JP2013079438A - Sintered bearing and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sintered bearing capable of reducing the amount of copper used and lowering production cost, while exhibiting excellent initial running-in characteristics and quietness as well as high durability.SOLUTION: A sintered bearing 1 contains an iron structure and copper structure both being bonded to each other through a low-melting-point metal. A portion or all of the copper structure is formed with flat copper powder, and ferrite phase αFe is used as the iron structure. The bearing 1 is provided with: a base part S2 where the copper content is made uniform; and a surface layer S1 that covers a surface of the base part S2 and whose copper content is larger than that of the base part S2.

Description

  The present invention relates to a sintered bearing made of a sintered metal and a method for manufacturing the same.

  For example, as a bearing for a precision small motor mounted on an information device such as a hard disk drive, a sintered bearing excellent in quietness may be used. With the recent high performance of motors, this type of sintered bearing is required to improve the limit PV value to PV> 200 MPa · m / min. Further, it is also necessary to reduce torque fluctuations (improvement of initial conformability), improve durability (improve seizure resistance), improve quietness (improve acoustic characteristics), and the like.

  Iron-based sintered bearings are known as sintered bearings, but iron-based ones have the disadvantage that they are inferior in initial conformability and quietness, although they are excellent in durability. Therefore, bronze sintered bearings are often used as bearings for precision small motors. As an example of a bronze-based sintered oil-impregnated bearing, for example, JP 2001-107162 A (Patent Document 1) contains 6 to 11% by weight of Sn, 1 to 5% by weight of Fe and / or Ni, and the balance is copper. Is disclosed (claim 1).

  Patent No. 3873275 (Patent Document 2) uses iron-based and copper-based raw material powder, the copper-based raw material powder is a flat powder, segregates copper on the surface side, and moves from the surface side toward the inside. A sliding component in which the ratio of copper is reduced and the ratio of iron is increased is disclosed (claim 1). Also, by filling the filling part with copper-based raw material powder and iron-based raw material powder and applying vibration, the copper-based flat powder is segregated to the surface side, the surface side is covered with copper, and from the surface side to the inside Thus, a bearing having a concentration gradient in which the ratio of iron is higher than copper is obtained (paragraph 0028).

JP 2001-107162 A Japanese Patent No. 3873275

  In recent years, the price of copper has soared, and bronze sintered bearings containing a large amount of copper as described in Patent Document 1 cannot meet the demand for cost reduction. Also, bronze-based sintered bearings have difficulty in load resistance and durability.

  On the other hand, in the configuration described in Patent Document 2, since the raw material powder made of flat powder and copper powder is vibrated, the molding process becomes complicated. In addition, “Even if the sliding surface on which the rotating body slides wears, copper is contained at a predetermined rate under the sliding surface, so that the durability of the sliding portion is excellent.” As is clear from the description (paragraph 0029 and the like), the wear of the mating member after the copper-rich surface layer is worn is suppressed by copper. In this configuration, if the durability is to be improved, the amount of copper used must be increased, and it is difficult to achieve both durability and cost reduction.

  Accordingly, the present invention provides a sintered bearing that can reduce the amount of copper used and reduce the cost, while having good initial conformability and quietness and high durability. Purpose.

  In order to achieve the above object, a sintered bearing according to the present invention is a sintered bearing containing an iron structure and a copper structure, wherein the copper structure and the iron structure are combined with a low melting point metal, and a part of the copper structure or The whole is formed with flat copper powder, and the iron structure is mainly composed of ferrite phase, covering the base part with uniform copper content and the surface of the base part, the copper content more than the base part And an enlarged surface layer.

  The flat copper powder has the property of adhering to the mold forming surface when the raw material powder is molded. For this reason, the green compact after molding contains a large amount of copper in the surface layer, whereas the core portion has a small copper content. Therefore, a surface layer with a high copper content and a base portion with a lower copper content are formed in the sintered body after sintering.

  Thus, by increasing the content of copper in the surface layer, it is possible to improve initial conformability and quietness. In addition, since the aggression against the shaft is reduced, the durability life is improved. These functions and effects can be obtained more conspicuously by forming a copper structure (structure containing copper as a main component) having a surface ratio of 60% or more on the surface of the surface layer. In addition, even when the base part containing a large amount of iron structure (structure containing iron as a main component) is exposed due to wear of the surface layer, the iron structure is mainly composed of a ferrite phase. The aggression against can be weakened and the durability is increased.

