JP2019085649A - Sintered bearing - Google Patents

Abstract

To provide a sintered bearing which has high moldability and quality stability and can be manufactured at a low cost.SOLUTION: A sintered bearing 1 is formed mainly of iron powder and copper powder and includes: a base part S2 in which the content of copper is made uniform; and a surface layer S1 which covers the surface of the base part S2 and has a higher copper content than the base part S2. As the copper powder, flat copper powder Cu1 whose aspect ratio is larger than that of the iron powder and normal copper powder Cu2 are used. The average particle diameter of the normal copper powder Cu2 is made larger than that of the flat copper powder Cu1.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a sintered bearing made of sintered metal containing iron powder and copper powder as main components.

  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, and is a flat copper-based copper-based raw material powder having a smaller average diameter and a larger aspect ratio than the iron-based raw material powder. A flat raw material powder and a copper based small raw material powder having a smaller average diameter than the copper flat raw material powder are used. When forming a green compact, a mixture of iron-based raw material powder, copper-based flat raw material powder, and copper-based small raw material powder is filled in a molding die, and then vibration is applied 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 smaller than that of the copper-based flat raw material powder. Although the compounding ratio of the copper-based small raw material powder is not specified in Patent Document 1, since it is usually used in a considerable amount, the copper-based small small diameter of the raw material powder is smaller than other main powders in a considerable proportion. It is considered that raw material powder is included. As a result, the flowability of the raw material powder tends to deteriorate. When the flowability of the raw material powder is reduced, the formability of the green compact is reduced, and further, the small-diameter small copper-based raw material powder is likely to be segregated to make the content of copper in a mass product uneven. Cause problems. In addition, in order to prepare a copper-based small raw material powder having a small average diameter, it is necessary to carefully screen the copper powder and there is also a problem that the powder cost rises.

  An object of the present invention is to provide a copper-iron-based sintered bearing which has high formability and quality stability and which can be manufactured at low cost.

  In order to achieve the above object, the 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 content of copper becomes uniform. Base portion, and a surface layer covering the surface of the base portion and having a copper content higher than that of the base portion, and as copper powder, flat cuprous powder having an aspect ratio larger than iron powder, and an average A 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 molding surface of the mold during molding of the raw material powder. Therefore, the green compact after molding contains much copper in the surface layer. On the other hand, the copper content is reduced in the core portion. Therefore, in the sintered body after sintering, a surface layer with a high content of copper and a base portion with a lower content of copper are formed.

  By thus 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 aggressivity to the axis is also reduced, the durable life is improved. These effects can be more remarkably obtained by forming a copper structure (structure having copper as a main component) of 60% or more in area ratio on the surface of the surface layer. Furthermore, the base portion has a hard structure having a lower copper content and a higher iron content than the surface layer. Thus, since the iron content is high at the base portion that occupies most of the bearing, the amount of copper used in the entire bearing can be reduced, and significant cost reduction can be achieved. .

  In particular, in the present invention, the average particle diameter of the second copper powder is made larger than the average particle diameter of the flat first copper powder. This means that the apparent density of cupric powder is greater than the apparent density of flat cuprous powder. From such a configuration, it is possible to reduce the difference in particle diameter of the main powder contained in the raw material powder to improve the flowability of the raw material powder, to improve the formability when forming a green compact, or to segregate various powders. It can prevent. In addition, since the first copper powder can be roughly sorted by a sieve, cost reduction can be achieved by reducing the powder cost.

  In order to obtain such an effect, it is preferable to set the average particle size of the iron powder to 60 μm to 150 μm, the average particle size of the first copper powder to 20 μm to 50 μm, and the average particle size of the second copper powder to 50 μm to 100 μm.

  By forming an iron structure (structure containing iron as a main component) in a ferrite phase, even when the base portion containing a large amount of iron structure is exposed due to the wear of the surface layer, the aggression against the axis of the bearing surface is weakened. Can.

