JP2004308917A - Manufacturing method for hydrodynamic porous oil impregnated bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and simply form a hydrodynamic groove on a surface of a bearing. <P>SOLUTION: A cylindrical sintered metal material with a density ratio α(%) of 75≤α<85 is manufactured. A core rod formed to be a protrusion/recess-shaped mold corresponding to shapes of for the surface of a bearing is inserted onto an inner periphery of the sintered metal material, and a pressure is applied to the sintered metal material. Thus, the inner periphery of the sintered metal material is pressurized onto the mold of the core rod, and the hydrodynamic groove on the surface of the bearing is formed by means of plastic work. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention impregnates a porous body made of a sintered metal with lubricating oil or lubricating grease to have a self-lubricating function, and floats and supports a sliding surface of a shaft by a hydrodynamic oil film of oil interposed in a bearing gap. The present invention relates to a method for manufacturing a hydrodynamic porous oil-impregnated bearing. The hydrodynamic porous oil-impregnated bearing manufactured by the manufacturing method of the present invention has high rotational accuracy at high speeds, such as a spindle motor for a polygon mirror of a laser beam printer (LBP) or a magnetic disk drive (HDD). It is suitable for a required device or a device such as a spindle motor for a DVD-ROM, which drives at a high speed due to a large unbalanced load acting on the disk.

  In such small spindle motors related to information equipment, further improvement in rotational performance and cost reduction are required, and as a means for this, replacing the bearing part of the spindle from a rolling bearing to a porous oil-impregnated bearing. Is being considered. However, since the porous oil-impregnated bearing is a kind of a perfect circular bearing, unstable vibration is easily generated in a place where the eccentricity of the shaft is small, and so-called whirling which oscillates at half the rotation speed is easily generated. There are drawbacks. Therefore, it has been attempted to provide a dynamic pressure groove, such as a herringbone type or spiral type, on the bearing surface, and to generate a dynamic pressure oil film in the bearing gap by the action of the dynamic pressure groove due to the rotation of the shaft to float and support the shaft. (Dynamic pressure type porous oil-impregnated bearing).

On the other hand, this type of hydrodynamic porous oil-impregnated bearing has a high effect on suppressing shaft runout, but has a high dynamic pressure due to oil in the bearing gap escaping into the bearing through surface openings in the bearing surface. There is a problem that the effect is reduced (dynamic pressure loss), and it is difficult to obtain the expected dynamic pressure effect. Conventionally, as a means for solving the problem of the dynamic pressure drop, there is known a configuration in which a dynamic pressure groove on a bearing surface is subjected to surface blanking processing to seal a region where the dynamic pressure groove is formed (Patent Document 1).
JP-A-63-19627

   The configuration of Patent Document 1 has the following problems.

  (1) Since the formation region of the dynamic pressure groove is completely sealed, the circulation of oil, which is the greatest feature of the porous oil-impregnated bearing, is inhibited in that region. Therefore, the oil once seeping into the bearing gap is pushed into the bent portion of the groove by the action of the dynamic pressure groove and stays there. Since a large shearing action is exerted in the bearing gap, the oil remaining in the groove tends to be denatured by the shearing force and the frictional heat, and the oxidative deterioration tends to be accelerated by the temperature rise. Therefore, the bearing life is shortened.

  (2) It is extremely difficult to completely seal the area where the dynamic pressure groove is formed. Although the above publication discloses that the sealing can be performed by plastic working, the groove depth of the dynamic pressure groove is usually on the order of μm, and the surface opening is not completely sealed by such plastic working.

  (3) Coating etc. is mentioned as another means for performing surface blanking, but the thickness of the coating film needs to be thinner than the groove depth, and a coating film of several μm is applied only to the area where the dynamic pressure groove is formed. It is extremely difficult to apply.

  Even if the formation region of the dynamic pressure groove is not completely sealed, the amount of oil returned from the bearing gap to the inside of the bearing is reduced by adjusting the area ratio of the surface openings (surface opening ratio). Therefore, a reasonable effect can be expected. However, in the adjustment of the surface opening ratio, the resistance to the oil flow is small, so the adjustment of the oil return amount is limited, and considering the recent trend of higher speed rotation and higher performance of spindle motors. In many cases, a sufficient dynamic pressure effect cannot be obtained.

