WO2016174985A1 - Mixed powder for powder metallurgy, powder compact and method for producing machine component - Google Patents

Abstract

This mixed powder for powder metallurgy contains a metal powder and an internal lubricant, and this internal lubricant contains 80 wt% or more of cellulose fibers. Consequently, the amount of a conventional lubricant such as a metallic soap used therefor is able to be lowered or reduced to zero, thereby avoiding decrease in the strength of a powder compact due to the conventional lubricant.

Description

[Name of the invention determined by ISA based on rule 37.2] Method of manufacturing mixed powder for powder metallurgy, green compact and machine part

The present invention relates to a mixed powder used in powder metallurgy.

Powder metallurgy is a technology capable of simultaneously producing a large number of complex shaped parts by pouring and molding mixed powder containing metal powder into a mold and then sintering. In particular, powder metallurgical products mainly made of iron powder are widely used in the automotive field and the industrial machinery field.

In this powder metallurgy field, a state in which the mixed powder is crushed at high pressure inside a mold and the powders are mechanically entangled to maintain one shape is called a green compact. A green compact has a weak and fragile property to an external force because the bonds between the powders are weak. For this reason, when transferring a green compact to a sintering process etc., a chipping and a crack arise, and there exists a possibility of causing the defect of quality, or the fall of a yield.

Therefore, various studies have been repeated for the purpose of improving the green strength. For example, using irregularly shaped reduced powder to increase mechanical entanglement between powders, or increasing the density of green compact (powder density) to increase contact points between powders Has been done.

By the way, in powder metallurgy, usually, an internal lubricant is often added to the raw material powder in order to improve the lubricity between the powders and between the powder and the mold. Conventionally, metal soaps and waxes (fatty acid amides etc.) have been used as internal lubricants, but since they have a low melting point of 200 ° C. or less and are rich in ductility, they are drawn thin when mixed. Exists as a thin film on the surface of the powder or mold. Since this weakens the contact force between powders, it is a factor that hinders improvement of green compact strength.

Therefore, it has also been proposed to improve the green strength by devising an internal lubricant. For example, in Patent Document 1 below, it is stated that the green strength is improved by adding fragmented cellulose fiber to a conventionally used lubricant. Specifically, according to the same document, no fiber is obtained by combining fragmented cellulose fibers having no lubricity with known lubricants such as fatty acid monoamides, fatty acid bisamides, metallic soaps and polyolefin waxes. It is believed that a "modified lubricant" is obtained which not only has the same physical properties as the lubricant but also provides the raw material of the shaped body with an equivalent apparent density and excellent strength.

Japanese Patent Publication No. 2007-517985

However, the modified lubricant disclosed in the above-mentioned Patent Document 1 essentially comprises a known lubricant such as metal soap, and the weight ratio of the known lubricant to the cellulose fiber is 1: 2 to 10: The range is 1 (paragraph 0016). Thus, the use of a modified lubricant containing a relatively large amount (1/3 or more) of known lubricants inevitably leads to a reduction in the strength of the green compact due to the known lubricants.

In view of the above circumstances, the problem to be solved by the present invention is to provide a mixed powder for powder metallurgy that can obtain a high-strength green compact.

The present invention made to solve the above problems is a mixed powder for powder metallurgy comprising a metal powder and an internal lubricant, wherein the internal lubricant comprises 80 wt. % Or more.

Conventionally, cellulose fiber was not recognized as one that functions as a lubricant, but the present inventors have found that cellulose fiber can function as a lubricant during molding. Cellulose fiber is not stretched during mixing and does not exist as a thin film on the surface of a powder or a mold, unlike metal soaps and waxes conventionally used as a lubricant, and does not reduce the strength of the green compact. Therefore, as described above, by using most of the internal lubricant (80 wt.% Or more) as the cellulose fiber, the amount of use of the conventional lubricant can be reduced or reduced to 0, and therefore, the green compact by the conventional lubricant Can be avoided.