  On the other hand, when the iron structure is formed of a ferrite phase, the surface layer wears and the wear resistance of the bearing surface decreases when the base portion is exposed. If this is a problem, iron structure can be formed of a ferrite phase and a pearlite phase present at grain boundaries of the ferrite phase by reacting iron with carbon at the time of sintering. With such a configuration, since the hard pearlite phase compensates for the wear resistance of the ferrite phase, wear of the bearing surface can be suppressed. On the other hand, if carbon diffuses and the percentage of perlite present becomes excessive, the aggression with respect to the shaft increases and the shaft tends to wear. From this point of view, the pearlite phase is present (dotted) at 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 becomes large, and thus the bonding strength between the iron structure and the copper structure may be reduced. is there. In order to compensate for this, low melting point metal powder is added to the raw material powder. By the addition of the low melting point metal powder, the iron particles and the copper particles are bonded by the low melting point metal melted at the time of sintering, so that the reduction in bearing strength can be minimized. Generally, if the content of the low melting point metal is increased, the strength of the bearing is increased as much. On the other hand, the flat copper powder becomes round and spherical in the liquid phase state of Cu-Sn due to surface tension. When the spheroidized flat copper is increased, the area occupied by the copper structure on the bearing surface is reduced, and the effects such as the improvement of initial conformability and quietness and the reduction of aggression on the counterpart material can not be achieved. 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 flowability of the raw material powder is improved, it is possible to improve the formability at the time of forming the green compact and to prevent segregation of various powders. Also, the powder cost can be suppressed. Therefore, it becomes possible to provide an inexpensive sintered bearing having high formability and quality stability.

It is a sectional view of a sintering bearing concerning the present invention. The upper part is a side view of flat copper powder, and the lower part is a plan view of flat copper powder. It is a side view showing flat copper powder and scale-like graphite which adhered mutually. It is a figure which shows the microscope picture of flat copper powder (1st copper powder). It is a figure which shows the microscope picture of a normal copper powder (2nd copper 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. It is an expanded sectional view of the area | region Q in FIG. It is an expanded sectional view of field P in FIG. It is a figure which shows the change of the content rate of copper in the radial direction of a bearing. It is a component table in one embodiment of the sintering bearing concerning the present invention. It is a figure which expands and shows the grain boundary structure of a base part.

  Hereinafter, an embodiment of the present invention will be described based on the attached drawings.

  As shown in FIG. 1, the sintered bearing 1 is formed in a cylindrical shape having a bearing surface 1 a 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 that state or the bearing 1 is rotated, the lubricating oil held in the innumerable holes of the sintered bearing 1 Exude to the bearing surface 1a as the temperature rises. An oil film is formed in the bearing gap between the outer peripheral surface of the shaft and the bearing surface 1 a by the leaking lubricating oil, and the shaft 2 is relatively rotatably supported by the bearing 1.

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

  The raw material powder is a mixed powder containing copper powder, iron powder, low melting point metal powder, and solid lubricant powder as main components. To this mixed powder, various molding assistants, for example, lubricants (metal soap etc.) for improving releasability are added as necessary. Hereinafter, the manufacturing procedure of the raw material powder and the bearing will be described in detail.

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

Flat copper powder Cu1 is obtained by flattening raw material copper powder made of atomized powder or the like by crushing. As flat copper powder, an average particle diameter 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 apparent density conforms to the provisions of JIS Z 8901 (the same applies hereinafter). The aspect ratio is represented by L / t, where L is the particle length and t is the thickness ("length" and "thickness" referred to here are individual flat copper powder 3 as shown in Fig. 2). The geometric maximum dimension of: the same as below). 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 flat copper powder. The aspect ratio of the flat copper powder is larger than the aspect ratio of ordinary copper powder or iron powder described later, and is approximately several times to several tens of times larger. With flat copper powder of the above size and apparent density, the adhesion of the flat copper powder to the molding surface of the mold is enhanced, so that a large amount of flat copper powder can be adhered to the molding surface of the mold. A photomicrograph of flat copper powder used in the present embodiment is shown in FIG.

