JP2006097780A - Sliding member and dynamic pressure bearing using the same, and motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that a crack or wear occurs in sliding faces and it is difficult to form stable lubricating layers on the sliding faces. <P>SOLUTION: A sliding member has the sliding faces 2a, 3a and 4a mainly composed of an aluminum oxide crystal phase and a glass phase. The occupied area rate of the glass phase existing in each sliding face 2a, 3a and 4a is 30-75%, and the occupied area rate of pores existing in the sliding faces 2a, 3a and 4a is 50% or less. Thus, the sliding faces 2a, 3a and 4a are hardly damaged and the peeling of the lubricating layers is suppressed. The lubricating layers mainly composed of the glass phases are formed on the sliding faces 2a, 3a and 4a in the process of usage. The sliding member can be effectively used for a dynamic pressure bearing having high-speed contact sliding operation, in particular. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sliding member such as a bearing, a gear, and a bearing, and is particularly used for a polygon mirror used in a laser beam printer (hereinafter referred to as LBP) and a hard disk drive (hereinafter referred to as HDD). The present invention relates to a hydrodynamic bearing and a motor.

  Conventionally, ceramics having high hardness and excellent wear resistance have been used as sliding members such as bearings, gears, and bearings. In recent years, in addition to the above characteristics, it has been used in dynamic pressure bearings, particularly air dynamic pressure bearings because of its excellent heat resistance and high precision processing.

  Fig.2 (a) shows the perspective view of the hydrodynamic bearing using the sliding member of this invention, (b) is sectional drawing in the DD line | wire of (a).

  For example, as shown in FIG. 2, the hydrodynamic bearing 51 is constituted by any combination of a shaft 52 (not shown in FIG. 2A), a sleeve 53, and a thrust 54, and the shaft 52 is formed in the hollow portion of the sleeve 53. Arranged, the shaft 52 is connected to the thrust 54 at the end.

  The shaft 52 and the sleeve 53 restrain displacement in the direction perpendicular to the rotation axis, and the thrust 54 restrains displacement in the rotation axis direction.

  A dynamic pressure generating groove 52b that generates dynamic pressure in the radial direction is formed on the surface 52a of the shaft 52, and a fluid such as air flows into the dynamic pressure generating groove 52b to generate dynamic pressure in the gap 55. Then, it rotates while maintaining a constant distance E from the inner diameter of the sleeve 53. Similarly, a dynamic pressure generating groove 54b that generates dynamic pressure in the thrust direction is formed on the surface 54a of the thrust 54, and dynamic pressure is generated in the gap 56 when ascending, and a certain distance F from the end face of the sleeve 53 is obtained. It is a structure that rotates in a maintained state.

  The rotational driving force can be obtained by assembling a motor component such as a coil or a magnet to either the shaft 52 or the sleeve 53 via a rotor hub or the like.

  However, the sleeve 53 may be a rotating member that floats and the shaft 52 and the thrust 54 may be fixed members. For example, there is an LBP polygon mirror as the shaft 52 rotates, and an HDD as the sleeve 53 rotates.

  The thrust 54 may be formed integrally with the shaft 52 or may be formed as an individual member and later fixed to the shaft 52 with an adhesive or a screw. Whether the thrust 54 and the shaft 52 are formed integrally or as individual members needs to be designed in consideration of the product shape, processing accuracy, manufacturing cost, and the like.

  Further, the distances E and F of the gaps 55 and 56 are set to about 1 to 5 μm in the case of a small dynamic pressure bearing used for an electronic device. This is because when the distances E and F of the gaps 55 and 56 are 1 μm or less, a large dynamic pressure can be obtained, but the roundness, cylindricity, surface roughness, etc. of the member need to be processed with extremely high accuracy. This is because the manufacturing cost is expensive, and conversely, when the distances E and F of the gaps 55 and 56 are set to 5 μm or more, the problem is that the rotating shaft is likely to be shaken.

  The dynamic pressure bearing 51 has a low rotational speed at the start of rotation and a low dynamic pressure. Therefore, the members rotate while the members are in contact with each other. However, when the rotational speed increases and the dynamic pressure increases, the members rise and become constant. Rotates with a gap. When the rotation is stopped, the rotation speed is decreased and the dynamic pressure is reduced. As in the case of the rotation start, the members rotate while being in contact with each other, and are stopped by the frictional force.

  Many of the characteristics required for the material used for the hydrodynamic bearing correspond to the sliding environment at the start / stop of rotation, and are mainly wear resistance and heat resistance.

  When the gap 55, 56 is filled with oil as a lubricating fluid, the oil is reliably sealed so that the oil does not scatter from the gap of the hydrodynamic bearing when ascending, and further, heat generation and rotation are performed so that the oil does not deteriorate due to oxidation or the like. It is necessary to design in consideration of the usage environment such as speed. In addition, when air is used as the lubricating fluid, the members are in direct contact with each other at the start / stop of rotation. Therefore, a method of forming the member with ceramics having excellent wear resistance and heat resistance, or a lubricating layer on the sliding surface There is a method of performing DLC (diamond-like carbon) coating.

  And as a member for sliding used for such a dynamic pressure bearing etc., there existed what was shown in patent documents 1-4, for example.

In Patent Document 1, the silicon nitride sintered body contains an Fe component in the range of 10 to 600 ppm and the electrical resistance value is set to 1 to 10 ⁵ Ω · m, so that static electricity generated during rotation is released to the peripheral members. Furthermore, there is shown a sliding member capable of improving the high-speed sliding characteristics by using 95% or more of the area ratio of the grain boundary phase as the glass phase.

