WO2021070712A1

WO2021070712A1 - Sintered oil-containing bearing

Info

Publication number: WO2021070712A1
Application number: PCT/JP2020/037234
Authority: WO
Inventors: 容敬伊藤; 山下　智典; 和慶原田
Original assignee: Ntn株式会社
Priority date: 2019-10-07
Filing date: 2020-09-30
Publication date: 2021-04-15
Also published as: JP2021060077A

Abstract

A sintered bearing 1 comprises a sintered body, and a lubricating oil with which the sintered body is impregnated, and further has a bearing surface 1a. The sintered body contains, as main components, Fe, Cu, an element having a melting point lower than that of Cu, and a solid lubricant component. The contained amount of Cu is 10 mass% or more. In addition, the sintered body has an iron structure and a copper structure that are formed by sintering of a partially diffused alloy powder in which copper powder is partially diffused in iron powder, wherein the element having a melting point lower than that of Cu is diffused at least in the copper structure. The lubricating oil contains an ester oil as a base oil, and, as an additive, an extreme pressure additive that reacts with the iron structure to form an inorganic coating.

Description

Sintered oil-impregnated bearing

The present invention relates to a sintered oil-impregnated bearing.

Sintered oil-impregnated bearings have the characteristic that they can be used without lubrication functionally, so they are widely used in places where sufficient lubrication cannot be expected environmentally or mechanically. This sintered oil-impregnated bearing is formed of a porous sintered body having innumerable pores. Lubricating oil held in the pores on the surface and inside of the sintered body seeps out to the bearing surface due to the pressure generated by thermal expansion and rotation due to the temperature rise. The exuded lubricating oil forms an oil film in the bearing gap between the sliding surface of the sintered oil-impregnated bearing and the outer peripheral surface of the shaft, and the shaft is rotatably supported.

This sintered oil-impregnated bearing is widely used in office equipment, home appliances, audio equipment, automobile electrical components, etc. In particular, copper-iron-based sintered oil-impregnated sinterings containing copper and iron as main components are widely used in applications where a balance between strength, wear resistance, initial familiarity, and quietness is required. In Patent Document 1 below, as an example of such a copper-iron-based sintered oil-impregnated bearing, copper-coated iron coated with copper of 10 wt% to less than 30 wt% with respect to iron powder and having a particle size of 80 mesh or less. It is disclosed that the powder is compactly molded and sintered.

Japanese Patent No. 361359

Since the copper-coated iron powder described in Patent Document 1 has a copper layer formed around the iron powder by means such as plating, the bonding force between the copper powder and the iron powder is weak. Therefore, even if a part of the copper layer diffuses into the iron powder due to sintering, the area of the diffused portion is small and the depth thereof is also shallow. Therefore, the neck strength between the copper structure and the iron structure in the sintered body is reduced. In this case, the iron structure and the copper structure are likely to fall off from the bearing surface, so that the bearing surface is worn at an early stage. This tendency is particularly problematic in sintered bearings (for example, sintered bearings for power windows of automobiles) used under conditions of low speed rotation and high surface pressure where sufficient boundary lubrication is not performed. In order to improve wear resistance, the base oil of the impregnated oil has been improved, the material of the shaft and bearing has been improved, and the shape of the bearing has been improved, but it is not sufficient to ensure wear resistance. I can't say.

Therefore, an object of the present invention is to improve the wear resistance of a copper-iron-based sintered oil-impregnated bearing.

In order to solve the above problems, the present invention is a sintered oil-impregnated bearing having a sintered body and a lubricating oil impregnated in the sintered body and having a bearing surface, wherein the sintered body is Fe, Cu, Cu. Formed by sintering a partially diffused alloy powder, which is mainly composed of an element having a lower melting point and a solid lubricant component, has a Cu content of 10% by mass or more, and is obtained by diffusing a part of copper powder into iron powder. The iron structure and the copper structure are provided, and an element having a melting point lower than that of Cu is diffused into the copper structure at least, and the lubricating oil uses an ester oil as a base oil and uses the ester oil as an additive to form the iron structure. It is characterized by containing an extreme pressure agent that reacts with and forms an inorganic film.

By forming the iron structure and the copper structure of the sintered oil-impregnated bearing by sintering the partial diffusion alloy powder in this way, a part of the copper powder is diffused into the iron powder from the beginning. Compared with the case of sintering copper-coated iron powder, the neck strength between the iron structure and the copper structure is increased. Therefore, it is possible to increase the wear resistance of the bearing surface while increasing the bearing strength. This effect can be obtained more effectively by diffusing an element having a melting point lower than that of Cu in the copper structure.

