JP6462053B2 - Sintered bearing - Google Patents

Description

  The present invention relates to a sintered bearing made of a sintered metal mainly composed of iron powder and copper powder.

  As a so-called copper-iron-based sintered bearing mainly composed of iron powder and copper powder, a sintered bearing described in JP-A-2006-299347 (Patent Document 1) is known. This sintered bearing uses an iron-based raw material powder and a copper-based raw material powder. As the copper-based raw material powder, a flat copper-based powder having an average diameter smaller than that of the iron-based raw material powder and a large aspect ratio. A flat raw material powder and a copper-based small raw material powder having an average diameter smaller than that of the copper-based flat raw material powder are used. When molding the green compact, fill the molding die with a mixture of iron-based raw material powder, copper-based flat raw material powder, and copper-based small raw material powder, and then give vibration to the raw material powder. The copper-based flat raw material powder is segregated on the surface side of the green compact.

JP 2006-299347 A

  In the invention described in Patent Document 1, the average diameter of the copper-based small raw material powder is made smaller than that of the copper-based flat raw material powder. The blending ratio of the copper-based small raw material powder is not specified in Patent Document 1, but since it is usually used in a considerable amount, the raw material powder has a small proportion of copper-based small particles whose average diameter is smaller than other main powders. It is thought that raw material powder is contained. As a result, the fluidity of the raw material powder tends to deteriorate. When the fluidity of the raw material powder is reduced, the moldability of the green compact is reduced, and further, the copper-based small raw material powder having a small particle size is easily segregated, and the content of copper in the mass-produced product becomes non-uniform Cause problems. Further, in order to prepare a copper-based small raw material powder having a small average diameter, it is necessary to carefully sort the copper powder through a sieve, and there is a problem that the powder cost increases.

  Therefore, an object of the present invention is to provide a copper-iron sintered bearing that has high formability and quality stability and can be manufactured at low cost.

  In order to achieve the above object, a sintered bearing according to the present invention is a sintered bearing having an iron structure formed of iron powder and a copper structure formed of copper powder, and the copper content becomes uniform. The base part and the surface layer that covers the surface of the base part and has a copper content higher than that of the base part. As the copper powder, a flat cuprous powder having an aspect ratio larger than that of the iron powder, and an average The second copper powder having a particle size larger than the average particle size of the first copper powder is used.

  The flat cuprous powder has the property of adhering to the mold forming surface during molding of the raw material powder. Therefore, the green compact after molding contains a large amount of copper in the surface layer. On the other hand, the copper content is reduced in the core. 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 copper content in the surface layer, it is possible to improve the initial conformability and quietness when used as a bearing. 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. Furthermore, the base part has a hard structure with a small copper content and a high iron content compared to the surface layer. As described above, since the iron content is large in the base portion that occupies most of the bearing, the amount of copper used in the entire bearing can be reduced, and a significant cost reduction can be achieved. .

  In particular, in the present invention, the average particle size of the second copper powder is made larger than the average particle size of the flat cuprous powder. This means that the apparent density of the cupric powder is larger than the apparent density of the flat cuprous powder. With this configuration, the difference in the particle size of the main powder contained in the raw material powder can be reduced to improve the fluidity of the raw material powder, improving the formability when forming the green compact, or segregating various powders Prevention can be achieved. Moreover, since the cupper powder can be roughly selected by the sieve, the cost can be reduced by reducing the powder cost.

  In order to obtain such an effect, it is preferable that the average particle size of the iron powder is 60 μm to 150 μm, the average particle size of the cuprous powder is 20 μm to 50 μm, and the average particle size of the cupric powder is 50 μm to 100 μm.

  By forming the iron structure (structure containing iron as a main component) with a ferrite phase, even when the base part containing much iron structure is exposed due to wear of the surface layer, the aggressiveness against the shaft of the bearing surface is weakened. Can do.

  On the other hand, if the iron structure is formed of a ferrite phase, the wear resistance of the bearing surface decreases 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).

