JP6921046B2 - Manufacturing method of sintered bearing - Google Patents

Description

The present invention relates to a method for manufacturing a sintered bearing.

The sintered bearing is a porous body having innumerable internal pores, and is usually used in a state where the internal pores are impregnated with a lubricating fluid (for example, lubricating oil). In this case, when the sintered bearing and the shaft inserted in the inner circumference of the sintered bearing rotate relative to each other, the lubricating oil held in the internal pores of the sintered bearing oozes to the inner peripheral surface (bearing surface) of the sintered bearing as the temperature rises. put out. Then, the exuded lubricating oil forms an oil film in the bearing gap between the bearing surface of the sintered bearing and the outer peripheral surface of the shaft, and the shaft is supported so as to be relatively rotatable.

For example, in Patent Document 1 below, as an iron-copper-based sintered bearing containing iron and copper as main components, copper is coated with 10% by mass or more and less than 30% by mass with respect to iron powder, and the particle size is 80. The ones obtained by compacting and sintering copper-coated iron powder having a mesh or less are described.

Patent No. 361359 Japanese Unexamined Patent Publication No. 2001-178100 Japanese Unexamined Patent Publication No. 2008-99355

However, as a result of verification by the present inventors, it has been clarified that when a sintered bearing to which the technical means of Patent Document 1 is applied is used for a vibration motor, the rotational fluctuation becomes large. This is because in the sintered bearing obtained by compacting and sintering copper-coated iron powder, the neck strength of the iron phase (iron structure) and the copper phase (copper structure) is low, so the bearing surface wears early. It is thought that this is due to this.

As a technical means for improving the wear resistance of the bearing surface, it is conceivable to use a mixed powder containing a metal powder such as Ni or Mo, and to compact and sinter the mixed powder. However, metal powders such as Ni and Mo are expensive, which leads to high cost of sintered bearings.

In view of the above circumstances, an object of the present invention is to make it possible to manufacture a sintered bearing having high rotational accuracy and little rotational fluctuation at low cost.

By the way, the above-mentioned vibration motor functions as a vibrator for notifying an incoming call, an incoming mail, or the like in a mobile terminal such as a mobile phone, and is described in, for example, Patent Documents 2 and 3. By rotating the shaft with a motor unit while supporting two points separated in the axial direction of the shaft to which the weight (eccentric weight) is attached by a cylindrical sintered bearing having a bearing surface on the inner circumference. It is designed to generate vibration throughout the terminal. The sintered bearing is fixed to the inner circumference of a housing made of, for example, a metal material. In this vibration motor, when the motor portion is energized, the shaft rotates while swinging along the entire bearing surface of the sintered bearing under the influence of the weight. That is, in this type of vibration motor, the shaft rotates with its center eccentric with respect to the bearing center of the sintered bearing in all directions.

In recent years, in consideration of mounting on so-called smartphones and the like, further miniaturization of vibration motors has been required. When the vibration motor is miniaturized, there is a limit to the increase in motor power. Even in such a situation, in order to secure the predetermined vibration performance, we are trying to deal with it by increasing the high speed rotation (10000 rpm or more) of the motor or increasing the unbalanced load of the weight, and the sintered bearing for the vibration motor. Conditions of use tend to be more severe. That is, in a vibration motor, the shaft rotates while swinging along the entire surface of the bearing surface as described above, and the bearing surface is frequently hit by the shaft due to an unbalanced load. It is already harsher than a sintered bearing for normal use (for example, a sintered bearing for a spindle motor), and the bearing surface is easily worn. Therefore, when the motor is rotated at a high speed or the like, the wear of the bearing surface is further promoted, and the rotation fluctuation caused by the wear of the bearing surface becomes larger.

The present invention, which was created in consideration of such circumstances, is a method for manufacturing a sintered bearing having a bearing surface forming a bearing gap between the shaft and the shaft to be supported on the inner circumference, and is made of copper with respect to iron powder. A compression molding process in which a partial diffusion alloy powder obtained by partially diffusing powder is used as a main raw material, and a raw material powder obtained by blending a low melting point metal powder and a solid lubricant powder is compression-molded to obtain a green compact, and a green compact. It is characterized by including a sintering step of obtaining a sintered body by sintering.

According to the above manufacturing method, since most of the metal structure is composed of iron (iron structure) and a sintered body containing a certain amount of copper in the metal structure can be obtained, wear resistance and mechanical strength can be obtained. , And a sintered bearing having excellent sliding characteristics such as initial compatibility can be obtained. Further, in the above manufacturing method, the low melting point metal powder contained in the green compact melts as the green compact is sintered in the sintering step. Since the low melting point metal has a high wettability with respect to copper, the iron structure and the copper structure of the adjacent partial diffusion alloy powders or the copper structures can be firmly bonded to each other by liquid phase sintering. Further, among the individual partial diffusion alloy powders, the molten low melting point metal diffuses to the portion where the Fe—Cu alloy is formed by the diffusion of a part of the copper powder on the surface of the iron powder. The neck strength between the iron structure and the copper structure is further increased. For these reasons, the bearing surface has excellent wear resistance even in so-called low-temperature sintering, in which the green compact is heated (sintered) at a relatively low temperature without using expensive metal powders such as Ni and Mo. Moreover, it is possible to manufacture a sintered body (sintered bearing) having a high annular strength (for example, 300 MPa or more).

