JP2010077474A - Iron-based sintered bearing, and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an iron-based sintered alloy bearing which has excellent abrasion resistance, and also has such seizure resistance and mitigated aggressiveness to an opponent part as to be equivalent to an iron-copper-based sintered alloy bearing. <P>SOLUTION: The iron-based sintered bearing has the bearing surface which supports an outer circumferential surface of a shaft. The whole composition of the sintered alloy comprises, by mass ratio, 2.0-9.0% Cu, 1.5-3.7% C and the balance Fe with unavoidable impurities. The inner part of the bearing has a metallographic structure in which copper phases that extend in such a direction as to intersect with a shaft direction of the bearing, graphite phases and pores are dispersed in an iron alloy phase comprising 20-85% ferrite and the balance pearlite by an area rate. The copper phases are exposed on the bearing surface at an area rate of 8-40%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an iron-based sintered bearing suitable for use as a bearing for a paper feed roller shaft of a motor bearing, a copying machine, and the like, and a method of manufacturing the same. The present invention relates to a technique for reducing the amount of wear.

Conventionally, a bearing made of a sintered alloy has been frequently used. Sintered alloys are widely used because they can provide self-lubricating properties with impregnated lubricating oils, and therefore have good seizure resistance and wear resistance.
For example, Patent Document 1 discloses a bearing in which an iron-copper-based sintered alloy layer made of Cu: 10 to 30% and the balance: Fe is provided on a sliding surface.

JP-A-11-117940

  However, since the price of copper has soared in recent years, a technique using 10 to 30% of copper as in Patent Document 1 is expensive and is not practical. For this reason, the need for bearings mainly composed of iron is increasing. However, in the case of a bearing containing iron as a main component, there are drawbacks that it is easy to seize and the shaft that is the counterpart part is easily damaged. In particular, when a combination of a shaft having a low hardness not subjected to heat treatment and a bearing mainly composed of iron is used, the above phenomenon becomes remarkable.

  Therefore, the present invention provides an iron-based sintered alloy bearing having excellent wear resistance, and having seizure resistance comparable to that of an iron-copper-based sintered alloy bearing and mitigating attack on a counterpart component, and a method for manufacturing the same. The purpose is to do.

  The present invention is an iron-based sintered bearing having a bearing surface that supports the outer peripheral surface of a shaft, and the overall composition of the sintered alloy is Cu: 2.0 to 9.0%, C: 1. .5 to 3.7%, balance: Fe and unavoidable impurities, the inside of the bearing is in an iron alloy phase consisting of 20 to 85% ferrite and balance of pearlite in the area ratio with respect to the axial direction of the bearing. A copper phase extending in a crossing direction and a metal structure in which a graphite phase and pores are dispersed are shown, and the copper phase is exposed on the bearing surface at an area ratio of 8 to 40%.

  Further, the present invention provides a raw material in a cavity including a die having a die hole, a core rod disposed in the die hole, and a lower punch that is slidably fitted to the die hole of the die and the outer periphery of the core rod. Iron that fills the powder, compacts this raw material powder with an upper punch and a lower punch that slidably fit into the die hole and the outer periphery of the core rod, and sinters the resulting green compact In the method for producing a sintered sintered bearing, the raw material powder is a flat copper powder having an average particle diameter of 20 to 150 μm, 2.0 to 9.0 mass%, and a graphite powder having an average particle diameter of 40 to 80 μm. 1.5 to 3.7 mass% is added to iron powder and mixed, and the sintering temperature is 950 to 1030 ° C.

  Hereinafter, the grounds for limiting the numerical values of the present invention will be described together with the operation of the present invention. In the following description, “%” means mass%.

In the method of manufacturing the iron-based sintered bearing of the particle size present invention copper powder, a mixture of flaky copper powder raw material powder filled in the cavity. Then, when the raw material powder falls in the die cavity, the copper powder clings to the core rod, and the copper powder adheres to the core rod. As a result, the amount of copper phase exposed on the inner diameter surface of the bearing, which requires sliding characteristics, as compared with the inside of the bearing is increased. In the present invention, by providing the entire amount of Cu as flat copper powder, the amount of Cu inside the bearing can be reduced while securing the amount of copper phase exposed on the inner surface of the bearing.

  When raw material powder containing flat copper powder is filled, the copper powder is oriented around or parallel to the core rod, but inside the bearing, when the flat copper powder falls into the die cavity, the shaft of the bearing It is easy to align in the direction perpendicular to the direction. For this reason, after compression molding and sintering the raw material powder, the copper phase extends in a state perpendicular to or close to the axial direction of the bearing inside the bearing.

  The copper phase has lower strength than the iron alloy phase, but the copper phase is dispersed as described above, so the amount of the copper phase in the axial direction is reduced, so the strength is ensured against the axial load. Is done. In order to obtain the above actions and effects, the particle size of the flat copper powder is 20 to 150 μm. When the particle size of the copper powder is less than 20 μm, the ratio of copper existing between the iron particles is excessively increased, and sintering between the particles is difficult to proceed. As a result, the bearing strength is reduced and the wear amount of the bearing is increased. On the other hand, when the particle size of the copper powder exceeds 150 μm, the copper powder is difficult to adhere to the core rod, and the area ratio of the copper phase exposed on the inner diameter surface of the bearing is lowered. As a result, seizure of the bearing is likely to occur and the amount of wear of the shaft increases. In addition, in order to ensure the flatness of copper powder, it is desirable that the ratio of the particle diameter and thickness of copper powder is 2.5-20.

