and a viscosity at 100 ° F. of 50 cSt or less is used as a binder in the mixed powder, and Reference Examples 1 to 5 show:
Although the effect when the styrene-based copolymer was used as the binder was shown, a more excellent segregation prevention effect can be obtained when the styrene-based copolymer is used in combination with the liquid fatty acid. Is shown.

Example 3 (Example of combined use of a liquid fatty acid and a styrene-based copolymer) To an iron powder for powder metallurgy (having a particle size of 180 µm or less), a graphite powder (average particle size: 3 µm) was added in an amount of 0.8% based on the total amount of the mixed powder.
Copper powder (average particle size 30μm)
% And then mix for several minutes at 100 rpm with a rotary wing mixer. After uniform mixing, a copolymer (weight average molecular weight: about 100,000) containing styrene / butadiene = 35/65 (weight ratio) as a monomer component dissolved in toluene at 8% was added to the total amount of the mixed powder. It is added with stirring so as to become 2% (as a copolymer). After stirring for a few more minutes, the toluene is evaporated to dryness while stirring the mixture, causing the graphite to adhere to the surface of the iron powder. After the drying is completed, a liquid fatty acid having an iodine value of 2 and a viscosity of 30 cSt at 100 ° F. is added and mixed for 2 minutes, and the first sampling is performed to obtain a test powder for a gas flow method. Next, a lubricant (zinc stearate: average particle size of 30 μm) was added at 0.75% to the total amount of the mixed powder.
The mixture was mixed at 100 rpm for 2 minutes so that At this point, a second sampling is performed to obtain a test powder for investigating the degree of segregation of copper powder and graphite powder and powder characteristics. Table 10 shows the results of the graphite adhesion rate and powder characteristics. In the same table, the case where only a styrene copolymer is added without adding a liquid fatty acid as a reference powder is shown.

[0048]

[Table 10]

As described above, it can be seen that the carbon adhesion rate of each of the sample names P and Q is greatly improved because the styrene copolymer is added as a binder. When a liquid fatty acid is added together with the styrene copolymer, an effect of improving the degree of copper segregation is also observed. Further, the fatty acid used in Example 3 had an iodine value of 15 or less and 100 °
Since the viscosity at F is 50 cSt or less, even when the styrene-based copolymer is added at the same time, there is no change over time and the effect of excellent fluidity is not changed. Based on the knowledge on the binder, the effect of using various physical property improving component powders together with the binder and the iron powder for powder metallurgy will be clarified.

Example 4 Ni obtained by a water atomization method: 57 parts by weight, M
o: 7 parts by weight, Mn: 14 parts by weight, Si: 7 parts by weight, C
r: alloy powder having a composition of 14 parts by weight (average particle size of 10
6 μm) was mixed with 0.6 parts by weight of graphite powder (average particle size 2 μm), 93.4 parts by weight of iron powder for powder metallurgy and a binder as defined in the present invention. In this example, 0.75 parts by weight of zinc stearate was post-added as a lubricant. Comparative Example 1 was obtained by simply mixing a powder metallurgy steel powder and an alloy powder, graphite powder and a lubricant (premix), and Comparative Examples 2 to 4 were heat-treated after mixing the powder metallurgy steel powder and the alloy powder. And powdered alloy powder is adhered to the surface of the powder for powder metallurgy (partial diffusion type steel powder). In Reference Examples 1 and 2, alloy powder was attached using a copolymer (solid binder) of styrene / butadiene = 35/65. Compressibility and moldability in the table are 5 tons each.
/ Cm ² is evaluated by the density of the molded body and the Rutler value when the mold is molded.

[0051]

[Table 11]

[0052]

[Table 12]

As can be seen from Table 11, when no binder was used (Comparative Examples 1 to 4), the adhesion of graphite was not sufficient, and segregation was likely to occur. Further, Comparative Examples 2 to 4 are effective in the formability and prevention of segregation of the alloy powder. However, in the case of the alloy powder having high hardenability as used in the present example, the steel powder for powder metallurgy and the alloy powder are used. The diffusion layer and the alloy powder become hard and reduce the compressibility, so that it becomes impossible to finally obtain sufficient strength (see Table 12).

Inventive Examples 1 to 4 show the cases where a solid binder (styrene / butadiene copolymer) and a liquid binder (liquid fatty acid) are used. The results show even better effects than those of Reference Examples 1 and 2, and all of them have improved moldability, graphite scatter, and segregation of alloy powder without substantially impairing the compressibility of the simple premix powder. Further, as shown in Table 12, the tensile strength is high and the variation is small.

Example 5 An alloy powder having a composition shown in Table 13 (maximum particle size: 75 μm) obtained by a mechanical grinding method, an atomizing method, a chemical reaction, or the like.
Hereinafter, 15 parts by weight were mixed with 85 parts by weight of powdered steel for powder metallurgy using a W-cone type mixer, and samples were taken every 50 kg at the position of the filling shoe of the automatic forming press to segregate the alloy powder in the lot. evaluated. FIG. 3 shows the relationship between the type of the binder used, the maximum particle size of the alloy powder (the physical property improving component powder) and the segregation (statistical value R). The plot in FIG.
These values are statistically estimated from the adhesion rates of the 26 alloy powders shown in Table 13.