If the wear resistance of the bearing surface is improved, it is possible to prevent rotational fluctuation caused by wear of the bearing surface. Further, if the sintered bearing does not have sufficient annulus strength, the bearing surface is deformed especially when the sintered bearing is press-fitted into the inner circumference of the housing (the roundness and cylindricity of the bearing surface are reduced). Therefore, it is necessary to additionally perform shape correction processing such as sizing after press fitting to finish the bearing surface into an appropriate shape. On the other hand, if a sintered body having a high annular strength can be obtained as described above, it is possible to prevent the bearing surface from being deformed as the sintered bearing is placed on the inner circumference of the housing as much as possible. Therefore, it is not necessary to additionally perform the above-mentioned shape correction processing. Therefore, even when used in a vibration motor, it is possible to provide a sintered bearing having both high durability and rotational accuracy at low cost.

The sintering temperature (heating temperature) of the green compact can be set to, for example, 820 ° C. or higher and 900 ° C. or lower. If such a sintering process is performed in a gas atmosphere containing carbon, the carbon contained in the gas diffuses into the iron structure, so that the iron structure is sintered with a two-phase structure of a ferrite phase and a pearlite phase. You can get a body. As the sintered body, the entire iron structure may be composed of a ferrite phase, but if the iron structure is composed of the above two-phase structure, the sintered body contains a hard pearlite phase. Thereby, the wear resistance of the bearing surface can be further improved. Further, under the above sintering conditions, the copper powder contained in the green compact does not melt, and therefore the copper does not diffuse into the iron structure during sintering. Therefore, an appropriate amount of copper structure (bronze phase) is formed on the surface of the sintered body. Therefore, it is possible to obtain a bearing surface having good initial compatibility with the shaft and a small friction coefficient.

In order to obtain the above-mentioned sintered bearing (sintered body), as a partial diffusion alloy powder, copper powder having an average particle size of 5 μm or more and less than 20 μm is partially diffused into iron powder and contains 10 to 30% by mass of Cu. It is preferable to use.

As a result of diligent studies by the present inventors, if the raw material powder contains a partial diffusion alloy powder having a large particle size exceeding an average particle size of 106 μm, coarse air pores are likely to be formed inside the sintered body. As a result, it was found that the required wear resistance and annulus strength of the bearing surface may not be ensured. Therefore, it is preferable to use a partial diffusion alloy powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less). By using such an alloy powder, it is possible to stably obtain a sintered body in which the metal structure after sintering is homogenized and the generation of coarse air pores in the metal structure (porous structure) is suppressed. can. This makes it possible to stably obtain a sintered bearing in which the wear resistance of the bearing surface and the annular strength of the bearing are further improved.

As the raw material powder, 0.5 to 3.0% by mass of tin powder as a low melting point metal powder is blended, and 0.3 to 1.5% by mass of graphite powder as a solid lubricant powder is blended. It is preferable to use. As a result, it is possible to stably mass-produce sintered bearings capable of appropriately exhibiting the above-mentioned effects.

As the iron powder constituting the partially diffused alloy powder (Fe—Cu partially diffused alloy powder), reduced iron powder can be used. As the iron powder, for example, atomized iron powder can be used in addition to the reduced iron powder. However, since the reduced iron powder is spongy (porous) having internal pores, it is compared with the atomized iron powder. The powder is soft and has excellent compression moldability. Therefore, the strength of the green compact can be increased even at a low density, and the occurrence of chipping or cracking of the green compact can be prevented. Further, since the reduced iron powder has a spongy shape as described above, it also has an advantage of being superior in oil retention property as compared with the atomized iron powder.

After the sintering step, an oil-impregnating step of impregnating the internal pores of the sintered body with lubricating oil can be provided. In this oil-containing process, lubricating oil kinematic viscosity of 40 ° C. is within the range of 10 to 50 mm ² / s, or 40 kinematic viscosity ° C. is within the range of 10 to 50 mm ² / s oil (lubricating oil) group The internal pores of the sintered body can be impregnated with liquid grease as oil. By impregnating the internal pores of the sintered body with lubricating oil or liquid grease having a kinematic viscosity of 40 ° C. within the above range, a highly rigid oil film can be formed in the bearing gap and the increase in rotational torque is suppressed. A capable sintered bearing (sintered oil-impregnated bearing) can be obtained.

As described above, according to the present invention, it is possible to manufacture a sintered bearing having high rotational accuracy and little rotational fluctuation at low cost. Therefore, when this sintered bearing is incorporated into a motor, particularly a vibration motor, it is possible to provide a vibration motor having excellent reliability and durability at low cost.