  Patent Document 2 discloses a dynamic pressure air bearing using, as a lubricating material, wear powder generated by sliding between a shaft and a bearing. As the lubricating material, colloidal silica (silicon oxide gel-like substance) in which a wear powder containing silicon generated by contact between a shaft and a bearing is incorporated into a substance having an OH bond, a carbonyl group, or an ether bond. It is shown. By using colloidal silica as the lubricating material, it is possible to obtain a dynamic pressure air bearing having wear resistance and a low friction coefficient and excellent workability.

  In Patent Document 3, a dynamic pressure bearing having excellent bending strength and hardness and good wear resistance is obtained by using an alumina ceramic having a content of aluminum component in terms of alumina of 90 to 99.5% by mass. It has been shown that it can be formed. If the alumina is less than 90% by mass, the amount of the sintering aid added is too large, the strength and wear resistance of the ceramic is impaired, and the grain growth of the ceramic proceeds excessively, while the alumina is 99.5% by mass. If it exceeds, the liquid phase becomes insufficient during sintering, so that the growth of crystal grains is suppressed, the surface vacancies formed by the drop-off of grains during the subsequent polishing process become smaller, and the dynamic pressure generation effect is reduced. Moreover, as a sintering auxiliary component of alumina ceramic, Li, Na, K, Mg, Ca, Sr, Ba, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho , Er, Tm, Yb, Lu, Si, one or two or more selected from a total of 0.5 to 10% by mass in terms of oxide, and a liquid phase produced during firing The effect of improving the fluidity of the particles, promoting the crystallization of the grain boundary phase, and improving the strength thereof is shown, and the average particle size of the ceramic crystal particles is adjusted to be in the range of 1 to 7 μm. Thus, it has been shown that surface pores having a preferable size can be formed by polishing, and problems such as adhesive wear and seizure can be suppressed. Furthermore, by setting the formation area ratio of surface vacancies of 2 to 20 μm in size to 10 to 60%, the effect of making seizure and linking less likely to occur on the dynamic pressure gap forming surface is obtained. It is shown that it is formed by particle dropout during polishing.

In patent document 4, what formed at least one of the support member and rotation member of a dynamic pressure bearing with crystallized glass is shown. By forming the hydrodynamic bearing member with crystallized glass with a low coefficient of thermal expansion, the variation in the gap between the shaft and the sleeve due to temperature changes is reduced, and it is possible to suppress the transfer of heat to other members It is said.
JP 2003-63871 A JP 1996-219145 JP2002-235746 JP2003-176825A

  However, it is described that 95% or more of the grain boundary phase is a glass phase when the silicon nitride sintered body shown in Patent Document 1 is used as a sliding member used in a hydrodynamic bearing or the like. However, the preferred form of the glass phase when aluminum oxide is used as the sliding member is not described, and the handling thereof is unknown. Further, since the silicon nitride sintered body has poor workability, there is a problem that chipping is likely to occur when it is processed into a dynamic pressure bearing. When the bearing starts / stops rotation, chipping is likely to occur due to contact or collision between the members. If the chip piece enters the clearance of the hydrodynamic bearing, rotation becomes unstable, biting occurs and rotation occurs. There was a problem of stopping. Furthermore, the raw material is more expensive than aluminum oxide, and there is a cost problem that the equipment cost becomes expensive because an atmosphere furnace is used for firing.

  The hydrodynamic bearing using the colloidal silica generated from the wear powder generated from the shaft and the bearing and the solvent shown in Patent Document 2 as a lubricating material requires a solvent for generating the colloidal silica, and the solvent is volatilized. Then, there was a problem that the function as a lubricating material could not be performed. Furthermore, since silica wear powder increases due to friction between members over time, there is also a problem that the characteristics of the lubricating material gradually change and it is difficult to keep the rotation characteristics constant.

  When high-purity alumina ceramics as shown in Patent Document 3 are used, places where vibrations and shaking are strong such that the members are intermittently contacted after dynamic pressure is generated and the bearing members are lifted When used in the above, there is a problem that the member is in a high-speed rotation state, so that chipping or severe wear occurs. Further, even when used in a place where there is little vibration or shaking, the same problem arises because the rotation becomes unstable if the wear of the member proceeds after a long period of use. That is, since it is a material that tends to chip, when assembled as a dynamic pressure bearing, the overall balance and the degree of freedom of design were low. This is because the structure of the alumina ceramics constituting the sliding member lacks a structure for mitigating the impact due to the high purity of alumina, and the slidability is lowered. And it has become a cause which further promotes the problem that it is easy to lack by adding the sintering auxiliary agent component which has the effect which accelerates | stimulates crystallization of a grain boundary phase.

  In addition, air is only interposed as a lubricating fluid between the sliding surfaces of each sliding member, so that individual ceramic crystal particles present on the sliding surface are directly impacted, and degranulation and wear progress. There was a problem that it was easy to do and the slidability could not be improved.

  The hydrodynamic bearing using crystallized glass shown in Patent Document 4 has insufficient wear resistance of the members. Therefore, particularly when used in an air dynamic pressure bearing, wear powder is generated by direct contact between the members. There was a problem that it was easy. Furthermore, although the hydrodynamic bearing of Patent Document 4 is composed of a glass component in terms of composition, since it is crystallized, the sliding characteristics due to the glass phase cannot be improved.

  In order to solve such a problem, the present invention is a sliding member whose sliding surface is mainly composed of an aluminum oxide crystal phase and a glass phase, and the occupied area ratio of the glass phase existing on the sliding surface is 30% or more. , 75% or less, and the area occupied by pores existing on the sliding surface is 50% or less.

  Further, when the sliding members of the present invention are slid against each other with the sliding surfaces facing each other, a lubricating layer mainly composed of the glass phase component is formed on at least a part of the sliding surfaces. Features.

  In the sliding member of the present invention, the glass phase contains 40% by mass or more of silicon oxide.

  The present invention also provides a hydrodynamic bearing using a sliding member, wherein the aluminum oxide has an average crystal grain size of 1.0 μm or more and 8 μm or less.