  Moreover, although the iron structure of the base portion is mainly composed of a soft ferrite phase, the base portion has high strength because the iron structure-copper structure and the copper structures are firmly bonded with a low melting point metal. Accordingly, the strength of the entire bearing is increased and the load resistance can be improved. The base portion occupies most of the volume of the bearing. However, since the copper content in the base portion can be reduced, the amount of copper used in the entire bearing can be reduced and the cost can be reduced.

  As described above, the present invention optimizes the distribution of iron and copper in the bearing, and at the same time, considers not only the copper structure but also the form of the iron structure, thereby improving both durability and cost reduction. It is a thing. With this configuration, according to the present invention, a sintered bearing having the advantages of both an iron-based sintered bearing and a copper-based sintered bearing (including an iron-copper-based sintered bearing) can be obtained at low cost.

  In this sintered bearing, if iron is sintered without reacting with carbon, the iron structure can be formed only of the ferrite phase. When the iron structure is formed of the ferrite phase as described above, the wear resistance of the bearing surface is lowered when the surface layer is worn and the base portion is exposed. When this becomes a problem, the iron structure can be formed by the ferrite phase and the pearlite phase present at the grain boundary of the ferrite phase by reacting iron with carbon during sintering. With such a configuration, since the hard pearlite phase supplements the wear resistance of the ferrite phase, wear of the bearing surface can be suppressed. On the other hand, when carbon diffuses and the pearlite is present in excess, the aggression against the shaft increases and the shaft tends to wear. From this point of view, the pearlite phase is present at the grain boundaries of the ferrite phase (see FIG. 12).

  Generally, as the content of the low melting point metal increases, the strength of the bearing increases accordingly. On the other hand, in the liquid phase state of Cu-Sn, the flat copper powder is rounded and spherical due to surface tension. When the spheroidized flat copper increases, the area occupied by the copper structure on the bearing surface decreases, and the object of the invention (improvement of initial conformability / quietness, reduction of attack on the counterpart material) cannot be achieved. From the above viewpoint, the ratio of the low melting point metal to copper is less than 10% by weight.

  By including a solid lubricant in the metal structure, the friction of the bearing surface can be reduced. The same effect can be obtained by including free graphite in the metal structure.

  If the content of free graphite is made larger in the surface layer than in the base portion, further reduction in friction can be achieved.

  The sintered bearing according to the present invention is prepared by mixing raw material powder containing iron powder, flat copper powder, and low melting point metal powder, filling the mold, and adhering the flat copper powder to the mold surface. The green compact can be compressed to form a green compact, and the green compact can be sintered.

  Adhering the fluid lubricant to the flat copper powder before mixing further increases the adhesion of the flat copper powder to the molding surface. If the ratio of the fluid lubricant to the flat copper powder is too small, the adhesion of the flat copper powder to the mold will be reduced, and the amount of flat copper powder on the mold forming surface will be insufficient. Moreover, when there is too much, flat same powder will adhere and the problem which aggregates will be produced. According to the verification by the present inventors, 0.1 wt% to 0.8 wt%, preferably 0.2 wt% to 0.7 wt% of a fluid lubricant is blended in a weight ratio to the flat copper powder. It was found that the above problems can be solved.

As the fluid lubricant, fatty acids, particularly linear saturated fatty acids are preferred. This type of fatty acid is represented by the general formula C _n-1 H _2n-1 COOH. In the present invention, it is desirable to use one having a Cn in the range of 12-22.

If the apparent density of the flat copper powder is 1.0 g / cm ³ or less, the thickness is 1.5 μm or less, and the length is 20 μm or more and 80 μm or less, the adhesion to the mold surface is further increased, and the copper content A large number of surface layers can be reliably formed.

  By adding graphite to the raw material powder, it is possible to reduce the friction of the bearing surface. In this case, if the scaly graphite is used, the scaly graphite and the flat copper powder are easily attached when the raw material powder is mixed, and a lot of graphite is attached to the molding surface along with the flat copper powder. In this case, the content of graphite as well as copper increases on the surface of the green compact, which is more effective in reducing the friction of the bearing surface.

  According to the present invention, it is possible to achieve both improvement in durability and cost reduction by reducing the amount of copper used. On the other hand, it is possible to provide a sintered bearing with good initial conformability and quietness.