When the shaft is rotated, frictional heat is generated due to the sliding between the shaft and the bearing surface. The oxide film covering the iron structure of the bearing surface is removed by this friction and frictional heat, and the surface of the iron structure becomes an activated new surface. The reaction between the new surface of the iron structure and the extreme pressure agent molecule forms an inorganic film covering the new surface of the iron structure. By covering the iron structure formed on the bearing surface with the inorganic film in this way, it is possible to improve the wear resistance of the bearing surface.

The ratio of the iron structure to the copper structure on the bearing surface is preferably 10% or more and 80% or less in terms of area ratio.

It is preferable to apply sizing to the bearing surface. By adjusting the sizing allowance, it is possible to control the area ratio of the copper structure and the iron structure on the bearing surface.

The inorganic film is preferably formed of a phosphorus compound. In this case, the activated surface of the iron structure reacts with phosphorus to form an inorganic film of a phosphorus compound such as iron phosphate on the bearing surface, so that the wear resistance of the bearing surface can be improved.

Density of the sintered body is 6.05 g / cm ³ or more, 6.3 g / cm ³ or less.

As the sintered oil-impregnated bearing, a bearing having the inorganic coating formed by reacting with the iron structure on the surface of the iron structure on the bearing surface can be used.

According to the present invention, it is possible to improve the wear resistance of a copper-iron-based sintered bearing.

It is sectional drawing which shows the sintered bearing. It is an enlarged view of the partial diffusion alloy powder. It is sectional drawing which shows the sizing process, and shows before the start of sizing. It is sectional drawing which shows the sizing process, and shows in the process of sizing. It is sectional drawing which shows the sizing process, and shows after the completion of sizing. It is sectional drawing which shows the contour of the sintered body before and after sizing in comparison. It is an enlarged view which shows the microstructure of a sintered body. It is a figure which shows typically the extreme pressure agent molecule. It is sectional drawing which shows the action of an extreme pressure agent, and shows the state in which the shaft is stopped. It is sectional drawing which shows the action of an extreme pressure agent, and shows the state during shaft rotation. It is sectional drawing which shows the action of an extreme pressure agent, and shows the state in which an inorganic film is formed. It is a figure which shows the relationship between the aperture ratio and density.

Hereinafter, embodiments of the sintered oil-impregnated bearing according to the present invention will be described with reference to the accompanying drawings.

The sintered oil-impregnated bearing of the present embodiment is used for supporting a shaft in various auxiliary machines or electrical components for automobiles such as wipers, power windows, sunroofs, and starter motors.

As shown in FIG. 1, the sintered oil-impregnated bearing 1 of the present embodiment is composed of a porous sintered body having a cylindrical bearing surface 1a on the inner circumference and a lubricating oil impregnated in the sintered body. Will be done. When the shaft 2 is inserted into the inner circumference of the sintered oil-impregnated bearing 1 and the shaft 2 is rotated in that state, the lubricating oil held in the innumerable holes of the sintered oil-impregnated bearing 1 causes the temperature to rise and the shaft 2 to rotate. It exudes to the bearing surface 1a due to the accompanying pressure. The exuded lubricating oil forms an oil film in the bearing gap (width of several μm to several tens of μm) between the outer peripheral surface 2a of the shaft 2 and the bearing surface 1a, and the shaft 2 is relatively rotated by the sintered oil-impregnated bearing 1. Be supported as much as possible. The shaft 2 is made of a steel material such as stainless steel. The sintered oil-impregnated bearing 1 is fixed to the inner peripheral surface of the housing 3 by, for example, press fitting.

In the sintered oil-impregnated bearing 1 of the present embodiment, a raw material powder in which various powders are mixed is filled in a mold, and the powder is compressed to form a green compact, and then the green compact is sintered, and then sizing and sizing are performed. Manufactured by impregnating with lubricating oil.

The raw material powder is a mixed powder consisting of a partial diffusion alloy powder, a low melting point element powder, and a solid lubricant powder. Various molding aids, for example, lubricants for improving releasability (metal soap, etc.) are added to the mixed powder as needed. Hereinafter, the manufacturing procedure of the raw material powder and the sintered oil-impregnated bearing 1 will be described in detail.

[Partial diffusion alloy powder]
As the partial diffusion alloy powder, as shown in FIG. 2, Fe—Cu partial diffusion alloy powder 11 in which a part of each of the plurality of copper powders 13 is diffused on the surface of the iron powder 12 is used. The average particle size of each copper powder diffused on the surface of the iron powder is smaller than that of the iron powder. The diffused portion of the partially diffused alloy powder 11 forms an Fe—Cu alloy, and as shown in the partially enlarged view in FIG. 2, the alloy portion is arranged in which iron atoms 12a and copper atoms 13a are mixed with each other and arranged. It has a crystal structure. Of the copper powders constituting the partial diffusion alloy powder 11, the copper powder is formed of pure copper except for the region where the Fe—Cu alloy is formed.