  Furthermore, a motor using the dynamic pressure bearing of the present invention is provided.

  The sliding member of the present invention is mainly composed of an aluminum oxide crystal phase and a glass phase, and maintains the strength of the member by setting the exclusive area ratio of the glass phase existing on the sliding surface to 30% or more and 75% or less. However, even when used under severe vibration and rocking conditions, the sliding surface is less likely to be chipped. Further, by reducing the occupied area ratio of pores existing on the sliding surface to 50% or less, the sliding surface Is less likely to be damaged, and it is possible to suppress peeling of the lubricating layer. In addition, since the lubricating layer mainly composed of the glass phase component is formed on the sliding surface, it is possible to suppress the wear of the sliding surface that contacts and slides at a high speed.

  Moreover, it becomes possible by supplying 40 mass% or more of silicon oxides in a glass phase to supply a sufficient amount of glass phase to form a lubricating layer.

  Further, by setting the average crystal grain size of aluminum oxide to 1.0 μm or more and 8 μm or less, the lubricating layer can be formed on the surface of the aluminum oxide crystal phase without interruption.

  In addition, by using the hydrodynamic bearing of the present invention, the risk that a motor used in an environment with vibration or swinging stops due to biting is reduced.

  The best mode for carrying out the present invention will be described. In this description, a description will be given using a dynamic pressure bearing which is an example of a sliding member.

  1A is a perspective view of a hydrodynamic bearing using the sliding member of the present invention, and FIG. 1B is a cross-sectional view taken along the line CC of FIG.

  The hydrodynamic bearing 1 is composed of a combination of a shaft 2 (not shown in (a)), a sleeve 3, and a thrust 4. The shaft 2 is disposed in the hollow portion of the sleeve 3, and the thrust 4 is provided at both ends. It is connected with. The shaft 2 and the thrust 4 or the sleeve 3 are set to rotate with the length direction of the shaft 2 as the rotation axis. The shaft 2 and the sleeve 3 restrain displacement in the direction perpendicular to the rotation axis, and the thrust 4 Restricts the displacement in the rotation axis direction.

  The surface 2a of the shaft 2 is formed with a dynamic pressure generating groove 2b that generates a dynamic pressure in the radial direction. When the shaft 2 rotates, a fluid such as air flows into the dynamic pressure generating groove 2b, and the gap 5 A dynamic pressure is generated, and the sleeve 3 rotates while maintaining a constant distance A from the inner diameter of the sleeve 3. Similarly, a dynamic pressure generating groove 4b for generating a dynamic pressure in the thrust direction is formed on the surface 4a of the thrust 4, and when the thrust 4 rotates, a dynamic pressure is generated in the gap 6 and is constant with the end face of the sleeve 3. The structure rotates in a state where the distance B is maintained.

A rotational driving force can be obtained by assembling a motor component such as a coil or a magnet to either the shaft 2 or the sleeve 3 via a rotor hub or the like. May be set so that the other is rotated and the other is rotated, and may be appropriately selected according to the application.
For example, in the case of an LBP polygon mirror, the shaft 2 may be rotated, and in the case of an HDD, the sleeve 3 may be set to rotate.

  In addition, the shaft 2 and the thrust 4 may be formed integrally or may be individually manufactured and connected with an adhesive, a screw, or the like.

  The distances A and B of the gaps 5 and 6 are set to about 1 to 5 μm in the case of a small dynamic pressure bearing used for an electronic device. This is because when the distances A and B of the gaps 5 and 6 are 1 μm or less, large dynamic pressure can be obtained, but the roundness, cylindricity, surface roughness, etc. of the members constituting the dynamic pressure bearing are extremely high accuracy. However, when the distance between the gaps A and B of the gaps 5 and 6 is set to 5 μm or more, the rotating shaft is likely to be shaken. This is because.

  The dynamic pressure bearing 1 has a low rotational speed at the start of rotation and a low dynamic pressure. Therefore, one of the shaft 2 or the thrust 4 and the sleeve 3 rotates while being in contact with each other. When the pressure increases, the sleeve 3 rotates with a constant gap from the shaft 2 or the thrust 4. When the rotation is stopped, the rotation speed is decreased and the dynamic pressure is reduced. As in the case of the start of rotation, the rotation is performed in a contact state and is stopped by a frictional force.

  Here, the sliding member of the present invention constitutes the shaft 2, the sleeve 3, and the thrust 4, and at least the sliding surfaces 2 a, 3 a, 4 a of the sliding members of the shaft 2, the sleeve 3, and the thrust 4 are provided. Is mainly composed of an aluminum oxide crystal phase and a glass phase, and the occupied area ratio of the glass phase existing on the sliding surface is 30% or more and 75% or less, and the occupied area ratio of the existing pores is 50% or less. It is characterized by being.

  Thereby, the aluminum oxide crystal phase ensures the strength and wear resistance of the sliding member, and further, when sliding, the glass phase acts as a lubricating layer in the portion where the sliding members strongly contact and slide, It acts as a supply source, has strength and wear resistance, exhibits excellent sliding characteristics, and even if the lubricating layer is worn by sliding, the lubricating layer is replenished by the presence of an appropriate glass phase. Therefore, it can be made excellent in durability. Unlike the liquid lubricant such as oil, the lubricating layer made of the glass phase does not have the disadvantage of scattering from the gap between the sliding surfaces 2a, 3a, and 4a, and therefore does not require a seal. There is no problem.

  Further, in order to specify the occupied area ratio of the glass phase on the sliding surfaces 2a, 3a, and 4a to be 30% or more and 75% or less, the sliding surfaces 2a, 3a, and 4a are provided even if each sliding member is in sliding contact. Without being damaged, it can be slid very smoothly while maintaining the rotational speed for a long period of time.