It is sectional drawing of the sintered bearing concerning this invention. The upper part is a side view of the flat copper powder, and the lower part is a plan view of the flat copper powder. It is a side view which shows the flat copper powder and scaly graphite which mutually adhered. It is sectional drawing which shows the formation process of the green compact by a metal mold | die. FIG. 5 is an enlarged sectional view of a region Q in FIG. 4. It is an organization chart showing the pearlite structure in steel. It is an expanded sectional view of the area | region P in FIG. It is a figure which shows the content rate of the copper in the radial direction of a bearing. It is a figure which shows the measurement result of initial conformability. It is a figure which shows the measurement result of a limit PV value. It is a figure which shows the measurement result of the abrasion loss which arises in a bearing after bearing operation. It is an organization chart showing the grain boundary organization of a base part. It is a component table | surface of the sintered bearing concerning this invention.

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

  As shown in FIG. 1, the sintered bearing 1 is formed in a cylindrical shape having a bearing surface 1a on the inner periphery. When the shaft 2 made of stainless steel or the like is inserted into the inner periphery of the sintered bearing 1 and the shaft is rotated in this state, or the bearing 1 is rotated, the lubricating oil retained in the countless holes of the sintered bearing 1 Oozes out to the bearing surface 1a as the temperature rises. The oil that has oozed out forms an oil film in the bearing gap between the outer peripheral surface of the shaft and the bearing surface 1 a, and the shaft 2 is supported by the bearing 1 so as to be relatively rotatable.

  The bearing 1 of the present invention is formed by filling raw material powder mixed with various powders in a mold, compressing this to form a green compact, and then sintering the green compact.

  The raw material powder is a mixed powder mainly composed of iron powder, copper powder, low melting point metal powder, and solid lubricant powder. To this mixed powder, various molding aids, for example, a lubricant (metal soap or the like) for improving releasability are added as necessary. Hereinafter, the raw material powder and the manufacturing procedure will be described in detail for the first embodiment of the sintered bearing.

[Iron powder]
As the iron powder, known powders such as reduced iron powder and water atomized iron powder can be widely used. In this embodiment, reduced iron powder excellent in oil impregnation is used. The reduced iron powder is also called spongy iron powder because it has a substantially spherical shape, an irregular shape and a porous shape, and a spongy shape having minute irregularities on the surface. As the iron powder, one having a particle size of 40 μm to 150 μm and an apparent density of about 2.0 to 2.8 g / cm ³ is used. The definition of the apparent density conforms to the rules of JIS Z 8901 (hereinafter the same). The amount of oxygen contained in the iron powder is 0.2% by weight or less.

[Copper powder]
As the copper powder, two types of foil-like flat copper powder and normal copper powder are used.

The flat copper powder is flattened by stamping raw material copper powder made of water atomized powder or the like. As the flat copper powder, one having a length L of 20 μm to 80 μm and a thickness t of 0.5 μm to 1.5 μm (aspect ratio L / t = 13.3 to 160) is mainly used. Here, “length” and “thickness” refer to the geometric maximum dimension of each flat copper powder 3 as shown in FIG. The apparent density of the flat copper powder is 1.0 g / cm ³ or less. If the flat copper powder has the above size and apparent density, the adhesion of the flat copper powder to the mold forming surface is increased, so that a large amount of flat copper powder can be attached to the mold forming surface.

Usually, as the copper powder, spherical and dendritic copper powders widely used for sintered bearings can be widely used. For example, reduced powder, electrolytic powder, water atomized powder and the like are used. These mixed powders can also be used. Usually, the particle size of copper powder is about 20 μm to 100 μm, and the apparent density is about 2.0 to 3.3 g / cm ³ . If only flat copper powder is used as the copper powder, the density of the flat copper powder will be small, so it will be hard to solidify when forming the green compact, but it is usually used together with the copper powder to form the green compact. Can increase the sex. In addition, if there is no particular problem, it is also possible to use only flat copper powder without using copper powder.

