Production method for sintered fluid dynamic pressure bearing
A sintered fluid dynamic pressure bearing completely seals or decreases the sizes of gaps formed in pores by shrinkage when a resin impregnated therein shrinks. The fluid dynamic pressure bearings can be reliably and easily produced using fewer processes while superior quality is maintained. A production method for a fluid dynamic pressure bearing includes a resin sealing process including a resin impregnating step in which a monomer of an anaerobic resin composed primarily of acrylate or methacrylate is impregnated in pores of a porous sintered compact, an excess resin washing off step in which excess resin adhering to the surface of the porous sintered compact is washed off, and a resin curing step in which the monomer of the anaerobic resin impregnated in the pores is cured by heating the porous sintered compact to at least the curing temperature of the resin after washing off the excess resin; the resin sealing process is repeatedly carried out, and a monomer of an anaerobic resin containing an organic peroxide at 0.1 to 1.0 mass % is used in at least the resin impregnating step of the last resin sealing process.
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1. Field of the Invention
The present invention relates to production methods for sintered fluid dynamic pressure bearings that are suitably used in spindle motors for disk drives and that can seal pores in porous sintered compacts.
2. Description of Related Art
Recently, in motors used in information-processing equipment, noise reduction, high rates of mass production, cost reduction, etc., are required, in addition to high speed revolution accuracy and high speed stability, in view of the need for increased data storage density and high-speed processing of information. Such performance is also required of bearings that support shafts therein. As a bearing structure, a structure in which various grooves for generating fluid dynamic pressure are provided on a bearing surface of a sintered bearing can be used. Such bearing is fixed in a housing, the housing is filled with lubricating oil, and a shaft is supported in a non-contact state by the fluid dynamic pressure of the lubricating oil generated by the grooves in the rotating shaft.
In the sintered fluid dynamic pressure bearing, in order to further increase the fluid dynamic pressure action, pores at the bearing surface or the like of the bearing are sealed or minimized. As a sealing method, a method in which the bearing is sealed by various types of blast processing or tumbler processing, or a method in which the bearing is sealed by impregnating resin in the pores of the sintered compact and curing, are disclosed in Japanese Unexamined Patent Application Publication No. 11-062948, in addition to methods for pressing sintered fluid dynamic pressure bearings at high density. In addition, in a method in which resin is impregnated and cured in pores of sintered compacts so as to seal them, a resin impregnating step, an excess resin removing step, and a resin curing step are contained, in that order, and an organic-monomer-type impregnating agent, organic-polymer-type impregnating agent, solvent-free-type impregnating agent, and aqueous-emulsion-type impregnating agent can be used (see Japanese Unexamined Patent Application Publication No. 7-216411). Furthermore, though gaps in the pores of the bearing are formed by shrinkage of the resin after the impregnated resin in the pores are cured, a method in which the gaps in the pores are decreased or sealed by deformation processing that presses a sintered compact inserted into a die, is also disclosed in Japanese Unexamined Patent Application Publication No. 2002-333023.
The above method for pressing a sintered fluid dynamic pressure bearing at a high density has a problem in that the amount of strain accumulating in a green compact is large and dimensional accuracy of the sintered compact after the sintering of the green compact is inferior because high compacting pressure is used in compacting raw material powder. In this case, the sintered compact is difficult to deform and cannot be accurately corrected, even if the dimensions are corrected by repressing, since the material has a high density. In addition, the method for sealing the bearing by various types of blast processing and tumbler processing has problems in that it is difficult to supply the bearing interior with media for the blast processing, etc., with the miniaturization of the fluid dynamic pressure bearing used for information-processing equipment, and the shape of the fluid dynamic pressure groove formed on at least one of a bore surface and an edge surface of the sintered bearing is deformed, if it is supplied by force.