As the partial diffusion alloy powder 11, it is preferable to use one having an average particle size of 150 μm or less. When a large particle size partial diffusion alloy powder having an average particle size of more than 150 μm is contained, coarse pores are likely to be formed in the sintered body 2, and as a result, the required wear resistance and pressure ring of the bearing surface 2a are required. This is because the strength may not be secured. On the other hand, if the raw material powder contains a large amount of the partially diffused alloy powder 11 having a small particle size, the filling property of the raw material powder with respect to the molding die (cavity) is lowered in the molding process described later, and the predetermined shape and density are reduced. It becomes difficult to stably obtain the green compact. Therefore, as the partial diffusion alloy powder 11, it is preferable to use a powder having an average particle size of 45 μm or less and a content of particles of less than 25% by mass.

As the iron powder 12 constituting the partial diffusion alloy powder 11 described above, reduced iron powder, atomized iron powder, or the like can be used, but in the present embodiment, reduced iron powder is used. Reduced iron powder is also called sponge iron powder because it has an irregular shape similar to a sphere and is spongy (porous) with internal pores. By using sponge iron powder, the lubricating oil is retained in the pores of the iron powder. The iron powder 12 to be used preferably has an average particle size of 45 μm to 150 μm, and more preferably an average particle size of 63 μm to 106 μm.

The above-mentioned average particle size is obtained by a laser diffraction / scattering method in which a group of particles is irradiated with laser light and the particle size distribution is calculated from the intensity distribution pattern of the diffraction / scattered light emitted from the particle group, and the average particle size is obtained. For example, it can be measured by (using SALD31000 manufactured by Shimadzu Corporation) (the average particle size of each powder described below can also be measured by the same method).

Further, as the copper powder 13 constituting the partial diffusion alloy powder 11, general-purpose irregular-shaped or dendritic copper powder can be widely used, and for example, electrolytic copper powder, atomized copper powder, or the like is used. In this embodiment, atomized copper powder is used, which has a large number of irregularities on the surface, has an irregular shape similar to a spherical shape as a whole particle, and has excellent moldability. The copper powder 13 to be used has a particle size smaller than that of the iron powder 12, and specifically, a copper powder containing 50% or more, preferably 60% or more of an average particle size of 5 μm or more and 20 μm or less is used. To. The proportion of Cu in the partial diffusion alloy powder 11 is preferably in the range of 10% by mass or more and 30% by mass or less (preferably 22% by mass or more and 26% by mass or less).

[Low melting point element powder]
The low melting point element powder is a powder having a melting point lower than that of copper, and in the present invention, a powder having a melting point of 700 ° C. or lower such as tin, zinc, and phosphorus is used. Of these, it is preferable to use tin, which has less transpiration during sintering. The average particle size of the low melting point element powder is preferably 5 μm to 45 μm, which is smaller than the average particle size of the partial diffusion alloy powder 11. These low melting point element powders have high wettability with respect to copper. By blending the low melting point element powder with the raw material powder, at the time of sintering, the low melting point element powder first melts to wet the surface of the copper powder and diffuses into copper to melt the copper. Liquid phase sintering proceeds by the alloy of molten copper and low melting point metal, and the bond strength between iron particles, between iron particles and copper particles, and between copper particles is strengthened.

[Solid lubricant powder]
The solid lubricant powder is added to reduce friction at the time of metal contact due to sliding with the shaft 2, and graphite is used, for example. As the graphite powder, it is desirable to use scaly graphite powder. As the solid lubricant, molybdenum disulfide can be used in addition to graphite.

[Mixing ratio]
In the raw material powder containing each of the above powders, the low melting point element powder (for example, tin powder) is 0.5 to 3.0% by mass, and the solid lubricant powder (for example, graphite powder) is 0.3 to 3.0% by mass. The rest is preferably a partial diffusion alloy powder. About 0.1 to 1% by mass of molding aids (zinc stearate, calcium stearate, etc.) for improving mold releasability with respect to 100% of the total of partial diffusion alloy powder, low melting point element powder, and solid lubricant powder. Is added. Pure iron powder or pure copper powder can be blended with this raw material powder, but if pure iron powder is blended, it becomes difficult to secure the annular strength, and if pure copper powder is blended, the wear resistance of the bearing surface 1a is improved. It becomes difficult to plan. Therefore, it is preferable not to mix pure iron powder or pure copper powder with the raw material powder.

