JP4275631B2 - Sintered oil-impregnated bearing - Google Patents

Description

  The present invention relates to a sintered oil-impregnated bearing obtained by impregnating a sintered metal with oil and a method for producing the same.

  Among the sintered oil-impregnated bearings, a groove for generating dynamic pressure, that is, a bearing having a dynamic pressure groove (a grooved hydrodynamic sintered oil-impregnated bearing) has features such as high rotational accuracy, high speed rotation, low noise, and low cost. In recent years, these characteristics have led to their use as spindle support bearings in spindle motors of magnetic disks such as HDDs, optical disks such as DVDs, magneto-optical disks such as MOs, and polygon scanner motors of laser beam printers. Expected or actually used.

  This grooved hydrodynamic sintered oil-impregnated bearing is manufactured by sequentially performing sizing, burnishing on both end faces, and processing of the hydrodynamic groove on a bearing member made of a cylindrical oil-impregnated sintered metal. Due to burnishing, the end surface of the bearing member has its surface open area ratio (surface open area refers to the portion where the pores of the porous structure are opened to the outer surface, and the surface open area is the unit area of the outer surface. The surface pores are crushed until the area ratio of the surface openings occupying inside is 20% or less.

  Conventionally, as shown in FIG. 5, burnishing is performed by arranging jigs 33 and 34 made of a hard material such as cemented carbide or ceramic at both ends in the axial direction of the sintered oil-impregnated metal 31. This is done by rotating the jigs 33 and 34 in the reverse direction while pressing the pressing portions 37 (see FIG. 6) of the ridges formed on the end surfaces against the both end surfaces of the sintered oil-impregnated metal 31 respectively.

  In the above-mentioned grooved hydrodynamic sintered oil-impregnated bearing, it is preferable to minimize the outflow of oil from the surface of the bearing member in order to ensure sufficient dynamic pressure in the bearing gap. Therefore, in the burnishing of the end face of the bearing member, it is desired that the surface opening rate be as small and uniform as possible.

  However, in the conventional method shown in FIGS. 5 and 6, it is difficult to uniformly seal, and the variation in the degree of sealing is large. Therefore, the surface area ratio after finishing must be allowed in a wide range, and the upper limit is 20% as described above. In addition, when forming a dynamic pressure groove for generating dynamic pressure in the thrust direction on the end surface of the bearing member, it is necessary to reduce the surface roughness in order to avoid torque fluctuation due to contact with the mating surface. In the conventional method, it has been difficult to achieve both reduction of the surface area ratio and improvement of the surface roughness. Further, it has been pointed out that the pressurizing member is rapidly deteriorated and the entire jig needs to be replaced at an early stage, resulting in an increase in cost.

  Therefore, an object of the present invention is to provide a sintered oil-impregnated bearing that can achieve improvement in bearing rigidity by enhancing oil film force and that can achieve reduction in torque fluctuation.

In order to achieve the above object, the present invention includes a bearing member made of an oil-impregnated sintered metal, a radial bearing surface on the inner periphery of the bearing member, and a hydrodynamic groove on one of both end surfaces of the bearing member. In the oil-impregnated bearing, one end face of the bearing member having the dynamic pressure groove is burnished by pressing a pressure member made of a hard material with a pressure applied via an elastic member, and then the dynamic pressure groove is processed. The surface open area ratio is a value of 10% or less including the region of the dynamic pressure groove, the surface roughness is 0.05 Ra or more and 0.4 Ra or less, and the surface of the other end face A configuration in which the open area ratio is a value of 20% or less is provided.

  The surface roughness of the one end face is preferably set to 0.05 Ra or more and 0.4 Ra or less.

  Sintered oil impregnation that supports the shaft member in a non-contact manner with a dynamic pressure in the thrust direction by forming a dynamic pressure groove on one end face of the bearing member for generating a dynamic pressure in the thrust direction when rotating relative to the shaft member A bearing can be provided. In this case, by setting the surface roughness of the one end face to 0.05 Ra or more and 0.4 Ra or less, it is possible to avoid contact with the shaft member and provide a sintered oil-impregnated bearing with less torque fluctuation. Become.