In contrast, the method for sealing the pores of the sintered compact using the resin does not have the above problems, and productivity is higher than for other sealing methods. However, the opening ratio at the surface and the degree of sealing are difficult to stabilize because the impregnated amount of resin is uneven and the shrinkage ratio in the curing of the resin impregnated in the pores changes. For example, in the case in which lubricating oil is supplied as a fluid to a bearing unit in which the sintered fluid dynamic pressure bearing is assembled, an amount of absorbed oil in the sintered fluid dynamic pressure bearing is partially uneven if the sealing degree is uneven, and thereby, this causes serious problems in that the lubricating oil may easily be locally insufficient or be discontinuous. In other words, in the sintered fluid dynamic pressure bearing, partial unevenness of the oil absorption is controlled by impregnating the entirety of the pores with resin, that is, not only at the surface of the pores of the bearing, but also the interiors of the pores. However, the amount of the absorbed oil cannot be stabilized by changing the shrinkage ratio, that is, the opening ratio in curing the resin.
In addition, in the method described in Japanese Unexamined Patent Application Publication No. 2002-333023, gaps in the pores formed by curing and shrinking the resin, etc., are sealed by deformation processing in order to solve the above problems. However, since the deformation processing is an additional process, production cost is increased. As a countermeasure to this problem, it is believed that a fluid dynamic pressure groove formation process at the bearing surface may serve as the deformation processing after impregnating the resin, and this would avoid an additional mechanical process such as a deformation processing. However, in this case, deformability of the sintered compact is decreased by the resin cured in the pores of the sintered compact, and therefore, a fluid dynamic pressure groove cannot be accurately formed.
SUMMARY OF THE INVENTIONAn object of the present invention is to solve the above problems. Specifically, an object of the present invention is to provide a production method for a sintered fluid dynamic pressure bearing which can reliably and easily produce a sintered fluid dynamic pressure bearing which decreases or seals the gaps in pores formed by shrinking due to curing impregnated resin, using fewer processes, while maintaining superior quality.
A production method for a fluid dynamic pressure bearing of the present invention includes a resin sealing process including, in this order, a resin impregnating step in which a monomer of an anaerobic resin composed primarily of acrylate or methacrylate is impregnated in pores of a porous sintered compact (for example, a compact having a pore ratio of 5 to 20%), an excess resin washing off step in which excess resin adhering to the surface of the porous sintered compact is washed off, and a resin curing step in which the monomer of the anaerobic resin impregnated in the pores is cured by heating the porous sintered compact to at least the resin curing temperature after washing off the excess resin, in which the resin sealing process is repeatedly carried out, and a monomer of an anaerobic resin containing an organic peroxide at 0.1 to 1.0 mass % is used in at least the resin impregnating step of the last resin sealing process.
In the present invention, the monomer of the anaerobic resin is a liquid resin or an adhesive, in which when air (atmosphere including oxygen) is excluded, free radicals are formed by an interaction of metal ions and polymerization reaction is spontaneously started by the free radical. In addition, in the case in which the monomer of the anaerobic resin contains an organic peroxide at 0.1 to 1.0 mass %, it easily reacts with the metal ion when air is excluded, and the polymerization reaction is activated in the pores of the porous sintered compact.
In a first aspect of the present invention, the monomer containing an organic peroxide is impregnated again in the gap formed by shrinking the resin in the resin curing step, and the pores are sealed by actively polymerizing the monomer, and therefore, the sealing can be reliably and stably carried out. The sintered fluid dynamic pressure bearing produced by the present invention has superior effects in that the absorption of lubricating oil is very slight and unevenness of the absorption thereof is stable, even if the lubricating oil is used as a fluid, and in that the fluid dynamic pressure is not completely decreased during use, since the pores of the sintered compact are perfectly sealed.
In a second aspect of the present invention, the impregnating agent can be impregnated into the interiors of the pores and to the bottoms of the pores in the porous sintered compact by containing an azo compound at 0.1 to 0.5 mass % as a monomer of the anaerobic resin used in at least the first resin impregnating step, since the polymerization reaction starts at a relatively high temperature. In other words, in the case of a monomer in which a polymerization reaction is activated at a low temperature, in an initial stage of the impregnating step, only the openings of the pores are sealed and the monomer does not penetrate to the bottom of the pores. Therefore, according to the second aspect of the present invention, the above problem is solved.