  Accordingly, the present invention provides a dynamic pressure-type porous oil-impregnated bearing of this type which solves the problem of dynamic pressure drop in the bearing gap while securing oil circulation between the inside of the bearing body and the bearing gap. An object of the present invention is to further improve the bearing function, particularly the bearing rigidity (bearing load capacity) and the service life of the bearing, by increasing the dynamic pressure effect by the pressure grooves.

  Another object of the present invention is to provide a manufacturing method capable of easily and accurately forming a dynamic pressure groove on a bearing surface.

  In order to solve the above problems, the present invention is a method for producing a hydrodynamic porous oil-impregnated bearing in which a bearing surface having a hydrodynamic groove is formed on an inner peripheral surface of a porous bearing body made of a sintered metal. A core rod in which a cylindrical sintered metal material having a density ratio α (%) of 75 ≦ α <85 is manufactured, and a concave / convex forming die corresponding to the shape of the bearing surface is formed, and the inner periphery of the sintered metal material is formed. The present invention provides a configuration including a step of forming a dynamic pressure groove on a bearing surface by plastic working by inserting the bearing into a surface and applying a pressing force to a sintered metal material to press the core rod forming die. Here, the density ratio α (%) is represented by the following equation.

Density ratio α (%) = (ρ1 / ρ0) × 100
ρ1: Density of the porous body ρ0: Density assuming that the porous body has no pores

  FIG. 4 shows the relationship between the density ratio α (%) and the porosity (volume ratio of pores in a unit volume) (%) in the porous body. The porosity is linearly proportional to the density ratio α, and decreases as the density ratio α increases. For example, when the density ratio α = 75%, the porosity is about 25%, when the density ratio α = 80%, the porosity is about 20%, when the density ratio α = 85%, the porosity is about 15%, and the density ratio α = 90%, the porosity is about 10%, and the density ratio α = 95%, the porosity is about 5%. The porosity on the outer surface is substantially the same as the surface porosity (area ratio of the surface porosity occupying a unit area of the outer surface) (when no surface treatment is performed).

  The reason why the density ratio α (%) of the sintered metal material is set in the range of 75 ≦ α <85 is as follows. That is, if the density ratio α of the sintered metal material is less than 75%, the porosity becomes too large, and the shape of the dynamic pressure groove cannot be finished with high accuracy when the bearing surface is formed. Conversely, if the density ratio α of the sintered metal material is 85% or more, the porosity becomes too small, and the amount of retained oil decreases. Therefore, from the viewpoint of securing the forming accuracy of the dynamic pressure grooves and securing the oil holding amount of the bearing body, it is preferable to set the density ratio α (%) of the sintered metal material within the range of 75 ≦ α <85. .

  In addition, the inner peripheral surface of the sintered metal material is pressed against the core rod forming die, so that at least the bearing surface of the manufactured hydrodynamic porous oil-impregnated bearing has a density ratio α of the above sintered metal material. A surface portion higher than the density ratio α is formed.

  The dynamic pressure type porous oil-impregnated bearing circulates the oil held in the pores inside the bearing body between the bearing body and the bearing gap, and creates a dynamic pressure oil film in the bearing gap by the dynamic pressure action of the dynamic pressure groove. It is characterized by the fact that the shaft is continuously lifted and supported by the dynamic pressure oil film.In order to achieve such a stable bearing function, it is necessary for proper oil circulation and shaft support. It is necessary to ensure the formation of a dynamic oil film. In particular, the circulation of oil has the function of suppressing deterioration of the oil and extending the life of the bearing, and also complements and reciprocates with the formation of the hydrodynamic oil film. Is an extremely important issue in this type of hydrodynamic porous oil-impregnated bearing. In other words, in order to always form a dynamic pressure oil film with sufficient dynamic pressure and oil film thickness in the bearing gap, a proper amount of fresh oil always oozes out of the bearing body into the bearing gap to form a dynamic pressure oil film. In addition, it is essential that the oil circulation cycle of returning to the bearing body from the bearing gap works properly. If the amount of oil circulation is too small, the oil will not sufficiently seep into the bearing gap, resulting in insufficient formation of the hydrodynamic oil film.At the same time, the oil will stay in the bearing gap, causing oxidation deterioration due to temperature rise. Come. On the other hand, if the circulation amount of the oil is excessive, the oil returns from the bearing gap to the bearing body excessively, and the above-described problem of the dynamic pressure drop occurs.