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

As the copper powder Cu 2, 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. In addition, these mixed powder can also be used. In this embodiment, atomized copper powder excellent in oil content is used. The atomized copper powder is a porous body having a large number of irregularities on the surface and has an irregular shape, but the overall shape of the particles is approximately spherical. In general, as copper powder, average particle diameter is about 50 μm to 100 μm (preferably 60 μm to 80 μm), apparent density 2.0 g / cm ^{3 to} 3.0 g / cm ³ (desirably 2.4 g / cm ^{3 to} 2.8 g / cm ³ What is about cm ³ ) and an aspect ratio of about 1 to 3 is used. If only flat copper powder is used as the copper powder, the density of the flat copper powder is small, so it is difficult to solidify at the time of compacting, but it is usually used together with the copper powder for compacting. Can be enhanced. The photomicrograph of the normal copper powder used in this embodiment is shown in FIG.

[Iron powder]
As iron powder Fe, widely known powders such as reduced iron powder and atomized iron powder can be used. In the present embodiment, reduced iron powder excellent in oil content is used. The reduced iron powder is also called spongy iron powder because it is approximately spherical, irregularly shaped and porous, and cancellous with 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 (desirably 2.4 g / cm ^{3 to} 2.6 g / cm) ³ ) Use one with an aspect ratio of 1 to 3 or so. The amount of oxygen contained in the iron powder is 0.2% by weight or less. A photomicrograph of the iron powder used in the present embodiment is shown in FIG.

[Fluid lubricant]
In order to make flat copper powder adhere to the mold molding surface, a fluid lubricant is previously attached to the flat copper powder. The fluid lubricant may be attached to the flat copper powder before filling the raw material powder in the mold, preferably before mixing the raw material powder, and more preferably adhering to the raw copper powder at the stage of crushing the raw copper powder. Let After crushing, the fluid lubricant may be attached to the flat copper powder by, for example, supplying the fluid lubricant to the flat copper powder and stirring the mixture before mixing with other raw material powder. In order to secure the adhesion amount of flat copper powder on the molding surface of the mold, the blending ratio of the fluid lubricant to the flat copper powder is 0.1% by weight or more in weight ratio, and aggregation due to adhesion of the flat copper powder In order to prevent this, the above blending ratio is made 0.8 wt% or less. Desirably, the lower limit of the mixing ratio is 0.2% by weight or more, and the upper limit is 0.7% by weight (eg, 0.3% by weight). As a fluid lubricant, fatty acids, especially linear saturated fatty acids are preferred. This type of fatty acid is represented by the general formula C _n-1 H _{2 n-1} COOH. As this fatty acid, Cn is a thing of the range of 12-22, for example, a 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, and in the present invention, a metal powder having a melting point of 700 ° C. or less, for example, a powder of tin, zinc, phosphorus or the like is used. Among them, tin powder having low transpiration at the time of 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 (desirably 1.8 g / cm ^{3 to} 2.2 g / cm) ³ ) About what is used. The low melting point metal powder has high wettability to copper, and therefore, when it is added to the raw material powder, liquid phase sintering proceeds and the bonding strength between iron structure and copper structure or copper structure is strengthened. The strength of the metallographic structure increases as the content of the low melting point metal increases, but when 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 area of copper on the bearing surface is reduced. In conventional copper-based sintered bearings and copper-iron-based sintered bearings, it is general to mix about 10% by weight of low melting point metal with respect to copper, but in the present invention, it is low for copper because of the above reasons. The proportion of the melting point metal is less than 10% by weight (desirably not more than 8.0% by weight).

