JP6176804B2 - Method for producing bronze composite iron powder and method for producing sintered metal - Google Patents

Description

  The present invention relates to a method for producing a bronze composite iron powder having both iron and copper properties and a method for producing a sintered metal.

  Sintered oil-impregnated bearings can be used in a self-lubricated state by impregnating 10-25% by volume of lubricating oil by utilizing the porosity of a sintered body obtained by sintering metal powder. In addition, it has an excellent feature that it can be operated without being seized even in a smoked state without the need to add lubricating oil. Such sintered oil-impregnated bearings are widely used in places where environmentally or mechanically sufficient oil supply cannot be expected, such as electrical equipment, acoustic equipment, civil engineering machines, and automobiles.

There are various kinds of metal powders used for the material of the sintered oil-impregnated bearing, and the main ones are copper and iron. The iron-based material is mainly composed of iron, and examples thereof include metallic iron and alloys such as Fe-C and Fe-Pb-C. The mechanical strength is high but the hardness is high, so that the conformability to the shaft material is inferior. It is easy to wear and has a property of being inferior in corrosion resistance.
On the other hand, copper-based materials are mainly composed of copper, and can be exemplified by alloys such as metallic copper and Cu-Sn, which are more expensive than iron-based materials and lack sufficient strength to withstand high loads. However, it has the property of having excellent lubricating properties.

  Therefore, in order to provide both advantages, a sintered oil-impregnated bearing in which iron-based raw material powder and copper-based raw material powder are mixed in an appropriate blending amount is also manufactured. However, the sintered material does not completely alloy the raw material powder, and the iron-based material is exposed to a certain degree on the sliding surface. It was difficult to pull out.

In order to solve such problems, raw material powders have been developed that cover the surface of a strong iron-based material with a copper-based material having excellent conformability.
For example, Japanese Patent Application Laid-Open No. 2003-184882 (Patent Document 1) and Japanese Patent Application Laid-Open No. 8-92604 (Patent Document 2) describe copper-coated iron powder in which the surface of iron powder particles is coated with copper.

JP 2003-184882 A JP-A-8-92604

  Japanese Patent Application Laid-Open No. 2003-184882 (Patent Document 1) describes a technique for producing a copper-coated iron powder by subjecting a known iron powder particle surface to copper plating. However, the copper-coated iron powder by such a plating method requires measures against the environment such as waste liquid treatment, and the cost is increased.

On the other hand, JP-A-8-92604 (Patent Document 2) discloses a technique in which iron powder and copper oxide powder are mixed, the copper oxide powder is reduced in a reducing atmosphere, and copper is adhered to the surface of the iron powder. Is described. However, in order to perform this method for producing copper-coated iron powder, the average particle size of secondary particles is 5 μm or less and primary particles of 0.1 μm or less are aggregated, and the specific surface area is 10 m ² / g or more. It is necessary to use a special copper oxide powder, and the obtained copper-coated iron powder is also unfavorable in terms of copper adhesion, and copper is easily peeled off.

  On the other hand, there is also a method for producing a copper-coated iron powder by heat-treating a mixed powder obtained by mixing iron powder and copper powder and attaching a copper film to the surface of the iron powder. Since the specific gravity of the copper powder is higher than that of the iron powder, the segregation is liable to occur when the iron powder and the copper powder are mixed. Moreover, it is necessary to process the mixed powder of iron powder and copper powder at high temperature, and the adhesiveness of the powder obtained after heating becomes high. For this reason, excessive effort is required to re-pulverize the solidified powder into fine particles.

  The present invention examines such problems and relates to the production of copper composite iron powder formed by combining a copper component on the surface of the iron powder, and has an object to obtain copper composite iron powder having excellent adhesion to copper and free from segregation. It is what.

In order to solve the above problems, the present invention has the following configuration.
[1] Bronze composite iron in which tin powder and copper oxide powder with an average particle size of 20 μm or less are mixed with iron powder, heated to reduce copper oxide with a reducing gas, and copper and tin adhered to the iron powder surface a method of manufacturing a bronze composite iron powder to produce a powder, the tin powder were mixed 0.4 to 4.0 wt% with respect to the iron powder content, the copper oxide powder to the iron powder content A first heat treatment for preparing a raw material powder by mixing 10 to 50 wt% in terms of metallic copper, raising the temperature of the raw material powder from 200 ° C. to 330 ° C. to reduce copper oxide, and within a temperature range of 700 ° C. to 950 ° C. It is the manufacturing method of the bronze composite iron powder which performs the 2nd heat processing baked by.