  Means for controlling the amount of oil circulation include adjustment of the surface porosity and adjustment of the kinematic viscosity of the oil. However, since the resistance to the oil flow is small in the adjustment of the surface porosity, there is a limit in adjusting the circulation amount. Excessive adjustment of the kinematic viscosity of the oil causes an increase in torque. Therefore, these measures may be insufficient.

  As described above, according to the present invention, since a surface portion having a high density ratio α is formed on at least the bearing surface of the hydrodynamic porous oil-impregnated bearing, resistance when oil passes through the pores of the surface portion is reduced. It becomes moderately large, and oil seepage from the bearing body into the bearing gap and return of oil from the bearing gap to the bearing body are adjusted to an appropriate amount. Therefore, the action of forming the dynamic pressure oil film by the dynamic pressure grooves is enhanced, and the bearing rigidity (bearing load capacity) is improved, and at the same time, appropriate circulation of oil is ensured, and the bearing life is improved.

  It is preferable that the density ratio α (%) of the surface layer portion is in the range of 85 ≦ α ≦ 95. If the density ratio α of the surface layer portion is less than 85%, the resistance to the flow of the oil becomes too small, and a dynamic pressure drop occurs, and a sufficient dynamic pressure effect cannot be expected. Conversely, if the density ratio α of the surface layer portion exceeds 95%, the resistance to the flow of the oil becomes too large, and appropriate circulation of the oil is hindered. In the hydrodynamic porous oil-impregnated bearing manufactured according to the present invention, the flow of oil is given resistance to the flow of oil by the pores in the surface layer from the surface of the bearing surface to a predetermined depth. The effect of adjusting the amount of oil seeping out and returning is high.

  The ratio (t / D1) of the average value (t) of the depth of the surface portion (hereinafter referred to as “average depth t”) to the inner diameter (D1) of the bearing surface is 1/60 ≦ t / D1 ≦. It is preferable to be within the range of 1/15. When t / D1 is less than 1/60, the resistance to the oil flow becomes too small. Conversely, when t / D1 exceeds 1/15, the resistance to the oil flow becomes too large, and the same as above. A phenomenon occurs.

  One of the parameters for controlling the amount of oil circulation is the kinematic viscosity of the oil. When the kinematic viscosity of the oil increases, the oil becomes difficult to move. Conversely, when the kinematic viscosity of the oil decreases, the oil moves easily. If the kinematic viscosity adjustment of the oil is added to the configuration described above, a better effect can be obtained. However, between the density ratio α (%) of the surface layer on the bearing surface and the kinematic viscosity of the oil, it is considered that there is an optimum range that can ensure proper circulation of the oil and formation of the hydrodynamic oil film. The kinematic viscosity of the oil should be selected in the optimal range. For example, the kinematic viscosity of the oil at 40 ° C. is preferably 5 cSt to 60 cSt, and more preferably 8 cSt to 40 cSt. By selecting the kinematic viscosity of the oil within this range, a sufficient dynamic pressure oil film is formed to support and float the shaft, and at the same time, appropriate circulation of the oil is ensured. Can be achieved.

  When the density ratio α of the surface layer on the bearing surface is in the range of 85% to 95%, the surface porosity (area ratio) on the bearing surface is approximately 5% to 15%. In addition, the surface porosity may be further reduced, for example, to about 2% to 5%.

  The present invention has the following effects.

  (1) The hydrodynamic porous oil-impregnated bearing manufactured by the manufacturing method of the present invention is configured such that the retained oil is circulated between the inside of the bearing main body and the bearing gap through pores in the surface layer of the bearing surface. Therefore, the seepage of oil from the bearing body into the bearing gap and the return of oil from the bearing gap to the bearing body are adjusted to an appropriate amount. Therefore, the action of forming the dynamic pressure oil film by the dynamic pressure grooves is enhanced, and the bearing rigidity (bearing load capacity) is improved, and at the same time, appropriate circulation of oil is ensured, and the bearing life is improved.