[0056]

[Table 13]

As shown in FIG. 3, in the premixing method, the segregation rate is smaller as the maximum particle size of the alloy powder is larger (closer to the average particle size of the powdered steel for powder metallurgy). Generally, it is said that the segregation in the mixed powder occurs due to a difference in particle size, shape, specific gravity, and the like. However, if the grain size of the alloy powder is excessively large, a homogeneous structure cannot be obtained after sintering. Therefore, the grain size of the alloy powder should be 75 μm or less. Further, the amount of the alloy powder added is generally 15 parts by weight or less, more specifically 0.5 to
Often 6.0 parts by weight. If the binder specified in the present invention is used, it is possible to deposit more than 15 parts by weight of the alloy powder by increasing the amount of the binder added, but excessive addition of the binder lowers the green compact density. May be invited. Therefore, in such a case, the alloy component that hardly reduces the compressibility is prealloyed or partially diffused steel powder,
It is desirable to employ a method of attaching alloy powder of not more than part by weight using a binder. Conventional Examples 2 and 3 have a slightly better adhesion rate than Invention Example 3, but have practical problems in terms of aging and fluidity as in the case of the spindle oil shown in the previous embodiment.

As described above, in the present invention, iodination and
A liquid fatty acid having a specified viscosity at 00 ° F. or a styrene-based copolymer obtained by copolymerizing styrene and butadiene and / or isoprene at a specified ratio or a hydride thereof is used as a binder. This prevents segregation of the physical property improving component powder, graphite powder, and lubricant powder in iron powder bases such as iron and steel powder and dust generation during handling. , Pure iron powder, pre-alloyed iron powder, partially diffused iron powder, plated iron powder, etc. These include not only the most common atomized powder but also other physical pulverization methods and reduction methods. All iron-based powders obtained by a chemical pulverization method or the like are included.

The physical property improving component powder to be incorporated into these powder metallurgy iron powders includes powder metallurgy product strength,
Various components used to improve various physical properties such as abrasion resistance and machinability can be exemplified, and typical examples include metals and alloys such as Ni, Cu, Mo, Cr, and Mn. These metal oxides, alloys of these alloy elements and iron, Si, P, S and their oxides or alloys of the above alloy elements and iron, and the like can be given.
One or more of them are used.

These physical property improving component powders can be rapidly diffused in the solid phase or liquid phase in the sintering step to be diffused or alloyed into the base metal, and can be used as a binder for powder metallurgy iron powder. In order to facilitate the adhesion, it is desirable that the fineness is 10 μm or less, but such a fine physical property improving component powder is very expensive. However, the present inventors have confirmed that, when the special binders used in the present invention are used, by appropriately adjusting the amount of addition, etc., the maximum amount that can be generally obtained at a low cost can be obtained. It was confirmed that even particles having a particle size of about 75 μm can be used without any problem. These physical property improving component powders may be pulverized by any method, but more preferable are powders having a small smooth surface and a large degree of irregularity obtained by a spraying method or the like. .

The lubricant powder is compounded for the purpose of reducing the friction between the mold and the mixed powder or the mixed powder at the time of compacting to increase the compaction density and extending the life of the mold. Metal soaps such as zinc stearate, amide waxes such as ethylene bis amide, or composites thereof are used.
It is usually about 0.1 to 3% by weight, more usually about 0.3 to 1% by weight, based on the total amount of the raw material powder.

The lubricant powder having a certain degree of coarseness has a lower resistance when the molded body is removed from the mold, but the compressibility and the uniform mixing property of the whole mixed powder tend to deteriorate. Therefore, preferably, the average particle size is 50 μm
It is better to use one having a thickness of not more than about 30 μm.

[0063]

According to the present invention, the segregation of the added powder is suppressed widely, regardless of the specific gravity difference or the particle size difference of the physical property improving component powder such as copper powder, and the fluidity is positively improved and the powder is improved. It has become possible to provide a mixed powder for powder metallurgy in which the change with time of the characteristics is extremely small and the graphite powder and the lubricant powder are not scattered.

[Brief description of the drawings]

FIG. 1 is a sectional view of a measuring instrument used for measuring a graphite adhesion rate.

FIG. 2 is a flowchart illustrating a method of measuring a graphite scattering rate and a fluidity employed in an experiment.

FIG. 3 is a graph showing the relationship between the maximum particle size of the alloy powder and the segregation rate.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Murakami 2-3-1 Shinhama, Arai-machi, Takasago-shi, Hyogo Kobe Steel, Ltd. Inside Takasago Works (56) References JP-A-5-86403 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22F 3/02 C04B 35/632

Claims (3)

(57) [Claims] (1) An iodine value of not more than 15 and a viscosity at 100 ° F. of not more than 50 μm.
A segregation preventing mixed powder for powder metallurgy, which is mixed with a powder metallurgy iron powder for powder metallurgy together with a powder metallurgy binder comprising a liquid fatty acid of cSt or less to prevent segregation. 2. A physical property improving component powder having a maximum particle size of 75 μm or less (1) having an iodine value of 15 or less and a viscosity at 100 ° F.
There the following liquid-like fatty acid 50 cSt (2) Styrene: 5 to 75 parts by weight of butadiene and / or isoprene: 95-25 consisting of parts from a styrene copolymer or hydrogenated product thereof as a monomer component <br / > A segregation-prevention mixed powder for powder metallurgy, which is mixed with an iron powder for powder metallurgy together with a binder for powder metallurgy to prevent segregation. (3) As another component, graphite powder and / or
The mixed powder for preventing segregation according to claim 1 or 2, further comprising a powder metallurgy lubricant.