In particular, in the above-mentioned mixed powder for powder metallurgy, if the internal lubricant is composed of only cellulose fibers, it is possible to eliminate the use of the conventional lubricant at all, and therefore the strength of the green compact can be further improved. In addition, "an internal lubricant consisting only of cellulose fiber" is not limited to the thing which does not contain components other than a cellulose fiber strictly at all, A slight impurity (For example, the impurity which arises inevitably in the manufacturing process of a cellulose fiber) May also be included.

It is preferable to use the above-mentioned cellulose fibers having an average diameter of 20 μm or less and an average length of 100 μm or less. If the size of the cellulose fiber is increased, there is no room for the powders to enter or between the powder and the mold, which may cause a decrease in lubricity and a decrease in fluidity. The average diameter and the average length are values obtained by an image analysis method (measurement based on an image photographed by a microscope or the like).

The content of the internal lubricant in the above powder metallurgical mixed powder is 0.2 wt. % Or more, 1.1 wt. It is preferable that it is% or less. When the addition amount of the internal lubricant is too small, the lubricity is insufficient, and when it is too large, the fluidity is insufficient.

As described above, since the mixed powder for powder metallurgy according to the present invention uses an internal lubricant containing cellulose fiber as a main component, a high-strength green compact can be obtained. As a result, it is possible to prevent the occurrence of chipping or cracking when transferring the green compact to the sintering step, etc., thereby improving the quality of the sintered body and the yield.

It is an enlarged photograph of the appearance of various cellulose fibers (100 GK, 10 MG2, 06 MG), and a conventional lubricant (ethylene bis-stearic acid amide (ACRA)). It is a graph which shows the particle size distribution of each powder of FIG.

Hereinafter, an embodiment of the mixed powder for powder metallurgy according to the present invention (hereinafter, simply referred to as "mixed powder") will be described.

The mixed powder contains a metal powder, a carbon-based powder, and an internal lubricant. As the metal powder, for example, iron powder (or iron alloy powder) or copper powder (or copper alloy powder), or both of them as a main component can be used. The iron powder can be used regardless of the production method, and for example, those produced by the atomization method, the reduction method, the stamp method, the carbonyl method and the like can be used. The copper powder can also be used regardless of the manufacturing method, and for example, those manufactured by an electrolytic method, an atomizing method, a reduction method, a stamp method and the like can be used. The mixed powder of the present embodiment is mainly composed of iron, and specifically, the ratio of iron in the mixed powder is 50 wt. % Or more, preferably 80 wt. % Or more, more preferably 90 wt. % Or more. More specifically, the metal powder of the present embodiment comprises only iron powder, or iron powder and copper powder, and the ratio of iron powder in the mixed powder is 50 wt. % Or more, preferably 80 wt. % Or more, more preferably 90 wt. % Or more.

As the metal powder, in addition to iron powder and copper powder, a low melting point metal (such as Sn or Zn) having a melting point lower than the sintering temperature may be blended. Moreover, you may mix | blend the metal powder with the alloy powder which alloyed multiple types of metals. As the alloy powder, for example, a pre-alloy powder obtained by pre-alloying a plurality of types of metals, a partial diffusion alloy powder obtained by partially diffusion alloying powders made of dissimilar metals, and the like can be used.

Graphite, carbon black or the like can be used as the carbon-based powder. In addition, it is not necessary to mix | blend carbon-type powder with mixed powder, if it is not necessary in particular.

The internal lubricant is mainly composed of cellulose fiber, and specifically, 80 wt. % Or more, preferably 90 wt. % Or more is included. In this embodiment, an internal lubricant composed only of cellulose fibers is used. Cellulose fiber is a plant-derived material and thermally decomposes at about 350 ° C. in an inert atmosphere.

As the cellulose fiber, it is preferable to use one having a size that is somewhat small in order to exhibit lubricity by intercalating powder and powder-mold. Specifically, it is preferable to use cellulose fibers having an average diameter of 20 μm or less and an average length of 100 μm or less according to an image analysis method, and those having an average diameter of 10 μm or less and an average length of 30 μm or less It is further preferred to use. The cellulose fiber preferably has an average particle size of 50 μm or less according to a particle size distribution measuring device (laser diffraction method), and more preferably 12 μm or less. On the other hand, if the size of the cellulose fiber is too small, the effect of improving the green strength may not be sufficiently obtained. Therefore, an average diameter of 0.1 μm or more, an average length of 1 μm or more, and an average particle diameter of 3 μm or more is used. It is preferable to do.