  (2) By setting the density ratio α (%) of the sintered metal material in the range of 75 ≦ α <85, the bearing surface (especially, the dynamic pressure groove) can be formed easily and accurately. Accordingly, it is possible to secure an appropriate oil holding amount of the bearing body.

  FIG. 5 conceptually shows a configuration example of a spindle motor of a laser beam printer (LBP). The spindle motor includes a shaft 2, a rotor (rotor hub) 8 provided on the shaft 2, and a hydrodynamic porous oil-impregnated bearing 1 that supports rotation of the shaft 2 and the rotor 8. In this embodiment, the hydrodynamic porous oil-impregnated bearing 1 is fixed inside a housing 7. The shaft 2 is inserted into the inner periphery of the hydrodynamic porous oil-impregnated bearing 1, and its shaft end is supported by a thrust receiver 9 in the thrust direction. The shaft 2 and the rotor 8 rotate at high speed by electromagnetic force generated between a magnet (rotor magnet) provided on the rotor side and the stator coil, and the rotation is supported by the dynamic pressure type porous oil-impregnated bearing 1 in a floating manner (non-contact support). ) Is done.

  FIG. 1 shows a configuration example of the above-described dynamic pressure type porous oil-impregnated bearing 1. The porous oil-impregnated bearing 1 has a bearing body 1a made of a porous body such as copper or iron, or a sintered alloy containing both of them as a main component, and impregnation of lubricating oil or lubricating grease into pores of the bearing body 1a. It is composed of retained oil (base oil of lubricating oil or lubricating grease).

  A bearing surface 1b is formed on the inner periphery of the bearing body 1a so as to face an outer peripheral surface of a shaft to be supported via a bearing gap, and an inclined dynamic pressure groove 1c is formed on the bearing surface 1b. The bearing surface 1b in this embodiment is provided with a first region m1 in which a plurality of hydrodynamic grooves 1c inclined in one direction with respect to the axial direction are formed in the circumferential direction, and is separated from the first region m1 in the axial direction. A second region m2 in which a plurality of dynamic pressure grooves 1c inclined in the other direction with respect to the direction are formed in the circumferential direction, and an annular smooth region n located between the first region m1 and the second region m2. Be composed. The spine 1d of the first area m1 (the area between the dynamic pressure grooves 1c) and the spine 1d of the second area m2 (the area between the dynamic pressure grooves 1c) are respectively continuous with the smooth area n. On the bearing surface 1b, surface openings are substantially uniformly distributed over the entire region including the region where the dynamic pressure groove 1c is formed. When the relative rotation occurs between the bearing main body 1a and the shaft, the oil in the bearing gap is directed to the smooth area n by the hydrodynamic grooves 1c which are formed in the first area m1 and the second area m2 in the opposite directions. And the oil is collected in the smooth region n, the oil film pressure in the smooth region n is increased. Therefore, the effect of forming the dynamic pressure oil film is high.

  The shape of the bearing surface 1b is not limited to the shape shown in the figure. For example, a dynamic pressure groove inclined to one side with respect to the axial direction and a dynamic pressure groove inclined to the other side are continuously formed in a V-shape. (In this case, there is no annular smooth region n). Further, a plurality of, for example, two bearing surfaces may be formed on the inner peripheral surface of one bearing body so as to be separated in the axial direction. Thereby, the coaxiality between the bearing surfaces can be ensured with high accuracy.

  FIG. 2 shows the flow of oil in the axial cross section when the shaft 2 is supported by the hydrodynamic porous oil-impregnated bearing 1 having the bearing surface 1b on which the inclined hydrodynamic grooves are formed. With the rotation of the shaft 2, oil retained in the pores inside the bearing body 1a oozes out from both sides (and the chamfer portion) of the bearing surface 1b in the axial direction into the bearing gap 4, and furthermore, the bearing gap is formed by the dynamic pressure groove. 4 is drawn toward the center in the axial direction. Due to the oil drawing action (dynamic pressure action), the pressure of the oil film interposed in the bearing gap 4 is increased, and a dynamic pressure oil film is formed. The dynamic pressure oil film formed in the bearing gap 4 allows the shaft 2 to float (non-contact support) on the bearing surface 1b without generating unstable vibration such as whirl. The oil that seeps into the bearing gap 4 is caused by the pressure generated by the rotation of the shaft 2, resulting in the surface opening of the bearing surface 1 b (“surface opening” refers to the portion where the pores of the porous body structure are open to the outer surface). ), Returns to the inside of the bearing body 1a, circulates through the inside of the bearing body 1a, and again seeps from the bearing surface 1b (and the chamfer portion) into the bearing gap 4.