In a third aspect of the present invention, the impregnating agent used in the final resin impregnating step is controlled so as to activate the polymerization reaction at the initial stage. Therefore, in the case in which the same monomer of the anaerobic resin is used in each resin sealing process (resin impregnating step) carried out several times, the porous sintered compact is impregnated into the interiors of pores and to the bottoms of the pores by carrying out at least the first resin impregnating step under conditions in which the polymerization reaction is controlled, that is, under a reduced pressure condition of 102 to 103 Pa.
In a fourth aspect of the present invention, specific organic peroxides are used. In a fifth aspect of the present invention, the monomer can be reliably impregnated and cured by containing a curing accelerator containing an organometallic compound of at most 1.0 mass %, even if the surface of the pore is covered by the first resin impregnating step and the metal ion is difficult to reach.
In a sixth aspect of the present invention, when the porous sintered compact contains Cu at at least 20 mass %, the above polymerization reaction can be activated by the presence of Cu, which is easily ionized. In addition, when copper foil powder is contained at 3 to 30 mass %, the ratio of Fe which is exposed at the surface of the pores is decreased and the exposure amount of Cu, which easily generates metal ions, is increased, and therefore, the above polymerization reaction can be further promoted. In a seventh aspect of the present invention, the quality of the sintered fluid dynamic pressure bearing is improved by carrying out a size adjusting repressing step and a fluid dynamic pressure groove forming repressing step before the resin sealing process.
DESCRIPTION OF THE PREFERRED EMBODIMENTSThe production method for sintered fluid dynamic pressure bearings of the present invention includes a resin sealing process including, in this order, a resin impregnating step in which a monomer of an anaerobic resin, composed primarily of methacrylate, is impregnated into pores of a porous sintered compact, an excess resin washing off step in which excess resin (solution) adhering on the surface of the porous sintered compact is washed off, and a resin curing step in which the monomer of the anaerobic resin impregnated into the pores is cured by heating the porous sintered compact to at least the resin curing temperature after washing off the excess resin. In particular, in the present invention, the resin sealing process is repeatedly carried out twice, and a monomer of anaerobic resin containing organic peroxide at 0.1 to 1.0 mass % is used in the resin impregnating step of the second resin sealing process.
Here, the sintered fluid dynamic pressure bearing is produced by a compacting step in which raw material powder is compacted so as to form a green compact, a sintering step which sinters the green compact, a repressing step which forms the sintered compact in a designed bearing shape by deformation processing such as sizing, etc., or the like, and then pores are sealed by the resin sealing process of the present invention. As a sealing state of the pores, it is preferable that the pores be filled 100 volume % with resin. However, in the case in which the pores are filled to 90 volume % or more, the absorption of the lubricating oil is very slight and unevenness of the absorption is stabilized, and therefore, there is no problem in practical use.
In the resin impregnating step in the above resin sealing process, a monomer of an anaerobic resin composed primarily of acrylate or methacrylate, can be used as an impregnating agent. The resin composed primarily of acrylate or methacrylate has low reactivity with lubricating oil and has a suitable strength. Therefore, it is preferable that a sintered fluid dynamic pressure bearing, in which the pores are sealed by this resin, be used in the lubricating oil, since lubricity of the lubricating oil is not deteriorated by reacting with the lubricating oil and the resin is not peeled or detached by deterioration. The monomer of the anaerobic resin composed primarily of acrylate or methacrylate includes monomers which contain acrylates or methacrylates which are well known as monomers for anaerobic resins, such as polyglycol dimethacrylate, epoxy acrylate, epoxy methacrylate, urethane acrylate, urethane methacrylate, etc., and further contains other acrylates or methacrylates as necessary. In the present invention, in order to improve the anaerobic resin, monomers other than these monomers may also be contained, as long as they do no adversely affect the present invention.