Addition amount of copper powder When the addition amount of copper powder is small, the area ratio of the copper phase exposed to the inner diameter surface of the bearing is lowered. On the other hand, when there is much addition amount of copper powder, the intensity | strength of a bearing will fall and the amount of wear of a bearing will increase. Therefore, the addition amount of copper powder shall be 2.0 to 9.0%.

The particle size of the graphite powder The above-mentioned flat copper powder can secure the amount of the copper phase exposed on the inner surface of the bearing. In the present invention, however, the graphite is further dispersed in the iron alloy phase. A graphite phase is formed. The free graphite phase acts as a solid lubricant and improves sliding properties. Here, when the particle size of the graphite powder is too small, C tends to diffuse into the iron alloy phase, the amount of pearlite increases, and the hardness of the iron alloy phase increases. As a result, the amount of wear on the shaft that is the sliding partner increases. In addition, the amount of free graphite phase is reduced and the sliding characteristics are lowered. On the other hand, if the particle size of the graphite powder is too large, it becomes difficult for C to diffuse into the iron alloy phase, the hardness of the base decreases, and the wear amount of the bearing increases. Moreover, when the particle diameter of graphite becomes too large, since the bond between metal powders is hindered and the material strength is reduced, the wear amount of the bearing is increased. Therefore, the average particle diameter of graphite powder shall be 40-80 micrometers.

Addition amount of graphite powder If the addition amount of graphite powder is small, the amount of ferrite in the iron alloy phase increases, the hardness decreases, and the wear amount of the bearing increases. In addition, the solid lubricating effect is reduced. On the other hand, if the amount of graphite powder added is large, the amount of pearlite increases, leading to an increase in the hardness of the iron part, and the bonding between the metal powders is hindered and the material strength is reduced. Increase. Therefore, the addition amount of the graphite powder is 1.5 to 3.7%.

Sintering temperature In the present invention, since the graphite phase is formed in the iron alloy phase, the sintering temperature is important. If the sintering temperature is low, the amount of ferrite in the iron alloy phase increases, the hardness decreases, and the wear amount of the bearing increases. On the other hand, when the sintering temperature is high, the amount of pearlite is increased and the hardness is increased, so that the wear amount of the shaft is increased, the strength of the iron alloy phase is lowered, and the wear amount of the bearing is increased. Therefore, the sintering temperature is 950 to 1030 ° C.

  According to the present invention, the copper phase and the graphite phase exposed on the inner diameter surface of the bearing have excellent wear resistance, and also have seizure resistance comparable to that of an iron-copper-based sintered alloy bearing and mitigation of attack on the counterpart part. The effect of having it etc. is acquired.

(1) Manufacture of a bearing Hereinafter, an Example demonstrates this invention further in detail.
In order to produce a sintered alloy of the bearing, the following raw material powders were prepared.
1. Ore reduced iron powder (average particle size: 100μm)
2. Copper foil powder (average particle size: 10 μm, 20 μm, 50 μm, 100 μm, 150 μm, 200 μm)
3. Electrolytic copper powder (average particle size: 50 μm)
4). Natural graphite powder (average particle size: 20μm, 60μm, 100μm)
5). Zinc stearate

  These powders were blended so that the total composition was as shown in Table 1, and mixed with a mixer. Zinc stearate is added for lubrication during molding. When the mixed powder excluding this is taken as 100%, 0.5% was added to all the mixed powders.

The mixed powder was compression molded into a cylindrical shape of a bearing, and sintered and sized. Sintering was performed at a temperature shown in Table 1 in a mixed gas of hydrogen gas and nitrogen gas, and sizing was performed by an ordinary method. The density of the bearing was 6.0 Mg / m ³ and the effective porosity was 20%. The bearing pores were impregnated with lubricating oil (mineral oil viscosity grade ISO VG56). 1-24 were obtained.

(2) Evaluation The area ratio of the copper phase on the inner diameter surface of the bearing, the ferrite area ratio in the iron alloy matrix, the hardness, the crushing strength, and the wear amount of the bearing and the shaft were measured for the above samples. The amount of wear is measured by attaching a shaft made of S45C to the horizontal rotation shaft of the motor, inserting the shaft into a bearing attached to the housing with a gap, and applying a vertical load to the housing. It was done by rotating. The ambient temperature of this test was maintained at 80 ° C., the rotational speed of the shaft was 3000 rpm, and the load surface pressure was 1 MPa. The amount of wear of the bearing and shaft was defined as the difference between the dimensions of the inner and outer diameters before the test and the dimensions after 1000 hours of operation. The results are shown in Table 2.