If the amount of the cellulose fiber is too small, there is a possibility that the lubricity at the time of molding may be insufficient to cause molding failure. For this reason, the addition amount of cellulose fiber is 0.2 wt. % Or more, preferably 0.3 wt. It is more preferable to make it% or more. Moreover, when there are too many cellulose fibers, the flowability of mixed powder will deteriorate. For this reason, the addition amount of the cellulose fiber is 1.1 wt. % Or less, preferably 1.0 wt. It is further more preferable to make it less than 0.5%. It is more preferable to make it% or less.

By supplying the above-mentioned mixed powder to the inside of the mold and performing compression molding, a green compact having a predetermined shape can be obtained. At this time, the internal lubricant consisting of cellulose fibers contained in the mixed powder penetrates one another or between the powder and the mold to perform a lubricating function, thereby enabling molding. Furthermore, since the mixed powder of the present embodiment does not contain a conventionally used lubricant (metal soap or wax), it is possible to avoid a reduction in the green strength due to the conventional lubricant. The internal lubricant to be mixed with the mixed powder may contain a small amount of a conventional lubricant as long as the majority (80 wt.% Or more) is a cellulose fiber, but the strength of the green compact can be increased. For this reason, it is preferable to use an internal lubricant consisting only of cellulose fiber, which does not contain any conventional lubricant as in the present embodiment.

The green compact thus formed is conveyed to the sintering step and introduced into the sintering furnace. At this time, since the strength of the green compact is increased as described above, the green compact can be prevented from being damaged when it is transferred from the green compact to the sintering furnace. Then, the green compact is sintered at a predetermined sintering temperature for a predetermined time to generate a sintered body. Although the cellulose fibers contained in the green compact are thermally decomposed by the sintering, the load on the environment is low because the cellulose fibers are a plant-derived material. Thereafter, if necessary, the sintered body is subjected to sizing and heat treatment to complete a powder metallurgy product. This powder metallurgical product is used, for example, as mechanical parts such as gears, cams and bearings.

The following experiments were performed to confirm the effects of the present invention.

In this experiment, a mixed powder consisting of iron, copper powder, carbon-based powder, and an internal lubricant was used. As iron powder, "JIP Sigma Roy 2010" which is a water atomized powder manufactured by JFE Steel Corporation was used. As the copper powder, “CE-25”, which is an electrolytic powder manufactured by Fukuda Metal Foil & Powder Co., Ltd., was used. As the graphite, “F-10” which is an artificial graphite manufactured by TIMCAL was used.

A mixed powder containing an internal lubricant consisting only of cellulose fibers was taken as an example, and a mixed powder containing a conventional lubricant was taken as a comparative example. Cellulose fibers can be powdered cellulose manufactured by Nippon Paper Industries Co., Ltd. “KC floc W-100 GK” (hereinafter referred to as “100 GK”), “NP fiber W-10 MG2” (hereinafter referred to as “10 MG2”), or “NP fiber W— "06MG" (hereinafter referred to as "06MG") was used. As a conventional lubricant, "ACRAWAXC atomize" (hereinafter referred to as ACRA), which is ethylenebisstearic acid amide manufactured by LONZA Corporation, was used. The appearance of each internal lubricant is shown in FIG. 1, and the particle size distribution is shown in FIG. The specifications of each internal lubricant are shown in Table 1 below.

The ratio of each powder in the mixed powder was 1.5 wt. %, 0.2 wt. %, Internal lubricant 0.5 wt. And the rest was iron powder. Then, as shown in Table 2 below, Example 1 using 06MG as an internal lubricant, Example 2 using 10MG 2 as an internal lubricant, and Example using 100 GK as an internal lubricant are performed. In Example 3, Comparative Example 1 using ACRA as the internal lubricant, and 50 wt. What used% each was set as Comparative Example 2. Each powder was individually weighed, and then mixed for 40 minutes with a V-type mixer manufactured by Tsutsui Rikagaku Instrument Co., Ltd.