[Molding process]
The mixed raw material powder is supplied to the mold of the molding machine. As the mold, a known mold having a core, a die, an upper punch, and a lower punch is used. After filling the cavities defined by these with the raw material powder, the upper and lower punches are brought close to each other to compress the raw material powder, whereby a cylindrical green compact is formed.

[Sintering process]
After that, the green compact is sintered in a sintering furnace. In the present embodiment, for example, the sintering conditions are determined so that the iron structure has a two-phase structure of a ferrite phase and a pearlite phase. If the iron structure is a two-phase structure consisting of a ferrite phase and a pearlite phase in this way, the hard pearlite phase contributes to the improvement of wear resistance, suppresses wear on the bearing surface under high surface pressure, and improves bearing life. Can be made to.

Due to the diffusion of carbon, the abundance ratio of pearlite (γFe) becomes excessive, and when the ratio is equal to or higher than that of ferrite (αFe), the aggression of pearlite to the shaft increases remarkably and the shaft is easily worn. In order to prevent this, the pearlite phase (γFe) is suppressed to the extent that it is present (spotted) at the grain boundaries of the ferrite phase (αFe) (see FIG. 5). The "grain boundary" here means both the grain boundary formed between the powder particles and the crystal grain boundary 18 formed in the powder particles. When the iron structure is formed by a two-phase structure of a ferrite phase (αFe) and a pearlite phase (γFe) in this way, the ratio of the ferrite phase (αFe) and the pearlite phase (γFe) to the iron structure is the area ratio, respectively. , 80 to 95% and 5 to 20% (αFe: γFe = 80 to 95%: 5 to 20%). As a result, it is possible to achieve both suppression of wear of the shaft 2 and improvement of wear resistance of the bearing surface 1a.

The growth rate of pearlite mainly depends on the sintering temperature. Therefore, in order to allow the pearlite phase to exist at the grain boundaries of the ferrite phase in the above embodiment, the sintering temperature (internal atmosphere temperature) is set to about 820 ° C to 900 ° C, and a gas containing carbon as the internal atmosphere, for example. Sinter using natural gas or heat absorbing gas (RX gas). As a result, carbon contained in the gas diffuses into iron during sintering, and a pearlite phase (γFe) can be formed. Note that sintering at a temperature exceeding 900 ° C. is not preferable because carbon in the graphite powder reacts with iron and the pearlite phase increases more than necessary. Along with sintering, the lubricant and other various molding aids contained in the green compact for improving the releasability are burned inside the sintered body or vaporized from the inside of the sintered body.

[Sizing process]
The sintered body that has undergone the sintering process is subjected to sizing for dimensional shaping. As shown in FIG. 3A, the die for sizing processing includes a die 20, an upper punch 21, a lower punch 22, and a core 23. With the core 23 and the upper punch 21 retracted upward, the sintered body 1 "is set on the lower punch 22. As shown in FIG. 3B, the core 23 first enters the inner diameter of the sintered body 1". After that, as shown in FIG. 3C, the upper punch 21 pushes the sintered body 1 "into the die 20, and the upper and

lower punches

21 and 22 compress the sintered body 1". As a result, the surface of the sintered body 1 "is sized. .. By the sizing process, the pores on the surface layer of the sintered body 1 "are crushed, and a density difference is generated between the inside of the product and the surface layer portion.

FIG. 4 shows the state before and after the sintered body 1 ”is compressed by the sizing process. The sintered body 1 before the sizing process is shown by a chain double-dashed line, and the sintered body after the sizing process is shown by a solid line. As is clear from the comparison between the chain line and the solid line, the sizing causes the sintered body 1 "to shrink in the axial and radial directions, and both the inner peripheral surface 1a and the outer peripheral surface 1b of the sintered body 1" are reduced in diameter. With the subsequent extraction of the core 23 and the release of the sintered body 1 ", the inner peripheral surface 1a of the sintered body 1" is squeezed by the core 23 and the outer peripheral surface 1b is squeezed by the die 20. A plastic flow is generated on the inner peripheral surface 1a and the outer peripheral surface 1b, respectively. As a result, the aperture ratio of the inner peripheral surface 1a and the outer peripheral surface 1b of the sintered body 1 ”is smaller than the aperture ratio of the core portion of the sintered body.

[Oiling process]
In the oil-impregnating step, a large number of sizing sintered bodies 1 "are charged into a tank to which lubricating oil is supplied, and then the inside of the tank is depressurized to lubricate the pores (including internal pores) of the sintered body 1 ". This is the process of impregnating with oil. By impregnation with the lubricating oil, the sintered oil-impregnated bearing 1 shown in FIG. 1 in which the lubricating oil is held in each of the surface pores and the internal pores is completed. The composition and properties of the lubricating oil used in the oil impregnation process will be described in detail later.

