JP2019031738A - Production method of sintered bearing - Google Patents
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Abstract
Description
本発明は、焼結軸受の製造方法に関する。 The present invention relates to a method for manufacturing a sintered bearing.
焼結軸受は、無数の内部気孔を有する多孔質体であり、通常は、内部気孔に潤滑流体（例えば、潤滑油）を含浸させた状態で使用される。この場合、焼結軸受およびその内周に挿入した軸が相対回転すると、焼結軸受の内部気孔に保持された潤滑油が温度上昇に伴って焼結軸受の内周面（軸受面）に滲み出す。そして、この滲み出した潤滑油によって、焼結軸受の軸受面と軸の外周面との間の軸受隙間に油膜が形成され、軸が相対回転自在に支持される。 Sintered bearings are porous bodies having innumerable internal pores, and are usually used in a state in which internal pores are impregnated with a lubricating fluid (for example, lubricating oil). In this case, when the sintered bearing and the shaft inserted in the inner periphery thereof rotate relative to each other, the lubricating oil retained in the inner pores of the sintered bearing oozes into the inner peripheral surface (bearing surface) of the sintered bearing as the temperature rises. put out. The oozed lubricating oil forms an oil film in the bearing gap between the bearing surface of the sintered bearing and the outer peripheral surface of the shaft, and the shaft is supported so as to be relatively rotatable.
例えば、下記の特許文献１には、鉄および銅を主成分とする鉄銅系の焼結軸受として、鉄粉に対し１０質量％以上３０質量％未満の銅を被覆してなり、粒度を８０メッシュ以下とした銅被覆鉄粉を圧粉・焼結することで得られるものが記載されている。 For example, in Patent Document 1 below, an iron-copper sintered bearing mainly composed of iron and copper is coated with 10% by mass or more and less than 30% by mass of copper with respect to iron powder, and the particle size is 80 It describes what is obtained by compacting and sintering copper-coated iron powder below mesh.
しかしながら、本発明者らが検証したところ、特許文献１の技術手段を適用した焼結軸受を振動モータに使用した場合には、回転変動が大きくなることが明らかになった。これは、銅被覆鉄粉を圧粉・焼結して得られた焼結軸受では、鉄相（鉄組織）と銅相（銅組織）のネック強度が低いため、軸受面が早期に摩耗したことに起因すると考えられる。 However, as a result of verification by the present inventors, it has been clarified that when a sintered bearing to which the technical means of Patent Document 1 is applied is used for a vibration motor, rotational fluctuation becomes large. This is because in sintered bearings obtained by compacting and sintering copper-coated iron powder, the neck surface of the iron phase (iron structure) and copper phase (copper structure) is low, so the bearing surface was worn early. It is thought to be caused by this.
軸受面の耐摩耗性向上を図るための技術手段として、ＮｉやＭｏ等の金属粉末を配合した混合粉末を使用し、これを圧粉・焼結することが考えられる。しかしながら、ＮｉやＭｏ等の金属粉末は高価であるため、焼結軸受の高コスト化を招く。 As a technical means for improving the wear resistance of the bearing surface, it is conceivable to use a mixed powder containing a metal powder such as Ni or Mo, and to compact and sinter the mixed powder. However, since metal powders such as Ni and Mo are expensive, the cost of sintered bearings is increased.
以上の実情に鑑み、本発明は、高い回転精度を有し、かつ回転変動が少ない焼結軸受を低コストに製造可能とすることを目的とする。 In view of the above circumstances, an object of the present invention is to make it possible to manufacture a sintered bearing having high rotational accuracy and low rotational fluctuation at low cost.
ところで、上述の振動モータとは、例えば携帯電話等の携帯端末において、電話の着信やメールの受信等を報知するバイブレータとして機能するものであり、例えば特許文献２，３に記載されているように、錘（偏芯錘）が取り付けられた軸の軸方向に離間した二箇所を内周に軸受面を有する円筒状の焼結軸受で支持しつつ、上記軸をモータ部で回転させることにより、端末全体に振動を発生させるようになっている。焼結軸受は、例えば金属材料で形成されたハウジングの内周に固定される。この振動モータでは、モータ部に通電されると、軸は、錘の影響を受けて焼結軸受の軸受面の全面に沿って振れ回りながら回転する。すなわち、この種の振動モータにおいて、軸は、その中心を焼結軸受の軸受中心に対してあらゆる方向に偏芯させた状態で回転する。 By the way, the above-described vibration motor functions as a vibrator for notifying incoming calls or mails in a portable terminal such as a cellular phone, for example, as described in Patent Documents 2 and 3, for example. By rotating the shaft with the motor part while supporting two places spaced apart in the axial direction of the shaft to which the weight (eccentric weight) is attached by a cylindrical sintered bearing having a bearing surface on the inner periphery, Vibration is generated throughout the terminal. The sintered bearing is fixed to the inner periphery of a housing formed of, for example, a metal material. In this vibration motor, when the motor portion is energized, the shaft rotates while swinging along the entire bearing surface of the sintered bearing under the influence of the weight. That is, in this type of vibration motor, the shaft rotates in a state where its center is eccentric in all directions with respect to the bearing center of the sintered bearing.
近年、いわゆるスマートフォン等への搭載を考慮して、振動モータにはさらなる小型化が要請されている。振動モータを小型化した場合、モータパワーの増大には限界がある。そのような状況下でも所定の振動性能を確保するために、モータを高速回転化（１００００ｒｐｍ以上）し、あるいは錘のアンバランス荷重を増大させることで対処しようとしており、振動モータ用の焼結軸受の使用条件はより過酷化する傾向にある。すなわち、振動モータでは、上記のように軸が軸受面全面に沿って振れ回りながら回転すること、また、アンバランス荷重により軸受面が軸に頻繁に叩かれることから、焼結軸受の使用条件は通常用途の焼結軸受（例えば、スピンドルモータ用の焼結軸受）よりもただでさえ過酷であり、軸受面が摩耗し易い。そのため、モータを高速回転化等すると、軸受面の摩耗が一層促進されることになり、軸受面の摩耗に起因した回転変動が一層大きくなる。 In recent years, vibration motors are required to be further downsized in consideration of mounting on so-called smartphones. When the vibration motor is downsized, there is a limit to the increase in motor power. In order to ensure the predetermined vibration performance even under such circumstances, the motor is being rotated at a high speed (10000 rpm or more) or the unbalance load of the weight is being increased, and a sintered bearing for the vibration motor The condition of use tends to be more severe. That is, in a vibration motor, the shaft rotates while swinging along the entire bearing surface as described above, and the bearing surface is frequently hit by the shaft due to an unbalanced load. It is even more severe than a sintered bearing for normal use (for example, a sintered bearing for a spindle motor), and the bearing surface is subject to wear. For this reason, when the motor is rotated at a high speed or the like, the wear of the bearing surface is further promoted, and the rotational fluctuation due to the wear of the bearing surface is further increased.
このような事情も考慮して創作された本発明は、支持すべき軸との間に軸受隙間を形成する軸受面を内周に有する焼結軸受の製造方法であって、鉄粉に対し銅粉を部分拡散させてなる部分拡散合金粉を主原料とし、これに低融点金属粉および固体潤滑剤粉を配合した原料粉末を圧縮成形して圧粉体を得る圧縮成形工程と、圧粉体を焼結して焼結体を得る焼結工程とを含むことを特徴とする。 The present invention created in view of such circumstances is a method of manufacturing a sintered bearing having a bearing surface on the inner periphery that forms a bearing gap with a shaft to be supported, which is made of copper against iron powder. A compression molding process for obtaining a green compact by compression molding a raw material powder containing a low diffusion metal powder and a solid lubricant powder as a main raw material, a partial diffusion alloy powder obtained by partially diffusing the powder; And a sintering step of obtaining a sintered body.
上記の製法によれば、金属組織の大部分が鉄（鉄組織）で構成され、しかも金属組織に一定量の銅を含んだ焼結体を得ることができるので、耐摩耗性、機械的強度、および初期なじみ性等の摺動特性に優れた焼結軸受を得ることができる。また、上記の製法であれば、焼結工程で圧粉体が焼結されるのに伴って、圧粉体に含まれる低融点金属粉が溶融する。低融点金属は銅に対して高いぬれ性を持つので、液相焼結により、隣り合う部分拡散合金粉の鉄組織と銅組織、あるいは銅組織同士を強固に結合させることができる。また、個々の部分拡散合金粉のうち、鉄粉の表面に銅粉の一部が拡散することでＦｅ−Ｃｕ合金が形成された部分には、溶融した低融点金属が拡散していくため、鉄組織と銅組織間のネック強度が一層高まる。これらのことから、ＮｉやＭｏ等の高価な金属粉末を使用することなく、また、圧粉体を比較的低温で加熱（焼結）するいわゆる低温焼結でも、軸受面の耐摩耗性に優れ、かつ高い圧環強度（例えば３００ＭＰａ以上）を有する焼結体（焼結軸受）を製造することができる。 According to the above manufacturing method, since most of the metal structure is composed of iron (iron structure), and a sintered body containing a certain amount of copper in the metal structure can be obtained, wear resistance and mechanical strength are obtained. In addition, a sintered bearing having excellent sliding characteristics such as initial conformability can be obtained. Moreover, if it is said manufacturing method, the low melting metal powder contained in a green compact will fuse | melt as a green compact is sintered by a sintering process. Since the low melting point metal has high wettability with respect to copper, the iron structure and the copper structure of adjacent partial diffusion alloy powders, or the copper structures can be firmly bonded by liquid phase sintering. In addition, among the individual partial diffusion alloy powders, the melted low melting point metal diffuses into the part where the Fe-Cu alloy is formed by diffusing a part of the copper powder on the surface of the iron powder, The neck strength between the iron and copper structures is further increased. Therefore, the bearing surface is excellent in wear resistance without using expensive metal powders such as Ni and Mo, and also in so-called low-temperature sintering where the green compact is heated (sintered) at a relatively low temperature. In addition, a sintered body (sintered bearing) having a high crushing strength (for example, 300 MPa or more) can be manufactured.