  As described above, when the average particle size of the cupric powder is made larger than that of the flat cuprous powder, the particle size of the copper structure is increased, which may reduce the binding force between the iron structure and the copper structure. is there. In order to compensate for this, low melting point metal powder is added to the raw material powder. By adding the low melting point metal powder, the iron particles and the copper particles are combined by the low melting point metal melted at the time of sintering, so that a decrease in bearing strength can be minimized. Generally, as the content of the low melting point metal increases, the strength of the bearing increases accordingly. On the other hand, the flat copper powder is rounded and spheroidized due to the surface tension in the liquid phase state of Cu-Sn. When the spheroidized flat copper increases, the area occupied by the copper structure on the bearing surface decreases, and it is impossible to achieve the effects of improving the initial conformability and quietness and reducing the aggressiveness to the mating material. From the above viewpoint, the ratio of the low melting point metal to copper is less than 10% by weight.

    Further, by including solid lubricant powder, it is possible to reduce the friction of the bearing surface.

  According to the present invention, since the fluidity of the raw material powder is improved, it is possible to improve the moldability when molding the green compact and prevent segregation of various powders. Moreover, powder cost can also be suppressed. Therefore, it is possible to provide an inexpensive sintered bearing having high formability and quality stability.

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 a figure which shows the microscope picture of flat copper powder (cuprous powder). It is a figure which shows the microscope picture of normal copper powder (cupric powder). It is a figure which shows the microscope picture of iron powder. It is sectional drawing which shows the formation process of the green compact by a metal mold | die. FIG. 8 is an enlarged cross-sectional view of a region Q in FIG. It is an expanded sectional view of the area | region P in FIG. It is a figure which shows the change of the copper content rate in the radial direction of a bearing. It is a component table | surface in one Embodiment of the sintered bearing concerning this invention. It is a figure which expands and shows the grain boundary structure of a base part.

  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 copper powder, iron 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 manufacturing procedure of raw material powder and a bearing is described in detail.

[Copper powder]
As the copper powder, two types of flat copper powder (also referred to as foil-like copper powder) as the first copper powder Cu1 and normal copper powder as the second copper powder Cu2 are used.

The flat copper powder Cu1 is flattened by stamping raw material copper powder made of atomized powder or the like. As the flat copper powder, those having an average particle size of about 20 μm to 50 μm (desirably 30 μm to 40 μm), an apparent density of 1.0 g / cm ³ or less, and an aspect ratio of about 20 to 60 are used. The definition of the apparent density conforms to the rules of JIS Z 8901 (hereinafter the same). The aspect ratio is expressed by L / t, where L is the length of the particle and t is the thickness (here, “length” and “thickness” are each flat copper powder 3 as shown in FIG. 2). The geometrical maximum dimension of the following: the same shall apply hereinafter). For example, those having a length L of about 20 μm to 50 μm and a thickness t of about 0.5 μm to 2.0 μm can be used as the flat copper powder. The aspect ratio of the flat copper powder is larger than the aspect ratio of normal copper powder and iron powder described later, and is a value of several times to several tens of times. 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. FIG. 4 shows a photomicrograph of the flat copper powder used in this embodiment.

  Here, the average particle diameter of the flat copper powder can be measured based on, for example, a laser diffraction scattering method. In this measurement method, a particle group is irradiated with a laser beam, and a particle size distribution and further an average particle size are obtained by calculation from the intensity distribution pattern of diffracted / scattered light emitted from the particle group. SALD 31000 from the factory is used. The apparent density can be measured based on JIS Z 2504. The method for measuring the average particle diameter and the apparent density described above is also applied to each powder described below.

Usually, as the copper powder Cu2, spherical or dendritic copper powder widely used for sintered bearings can be widely used. For example, reduced powder, electrolytic powder, atomized powder and the like are used. These mixed powders can also be used. In this embodiment, atomized copper powder having excellent oil impregnation is used. Atomized copper powder is a porous body having a large number of irregularities on the surface and has an irregular shape, but the shape of the entire particle is generally spherical. In general, the copper powder has an average particle size of about 50 μm to 100 μm (preferably 60 μm to 80 μm) and an apparent density of 2.0 g / cm ^{3 to} 3.0 g / cm ³ (preferably 2.4 g / cm ^{3 to} 2.8 g / cm ³ ) and an aspect ratio of 1 to 3 are used. 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. A photomicrograph of the normal copper powder used in this embodiment is shown in FIG.