The sintered oil-impregnated bearing 1 (excluding lubricating oil) manufactured through the above steps contains 10 to 30% by mass of Cu, 0.5 to 3.0% by mass of a low melting point element (for example, Sn), and a solid lubricant. It contains 0.3 to 3.0% by mass of a component (for example, C), and the balance is Fe and unavoidable impurities. The sintered body has the highest Fe content, followed by the Cu content. In this way, the sintered body is formed only of Fe, Cu, low melting point elements, solid lubricant components, and unavoidable impurities, and is limited to an amount that does not impair the required wear resistance and bearing strength. Other elements other than the above can also be added. As an example of other elements, any one or more of S, Si, Ni, Mo, Cr, Mn and the like can be mentioned. However, the content of the other elements in the sintered body shall be less than the contents of Fe, Cu, the low melting point element, and the solid lubricant component, respectively.

FIG. 5 is an enlarged view showing the microstructure of the "sintered body after sintering". Tin as a low melting point element is first melted at the time of sintering, and the partial diffusion alloy powder 11 (see FIG. 2). The bronze phase 16 (Cu—Sn) is formed by diffusing into the copper powder 13 constituting the above. Liquid phase sintering proceeds by the bronze layer 16, and iron particles, iron particles and copper particles, or copper particles are separated from each other. Of the individual partial diffusion alloy powders 11, a part of the copper powder 13 is diffused and the molten tin is diffused to the portion where the Fe—Cu alloy is formed to form the Fe—Cu—. A Sn alloy (alloy phase 17) is formed. The bronze layer 16 and the alloy phase 17 are combined to form a copper structure 14. The copper structure 14 is formed so as to cover the periphery of the iron structure 15. In FIG. 5, the ferrite phase (αFe), the pearlite phase (γFe), and the like are represented by shades of color. Specifically, the ferrite phase (αFe) → the bronze phase 16 → the alloy phase 17 (Fe—Cu). The colors are darkened in the order of −Sn alloy) → pearlite phase (γFe).

A sintered structure in which the circumference of the iron structure is covered with a copper structure can also be obtained by using a so-called copper-coated iron powder in which a copper layer is formed by plating around the iron powder. However, when copper-coated iron powder is used, the copper layer is only in contact with the surface of the iron powder, so even if a part of the copper layer is diffused into the iron powder due to sintering, partial diffusion is performed. Compared with the case of using an alloy, the area of the diffusion region is small and the depth is shallow. Therefore, the neck strength between the iron structure and the copper structure after sintering is lowered, and the bearing strength and the wear resistance of the bearing surface are lowered as compared with the sintered oil-impregnated bearing 1 of the present embodiment.

Further, as in the present embodiment, a predetermined amount of an element having a melting point lower than that of copper is blended in the raw material powder, and metal particles (between iron particles, between iron particles and copper particles, or between copper particles) are subjected to liquid phase sintering. ), The bearing strength and the abrasion resistance of the bearing surface 1a can be further improved. The sintered oil-impregnated bearing 1 of the present embodiment can achieve an annular strength (300 MPa or more) twice or more that of the existing copper-iron-based sintered oil-impregnated bearing. Therefore, as shown in FIG. Even when the sintered bearing 1 is press-fitted and fixed to the inner circumference of the housing 3, the bearing surface 1a does not deform following the shape of the inner circumference of the housing 3. Therefore, the roundness, cylindricity, etc. of the bearing surface 1a can be stably maintained even after mounting, and after the sintered oil-impregnated bearing 1 is press-fitted and fixed to the inner circumference of the housing 3, the bearing surface 1a has an appropriate shape. It is possible to secure a desired roundness (for example, a roundness of 3 μm or less) without additionally performing processing (for example, sizing) for finishing with high accuracy. In addition, since free graphite as a solid lubricant is deposited on the bearing surface 1a, the friction of the bearing surface 1a can be reduced and the durability of the sintered oil-impregnated bearing 1 can be increased.

In the above-described embodiment, the iron structure has a two-layer structure of a ferrite phase and a pearlite phase, but the pearlite phase (γFe) has a hard structure (HV300 or more) and has strong aggression against the mating material. Depending on the usage conditions of, the shaft 2 may be worn. In order to prevent this, the entire iron structure 15 can be formed of a ferrite phase (αFe).

Since all of the iron structure 15 is formed of the ferrite phase in this way, the sintering atmosphere is a carbon-free gas atmosphere (hydrogen gas, nitrogen gas, argon gas, etc.) or a vacuum. The sintering temperature is about 800 ° C. to 880 ° C. With these measures, the reaction between carbon and iron does not occur in the raw material powder, and therefore the iron structure after sintering becomes a soft (HV200 or less) ferrite phase (αFe). With such a configuration, the aggression against the shaft 2 can be weakened and the wear resistance of the shaft 2 can be improved.