そして、軸受面の耐摩耗性が向上すれば、軸受面の摩耗に起因した回転変動を防止することができる。また、焼結軸受が十分な圧環強度を具備していないと、特にハウジング内周に焼結軸受を圧入した際に軸受面が変形する（軸受面の真円度や円筒度などが低下する）ため、圧入後にサイジング等の形状修正加工を追加的に実行し、軸受面を適正形状に仕上げる必要がある。これに対し、上記のように高い圧環強度を有する焼結体を得ることができれば、焼結軸受をハウジング内周にするのに伴って軸受面が変形するのを可及的に防止することができるので、上述の形状修正加工を追加的に実行する必要がなくなる。従って、振動モータに使用した場合でも、高い耐久性と回転精度とを両立した焼結軸受を低コストに提供することが可能となる。 If the wear resistance of the bearing surface is improved, it is possible to prevent rotational fluctuation due to wear of the bearing surface. In addition, if the sintered bearing does not have sufficient crushing strength, the bearing surface is deformed particularly when the sintered bearing is press-fitted into the inner periphery of the housing (the roundness or cylindricity of the bearing surface is reduced). Therefore, it is necessary to additionally execute a shape correction process such as sizing after press-fitting to finish the bearing surface into an appropriate shape. On the other hand, if a sintered body having a high crushing strength as described above can be obtained, it is possible to prevent the bearing surface from being deformed as much as possible when the sintered bearing is made into the inner periphery of the housing. Therefore, it is not necessary to additionally execute the above-described shape correction processing. Therefore, even when used in a vibration motor, it is possible to provide a sintered bearing that achieves both high durability and rotational accuracy at low cost.
圧粉体の焼結温度（加熱温度）は、例えば８２０℃以上９００℃以下に設定することができる。このような焼結処理を、炭素を含むガス雰囲気で実行すれば、ガスに含まれる炭素が鉄組織中に拡散していくので、鉄組織がフェライト相とパーライト相の二相組織からなる焼結体を得ることができる。焼結体としては、鉄組織の全てがフェライト相からなるものとすることもできるが、鉄組織が上記の二相組織で構成されていれば、焼結体が硬質のパーライト相を含んでいることにより、軸受面の耐摩耗性を一層高めることができる。また、上記の焼結条件であれば、圧粉体に含まれる銅粉が溶融せず、従って、焼結に伴って銅が鉄組織中に拡散しない。このため、焼結体の表面には適量の銅組織（青銅相）が形成される。そのため、軸との初期なじみ性が良好で、摩擦係数が小さい軸受面を得ることができる。 The sintering temperature (heating temperature) of the green compact can be set to 820 ° C. or higher and 900 ° C. or lower, for example. If such a sintering process is carried out in a gas atmosphere containing carbon, the carbon contained in the gas diffuses into the iron structure, so that the iron structure consists of a two-phase structure of a ferrite phase and a pearlite phase. You can get a body. As the sintered body, all of the iron structure may be composed of a ferrite phase, but if the iron structure is composed of the above two-phase structure, the sintered body contains a hard pearlite phase. As a result, the wear resistance of the bearing surface can be further enhanced. Moreover, if it is said sintering conditions, the copper powder contained in a green compact will not fuse | melt, Therefore, copper does not diffuse in an iron structure with sintering. For this reason, an appropriate amount of copper structure (bronze phase) is formed on the surface of the sintered body. Therefore, it is possible to obtain a bearing surface having good initial conformability with the shaft and a small friction coefficient.
上記の焼結軸受（焼結体）を得るには、部分拡散合金粉として、平均粒径５μｍ以上２０μｍ未満の銅粉が鉄粉に部分拡散し、かつＣｕを１０〜３０質量％含有するものを使用するのが好ましい。 In order to obtain the above sintered bearing (sintered body), as the partial diffusion alloy powder, copper powder having an average particle size of 5 μm or more and less than 20 μm is partially diffused into iron powder and contains 10 to 30% by mass of Cu. Is preferably used.
本発明者らが鋭意検討を重ねた結果、平均粒径１０６μｍを超える大粒径の部分拡散合金粉が原料粉末中に含まれていると、焼結体の内部に粗大気孔が形成され易く、その結果、必要とされる軸受面の耐摩耗性や圧環強度等を確保できない場合があることが判明した。従って、部分拡散合金粉は、平均粒度１４５メッシュ以下（平均粒径１０６μｍ以下）のものを使用するのが好ましい。このような合金粉を使用することで、焼結後の金属組織が均一化され、金属組織（多孔質組織）中での粗大気孔の発生が抑制された焼結体を安定的に得ることができる。これにより、軸受面の耐摩耗性や軸受の圧環強度が一層向上した焼結軸受を安定的に得ることが可能となる。 As a result of repeated extensive studies by the inventors, when a partially diffused alloy powder having a large particle size exceeding the average particle size of 106 μm is contained in the raw material powder, rough atmospheric pores are easily formed inside the sintered body, As a result, it has been found that there are cases in which the required wear resistance of the bearing surface, the crushing strength, and the like cannot be ensured. Accordingly, it is preferable to use a partially diffused alloy powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less). By using such an alloy powder, it is possible to stably obtain a sintered body in which the sintered metal structure is homogenized and the generation of rough air holes in the metal structure (porous structure) is suppressed. it can. Thereby, it becomes possible to stably obtain a sintered bearing in which the wear resistance of the bearing surface and the crushing strength of the bearing are further improved.
原料粉末としては、低融点金属粉としての錫粉が０．５〜３．０質量％配合されると共に、固体潤滑剤粉としての黒鉛粉が０．３〜１．５質量％配合されたものを使用するのが好ましい。これにより、上述した作用効果を適切に奏し得る焼結軸受を安定的に量産することができる。 As the raw material powder, 0.5 to 3.0% by mass of tin powder as a low melting metal powder and 0.3 to 1.5% by mass of graphite powder as a solid lubricant powder are mixed. Is preferably used. Thereby, the sintered bearing which can show the effect mentioned above appropriately can be mass-produced stably.
部分拡散合金粉（Ｆｅ−Ｃｕ部分拡散合金粉）を構成する鉄粉としては、還元鉄粉を使用することができる。鉄粉としては、還元鉄粉以外にも、例えばアトマイズ鉄粉を使用することができるが、還元鉄粉は内部気孔を有する海綿状（多孔質状）をなすことから、アトマイズ鉄粉に比べて粉末が柔らかく、圧縮成形性に優れる。そのため、低密度でも圧粉体強度を高めることができ、圧粉体の欠けや割れの発生を防止することができる。また、還元鉄粉は、上記のとおり海綿状をなすことから、アトマイズ鉄粉に比べて保油性に優れる利点も有する。 As iron powder constituting the partial diffusion alloy powder (Fe—Cu partial diffusion alloy powder), reduced iron powder can be used. As the iron powder, for example, atomized iron powder can be used in addition to the reduced iron powder. However, since the reduced iron powder has a spongy shape (porous shape) having internal pores, it is compared with the atomized iron powder. The powder is soft and excellent in compression moldability. Therefore, the green compact strength can be increased even at low density, and chipping and cracking of the green compact can be prevented. Moreover, since reduced iron powder makes a spongy shape as described above, it also has an advantage of superior oil retention as compared with atomized iron powder.
焼結工程の後には、焼結体の内部気孔に潤滑油を含浸させる含油工程を設けることができる。この含油工程では、４０℃の動粘度が１０〜５０ｍｍ2／ｓの範囲内にある潤滑油、あるいは４０℃の動粘度が１０〜５０ｍｍ2／ｓの範囲内にある油（潤滑油）を基油とした液状グリースを焼結体の内部気孔に含浸させることができる。４０℃の動粘度が上記範囲内にある潤滑油あるいは液状グリースを焼結体の内部気孔に含浸させれば、軸受隙間に高剛性の油膜を形成することができ、しかも回転トルクの上昇を抑えることのできる焼結軸受（焼結含油軸受）が得られる。 After the sintering step, an oil impregnation step of impregnating the internal pores of the sintered body with the lubricating oil can be provided. In this oil-containing process, lubricating oil kinematic viscosity of 40 ° C. is within the range of 10 to 50 mm 2 / s, or 40 kinematic viscosity ° C. is within the range of 10 to 50 mm 2 / s oil (lubricating oil) group The internal pores of the sintered body can be impregnated with liquid grease as oil. By impregnating the internal pores of the sintered body with lubricating oil or liquid grease having a kinematic viscosity at 40 ° C. within the above range, it is possible to form a highly rigid oil film in the bearing gap and to suppress an increase in rotational torque. A sintered bearing (sintered oil-impregnated bearing) that can be obtained is obtained.