It is a schematic cross-sectional view of the main part of the vibration motor provided with a sintered bearing. It is a cross-sectional view taken along the line AA in FIG. It is a block diagram which shows the manufacturing process of a sintered bearing. It is a figure which shows typically the partial diffusion alloy powder. It is a schematic cross-sectional view which shows the compression molding process. It is a schematic cross-sectional view which shows the compression molding process. It is a figure which shows a part of a green compact conceptually. It is a figure which shows typically the metal structure of a sintered body. It is a micrograph of the X part in FIG. It is a micrograph of the vicinity of the bearing surface of the sintered bearing which concerns on the prior art.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a main part of a typical vibration motor. The vibration motor 1 of the illustrated example has a ring-shaped housing 2 formed in a substantially cylindrical shape and a ring-shaped housing 2 which is arranged at two positions apart from each other in the axial direction and is press-fitted and fixed to the inner circumference of the housing 2. It includes a sintered bearing 4 (41, 42) and a shaft 3 inserted in the inner circumference of the sintered bearing 4 (41, 42), and the shaft 3 is arranged between the two sintered bearings 41, 42. The motor unit M is driven to rotate at a rotation speed of 10,000 rpm or more. The shaft 3 is made of a metal material such as stainless steel, and here, a shaft 3 having a diameter of 2 mm or less (preferably 1.0 mm or less) is used. At one end of the shaft 3, a weight W for eccentric rotation of the shaft 3 with respect to the sintered bearing 4 is provided integrally or separately. The gap width of the gap (bearing gap) formed between the outer peripheral surface 3a of the shaft 3 and the bearing surface 4a of the sintered bearing 4 is set to, for example, about 4 μm on one side (radius value). The internal pores of the sintered bearing 4 are impregnated with a lubricating oil (for example, a synthetic hydrocarbon-based lubricating oil) having ^{a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm 2 / s.} As the lubricating oil to impregnate the internal pores of the sintered bearing 4, such a low-viscosity lubricant was selected and used in order to suppress an increase in rotational torque while ensuring the rigidity of the oil film formed in the bearing gap. be. The internal pores of the sintered bearing 4 may be impregnated with liquid grease based on oil having ^{a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm 2 / s instead of the above lubricating oil.} good.

In the vibration motor 1 having the above configuration, when the motor portion M is energized and the shaft 3 rotates relative to the sintered bearing 4, the lubricating oil held in the internal pores of the sintered bearing 4 rises in temperature. It exudes to the bearing surface 4a. The exuded lubricating oil forms an oil film in the bearing gap between the outer peripheral surface 3a of the opposing shaft 3 and the bearing surface 4a of the sintered bearing 4, and the shaft 3 is supported by the sintered bearing 4 so as to be relatively rotatable. Will be done. The shaft 3 rotates while swinging along the entire surface of the bearing surface 4a due to the influence of the weight W provided at one end thereof. That is, as shown in FIG. 2, the shaft 3 rotates in a state where its center Oa is eccentric with respect to the center Ob of the sintered bearings 4 (41, 42) in all directions.

In the illustrated example, the axial lengths (area of the bearing surface 4a) and the radial thicknesses of the two sintered bearings 41 and 42 are different from each other. Specifically, the area of the bearing surface 4a of the sintered bearing 41 on the side closer to the weight W is set to be larger than the area of the bearing surface 4a of the sintered bearing 42 on the side farther from the weight W. This is because on the side closer to the weight W, a larger unbalanced load acts on the shaft 3 than on the side far from the weight W, so that the bearing capacity is improved by expanding the area of the bearing surface 4a, while on the side far from the weight W, the support capacity is improved. This is because the bearing surface closer to the weight W is not required to have a supporting capacity, so that the area of the bearing surface 4a is reduced to reduce the torque.

Although not shown, the vibration motor 1 has a housing in order to prevent the lubricating oil (or liquid grease) impregnated in the internal pores of the sintered bearing 4 from leaking or scattering to the outside of the housing 2. A sealing member for sealing the opening of 2 may be provided.

The sintered bearing 4 described above is made of an iron-copper-based sintered body containing iron as a main component and copper in an amount of 10 to 30% by mass, and has an annular strength of 300 MPa or more. As shown in FIG. 3, for example, such a sintered bearing 4 includes (A) raw material powder producing step P1, (B) compression molding step P2, (C) sintering step P3, (D) sizing step P4 and (E) Manufactured through the oil-impregnating step P5 in order. Hereinafter, each of these steps will be described. The two sintered bearings 4 (41, 42) have substantially the same structure and are manufactured by the same manufacturing procedure.

(A) Raw material powder mixing step P1
In this raw material powder generation step P1, the raw material powder 10 [see FIG. 5A], which is a material for manufacturing the sintered bearing 4, is made uniform by mixing a plurality of types of powders described later. The raw material powder 10 used in the present embodiment is a mixed powder in which a partially diffused alloy powder is used as a main raw material, and a low melting point metal powder and a solid lubricant powder are mixed therein. Various molding lubricants (for example, lubricants for improving releasability) may be added to the raw material powder 10 as needed. Hereinafter, each of the above powders will be described in detail.

[Partial diffusion alloy powder]
As shown in FIG. 4, as the partial diffusion alloy powder 11, Fe—Cu partial diffusion alloy powder in which the copper powder 13 is partially diffused on the surface of the iron powder 12 is used. In the present embodiment, the surface of the iron powder 12 is covered. , Fe—Cu partially diffused alloy powder in which a large number of copper powders 13 having an average particle size smaller than that of iron powder 12 are partially diffused is used. The diffused portion of this partially diffused alloy powder forms an Fe—Cu alloy, and as shown in the partially enlarged view in FIG. 4, the alloy portion is arranged with iron atoms 12a and copper atoms 13a bonded to each other. It has a crystal structure. As the partial diffusion alloy powder 11, only particles having an average particle size of 145 mesh or less (average particle size of 106 μm or less) are used.