[Lubricant]
As the lubricating oil to be impregnated in the sintered body 1, a synthetic lubricating oil obtained by adding an additive to an ester-based oil as a base oil is used.

Lubricating oil, the lower limit of the kinematic viscosity of 40 ° C. is, 5 mm ² / s or more, preferably set to 10 mm ² / or more, the upper limit of the kinematic viscosity of 40 ° C. is 200 mm ² / s or less, preferably 60 mm ² / s, More preferably, it is 50 mm ² / s or less. If the kinematic viscosity is in this range, the coefficient of static friction can be lowered and the coefficient of kinematic friction can be increased while ensuring the rigidity of the oil film formed in the bearing gap.

Regarding the lubricating oil, it is preferable to control not only the kinematic viscosity at 40 ° C. but also the kinematic viscosity at 100 ° C. Specifically, 100 the lower limit of the kinematic viscosity ° C. is 1 mm ² / s or more, preferably 2 mm ² / or more, the upper limit of the kinematic viscosity of 100 ° C. is 20 mm ² / s or less, preferably 15 mm ² / s, more preferably The viscosity of 10 mm ² / s or less is used as the lubricating oil. Within this kinematic viscosity range, the lubricating oil can withstand the frictional heat when a new surface activated by the frictional heat of sliding appears on the sliding surface. As a method for measuring the kinematic viscosity, for example, a kinematic viscosity test method based on JIS K2283 can be adopted. In measuring the kinematic viscosity, for example, a glass capillary viscometer such as an Ubbelohde viscometer is used.

As the lubricating oil to be impregnated in the sintered body 2, a liquid grease using the ester-based oil having the above-mentioned kinematic viscosity can be used as the base oil.

As the ester-based oil described above, a polyol ester-based oil or a diester-based oil can be used. Since the polyol ester system does not contain β-hydrogen, it is superior in thermal stability to the diester system. In ester-based oils, a part of the ester is adsorbed on the metal surface to form a lubricating film, but since polyol ester-based oils have more adsorbing groups than diester-based oils, a stronger lubricating oil film should be formed. Can be done. Therefore, it is preferable to use a polyol ester system from the viewpoint of chemical bond stability and lubricity. On the other hand, since the diester system has an advantage of low cost, it is preferable to use the diester system when the cost aspect is important.

The diester is, for example, an ester of a divalent base such as adipic acid or sebacic acid and a monohydric alcohol, and a typical example thereof is dioctyl sebacate.

As the base oil, a polyol ester type and a diester type may be mixed and used. Further, either one of the polyol ester type and the diester type may be mixed with a poly-alpha-Olefins (hereinafter referred to as "PAO"), and both may be further mixed with PAO.

[Additive]
An extreme pressure agent (or anti-wear agent) is added to the base oil as an additive. Since the extreme pressure agent causes a chemical reaction with the surface of iron or iron oxide on the friction surface, by using the extreme pressure agent, an extreme pressure film of an inorganic compound composed of a compound of the element and iron in the extreme pressure agent can be formed. Generated on the friction surface. Since the extreme pressure film is a film that is relatively soft and easily sheared, by forming the extreme pressure film, it is possible to prevent bonding between metals, reduce wear, and avoid seizure. Among the extreme pressure agents, those having a better anti-wear effect than anti-seizure agents are called anti-wear agents.

It is considered that the reaction between the extreme pressure agent and iron proceeds due to friction and wear, and the reaction is promoted by the temperature rise due to frictional heat and the activation of the new surface generated by wear. The extreme pressure film having such a function is an inorganic film, and has a feature that it is more stable even at a higher load and a higher temperature than an adsorption film which is a film of organic molecules.

There are sulfur-based extreme pressure agents and phosphorus-based extreme pressure agents (including sulfur-phosphorus zinc compounds) as extreme pressure agents, but in this embodiment, a phosphorus-based extreme pressure agent having excellent reactivity with iron is used. Is preferable. Phosphite esters, phosphite esters and the like exist as phosphorus-based extreme pressure agents. Typical phosphorus-based extreme pressure agents include, for example, trialkyl phosphate (trialkyl phosphate), tricresyl phosphate [tricresyl phosphate), and alkylamine salts of dialkyl phosphate (amine phosphate). And so on. A more detailed description of the phosphorus-based extreme pressure agent includes, for example, dialkyl phosphate (dialkyl acidic phosphate), alkylamine salt of dialkyl dithiophosphate (amine dithiophosphate), trialkyl phosphite (trialkyl phosphate) and the like. Be done. In dialkyl dithiophosphate, phosphorus and sulfur act as effective elements.