以上に示すように、本発明によれば、高い回転精度を有し、かつ回転変動の少ない焼結軸受を低コストに製造することができる。そのため、この焼結軸受をモータ、特に振動モータに組み込んで使用した際には、信頼性および耐久性に優れる振動モータを低コストに提供することが可能となる。 As described above, according to the present invention, it is possible to manufacture a sintered bearing having high rotational accuracy and little rotational fluctuation at low cost. Therefore, when this sintered bearing is used by being incorporated in a motor, particularly a vibration motor, a vibration motor having excellent reliability and durability can be provided at low cost.
以下、本発明の実施の形態を図面に基づいて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
図１は、代表的な振動モータの要部概略断面図である。図示例の振動モータ１は、略円筒状に形成された金属製又は樹脂製のハウジング２と、軸方向の二箇所に離間して配置され、ハウジング２の内周に圧入固定されたリング状の焼結軸受４（４１，４２）と、焼結軸受４（４１，４２）の内周に挿入された軸３とを備え、軸３は、二つの焼結軸受４１，４２の間に配置されたモータ部Ｍによって１００００ｒｐｍ以上の回転数で回転駆動されるようになっている。軸３は、ステンレス鋼等の金属材料で形成され、ここでは直径２ｍｍ以下（好ましくは１．０ｍｍ以下）のものが使用される。軸３の一端には、軸３を焼結軸受４に対して偏心回転させるための錘Ｗが一体又は別体に設けられている。軸３の外周面３ａと焼結軸受４の軸受面４ａとの間に形成される隙間（軸受隙間）の隙間幅は、例えば片側（半径値）で４μｍ程度に設定されている。焼結軸受４の内部気孔には、４０℃の動粘度が１０〜５０ｍｍ2／ｓの範囲内にある潤滑油（例えば合成炭化水素系潤滑油）が含浸されている。焼結軸受４の内部気孔に含浸させる潤滑油として、このような低粘度のものを選択使用したのは、軸受隙間に形成される油膜の剛性を確保しつつ、回転トルクの上昇を抑えるためである。なお、焼結軸受４の内部気孔には、上記の潤滑油に替えて、４０℃の動粘度が１０〜５０ｍｍ2／ｓの範囲内にある油を基油とした液状グリースを含浸させても良い。 FIG. 1 is a schematic cross-sectional view of a main part of a typical vibration motor. The vibration motor 1 in the illustrated example has a ring-shaped metal or resin housing 2 formed in a substantially cylindrical shape and spaced apart at two axial positions and press-fitted and fixed to the inner periphery of the housing 2. The sintered bearing 4 (41, 42) and the shaft 3 inserted in the inner periphery of the sintered bearing 4 (41, 42) are provided, and the shaft 3 is disposed between the two sintered bearings 41, 42. The motor unit M is driven to rotate at a rotational speed of 10,000 rpm or more. The shaft 3 is formed of a metal material such as stainless steel, and a shaft having a diameter of 2 mm or less (preferably 1.0 mm or less) is used here. At one end of the shaft 3, a weight W for eccentrically rotating the shaft 3 with respect to the sintered bearing 4 is provided integrally or separately. The gap width of the gap (bearing gap) formed between the outer peripheral surface 3a of the shaft 3 and the bearing surface 4a of the sintered bearing 4 is set to about 4 μm on one side (radius value), for example. The internal pores of the sintered bearing 4 are impregnated with a lubricating oil (for example, a synthetic hydrocarbon-based lubricating oil) having a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm 2 / s. The reason why the low-viscosity lubricating oil impregnated in the internal pores of the sintered bearing 4 is selected and used is to suppress the increase in rotational torque while ensuring the rigidity of the oil film formed in the bearing gap. is there. In addition, the internal pores of the sintered bearing 4 may be impregnated with a liquid grease based on an oil having a kinematic viscosity at 40 ° C. in the range of 10 to 50 mm 2 / s instead of the lubricating oil. good.
以上の構成を有する振動モータ１において、モータ部Ｍに通電され、軸３が焼結軸受４に対して相対回転すると、焼結軸受４の内部気孔に保持された潤滑油が温度上昇に伴って軸受面４ａに滲み出す。この滲み出した潤滑油によって、対向する軸３の外周面３ａと焼結軸受４の軸受面４ａとの間の軸受隙間に油膜が形成され、軸３が焼結軸受４によって相対回転自在に支持される。なお、軸３は、その一端に設けられた錘Ｗの影響を受けることにより、軸受面４ａの全面に沿って振れ回りながら回転する。すなわち、軸３は、図２に示すように、その中心Ｏａを焼結軸受４（４１，４２）の中心Ｏｂに対してあらゆる方向に偏芯させた状態で回転する。 In the vibration motor 1 having the above-described configuration, when the motor unit M is energized and the shaft 3 rotates relative to the sintered bearing 4, the lubricating oil held in the internal pores of the sintered bearing 4 increases as the temperature rises. It oozes out to the bearing surface 4a. Due to the oozed lubricating oil, an oil film is formed in the bearing gap between the outer peripheral surface 3a of the opposed shaft 3 and the bearing surface 4a of the sintered bearing 4, and the shaft 3 is supported by the sintered bearing 4 so as to be relatively rotatable. Is done. Note that the shaft 3 rotates while swinging along the entire surface of the bearing surface 4a due to the influence of the weight W provided at one end thereof. That is, as shown in FIG. 2, the shaft 3 rotates in a state where its center Oa is decentered in all directions with respect to the center Ob of the sintered bearing 4 (41, 42).
図示例では、二つの焼結軸受４１，４２の軸方向長さ（軸受面４ａの面積）および径方向の厚さを相互に異ならせている。具体的には、錘Ｗに近い側の焼結軸受４１の軸受面４ａの面積を、錘Ｗから遠い側の焼結軸受４２の軸受面４ａの面積よりも大きく設定している。これは、錘Ｗに近い側では、錘Ｗから遠い側よりも大きなアンバランス荷重が軸３に作用するため、軸受面４ａの面積拡大を通じて支持能力向上を図る一方、錘Ｗから遠い側では、錘Ｗに近い側ほどの支持能力を必要としないため、軸受面４ａの面積を小さくして低トルク化を図るためである。 In the illustrated example, the two sintered bearings 41 and 42 have different axial lengths (area of the bearing surface 4a) and radial thicknesses. Specifically, the area of the bearing surface 4a of the sintered bearing 41 on the side closer to the weight W is set larger than the area of the bearing surface 4a of the sintered bearing 42 on the side farther from the weight W. This is because, on the side closer to the weight W, a larger unbalance load acts on the shaft 3 than on the side far from the weight W, so that the supporting ability is improved through the area expansion of the bearing surface 4a, while on the side far from the weight W, This is because the bearing capacity closer to the weight W is not required, so the area of the bearing surface 4a is reduced to reduce the torque.
図示は省略しているが、焼結軸受４の内部気孔に含浸させた潤滑油（あるいは液状グリース）がハウジング２の外部に漏れ出し、あるいは飛散するのを防止するため、振動モータ１にはハウジング２の開口部をシールするシール部材を設けても良い。 Although not shown, in order to prevent the lubricating oil (or liquid grease) impregnated in the internal pores of the sintered bearing 4 from leaking out or splashing outside the housing 2, the vibration motor 1 includes a housing. A sealing member for sealing the two openings may be provided.
以上で説明した焼結軸受４は、鉄を主成分とし、銅を１０〜３０質量％含んだ鉄銅系の焼結体からなり、かつ３００ＭＰａ以上の圧環強度を有する。このような焼結軸受４は、例えば、図３に示すように、（Ａ）原料粉末生成工程Ｐ１、（Ｂ）圧縮成形工程Ｐ２、（Ｃ）焼結工程Ｐ３、（Ｄ）サイジング工程Ｐ４および（Ｅ）含油工程Ｐ５を順に経て製造される。以下、これらの各工程について説明する。なお、二つの焼結軸受４（４１，４２）は、実質的に同一の構造を有しており、同じ製造手順で製造される。 The sintered bearing 4 described above is made of an iron-copper-based sintered body containing iron as a main component and containing 10 to 30% by mass of copper, and has a crushing strength of 300 MPa or more. Such a sintered bearing 4 includes, for example, as shown in FIG. 3, (A) a raw material powder production step P1, (B) a compression molding step P2, (C) a sintering step P3, (D) a sizing step P4, and (E) It is manufactured through the oil impregnation step P5 in order. Hereinafter, each of these steps will be described. The two sintered bearings 4 (41, 42) have substantially the same structure and are manufactured by the same manufacturing procedure.
（Ａ）原料粉末混合工程Ｐ１
この原料粉末生成工程Ｐ１では、後述する複数種の粉末を混合することにより、焼結軸受４の作製用材料である原料粉末１０［図５（ａ）参照］を均一化する。本実施形態で使用する原料粉末１０は、部分拡散合金粉を主原料とし、これに低融点金属粉および固体潤滑剤粉を配合した混合粉末である。この原料粉末１０には、必要に応じて各種成形潤滑剤（例えば、離型性向上のための潤滑剤）を添加しても良い。以下、上記の各粉末について詳細に述べる。
(A) Raw material powder mixing step P1
In this raw material powder production step P1, a plurality of types of powders to be described later are mixed to make the raw material powder 10 (see FIG. 5A), which is a material for producing the sintered bearing 4, uniform. The raw material powder 10 used in the present embodiment is a mixed powder in which a partial diffusion alloy powder is used as a main raw material, and a low melting point metal powder and a solid lubricant powder are blended therein. Various raw lubricants (for example, lubricants for improving releasability) may be added to the raw material powder 10 as necessary. Hereinafter, each of the above powders will be described in detail.