  If the occupied area ratio is less than 30%, the chipping caused by the contact sliding of each sliding member damages the sliding surfaces 2a, 3a, 4a, thereby reducing the sliding characteristics such as the sliding speed. In the case of a dynamic pressure bearing or the like, there is a problem that the dynamic pressure bearing is damaged in a severe case, for example, sliding characteristics such as rotational speed are reduced due to the engagement between the shaft 2 or the thrust 4 and the sleeve 3. It is. On the other hand, when the occupied area ratio of the glass phase exceeds 75%, there is a problem that the wear resistance is remarkably lowered because there are few aluminum oxide crystal phases with high hardness. Therefore, the occupied area ratio of the glass phase on the sliding surfaces 2a, 3a and 4a is specified as 30% or more and 75% or less, preferably 35% or more and 65% or less, more preferably 50% or more and 60% or less. To do.

  Further, in the sliding member of the present invention, the surfaces on which the sliding members are in contact with each other, that is, only the sliding surfaces 2a, 3a, 4a are formed from the sintered body mainly composed of the aluminum oxide crystal phase and the glass phase. However, for example, the entire sliding member such as the shaft 2, the sleeve 3, and the thrust 4 may be composed of a sintered body mainly composed of an aluminum oxide crystal phase and a glass phase.

  Furthermore, in the present embodiment, in the dynamic pressure shaft 1, the sliding surfaces 2a, 3a, 4a of the sliding members of the shaft 2, the sleeve 3, and the thrust 4 are all configured. The sliding member of this invention may be used and the case where the one sliding surface of the opposing member is comprised may be sufficient.

Here, the occupied area ratio Sg of the glass phase existing on the sliding surfaces 2a, 3a, and 4a is determined by determining the area occupied by the aluminum oxide crystal phase after the sliding member is fire-etched to improve the visibility of the aluminum oxide crystal phase. Similarly, the rate Sa is quantified by the image analyzer,
It calculates and calculates | requires by Sg = 100-Sa-Sv.

  In addition, the presence of pores is important in the sliding surfaces 2a, 3a, and 4a. The pores are an important element for the sliding characteristics because air is introduced into the sliding surfaces 2a, 3a, and 4a on which the sliding members come into contact and slide to suppress linking. The larger the occupied area ratio of the pores existing on the sliding surfaces 2a, 3a, and 4a, the more air can be introduced into the contact portion between the sliding members, so that the sliding characteristics are improved. On the other hand, the open ends of the pores existing on the sliding surfaces 2a, 3a, and 4a are damaged by the chipped pieces due to chipping of the open ends of the pores when the sliding members come into contact with each other. Therefore, if there are too many pores, even if the lubricating layer is formed on the sliding surfaces 2a, 3a, 4a, fragments due to chipping of the open ends of the pores are generated and the sliding surfaces 2a, 3a, 4a are easily damaged. . Therefore, the occupied area ratio of the pores on the sliding surfaces 2a, 3a, and 4a is specified to be 50% or less, and more preferably 30% or less. In addition, the pores described here include those in which the pores present in the sintered body forming the sliding surfaces 2a, 3a, and 4a appear on the surface and those formed by the graining during processing. .

  Furthermore, the pores in the sliding surfaces 2a, 3a, and 4a preferably have an average diameter of 50 μm or less, and more preferably 8 μm or less. When the average diameter exceeds 50 μm, this effect becomes remarkable and formation of the lubricating layer is remarkably prevented. In addition, when the average diameter of the pores is small, the action of scraping off the lubricating layer is also reduced. Therefore, when using a material having a large occupied area ratio of pores, it is desirable to use a material having as small an average diameter of pores as possible.

  Furthermore, the expanded sectional view of the sliding face 2a is shown in FIG.1 (c). The angle θ formed by the sliding surface 2a in the vicinity of the opening end of the pore 30 and the inner wall surface 30b of the pore 30 is preferably an obtuse angle, and more preferably 45 ° or more. The same applies to the sliding surfaces 3a and 4a.

In addition, the occupied area ratio Sv of the pores is numerically expressed at a magnification of 100 times using an image analysis apparatus by taking an image of a metal microscope with a CCD camera in an area of 0.9 mm ² of each sliding surface 2a, 3a, 4a. did.

  Each sliding member preferably contains 40% by mass or more of silicon oxide as a glass phase component.

  Silicon oxide is used along with magnesium oxide and calcium oxide as a sintering aid for aluminum oxide. In the present invention, silicon oxide acts as a sintering aid for aluminum oxide and is slid in the glass phase. It is important to make it exist in the sintered compact which comprises moving surface 2a, 3a, 4a. Components that form the glass phase include phosphorus oxide, germanium oxide, and boron oxide. However, these materials have a low melting point, the aluminum oxide does not match the firing temperature, and the chemical stability is also silicon oxide. It is not practical because it is inferior to

  The reason why the silicon oxide contained in the glass phase is 40% by mass or more is that when the silicon oxide is less than 40% by mass, the phase that should originally become the glass phase tends to be a crystalline phase during the sintering process. This is because when the sliding member is slid, it becomes difficult to form a lubricating layer on the sliding surfaces 2a, 3a, and 4a, and even if a lubricating layer is formed, it is easy to peel off. In order to form a stable lubricating layer, the silicon oxide content is more preferably 54% by mass or more.