[Iron powder]
As the iron powder Fe, known powders such as reduced iron powder and 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. The iron powder has an average particle size of about 60 μm to 150 μm (preferably 80 μm to 120 μm) and an apparent density of 2.0 g / cm ^{3 to} 3.0 g / cm ³ (preferably 2.4 g / cm ^{3 to} 2.6 g / cm). ³ ) Use a material with an aspect ratio of about 1 to 3. The amount of oxygen contained in the iron powder is 0.2% by weight or less. The micrograph of the iron powder used in this embodiment is shown in FIG.

[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 set to 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 (eg, 0.3% 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. Among these, tin powder with little transpiration during sintering, particularly water atomized tin powder is preferable. The tin powder has an average particle size of about 20 μm to 60 μm (preferably 30 μm to 40 μm) and an apparent density of 1.5 g / cm ^{3 to} 2.5 g / cm ³ (preferably 1.8 g / cm ^{3 to} 2.2 g / cm). ³ ) About grades are used. Since the low melting point metal powder has high wettability with respect to copper, liquid phase sintering proceeds by adding it to 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. The solid lubricant powder has an average particle size of about 20 μm to 60 μm (preferably 30 μm to 40 μm) and an apparent density of 0.1 g / cm ^{3 to} 0.6 g / cm ³ (preferably 0.2 g / cm ^{3 to} 0.4 g / cm). ³ ) About grades are used. 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, when the copper-rich surface layer portion S1 (described later) disappears due to wear, the base portion S2 has at least 10% by weight or more of copper to reduce the aggression with respect to the shaft of the surface of the base portion S2 that becomes the bearing surface. It is necessary to have an organization. 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 20 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, and even if the blending amount is further increased, the cost is increased by using high-cost flat copper powder. 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. 11 shows a particularly preferable blending ratio of various raw material powders described above. As shown in the figure, flat copper powder is 8 wt% or more and 10 wt% or less, normal copper powder is 10 wt% or more and 12 wt% or less, and low melting metal powder is 1.2 wt% or more and 2.0 wt% or less (for example, 1.2 wt%), and the solid lubricant powder is particularly preferably 0.6 wt% or more and 1.0 wt% or less (for example, 0.8 wt%).

[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 Cu <b> 1 and the graphite powder C adhere to each other and overlap in layers due to the fluid lubricant or the like attached to the flat copper powder, thereby increasing the apparent density of the flat copper powder. 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.

  The adhesion state between the flat copper powder Cu1 and the scaly graphite powder C shown in FIG. 3 is maintained to some extent even after the secondary mixing. 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. 7, the mold 6 includes a core 6a, a die 6b, an upper punch 6c, and a lower punch 6d, and a raw material powder is filled into a cavity defined 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 Cu1 is the smallest. Moreover, the flat copper powder Cu1 is a foil having the length L and the thickness t, and the area of the wide surface per unit weight is large. For this reason, the flat copper powder is easily affected by the adhesive force of the fluid lubricant adhered to the surface thereof, and further by static electricity, etc., and after filling the mold 6 with the raw material powder, as shown in FIG. In addition, the flat copper powder Cu1 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, the scaly graphite adhering to the flat copper powder Cu1 also adheres to the molding surface 61 of the mold accompanying the flat copper powder Cu1 (illustration of graphite is omitted in FIG. 8). On the other hand, in the inner region (region on the cavity center side) of the layered structure of the flat copper powder Cu1, the iron powder Fe, the normal copper powder Cu2, and the low melting point metal (tin) powder Sn are substantially uniformly dispersed. Become. 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 starts, and a pearlite phase γFe is generated in the steel structure. However, in sintering, carbon ( The reaction between graphite and iron begins, 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 FIG. 1 is completed by sizing the sintered body and further impregnating with lubricating oil by a technique such as vacuum impregnation. 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. 9 schematically shows the metal structure near the surface of the sintered bearing 1 (region P in FIG. 1) that has undergone the above manufacturing process. In FIG. 9, the copper structure is hatched (the direction of the hatching line is reversed between the flat copper powder Cu1 and the normal copper powder Cu2), and the dotted pattern is added to the graphite.