[2 ] A method for producing a bronze composite iron powder in which a raw material powder is prepared by further mixing 3 to 25 wt% bronze powder with respect to the iron powder content before the temperature rise .
[ 3 ] A sintered metal production method for producing a sintered metal obtained by sintering a bronze composite iron powder produced by any one of the above-described bronze composite iron powder after compacting.

ADVANTAGE OF THE INVENTION According to this invention, the bronze composite iron powder excellent in the adhesiveness of copper with respect to iron can be manufactured.
Moreover, according to this invention, the bronze composite iron powder without segregation can be manufactured.

The manufacturing method of the bronze composite iron powder of the present invention and the sintered oil-impregnated bearing using the bronze composite iron powder will be described in detail based on the embodiments.
The present invention is a bronze composite in which tin powder and copper oxide powder having an average particle size of 20 μm or less are mixed with iron powder, heated to reduce copper oxide with a reducing gas, and copper and tin are adhered to the iron powder surface. A method for producing a bronze composite iron powder for producing an iron powder, wherein the tin powder is mixed in an amount of 0.4 to 4.0 wt% with respect to the iron powder, and the copper oxide powder is metal with respect to the iron powder. The first heat treatment is performed by mixing 10 to 50 wt% in terms of copper, raising the temperature from 200 ° C. to 330 ° C. to reduce copper oxide, and performing the second heat treatment for firing within a temperature range of 700 ° C. to 950 ° C. It is the manufacturing method of the bronze composite iron powder which was made.

As the iron powder, commercially available iron powder that can be used for producing a sintered oil-impregnated bearing can be used, and electrolytic iron powder, reduced iron powder, atomized iron powder, and the like can be used.
A specific surface area of about 50 to 4000 cm ² / g can be preferably used. When the specific surface area is less than 50 cm ² / g, the particle size also becomes small and the powder for a sintered oil-impregnated bearing becomes small and difficult to use. When the specific surface area is larger than 4000 cm ² / g, the particle size tends to be large, and the powder for a sintered oil-impregnated bearing becomes large and difficult to use.
The average particle size is preferably about 30 to 200 μm. This is because it is a suitable size as a raw material powder for sintered oil-impregnated bearings.

  The copper oxide powder has an average particle size of 20 μm or less. If the average particle size exceeds 20 μm, the contact between the iron powder and the copper oxide powder will not be dense, and the voids around the iron powder will become large, and the iron powder cannot be completely covered, and Adhesion also deteriorates. The smaller the average particle diameter, the larger the area where the copper oxide powder is brought into contact with the surface of the iron powder, and the copper coverage and adhesion to the iron powder surface are improved.

  The reason for using copper oxide powder is that it is reduced at a very low temperature of about 250 ° C. in an atmosphere containing a reducing gas such as hydrogen gas or ammonia decomposition gas, and metallic copper has ductility. This is because, although it is difficult to make fine powder, it is brittle if copper oxide is used, so that a powder in the form of fine powder can be obtained more easily than metal copper. Furthermore, when making a mixed powder in which iron powder and other fine particles are mixed, metallic copper has a higher specific gravity than iron, so segregation is likely to occur if fine powder is used, whereas copper oxide has a specific gravity much lower than iron. This is because segregation hardly occurs.

  Copper oxide may be copper oxide (I) or copper oxide (II). The production of copper oxide powder can be performed by air-oxidizing copper powder such as electrolytic copper powder or atomized copper powder.

  The mixing amount of the copper oxide powder is 10 to 50 wt% in terms of metallic copper with respect to the iron powder, and preferably 15 to 40 wt% when the copper oxide powder is less than 10 wt%, the iron powder surface is completely covered. It becomes difficult. Moreover, when copper oxide powder exceeds 50 wt%, there exists a possibility that excess copper may be liberated from bronze composite iron powder.

As the tin powder, a commercially available tin powder that can be used for producing a sintered oil-impregnated bearing can be used.
The tin powder preferably has a maximum particle size of 45 μm or less and an average particle size of about 10 to 20 μm. If it is too fine, segregation is likely to occur during mixing with other powders, which is not preferable, and if it is too large, the amount of tin powder itself is not large, and therefore, a portion where tin does not spread is generated.