［部分拡散合金粉］
図４に示すように、部分拡散合金粉１１としては、鉄粉１２の表面に銅粉１３が部分拡散したＦｅ−Ｃｕ部分拡散合金粉が使用され、本実施形態では、鉄粉１２の表面に、鉄粉１２よりも平均粒径が小さい多数の銅粉１３を部分拡散させたＦｅ−Ｃｕ部分拡散合金粉が使用される。この部分拡散合金粉の拡散部分はＦｅ−Ｃｕ合金を形成しており、図４中の部分拡大図に示すように、合金部分は鉄原子１２ａと銅原子１３ａとが相互に結合し、配列した結晶構造を有する。部分拡散合金粉１１としては、平均粒度１４５メッシュ以下（平均粒径１０６μｍ以下）の粒子のみが使用される。
[Partial diffusion alloy powder]
As shown in FIG. 4, as the partial diffusion alloy powder 11, Fe—Cu partial diffusion alloy powder in which the copper powder 13 is partially diffused on the surface of the iron powder 12 is used, and in this embodiment, on the surface of the iron powder 12. Fe-Cu partial diffusion alloy powder obtained by partially diffusing a large number of copper powders 13 having an average particle size smaller than that of the iron powder 12 is used. The diffusion part of this partial diffusion alloy powder forms an Fe—Cu alloy, and as shown in the partial enlarged view in FIG. 4, the iron part 12 a and the copper atom 13 a are bonded and arranged in the alloy part. It has a crystal structure. As the partial diffusion alloy powder 11, only particles having an average particle size of 145 mesh or less (average particle size of 106 μm or less) are used.
なお、粉末はその粒径が小さくなるほど見掛密度が下がり、浮遊し易くなる。そのため、原料粉末中に小粒径の部分拡散合金粉１１が多く含まれていると、後述する圧縮成形工程Ｐ２において成形金型（キャビティ）に対する原料粉末の充填性が低下し、所定形状・密度の圧粉体を安定的に得ることが難しくなる。具体的には、粒径４５μｍ以下の部分拡散合金粉１１が２５質量％以上含まれていると、上記の問題が生じ易くなることを本発明者らは見出した。従って、部分拡散合金粉１１としては、平均粒度１４５メッシュ以下（平均粒径１０６μｍ以下）で、かつ平均粒度３５０メッシュ（平均粒径４５μｍ）以下の粒子を２５質量％以上含まないものを選択使用するのが望ましい。平均粒径は、粒子群にレーザ光を照射し、そこから発せられる回析・散乱光の強度分布パターンから計算によって粒度分布、さらには平均粒径を求めるレーザ回析散乱法（例えば株式会社島津製作所製のＳＡＬＤ３１０００を用いる）により測定することができる（以下に述べる粉末の平均粒径も同様の方法で測定することができる）。 In addition, an apparent density falls and the powder tends to float, so that the particle size becomes small. For this reason, if the raw material powder contains a large amount of the partially diffused alloy powder 11 having a small particle size, the filling property of the raw material powder into the molding die (cavity) is lowered in the compression molding step P2 described later, and the predetermined shape and density are reduced. It becomes difficult to obtain a green compact stably. Specifically, the present inventors have found that the above problem is likely to occur when the partially diffused alloy powder 11 having a particle size of 45 μm or less is contained in an amount of 25 mass% or more. Therefore, as the partial diffusion alloy powder 11, one having an average particle size of 145 mesh or less (average particle size of 106 μm or less) and not containing 25% by mass or more of particles having an average particle size of 350 mesh (average particle size of 45 μm) or less is selectively used. Is desirable. The average particle size is determined by irradiating a particle group with laser light, and calculating the particle size distribution from the intensity distribution pattern of diffraction / scattered light emitted from the particle group. (The average particle size of the powder described below can also be measured by the same method).
上記の部分拡散合金粉１１を構成する鉄粉１２としては、還元鉄粉、アトマイズ鉄粉等、公知の鉄粉を問題なく使用することができるが、本実施形態では還元鉄粉を使用する。還元鉄粉は、球形に近似した不規則形状で、かつ内部気孔を有する海綿状（多孔質状）であるから、海綿鉄粉とも称される。使用する鉄粉１２は、平均粒径２０μｍ〜１０６μｍのものが好ましく、平均粒径３８μｍ〜７５μｍのものが一層好ましい。 As the iron powder 12 constituting the partial diffusion alloy powder 11, known iron powders such as reduced iron powder and atomized iron powder can be used without any problem, but reduced iron powder is used in the present embodiment. The reduced iron powder has an irregular shape that approximates a spherical shape and has a sponge shape (porous shape) having internal pores, and is also referred to as sponge iron powder. The iron powder 12 used preferably has an average particle size of 20 μm to 106 μm, and more preferably an average particle size of 38 μm to 75 μm.
また、部分拡散合金粉１１を構成する銅粉１３としては、汎用されている不規則形状や樹枝状の銅粉が広く使用可能であり、例えば、電解銅粉、アトマイズ銅粉等が用いられる。本実施形態では、表面に多数の凹凸を有すると共に、粒子全体として球形に近似した不規則形状をなし、成形性に優れたアトマイズ銅粉を使用している。銅粉１３としては、鉄粉１２よりも小粒径のものが使用され、具体的には平均粒径５μｍ以上２０μｍ以下（好ましくは２０μｍ未満）のものが使用される。なお、個々の部分拡散合金粉１１におけるＣｕの割合は１０〜３０質量％（好ましくは２２〜２６質量％）であり、焼結工程Ｐ３で得られる焼結体４”に含まれる銅の質量比（厳密には、焼結体４”がＳｎやＣを含まないとした場合における銅の質量比）と同じである。すなわち、本実施形態において、原料粉末１０には、単体の銅粉や鉄粉を配合しない。原料粉末には、単体の銅粉や鉄粉を配合しても構わないが、単体の銅粉を配合すると、軸受面４ａの耐摩耗性向上を図ることが難しくなる。そのため、例えば軸３が回転するのに伴って軸受面４ａに軸３が衝突した際などに、軸受面４ａに圧痕（凹み）が形成され易くなる。また、単体の鉄粉を配合すると、所望の圧環強度を有する焼結体（焼結軸受）を得ることが難しくなる。従って、原料粉末には、単体の銅粉や鉄粉を配合しないのが好ましい。 Moreover, as the copper powder 13 which comprises the partial diffusion alloy powder 11, the irregular-shaped and dendritic copper powder currently used widely can be used widely, for example, electrolytic copper powder, atomized copper powder, etc. are used. In the present embodiment, an atomized copper powder having a large number of irregularities on the surface, an irregular shape that approximates a spherical shape as a whole particle, and excellent in formability is used. As the copper powder 13, one having a smaller particle diameter than the iron powder 12 is used, and specifically, one having an average particle diameter of 5 μm or more and 20 μm or less (preferably less than 20 μm) is used. In addition, the ratio of Cu in each partial diffusion alloy powder 11 is 10 to 30% by mass (preferably 22 to 26% by mass), and the mass ratio of copper contained in the sintered body 4 ″ obtained in the sintering step P3. (Strictly speaking, it is the same as the mass ratio of copper when the sintered body 4 ″ does not contain Sn or C). That is, in this embodiment, the raw material powder 10 does not contain a single copper powder or iron powder. The raw material powder may contain a single copper powder or iron powder, but if a single copper powder is mixed, it is difficult to improve the wear resistance of the bearing surface 4a. Therefore, for example, when the shaft 3 collides with the bearing surface 4a as the shaft 3 rotates, an indentation (dent) is easily formed on the bearing surface 4a. Moreover, when a single iron powder is blended, it becomes difficult to obtain a sintered body (sintered bearing) having a desired crushing strength. Therefore, it is preferable not to mix a single copper powder or iron powder into the raw material powder.
［低融点金属粉］
低融点金属粉としては、融点が７００℃以下の金属粉、例えば錫、亜鉛、リン等の粉末が使用される。本実施形態では、これらの中でも銅と鉄に拡散し易く（相性が良く）、また単粉で使用できる錫粉１４（図６参照）、特にアトマイズ錫粉を使用する。錫粉（アトマイズ錫粉）１４としては、平均粒径５〜６３μｍのものが好ましく使用され、平均粒径２０〜４５μｍのものが一層好ましく使用される。錫粉１４は、原料粉末１０に対して０．５〜３．０質量％配合される。
[Low melting point metal powder]
As the low melting point metal powder, 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. In this embodiment, among these, tin powder 14 (see FIG. 6), which is easily diffused into copper and iron (good compatibility) and can be used as a single powder, particularly atomized tin powder is used. As the tin powder (atomized tin powder) 14, one having an average particle diameter of 5 to 63 μm is preferably used, and one having an average particle diameter of 20 to 45 μm is more preferably used. The tin powder 14 is blended in an amount of 0.5 to 3.0 mass% with respect to the raw material powder 10.