  FIG. 3 schematically shows a density distribution in a longitudinal section of the bearing main body 1a. In the bearing body 1a, the density of the surface layer portion 1a1 from the outer surface to the average depth t is high, and the density of the inner side portion 1a2 on the inner side of the surface layer portion 1a1 is lower. The density of the surface layer portion 1a1 is in the range of 85 ≦ α ≦ 95 in terms of the density ratio α (%), and the density of the inner side portion 1a2 is in the range of 75 ≦ α <85 in terms of the density ratio α (%). Within range. The inner diameter D1 of the bearing surface 1b of the bearing body 1a (based on the area other than the area where the dynamic pressure groove 1c is formed) is φ3 mm, the outer diameter D2 is φ6 mm, and the depth h of the dynamic pressure groove 1c is 2 to 4 μm. It is. The average depth t of the surface layer portion 1a1 in the bearing surface 1b is within the range of 1/60 ≦ t / D1 ≦ 1/15 with respect to the inner diameter D1 of the bearing surface 1b. / 60 is 50 μm. The average depth t of the surface layer portion 1a1 on the outer peripheral surface and both end surfaces of the bearing main body 1a is also substantially the same as that of the bearing surface 1b, and is approximately 50 μm in this embodiment. In the drawing, the depth h of the dynamic pressure groove 1c and the average depth t of the surface portion 1a1 are considerably exaggerated. Also, the dimensional ratio between the depth h and the average depth t is shown in a different ratio from the actual one. The surface layer portions 1a1 on the outer peripheral surface and both end surfaces of the bearing main body 1a are formed in order to prevent oil held inside the bearing main body 1a from flowing out from the outer peripheral surface and the end surface to the outside. The density (density ratio α) and the average depth t may be managed somewhat rougher than the surface layer portion 1a1 of the bearing surface 1b. For example, the density ratio α may be close to 100% (there is almost no pores), and the average depth t may be larger or smaller than the surface portion 1a1 of the bearing surface 1b. Further, the surface layer portion 1a1 on the outer peripheral surface or both end surfaces may not be provided.

  As shown in FIG. 6, a cylindrical sintered alloy material 1 as shown in FIG. 6 is obtained by compacting a metal powder containing copper or iron or both of them as a main component and then firing the metal powder. Can be manufactured by performing, for example, sizing → rotational sizing → bearing surface forming processing. The density ratio α (%) of the sintered alloy material 1 ′ is set in the range of 75 ≦ α <85.

  The sizing step is a step of sizing the outer peripheral surface and the inner peripheral surface of the sintered alloy material 1 ′. The outer peripheral surface of the sintered alloy material 1 ′ is pressed into a cylindrical die, and a sizing pin is inserted into the inner peripheral surface. Press in. The sizing margin is performed, for example, at an outer peripheral surface of 20 μm or less (radius amount of 10 μm or less) and at an inner peripheral surface of 10 μm or less (radius amount of 5 μm or less).

  The rotation sizing step is a step of pressing a polygonal sizing pin into the inner peripheral surface of the sintered alloy material 1 ′ and sizing the inner peripheral surface while rotating it. The sizing margin is set to about 5 μm (radius amount: about 2.5 μm).

  In the bearing surface forming step, a molding die having a shape corresponding to the bearing surface 1b of the finished product 1a is pressed onto the inner peripheral surface of the sintered alloy material 1 'subjected to the sizing processing as described above, thereby forming the bearing surface 1b. This is a step of simultaneously forming the formation area of the dynamic pressure groove 1c and the other area (back 1d, smooth area n). This step is, for example, as follows.