[Solid lubricant powder]
Solid lubricant powder is added to reduce friction at the time of metal contact by sliding with the shaft 2, for example, graphite is used. At this time, as graphite, it is desirable to use sickle-like graphite so as to obtain adhesion to flat copper powder. The solid lubricating powder has an average particle size of about 20 μm to 60 μm (preferably 30 μm to 40 μm), an apparent density of 0.1 g / cm ^{3 to} 0.6 g / cm ³ (desirably 0.2 g / cm ^{3 to} 0.4 g / cm) ³ ) About what is used. As solid lubricant powder, molybdenum disulfide powder can be used besides graphite. Molybdenum disulfide powder has a layered crystal structure and exfoliates in a layered manner, so that the adhesion to flat copper powder is obtained in the same manner as flaky graphite.

[Blending ratio]
The raw material powder containing the above-mentioned respective powders contains 18% by weight to 40% by weight of copper powder, 1% by weight to 4% by weight of low melting point metal powder (for example, tin powder), solid lubricant powder (for example, graphite powder) It is desirable to mix 0.5 to 2.5% by weight and to make the balance iron powder.

  In the present invention, as described later, the flat copper powder is deposited in a layer form on the mold when the raw material 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 attached to the mold is insufficient, and the effect of the present invention can not be expected. In addition, when the copper-rich surface layer portion S1 (described later) disappears due to wear, copper having a base portion S2 of at least 10% by weight or more reduces the aggression with respect to the axis of the surface of the base portion S2 serving as a 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 the two. On the other hand, when the proportion of copper powder exceeds 40% by weight, the amount of copper powder used becomes excessive, and the cost merit by using flat copper powder becomes poor. As mentioned above, the compounding quantity of the copper powder in raw material powder shall be 18 weight% or more and 40 weight% or less. In addition, the blending amount of flat copper powder in the raw material powder is 8 wt% or more and 20 wt% or less, desirably 8 wt% or more and 20 wt% or less. The reason why 20% by weight or less is preferable is that the amount of flat copper powder attached to the mold saturates at about 20% by weight, and even if the compounding amount is further increased, the cost is increased by using high cost flat copper powder. Is a problem.

  If the proportion of the low melting point metal powder is less than 1% by weight, the strength of the bearing can not be secured, and if it exceeds 4% by weight, the problem of the spheroidization of the flat copper powder occurs as described above. If the proportion of the solid lubricant powder is less than 0.5% by weight, the friction reduction effect on the bearing surface can not 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).

  A particularly preferable compounding ratio of the various raw material powders described above is shown in FIG. As illustrated, flat copper powder is 8 wt% or more and 10 wt% or less, usually 10 wt% or more and 12 wt% or less of copper powder, and 1.2 wt% or more and 2.0 wt% or less of low melting point metal powder (for example, It is particularly preferable to set the solid lubricant powder at not less than 0.6 wt% and not more than 1.0 wt% (for example, 0.8 wt%).

[mixture]
It is desirable to perform mixing of each powder described above in two steps. First, as primary mixing, flaky graphite powder and flat copper powder to which a fluid lubricant has been deposited are mixed by a known mixer. Next, as secondary mixing, iron powder, usually copper powder, and low melting point metal powder are added to the primary mixed powder and mixed, and further, graphite powder is also added and mixed if necessary. Flat copper powder is difficult to disperse uniformly in raw material powder because the apparent density is low among various raw material powders, but flat copper powder and graphite powder with the same level of apparent density in primary mixing are mixed in advance When this is done, as shown in FIG. 3, the flat copper powder Cu1 and the graphite powder C adhere to each other and overlap in layers due to the fluid lubricant and the like adhering to the flat copper powder, and the apparent density of the flat copper powder increases. Therefore, it becomes possible to disperse | distribute flat copper powder uniformly in raw material powder at the time of secondary mixing. If a lubricant is separately added at the time of primary mixing, adhesion of the flat copper powder and the graphite powder is further promoted, so it becomes possible to disperse the flat copper powder more uniformly at the time of secondary mixing. As the lubricant to be added here, powdery ones may be used in addition to the same or different fluidic lubricants as the above-mentioned fluid lubricants. For example, since the forming assistant such as the above-mentioned metal soap is generally in the form of powder and has a certain degree of adhesion, it can be promoted from the adhesion of the flat copper powder and the graphite powder.