［固体潤滑剤］
固体潤滑剤としては、黒鉛、二硫化モリブデン等の粉末を一種又は二種以上使用することができる。本実施形態では、コストを考えて黒鉛粉、特に鱗片状黒鉛粉を使用する。黒鉛粉は、原料粉末１０に対して０．３〜１．５質量％配合される。
[Solid lubricant]
As the solid lubricant, one or more powders such as graphite and molybdenum disulfide can be used. In the present embodiment, graphite powder, particularly scaly graphite powder is used in consideration of cost. The graphite powder is blended in an amount of 0.3 to 1.5 mass% with respect to the raw material powder 10.
（Ｂ）圧縮成形工程Ｐ２
この圧縮成形工程Ｐ２では、図５（ａ）（ｂ）に示すような成形金型２０を使用して原料粉末１０を圧縮成形することにより、図１等に示す焼結軸受４に近似した形状（略完成品形状）をなしたリング状の圧粉体４’を得る。成形金型２０は、主要な構成として、同軸配置されたコア２１、上下パンチ２２，２３およびダイ２４を有する。成形金型２０は、例えばカム式成形プレス機のダイセットにセットされる。
(B) Compression molding process P2
In this compression molding process P2, the shape approximated to the sintered bearing 4 shown in FIG. 1 and the like is obtained by compression molding the raw material powder 10 using a molding die 20 as shown in FIGS. A ring-shaped green compact 4 ′ (substantially finished product shape) is obtained. The molding die 20 has a core 21, upper and lower punches 22 and 23, and a die 24 that are coaxially arranged as main components. The molding die 20 is set in a die set of a cam type molding press, for example.
上記構成の成形金型２０において、コア２１、下パンチ２３およびダイ２４で画成されるキャビティ２５内に原料粉末１０を充填してから、上パンチ２２を下パンチ２３に対して相対的に接近移動させ、原料粉末１０を適当な加圧力（成形すべき圧粉体の形状や大きさに応じて設定される）で圧縮成形する。これにより、焼結軸受４に近似した形状の圧粉体４’が得られる。そして、上パンチ２２を上昇移動させると共に下パンチ２３を上昇移動させ、圧粉体４’をキャビティ２５外に排出する。図６に模式的に示すように、圧粉体４’では、部分拡散合金粉１１、錫粉１４および黒鉛粉（図示せず）が均一に分散している。本実施形態では部分拡散合金粉１１を構成する鉄粉１２として還元鉄粉を使用しているため、アトマイズ鉄粉を使用した部分拡散合金粉に比べて粉末が柔らかく、圧縮成形性に優れる。そのため、低密度でも圧粉体４’の強度を高めることができ、圧粉体４’に欠けや割れが生じるのを防止することができる。 In the molding die 20 having the above-described configuration, the raw powder 10 is filled in the cavity 25 defined by the core 21, the lower punch 23 and the die 24, and then the upper punch 22 is moved closer to the lower punch 23. The raw material powder 10 is compressed and molded with an appropriate pressure (set according to the shape and size of the green compact to be molded). Thereby, a green compact 4 ′ having a shape approximating that of the sintered bearing 4 is obtained. Then, the upper punch 22 is moved up and the lower punch 23 is moved up, and the green compact 4 ′ is discharged out of the cavity 25. As schematically shown in FIG. 6, in the green compact 4 ′, the partial diffusion alloy powder 11, tin powder 14, and graphite powder (not shown) are uniformly dispersed. In this embodiment, since reduced iron powder is used as the iron powder 12 constituting the partial diffusion alloy powder 11, the powder is softer and more excellent in compression moldability than the partial diffusion alloy powder using atomized iron powder. Therefore, the strength of the green compact 4 ′ can be increased even at a low density, and chipping and cracking can be prevented from occurring in the green compact 4 ′.
（Ｃ）焼結工程Ｐ３
焼結工程Ｐ３では、圧粉体４’に焼結処理を施すことで焼結体を得る。本実施形態における焼結条件は、黒鉛粉に含まれる炭素が鉄と反応しない（炭素の拡散が生じない）条件とする。鉄−炭素の平衡状態では７２３℃に変態点があり、これを超えると鉄と炭素の反応が開始されて鉄組織中にパーライト相（γＦｅ）が形成されるが、焼結では９００℃を超えてから炭素（黒鉛）と鉄の反応が始まり、パーライト相が形成される。パーライト相はＨＶ３００以上と高硬度であることから、これが焼結軸受４の鉄組織中に存在していれば軸受面４ａの耐摩耗性を高め、高面圧下での軸受面４ａの摩耗を抑制して軸受寿命を向上させることができる。
(C) Sintering process P3
In the sintering step P3, a sintered body is obtained by subjecting the green compact 4 ′ to a sintering process. The sintering conditions in the present embodiment are such that the carbon contained in the graphite powder does not react with iron (carbon diffusion does not occur). In the iron-carbon equilibrium state, there is a transformation point at 723 ° C., and beyond this, the reaction between iron and carbon is initiated and a pearlite phase (γFe) is formed in the iron structure. After that, the reaction between carbon (graphite) and iron begins, and a pearlite phase is formed. Since the pearlite phase has a high hardness of HV300 or higher, if it is present in the iron structure of the sintered bearing 4, it enhances the wear resistance of the bearing surface 4a and suppresses the wear of the bearing surface 4a under high surface pressure. Thus, the bearing life can be improved.
そこで、本実施形態では、焼結後の鉄組織（焼結体の鉄組織）中にパーライト相が含まれるような条件、より詳しくは、焼結後の鉄組織が、相対的に軟質のフェライト相（ＨＶ２００以下）と、相対的に硬質のパーライト相の二相組織で構成されるような条件で圧粉体４’を焼結する。但し、高硬度のパーライト相は相手材に対する攻撃性が強いため、焼結軸受４の鉄組織中に過剰にパーライト相が存在すると、軸３の摩耗を進行させるおそれがある。これを防止するため、図７に示すように、パーライト相γＦｅはフェライト相αＦｅの粒界に存在（点在）する程度に抑える。ここでいう「粒界」は、粉末粒子間に形成される粒界の他、粉末粒子中に形成される結晶粒界の双方を意味する。定量的に示すならば、鉄組織におけるフェライト相αＦｅおよびパーライト相γＦｅの存在割合は、焼結体の任意断面における面積比でそれぞれ８０〜９５％および５〜２０％（αＦｅ：γＦｅ＝８０〜９５％：５〜２０％）程度とするのが望ましい。これにより、軸３の摩耗抑制と軸受面４ａの耐摩耗性向上の両立が図られた焼結軸受４を得ることができる。 Therefore, in the present embodiment, the condition that the pearlite phase is included in the sintered iron structure (iron structure of the sintered body), more specifically, the iron structure after sintering is a relatively soft ferrite. The green compact 4 ′ is sintered under such a condition that it is composed of a two-phase structure of a phase (HV200 or less) and a relatively hard pearlite phase. However, since the high-hardness pearlite phase has a strong attacking property against the counterpart material, if the pearlite phase is excessively present in the iron structure of the sintered bearing 4, the shaft 3 may be worn. In order to prevent this, as shown in FIG. 7, the pearlite phase γFe is suppressed to the extent that it exists (is scattered) at the grain boundary of the ferrite phase αFe. The term “grain boundary” as used herein means both a grain boundary formed between powder particles and a crystal grain boundary formed in the powder particle. If quantitatively shown, the abundance ratios of the ferrite phase αFe and the pearlite phase γFe in the iron structure are 80 to 95% and 5 to 20% (αFe: γFe = 80 to 95) in the area ratio in the arbitrary cross section of the sintered body, respectively. %: About 5 to 20%). As a result, it is possible to obtain the sintered bearing 4 in which the wear of the shaft 3 is suppressed and the wear resistance of the bearing surface 4a is improved.
パーライト相γＦｅの析出量は、主に焼結温度と雰囲気ガスに依存する。従って、パーライト相γＦｅとフェライト相αＦｅの二相組織からなり、かつパーライト相γＦｅがフェライト相αＦｅの粒界に存在する程度の鉄組織を得るためには、圧粉体４’の加熱温度（焼結温度）を８２０℃以上９００℃以下に設定する。また、焼結雰囲気は、ブタンやプロパン等の液化石油ガスと空気を混合してＮｉ触媒で熱分解させた吸熱型ガス（ＲＸガス）、あるいは天然ガス等、炭素を含むガス雰囲気とする。これにより、焼結時にはガスに含まれる炭素が鉄に拡散するので、上述した程度のパーライト相γＦｅを形成することができる。なお、上述のとおり、９００℃を超える温度で圧粉体４’を加熱・焼結すると、黒鉛粉に含まれる炭素が鉄と反応するため、焼結体の鉄組織中にパーライト相γＦｅが過剰に形成されることになる。従って、圧粉体４’の焼結温度は９００℃以下に設定するのが肝要である。なお、原料粉末１０に流体潤滑材等の各種成形潤滑剤を含めていた場合、成形潤滑剤は、焼結に伴って揮散する。 The precipitation amount of the pearlite phase γFe mainly depends on the sintering temperature and the atmospheric gas. Therefore, in order to obtain an iron structure having a pearlite phase γFe and a ferrite phase αFe and a pearlite phase γFe existing at the grain boundary of the ferrite phase αFe, a heating temperature (firing temperature) of the green compact 4 ′ is obtained. Setting temperature) is set to 820 ° C. or higher and 900 ° C. or lower. The sintering atmosphere is an endothermic gas (RX gas) obtained by mixing liquefied petroleum gas such as butane or propane and air and thermally decomposing with a Ni catalyst, or a gas atmosphere containing carbon such as natural gas. Thereby, carbon contained in the gas diffuses into iron during sintering, so that the pearlite phase γFe of the above-described degree can be formed. As described above, when the green compact 4 ′ is heated and sintered at a temperature exceeding 900 ° C., carbon contained in the graphite powder reacts with iron, so that the pearlite phase γFe is excessive in the iron structure of the sintered body. Will be formed. Therefore, it is important to set the sintering temperature of the green compact 4 'to 900 ° C or lower. In addition, when various shaping | molding lubricants, such as a fluid lubricant, are included in the raw material powder 10, a shaping | molding lubricant volatilizes with sintering.