  According to the present invention, it is possible to restrict the upper limit value of the permissible range by suppressing variations in the surface area ratio of one end face of the bearing member. Therefore, the oil film force can be strengthened to increase the bearing rigidity, and contact between the thrust bearing surface formed on the end surface of the bearing member and the shaft member can be avoided to reduce torque fluctuation.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, in the hydrodynamic sintered oil-impregnated bearing according to the present embodiment, a plurality of dynamic pressure generating grooves 3 (dynamic pressure grooves) are formed on the inner periphery of a bearing member 1 made of a cylindrical oil-impregnated sintered metal. ) Is formed. In the illustrated example, the case where two radial bearing surfaces 5 are formed apart from each other in the axial direction is illustrated. However, the number of radial bearing surfaces 5 is not limited to two, and may be one or three or more. You can also. As the dynamic pressure groove shape of the radial bearing surface 5, a spiral shape can be selected in addition to the herringbone shape as shown in the figure. In addition, it is also possible to use a non-round radial bearing surface such as a step type or a harmonic waveform.

  The shaft member 7 supported in a non-contact manner by the bearing member 1 includes a straight shaft portion 7a and a flange portion 7b provided at the end of the shaft portion 7a. The shaft portion 7a and the flange portion 7b can be formed by separate press-fitted parts, or can be integrally formed by means such as forging.

  The bearing member 1 is fixed to the inner periphery of the bottomed cylindrical housing 9 by means such as press fitting or adhesion. At this time, the shaft portion 7a of the shaft member 7 is disposed on the inner periphery of the bearing member 1, and the flange portion 7b is disposed in a space between the bottom portion 9a of the housing 9 and the end surface 1a of the bearing member. As shown in the figure, the housing bottom portion 9a can be integrally formed with the cylindrical housing body 9b, or formed as a separate part from the housing body 9b, and can be assembled by fitting and adhering them. The opening of the housing body 9b is sealed with a seal member 10 to prevent oil from flowing out.

  Both end surfaces 7b1 and 7b2 of the flange portion 7b are opposed to one end surface 1a of the bearing member 1 and the thrust receiving surface 9a1 of the housing bottom portion 9a. Thrust bearing surfaces 11a and 11b having a plurality of dynamic pressure grooves (not shown) are formed on the end surface 1a of the bearing member 1 and the thrust receiving surface 9a1 facing the flange portion 7b, respectively. The dynamic pressure groove shape of the thrust bearing surfaces 11a and 11b is arbitrary. Like the radial bearing surface 5, the dynamic pressure groove shape can be formed in a step shape in addition to forming a herringbone type or spiral type dynamic pressure groove. The dynamic pressure grooves can be formed on both end faces 7b1 and 7b2 of the flange portion 7b instead of the bearing member end face 1a and the thrust receiving face 9a1, and in this case, the end faces 7b1 and 7b2 of the flange portion 7b A thrust bearing surface is formed.

  The bearing member 1 is formed of an oil-impregnated sintered metal in which a sintered metal is impregnated with lubricating oil or lubricating grease so that the oil is retained in the pores. As the sintered metal, for example, a copper-based or iron-based material, or a material containing both of them as a main component can be used. Preferably, the sintered metal is formed using 20 to 95% of copper. This bearing member 1 is manufactured through the steps of compacting, sintering, sizing, oil impregnation, burnishing on both end faces, and dynamic pressure groove machining, as in the conventional case. In addition, each said process can be performed with the method and apparatus similar to the past except a burnishing process. Details of the burnishing process will be described later.

  A minute gap (radial bearing gap) between the radial bearing surface 5 and the outer peripheral surface of the shaft portion 7a, and thrust bearing surfaces 11a, 11b and surfaces facing the same (in the illustrated example, both end surfaces 7b1, 7b2 of the flange portion 7b) Each of the minute gaps (thrust bearing gaps) between them is filled with oil as a lubricating fluid. At the time of relative rotation of the shaft member 7 and the bearing member 1 (when the shaft member 7 is rotated in the present embodiment), the radial bearing gap and the thrust are caused by the action of the dynamic pressure grooves provided on the bearing surfaces 5, 11a, 11b. Oil dynamic pressure is generated in the bearing gap, and the shaft member 7 is supported in a non-contact manner relative to the bearing member 1 in both the radial direction and the thrust direction.

