JP2007057068A - Method for manufacturing hydrodynamic bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a hydrodynamic bearing which can improve its corrosion resistance and wear resistance by improving its surface roughness by forming a coating film of triiron tetraoxide (Fe<SB>3</SB>O<SB>4</SB>) on the bearing. <P>SOLUTION: The coating film of Fe<SB>3</SB>O<SB>4</SB>is formed on a porous material of pressed powder sintered metallic body by carrying out the steam treatment within the atmospheric temperature from 400 to 600°C. By this method, the corrosion resistance and wear resistance can be improved. In addition, the coating film is suitable for the substrate treatment for plating, and is particularly optimum for the hydrodynamic bearing. Further, the reduction of costs is expectable. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a fluid dynamic bearing that supports a rotating shaft by non-contact sliding, and an object thereof is to improve motor durability and rotational accuracy, reduce noise, and reduce costs.

  In recent years, with the increase in accuracy of AV equipment and OA equipment, there has been a significant increase in demands for improving the rotational accuracy and reducing noise of motors such as hard disk drives, spindle motors for reading various DVDs and CDs, and fan motors. In order to meet these demands, fluid dynamic pressure type bearings that support a motor shaft in a non-contact manner are attracting attention.

  With the widespread use of fluid dynamic pressure bearings with grooves on the inner peripheral surface and end surface of the bearing, such as with herringbone grooves, the demand for further improvements in performance such as improved rotational accuracy and lower costs has increased. Metal powder compacts that do not require cutting of grooves on the end face have come to be used frequently. Bearings molded from metal powder compacts are used due to differences in the coefficient of thermal expansion of each component, such as the problem of conventional bearing devices, that is, the combination of brass bearings such as brass and stainless steel rotating shafts. Problems such as a narrow environmental temperature range and a difficulty in maintaining an appropriate clearance between the rotating shaft and the bearing are inherently limited in improving rotational accuracy.

  In addition, by making the bearing material iron-based, the difference in the coefficient of thermal expansion from the rotating shaft can be reduced, but generally iron-based materials have poor cutting workability such as dynamic pressure grooves, and cutting tools It is possible to solve problems that are not practical because it is difficult to reduce mass production and cost due to an increase in management costs due to the shortening of the service life and the deterioration of the bearing inner diameter accuracy after cutting.

  However, since bearings molded from a sintered compact use metal powder as a raw material, it is impossible to completely eliminate the presence of communication holes due to voids between sintered particles in a normal process. The air permeability is enhanced, and the dynamic pressure generated on the bearing surface leaks through the above-described communication holes, and tends to adversely affect the pressure drop, the rigidity of the rotating shaft, and the rotation accuracy.

Thus, a technique has been proposed in which a sintered body bearing is impregnated with resin to seal pores (see Patent Document 1). In pure iron, a sintered body bearing is impregnated with resin to seal pores, and then plated to compensate for insufficient surface hardness. Furthermore, the pores are reduced by impregnating the sintered body with resin, metal, glass or other material to seal the pores, and then subjecting the sintered body bearing surface to shot blasting using metal particles or resin particles. It is possible to make it.
JP-A-8-221897

  However, when impregnating a powder sintered compact bearing with resin, the resin impregnated material tends to remain on the surface of the bearing material in a normal process, and the dimensional accuracy is likely to be adversely affected, and the resin surface is plated. It is difficult, and if the pores before resin impregnation are large, plating as a post-treatment tends to be incomplete. In addition, pure iron is plated on the bearing material surface because it is necessary to compensate for insufficient surface hardness. Since it is difficult to completely remove the plating solution in the hole, it is easy to cause metal corrosion due to the residual plating solution. Furthermore, it is difficult to control the amount of resin impregnation, and it is possible to reach true density (= no voids) by resin impregnation. Further problems remain, such as difficulty in re-compression within the mold for the purpose of improving dimensional accuracy after resin impregnation.

  In addition, after the resin impregnation, it is necessary to clean the individual bearing materials, but if these are performed all at once, the bearing materials will hit each other and a dent will be formed. This leads to cost increase from the need for individual cleaning, and the impregnated resin may react with fluids such as lubricating oil used in fluid dynamic bearing units, causing swelling and shrinkage. There are problems such as tending to be anxiety above.

  Furthermore, when a sintered body bearing is impregnated with resin or other substances to seal pores and then shot blasted on the surface of the sintered body bearing, the surface roughness of the bearing generally deteriorates and the fluid dynamic pressure is reduced. Not only is it unsuitable as a bearing, but also the dimensional accuracy deteriorates, resulting in product variations, and there is a problem that the cost is high because a separate cleaning process for removing shot powder remaining on the bearing material is required. .