圧粉体４’を上記の条件で加熱・焼結することにより得られた焼結体４”は、Ｃｕを１０〜３０質量％（好ましくは２２〜２６質量％）、Ｓｎを０．５〜３．０質量％（好ましくは１．０〜３．０質量％）、Ｃを０．３〜１．５質量％（好ましくは０．５〜１．０質量％）含有し、残部が鉄および不可避的不純物からなる。このように、焼結体４”は、その金属組織の大部分が鉄（鉄組織）で構成されるので、機械的強度に優れたものとなる。その一方、この焼結体４”は、金属組織中に一定量の銅を含むので、軸３との初期なじみ性に優れた軸受面４ａを得ることができる。特に、圧粉体４’の焼結温度を銅の融点（１０８３℃）よりも低温に設定した上記の焼結条件であれば、焼結に伴って圧粉体４’に含まれる銅粉１３は溶融せず、従って、焼結に伴って銅が鉄（鉄組織）中に拡散しない。そのため、焼結体４”の表面（軸受面４ａ）には青銅相を含む適量の銅組織が形成されている。また、焼結体４”の表面には遊離黒鉛も露出する。そのため、軸３との初期なじみ性が良好で、摩擦係数が小さい軸受面４ａを得ることができる。Ｓｎの配合量を増やせば機械的強度の高い焼結体４”（焼結軸受４）を得ることができるが、Ｓｎの量が過剰となると粗大気孔が増え、軸受面４ａの耐摩耗性低下を招来するため、上記の配合割合（Ｃｕの配合割合に対して１０％程度の配合割合）としている。 The sintered body 4 ″ obtained by heating and sintering the green compact 4 ′ under the above conditions has a Cu content of 10 to 30 mass% (preferably 22 to 26 mass%) and an Sn content of 0.5 to 0.5%. 3.0% by mass (preferably 1.0-3.0% by mass), 0.3-1.5% by mass (preferably 0.5-1.0% by mass) of C, the balance being iron and Thus, the sintered body 4 ″ is excellent in mechanical strength because most of its metal structure is composed of iron (iron structure). On the other hand, since this sintered body 4 ″ contains a certain amount of copper in the metal structure, it is possible to obtain a bearing surface 4a that is excellent in initial conformability with the shaft 3. In particular, the green compact 4 ′. If the above sintering conditions are set at a sintering temperature lower than the melting point of copper (1083 ° C.), the copper powder 13 contained in the green compact 4 ′ does not melt with the sintering, so As a result, copper does not diffuse into the iron (iron structure). Therefore, an appropriate amount of copper structure including a bronze phase is formed on the surface (bearing surface 4a) of the sintered body 4 ″. Further, free graphite is also exposed on the surface of the sintered body 4 ″. Therefore, it is possible to obtain a bearing surface 4a having good initial conformability with the shaft 3 and a small friction coefficient. If the amount of Sn is increased, A sintered body 4 ″ (sintered bearing 4) having a high mechanical strength can be obtained. However, if the amount of Sn is excessive, rough air holes increase and the wear resistance of the bearing surface 4a is reduced. The blending ratio (mixing ratio of about 10% with respect to the Cu blending ratio) is used.
焼結体４”には、鉄を主成分とする鉄組織および銅からなる銅組織が形成される。本実施形態では、原料粉末に鉄粉単体や銅粉単体が添加されておらず、添加されているにしても微量であるので、焼結体４”の全ての鉄組織および銅組織が部分拡散合金粉１１を主体として形成される。部分拡散合金粉では、銅粉の一部が鉄粉に拡散しているため、焼結後の鉄組織と銅組織の間で高いネック強度を得ることができる。また、圧粉体４’の焼結時には、圧粉体４’中の錫粉１４が溶融し、部分拡散合金粉１１を構成する銅粉１３の表面を濡らす。これに伴い、液相焼結が進行し、図７に示すように、隣り合う部分拡散合金粉１１の鉄組織と銅組織、あるいは銅組織同士を結合する青銅相（Ｃｕ−Ｓｎ）１６が形成される。また、個々の部分拡散合金粉１１のうち、鉄粉１２の表面に銅粉１３の一部が拡散してＦｅ−Ｃｕ合金が形成された部分には、溶融したＳｎが拡散してＦｅ−Ｃｕ−Ｓｎ合金（合金相）１７が形成されるため、焼結体４”における鉄組織と銅組織間のネック強度が一層高くなる。そのため、ＮｉやＭｏ等の高価な金属粉末を使用することなく、また、上述したような低温焼結でも、高い機械的強度（圧環強度）、具体的には３００ＭＰａ以上の圧環強度を有する焼結体４”、ひいては焼結軸受４を得ることができる。また、軸受面４ａを硬くして軸受面４ａの耐摩耗性を向上させることもできる。なお、図７においては、フェライト相αＦｅやパーライト相γＦｅなどを色の濃淡で表現している。具体的には、フェライト相αＦｅ→青銅相１６→Ｆｅ−Ｃｕ−Ｓｎ合金１７→パーライト相γＦｅの順に色を濃くしている。 In the sintered body 4 ″, an iron structure mainly composed of iron and a copper structure composed of copper are formed. In the present embodiment, the iron powder alone or the copper powder alone is not added to the raw material powder. However, since the amount is very small, all the iron structure and copper structure of the sintered body 4 ″ are formed mainly of the partial diffusion alloy powder 11. In the partial diffusion alloy powder, since a part of the copper powder is diffused in the iron powder, a high neck strength can be obtained between the sintered iron structure and the copper structure. Further, when the green compact 4 ′ is sintered, the tin powder 14 in the green compact 4 ′ is melted and wets the surface of the copper powder 13 constituting the partial diffusion alloy powder 11. Along with this, liquid phase sintering proceeds, and as shown in FIG. 7, an iron structure and a copper structure of adjacent partial diffusion alloy powder 11, or a bronze phase (Cu—Sn) 16 that bonds the copper structures to each other is formed. Is done. In addition, among the individual partial diffusion alloy powders 11, molten Sn is diffused and Fe—Cu is diffused in a part where a part of the copper powder 13 is diffused on the surface of the iron powder 12 to form an Fe—Cu alloy. Since the Sn alloy (alloy phase) 17 is formed, the neck strength between the iron structure and the copper structure in the sintered body 4 ″ is further increased. Therefore, without using expensive metal powders such as Ni and Mo Further, even by low-temperature sintering as described above, a sintered body 4 ″ having a high mechanical strength (crushing strength), specifically a crushing strength of 300 MPa or more, and thus a sintered bearing 4 can be obtained. Further, the bearing surface 4a can be hardened to improve the wear resistance of the bearing surface 4a. In FIG. 7, the ferrite phase αFe, the pearlite phase γFe, and the like are represented by shades of color. Specifically, the colors are darkened in the order of ferrite phase αFe → bronze phase 16 → Fe—Cu—Sn alloy 17 → pearlite phase γFe.
また、部分拡散合金粉１１として、平均粒度１４５メッシュ以下（平均粒径１０６μｍ以下）の粉末を使用しているので、焼結体４”の多孔質組織を均一化して粗大気孔の生成を防止することができる。そのため、焼結体４”を高密度化して軸受面４ａの耐摩耗性や圧環強度をさらに高めることができる。 Further, since the powder having an average particle size of 145 mesh or less (average particle size of 106 μm or less) is used as the partial diffusion alloy powder 11, the porous structure of the sintered body 4 ″ is made uniform to prevent the formation of rough atmospheric pores. Therefore, the sintered body 4 ″ can be densified to further increase the wear resistance and the crushing strength of the bearing surface 4a.
粗大気孔は特に焼結体４”の表層部（焼結体表面から深さ１００μｍに至るまでの領域）で生じやすいが、以上のようにして得られた焼結体４”であれば、上記のように表層部における粗大気孔の発生を防止して表層部の高密度化を図ることができる。具体的には、表層部の気孔率を、５〜２０％にすることができる。この気孔率は、例えば焼結体４”の任意断面における気孔部の面積比率を画像解析することで求めることができる。 The coarse air holes are particularly likely to occur in the surface layer portion (region from the sintered body surface to a depth of 100 μm) of the sintered body 4 ″, but if the sintered body 4 ″ obtained as described above is used, As described above, it is possible to prevent the formation of rough air holes in the surface layer portion and increase the density of the surface layer portion. Specifically, the porosity of the surface layer portion can be 5 to 20%. This porosity can be obtained, for example, by image analysis of the area ratio of the pores in an arbitrary cross section of the sintered body 4 ″.