[Fluid lubricant]
In order to attach the flat copper powder to the molding surface, a fluid lubricant is previously attached to the flat copper powder. This fluid lubricant only needs to be attached to the flat copper powder before filling the raw material powder into the mold, preferably before mixing the raw material powder, more preferably to the raw material copper powder at the stage of crushing the raw material copper powder. Let The fluid lubricant may be attached to the flat copper powder by means such as supplying the fluid lubricant to the flat copper powder and stirring it after mixing and before mixing with other raw material powders. In order to secure the adhesion amount of the flat copper powder on the molding surface, the blending ratio of the fluid lubricant to the flat copper powder should be 0.1% by weight or more, and aggregation due to the adhesion of the flat copper powders In order to prevent this, the blending ratio is 0.8% by weight or less. Desirably, the lower limit of the blending ratio is 0.2% by weight or more, and the upper limit is 0.7% by weight. As the fluid lubricant, fatty acids, particularly linear saturated fatty acids are preferred. This type of fatty acid is represented by the general formula C _n-1 H _2n-1 COOH. As this fatty acid, Cn is in the range of 12 to 22, and for example, stearic acid can be used as a specific example.

[Low melting point metal powder]
The low melting point metal powder is a metal powder having a melting point lower than the sintering temperature. In the present invention, 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. Of these, tin is preferred because it causes less transpiration during sintering. Since these low melting point metal powders have high wettability with respect to copper, liquid phase sintering proceeds by blending with the raw material powder, and the bond strength between the iron structure and the copper structure or between the copper structures is enhanced. The strength of the metal structure increases as the blending amount of the low melting point metal increases, but when the flat copper powder is used as in the present invention, if the amount of the low melting point metal is too large, the flat copper powder becomes spherical as described above, There is a problem that the copper area on the bearing surface is reduced. In conventional copper-based sintered bearings and copper-iron-based sintered bearings, it is common to blend a low melting point metal of about 10% by weight with respect to copper. The ratio of the melting point metal is less than 10% by weight (desirably 8.0% by weight or less).

[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 for example, graphite is used. At this time, as the graphite, it is desirable to use scaly graphite so that adhesion to the flat copper powder can be obtained. As solid lubricant powder, molybdenum disulfide powder can be used in addition to graphite. Molybdenum disulfide powder has a layered crystal structure and peels into layers, and thus adheres to flat copper powder in the same manner as scale graphite.

[Combination ratio]
The raw material powder blended with each of the above powders is copper powder of 18 wt% to 40 wt%, low melting point metal powder (for example, tin powder) of 1 wt% to 4 wt%, solid lubricant powder (for example, graphite powder) Is preferably blended in an amount of 0.5 to 2.5% by weight, with the balance being iron powder.

  In the present invention, as will be described later, the flat copper powder is adhered to the mold in layers when the raw powder is filled into the mold. If the blending ratio of flat copper in the raw material powder is less than 8% by weight, the amount of flat copper adhering to the mold becomes insufficient, and the effect of the present invention cannot be expected. Further, in the present embodiment, as described later, when the copper-rich surface layer portion S1 (described later) disappears due to wear, the surface of the base portion S2 serving as a bearing surface is configured by the ferrite phase αFe and the copper structure. Thus, the aggression with respect to the shaft is reduced, but in order to obtain such an effect, the base portion S2 needs to have a copper structure of at least 10% by weight or more. Therefore, the compounding ratio of the copper powder is 18% by weight or more, which is the total of both. On the other hand, if the proportion of copper powder exceeds 40% by weight, the amount of copper powder used becomes excessive, and the cost merit due to the use of flat copper powder becomes poor. From the above, the blending amount of the copper powder in the raw material powder is 18 wt% or more and 40 wt% or less. Moreover, the compounding quantity of the flat copper powder in raw material powder shall be 8 to 40 weight%, desirably 8 to 20 weight%. The reason why 20% by weight or less is preferable is that the amount of flat copper powder adhering to the mold saturates at about 20% by weight. Is a problem.

  If the ratio of the low melting point metal powder is less than 1% by weight, the strength of the bearing cannot be secured, and if it exceeds 4% by weight, the problem of spheroidizing the flat copper powder occurs as described above. On the other hand, if the ratio of the solid lubricant powder is less than 0.5% by weight, the friction reducing effect on the bearing surface cannot be obtained, and if it exceeds 2.5% by weight, the strength is reduced. From the above, the low melting point metal powder is blended in an amount of 1 to 4% by weight, and the solid lubricant powder is blended in an amount of 0.5 to 2.5% by weight. As described above, the blending ratio of the low melting point metal powder to the copper powder is preferably less than 10% by weight (desirably 8% by weight or less).