  Therefore, the present invention solves the problem of the bearing using the metal powder sintered body, which is insufficient with the above-described conventional technology, improves the durability and rotational accuracy of the motor using the fluid dynamic pressure bearing, and reduces noise. Is to reduce the cost. Specifically, in the first invention, the Fe3O4 film is formed on the porous surface by subjecting the green compact metal sintered body to water vapor treatment. The present invention relates to a method for manufacturing a fluid dynamic pressure bearing. Further, the second invention is a fluid dynamic pressure bearing in which a Fe3O4 film is formed on a porous surface by subjecting a powder-molded metal sintered body material to a water vapor treatment at an ambient temperature of 400 to 600 ° C. It relates to the manufacturing method.

  In the present invention, as described above, the porous material of the compacted metal sintered body is subjected to water vapor treatment to form a Fe3O4 film on the porous surface, and the porous compacted metal sintered body is porous. Since the Fe3O4 film is formed by subjecting the material to water vapor treatment at an ambient temperature of 400 to 600 ° C., the Fe3O4 film is generated to the inside through the pores of the sintered material, and is porous. The quality pores are sufficiently sealed to increase the mechanical strength and the surface roughness of the sintered body bearing is improved, and the impregnated material is Fe3O4 film instead of resin, so it has corrosion resistance and wear resistance. It is possible to improve the performance, and it is convenient as a base treatment for plating, and the finished bearing product is particularly suitable as a fluid dynamic pressure bearing.

  The specific contents of the present invention will be described below. In the first invention, a porous material of a compacted metal sintered body (sleeve) material is subjected to a steam treatment to form a ferric oxide trioxide (Fe3O4) film. It is to be formed. In this case, the metal powder used for compacting may be copper-based such as brass, but iron-based powder is preferable in order to reduce the difference in the coefficient of thermal expansion from the rotation shaft of the motor. After iron powder is compacted, it is sintered to form a sintered body material for bearings.

  The sintered body material is porous, and when this is used as a fluid dynamic pressure bearing, in order to cause a pressure drop due to dynamic pressure leakage, at least the inner peripheral surface of the sintered metal bearing material subjected to sizing treatment A triiron tetroxide (Fe 3 O 4) film is formed on the portion that is in sliding contact with the motor shaft. However, in this case, even if the surface of the sintered metal bearing material is simply subjected to a water treatment, the surface of the sintered metal bearing material is not easily sealed, and the motor is driven. It tends to cause problems such as increasing the weight by sucking lubricant.

  Therefore, the method of forming this triiron tetroxide (Fe3O4) film on the sintered metal bearing material is the second invention of the present invention, and the second invention is based on the compacted metal sintered body material. The Fe3O4 film is formed on the porous surface by performing water vapor treatment in an ambient temperature of 400 to 600 ° C.

  Steam treatment is generally performed by supplying hydrogen gas that has been passed through saturated steam to oxidize the material, so far, the separation of wood components and permanent fixation of wood in a relatively low temperature atmosphere of 230 ° C or less, woody Although known as a means for imparting dimensional stability to boards or stabilizing foods, it has been successfully transferred to sintered metal bearing materials by changing the treatment temperature and treatment time.

  A heat-resistant furnace having a pressure-resistant structure is preferably used for the steam treatment. A sintered metal bearing material and water are put inside, the inside is sealed with a lid, and then heated to a high temperature of 400 to 600 ° C. The internal water evaporates by heating, the pressure in the chamber rises, and heat treatment of the sintered metal bearing material is started. Although depending on the temperature in the furnace, when a steam treatment time of about 25 to 80 minutes elapses, a dense and stable oxide film of Fe3O4 which is a spinel phase oxide is formed on the surface of the sintered metal bearing material. Incidentally, the film thickness in this case is about 5 μm, and there is almost no influence on the dimensional accuracy of the bearing.

  Note that if the atmospheric temperature of the steam treatment is less than 400 ° C., sufficient film formation of Fe 3 O 4 on the bearing material is not performed. On the other hand, even if the temperature exceeds 600 ° C., there is no change in the formation of Fe 3 O 4, and it is economical that the heat treatment furnace is expensive and within the range of 400 to 600 ° C., more preferably within the range of 450 to 550 ° C. Ideal from a viewpoint.

  As for the time required for the water vapor treatment, in order to obtain a film thickness of about 5 μm of Fe 3 O 4 when the atmospheric temperature is in the range of 400 to 600 ° C. as described above, the atmospheric temperature is 600 ° C. for about 25 minutes. In the case of 550 ° C., about 40 minutes, in the case of 450 ° C., about 65 minutes, and in the case of 400 ° C., about 80 minutes, it is preferably within the range of 25 to 80 minutes.