このように表層部が高密度化されることで表面開孔率が比較的小さい軸受面４ａ、具体的には、表面開孔率が５％以上２０％以下に設定された軸受面４ａを得ることができる。なお、特に軸受面４ａの表面開孔率が５％を下回ると、軸受隙間に必要十分量の潤滑油を滲み出させることが難しくなり（油膜形成能力が不十分となり）、焼結軸受４としてのメリットを得ることができない。 By increasing the density of the surface layer portion in this manner, a bearing surface 4a having a relatively small surface opening ratio, specifically, a bearing surface 4a having a surface opening ratio set to 5% or more and 20% or less is obtained. be able to. In particular, when the surface opening ratio of the bearing surface 4a is less than 5%, it becomes difficult to exude a necessary and sufficient amount of lubricating oil into the bearing gap (the oil film forming ability becomes insufficient), and the sintered bearing 4 is obtained. The benefits of can not be obtained.
また、この焼結体４”を得るための原料粉末は、鉄粉１２の表面に銅粉１３を部分拡散させた部分拡散合金粉１１を主原料としているため、既存の鉄銅系焼結軸受で問題となる銅の偏析を防止することができる。 Moreover, since the raw material powder for obtaining this sintered body 4 '' uses, as a main raw material, a partial diffusion alloy powder 11 in which the copper powder 13 is partially diffused on the surface of the iron powder 12, the existing iron-copper sintered bearing Thus, segregation of copper which is a problem can be prevented.
圧粉体４’の焼結条件は、以上で述べたように、焼結後の鉄組織がフェライト相αＦｅとパーライト相γＦｅの二相組織で構成されるように設定する他、焼結後の鉄組織が全てフェライト相αＦｅとなるように設定することもできる。具体的には、圧粉体４’の加熱温度を８００℃（好ましくは８２０℃）以上８８０℃以下に設定し、また、焼結雰囲気を、炭素を含有しないガス雰囲気（水素ガス、窒素ガス、アルゴンガス等）あるいは真空とする。このような焼結条件であれば、原料粉末で炭素と鉄の反応が生じず、また、ガスに含まれる炭素が鉄に拡散することもない。従って、焼結後の鉄組織を全て軟質のフェライト相で構成することができる。 As described above, the sintering condition of the green compact 4 ′ is set so that the iron structure after sintering is composed of a two-phase structure of the ferrite phase αFe and the pearlite phase γFe. It can also be set so that the entire iron structure becomes the ferrite phase αFe. Specifically, the heating temperature of the green compact 4 ′ is set to 800 ° C. (preferably 820 ° C.) or more and 880 ° C. or less, and the sintering atmosphere is a gas atmosphere containing no carbon (hydrogen gas, nitrogen gas, Argon gas etc.) or vacuum. Under such sintering conditions, the reaction between carbon and iron does not occur in the raw material powder, and carbon contained in the gas does not diffuse into iron. Therefore, the iron structure after sintering can be composed entirely of a soft ferrite phase.
（Ｄ）サイジング工程Ｐ４
以上のようにして得られた焼結体４”は、サイジング工程Ｐ４においてサイジングが施される。これにより、焼結体４”が仕上がり形状・寸法に仕上げられる。なお、サイジングは必要に応じて施せば足り、必ずしも施す必要はない。すなわち、焼結工程Ｐ３で得られた焼結体４”の各部が所望の形状・寸法等に仕上がっていれば、サイジング工程Ｐ４を省略しても構わない。
(D) Sizing process P4
The sintered body 4 ″ obtained as described above is subjected to sizing in the sizing step P4. Thus, the sintered body 4 ″ is finished into a finished shape and size. Note that sizing is sufficient if necessary, and is not necessarily performed. That is, the sizing step P4 may be omitted if each part of the sintered body 4 ″ obtained in the sintering step P3 is finished in a desired shape and size.
（Ｅ）含油工程Ｐ５
各部が仕上がり形状・寸法に仕上げられた焼結体４”は、含油工程Ｐ５において、その内部気孔に真空含浸等の手法により、上述した潤滑油（あるいは液状グリース）が含浸させられる。これにより、図１に示す焼結軸受４が完成する。用途によってはこの含油工程Ｐ５を省略し、無給油下で使用する焼結軸受とすることもできる。
(E) Oil impregnation process P5
The sintered body 4 ″ having each part finished to the finished shape and size is impregnated with the above-described lubricating oil (or liquid grease) in the internal pores by a technique such as vacuum impregnation in the oil impregnation step P5. The sintered bearing 4 shown in Fig. 1 is completed, and depending on the application, the oil impregnation step P5 may be omitted and a sintered bearing used without oil supply may be used.
上述したように、本実施形態の製造工程を経て得られた焼結軸受４（焼結体４”）は３００ＭＰａ以上の圧環強度を有しており、この圧環強度の値は、既存の鉄銅系焼結軸受のそれに比べて２倍以上の値である。また、本実施形態の焼結軸受４の密度は６．８±０．３ｇ／ｃｍ3となり、既存の鉄銅系焼結軸受の密度（６．６ｇ／ｃｍ3程度）よりも高密度となる。既存の鉄銅系焼結軸受でも圧粉体の成形工程で高圧縮することで高密度化することは可能であるが、このようにすると、内部の流体潤滑剤が焼結時に燃焼できずにガス化するため、表層部の気孔が粗大化してしまう。本発明に係る製法では圧粉体の圧縮成形時に高圧縮する必要はなく、そのような不具合を防止することができる。 As described above, the sintered bearing 4 (sintered body 4 ″) obtained through the manufacturing process of the present embodiment has a crushing strength of 300 MPa or more. The density of the sintered bearing 4 of this embodiment is 6.8 ± 0.3 g / cm 3 , which is more than twice that of the sintered sintered bearing. The density is higher than the density (about 6.6 g / cm 3 ) .Although existing iron-copper sintered bearings can be densified by high compression in the green compact molding process, As a result, the internal fluid lubricant cannot be combusted during sintering and gasifies, and the pores of the surface layer portion become coarse.In the manufacturing method according to the present invention, it is necessary to perform high compression during compression molding of a green compact. Therefore, such a problem can be prevented.
このように焼結体４”を高密度化させる一方で、含油率を１５ｖｏｌ％以上にすることができ、既存の鉄銅系焼結軸受と同程度の含油率を確保できる。これは、主に部分拡散合金粉１１を構成する鉄粉１２として、海綿状をなし、保油性に優れた還元鉄粉を使用していることに由来する。この場合、焼結体４”に含浸させた潤滑油は、焼結組織の粒子間に形成された気孔だけでなく、還元鉄粉が有する気孔にも保持される。 Thus, while densifying the sintered body 4 ″, the oil content can be increased to 15 vol% or more, and an oil content comparable to that of an existing iron-copper sintered bearing can be secured. This is because the iron powder 12 constituting the partial diffusion alloy powder 11 is spongy and uses reduced iron powder excellent in oil retaining property. In this case, lubrication impregnated in the sintered body 4 ″ The oil is held not only in the pores formed between the particles of the sintered structure, but also in the pores of the reduced iron powder.
以上で説明したように、本発明に係る製造方法で得られた焼結軸受４は高い圧環強度（３００ＭＰａ以上の圧環強度）を有する焼結体４”からなるため、ハウジング２の内周に圧入固定した場合でも、軸受面４ａがハウジング２の内周面形状に倣って変形することがなく、取り付け後も軸受面４ａの真円度や円筒度等を安定的に維持することができる。そのため、ハウジング２の内周に焼結軸受４を圧入固定した後、軸受面４ａを適正形状・精度に仕上げるための加工（例えばサイジング）を追加的に実行することなく、所望の真円度（例えば３μｍ以下の真円度）を得ることができる。加えて、軸受面４ａが高い耐摩耗性を有するため、たとえ軸受面４ａの全面を軸３が振れ回り、あるいは軸３が軸受面４ａに頻繁に衝突したとしても、軸受面４ａの摩耗や損傷が抑えられる。従って、本発明に係る製造方法で得られた焼結軸受４によれば、信頼性および耐久性に優れた振動モータを低コストに提供することができる。 As described above, since the sintered bearing 4 obtained by the manufacturing method according to the present invention is composed of the sintered body 4 ″ having a high crushing strength (crushing strength of 300 MPa or more), it is press-fitted into the inner periphery of the housing 2. Even when the bearing surface 4a is fixed, the bearing surface 4a does not deform following the shape of the inner peripheral surface of the housing 2, and the roundness, cylindricity, etc. of the bearing surface 4a can be stably maintained even after the mounting. After the sintered bearing 4 is press-fitted and fixed to the inner periphery of the housing 2, a desired roundness (for example, a desired roundness (for example, sizing) without additional processing (for example, sizing) for finishing the bearing surface 4 a to an appropriate shape and accuracy) is performed. In addition, since the bearing surface 4a has high wear resistance, the shaft 3 swings around the entire bearing surface 4a or the shaft 3 frequently contacts the bearing surface 4a. Even if it collides with Wear and damage of the surface 4a can be suppressed. Therefore, according to the sintered bearing 4 obtained by the manufacturing method according to the present invention, it is possible to provide a vibration motor having excellent reliability and durability at a low cost.