In addition, the anaerobic resin generally includes resins containing a peroxidation catalyst as an organic peroxide, and it is a resin in which the peroxidation catalyst converts to free radicals by metal ions in air-free conditions (the “air” being an atmosphere including oxygen) and the monomers are polymerized by the free radicals, so as to form polymers that are firmly crosslinked. However, when exposed to the air, the free radicals are not formed, since the monomers are stabilized by supplying oxygen, and the polymerization reaction is not started. Therefore, in such an anaerobic resin, the peroxidation catalyst is important as an initiator of the polymerization reaction. That is, in the case in which the monomer of the anaerobic resin is used as an impregnating agent, the polymerization reaction actively progresses if the peroxidation catalyst easily reacts with metal ions. In contrast, the polymerization reaction progresses slowly if it is difficult to react with metal ions.
Furthermore, the resin impregnating step is carried out by a vacuum impregnation method. Specifically, a method in which a porous sintered compact is immersed in an anaerobic resin monomer in an impregnation tank, air in pores of the porous sintered compact is removed by reducing the pressure in the impregnation tank, and the monomer is impregnated in the pores by returning to atmospheric pressure so as to draw the monomer into the pores; a method in which a porous sintered compact is placed on a stage in an impregnation tank, air in pores of the porous sintered compact is removed by reducing pressure in the impregnation tank, the porous sintered compact is immersed in an anaerobic resin monomer in the impregnation tank by lowering the stage, and the monomer is impregnated in the pores by returning to atmospheric pressure so as to draw the monomer in the pores, or the like, can be used. In these vacuum impregnation methods, pressure may be increased after returning to atmospheric pressure.
It is preferable that, as a sealing state in the sintered fluid dynamic pressure bearing, the porous sintered compact be perfectly sealed in the interior of the pores and to the bottoms thereof by the resin. That is, in a state in which only pores on the surface and in a vicinity of the surface and an opening side of the pores are sealed, the interior of the pores and the bottom sides of the pores of the porous sintered compact are deaired in the resin impregnating step so as to be in a reduced pressure state. Thus, in the case in which the seal is broken during use, there is a problem in that the lubricating oil, which is necessary for fluid lubrication, is insufficient or is removed by the lubricating oil being drawn into the pores.
Therefore, in the resin impregnating step, it is not preferable that the polymerization reaction be activated rapidly since the impregnating agent cannot reach the interior of the pores or the bottom side of the pores of the porous sintered compact by sealing the pores only on the surface and in a vicinity of the surface and an open side of the pores at an initial stage in the resin impregnation. From this point of view, it is preferable that the impregnating agent used in the first resin impregnating step be a monomer of an anaerobic resin which is composed primarily of methacrylate, which is also used in the conventional techniques and which contains azo compounds at 0.1 to 0.5 mass %. Specifically, Resinol 90C (trade name), produced by Henkel KGaA, described in Japanese Unexamined Application Publication No. 11-062948, is an anaerobic resin composed primarily of methacrylate containing azo compounds (2,2-azobis compounds) as a peroxidation catalyst. The resin can be impregnated into the interiors of pores and to the bottoms of pores of the porous sintered compact since the polymerization reaction thereof starts at about 90° C.
However, in the case in which such an impregnating agent is used and controls the polymerization reaction, in the heating and curing step, after washing off excess resin, the resin shrinks due to the polymerization and gaps are generated by the shrinkage. The gaps can be perfectly filled by repeatedly carrying out the resin-impregnating step several times. However, the time necessary for production and the production costs therefor are increased by carrying out the resin impregnating step several times.