  As shown in Table 2, the sample No. 2 in which the amount of copper foil powder added falls below the range of the present invention. In No. 1, wear of the shaft increased because the area ratio of the copper phase on the inner diameter surface of the bearing was small. In addition, Sample No. in which the added amount of copper foil powder exceeds the range of the present invention. In No. 5, the amount of wear of the bearing increased because the strength of the bearing decreased. Sample No. In No. 6, electrolytic copper powder was used as the copper powder to be added, but the wear amount of both the bearing and the shaft increased. This is presumably because the amount of copper powder clinging to the core rod is reduced because the area ratio of the copper phase on the inner diameter surface of the bearing is low. In contrast, Sample No. which is an example of the present invention. In 2 to 4, the amount of wear of the bearing and the shaft is small.

  Sample No. in which the amount of graphite powder added falls below the range of the present invention. In No. 7, since the area ratio of ferrite in the iron alloy phase was large, the hardness decreased and the wear amount of the bearing increased. In addition, the amount of free graphite phase was small and the solid lubricity was poor, so the amount of wear on the shaft also increased. Sample No. in which the amount of graphite powder added exceeds the range of the present invention. In No. 11, the area ratio of pearlite in the iron alloy phase was large, so that the hardness was high and the wear amount of the shaft was increased. Further, since the crushing strength (or strength) of the bearing has decreased, the wear amount of the bearing has also increased. In contrast, Sample No. which is an example of the present invention. In 8-10, there is little abrasion amount of a bearing and a shaft.

  Sample No. in which the particle size of the graphite powder is below the range of the present invention. In No. 12, since the area ratio of pearlite in the iron alloy phase was large, the hardness increased and the wear amount of the shaft increased. Further, as a result of the shaft wear powder acting as an abrasive, the amount of wear on the bearing is also large. Sample No. whose graphite particle size exceeds the range of the present invention. In No. 15, the crushing strength (or strength) of the bearing decreased and the wear amount of the bearing increased. In contrast, Sample No. which is an example of the present invention. In Nos. 13 and 14, the wear amount of the bearing and the shaft is small.

  Sample No. in which the particle size of the copper foil powder is below the range of the present invention. In No. 16, the proportion of copper present between iron particles increased too much, and sintering between particles became difficult to proceed, resulting in a decrease in bearing strength and an increase in bearing wear. Sample No. in which the particle size of the copper foil powder exceeds the range of the present invention. In No. 20, the copper powder hardly adheres to the core rod, and the area ratio of the copper phase exposed on the inner diameter surface of the bearing is reduced. As a result, the wear amount of the shaft is increased. In contrast, Sample No. which is an example of the present invention. In 17-19, the amount of wear of a bearing and a shaft is small.

  Sample No. whose sintering temperature is below the range of the present invention. In No. 21, the amount of ferrite in the iron alloy phase increases, the hardness decreases, and the amount of wear on the bearing increases. Sample No. whose sintering temperature exceeded the range of the present invention. In No. 24, the amount of pearlite increased and the hardness became hard, so the amount of wear on the shaft increased. In contrast, Sample No. which is an example of the present invention. In 22 and 23, the amount of wear of the bearing and the shaft is small.

(3) Microstructure observation FIG. 1 is an SEM photograph of the inner diameter surface of the bearing of the present invention. As shown in FIG. 1, a copper phase and a graphite phase are dispersed in an iron alloy phase on the inner diameter surface of the bearing of the present invention example, and the copper phase is arranged in parallel to the inner diameter surface of the bearing. Such a copper phase increases the area ratio of the copper phase on the inner diameter surface of the bearing, and the above-described improvement in sliding performance can be obtained.

It is an optical microscope photograph of the bearing inner surface of the example of the present invention.

Claims (3)

An iron-based sintered bearing having a bearing surface that supports the outer peripheral surface of the shaft, wherein the overall composition of the sintered alloy is Cu: 2.0 to 9.0%, C: 1.5 to 3 .7%, balance: Fe and inevitable impurities,
The interior of the bearing has an area ratio of 20 to 85% of ferrite and the balance of pearlite in an iron alloy phase, in which the copper phase extending in the direction intersecting the axial direction of the bearing, the graphite phase, and the pores are dispersed. Showing the metal structure
An iron-based sintered bearing, wherein a copper phase is exposed at an area ratio of 8 to 40% on the bearing surface. Raw material powder is filled into a cavity composed of a die having a mold hole, a core rod disposed in the mold hole, and a lower punch that is slidably fitted to the mold hole of the die and the outer periphery of the core rod. Then, this raw material powder is compacted by an upper punch and a lower punch that are slidably fitted to the die hole of the die and the outer periphery of the core rod, and the resulting green compact is sintered. In the manufacturing method of the sintered ceramic bearing,
The raw material powder is a flat copper powder having an average particle diameter of 20 to 150 μm, 2.0 to 9.0 mass%, and a graphite powder having an average particle diameter of 40 to 80 μm is 1.5 to 3.7 mass. Is added to iron powder and mixed,
The method for producing an iron-based sintered bearing, wherein the sintering temperature is 950 to 1030 ° C.   The method for producing an iron-based sintered bearing according to claim 2, wherein a ratio of a particle diameter and a thickness of the copper powder is 2.5 to 20.

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