  Further, the glass phase preferably contains at least one of magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, iron oxide, sodium oxide, and boron oxide. These additives are added to improve the sinterability of the sliding member and the properties of the glass phase. Sodium oxide has the effect of promoting the progress of the lubricating layer by lowering the melting temperature and viscosity of the glass phase, and calcium oxide has the effect of increasing the chemical stability of the glass phase and the lubricating layer. Zirconium oxide and titanium oxide have the effect of increasing the rigidity of the glass phase, and magnesium oxide has the effect of improving the sinterability of the aluminum oxide crystal phase. Furthermore, a part of aluminum oxide is contained in the glass phase, and it has the effect of improving the chemical stability of the glass phase and suppressing the crystallization of the glass phase to easily form a lubricating layer. Boron oxide forms borosilicate glass, and since it has a low coefficient of thermal expansion, it has the effect of improving thermal shock resistance and excellent corrosion resistance. Iron oxide has the effect of a colorant, and when added, it develops a beige color. Therefore, particularly when used in a dynamic pressure bearing, it has the effect of increasing the visibility of the dynamic pressure generating grooves formed on the surface of the member.

  The average crystal grain size of the aluminum oxide crystal phase in each sliding member is preferably 1.0 to 8 μm.

  There is a close relationship between the average grain size of the aluminum oxide crystal phase, the area occupied by the pores, and the formation process of the lubricating layer on which the glass phase acts during use. That is, in the sintering process of the sintered body constituting the sliding member, pores existing in the sliding surfaces 2a, 3a, 4a are set by setting the average crystal grain size of the aluminum oxide crystal phase in the range of 1.0 to 8 μm. In addition, the occupation area ratio is set to 50% or less, and the lubricating phase is easily fixed to the sliding surfaces 2a, 3a, and 4a. Here, the average crystal grain size of the aluminum oxide crystal phase is set to 1.0 μm or more when the average crystal grain size is less than 1.0 μm in the process of firing the slide member molded body into a sintered body. This is because the sintering is insufficient and a large number of pores remain in the glass phase, making it difficult to reduce the occupied area ratio of the pores on the sliding surfaces 2a, 3a, and 4a to 50% or less. Further, the average crystal grain size of aluminum oxide is set to 8 μm or less. When the average crystal grain size exceeds 8 μm, the time for the lubricating layer to develop and cover the surface of the aluminum oxide crystal phase increases, and the sliding surface 2a, This is because 3a and 4a are easily damaged. A more preferable range of the average crystal grain size is 6 μm or less.

  Next, the sliding member of the present invention is a lubricating layer mainly composed of the glass phase component on at least a part of the sliding surfaces 2a, 3a, 4a by sliding on the sliding surfaces 2a, 3a, 4a. Is preferably formed.

  That is, when the sliding member of the present invention is slid, wear and plastic flow start from the glass phase having a low hardness, and when this state continues, the lubricating layer mainly composed of the glass phase component is formed on the surface of the aluminum oxide crystal phase. As a result, it becomes a lubricating layer of a sliding surface having lubricity, and it is possible to suppress the abrasive wear in which the sliding members are scraped together. The lubricating layer also has an action of taking the wear powder generated from the aluminum oxide crystal phase into the inside thereof, and also has an effect of suppressing the wear powder from scattering from the sliding surfaces 2a, 3a, and 4a.

  Further, it is considered that the progress of the lubricating layer is affected by frictional heat in addition to the pressure applied to the sliding surfaces 2a, 3a, and 4a. In particular, when the sliding members are in contact with each other at high speed due to the start / stop of rotation, vibration, swinging, inclination, etc. like the hydrodynamic bearing 1, the sliding surfaces 2a, 3a, 4a are in a very small area. It is considered that the heat is instantaneously increased, and the lubricating layer is softened to promote progress.

  That is, the lubricating layer formed on the sliding member of the present invention is fixed on the sliding surfaces 2a, 3a, and 4a in a state where each sliding member is floating, but the members are in contact with each other at high speed. When sliding, it exhibits fluidity and absorbs shocks to protect the sliding surfaces 2a, 3a, 4a.

  The lubricating layer in the present invention is formed on the sliding surfaces 2a, 3a, 4a when sliding at a rotational speed of 5000 rpm or more (circumferential speed of about 2.6 m / s or more) for 5 seconds or more. The composition is such that the wear component of the aluminum oxide crystal phase is mixed into the main component consisting of the glass phase, and the lubricating layer is formed with a thickness of 2 μm or less from the viewpoint of maintaining the dimensional accuracy of the sliding member. It is preferable.

  Confirmation of the lubricating layer can be made by observing the sliding surface with a scanning electron microscope (hereinafter referred to as SEM). The surface state may be, for example, a smooth surface in which pores or an aluminum oxide crystal phase are not observed by being covered with a lubricating layer, or a case where the lubricating layer forms a scale-like pattern.

  In the process of forming the lubricating layer, since the lubricating layer component is supplied from the contacted and slid portion, the dimensional accuracy of the member is hardly deteriorated due to wear, and the dynamic pressure can be stably generated. Is possible.

  Next, the manufacturing method of the sliding member of the present invention will be described in the case where the sleeve 3 is formed of a sintered body mainly composed of an aluminum oxide crystal phase and a glass phase as the sliding member.

First, aluminum oxide and a glass phase component are prepared, pulverized with a ball mill or a vibration mill to a predetermined particle size, and then a binder made of polyvinyl alcohol, polyethylene glycol, acrylic, etc. is added and granulated by spray drying. To do. And the compact | molding | casting is obtained by applying the pressure of 0.8-1.5 ton / cm < ² > with a powder press apparatus using this granulated raw material.

  Thereafter, the sintered body is obtained by firing at 1500 to 1650 ° C. for 1 to 5 hours using an electric furnace or a gas furnace, and finally, the sintered body is processed into a predetermined shape. At this time, in order to make the occupied area ratio of the glass phase present on the sliding surface 3a corresponding to the inner peripheral surface 30% or more and 75% or less, the aluminum oxide is 55% by mass or more and less than 95% by mass, the glass phase component The auxiliary agent to be used may be 5% by mass or more and less than 45% by mass, and in order to make the occupied area ratio of the glass phase 35% or more and 65% or less, aluminum oxide is 60% by mass or more and 90% by mass. In order to make the glass phase component 10 mass% or more and less than 40 mass%, and further to make the occupied area ratio of the glass phase 50% or more and 60% or less, the aluminum oxide is 65 mass% or more and 75 mass%. And the glass phase component may be adjusted to 25% by mass or more and less than 35% by mass, respectively.