  In the sintered bearing 1 of the present invention, the green compact 9 is formed in a state in which the flat copper Cu1 is adhered in a layered manner to the mold forming surface 61, and this is derived from the fact that the layered flat copper Cu1 is sintered. As shown in FIG. 9, a surface layer S <b> 1 having a high copper concentration is formed on the entire surface including the bearing surface 1 a of the bearing 1. Moreover, since the wide surface of the flat copper Cu1 is attached to the molding surface 61, 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. 10, 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 shifting from the surface layer S1 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 Cu1, 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.

  As is clear from the comparison between FIG. 4 and FIG. 5, in the present invention, the average particle size of the normal copper powder Cu2 as the second copper powder is larger than the average particle size of the flat copper powder Cu1 as the first copper powder. . This usually means that the apparent density of the copper powder is larger than the apparent density of the flat copper powder. Moreover, as is clear from the comparison of FIGS. 4 to 6, the average particle size of the iron powder Fe is larger than the average particle size of the flat copper powder Cu1 and the normal copper powder Cu2. Even if there is a slight difference in the average particle diameter of the main powder (flat copper powder Cu1, normal copper powder Cu2, iron powder Fe) contained in the raw material powder from such a configuration, it is compared with the invention described in Patent Document 1. The difference can be reduced. Therefore, it is possible to improve the fluidity of the raw material powder, to improve the moldability when molding the green compact, or to prevent segregation of various powders. Moreover, since the normal copper powder can be roughly selected by the sieve, cost reduction can be achieved by reducing the powder cost. Therefore, it is possible to improve the moldability when molding the green compact, prevent segregation of various powders, and suppress the powder cost. From the above, it is possible to provide an inexpensive copper-iron sintered bearing having high formability and quality stability.

  Thus, when the average particle diameter of copper powder is made larger than the average particle diameter of flat copper powder, the particle diameter of the entire copper powder is increased, which may reduce the binding force between iron particles and copper particles. However, by adding an appropriate amount of low melting point metal powder to the raw material powder, the iron structure and the copper structure can be firmly bonded. Therefore, a decrease in bearing strength can be minimized.

[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 S2 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). When carbon is diffused, the existing ratio of pearlite γFe becomes excessive, and when the ratio is the same as that of ferrite αFe, the aggressiveness of the pearlite against the shaft is remarkably increased, and the shaft is easily worn. 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 6 Mold 9 Green compact 61 Molding surface Cu1 Flat copper powder (1st copper powder)
Cu2 Normal copper powder (cupric powder)
L Length of flat copper powder t Thickness of flat copper powder

Claims (6)

A sintered bearing having an iron structure formed of iron powder and a copper structure formed of copper powder,
A base part having a uniform copper content and a surface layer covering the surface of the base part and having a higher copper content than the base part,
On the surface of the surface layer, the area of the copper structure is larger than the area of the iron structure,
As the copper structure, a structure obtained by sintering a first copper powder made of a foil-like copper powder having an aspect ratio larger than that of an iron powder, and a structure obtained by sintering a second copper powder made of a spherical or dendritic copper powder. Among the iron powder, cuprous powder, and cupric powder, the apparent density of the cuprous powder is the smallest,
A sintered bearing characterized in that the iron structure is formed of a ferrite phase. A sintered bearing having an iron structure formed of iron powder and a copper structure formed of copper powder,
A base part having a uniform copper content and a surface layer covering the surface of the base part and having a higher copper content than the base part,
On the surface of the surface layer, the area of the copper structure is larger than the area of the iron structure,
As the copper structure, a structure obtained by sintering a first copper powder made of a foil-like copper powder having an aspect ratio larger than that of an iron powder, and a structure obtained by sintering a second copper powder made of a spherical or dendritic copper powder. Among the iron powder, cuprous powder, and cupric powder, the apparent density of the cuprous powder is the smallest,
A sintered bearing characterized in that 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 claim 1 or 2, wherein the second copper powder is one of reduced copper powder, electrolytic copper powder, and atomized copper powder, or a mixed powder thereof.   Furthermore, the sintered bearing of Claim 1 or 2 containing a low melting metal.   The sintered bearing according to claim 4, wherein the 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, further comprising free graphite.