Then, in order to investigate the flowability of each mixed powder, the fluidity was measured. The measurement method was in accordance with JIS Z 2502, and the mixed powder weighed to 50 g was dropped from a container with an orifice, and the time until it flowed was measured. The results are shown in Table 2 above.

Thereafter, the mixed powder was compacted, and cylindrical test pieces of outer diameter 23.2 mm × inner diameter 16.4 mm × axial length 7 mm and φ11.3 mm × axial length 10 mm were produced. The molding conditions were such that the molding pressure was 1176 MPa at room temperature.

Then, the rattler value was measured in order to investigate the chipping tendency of the green compact. The measurement method pursuant to JPMA P11, five cylindrical test piece was placed in a cylindrical cage stainless wire mesh is stretched, is 1000 rotated at a rotational speed of 87Min ^-1, measured its weight reduction rate. The results are shown in Table 2 above.

Next, in order to investigate the strength of the green compact, the radial crushing strength was measured. According to JIS Z 2507, the load was applied to the cylindrical test piece in the direction perpendicular to the axis, and the load at break was measured. The test was performed using a universal testing machine with stroke control. The stroke speed at the time of the test was 0.1 mm / min. The results are shown in Table 2 above.

As shown in Table 2 above, Examples 1 to 3 using a cellulose fiber as an internal lubricant all had excellent fluidity, latra value and radial crushing strength, and exhibited good physical properties. In particular, Example 1 using 06MG showed a very excellent value of less than 35 sec / 50 g in fluidity. On the other hand, Comparative Examples 1 and 2 including the conventional lubricant (ACRA) resulted in inferior physical properties to Examples 1 to 3 using cellulose fibers.

Next, using a cellulose fiber (10MG2) as a lubricant, various physical properties of the mixed powder and the green compact when the amount of addition was changed were investigated. The amount of lubricant added is 0, 0.3, 0.5, 1.0, 1.2 wt. %. As a result, as shown in Table 3 below, in Comparative Example 3 in which no cellulose fiber was added, although a green compact could not be formed because of insufficient lubricity, Example 1 in which cellulose fiber was added And 4 to 6 were able to form a green compact. From this, it was confirmed that the cellulose fiber functions as a lubricant at the time of molding. In particular, green compacts using the mixed powders of Examples 1, 4 and 5 in which the amount of cellulose fiber added was in the range of 0.3 to 1.0 wt.% Showed excellent physical properties. On the other hand, the amount of cellulose fiber added is 1.2 wt. Although Example 6 which is% showed the physical property which was excellent in the green compact, the fluidity was low. From the above, the addition amount of cellulose fiber is 0.2 to 1.1 wt. It can be said that% is preferable.

Claims (7)

1. A mixed powder for powder metallurgy comprising a metal powder and an internal lubricant,
   The internal lubricant comprises 80 wt. The mixed powder for powder metallurgy characterized by containing more than%.
2. The mixed powder for powder metallurgy according to claim 1, wherein the internal lubricant consists only of cellulose fibers.
3. The mixed powder for powder metallurgy according to claim 1 or 2, wherein the cellulose fiber has an average diameter of 20 μm or less and an average length of 100 μm or less.
4. The content of the internal lubricant is 0.2 wt. % Or more, 1.1 wt. The mixed powder for powder metallurgy according to any one of claims 1 to 3, which is at most%.
5. The mixed powder for powder metallurgy according to any one of claims 1 to 4, wherein the main component of the metal powder is iron powder.
6. A green compact comprising the mixed powder for powder metallurgy according to any one of claims 1 to 5.
7. A machine comprising the steps of compression molding the mixed powder for powder metallurgy according to any one of claims 1 to 5 to obtain a green compact, and sintering the green compact to obtain a sintered body. Method of manufacturing parts.

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