ここで、参考までに、本発明に係る製造方法で得られた焼結軸受４の表層部の顕微鏡写真を図８に示し、特許文献１に記載の技術手段に係る焼結軸受（以下、「銅被覆鉄粉軸受」という）の表層部の顕微鏡写真を図９に示す。図８と図９とを比較すると、焼結軸受４は、銅被覆鉄粉軸受に比べて表層部の多孔質組織が緻密であることが容易に理解される。実際、焼結軸受４の表層部の気孔率は１３．６％だったのに対し、銅被覆鉄粉軸受の表層部の気孔率は２５．５％程度であった。このような差を生じた要因として、銅被覆鉄粉では鉄粉に銅膜が密着しているにすぎず、鉄組織と銅組織の間のネック強度が不足していることが挙げられる。 Here, for reference, a micrograph of a surface layer portion of the sintered bearing 4 obtained by the manufacturing method according to the present invention is shown in FIG. 8, and a sintered bearing (hereinafter, “ FIG. 9 shows a micrograph of the surface layer portion of “copper-coated iron powder bearing”. Comparing FIG. 8 and FIG. 9, it is easily understood that the sintered bearing 4 has a dense porous structure in the surface layer portion as compared with the copper-coated iron powder bearing. Actually, the porosity of the surface layer portion of the sintered bearing 4 was 13.6%, whereas the porosity of the surface layer portion of the copper-coated iron powder bearing was about 25.5%. As a factor causing such a difference, copper-coated iron powder only has a copper film in close contact with the iron powder, and the neck strength between the iron structure and the copper structure is insufficient.
本発明の実施の形態は以上に述べたものに限定されず、本発明の要旨を逸脱しない範囲で適宜の変更を施すことが可能である。 Embodiments of the present invention are not limited to those described above, and appropriate modifications can be made without departing from the scope of the present invention.
例えば、焼結軸受４の鉄組織や銅組織の全てを部分拡散合金粉だけで形成する場合を説明したが、原料粉末に単体鉄粉および単体銅粉のうちどちらか一方または双方を添加し、鉄組織や銅組織の一部を単体鉄粉や単体銅粉で形成することもできる。この場合、最低限の耐摩耗性、強度、および摺動特性を確保するため、原料粉末における部分拡散合金粉の割合は５０質量％以上にするのが好ましい。また、この場合、原料粉末中の固体潤滑剤粉の配合割合は０．３〜１．５質量％が適量である。さらに原料粉末における低融点金属粉の配合割合は０．５〜５．０質量％とする。この配合割合は原料粉末中における銅粉の総量（部分拡散合金粉中の銅粉と別途添加された単体銅粉の和）の１０質量％程度に設定するのが好ましい。原料粉末の残部が単体鉄粉もしくは単体銅粉（あるいは双方の単体粉）、および不可避的不純物で形成されることになる。 For example, the case where all of the iron structure and the copper structure of the sintered bearing 4 are formed only by the partial diffusion alloy powder has been described, but one or both of the simple iron powder and the simple copper powder are added to the raw material powder, A part of the iron structure or copper structure can also be formed of simple iron powder or simple copper powder. In this case, in order to ensure the minimum wear resistance, strength, and sliding characteristics, the proportion of the partial diffusion alloy powder in the raw material powder is preferably 50% by mass or more. Further, in this case, the blending ratio of the solid lubricant powder in the raw material powder is 0.3 to 1.5% by mass. Furthermore, the blending ratio of the low melting point metal powder in the raw material powder is 0.5 to 5.0 mass%. This blending ratio is preferably set to about 10% by mass of the total amount of copper powder in the raw material powder (the sum of the copper powder in the partial diffusion alloy powder and the single copper powder added separately). The remainder of the raw material powder is formed of simple iron powder or simple copper powder (or simple powders of both) and inevitable impurities.
かかる構成では、単体鉄粉や単体銅粉の配合量を変更することにより、部分拡散合金粉を使用することで得られる耐摩耗性、高強度、および良好な摺動特性を維持しつつ、軸受特性を調整することが可能となる。例えば単体鉄粉を添加すれば、部分拡散合金粉の使用量減による低コスト化を図りつつ軸受の耐摩耗性や強度を高めることができ、単体銅粉を添加すれば摺動特性をさらに改善することができる。そのため、各種用途に適合した焼結軸受の開発コストを低廉化することができ、焼結軸受の多品種少量生産にも対応可能となる。 In such a configuration, the bearing amount is maintained while maintaining the wear resistance, high strength, and good sliding characteristics obtained by using the partial diffusion alloy powder by changing the blending amount of the single iron powder and the single copper powder. The characteristics can be adjusted. For example, by adding simple iron powder, it is possible to increase the wear resistance and strength of the bearing while reducing the cost by reducing the amount of partially diffused alloy powder, and by adding simple copper powder, the sliding characteristics are further improved. can do. As a result, the development cost of sintered bearings suitable for various applications can be reduced, and it is possible to cope with the production of various types of sintered bearings in small quantities.
例えば、圧粉体４’を圧縮成形する圧縮成形工程Ｐ２では、成形金型２０および原料粉末１０の少なくとも一方を加熱した状態で圧粉体４’を圧縮成形する、いわゆる温間成形法や、成形金型２０の成形面（キャビティ２５の画成面）に潤滑剤を塗布した状態で圧粉体４’を圧縮成形する金型潤滑成形法を採用しても良い。このような方法を採用すれば、圧粉体４’を一層精度良く成形することができる。 For example, in the compression molding step P2 of compressing the green compact 4 ′, a so-called warm molding method in which the green compact 4 ′ is compression molded in a state where at least one of the molding die 20 and the raw material powder 10 is heated, A mold lubrication molding method may be employed in which the green compact 4 ′ is compression molded in a state where a lubricant is applied to the molding surface of the molding die 20 (the defined surface of the cavity 25). By adopting such a method, the green compact 4 ′ can be molded with higher accuracy.
また、以上で説明した振動モータ１は、軸３を回転側、焼結軸受４を静止側とした軸回転タイプであるが、振動モータ１としては、軸３を静止側、焼結軸受４を回転側とした軸固定タイプもあり、このような軸固定タイプの振動モータ１であっても本発明に係る製造方法で得られた焼結軸受４を好ましく使用することができる。また、焼結軸受４の軸受面４ａには、動圧溝等の動圧発生部を設けることもできる。このようにすれば、軸受隙間に形成される油膜の剛性を高めることができるので回転精度を一層高めることができる。さらに、本発明に係る製造方法で得られた焼結軸受４は、機械的強度が高く、軸受面４ａの耐摩耗性にも優れていることから、振動モータに限らず、高速でアンバランス荷重の大きいモータの主軸支持用途をはじめ、各種モータに組み込んで軸を回転自在に支持する軸受として広く使用することができる。 The vibration motor 1 described above is a shaft rotation type in which the shaft 3 is the rotation side and the sintered bearing 4 is the stationary side. However, as the vibration motor 1, the shaft 3 is the stationary side and the sintered bearing 4 is There is also a shaft-fixed type on the rotation side, and the sintered bearing 4 obtained by the manufacturing method according to the present invention can be preferably used even with such a shaft-fixed type vibration motor 1. Further, the bearing surface 4 a of the sintered bearing 4 can be provided with a dynamic pressure generating portion such as a dynamic pressure groove. In this way, since the rigidity of the oil film formed in the bearing gap can be increased, the rotational accuracy can be further increased. Furthermore, since the sintered bearing 4 obtained by the manufacturing method according to the present invention has high mechanical strength and excellent wear resistance of the bearing surface 4a, the unbalanced load is not limited to a vibration motor. It can be widely used as a bearing for rotatably supporting a shaft by incorporating it into various motors, including a main shaft supporting application of a large motor.
１ 振動モータ
２ ハウジング
３ 軸
４ 焼結軸受
４’ 圧粉体
４” 焼結体
４ａ 軸受面
１０ 原料粉末
１１ 部分拡散合金粉
１２ 鉄粉
１３ 銅粉
１４ 錫粉（低融点金属粉）
１６ 青銅相
１７ Ｆｅ−Ｃｕ−Ｓｎ合金
２０ 成形金型
αＦｅ フェライト相
γＦｅ パーライト相
Ｍ モータ部
Ｐ１ 原料粉末生成工程
Ｐ２ 圧縮成形工程
Ｐ３ 焼結工程
Ｗ 錘
DESCRIPTION OF SYMBOLS 1 Vibration motor 2 Housing 3 Shaft 4 Sintered bearing 4 'Compact 4 "Sintered body 4a Bearing surface 10 Raw material powder 11 Partially diffused alloy powder 12 Iron powder 13 Copper powder 14 Tin powder (low melting point metal powder)
16 Bronze phase 17 Fe-Cu-Sn alloy 20 Molding die αFe Ferrite phase γFe Pearlite phase M Motor part P1 Raw material powder generation process P2 Compression molding process P3 Sintering process W Weight
Claims (8)
鉄粉に対し銅粉を部分拡散させてなる部分拡散合金粉を主原料とし、これに低融点金属粉および固体潤滑剤粉を配合した原料粉末を圧縮成形して圧粉体を得る圧縮成形工程と、圧粉体を焼結して焼結体を得る焼結工程と、を含むことを特徴とする焼結軸受の製造方法。 A method of manufacturing a sintered bearing having a bearing surface on the inner periphery that forms a bearing gap with a shaft to be supported,
Compression molding process to obtain a green compact by compression molding a raw material powder containing a low diffusion metal powder and a solid lubricant powder as a main raw material, a partial diffusion alloy powder obtained by partial diffusion of copper powder to iron powder And a sintering step of obtaining a sintered body by sintering the green compact.
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