  FIG. 13 shows a particularly preferable ratio of the various raw material powders described above. As shown, the copper powder is usually 8% by weight to 12% by weight, the flat copper powder is 10% by weight to 15% by weight, the low melting point metal powder is 1.0% by weight to 2.0% by weight, solid It is particularly preferable that the lubricant powder be 0.6 wt% or more and 1.0 wt% or less.

[mixture]
It is desirable to mix the powders described above in two steps. First, as primary mixing, scaly graphite powder and flat copper powder to which a fluid lubricant is previously attached are mixed with a known mixer. Next, as secondary mixing, iron powder, normal copper powder, and low melting point metal powder are added to and mixed with the primary mixed powder, and graphite powder is also added and mixed as necessary. Flat copper powder has a low apparent density among various raw material powders, so it is difficult to disperse uniformly in the raw material powder, but it is premixed with flat copper powder and graphite powder that have the same apparent density in the primary mixing. In this case, as shown in FIG. 3, the flat copper powder 3 and the graphite powder 4 adhere to each other and overlap in layers due to the fluid lubricant or the like adhering to the flat copper powder, and the apparent density of the flat copper powder increases. Therefore, it becomes possible to uniformly disperse the flat copper powder in the raw material powder during the secondary mixing. If a lubricant is added separately during the primary mixing, the adhesion between the flat copper powder and the graphite powder is further promoted, so that the flat copper powder can be more uniformly dispersed during the secondary mixing. As the lubricant to be added, a powdery lubricant can be used in addition to the same or different fluid lubricant as the fluid lubricant. For example, the above-mentioned forming aid such as metal soap is generally powdery and has a certain degree of adhesion, which can be promoted by adhesion of flat copper powder and graphite powder.

  Since the adhesion state between the flat copper powder 3 and the scaly graphite powder 4 shown in FIG. 3 is maintained to some extent even after secondary mixing, when the raw material powder is filled in the mold, the flat copper powder is put on the mold surface. A lot of graphite powder will adhere.

[Molding]
The raw material powder after the secondary mixing is supplied to the mold 6 of the molding machine. As shown in FIG. 4, the mold 6 includes a core 6 a, a die 6 b, an upper punch 6 c, and a lower punch 6 d, and a raw material powder is filled into a cavity partitioned by these. When the upper and lower punches 6c and 6d are brought close to each other and the raw material powder is compressed, the raw material powder is formed by the molding surface composed of the outer peripheral surface of the core 6a, the inner peripheral surface of the die 6b, the end surface of the upper punch 6c, and the end surface of the lower punch 6d. A cylindrical green compact 9 is obtained by molding.

  Among the metal powders in the raw material powder, the apparent density of the flat copper powder 3 is the smallest. Moreover, the flat copper powder 3 is a foil shape having the above-mentioned length L and thickness t, and the area of the wide surface per unit weight is large. Therefore, the flat copper powder is easily affected by the adhesive force due to the fluid lubricant adhering to the surface thereof, and further by the coulomb force. After filling the raw material powder into the mold 6, it is enlarged in FIG. 5. As described above, the flat copper powder 3 adheres to the entire area of the molding surface 61 in a layered state in which the wide surface is directed to the molding surface 61 and a plurality of layers (about 1 to 3 layers) overlap. At this time, scaly graphite adhering to the flat copper powder 3 also adheres to the flat copper powder 3 and adheres to the molding surface 61 of the mold (illustration of graphite is omitted in FIG. 5). On the other hand, iron powder (Fe), normal copper powder (Cu), and low-melting-point metal powder (Sn) are dispersed substantially uniformly in the inner region (region on the cavity center side) of the layered structure of flat copper 3. It becomes a state. The green compact 9 after molding retains such a distribution state of each powder almost as it is.

[Sintering]
Thereafter, the green compact 9 is sintered in a sintering furnace. The sintering conditions are such that carbon contained in the graphite 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 the reaction between iron and carbon exceeding this occurs, and a pearlite phase γFe is generated in the steel structure as shown in FIG. The reaction between carbon (graphite) and iron begins after the temperature exceeds, and a pearlite phase γFe is produced. Since the pearlite phase γFe is a hard structure (HV300 or higher) and has a strong attacking property on the counterpart material, excessive precipitation of the pearlite phase may cause wear of the shaft 2.