Mixing amount of tin powder is 0.4 to 4.0 wt% with respect to iron powder. When the tin powder is less than 0.4 wt%, it is difficult to sufficiently penetrate the tin component into the entire mixed powder .

When adding zinc chloride, it is preferable to add 0.2-1.5 wt% with respect to copper oxide, and it is more preferable to add 0.5-1.0 wt%.
When the mixing amount of zinc chloride is less than 0.2 wt%, the effect of adding zinc chloride does not appear, and when it exceeds 1.5 wt%, the raw iron powder is easily oxidized.

3-25 wt% bronze powder can be further mixed with the iron powder.
By adding bronze powder, it is possible to obtain a bronze composite iron powder in which a powder having iron powder as a core material and a powder having bronze powder as a core material are mixed. In this mixed powder, since the surface of any powder is coated with copper, the surface characteristics are the same as in the case of only the powder having iron powder as a core material. In other words, in terms of exposing copper to the sliding surface when processed into a sintered oil-impregnated bearing, only powder with iron powder as the core and powder with bronze powder as the core are mixed. The case is equivalent. However, with this mixed powder, the overall hardness is slightly lower, and it is considered that the adhesion to bronze is superior to iron than to iron, so the shaft body when processed into a sintered oil-impregnated bearing Excellent bronze composite iron powder is obtained due to the familiarity with it.

  The mixing ratio of the bronze powder is 3 to 25 wt% with respect to the iron powder. If the content is less than 3 wt%, the mixed characteristics of the bronze powder cannot be extracted. Because it becomes.

  The various powders are stirred and mixed using a known mixer such as a Henschel mixer, V-type mixer, or W-type mixer. The mixed powder thus obtained is spread on a tray or the like and subjected to the heat treatment described below.

In the heat treatment, a first heat treatment for reducing copper oxide by raising the temperature from 200 ° C. to 330 ° C. and a second heat treatment for firing within a temperature range of 700 ° C. to 950 ° C. are performed.
The first heat treatment is a heat treatment step in which the temperature is raised from 200 ° C. to 330 ° C. in an atmosphere through which a reducing gas such as hydrogen gas or ammonia decomposition gas is passed. This process is a preparatory stage for liquid phase sintering in which tin powder is dissolved and tin is interposed in addition to copper and iron produced by reducing copper oxide.
When the copper oxide is reduced, water vapor is generated in an atmosphere containing hydrogen gas, so that an oxidizing atmosphere is formed. If it does so, the surface of iron powder will be oxidized and the film of iron oxide will be easy to be formed. However, when this iron oxide film is formed, there is a possibility that suitable adhesion of copper to the iron powder surface may be hindered. However, since the melting point of tin is 230 ° C., which is lower than the reduction temperature of copper oxide, which is about 250 ° C., the first heat treatment diffuses tin to the iron powder surface before the reduction of copper oxide proceeds. Therefore, it is considered that the formation of the iron oxide film is suppressed.

The second heat treatment is a heat treatment step in which baking is performed in a temperature range of 700 ° C. to 950 ° C. in a reducing atmosphere through a reducing gas. In this process, it is considered that liquid phase sintering is caused by iron, copper, and tin on the surface of the iron powder. Thereby, it is thought that the bronze composite iron powder with which copper adhered firmly to the surface of the iron powder is obtained.
In this case, since the heating temperature does not exceed 950 ° C. even at a high temperature, the bonding strength between the powders after the heat treatment is weaker than that in the case of heating exceeding 950 ° C., and thus the pulverization after the heating is easy.

When zinc chloride is added, it has a melting point of 275 ° C. and dissolves in the same manner as tin in the first heat treatment. This zinc chloride is hydrolyzed by water vapor generated in the process of reducing copper oxide to form an acidic atmosphere, which is considered to work in the direction of inhibiting the formation of iron oxide film in cooperation with the dissolution of tin. It is done.
In addition, if it exposes to high temperature suddenly without passing through 1st heat processing, since zinc chloride will change to a zinc oxide and will not melt | dissolve and there exists a possibility of depositing on the surface, it is unpreferable.

  In the first heat treatment stage, in order to make it difficult to form an iron oxide film, the N: H ratio is changed without using the ammonia decomposition gas as a reducing gas so as to suppress the generation of water vapor. Decreasing the fraction can be adopted as a preferred embodiment.