The lubricating oil containing such a phosphorus-based extreme pressure agent, the use as impregnating oil impregnated in the sintered body of sintered bearing, when a predetermined time operated _{_{bearings, Fe 2 P, FeP 2,}} FePO 4 _{_{, FePO 4 · 2H 2 O,}} Fe 3 P, Fe (PO 4) 2, Fe 3 (PO 4) 2, selected from _{_{_{(PO 4 C x H y)}}} n, 2FeFe 4 (PO 4) 3 (OH) 5 An inorganic film containing at least one of these phosphorus compounds is formed on the bearing surface 1a as an extreme pressure film. Further, for example, depending on the sliding conditions and the like, _{an inorganic film containing FeO—Fe 3} O ₄ is formed on the bearing surface 1a as an extreme pressure film.

As shown in FIG. 6, the molecule 30 of the phosphorus-based extreme pressure agent is composed of a polar group 31 having a strong polarity including O and S in addition to P, and a non-polar group 32 composed of a hydrocarbon group and having almost no polarity. .. As shown in FIG. 7A, in the state before the start of operation of the bearing (rotation stopped state), the polar group 31 of the extreme pressure agent molecule 30 contained in the lubricating oil exuded from the sintered oil-impregnated bearing 1 is the sintered oil-impregnated bearing 1. It is attracted to the bearing surface 1a of. Therefore, a large number of extreme pressure agent molecules 30 are attracted to the bearing surface 1a in the same direction, and a large number of extreme pressure agent molecules 30 are interposed between the bearing surface 1a and the outer peripheral surface 2a of the shaft 2. As shown in FIG. 7B, when the shaft 2 is rotated, frictional heat is generated due to the sliding of the shaft 2 and the bearing surface 1a. By this friction and frictional heat, the oxide film covering the iron structure of the bearing surface 1a is removed, and the surface of the iron structure becomes an activated new surface. As shown in FIG. 7C, the reaction between the new surface of the iron structure and the extreme pressure agent molecule 30 forms an inorganic film 33 covering the new surface of the iron structure.

The inorganic coating 33 improves the wear resistance of the sintered oil-impregnated bearing 1. Therefore, it is used under conditions of low speed (peripheral speed 10 m / min or less) and high surface pressure (surface pressure 3 MPa or more), and even under conditions where boundary lubrication cannot be expected, sintered oil impregnation with improved wear resistance of the bearing surface 1a. It becomes possible to provide the bearing 1.

Note that, in FIGS. 7A to 7C, the extreme pressure agent molecule 30 is shown enlarged as compared with the size of the shaft 2. Further, for ease of understanding, the cylindrical bearing surface 2a is shown in a flatly developed state.

As described above, according to the present invention, the lubricating oil impregnated in the sintered body contains an extreme pressure agent (particularly a phosphorus-based extreme pressure agent) that forms an inorganic film on the surface of the iron structure as an additive. It is possible to improve the wear resistance even in the copper-iron-based sintered oil-impregnated bearing 1 in which the iron structure and the copper structure in which the inorganic film 33 is difficult to be formed due to the low reactivity with the extreme pressure agent are mixed on the surface 1a. It is characterized by the points found.

From the viewpoint of improving wear resistance, it is preferable to increase the abundance ratio of the iron structure on the bearing surface 1a and form the inorganic coating 33 in as wide a range as possible. On the other hand, in order to improve the initial familiarity and quietness required for the copper-iron-based sintered bearing, it is necessary to form a certain amount of copper structure on the bearing surface 1a. From the above viewpoint, the ratio of the iron structure 15 to the metal structure (iron structure and copper structure) of the bearing surface 1a is 20% or more (preferably 25% or more, more preferably 30% or more, still more preferably 35%) in terms of area ratio. Above, more preferably 40% or more), 90% or less (preferably 85% or less, more preferably 80% or less, still more preferably 75% or less). The proportion of the copper structure 14 in the metal structure of the bearing surface 1a is 10% or more (preferably 15% or more, more preferably 20% or more, still more preferably 25% or more), 80% or less (preferably) in terms of area ratio. 75% or less, more preferably 70% or less, still more preferably 65% or less). In the bearing surface 1a, except for the metal structure (alloy surface portion) composed of the iron structure 15 and the copper structure 14, the graphite structure and the pores opened on the surface are formed. The area ratio of the iron structure 15 and the copper structure 14 is determined by taking a photomicrograph of the surface of the sintered body subjected to the corrosion treatment and then performing image analysis of the image data.