  In the conventional sintered bearing manufacturing process, an endothermic gas (RX gas) obtained by mixing liquefied petroleum gas (butane, propane, etc.) and air and thermally decomposing with a Ni catalyst is used as the sintering atmosphere. There are many. However, the endothermic gas (RX gas) may cause carbon to diffuse and harden the surface, resulting in the same problem.

  From the above viewpoint, in the present invention, sintering is performed at a low temperature of 900 ° C. or lower, specifically, 700 ° C. (preferably 760 ° C.) to 840 ° C. The sintering atmosphere is a gas atmosphere containing no carbon (hydrogen gas, nitrogen gas, argon gas, etc.) or a vacuum. By 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 ferrite phase αFe (HV200 or less). With the sintering, the fluid lubricant, other lubricants, and various molding aids are volatilized from the inside of the sintered body.

  By passing through the sintering step described above, a porous sintered body can be obtained. The sintered bearing 1 shown in the drawing is completed by sizing the sintered body and further impregnating with a lubricating oil by a technique such as vacuum impregnation. As described above, carbon and iron are not reacted at the time of sintering, and the iron structure is made into a soft ferrite phase, so that the sintered body is likely to cause plastic flow during sizing, and high-precision sizing can be performed. . In addition, depending on a use, the impregnation process of lubricating oil can be abbreviate | omitted and it can also be set as the sintered bearing 1 used under oil-free.

  FIG. 7 schematically shows the metal structure near the surface (region P in FIG. 1) of the sintered bearing 1 that has undergone the above manufacturing process. In FIG. 7, the copper structure is hatched, and the dotted pattern is added to the graphite.

  As shown in FIG. 7, in the sintered bearing 1 of the present invention, the green compact 9 is formed in a state in which the flat copper 3 is adhered in a layered manner on the mold forming surface 61, and the layered flat copper 3 is sintered. As a result, a surface layer S1 having a high copper concentration is formed on the entire surface including the bearing surface 1a of the bearing 1. In addition, the wide surface of the flat copper 3 may have adhered to the molding surface 61, so that most of the copper structure of the surface layer S1 is flat and oriented so that the wide surface faces the surface. The thickness of the surface layer S1 corresponds to the thickness of the flat copper adhering to the mold forming surface 61 in a layer form, and is about 1 μm to 6 μm. In the arbitrary cross section of the surface layer S1, the area of the copper structure is larger than the area of the iron structure, specifically, 60% or more of the copper structure is the copper structure.

  The base portion S2 inside the surface layer S1 is basically covered with the surface layer S1. As shown in FIG. 8, the copper content in the base portion S2 is less than the copper content in the surface layer S1, and the copper content rapidly decreases when the surface layer S1 moves to the base portion S2. doing. Further, the copper content (% by weight) in each part of the base part S2 is uniform in each part.

  From the above configuration, the area ratio of the copper structure to the iron structure is 60% or more over the entire surface of the surface layer S1 including the bearing surface 1a. Therefore, the initial conformability and quietness of the sintered bearing 1 can be improved. Further, since all the iron structure contained in the bearing 1 is the ferrite phase αFe, even if the surface layer S1 is worn and the iron structure of the base portion S2 appears on the surface, the bearing surface can be softened, Aggressiveness against the axis 2 can be weakened.

  On the other hand, the base portion S2 inside the surface layer S1 has a hard structure with a small copper content and a large iron content compared to the surface phase S1. As described above, since the iron content is increased in the base portion S2 that occupies most of the bearing 1, the amount of copper used in the entire bearing 1 can be reduced, and compared with a copper-based sintered bearing. Significant cost reduction can be achieved. Furthermore, when the surface layer S1 is worn by sliding with the shaft 2 and the base portion S2 containing a large amount of iron structure appears on the bearing surface 1a, the iron structure is the ferrite phase αFe. Even in a reduced state, the aggressiveness against the shaft 2 can be weakened, and the durability as a bearing can be ensured. This durability is sufficiently obtained if the content of the copper structure in the base portion S2 is at least 10% by weight or more.

  Thus, in this invention, while using flat copper powder and shape | molding a compact in the state which made this adhere to the metal mold | die molding surface 61, while increasing copper content in surface layer S1, surface Except for the layer S1, the iron content is increased to realize an optimal distribution of the copper structure and the iron structure. In addition, by intentionally setting the iron structure to the ferrite phase αFe, the wear of the shaft 2 is suppressed when the copper-rich surface layer S1 is worn. Therefore, it is possible to achieve both improvement in durability and cost reduction by reducing the amount of copper used.