The smaller the particle size of the powder, the lower the apparent density and the easier it is to float. Therefore, 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 in the molding die (cavity) in the compression molding step P2 described later is lowered, and the predetermined shape and density are reduced. It becomes difficult to stably obtain the green compact. Specifically, the present inventors have found that the above problem is likely to occur when the partial diffusion alloy powder 11 having a particle size of 45 μm or less is contained in an amount of 25% by mass or more. Therefore, as the partial diffusion alloy powder 11, a powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less) and containing 25% by mass or more of particles having an average particle size of 350 mesh (average particle size of 45 μm or less) is selectively used. Is desirable. The average particle size is determined by a laser diffraction / scattering method (for example, Shimadzu Co., Ltd.) 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. It can be measured by (using SALD31000 manufactured by Mfg. Co., Ltd.) (the average particle size of the powder described below can also be measured by the same method).

As the iron powder 12 constituting the partial diffusion alloy powder 11, known iron powder such as reduced iron powder and atomized iron powder can be used without any problem, but in the present embodiment, the 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. The iron powder 12 to be used preferably has an average particle size of 20 μm to 106 μm, and more preferably an average particle size of 38 μm to 75 μm.

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 sphere as a whole particle, and has excellent moldability. As the copper powder 13, a copper powder having a particle size smaller than that of the iron powder 12 is used, and specifically, a copper powder having an average particle size of 5 μm or more and 20 μm or less (preferably less than 20 μm) is used. The proportion of Cu in each partial diffusion alloy powder 11 is 10 to 30% by mass (preferably 22 to 26% by mass), and the mass ratio of copper contained in the sintered body 4 "obtained in the sintering step P3. (Strictly speaking, it is the same as the mass ratio of copper when the sintered body 4 "does not contain Sn or C). That is, in the present embodiment, the raw material powder 10 does not contain a single copper powder or iron powder. A single copper powder or iron powder may be blended with the raw material powder, but if a single copper powder is blended, it becomes difficult to improve the wear resistance of the bearing surface 4a. Therefore, for example, when the shaft 3 collides with the bearing surface 4a as the shaft 3 rotates, indentations (dents) are likely to be formed on the bearing surface 4a. Further, when a single iron powder is blended, it becomes difficult to obtain a sintered body (sintered bearing) having a desired annular strength. Therefore, it is preferable that the raw material powder does not contain a single copper powder or iron powder.

[Low melting point metal powder]
As the low melting point metal powder, a metal powder having a melting point of 700 ° C. or lower, for example, a powder of tin, zinc, phosphorus or the like is used. In the present embodiment, among these, tin powder 14 (see FIG. 6), which easily diffuses into copper and iron (good compatibility) and can be used as a single powder, particularly atomized tin powder is used. As the tin powder (atomized tin powder) 14, those having an average particle size of 5 to 63 μm are preferably used, and those having an average particle size of 20 to 45 μm are more preferably used. The tin powder 14 is blended in an amount of 0.5 to 3.0% by mass with respect to the raw material powder 10.

[Solid lubricant]
As the solid lubricant, one or more powders such as graphite and molybdenum disulfide can be used. In this embodiment, graphite powder, particularly scaly graphite powder, is used in consideration of cost. The graphite powder is blended in an amount of 0.3 to 1.5% by mass with respect to the raw material powder 10.

(B) Compression molding step P2
In this compression molding step P2, the raw material powder 10 is compression-molded using the molding die 20 as shown in FIGS. 5A and 5B to form a shape similar to that of the sintered bearing 4 shown in FIG. 1 and the like. A ring-shaped green compact 4'forming (substantially finished product shape) is obtained. The molding die 20 has a core 21, upper and lower punches 22, 23 and a die 24 arranged coaxially as a main configuration. The molding die 20 is set in, for example, a die set of a cam-type molding press.

In the molding die 20 having the above configuration, the raw material powder 10 is filled in the cavity 25 defined by the core 21, the lower punch 23, and the die 24, and then the upper punch 22 is relatively close to the lower punch 23. The raw material powder 10 is moved and compression-molded with an appropriate pressing force (set according to the shape and size of the green compact to be molded). As a result, a green compact 4'having a shape similar to that of the sintered bearing 4 can be obtained. Then, the upper punch 22 is moved upward and the lower punch 23 is moved upward to discharge the green compact 4'out of the cavity 25. As schematically shown in FIG. 6, in the green compact 4', the partial diffusion alloy powder 11, the tin powder 14, and the graphite powder (not shown) are uniformly dispersed. In the present embodiment, since the reduced iron powder is used as the iron powder 12 constituting the partial diffusion alloy powder 11, the powder is softer than the partial diffusion alloy powder using the atomized iron powder and is excellent in compression moldability. Therefore, the strength of the green compact 4'can be increased even at a low density, and it is possible to prevent the green compact 4'from being chipped or cracked.

(C) Sintering step P3
In the sintering step P3, a sintered body is obtained by subjecting the green compact 4'to a sintering treatment. The sintering conditions in this embodiment are conditions in which carbon contained in the graphite powder does not react with iron (carbon diffusion does not occur). In the iron-carbon equilibrium state, there is a transformation point at 723 ° C, and if it exceeds this, the reaction between iron and carbon is started and a pearlite phase (γFe) is formed in the iron structure, but in sintering it exceeds 900 ° C. After that, the reaction between carbon (graphite) and iron begins, and a pearlite phase is formed. Since the pearlite phase has a high hardness of HV300 or higher, if it exists in the iron structure of the sintered bearing 4, the wear resistance of the bearing surface 4a is enhanced and the wear of the bearing surface 4a under high surface pressure is suppressed. Therefore, the bearing life can be improved.