Therefore, in a production method of the present invention, the impregnating agent is penetrated into and fills the interiors of pores and fills to the bottoms of pores in the porous sintered compact as deeply as possible in at least the first resin impregnating step, and thereby, the gap is filled by the resin impregnating step in less time and the pores are filled to at least 90 volume % by the resin. Simultaneously, the gap generated by heating and curing can be reliably filled by using an impregnating agent which is different from the first impregnating agent in a second or later resin impregnating step, or by impregnating under conditions which are different from the first impregnation condition such as reduced pressure, etc. In other words, the present invention is characterized in that the monomer of the anaerobic resin which contains the organic peroxide at 0.1 to 1.0 mass % as an impregnating agent is used in at least the final resin impregnating step. The organic peroxide is most easily reacted with metal ions among peroxidation catalysts, and it is preferably cured by actively polymerizing it in the pores of the porous sintered compact.
In order to carry out the above polymerization reaction within a suitable range, it is necessary that the organic peroxide be added at at least 0.1 mass % to the anaerobic resin. In the case in which the content of the organic peroxide is less than 0.1 mass %, the polymerization reaction is not sufficiently activated, and resealing of the pores is insufficient. In contrast, in the case in which it exceeds 1.0 mass %, the polymerization reaction is excessively activated, and it is difficult to remove excess resin since the resin is cured on the surface of the porous sintered compact.
In order to more actively carry out the polymerization reaction, it is preferable that hydroperoxides be used from among the organic peroxides. As a hydroperoxide, t-butyl hydroperoxide, cumene hydroperoxide, di-isopropyl peroxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, benzoyl peroxide, etc., can be used, and these may be used alone or in combinations.
Additionally, in the present invention, there are the following important points about the material composition of the porous sintered compact. In the case in which the porous sintered compact contains Cu at at least 20 mass %, the above polymerization reaction can be actively carried out. That is, since Cu is an element which is easy to ionize, the above polymerization reaction in (the resin curing step of) the second resin sealing process can be actively carried out. In addition, it is desirable that Cu be used by adding copper foil powder at 3 to 30 mass %. This is explained by the following mechanism. For example, in the case in which the porous sintered compact made of a copper-iron-based material is produced, the copper foil powder is adhered to the surface of the iron powder so as to cover the surface of the iron powder when the copper foil powder is added at 3 to 30 mass % to the raw material powder. In the porous sintered compact produced by pressing such raw material powder and by sintering, the ratio of Fe that is exposed on the inner wall of the pores is drastically decreased, and an exposure amount of Cu, which easily generates metal ions, is increased. As a result, Cu ions can be sufficiently supplied and the polymerization reaction can be further activated, even if the Cu content is low. Here, when the content of the copper foil powder is less than 3 mass %, the iron powder cannot be sufficiently covered. In contrast, when it exceeds 30 mass %, covering of the iron powder cannot be further improved and the production cost is increased. Therefore, the content of the copper foil powder is set to be in a range of 3 to 30 mass %.
In the present invention, the monomer of the anaerobic resin composed primarily of acrylate or methacrylate containing an organic peroxide at 0.1 to 1.0 mass %, which is used in the final resin impregnating step as an impregnating agent, can be used in the first resin impregnating step. In this case, resins that seal the pores have identical components, and therefore, the adhesion is improved and is better than that in the case in which components having different resin strength are impregnated. Here, since the impregnating agent used in the final resin impregnating step is adjusted so as to activate the polymerization reaction, in the case in which the impregnating agent is used in the first resin impregnating step, it is necessary that the impregnating agent be penetrated into and be filled into the interiors of the pores and to the bottoms of the pores of the porous sintered compact by impregnating under conditions which control the polymerization reaction. It is preferable that the polymerization reaction be controlled by the following method. That is, as described above, since in the anaerobic resin, oxygen in the organic peroxide (peroxidation catalyst) is converted to free radicals by metal ions in conditions in which oxygen is blocked from the outside, and the polymerization reaction is thereby started, the polymerization reaction can be controlled by increasing the content of the external oxygen. Specifically, by carrying out the resin impregnating step under a pressure of 102 to 103 Pa so that a small amount of oxygen remains in an impregnation tank, the impregnating agent can be reliably penetrated into and be filled into the interiors of the pores and to the bottoms of the pores of the porous sintered compact, even if the monomer of the anaerobic resin composed primarily of acrylate or methacrylate containing an organic peroxide at 0.1 to 1.0 mass % is used. Here, in order to seal gaps by activating the polymerization reaction, it is necessary that the final resin impregnating step be carried out under a pressure of not more than 102 Pa.