  In addition, free graphite is deposited on the entire surface including the bearing surface 1a, and since the scaly graphite is attached to the mold forming surface 61 in a form accompanying the flat copper powder 3, the free graphite in the surface layer S1. The content of is also high. Therefore, the bearing surface 1a can be reduced in friction, and the durability of the bearing 1 can be increased. In addition, the copper structure and the iron structure are bonded with a low melting point metal in both the surface layer S1 and the base portion S2, and a high bonding strength is obtained between the copper structure and the iron structure and between the copper structures. . Therefore, the strength of the entire bearing 1 is increased and the durability is improved as compared with the conventional bronze-based sintered bearing. Furthermore, it is also possible to achieve a limit PV value of PV> 200 MPa · m / min, and it is possible to cope with further increase in load capacity and high-speed rotation that are expected in the future because of low friction even under such use conditions. . Therefore, according to the present invention, a sintered bearing having only the merit of both a bronze bearing and an iron sintered bearing (or an iron copper sintered bearing) can be obtained.

  In order to confirm the above-mentioned effects achieved by the present invention, the initial conformability, the limit PV value, and the amount of wear are compared between the product of the present invention and the conventional bronze-based sintered bearing and copper-iron-based sintered bearing. A test was conducted.

The composition (weight ratio) of each bearing in the comparative test was as follows.
Invention product: Iron: 80.2%, Copper: 18.0% (flat copper powder 8%), Tin: 1.0%, Graphite 0.8%
Bronze bearings: Copper: 88.8%, Tin: 9.9%, Graphite: 1.3%
Copper-iron sintered bearings: Iron: 77.2%, Copper: 20.0%, Tin: 2.0%, Graphite 0.8%

  Each test condition is as follows.

[Initial conformability measurement test]
・ Peripheral speed: 38 m / min
・ Load: 1.1 MPa
・ Shaft specifications: SUS420J2 (HRC55)
Bearing size: 6 × 12 × 6 (Inner diameter diameter dimension, outer diameter diameter dimension, and length are expressed in millimeters. The same applies hereinafter.)
・ Operation gap: 0.020mm
・ Temperature: Normal temperature

[Limit PV value measurement test]
・ Shaft specifications: SUS420J2 (HRC55)
・ Bearing size: 6 × 12 × 6
・ Operation gap: 0.020mm
・ Temperature: Normal temperature

[Abrasion test]
・ Peripheral speed: 38 to 75 m / min
・ Load: 0.7-4.0MPa
・ Shaft specifications: SUS420J2 (HRC55)
・ Bearing size: 6 × 12 × 6
・ Operation gap: 0.020mm
・ Temperature: Normal temperature ・ Time: 8 hours

  FIG. 9 shows the results of the initial conformability characteristic measurement test, FIG. 10 shows the results of the limit PV value measurement test, and FIG. 11 shows the results of the wear amount test.

  From FIG. 9, in the product of the present invention, even when the blending ratio of copper is the above lower limit value, the friction is low immediately after the start of operation, which is good compared to the copper iron system, and is equal to or better than the bronze bearing. It was found to have a good initial conformability. Further, it can be understood from FIG. 10 that even with a PV value exceeding 200 MPa · m / min, the friction is sufficiently low, and a PV value of about 500 MPa · m / min is practical. Furthermore, it can be understood from FIG. 11 that the wear amount of the product of the present invention is small and has durability equal to or higher than that of bronze-based and copper-iron-based products.

[Other Embodiments]
In the first embodiment described above, the iron structure is entirely formed of a ferrite phase. However, in such a configuration, the surface layer is worn due to the use conditions of the bearing (for example, when used at a high surface pressure). When the base portion is exposed, the wear resistance of the bearing surface may be insufficient.