  The adhesion state of 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, so when the raw material powder is filled in the mold, the flat copper powder is added to the mold surface. A large amount of graphite powder will be attached.

[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 comprises a core 6a, a die 6b, an upper punch 6c, and a lower punch 6d, and the cavities partitioned by these are filled with the raw material powder. When the upper and lower punches 6c and 6d are brought close to compress the raw material powder, the raw material powder is formed by the molding surface comprising 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 green compact 9 having a cylindrical shape is obtained.

  Among the metal powders in the raw material powder, the apparent density of the flat copper powder Cu1 is the smallest. Flat copper powder Cu1 is foil-like which has the above-mentioned length L and thickness t, and the area of the wide field per unit weight is large. Therefore, the flat copper powder is susceptible to the adhesion by the fluid lubricant adhering to the surface, the static electricity, etc., and after filling the raw material powder into the mold 6, as shown in FIG. The flat copper powder Cu1 adheres to the entire area of the molding surface 61 in a layered state in which the wide surface faces the molding surface 61 and a plurality of layers (about 1 to 3 layers) overlap. At this time, the scaly graphite attached to the flat copper powder Cu1 is also attached to the molding surface 61 of the mold along with the flat copper powder Cu1 (illustration of the graphite is omitted in FIG. 8). On the other hand, iron powder Fe, usually copper powder Cu2, and low melting point metal (tin) powder Sn are substantially uniformly dispersed in the inner region (region on the cavity center side) of the layered structure of flat copper powder Cu1. Become. The green compact 9 after molding holds the 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 graphite does not react with iron (no carbon diffusion occurs). In the iron-carbon equilibrium state, there is a transformation point at 723 ° C, and the reaction between iron and carbon starts to generate pearlite phase γFe in the steel structure, but in sintering, it exceeds 900 ° C before carbon ( The reaction between graphite) and iron starts, and the pearlite phase γFe is generated. Since the pearlite phase γFe has a hard structure (HV 300 or more) and has high aggressivity with respect to the opposite material, excessive precipitation of the pearlite phase may promote the wear of the shaft 2.

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

  From the above viewpoint, in the present invention, sintering is performed at a low temperature of 900 ° C. or lower, specifically at a sintering temperature of 700 ° C. (desirably 760 ° C.) to 840 ° C. Further, the sintering atmosphere is a gas atmosphere containing no carbon (hydrogen gas, nitrogen gas, argon gas, etc.) or vacuum. By these measures, in the raw material powder, no reaction between carbon and iron occurs, so that the iron structure after sintering becomes all soft ferrite phase αFe (HV 200 or less). During the sintering, the fluid lubricant, other lubricants, and various forming assistants volatilize from the inside of the sintered body.

  By passing through the above-described sintering step, a porous sintered body can be obtained. The sintered body is sized and impregnated with lubricating oil by a method such as vacuum impregnation, whereby the sintered bearing 1 shown in FIG. 1 is completed. Depending on the application, the impregnation process of the lubricating oil may be omitted, and the sintered bearing 1 may be used without oil.

  The metal structure in the vicinity of the surface (region P in FIG. 1) of the sintered bearing 1 which has undergone the above manufacturing steps is schematically shown in FIG. 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 graphite is given a scatter pattern.

  In the sintered bearing 1 of the present invention, the green compact 9 is formed in a state where the flat copper Cu1 is attached in a layer to the mold forming surface 61, and it is derived from the sintering of the layer flat copper Cu1. As shown in FIG. 9, the surface layer S <b> 1 with 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 flat copper Cu1 is attached to the forming surface 61, most of the copper structure of the surface layer S1 is flat and oriented with the wide surface facing the surface. The thickness of the surface layer S1 corresponds to the thickness of the flat copper layer-likely attached to the mold molding surface 61, and is approximately 1 μm to 6 μm. In an arbitrary cross section of the surface layer S1, the area of the copper structure is larger than the area of the iron structure, and specifically 60% or more is the copper structure.