Therefore, in the present embodiment, the condition that the pearlite phase is contained in the iron structure after sintering (iron structure of the sintered body), more specifically, the iron structure after sintering is relatively soft ferrite. The green compact 4'is sintered under the condition that it is composed of a phase (HV200 or less) and a relatively hard pearlite phase two-phase structure. However, since the high-hardness pearlite phase has a strong aggression against the mating material, if the pearlite phase is excessively present in the iron structure of the sintered bearing 4, the shaft 3 may be worn. In order to prevent this, as shown in FIG. 7, the pearlite phase γFe is suppressed to the extent that it is present (spotted) at the grain boundaries of the ferrite phase αFe. The "grain boundary" here means both the grain boundary formed between the powder particles and the crystal grain boundary formed in the powder particles. Quantitatively, the abundance ratios of the ferrite phase αFe and the pearlite phase γFe in the iron structure are 80 to 95% and 5 to 20%, respectively, in terms of the area ratio of the sintered body in an arbitrary cross section (αFe: γFe = 80 to 95). %: 5 to 20%) is desirable. As a result, it is possible to obtain a sintered bearing 4 in which wear suppression of the shaft 3 and improvement of wear resistance of the bearing surface 4a are achieved at the same time.

The amount of pearlite phase γFe deposited depends mainly on the sintering temperature and the atmospheric gas. Therefore, in order to obtain an iron structure having a two-phase structure of a pearlite phase γFe and a ferrite phase αFe and having a pearlite phase γFe present at the grain boundary of the ferrite phase αFe, the heating temperature of the green compact 4'(baking). (Consolidation temperature) is set to 820 ° C or higher and 900 ° C or lower. The sintering atmosphere is an endothermic gas (RX gas) obtained by mixing air with liquefied petroleum gas such as butane or propane and thermally decomposing it with a Ni catalyst, or a gas atmosphere containing carbon such as natural gas. As a result, carbon contained in the gas diffuses into iron during sintering, so that the above-mentioned pearlite phase γFe can be formed. As described above, when the green compact 4'is heated and sintered at a temperature exceeding 900 ° C., carbon contained in the graphite powder reacts with iron, so that the pearlite phase γFe is excessive in the iron structure of the sintered body. Will be formed in. Therefore, it is important to set the sintering temperature of the green compact 4'to 900 ° C. or lower. When various molding lubricants such as a fluid lubricant are contained in the raw material powder 10, the molding lubricant volatilizes with sintering.

The sintered body 4 "obtained by heating and sintering the green compact 4'under the above conditions has Cu in an amount of 10 to 30% by mass (preferably 22 to 26% by mass) and Sn in an amount of 0.5 to 30%. It contains 3.0% by mass (preferably 1.0 to 3.0% by mass), C 0.3 to 1.5% by mass (preferably 0.5 to 1.0% by mass), and the balance is iron and It is composed of unavoidable impurities. As described above, since most of the metal structure of the sintered body 4 "is composed of iron (iron structure), the sintered body 4" has excellent mechanical strength. On the other hand, since the sintered body 4 "contains a certain amount of copper in the metal structure, it is possible to obtain a bearing surface 4a having excellent initial compatibility with the shaft 3. In particular, the green compact 4'. Under the above-mentioned sintering conditions in which the sintering temperature is set lower than the melting point of copper (1083 ° C.), the copper powder 13 contained in the green compact 4'does not melt with the sintering, and therefore is baked. Copper does not diffuse into the iron (iron structure) due to the formation. Therefore, an appropriate amount of copper structure containing a bronze phase is formed on the surface (bearing surface 4a) of the sintered body 4 ". In addition, free graphite is also exposed on the surface of the sintered body 4 ". Therefore, a bearing surface 4a having good initial compatibility with the shaft 3 and a small friction coefficient can be obtained. If the blending amount of Sn is increased, the bearing surface 4a can be obtained. A sintered body 4 ”(sintered bearing 4) having high mechanical strength can be obtained, but if the amount of Sn is excessive, coarse air holes increase and the wear resistance of the bearing surface 4a is lowered. The blending ratio (a blending ratio of about 10% with respect to the blending ratio of Cu) is used.

An iron structure containing iron as a main component and a copper structure composed of copper are formed in the sintered body 4 ”. In the present embodiment, iron powder alone or copper powder alone is not added to the raw material powder, and is added. Even if it is, since it is a very small amount, all the iron structure and the copper structure of the sintered body 4 "are formed mainly of the partial diffusion alloy powder 11. In the partially diffused alloy powder, since a part of the copper powder is diffused in the iron powder, a high neck strength can be obtained between the iron structure and the copper structure after sintering. Further, when the green compact 4'is sintered, the tin powder 14 in the green compact 4'melts and wets the surface of the copper powder 13 constituting the partial diffusion alloy powder 11. Along with this, liquid phase sintering progresses, and as shown in FIG. 7, the iron structure and the copper structure of the adjacent partial diffusion alloy powders 11 or the bronze phase (Cu—Sn) 16 that bonds the copper structures to each other is formed. Will be done. Further, among the individual partial diffusion alloy powders 11, the molten Sn is diffused to the portion where a part of the copper powder 13 is diffused on the surface of the iron powder 12 to form the Fe—Cu alloy, and the Fe—Cu is diffused. Since the −Sn alloy (alloy phase) 17 is formed, the neck strength between the iron structure and the copper structure in the sintered body 4 ”is further increased. Therefore, expensive metal powders such as Ni and Mo are not used. Further, even by low-temperature sintering as described above, a sintered body 4 "having a high mechanical strength (annular strength), specifically, an annular strength of 300 MPa or more, and thus a sintered bearing 4 can be obtained. Further, the bearing surface 4a can be hardened to improve the wear resistance of the bearing surface 4a. In FIG. 7, the ferrite phase αFe, the pearlite phase γFe, and the like are represented by shades of color. Specifically, the colors are darkened in the order of ferrite phase αFe → bronze phase 16 → Fe—Cu—Sn alloy 17 → pearlite phase γFe.