  In this case, if the iron structure is a two-phase structure consisting of a ferrite phase and a pearlite phase, the hard pearlite phase contributes to the improvement of wear resistance, and the wear of the bearing surface under high surface pressure is suppressed and the bearing life is extended. It can be improved (second embodiment). Due to the diffusion of carbon, as shown in FIG. 6, when the proportion of pearlite γFe becomes excessive and the proportion is the same level as that of ferrite αFe, the aggressiveness of the pearlite against the shaft increases remarkably and the shaft is likely to wear. In order to prevent this, as shown in FIG. 12, the pearlite phase (γFe) is suppressed to the extent that it exists (is scattered) at the grain boundary of the ferrite phase (αFe). The “grain boundary” here means both the grain boundary formed between the ferrite phases and between the ferrite phase and other particles, as well as the crystal grain boundary 10 in the ferrite phase (αFe). In FIG. 12, the pearlite phase existing at the former grain boundary is represented by γFe1, and the pearlite phase present at the latter grain boundary is represented by γFe2. The ratio of the pearlite phase γFe (γFe1 + γFe2) to the ferrite phase αFe is preferably 5 to 20% in area ratio in the arbitrary cross section of the base portion S2.

  The growth rate of pearlite mainly depends on the sintering temperature. Therefore, in order for the pearlite phase to be present at the grain boundary of the ferrite phase in the above-described manner, the sintering temperature is raised to about 820 ° C. to 900 ° C. compared to the first embodiment, and carbon is included as the furnace atmosphere. Sintering is performed using a gas such as natural gas or endothermic gas (RX gas). As a result, carbon contained in the gas diffuses into iron during sintering, and pearlite phase γFe can be formed. When sintered at a temperature exceeding 900 ° C., carbon in the graphite powder reacts with iron. Other configurations, such as the composition of the raw material powder and the manufacturing procedure, are the same as those in the first embodiment, and a duplicate description is omitted.

  In the above description, the case where the present invention is applied to a perfect circle bearing having a perfect circle shape on the bearing surface 1a is illustrated. However, the present invention is not limited to a perfect circle bearing, and the outer circumference of the bearing surface 1a and the shaft 2 is exemplified. The present invention can be similarly applied to a fluid dynamic pressure bearing in which a dynamic pressure generating portion such as a herringbone groove or a spiral groove is provided on the surface.

DESCRIPTION OF SYMBOLS 1 Bearing 1a Bearing surface 2 Shaft 3 Flat copper powder 4 Scale-like graphite 6 Mold 9 Compact 10 Grain boundary 61 Forming surface L Flat powder length t Flat powder thickness

Claims (15)

In sintered bearings containing iron and copper structures,
Copper structure and iron structure are bonded with a low melting point metal, and part or all of the copper structure is formed of flat copper powder, and the iron structure is formed mainly of a ferrite phase, and the copper content becomes uniform. A sintered bearing comprising: a base portion; and a surface layer that covers a surface of the base portion and has a copper content larger than that of the base portion.   The sintered bearing according to claim 1, wherein the iron structure is formed of a ferrite phase.   The sintered bearing according to claim 1, wherein the iron structure is formed of a ferrite phase and a pearlite phase existing at a grain boundary of the ferrite phase.   The sintered bearing according to any one of claims 1 to 3, wherein a copper structure having an area ratio of 60% or more is formed on the surface of the surface layer.   The sintered bearing according to any one of claims 1 to 4, wherein a ratio of the low melting point metal to copper is less than 10% by weight.   The sintered bearing according to any one of claims 1 to 5, wherein the structure has a solid lubricant.   The sintered bearing according to any one of claims 1 to 5, wherein the structure has free graphite.   The sintered bearing according to claim 7, wherein the content of free graphite is larger in the surface layer than in the base portion.   Raw material powder containing iron powder, flat copper powder, and low melting point metal powder is mixed and filled into the mold, and the raw powder is compressed with the flat copper powder adhered to the mold surface to form a green compact. And a method for producing a sintered bearing, comprising sintering the green compact.   The method for manufacturing a sintered bearing according to claim 9, wherein a fluid lubricant is attached to the flat copper powder before mixing.   The method for manufacturing a sintered bearing according to claim 9, wherein 0.1 to 0.8 wt% of a fluid lubricant is adhered to the flat copper powder before mixing in a weight ratio with respect to the flat copper powder.   The method for producing a sintered bearing according to claim 10 or 11, wherein a fatty acid is used as the fluid lubricant. The method for producing a sintered bearing according to any one of claims 9 to 12, wherein the apparent density of the flat copper powder is 1.0 g / cm ³ or less, the thickness is 1.5 µm or less, and the length is 20 µm or more and 80 µm or less. .   The method for manufacturing a sintered bearing according to any one of claims 9 to 13, wherein graphite is added to the raw material powder.   The method for producing a sintered bearing according to claim 14, wherein scaly graphite is used as the graphite.

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