  During the bearing operation, the oil returns to the inside of the bearing member 1 from the holes opened in the surfaces of the bearing surfaces 5, 11a, 11b due to the positive pressure generated in the bearing gaps. On the other hand, since the new oil continues to be pushed into the bearing gaps one after another by the action of the dynamic pressure grooves, the oil film force and the bearing rigidity are maintained in a high state.

  In this case, if the pores opened in the bearing surfaces 5, 11 a, 11 b are crushed to reduce the surface opening ratio, the return of oil to the inside of the bearing member 1 can be reduced, and the oil film force is increased and the bearing rigidity is increased. Can be further improved. In order to achieve this, in the present invention, the end surface 1a of the bearing member 1 having the thrust bearing surface 11a is restricted to a range below the upper limit of the surface open area of 10% (preferably 7%). Sealing was performed by burnishing. If the surface opening ratio is less than or equal to this upper limit value, the amount of oil recirculated from the thrust bearing surface 11a into the bearing member 1 can be effectively suppressed. On the other hand, if it is attempted to always obtain a surface area ratio of 2% or less, the pressurizing force of a jig (described later) during burnishing is remarkably increased, which increases the processing cost. Therefore, the surface area ratio of the end face 1a is set in the range of 2% to 10% (preferably 7% or less).

  In this case, the surface roughness of the thrust bearing surface 11a formed on the end surface 1a of the bearing member 1 is set within a range of 0.05Ra to 0.4Ra. If the surface roughness is greater than 0.4 Ra, the surface irregularities increase, so that during the operation of the bearing, the thrust bearing surface 11a comes into contact with the opposite surface (flange end surface 7b1) to cause torque fluctuation and the like. It becomes a factor. On the other hand, when the surface roughness is smaller than 0.05 Ra, a high pressurizing force is required for burnishing, which will be described later, and the processing time becomes longer, which increases the processing cost.

  In addition, it is desirable to set the surface opening ratio of the radial bearing surface 5 to about 5% to 15%. The surface area ratio in this range can be obtained by adjusting the pressing force when pressing the inner peripheral surface of the bearing member 1 against the inner mold (core rod or the like) when sizing the bearing member 1.

  Burnishing of both end faces 1a and 1b of the bearing member 1 is performed by arranging jigs 13 and 14 on both sides in the axial direction of the bearing member 1 as in the conventional method shown in FIG. As shown in FIGS. 2A to 2C, a pressing member 17 made of a hard material such as cemented carbide or ceramic is attached to the jigs 13 and 14 via an elastic member 18. The elastic member 18 is made of an elastic material such as urethane rubber, and includes a thick disc-shaped cushion portion 18a and a connecting portion 18b protruding from the back surface of the cushion portion 18a. A pressure member 17 having a bar shape with a circular cross section is embedded in the end surface 18a1 of the cushion portion 18a so that a part of the circumferential surface protrudes from the end surface 18a1 along the diameter direction, and the elastic member 18 is fixed by fixing means such as adhesion. It is fixed to. The connecting portion 18b of the elastic member 18 is inserted into an attachment hole provided in a metal base 19 such as steel, and is further detachably attached to the base 19 by attaching / detaching means such as a set screw 20 or the like. The elastic member 18 and the pressure member 17 can be attached to and detached from the base 19 by the attachment / detachment means, and even when the pressure member 17 deteriorates, it can be replaced at an early stage.

  The jigs 13 and 14 including the base 19, the elastic member 18, and the pressure member 17 are in a state in which the pressure member 17 is pressed against both end surfaces 1 a and 1 b of the bearing member 1 on both axial sides of the bearing member 1. Be placed. The two end faces 1a and 1b of the bearing member 1 are rubbed against the pressurizing member 17 and finished by rotating both jigs 13 and 14 in reverse directions while pressurizing them in the approaching direction with a predetermined pressing force. Therefore, end faces 1a and 1b having a good surface roughness and a low surface area ratio can be formed.