Further, since the powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less) is used as the partial diffusion alloy powder 11, the porous structure of the sintered body 4 ”is made uniform and the formation of coarse air pores is prevented. Therefore, it is possible to increase the density of the sintered body 4 "and further enhance the wear resistance and the annular strength of the bearing surface 4a.

Coarse air pores are particularly likely to occur in the surface layer portion of the sintered body 4 "(the region from the surface of the sintered body to the depth of 100 μm), but the sintered body 4" obtained as described above is described above. As described above, it is possible to prevent the generation of coarse air pores in the surface layer portion and increase the density of the surface layer portion. Specifically, the porosity of the surface layer portion can be set to 5 to 20%. This porosity can be obtained, for example, by image analysis of the area ratio of the pores in an arbitrary cross section of the sintered body 4 ".

By increasing the density of the surface layer portion in this way, a bearing surface 4a having a relatively small surface opening rate, specifically, a bearing surface 4a having a surface opening rate of 5% or more and 20% or less is obtained. be able to. In particular, when the surface opening rate of the bearing surface 4a is less than 5%, it becomes difficult to exude a necessary and sufficient amount of lubricating oil into the bearing gap (the oil film forming ability becomes insufficient), and the sintered bearing 4 is used. I can't get the benefits of.

Further, since the raw material powder for obtaining the sintered body 4 "is mainly made of the partial diffusion alloy powder 11 in which the copper powder 13 is partially diffused on the surface of the iron powder 12, the existing iron-copper-based sintered bearing It is possible to prevent the segregation of copper, which is a problem in the above.

As described above, the sintering conditions of the green compact 4'are set so that the iron structure after sintering is composed of a two-phase structure of a ferrite phase αFe and a pearlite phase γFe, and after sintering. It is also possible to set so that the iron structure is all ferrite phase αFe. Specifically, the heating temperature of the green compact 4'is set to 800 ° C. (preferably 820 ° C.) or more and 880 ° C. or lower, and the sintering atmosphere is a carbon-free gas atmosphere (hydrogen gas, nitrogen gas, etc.). Argon gas, etc.) or vacuum. Under such sintering conditions, the reaction between carbon and iron does not occur in the raw material powder, and the carbon contained in the gas does not diffuse into iron. Therefore, the iron structure after sintering can be entirely composed of a soft ferrite phase.

(D) Sizing step P4
The sintered body 4 "obtained as described above is sized in the sizing step P4. As a result, the sintered body 4" is finished into a finished shape and dimensions. It is sufficient to apply sizing as needed, and it is not always necessary. That is, the sizing step P4 may be omitted as long as each part of the sintered body 4 "obtained in the sintering step P3 is finished in a desired shape, dimensions, and the like.

(E) Oil-impregnating step P5
The above-mentioned lubricating oil (or liquid grease) is impregnated into the internal pores of the sintered body 4 ”in which each part is finished to the finished shape and dimensions by a method such as vacuum impregnation in the oil impregnation step P5. The sintered bearing 4 shown in FIG. 1 is completed. Depending on the application, this oil impregnation step P5 may be omitted, and the sintered bearing may be used without lubrication.

As described above, the sintered bearing 4 (sintered body 4 ") obtained through the manufacturing process of the present embodiment has an annulus strength of 300 MPa or more, and the value of the annulus strength is the existing iron copper. The value is more than twice that of the system-based sintered bearing. Further, the density of the sintered bearing 4 of the present embodiment is 6.8 ± 0.3 g / cm ³ , which is the value of the existing iron-copper-based sintered bearing. The density is higher than the density (about 6.6 g / cm ³ ). Even with existing iron-copper-based sintered bearings, it is possible to increase the density by high compression in the powder molding process. If this is done, the internal fluid lubricant cannot be burned during sintering and is gasified, so that the pores on the surface layer become coarse. In the production method according to the present invention, it is necessary to perform high compression during compression molding of the green compact. It is possible to prevent such a problem.

While increasing the density of the sintered body 4 "in this way, the oil content can be increased to 15 vol% or more, and the same level of oil content as the existing iron-copper-based sintered bearing can be secured. It is derived from the fact that reduced iron powder, which has a spongy shape and is excellent in oil retention, is used as the iron powder 12 constituting the partially diffused alloy powder 11. In this case, the lubricant impregnated in the sintered body 4 ”is used. The oil is retained not only in the pores formed between the particles of the sintered structure but also in the pores of the reduced iron powder.