After impregnating the resin, excess resin adhering to the surface of the sintered compact is washed off and removed in an excess resin washing off step, and the impregnated resin is polymerized and cured by heating the porous sintered compact in which the resin is impregnated in a resin curing step. At this time, in the final resin impregnating step, it is necessary to seal the gap formed in previous resin impregnating steps. However, since the polymerization reaction can be activated in the case in which the monomer of the anaerobic resin containing an organic peroxide is used, the heating temperature for curing the resin may be reduced. In this case, blowing of uncured monomer with thermal expansion of the resin can be decreased during heating from room temperature to a curing temperature.
In addition, the impregnating agent used in the resin impregnating step may have added therein curing accelerators made of an organometallic compound at up to 1 mass % which are used in typical anaerobic resins. In particular, in the final resin impregnating step, most of the inner wall of the pores is covered by the resin which is impregnated in previous resin impregnating steps, and metal ions are difficult to reach the monomer impregnated in the final resin impregnating step, and therefore, it is preferable that a curing accelerator made of an organometallic compound be used. Here, in the case in which too much of the organometallic compound is added, the polymerization reaction is excessively in impregnating the monomer, and therefore, the addition amount of the organometallic compound should not exceed 1 mass %. As an organometallic compound, lithium dimethylcuprate, diacetyl acetone copper, calcium carbide, phenyl lithium, etc., can be used. In the present invention, organic fillers, inorganic fillers, viscosity modifiers, stabilizers, or the like, can be added in addition to these compounds, as long as they do not adversely affect the present invention.
In the case in which a fluid dynamic pressure groove is formed in a pressing process and a repressing process for adjusting dimensions and for forming a fluid dynamic pressure groove is not carried out thereafter, the above resin impregnating step may be carried out after the sintering process. However, in the case in which the repressing process is carried out after the sintering process, deformability of the sintered compact is decreased by the resin cured in the pores of the porous sintered compact, and the porous sintered compact is difficult to produce with precision, and therefore, it is necessary that the above resin impregnating step be carried out after each repressing process for adjusting dimensions and for forming a fluid dynamic pressure groove.
In the excess resin washing off step, the excess resin is completely removed. However, in the case in which a very small amount of the excess resin remains, it is preferable that the surface of the bearing be mechanically struck by a magnetic barrel or an electromagnetic barrel using stainless steel pins having a diameter of 0.1 to 1.0 mm, and preferably 0.1 to 0.6 mm, after the resin impregnating step, so that the remaining resin is completely removed.
In the sintered fluid dynamic pressure bearing produced by the above production method for a sintered fluid dynamic pressure bearing, a polymer of an anaerobic resin composed primarily of acrylate or methacrylate is perfectly impregnated and cured in the entirety of the space of the pores, which is the interior of the pores and from the bottoms to the openings of the pores. Therefore, for example, in the case in which the lubricating oil is supplied as a fluid in a bearing unit which contains the sintered fluid dynamic pressure bearing, there is no loss of the fluid dynamic pressure and no absorption of the lubricating oil.
EXAMPLES In the Examples, iron powder, electrolytic copper powder, copper foil powder, tin powder, and graphite powder were used, and a raw material powder was prepared by adding and mixing the powders at the mixing ratio shown in Table 1. Then, the raw material powder was compacted so as to form a bearing shape having an inner diameter of 2.5 mm, an outer diameter of 7 mm, and a height of 5 mm, and so as to have a density ratio of 85%, and this was sintered under an ammonia decomposition gas atmosphere at 770° C. for 30 minutes. Next, the sintered compact was subjected to a repressing step for adjusting the size thereof, and a fluid dynamic pressure groove formation repressing step for forming five circular fluid dynamic pressure shapes in bearing bore, and by doing this, 55 porous sintered compacts were produced.