  FIG. 8 illustrates a schematic structure of a forming apparatus used in the bearing surface forming step. This apparatus includes a cylindrical die 20 for press-fitting an outer peripheral surface of a sintered alloy material 1 ′, a core rod 21 for molding an inner peripheral surface of the sintered alloy material 1 ′, and a vertical direction of both end surfaces of the sintered alloy material 1 ′. The upper and lower punches 22 and 23 pressed from above are configured as main elements. As shown in FIG. 2B, an outer peripheral surface of the core rod 21 is provided with a concave-convex mold 21a corresponding to the shape of the bearing surface 1b of the finished product. The convex portion 21a1 of the molding die 21a forms a region of the dynamic pressure groove 1c in the bearing surface 1b, and the concave portion 21a2 forms a region other than the dynamic pressure groove 1c (back 1d, annular smooth region n). The step (depth H) between the convex portion 21a1 and the concave portion 21a2 in the molding die 21a is 2 to 4 μm, which is the same as the depth h of the dynamic pressure groove 1c in the bearing surface 1b. ing.

  Before press-fitting into the die 20, there is an inner diameter clearance T between the inner peripheral surface of the sintered alloy material 1 'and the forming die 21a (based on the convex portion 21a1) of the core rod 21. The size of the inner diameter clearance T is 25 μm (radius clearance). The press-fit allowance (outer diameter interference S) of the outer peripheral surface of the sintered alloy material 1 ′ into the die 20 is 75 μm (radius allowance).

  After the sintered alloy material 1 ′ is positioned and arranged on the upper surface of the die 20, as shown in FIG. 9, the upper punch 22 and the core rod 21 are lowered, and the sintered alloy material 1 ′ is pressed into the die 20, Further, it is pressed against the lower punch 23 to apply pressure from above and below.

  The sintered alloy material 1 ′ is deformed by receiving a pressing force from the die 20 and the upper and lower punches 22 and 23, and the inner peripheral surface is pressed against the forming die 21 a of the core rod 21. The amount of pressure applied to the inner peripheral surface is substantially equal to the difference 50 μm (radius amount) between the outer diameter interference S (radius amount 75 μm) and the inner diameter clearance T (radius amount 25 μm), and the surface layer from the inner peripheral surface to a depth of 50 μm. The portion is pressed against the molding die 21a of the core rod 21 and causes plastic flow to bite into the molding die 21a. Thereby, the shape of the mold 21a is transferred to the inner peripheral surface of the sintered alloy material 1 ', and the bearing surface 1b is formed into the shape shown in FIG. During molding, the outer peripheral surface of the sintered alloy material 1 ′ is pressed by the die 20, and both end surfaces are pressed by the upper and lower punches 22 and 23, respectively. The amount of pressure on the outer peripheral surface is 50 μm, and the amount of pressure on both end surfaces is about 50 μm on one side.

  After the molding of the bearing surface 1b is completed, as shown in FIG. 11, the lower punch 23 and the core rod 21 are raised in conjunction with the core rod 21 inserted in the sintered alloy material 1 '(state 2). Then, the sintered alloy material 1 'is pulled out of the die 20 (state 3). When the sintered alloy material 1 ′ is pulled out of the die 20, springback occurs in the sintered alloy material 1 ′ and the inner diameter thereof increases (see FIG. 10). The core rod 21 can be removed from the inner peripheral surface of the material 1 '(state 4). Thereby, the bearing main body 1a is completed.

  In the above-described forming step of the bearing surface 1b, the inner peripheral surface of the sintered alloy material 1 'in which the density ratio α (%) is set within the range of 75 ≦ α <85 is formed with a pressing amount of 50 μm. By pressing the mold 21a, the density of the surface layer portion is increased, and in a state where the bearing body 1a is completed, as shown in FIG. The surface portion 1a1 having a density ratio α (%) of 85 ≦ α ≦ 95 is formed. At the same time, the outer peripheral surface and both end surfaces of the sintered alloy material 1 ′ are pressed by the die 20 and the upper and lower punches 22 and 23 with a pressing amount of 50 μm, respectively, so that the surface reaches an average depth of 50 μm from those surfaces. The surface portion 1a1 having a density ratio α (%) of 85 ≦ α ≦ 95 is formed. Since the inner side portion 1a2 of the bearing main body 1a is hardly affected by molding, the density ratio α (%) is within the range of 75 ≦ α <85 which is the density ratio α (%) of the sintered alloy material 1 ′. Is maintained.