  Furthermore, in order to sufficiently improve the sealing performance and the surface roughness improvement effect after the steam treatment, the relative density of the sintered metal bearing material to be used must be high to some extent. That is, when the relative density of the sintered metal bearing material is low, the sealing performance by Fe3O4 is not sufficient, the surface roughness is not improved so much, and the lubricating oil is easily sucked during use of the motor.

  Therefore, as a result of further experiments conducted by the present inventors, the relative density of the sintered metal bearing material used in this case is less than 80%, and the surface roughness is conspicuous and the sealing property is sufficient. It wasn't. Further, it was found that the surface roughness and the sealing performance are sufficient when the content is 80% or more, more preferably 85% or more.

  About the metal sintered bearing raw material which performed said water vapor | steam processing, the further improvement of a precision can be aimed at by performing a sizing process again as needed after that. Sintered bearings that have undergone steam treatment not only improve corrosion resistance, wear resistance, and mechanical strength, but are also excellent as a base treatment for plating because the surface is covered with metal. By filling it, the surface roughness is eliminated and it can be optimally used as a fluid dynamic pressure bearing.

  When these points are specifically described, the pores can be reduced by subjecting the porous material of the compacted metal sintered body to a water vapor treatment at an ambient temperature of 400 to 600 ° C. The difficulty of plating adhesion to the surface is reduced to improve the effect of subsequent plating treatment, and depending on the treatment conditions, it is possible to make the air permeability almost zero, eliminating the pressure drop due to dynamic pressure leakage, shaft rigidity and In addition to improving the rotation accuracy, the plating solution can be prevented from entering and the corrosion resistance can be improved, and in some cases, the plating process itself can be made unnecessary.

  Furthermore, compared with the case of impregnating with resin, it is easy to control the steam treatment conditions such as pressure and treatment time, and the film thickness of Fe3O4 produced can be freely adjusted, and the standard film thickness is about 5 μm. In addition, the amount of deterioration in dimensional accuracy due to the residual surface of the impregnated resin seen in the case of resin impregnation is extremely small, and dimensional correction by recompression using a mold is also possible.

  In the case of performing steam treatment, the processing work can be carried out without causing the individual bearing materials to collide with each other, so there is no dent in the product, and the processing oil remaining inside is treated at a high temperature before the treatment. This eliminates the need for an extra cleaning step. Further, the produced Fe3O4 film is extremely stable without reacting with the lubricating oil of the bearing unit as in the case of conventional resin impregnation, and does not swell or shrink.

  Furthermore, compared with conventional technology, the sintered body bearing is impregnated with resin, etc., and the pores are sealed, and then the surface of the sintered body bearing is shot blasted and the surface roughness is extremely low. Because of its small size and high dimensional accuracy and product yield, it is particularly suitable for fluid dynamic pressure bearing motor units, and it does not require a cleaning process to remove residual shot powder, so costs can be reduced. .

  After compacting the iron-based powder, it is sintered and further sized to obtain three types of bearing materials, which are pressure-resistant heat treatment furnaces (batch-type homo-processing furnaces of Tokyo Heat Treatment Industry Co., Ltd.) It was put in and heated with steam to 550 ° C., and then maintained for 55 minutes to perform steam treatment. As a result, an Fe3O4 coating layer having an average thickness of 5.0 μm was formed on the surface of each bearing material. The following tests were conducted using this as samples 1 to 3. In addition, the heat treatment furnace used in this case is not limited to the above, but other than that, for example, an industrial superheated steam treatment furnace (ST furnace) manufactured by Sunray Cooling Co., Ltd., or a combination of a bit furnace and a steam generator. It may be.

  The results of measuring the dimensions, air permeability, and surface roughness of Samples 1 to 3 and a sample impregnated with resin after shot blasting are shown in the drawings. 1 is after sizing and before steaming, FIG. 2 is after sizing and after steaming, FIG. 3 is before sizing and before steaming, FIG. 4 is before sizing and after steaming, FIG. Represents a product after shot blasting and impregnated with resin.

[Change in outer diameter]
When comparing the outer diameter change of each sample,

(Process) (Sample) (Outer diameter (mm))

[After sizing and before steaming] 1 11.497
2 11.496
3 11.498
Ave. 11.4970

[After sizing, steam treatment] 1 11.505
2 11.505
3 11.506
Ave. 11.5053

* As mentioned above, the amount of change in the outer diameter due to steam treatment is 0.0083 and the average film thickness is about 0.004. The thickness was stable on average.