In the sintered body immediately after sintering, as shown in FIG. 5, the copper structure 14 covers the circumference of the iron structure 15, so that the proportion of the copper structure on the bearing surface 1a is large. After sintering, the bearing surface 1a is squeezed by the core 23 (see FIGS. 3A to 3C) during sizing, so that the copper structure 14 softer than the iron structure 15 is dragged by the core 23 and plastically deformed (plastic flow). However, a large amount of iron structure 15 is exposed on the bearing surface because it falls off. The area ratio of the copper structure to the iron structure on the bearing surface 1a can be controlled by adjusting the sizing allowance α (see FIG. 4) of the bearing surface 1a during sizing (the copper structure can be increased by increasing the sizing allowance α). The area can be reduced). Therefore, it is possible to achieve both wear resistance and initial familiarity (quietness), which are in a trade-off relationship.

The pore opening ratio of the sintered body (the area ratio of pores in the bearing surface 1a of the sintered body) is 20% or more (preferably 25% or more) and 55% or less (preferably 50% or less). If the aperture ratio is below the above lower limit, the amount of lubricating oil that seeps into the bearing gap will decrease, leading to poor lubrication, and if the aperture ratio exceeds the above upper limit, the strength of the sintered body will decrease. This is to become. A proportional relationship as shown by the solid line L in FIG. 8 is generally established between the aperture ratio of the sintered body and the density of the sintered body. Therefore, as understood from FIG. 8, a density of the sintered body 6.05 g / cm ³ or more (preferably 6.1 g / cm ³ or more), 6.3 g / cm ³ or less (preferably 6.25g / Cm ³ or less) is preferable. It is desirable to use a sintered body with an aperture ratio and density within the range of region X indicated by hatching.

For existing copper-iron sintered bearings that do not use partial diffusion alloy powder, it is necessary to increase the molding pressure to increase the density of the sintered body in order to increase the bearing strength and wear resistance. Therefore, there is a problem that the aperture ratio of the sintered body is reduced and the oil film forming property is lowered. On the other hand, in the sintered oil-impregnated bearing 1 of the present embodiment, sufficient bearing strength and wear resistance can be ensured without increasing the density. Therefore, it is possible to increase the opening ratio of the core portion and supply abundant lubricating oil to the bearing gap, and it is possible to obtain good oil film formability.

In the above description, the case where the sintered oil-impregnated bearing 1 is applied to a perfect circular bearing having a bearing surface 1a having a perfect circular shape has been illustrated, but the bearing surface 1a and the outer peripheral surface of the shaft 2 are not limited to the perfect circular bearing. It can also be used as a fluid dynamic bearing provided with a dynamic pressure generating portion such as a herringbone groove or a spiral groove. Further, the sintered oil-impregnated bearing 1 may not only support rotational motion but also linear motion. It can also be used in applications where the shaft 2 side is stationary and the bearing side is rotated or linearly moved.

Further, in the present embodiment, as the use of the sintered oil-impregnated bearing 1, an auxiliary machine for an automobile such as a power window or an electrical component is exemplified, but the use is not limited to this, and the use is not limited to this, and office equipment, home appliances, audio equipment, information. It can be used for a wide range of applications such as processing equipment.

1 Sintered oil-impregnated bearing 1a Bearing surface 2 Shaft 11 Partial diffusion alloy powder 12 Iron powder 13 Copper powder 14 Copper structure 15 Iron structure 30 Extreme pressure agent molecule 33 Inorganic film

Claims

A sintered oil-impregnated bearing having a sintered body and a lubricating oil impregnated in the sintered body and having a bearing surface.
The sintered body contains Fe, Cu, an element having a melting point lower than that of Cu, and a solid lubricant component as main components, and has a Cu content of 10% by mass or more.
It has an iron structure and a copper structure formed by sintering a partial diffusion alloy powder in which a part of copper powder is diffused into iron powder, and an element having a melting point lower than that of Cu is diffused into at least the copper structure.
A sintered oil-impregnated bearing, wherein the lubricating oil contains an ester-based oil as a base oil and, as an additive, an extreme pressure agent that reacts with the iron structure to form an inorganic film.
The sintered oil-impregnated bearing according to claim 1, wherein the ratio of the iron structure to the copper structure on the bearing surface is 10% or more and 80% or less in terms of area ratio.
The sintered oil-impregnated bearing according to claim 1, wherein the bearing surface is sized.
The sintered oil-impregnated bearing according to any one of claims 1 to 3, wherein the inorganic coating is a phosphorus compound.
A density of the sintered body is 6.05 g / cm 3 or more, the oil-impregnated sintered bearing according to any one of claims 1 to 4, is 6.3 g / cm 3 or less.
The sintered bearing according to any one of claims 1 to 5, which has the inorganic coating formed by reacting with the iron structure on the surface of the iron structure on the bearing surface.