As an anaerobic resin 1, Resinol 90C (trade name), produced by Henkel KGaA, which primarily uses polyglycol dimethacrylate, described in Japanese Unexamined Patent Application Publication No. 11-062948, and containing 0.3 mass % of an azo compound (2,2-azobis compound), which is a peroxidation catalyst, was prepared. In addition, as an anaerobic resin 2, PMS-50E (trade name), produced by Henkel KGaA, which primarily uses polyglycol dimethacrylate, and contains 0.8 mass % of cumene hydroperoxide, which is a peroxidation catalyst, was prepared.
With respect to the 55 porous sintered compacts produced as above, each resin sealing process in a combination of anaerobic resin and reduced pressure shown in Table 2 was carried out on 11 porous sintered compacts thereof, and Samples A to E were produced. Here, the resin sealing process was carried out by the following steps. That is, in the resin impregnating step, the porous sintered compact was placed on a stage in an impregnation tank and air in the pores of the porous sintered compact was removed by reducing the pressure in the impregnation tank. Then, the porous sintered compact on the stage was immersed in the anaerobic resin monomer in the impregnation tank by lowering the stage. Subsequently, the porous sintered compact was impregnated by pressing so as to draw the monomer in the pores. After impregnating the resin, excess resin solution adhering to the surface of the porous sintered compact was washed off, and the anaerobic resin monomer impregnated in the pores was cured by heating the anaerobic resin 1 in warm water at 90° C. or by heating the anaerobic resin 2 in warm water at 50° C. (both temperatures are recommended by the manufacturer).
One sample of each of the produced samples was cut off and polished to observing structure, and sealing states of cross sections on the surface and the interior thereof were observed by a microscope. The results are shown in the column “Sealing State” in Table 2. Here, the observed results were evaluated according to the following standard. In the case in which the resin was observed by microscopy to be sealed, it was evaluated as “Superior”. In the case in which the resin was observed by microscopy to not be sealed, it was evaluated as “Inferior”.
After measuring weights thereof, another 10 Samples of each the produced Samples were immersed in lubricating oil filled in a beaker, and the pressure was reduced to 5 Pa, and was then returned to atmospheric pressure. Then, the weights thereof were measured again, and the lubricating oil absorption tests for measuring weight differences between non-tested Samples and tested Samples (indicating that the lubricating oil had been absorbed) were repeatedly carried out. In the case in which the weight did not increase even if the test was repeated 5 times, the test was repeated a further 5 times (a total of 10 tests) and the increase in the weight was measured in the same manner. Here, the measured results are evaluated according to the following standards and are shown in Table 2. In the case in which absorption of the lubricating oil (increase of weight) was observed in 10 Samples, this was evaluated to be “Inferior”. In the case in which absorption of the lubricating oil was observed in several Samples, this was evaluated to be “Not superior”. In the case in which the increase of the weight was not observed at all, this was evaluated to be “Superior”.
As is apparent from Table 2, in the first resin sealing process, in the Samples A to C using the anaerobic resin 1 which contained an azo compound as a peroxidation catalyst, it was confirmed that the porous sintered compact was impregnated and sealed in the interiors of the pores by the resin. In contrast, in the Sample D using the anaerobic resin 2 which contained an organic peroxide as a peroxidation catalyst, which was subjected to the resin sealing processes under a reduced pressure of 50 Pa, it was confirmed that the pores on the surface thereof were sealed at an initial stage by actively generating a polymerization reaction from the time the impregnation started, and that in the porous sintered compact was not impregnated into the interiors of pores by the resin. However, in the Sample E using the same anaerobic resin 2, which was subjected to the resin sealing process under a reduced pressure of 200 Pa, it was confirmed that the polymerization reaction was controlled by increasing oxygen partial pressure, and that the porous sintered compact was filled into the interiors of the pores by the resin.