  The base portion S2 inside the surface layer S1 is basically covered by the surface layer S1. As shown in FIG. 10, the content of copper in the base portion S2 is less than the content of copper in the surface layer S1, and the content of copper rapidly decreases when transitioning from the surface layer S1 to the base portion S2 doing. Further, the content (% by weight) of copper in each portion of the base portion S2 is uniform in each portion.

  From the above configuration, the area ratio of the copper structure to the iron structure is 60% or more over the entire 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, The aggression against axis 2 can be weakened.

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

  As described above, in the present invention, the flat copper powder is used, and the green compact is molded in a state where the flat copper powder is attached to the mold molding surface 61, thereby increasing the copper content in the surface layer S1 and Except for the layer S1, the iron content is increased to realize the optimum distribution of the copper structure and the iron structure. Further, by intentionally setting the iron structure to the ferrite phase αFe, wear of the shaft 2 when the copper-rich surface layer S1 is worn is also suppressed. Therefore, it is possible to simultaneously improve the durability and reduce the cost by reducing the amount of copper used.

  In addition, free graphite is deposited over the entire surface including the bearing surface 1a, and moreover, since scaly graphite is attached to the mold forming surface 61 in a manner associated with the flat copper powder Cu1, free graphite in the surface layer S1 The content rate of is also high. Therefore, the friction of the bearing surface 1a can be reduced, and the durability of the bearing 1 can be increased. Further, the copper structure and the iron structure are bonded by the low melting point metal in both the surface layer S1 and the base portion S2, and high bond 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 also improved as compared with the conventional bronze-based sintered bearing. Furthermore, it is also possible to achieve the limit PV value of PV> 200 MPa · m / min, and the friction is low even under such use conditions, and it is possible to cope with further increase in load capacity and high speed rotation expected in the future. . Therefore, according to the present invention, it is possible to obtain a sintered bearing having only the merits of both a bronze-based bearing and an iron-based sintered bearing (or an iron-copper sintered bearing).

  As apparent from the comparison between FIG. 4 and FIG. 5, in the present invention, the average particle diameter of the normal copper powder Cu2 as the second copper powder is larger than the average particle diameter of the flat copper powder Cu1 as the first copper powder. . This usually means that the apparent density of copper powder is greater than the apparent density of flat copper powder. Further, as apparent 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. From this configuration, even if the average particle diameter of the main powder (flat copper powder Cu1, usually copper powder Cu2, iron powder Fe) contained in the raw material powder has a slight difference, compared to the invention described in Patent Document 1 The difference can be reduced. Therefore, the flowability of the raw material powder can be improved, and the formability at the time of forming the green compact can be improved, or segregation of various powders can be prevented. In addition, since sorting of normal copper powder can be roughly performed by a sieve, cost reduction can be achieved by reducing powder cost. Therefore, it is possible to improve the formability at the time of forming the green compact and to prevent segregation of various powders, and it is also possible to suppress the powder cost. From the above, it becomes possible to provide an inexpensive copper-iron-based sintered bearing having high formability and quality stability.

  Thus, when the average particle size of the copper powder is generally larger than the average particle size of the flat copper powder, the particle size of the entire copper powder is increased, and thus the bonding strength between the iron particles and the copper particles may be reduced. However, the iron structure and the copper structure can be firmly bonded by adding an appropriate amount of low melting point metal powder to the raw material powder. Therefore, the decrease in bearing strength can be minimized.