After passing through such a temperature treatment, the obtained mixed powder (cake) can be used as raw powder for a sintered oil-impregnated bearing having a desired particle size after pulverization and sieving.
This bronze composite iron powder is a kind of copper composite iron powder, but is superior in the adhesion and adhesion of copper to the surface of the iron powder as compared with the copper-coated iron powder produced by the conventional method.

Next, the manufacturing method of a sintered oil-impregnated bearing in the sintered metal using this bronze composite iron powder is demonstrated. The sintered metal is a molded body obtained by sintering metal powder, and is a concept including a sintered oil-impregnated bearing used by containing oil and a sintered part used without containing oil.
Bronze composite iron powder as a raw material is filled in a mold and compressed by a press machine, and then sintered in a sintering furnace. Then, the obtained sintered body is sized to obtain a bearing having a predetermined shape. Thereafter, post-treatment steps such as washing and oil impregnation are sequentially performed. In this way, a sintered oil-impregnated bearing is manufactured.

  The above embodiment is an example of the present invention, and the present invention is not limited to such a form, and other metal material powders and various additives can be mixed as long as not departing from the spirit of the present invention. .

Experimental example

  Hereinafter, more specific examples of the present invention will be described together with comparative examples. However, the present invention is not limited to the following examples.

<Manufacture of bronze composite iron powder>
[Sample 1]:
To 80 parts by weight of iron powder having an average particle diameter of 90 μm, 19 parts by weight of copper oxide powder 1 (copper oxide (II) average particle diameter of 5 μm) and 1.6 parts by weight of tin powder having an average particle diameter of 15 μm are mixed. And mixed well to obtain a mixed powder. All of these raw material powders are commercially available.

The mixture was spread on a tray and placed in a sintering furnace, and the temperature was raised from room temperature in a reducing atmosphere into which ammonia decomposition gas was introduced. In the middle, a first treatment for gradually raising the temperature from 200 ° C. to 330 ° C. was performed, and then a second heat treatment for raising the temperature to 820 ° C. was performed. Then, the state of the mixed powder (cake) taken out from the furnace was observed.
The mixed powder solidified by sintering was pulverized by a pulverizer to obtain Sample 1 which is a bronze composite iron powder for a sintered oil-impregnated bearing.

[Sample 2 to Sample 15]:
Under the same conditions as Sample 1 except that the conditions and the conditions of the various raw material powders used in the production of the bronze composite iron powder of Sample 1 and the heat treatment were changed to the conditions shown in Tables 1 and 2 Samples 2 to 15 of bronze composite iron powder were obtained. Sample 1 is also shown in Table 1 for comparison. (In addition, since the sample 5 does not contain tin powder, bronze composite iron powder is not generated, but for convenience, it is referred to as bronze composite iron powder.)

Details of various raw material powders shown in Tables 1 and 2 and conditions such as heat treatment are as follows.
The copper oxide powder 2 has an average particle diameter of 20 μm, and the copper oxide powder 3 is a copper oxide powder having an average particle diameter of 30 μm. The average particle diameter is different from that of the copper oxide powder 1.
Zinc chloride is commercially available zinc chloride, but is deliquescent due to its nature, and the blending amount is very small. Therefore, the sample added with zinc chloride was immediately weighed after being taken out of the storage bottle and mixed with other raw material powders.
Bronze powder is a commercially available bronze powder having an average particle size of 50 μm.

  In the “first heat treatment” and “second heat treatment” lists in Tables 1 and 2, “DO” indicates that each treatment was performed, and “−” indicates that no treatment was performed. In the sample 10 not subjected to the first heat treatment, the mixed powder was put in a 350 ° C. furnace instead of the step of raising the temperature from room temperature, and then heated to 820 ° C. The time from charging the mixed powder into the furnace to carrying it out is the same as for Sample 1. Sample 11 that was not subjected to the second heat treatment was maintained at 600 ° C. after the temperature was raised from room temperature to 600 ° C. This sample 11 also has the same time as the sample 1 from the introduction of the mixed powder into the furnace to the carrying out. Furthermore, Sample 15 that was not subjected to the second heat treatment was fired by raising the temperature from room temperature to 1050 ° C. Sample 15 is the same as Sample 1 in terms of the time from the introduction of the mixed powder into the furnace to the removal.