  As described above, in the present invention, since the elastic member 18 is interposed between the pressure member 17 and the base 19, the pressure member 17 is shaped as an end surface of the bearing member 1 that becomes a workpiece by the cushion function of the elastic member 18. The end surfaces 1a and 1b are slid while following. Therefore, compared with the conventional jigs 33 and 34 shown in FIG. 6, the surface open area ratio can be made smaller by suppressing the variation, and the surface accuracy can be further improved to achieve both of them. It is possible to easily obtain a surface area ratio with a maximum of 7%) and a surface roughness of about 0.05 Ra to 0.4 Ra.

  Further, since the pressure member 17 is elastically attached, the deterioration thereof is slower than the conventional one, and even when the wear is deteriorated, the elastic member 18 and the pressure member 17 can be replaced as a unit. Compared with the conventional method (see FIG. 6) in which the whole must be replaced at an early stage, the manufacturing cost can be reduced.

  FIG. 3 shows a surface micrograph after burnishing of the conventional product (A) and the product of the present invention (B), and the black portion in the figure represents the surface opening portion. As is apparent from the figure, it can be understood that the product of the present invention has fewer black portions than the conventional product, and the surface area ratio is smaller.

FIG. 4 shows the measurement results of the cross-sectional curve after burnishing in the conventional product (A) and the product of the present invention (B). In all cases, the stylus speed is 0.5 [mm / s], the cut-off value is 0.8 [mm], the reference length is 3.20 [mm], and the polarity is normal. When the surface roughness was measured under these conditions, the center line average roughness Ra, the ten-point average roughness Ry, and the maximum height Rz were as follows: Ra = 0.4875 [μm]
Ry = 5.622 [μm]
Rmax = 10.30 [μm]
In the product of the present invention, Ra = 0.1750 [μm]
Ry = 1.828 [μm]
Rmax = 2.700 [μm]
Therefore, it was confirmed that the surface roughness of the product of the present invention was smaller at any standard value.

  In the above description, the jigs 13 and 14 shown in FIG. 2 are used for finishing the both end faces 1a and 1b of the bearing member 1. However, if the surface roughness and the surface aperture ratio are not particularly problematic, The finishing of one of the end surfaces (particularly, the end surface 1b opposite to the side facing the flange portion 7b) can also be performed using a jig similar to the conventional one (see FIG. 6).

  The above-mentioned sintered oil-impregnated bearing includes, for example, a bearing having no dynamic pressure groove on the end surface of the bearing member, such as a perfect circle bearing, and the present invention is similarly applied to such a bearing. Can do.

It is sectional drawing of the bearing apparatus using the sintered oil impregnation bearing concerning this invention. The jig | tool used by this invention method is shown, (A) A figure is AA sectional drawing in (B) figure, (B) figure is (B) arrow figure in (A) figure, (C) figure. (B) It is CC sectional drawing in a figure. It is a microscope picture of the bearing member end face after burnishing, (A) figure represents a conventional product, and (B) figure represents the product of the present invention. It is a figure which shows the cross-sectional curve of the bearing member end surface after burnishing, (A) A figure shows a conventional product and (B) figure represents this invention product. It is a side view which shows the burnishing process of a bearing member end surface. The jig | tool used by the conventional method is shown, (A) A figure is AA sectional drawing in (B) figure, (B) figure is a B arrow view in (A) figure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bearing member 1a One end surface 1b The other end surface 3 Dynamic pressure groove 5 Radial bearing surface

Claims (1)

In a sintered oil-impregnated bearing comprising a bearing member made of an oil-impregnated sintered metal, having a radial bearing surface on the inner periphery of the bearing member, and having a dynamic pressure groove on one of both end faces of the bearing member,
One end face of the bearing member having the dynamic pressure groove is formed by pressurizing a pressure member made of a hard material with a pressure applied through an elastic member to finish burnishing, and then processing the dynamic pressure groove. is a 10% the following values, including the area of the surface porosity is the dynamic pressure grooves, and the surface roughness is more than 0.05Ra, or less 0.4 Ra, the surface porosity of the other end face Sintered oil-impregnated bearing characterized in that the value is 20% or less.

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