  In addition, in order that the occupation area ratio of the glass phase existing on the sliding surface 3a corresponding to the inner peripheral surface is 30% or more and 75% or less, the aluminum oxide is 55% by mass or more and less than 95% by mass, and the glass phase component is 5%. What is necessary is just to be mass% or more and 45 mass% or less, and in order to make the occupation area rate of a glass phase 35% or more and 65% or less, aluminum oxide is 62 mass% or more and less than 90 mass%, glass phase In order to make the components 10 mass% or more and less than 38 mass%, and further to make the occupied area ratio of the glass phase 50% or more and 60% or less, aluminum oxide is 65 mass% or more and less than 75 mass%, glass phase What is necessary is just to make a component into 25 mass% or more and less than 35 mass%.

  The occupied area ratio of the glass phase on the sliding surface 3a is adjusted by the composition ratio of the aluminum oxide and the glass phase component as described above when the sliding surface 3a has a surface roughness Ra of 0.3 μm or less. However, it is easily affected by surface conditions such as surface roughness described later. Therefore, it is necessary to adjust the occupied area ratio of the glass phase by changing the processing conditions according to the surface condition required by the processing conditions described later.

  Further, the content of silicon oxide in the auxiliary agent added to the glass phase component may be 40% by mass or more, and the balance of the glass phase is magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, iron oxide, sodium oxide. In order to make it one or more, these may be added as appropriate to the glass phase component, and in order to make the silicon oxide content 40% by mass or more, the ratio of silicon oxide in the auxiliary agent should also be 40% by mass or more. Is preferred.

  In order to make the occupied area ratio of the pores existing on the sliding surface 3a 50% or less, it is necessary to reduce the pores as much as possible at the manufacturing stage. In this stage, the portion corresponding to the sliding surface 3a is finally processed by lapping, centerless, honing, super finishing, etc. Depending on the processing method at this time, the surface of the sintered body The crystal grains fall off due to the processing pressure and new pores are generated. Therefore, the occupied area ratio of the pores existing on the sliding surface 3a can be adjusted by the processing method. Is preferably diamond of about # 1000 to # 10000. Specifically, the occupation area ratio of the pores can be reduced by making the grinding wheel finer and slowing the processing speed, and increasing the porosity and increasing the machining speed to increase the occupation area ratio of the pores. When the sleeve 3 is processed, the outer diameter is centerless processed, the inner diameter is processed with an inner diameter processing machine, and then the honing is performed so that the pores are within the range of the present invention. The honing process is performed at a rotational speed of 1000 to 3000 rpm, and the grinding wheel is adjusted in a range of # 1000 to # 10000. In addition, cerium oxide, silicon oxide, aluminum oxide, silicon carbide, boron carbide, boron nitride, diamond and the like can be added as free abrasive grains to the grinding fluid, and SK steel can be used instead of the grindstone. Further, when the shaft 2 is processed, after performing the centerless processing, it may be processed by super finishing so that the pores of the sliding surface are within the scope of the present invention. The superfinishing conditions are as follows: the workpiece feed rate is 0.5 to 2.0 m / min, the workpiece peripheral speed is 10 to 50 m / min, and the grinding wheel is adjusted in the range of # 1000 to # 10000.

That is, the ratio of the glass phase can be adjusted within the scope of the present invention by adjusting the mixing ratio of aluminum oxide and auxiliary agent, the firing temperature, and the finishing conditions.

  Furthermore, in order to reduce the occupied area ratio of the pores to 30% or less, the shaft 2 may be superfinished and the grinding wheel may be set to # 3000 to # 10000, and if the sleeve 3, the SK steel may be used as a tool. For example, diamond, cerium oxide, silicon oxide or the like may be used for a metal plate such as a free abrasive grain.

  When these sliding members are used for hydrodynamic bearings, many of the properties required for the material correspond to the sliding environment at the start / stop of rotation, and are mainly wear and heat resistant. Therefore, the gaps 5 and 6 may be filled with oil as a lubricating fluid. However, the oil is surely sealed so that the oil does not scatter from the gaps of the hydrodynamic bearings, and heat is generated so that the oil does not oxidize and deteriorate. It is necessary to design in consideration of the usage environment such as rotation speed. When air is used as the lubricating fluid, the shaft 2 or thrust 4 and the sleeve 3 are in direct contact with each other at the start / stop of rotation, so that the lubricating fluid may be composed of a sintered body having excellent wear resistance and heat resistance. . There is also a method of coating the sliding surfaces 2a, 3a and 4a with a solid lubricant such as DLC (diamond-like carbon) or molybdenum disulfide to form a lubricating layer, but these coating layers are formed over time. Since wear and peeling occur, it is desirable to design in consideration of the case where the substrate is exposed.

And each sliding member manufactured in this way can be used suitably as a dynamic pressure bearing as shown in the above-mentioned FIG. 1, Furthermore, as a motor as shown in FIG. 3 using this dynamic pressure bearing, It can be used suitably.
The motor 10 in FIG. 3 is a longitudinal sectional view showing an example of a motor using the sliding member of the present invention, and includes a shaft 11, which is a rotating member, a rotor hub 15, a thrust 13, a base 18 which is a stationary member, and a sleeve 12. And the thrust 14, both of which are cylindrical in shape, and as a means for giving a rotational driving force, the stator 17 fixed to the base 18 and the inner wall of the rotor hub 15 have N and S poles alternately in an annular shape. A magnet 16 is provided. A plurality of stators 17 and magnets 16 are installed in the same number on the base 18 and the funnel hub 15, respectively, and are arranged concentrically with respect to the rotating shaft 20.