<Manufacture of sintered oil-impregnated bearings>
Using the bronze composite iron powders of Samples 1 to 15, sintered oil-impregnated bearings of Samples 1 to 15 were manufactured through the steps described below.
Each bronze composite iron powder was put in a mold and compressed into a cylindrical shape, and then sintered in a hydrogen atmosphere sintering furnace at 850 ° C. for 20 minutes. The obtained sintered body was sized to an inner diameter × outer diameter × full length = 3 mm × 6 mm × 4 mm, and impregnated with a lubricating oil (“Heiwa Sangyo, synthetic oil HS-32 (trade name)”). Thus, samples 1 to 15 which are sintered oil-impregnated bearings were obtained.

<Acceleration test>
The shaft body was passed through each of the sintered oil-impregnated bearings of Samples 1 to 15, and the peripheral speed (V value) of the shaft body was 90 m / min. The surface pressure (P value) applied to the bearing was 5.56 kg / cm ² and the shaft was rotated for 60 minutes. After the test, the sliding surface of the bearing was observed with the naked eye and an optical microscope.

<Evaluation>
The following evaluation was performed on the various bronze composite iron powders of Sample 1 to Sample 15 and the various sintered oil-impregnated bearings of Sample 1 to Sample 15 obtained as described above.

[Production of bronze composite iron powder (cake state) (1)]:
The surface state of the bronze composite iron powder when taken out from the sintering furnace was observed with the naked eye and an optical microscope.
"◎" if the surface is uniform and copper-colored, "○" if the surface is copper-colored but slightly uneven, and what is iron and surroundings not covered by copper? A case where a different part occurred was evaluated as “x”. The evaluation results are shown in Tables 1 and 2 as “cake state”.

[Production of bronze composite iron powder (ease of crushing cake) (2)]:
When the bronze composite iron powder is taken out from the sintering furnace, it is in a sintered and solidified state, so it is necessary to grind it. Therefore, the ease of pulverization was compared.
Cake-like bronze composite iron powder can be easily broken into several blocks by hand. By putting this block into a hammer-type crusher (blade diameter φ250, rotation speed 850 rpm) made by Heiwa Sangyo Co., Ltd. , “○” indicates that there are no lumps such that some grains are aggregated. Those that remained large lumps that needed to be crushed were evaluated as “x”. The evaluation results are shown in Tables 1 and 2 as “Ease of grinding”.

[Bearing characteristics]:
According to the observation of the sliding surface of the sintered oil-impregnated bearing after the acceleration test, the case where the appearance is almost the same as before the acceleration test is “◎”. Was evaluated as “◯”, and “×” was evaluated for changes that occurred such as the iron surface being exposed or the rotation of the shaft becoming heavy during the acceleration test. The evaluation results are shown as “Bearing characteristics” in Tables 1 and 2.

<Discussion>
From the above test results, the sintered oil-impregnated bearings of Samples 1 to 3, 6, 7, 9, 12, and 14 are suitable for practical use, but Samples 4, 5, 8, 10, 11, 13, and 15 It can be seen that the sintered oil-impregnated bearing is not preferable.

Claims (3)

Produces bronze composite iron powder in which tin powder and copper oxide powder with an average particle size of 20 μm or less are mixed with iron powder, heated to reduce copper oxide with a reducing gas, and copper and tin adhered to the iron powder surface. A method for producing bronze composite iron powder,
The tin powder is mixed with 0.4 to 4.0 wt% with respect to the iron powder content , and the copper oxide powder is mixed with 10 to 50 wt% in terms of metallic copper with respect to the iron powder content to prepare a raw material powder. And the manufacturing method of the bronze composite iron powder which performs the 1st heat processing which heats up this raw material powder from 200 degreeC to 330 degreeC, and reduces a copper oxide, and the 2nd heat processing baked within the temperature range of 700 to 950 degreeC. . Method for producing bronze composite iron powder according to claim 1 Symbol placement to prepare a raw material powder was further mixed 3～25Wt% of bronze powder to the iron powder content in the pre said heating. The manufacturing method of the sintered metal which manufactures the sintered metal formed by compacting the bronze composite iron powder manufactured by the manufacturing method of the bronze composite iron powder of Claim 1 or Claim 2 , and sintering.