As described above, since the sintered bearing 4 obtained by the manufacturing method according to the present invention is made of a sintered body 4 "having a high annular strength (an annular strength of 300 MPa or more), it is press-fitted into the inner circumference of the housing 2. Even when fixed, the bearing surface 4a does not deform following the shape of the inner peripheral surface of the housing 2, and the roundness, cylindricity, etc. of the bearing surface 4a can be stably maintained even after mounting. After the sintered bearing 4 is press-fitted and fixed to the inner circumference of the housing 2, the desired roundness (for example, sizing) for finishing the bearing surface 4a to an appropriate shape and accuracy is not additionally executed. (Roundness of 3 μm or less) can be obtained. In addition, since the bearing surface 4a has high wear resistance, the shaft 3 swings around the entire surface of the bearing surface 4a, or the shaft 3 frequently moves to the bearing surface 4a. Even if the bearing surface 4a collides with the bearing surface 4a, wear and damage to the bearing surface 4a can be suppressed. Therefore, according to the sintered bearing 4 obtained by the manufacturing method according to the present invention, a vibration motor having excellent reliability and durability can be produced at low cost. Can be provided to.

Here, for reference, a photomicrograph of the surface layer portion of the sintered bearing 4 obtained by the manufacturing method according to the present invention is shown in FIG. 8, and the sintered bearing according to the technical means described in Patent Document 1 (hereinafter, "" A micrograph of the surface layer portion of the "copper-coated iron powder bearing") is shown in FIG. Comparing FIGS. 8 and 9, it is easily understood that the sintered bearing 4 has a denser porous structure on the surface layer than the copper-coated iron powder bearing. In fact, the porosity of the surface layer portion of the sintered bearing 4 was 13.6%, whereas the porosity of the surface layer portion of the copper-coated iron powder bearing was about 25.5%. One of the factors that caused such a difference is that in the copper-coated iron powder, the copper film is only in close contact with the iron powder, and the neck strength between the iron structure and the copper structure is insufficient.

The embodiments of the present invention are not limited to those described above, and appropriate modifications can be made without departing from the gist of the present invention.

For example, the case where all the iron structure and the copper structure of the sintered bearing 4 are formed only by the partial diffusion alloy powder has been described, but one or both of the single iron powder and the single copper powder are added to the raw material powder, and the powder is added. A part of the iron structure or the copper structure can also be formed of a single iron powder or a single copper powder. In this case, in order to secure the minimum wear resistance, strength, and sliding characteristics, the ratio of the partial diffusion alloy powder in the raw material powder is preferably 50% by mass or more. Further, in this case, the appropriate amount of the solid lubricant powder in the raw material powder is 0.3 to 1.5% by mass. Further, the blending ratio of the low melting point metal powder in the raw material powder is 0.5 to 5.0% by mass. This blending ratio is preferably set to about 10% by mass of the total amount of copper powder in the raw material powder (the sum of the copper powder in the partial diffusion alloy powder and the single copper powder added separately). The balance of the raw material powder will be formed by elemental iron powder or elemental copper powder (or both elemental powders), and unavoidable impurities.

In such a configuration, by changing the blending amount of the elemental iron powder or the elemental copper powder, the bearing can maintain the wear resistance, high strength, and good sliding characteristics obtained by using the partial diffusion alloy powder. It is possible to adjust the characteristics. For example, if elemental iron powder is added, the wear resistance and strength of the bearing can be improved while reducing the cost by reducing the amount of partial diffusion alloy powder used, and if elemental copper powder is added, the sliding characteristics are further improved. can do. Therefore, it is possible to reduce the development cost of sintered bearings suitable for various applications, and it is possible to support high-mix low-volume production of sintered bearings.

For example, in the compression molding step P2 for compression molding the green compact 4', a so-called warm molding method in which the green compact 4'is compression molded while at least one of the molding die 20 and the raw material powder 10 is heated is used. A mold lubrication molding method may be adopted in which the green compact 4'is compression-molded with the lubricant applied to the molding surface (definition surface of the cavity 25) of the molding die 20. If such a method is adopted, the green compact 4'can be molded with higher accuracy.

Further, the vibration motor 1 described above is a shaft rotation type in which the shaft 3 is on the rotating side and the sintered bearing 4 is on the stationary side. However, as the vibration motor 1, the shaft 3 is on the stationary side and the sintered bearing 4 is on the stationary side. There is also a shaft-fixed type with the rotation side, and even with such a shaft-fixed type vibration motor 1, the sintered bearing 4 obtained by the manufacturing method according to the present invention can be preferably used. Further, the bearing surface 4a of the sintered bearing 4 may be provided with a dynamic pressure generating portion such as a dynamic pressure groove. By doing so, the rigidity of the oil film formed in the bearing gap can be increased, so that the rotation accuracy can be further improved. Further, since the sintered bearing 4 obtained by the manufacturing method according to the present invention has high mechanical strength and excellent wear resistance of the bearing surface 4a, it is not limited to a vibration motor, and an unbalanced load is applied at high speed. It can be widely used as a bearing that supports the shaft rotatably by incorporating it into various motors, including applications for supporting the spindle of large motors.