  In this dynamic pressure bearing, the shaft 11, the thrust 13, the sleeve 12 of the stationary member, and the thrust 14 are constituted by the sliding member of the present invention. The shaft 11 is rotatably inserted into the sleeve 12 with the central portion of the rotor hub 15 fixed at the upper end, and the thrust 13 is fixed at the lower end. The sleeve 12 and the thrust 14 are fixed to the base 18 and receive dynamic pressure in the radial direction and the thrust direction, respectively. The sliding member of the present invention is used for the shaft 11, the sleeve 12, the thrust 13, and the thrust 14. The shaft sliding surface 11a and the thrust sliding surfaces 13a and 13b are formed with dynamic pressure generating grooves. It has a structure in which dynamic pressure is generated in the gap between the opposing members, and it floats and rotates without contact.

  The shape of the dynamic pressure generating groove may be a general herring bone or a type in which flat surfaces parallel to the axial direction are formed at equal intervals on the outer periphery of the shaft as disclosed in JP-A-9-14257. In the case of a small motor used in an electronic apparatus, the groove depth of the herring bone is preferably about several μm, and the groove depth is preferably 20 μm or less when the flat surface is regarded as a groove.

  In the motor 10 configured as described above, when an alternating current flows through the stator 17, a magnetic field is generated, attracted (repels) the magnetic force of the magnet 16, and the rotor hub 12 rotates. When the rotor hub 12 is rotated, the shaft 11 and the thrust 13 are also rotated. When the rotation is started, they slide in contact with the opposing members. When the number of rotations increases, dynamic pressure is generated by the dynamic pressure generating grooves formed in the respective members. Then, the member floats and the non-contact rotation is continued in a state where a certain gap is maintained.

  Then, a hard disk, a polygon mirror, or the like is mounted on the outer peripheral portion 19 of the rotor hub 15 and used for an HDD, LBP, or the like.

  In addition, the motor of the present invention includes, for example, a server HDD having a rotation speed of 10,000 rpm or more, a personal computer HDD having a rotation speed of 15,000 rpm or more, an LBP having a rotation speed of 50,000 rpm or more, and a rotation speed of 10 It can be used for a DLP (digital light processor) of 000 rpm or more. These motor speeds are the values at which the motor bearings used in each product cannot be used with ball bearings or oil dynamic pressure bearings due to wear or seizure. By forming the bearing, the problem can be solved. Furthermore, the motor of the present invention is used in an environment where vibration is intense like an in-vehicle HDD, and the lubricating layer protects the sliding surface even if the bearing members come into contact with each other. Is possible.

Example 1
Next, as an example using the sliding member of the present invention, a case where a dynamic pressure bearing is configured will be described as an example.

  First, in the composition shown in Table 1, silicon oxide and additives magnesium oxide, calcium oxide and zirconium oxide were added to aluminum oxide as an auxiliary agent to prepare a raw material for preparation. At this time, the ratio of the mass of silicon oxide to the mass of the additive was kept constant at 4: 6. In addition, magnesium oxide, calcium oxide, and zirconium oxide were prepared in a mass ratio of 4: 9: 7, respectively.

And the said mixing raw material was wet-ground with water using a ball mill, it was set as the slurry, the binder was added, and it spray-dried with spray drying to make the powder raw material.
Thereafter, an appropriate amount of the powder raw material is weighed and pressure-molded at a pressure of about 1 ton / cm ² using a powder press machine, and the shaft 2, sleeve 3 and thrust 4 of the hydrodynamic bearing 1 as shown in FIG. A molded body was prepared.

  Next, the compact was fired in an electric furnace at 1400 to 1700 ° C. for 1 to 5 hours to obtain ceramics for the shaft 2, the sleeve 3, and the thrust 4.

  The shaft 2 of the present invention was subjected to centerless processing and then processed by superfinishing so that the pores of the sliding surface were within the scope of the present invention. The superfinishing conditions were such that the workpiece feed speed was 0.5 to 1.0 m / min, the workpiece peripheral speed was 30 to 40 m / min, and the grinding wheel was adjusted in the range of # 2000 to # 6000.

  The sleeve 3 was subjected to centerless processing on the outer diameter, then processed with an inner diameter processing machine, and then processed by honing so that the pores were within the scope of the present invention. The honing process was performed at a rotational speed of 1200 to 2000 rpm, and the grinding stones were adjusted in the range of # 1000 to # 3000. Further, a processing method using SK steel instead of the grindstone and using diamond abrasive grains having a particle diameter of 2 to 4 μm as the grinding liquid was also used.

  Specifically, the occupation ratio of the pores was reduced by making the grinding wheel finer and slowing the processing speed, and increasing the pores by increasing the coarseness and the machining speed.

  Then, in order to confirm that the aluminum oxide crystal phase and the glass phase are present on the sliding surface, analysis is performed using an X-ray diffractometer to confirm the peak of the aluminum oxide crystal and the peak of the silicon oxide crystal. It was confirmed that no glass was detected, and further a halo pattern was shown by the method of limited-field electron diffraction image analysis, so the presence of the glass phase was confirmed.

Further, the occupied area ratio Sv of the pores was quantified at a magnification of 100 using an image analysis apparatus by taking an image of a metal microscope with a CCD camera in the range of the sliding surface area of 0.9 mm ² . The occupied area ratio Sg of the glass phase is obtained by subjecting the sliding member to fire etching to improve the visibility of the aluminum oxide crystal phase, and then quantifying the occupied area ratio Sa of the aluminum oxide crystal phase with an image analysis device in the same manner. ).