[Other embodiments]
In the first embodiment described above, all the iron structure is formed of the ferrite phase, but in such a configuration, the surface layer wears due to the use conditions of the bearing (for example, when used under 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 of a ferrite phase and a pearlite phase, the hard pearlite phase contributes to the improvement of the wear resistance and suppresses the wear of the bearing surface under high surface pressure to achieve bearing life. It can be improved (second embodiment). By the diffusion of carbon, the presence ratio of pearlite γFe becomes excessive, and when the ratio is equal to that of ferrite αFe, the aggressivity to the shaft by pearlite is significantly increased and the shaft is apt to be worn. In order to prevent this, as shown in FIG. 12, the pearlite phase (γFe) is suppressed to the extent of being present (dotted) in the grain boundaries of the ferrite phase (αFe). The term "grain boundary" as used herein means both grain boundaries 10 in the ferrite phase (α-Fe), as well as grain boundaries formed between the ferrite phase and between the ferrite phase and other particles. In FIG. 12, the pearlite phase existing in the former grain boundary is represented by γFe1, and the pearlite phase existing in the latter grain boundary is represented by γFe2. The ratio of the pearlite phase γFe (γFe1 + γFe2) to the ferrite phase αFe is desirably 5 to 20% in area ratio in an arbitrary cross section of the base portion S2.

  The growth rate of pearlite depends mainly on the sintering temperature. Therefore, in order to cause the pearlite phase to exist at the grain boundaries of the ferrite phase in the above aspect, the sintering temperature is raised to about 820 ° C. to 900 ° C. than in the first embodiment, and carbon is contained 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 can diffuse into iron during sintering to form pearlite phase γFe. In addition, when it sinters at temperature over 900 ° C, carbon in graphite powder reacts with iron. The configuration other than this, for example, the composition of the raw material powder, the production procedure, and the like are the same as in the first embodiment, and thus the description thereof will not be repeated.

  In the above description, the present invention is applied to a perfect circular bearing in which the bearing surface 1a has a perfect circular shape, but the present invention is not limited to the perfect circular bearing, and the outer periphery of the bearing surface 1a and the shaft 2 The present invention can be similarly applied to a fluid dynamic pressure bearing provided with dynamic pressure generating parts such as herringbone grooves and spiral grooves on the surface.

Reference Signs List 1 bearing 1a bearing surface 2 axis 6 mold 9 green compact 61 molding surface Cu1 flat copper powder (first copper powder)
Cu2 normal copper powder (second copper powder)
L Flat Copper Powder Length t Flat Copper Powder Thickness

Claims (9)

A sintered bearing having an iron structure formed of iron powder and a copper structure formed of copper powder,
A base portion having a uniform copper content, and a surface layer covering the surface of the base portion and having a copper content higher than that of the base portion;
It is characterized by using, as a copper powder, flat cuprous copper powder having an aspect ratio larger than that of iron powder, and cupric copper powder having an average particle size larger than that of copper powder. Bearing. A sintered bearing having an iron structure formed of iron powder and a copper structure formed of copper powder,
A base portion having a uniform copper content, and a surface layer covering the surface of the base portion and having a copper content higher than that of the base portion;
A sintered bearing characterized by using, as a copper powder, a flat cuprous copper powder having an aspect ratio larger than that of an iron powder and a second copper powder having an apparent density higher than the apparent density of the first copper powder. .   The sintered bearing according to claim 1 or 2, wherein the average particle size of the iron powder is 60 μm to 150 μm, the average particle size of the first copper powder is 20 μm to 50 μm, and the average particle size of the second copper powder is 50 μm to 100 μm.   The sintered bearing according to any one of claims 1 to 3, wherein the iron structure is formed of a ferrite phase.   The sintered bearing according to any one of claims 1 to 3, wherein the iron structure is formed of a ferrite phase and a pearlite phase present at grain boundaries of the ferrite phase.   The sintered bearing according to any one of claims 1 to 5, 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 6, further comprising a low melting point metal powder.   The sintered bearing according to claim 7, wherein the ratio of the low melting point metal powder to copper is less than 10% by weight.   The sintered bearing according to any one of claims 1 to 8, further comprising solid lubricant powder.