1 Vibration motor 2 Housing 3 Shaft 4 Sintered bearing 4'Compact powder 4 "Sintered body 4a Bearing surface 10 Raw material powder 11 Partial diffusion alloy powder 12 Iron powder 13 Copper powder 14 Tin powder (low melting point metal powder)
16 Bronze phase 17 Fe-Cu-Sn alloy 20 Molding mold αFe ferrite phase γFe pearlite phase M Motor unit P1 Raw material powder production process P2 Compression molding process P3 Sintering process W weight

Claims (11)

It has a bearing surface on the inner circumference that forms a bearing gap with the shaft to be supported, and is composed of a sintered body containing iron as the main component and then a large amount of copper, and the sintered body has a lower melting point. A method for manufacturing a sintered bearing, which contains tin as an element and uses the balance as a solid lubricant and unavoidable impurities.
A partial diffusion alloy having a copper content of 10 to 30% by mass, which is formed by partially diffusing a plurality of copper powders having a particle size smaller than that of the iron powder and having an average particle size of 5 μm or more and 20 μm or less on the surface of the iron powder. A compression molding step in which powder is used as the main raw material, and the raw material powder obtained by blending the low melting point element powder and the solid lubricant powder is compression-molded to obtain a green compact.
It includes a sintering step of sintering a green compact at a temperature of 820 ° C. or higher and 900 ° C. or lower, which is lower than the melting point of copper, to obtain a sintered body.
A method for manufacturing a sintered bearing, which comprises using only the copper powder of the partial diffusion alloy powder as a copper source. The method for manufacturing a sintered bearing according to claim 1, wherein the green compact is sintered in a gas atmosphere containing carbon. It has a bearing surface on the inner circumference that forms a bearing gap with the shaft to be supported, and is composed of a sintered body containing iron as the main component and then a large amount of copper, and the sintered body has a lower melting point. A method for manufacturing a sintered bearing, which contains tin as an element and uses the balance as a solid lubricant and unavoidable impurities.
A partial diffusion alloy having a copper content of 10 to 30% by mass, which is formed by partially diffusing a plurality of copper powders having a particle size smaller than that of the iron powder and having an average particle size of 5 μm or more and 20 μm or less on the surface of the iron powder. A compression molding step in which powder is used as the main raw material, and the raw material powder obtained by blending the low melting point element powder and the solid lubricant powder is compression-molded to obtain a green compact.
It includes a sintering step of sintering a green compact at a temperature lower than the melting point of copper in a gas atmosphere containing carbon to obtain a sintered body.
Only the copper powder of the partial diffusion alloy powder was used as the copper source.
A method for manufacturing a sintered bearing, which is characterized in that. It has a bearing surface on the inner circumference that forms a bearing gap with the shaft to be supported, and is composed of a sintered body containing iron as the main component and then a large amount of copper, and the sintered body has a lower melting point. A method for manufacturing a sintered bearing, which contains tin as an element and uses the balance as a solid lubricant and unavoidable impurities.
A partial diffusion alloy having a copper content of 10 to 30% by mass, which is formed by partially diffusing a plurality of copper powders having a particle size smaller than that of the iron powder and having an average particle size of 5 μm or more and 20 μm or less on the surface of the iron powder. Powder is the main raw material, and the low melting point element powder, solid lubricant powder, and single copper powder are mixed, and the raw material powder having the partial diffusion alloy powder ratio of 50% by mass or more is compression-molded. And the compression molding process to obtain the green compact
It includes a sintering step of sintering a green compact at a temperature of 820 ° C. or higher and 900 ° C. or lower, which is lower than the melting point of copper, to obtain a sintered body.
A method for manufacturing a sintered bearing, which comprises using only the copper powder of the partial diffusion alloy powder and the single copper powder as the copper source. The method for manufacturing a sintered bearing according to claim 4 , wherein the green compact is sintered in a gas atmosphere containing carbon. It has a bearing surface on the inner circumference that forms a bearing gap with the shaft to be supported, and is composed of a sintered body containing iron as the main component and then a large amount of copper, and the sintered body has a lower melting point. A method for manufacturing a sintered bearing, which contains tin as an element and uses the balance as a solid lubricant and unavoidable impurities.
A partial diffusion alloy having a copper content of 10 to 30% by mass, which is formed by partially diffusing a plurality of copper powders having a particle size smaller than that of the iron powder and having an average particle size of 5 μm or more and 20 μm or less on the surface of the iron powder. A raw material powder containing the powder as a main raw material, the powder of the element having a low melting point, the solid lubricant powder, and the single copper powder is mixed, and the ratio of the partial diffusion alloy powder is 50% by mass or more is compression molded. And the compression molding process to obtain the green compact
It includes a sintering step of sintering a green compact at a temperature lower than the melting point of copper in a gas atmosphere containing carbon to obtain a sintered body.
As the copper source, only the copper powder of the partial diffusion alloy powder and the simple substance copper powder were used.
A method for manufacturing a sintered bearing, which is characterized in that. The method for manufacturing a sintered bearing according to any one of claims 4 to 6, wherein the raw material powder is further mixed with elemental iron powder. The method for manufacturing a sintered bearing according to any one of claims 1 to 7 , wherein a partially diffused alloy powder having an average particle diameter of 106 μm or less is used. Claim 1 to use a raw material powder containing 0.5 to 3.0% by mass of tin powder as a low melting point metal powder and 0.3 to 1.5% by mass of graphite powder as a solid lubricant powder. The method for manufacturing a sintered bearing according to any one of 8 to 8. The method for manufacturing a sintered bearing according to any one of claims 1 to 9 , wherein reduced iron powder is used as the iron powder of the partial diffusion alloy powder. The method for manufacturing a sintered bearing according to any one of claims 1 to 10 , further comprising an oil-impregnating step of impregnating a sintered body with a lubricating oil having a kinematic viscosity of 10 to 50 mm ^{2 / s at 40 ° C.}

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