In addition, as is apparent from Table 2, in the Sample A (conventional technique) in which the resin sealing process was carried out only once using the anaerobic resin 1, it was confirmed that absorption of the lubricating oil was observed in all 10 samples when the lubricating oil absorption test was carried out 5 times, and it was confirmed that gaps were formed between the pores and the resin, although this was not observed by microscopy. In addition, also in Sample B in which the resin sealing process was carried out twice using the anaerobic resin 1, it was confirmed that absorption of the lubricating oil was observed after the lubricating oil absorption test was carried out 5 times, and it was confirmed that the gaps formed in the first sealing process often could not be sealed in the second sealing process. Furthermore, in the Sample D in which the resin sealing process was carried out only once using the anaerobic resin 2, the absorption of the lubricating oil was not observed after the lubricating oil absorption test was carried out 5 times. However, it was confirmed that absorption of the lubricating oil was observed in one sample after the lubricating oil absorption test was carried out 10 times, and it was confirmed that there was a problem in the stability of the sealed condition. In contrast, in the Samples C and E in which the second resin sealing process was carried out using the anaerobic resin 2, absorption of the lubricating oil was not observed even if the lubricating oil absorption test was carried out 10 times, and it was confirmed that a superior and stable sealed state was formed. As explained above, it was confirmed that the pores could be reliably and stably sealed by carrying out the second resin impregnation step using a monomer of an anaerobic resin containing an organic peroxide, in the case in which the pores of the porous sintered compact were sealed by carrying out the resin sealing process twice.
Claims
1. A production method for a fluid dynamic pressure bearing, comprising a resin sealing process comprising:
- a resin impregnating step in which a monomer of an anaerobic resin composed primarily of one of acrylate and methacrylate is impregnated into pores of a porous sintered compact;
- an excess resin washing off step in which excess resin adhering to a surface of the porous sintered compact is washed off; and
- a resin curing step in which the monomer of the anaerobic resin impregnated in the pores is cured by heating the porous sintered compact to at least a resin curing temperature after washing off the excess resin,
- wherein the resin sealing process is carried out at least twice, and the monomer of the anaerobic resin containing an organic peroxide at 0.1 to 1.0 mass % is used in at least the resin impregnating step of the last resin sealing process.
2. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the monomer of the anaerobic resin containing an azo compound at 0.1 to 0.5 mass % is used in at least the resin impregnating step of the first resin sealing process.
3. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the monomer of the anaerobic resin containing an organic peroxide at 0.1 to 1.0 mass % is used in the resin impregnating step of the first resin sealing process, and the resin impregnating step is carried out under a pressure of 102 to 103 Pa.
4. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the organic peroxide is at least one hydroperoxide selected from t-butyl hydroperoxide, cumene hydroperoxide, di-isopropyl peroxide, p-methane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, and benzoyl peroxide.
5. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the anaerobic resin composed primarily of acrylate or methacrylate contains a curing accelerator comprising an organometallic compound at not more than 1.0 mass %.
6. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the porous sintered compact is made of a copper-iron-based material in which 3.0 to 30 mass % of copper foil powder is contained in a raw material powder and Cu content is at least 20 mass %.
7. The production method for a fluid dynamic pressure bearing, according to claim 1, wherein the porous sintered compact is subjected to a size adjusting repressing step which adjusts a size of the porous sintered compact, and a fluid dynamic pressure groove forming repressing step in which a groove for generating fluid dynamic pressure is provided on at least one of a bore surface and an edge surface of the porous sintered compact by a deformation processing, before the resin sealing process.
Type: Application
Filed: Feb 27, 2007
Publication Date: Jan 17, 2008
Applicant: HITACHI POWDERED METALS CO., LTD. (MATSUDO-SHI)
Inventors: Hidekazu Tokushima (Matsudo-shi), Takahiro Jinushi (Matsudo-shi), Katsutoshi Nii (Matsudo-shi), Zenzo Ishijima (Matsudo-shi)
Application Number: 11/711,028
International Classification: B21K 1/10 (20060101);