(Breathability)
When comparing the breathability of each sample,

(Process) (Sample) (Pressure difference (mmH2O)) (Flow rate (cm3))

[After sizing and before steaming] 1 1781 37
2 1786 31
3 1789 44

[After sizing, after steam treatment] 1 1798 2
2 1816 1
3 1810 0

[Before sizing, before steam treatment] 1 1778 307
2 1783 388
3 1785 373

[Before sizing, after steam treatment] 1 1804 2
2 1834 2
3 1828 2

[After sizing, shot blasting + resin impregnation]
4 1819 4
5 1807 2
6 1815 1

* Regardless of before and after sizing, the vapor permeability of the samples subjected to steam treatment is 4 or less, and in this case, it is considered to be almost zero considering the measurement error.

〔Surface roughness〕
When comparing the surface roughness of each sample,

[Process] [Sample] [Ra (μm)] [Rmax (μm)]

[After sizing and before steaming] 1 0.1708 8.216
2 0.1014 4.292
3 0.1250 4.504
Ave. 0.1324 5.6707

[After sizing, after steam treatment] 1 0.1368 2.008
2 0.3479 5.792
3 0.3085 4.608
Ave. 0.2644 4.1360

[Before sizing, before steam treatment] 1 0.1726 2.984
2 0.1632 3.924
3 0.1966 4.676
Ave. 0.1775 3.8613

[Before sizing, after steam treatment] 1 0.3997 5.640
2 0.5214 6.088
3 0.5044 7.004
Ave. 0.4752 6.2440

[After sizing, shot blasting and resin impregnation]
4 0.7616 9.456
5 0.8493 6.784
6 0.5481 6.600
Ave. 0.7197 7.6133

When considering the above surface roughness,
* 1. As for Ra, there is a tendency to be slightly deteriorated by the steam treatment, but a sufficient improvement tendency is seen as compared with the case of shot blast + resin impregnation.
* 2. Regarding Rmax, there was a tendency to be slightly deteriorated by steam treatment before sizing, but it was sufficiently improved after sizing. This is thought to be due to the difference in pore volume before steaming.
* 3. Compared to shot blasting + resin impregnation, water vapor treatment was much better both before and after sizing.

  It should be noted that the steam treatment for the porous material of the compacted metal sintered body in the present invention was performed under the condition that the atmosphere temperature was 400 to 600 ° C. By using far-infrared heating together with superheated steam treatment that can be easily heat-processed, the same Fe3O4 can be obtained at lower temperature conditions using a low energy load type superheated steam treatment apparatus lower than the above atmospheric temperature range. It is also possible to form a film.

  The superheated steam treatment has the disadvantage that the heat transfer rate is high but the thermal efficiency is low.According to the above oxygen-free heat treatment method, in addition to the advantages of the superheated steam treatment, extremely high thermal efficiency can be realized, and the bearing quality In addition to improving the process time, the processing time can be shortened and the cost can be reduced.

A parameter graph showing the measurement results of dimensions, air permeability, and surface roughness after sizing and before steam treatment. A parameter graph showing the results of measurements on dimensions, air permeability, and surface roughness after sizing and steam treatment. A parameter graph showing the measurement results of dimensions, air permeability, and surface roughness before sizing and before steaming. A parameter graph showing the results of measurement of dimensions, air permeability and surface roughness after sizing and after steam treatment. A parameter graph showing the results of measurement of dimensions, air permeability, and surface roughness after sizing and shot blasting and impregnating with resin.

Claims (6)

  A method for manufacturing a fluid dynamic pressure bearing in which a Fe3O4 film is formed on a porous surface by subjecting a powder-molded metal sintered body to water vapor treatment.   A method for manufacturing a fluid dynamic pressure bearing in which a Fe3O4 coating is formed on a porous surface by subjecting a compacted metal sintered body material to a water vapor treatment at an ambient temperature of 400 to 600C.   The method for producing a fluid dynamic bearing according to claim 2, wherein the steam treatment time for the compacted metal sintered body material is 25 to 80 minutes.   A method for producing a fluid dynamic pressure bearing in which a Fe3O4 coating is formed on a porous surface by subjecting a compacted metal sintered body material to steam treatment at an atmospheric temperature of 450 to 550C.   The method for producing a fluid dynamic bearing according to claim 4, wherein the steam treatment time for the compacted metal sintered body material is 40 to 65 minutes.   The method for producing a fluid dynamic pressure bearing according to any one of claims 1, 2, and 4, wherein a volume density of the compacted metal sintered body material is 80% or more, more preferably 85% or more.

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