  The density ratio α (%) of the sintered alloy material 1 ′ has a close relationship with the springback amount of the material 1 ′ when the core rod 21 is extracted in the above-described bearing surface forming step.

  FIG. 7 shows the result of experimentally determining the relationship between the density ratio α (%) of the sintered alloy material 1 ′ and the amount of springback (μm: diameter). The springback amount decreases as the density ratio α of the material 1 'increases. When the depth h of the dynamic pressure groove 1c in the bearing surface 1b is 2 to 4 μm, and when the density ratio α of the sintered alloy material 1 ′ exceeds 85%, the springback amount becomes less than 3 μm (diameter amount) and the core rod 21 There is a possibility that the dynamic pressure groove 1c of the bearing surface 1b will be broken when removing the bearing. On the other hand, if the density ratio α of the sintered alloy material 1 ′ is less than 75%, the springback amount becomes larger than 5 μm (diameter amount), but the forming accuracy of the dynamic pressure groove 1 c decreases. Therefore, from the viewpoint that the core rod 21 can be extracted without breaking the dynamic pressure groove 1c and the forming accuracy of the dynamic pressure groove 1c can be ensured, the density ratio α (%) of the sintered alloy material 1 ′ is 75 ≦ It must be set within the range of α <85. When the radius of the springback amount of the material 1 'is larger than the depth of the dynamic pressure groove 1c, the mold 21a can be released without interfering with the inner peripheral surface of the material 1'. Even if the radius of the springback amount of 1 'is smaller than the depth of the dynamic pressure groove 1c and the molding die 21a slightly interferes with the inner peripheral surface of the material 1', the diameter expansion due to the material elasticity of the material 1 '. It suffices if an amount (radial amount) is added so that the mold 21a can be released from the inner peripheral surface of the material 1 'without breaking the dynamic pressure groove 1c.

  When the bearing body 1a is manufactured through the above-described steps and is impregnated with lubricating oil or lubricating grease to retain the oil, the hydrodynamic porous oil-impregnated bearing 1 of this embodiment shown in FIGS. Complete.

It is a longitudinal section showing one embodiment of a dynamic pressure type porous oil-impregnated bearing concerning the present invention. It is a figure which shows typically the flow of oil in the axial direction cross section at the time of supporting a shaft by a dynamic pressure type porous oil-impregnated bearing. It is a longitudinal cross-sectional view which shows typically the density distribution of a bearing main body in a dynamic pressure type porous oil-impregnated bearing. It is a figure which shows the relationship between the density ratio (alpha) of a porous body, and a porosity. FIG. 2 is a cross-sectional view conceptually showing a configuration of an LBP spindle motor. It is sectional drawing which shows the sintered alloy raw material used as the raw material of a bearing main body. FIG. 4 is a diagram illustrating a relationship between a density ratio α of a sintered alloy material and a springback amount. It is a figure (Drawing a) showing an outline of a forming device used for forming processing of a bearing surface, and a figure (Drawing b) which shows a core rod which forms a bearing surface. It is a figure which shows the shaping process of a bearing surface. It is a figure which shows the shaping process of a bearing surface. It is a figure which shows the shaping process of a bearing surface.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Hydrodynamic porous oil-impregnated bearing 1a Bearing original 1a1 Surface part 1a2 Inner part 1b Bearing surface 1c Dynamic pressure groove

Claims (2)

A method for producing a hydrodynamic porous oil-impregnated bearing in which a bearing surface having a hydrodynamic groove is formed on an inner peripheral surface of a porous bearing main body made of a sintered metal,
A cylindrical sintered metal material having a density ratio α (%) represented by the following formula of 75 ≦ α <85 is manufactured,
A core rod formed with an uneven mold corresponding to the shape of the bearing surface is inserted into the inner peripheral surface of the sintered metal material, and a pressing force is applied to the sintered metal material to apply pressure to the core rod mold. Forming a dynamic pressure groove on the bearing surface by plastic working.
Density ratio α (%) = (ρ1 / ρ0) × 100
ρ1: Density of the porous body ρ0: Density assuming that the porous body has no pores   The method for manufacturing a hydrodynamic porous oil-impregnated bearing according to claim 1, further comprising a step of sizing the inner peripheral surface of the sintered metal material before the step of forming the dynamic pressure groove.

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