Sg = 100−Sa−Sv (1)
Next, a motor as shown in FIG. 3 is assembled using the produced shaft 2, sleeve 3 and thrust 4, and a start and stop test is performed 50,000 times at a rotational speed of 10,000 rpm, and the sliding surface is damaged or worn. Observed with SEM and metallurgical microscope, ◎ indicates that the sliding surface is not damaged due to scratches or crystal grains falling, and ◯ indicates that there are linear marks but no crystal grain falling off or damage. It was determined that the product was excellent, and a product with breakage or crystal grain loss was evaluated as x, which was determined as a defective product with poor slidability.

  Furthermore, after the test, each sliding surface was observed with an SEM to investigate whether a lubricating layer was formed. The part where the sliding layer is in contact with the sliding member is judged as a non-defective product when the lubricating layer is formed entirely on the surface, and at least part of the lubricating layer is judged as good. Those not present were judged as defective products as x.

The results are shown in Table 1.

  From Table 1, the samples (No, 2-6, 9-16) in which the occupied area ratio of the glass phase within the scope of the present invention is 30 to 75% and the occupied area ratio of the pores is 50% or less are sliding. Some of the sliding surfaces had linear traces after the test, but it was found that the sliding surface was excellent in slidability with no drop of crystal grains or breakage.

  In particular, the samples (No. 4 to 6) in which the occupied area ratio of the glass phase is 50 to 60% and the occupied area ratio of the pores is 50% or less have no linear trace after the sliding test, and more excellent sliding It was found to have sex.

  On the other hand, samples (No. 17 and 18) in which the occupied area ratio of the glass phase is less than 30% are poorly slidable due to large wear, and the samples (No. 1 in which the occupied area ratio of the glass phase exceeds 75%). ) Was damaged due to a decrease in the strength of the sliding surface because the glass phase was too much. Further, it was found that the samples (Nos. 7 and 8) in which the occupied area ratio of the pores exceeded 50% were peeled off although the lubrication layer was formed, and linear traces and crystal grains were dropped on the sliding surface. .

(Example 2)
Next, the ratio of silicon oxide and additive in the auxiliary agent of Sample 13 in Table 1 was changed, and the shaft 2, sleeve 3 and thrust 4 were produced in the same manner as in Example 1, the motor was assembled in the same manner, and sliding In order to make the conditions strict, the rotation axis of the motor was set to be horizontal, and the start / stop test was performed 100 times at a rotation speed of 15000 rpm to evaluate the slidability. The evaluation of the slidability was measured by observing the state of the sliding surface with an SEM to see if there was any dimensional change due to wear before and after the test, with 1.5 μm or less ◎, 2 μm or less ○, and more than × evaluated. In addition, after the test, each sliding surface was observed with an SEM to investigate whether a lubricating layer was formed. The part where the sliding layer is in contact with the sliding member is judged as a non-defective product when the lubricating layer is formed entirely on the surface, and at least part of the lubricating layer is judged as good. Those not present were judged as defective products as x.

The results are shown in Table 2.

  As is apparent from the table, the occupied area ratio of the glass phase is 30 to 75%, the occupied area ratio of the pores is 50% or less, and the silicon oxide content of the auxiliary agent as a glass component to be added is 40% by mass or more. Samples (Nos. 13-1 to 13-4, 13) were found to have a lubrication layer uniformly formed on the sliding surface and to have excellent sliding properties. Moreover, these samples were also suppressed in the thickness change to 2 micrometers or less, and when the sliding surface was observed with SEM, it turned out that the lubricating layer is formed.

On the other hand, even when the occupied area ratio of the glass phase is 30 to 75% and the occupied area ratio of the pores is 50% or less, the content of silicon oxide of the auxiliary agent which is a glass component to be added is less than 40% by mass. In the sample (No. 13-5 to 13-7), although the dimensional change was suppressed to 2 μm or less,
In some cases, the lubricating layer was not formed, and it was found that the wear resistance was reduced as compared with a sample containing 40% by mass or more of silicon oxide.

An example of the dynamic pressure bearing using the sliding member of this invention is shown, (a) is a perspective view, (b) is sectional drawing in CC line. The conventional dynamic pressure bearing is shown, (a) is a perspective view, (b) is sectional drawing in the DD line.

(C) is an enlarged sectional view of a sliding surface.
It is sectional drawing which shows an example of the motor using the sliding member of this invention.

Explanation of symbols

1: Dynamic pressure bearing 2: Shaft 2 a: Shaft surface 2 b: Dynamic pressure generating groove 3: Sleeve 3 a: Sleeve sliding surface 4: Thrust 4 a: Thrust surface 4 b: Dynamic pressure generating groove 5: Radial clearance 10: Motor 11 : Shaft 11a: Shaft sliding surface 12: Sleeve 13: Thrust 13a: Thrust sliding surface 13b: Thrust sliding surface 14: Thrust 15: Rotor hub 16: Magnet 17: Stator 18: Base 19: Outer portion 20: Rotating shaft 30 : Pore 30b: Inner wall surface 51: Dynamic pressure bearing 52: Shaft 52a: Shaft surface 52b: Dynamic pressure generating groove 53: Sleeve 54: Thrust 54a: Thrust surface 54b: Dynamic pressure generating groove 55: Clearance in radial direction

Claims (6)

At least the sliding surface is mainly composed of an aluminum oxide crystal phase and a glass phase, the occupied area ratio of the glass phase on the sliding surface is 30% or more and 75% or less, and the occupied area ratio of the pores is 50% or less. A sliding member characterized by that. The sliding member according to claim 1, wherein the glass phase contains 40% by mass or more of silicon oxide. The sliding member according to claim 1 or 2, wherein an average crystal grain size of the aluminum oxide is 1.0 µm or more and 8 µm or less. 4. The bond issuance according to claim 1, wherein a lubricating layer mainly composed of the glass phase component is formed on at least a part of the sliding surface by sliding on the sliding surface. Sliding member. A hydrodynamic bearing using the sliding member according to claim 1. A motor using the hydrodynamic bearing according to claim 5.

Images