Abstract:
Disclosed herein is a method of manufacturing a hydrodynamic bearing in which a metal bearing made of sintered metal powder is internally subjected to chemical etching, to form hydrodynamic pressure grooves thereon, thus assuring a high-precision and reliable hydrodynamic bearing. The method includes: compressing metal powder that is a raw material of the bearing in a press unit, and sintering the compressed metal powder at a predetermined temperature, thus preparing a sintered bearing; removing foreign substances adhering to the sintered bearing through a deburring process, and pressing the sintered bearing into a desired shape; forming a hydrodynamic groove, configured to generate hydrodynamic pressure, on an internal surface of the shaped bearing using chemical etching; and conducting a post treatment of cleaning the bearing including the hydrodynamic grooves thereon and drying the bearing.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2008-0067628, filed Jul. 11, 2008, entitled “METHOD FOR MANUFACTURING THE HYDRODYNAMICS BEARING”, which is hereby incorporated by reference in its entirety into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a method of manufacturing a hydrodynamic bearing, and, more particularly, to a method of manufacturing a hydrodynamic bearing in which a metal bearing, which is prepared by sintering metal powder, is internally subjected to chemical etching, such as done by an electrochemical machining process or an etching process, to form hydrodynamic pressure grooves thereon, thus assuring a high-precision and reliable hydrodynamic bearing. 
         [0004]    2. Description of the Related Art 
         [0005]    The hydrodynamic bearing, which is intended to rotatably support a rotating shaft that is rotated by externally applied electric current, holds a predetermined type of fluid between the rotating shaft and the bearing. In order to assure the smooth rotation of the rotating shaft, fine hydrodynamic pressure grooves, which perform a hydrodynamic pumping action of the fluid, are provided between either the rotating shaft or the hydrodynamic bearing. 
         [0006]    An example of the methods of manufacturing such a hydrodynamic bearing is disclosed in Japanese Unexamined Patent Publication No. 2006-316896, which is schematically illustrated in  FIGS. 9 and 10 . 
         [0007]    As shown in  FIG. 9 , the conventional method of manufacturing a hydrodynamic bearing is conducted in such a manner that metal powder M, which is a raw material of a shaft-supporting sleeve, is compressed between an upper punch  14  and a lower punch  13  which are forcedly moved toward each other, and the resulting compressed body Ma is sintered at a predetermined temperature, resulting in a sintered bearing body  15 . 
         [0008]    Subsequently, as shown in  FIG. 10 , in order to form hydrodynamic grooves on the internal surface of the sintered body  15 , the sintered body  15  is put into a press die  16 , and a core rod  17 , having thereon protrusions corresponding to the desired hydrodynamic grooves, is inserted into the internal space of the sintered body  15 . Thereafter, the external surface of the sintered body  15  is pressed using the press die  16 , with the result that the internal surface of the sintered body  15  is formed with the hydrodynamic grooves. 
         [0009]    The core rod  17  is separated from the sintered body  15 , and then the sintered body  15  is separated from the press die  16 , thus producing a desired shaft-supporting sleeve. 
         [0010]    However, in the above conventional method of manufacturing a shaft-supporting sleeve, when the core rod  17  is separated from the sintered body  15 , the hydrodynamic grooves of the sintered body may be damaged due to the protrusions of the external surface of the core rod  17 , thus causing uneven hydrodynamic pressure to occur. 
         [0011]    Furthermore, since the sintered body  15  must be made of metal powder having a spring back behavior, the raw material of the sintered body  15  is inevitably selected from restricted kinds of materials. 
         [0012]    In addition, since the hydrodynamic grooves are formed by pressing the sintered body  15  after the compression and sintering processes of the metal powder M, the compressed structure of the sintered body  15  is not dense, thus deteriorating the durability of the sintered body  15 . 
       SUMMARY OF THE INVENTION 
       [0013]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and the present invention provides a method of manufacturing a hydrodynamic bearing, which is conducted in such a manner that a bearing is prepared by compressing and sintering metal powder at high pressure and temperature, and the bearing is subjected to an electrochemical machining process or an etching process to form hydrodynamic grooves on the internal surface of the bearing, thus providing a hydrodynamic bearing having durability and accuracy superior to those made by conventional methods. 
         [0014]    In one aspect, the present invention provides a method of manufacturing a hydrodynamic bearing having an internal space and configured to exert hydrodynamic pressure between fluid and the bearing, including: compressing metal powder that is a raw material of the bearing in a press unit, and sintering the compressed metal powder at a predetermined temperature, thus preparing a sintered bearing; removing foreign substances adhering to the sintered bearing through a deburring process, and pressing the sintered bearing into a desired shape; forming a hydrodynamic groove, configured to generate hydrodynamic pressure, on an internal surface of the shaped bearing using chemical etching; and conducting a post treatment of cleaning the bearing including the hydrodynamic grooves thereon and drying the bearing. 
         [0015]    In this method, forming the hydrodynamic groove may be conducted using electrochemical machining (EXM) in a manner that an electrode tool, having an electrode portion corresponding to the hydrodynamic groove, is inserted into the internal space of the shaped bearing, positive current is applied to the shaped bearing while negative current is applied to the electrode tool, and flowing electrolyte between the shaped bearing and the electrode tool. 
         [0016]    The electrode tool may be covered with nonconductive insulating layer at a separate portion other than the electrode portion. 
         [0017]    In forming the hydrodynamic groove, the shaped bearing may be covered with photoresist at an entire area other than an area at which the hydrodynamic groove is to be formed, and thus the area, at which the hydrodynamic groove is to be formed, is chemically etched. 
         [0018]    The photoresist may be positive photoresist that is cured due to exposure to ultraviolet rays. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0020]      FIG. 1  is a schematic flowchart showing a method of manufacturing a hydrodynamic bearing, according to a first embodiment of the present invention; 
           [0021]      FIG. 2  is a schematic cross-sectional view showing compression and sintering processes in the method shown in  FIG. 1 ; 
           [0022]      FIG. 3  is a schematic cross-sectional view showing electrochemical machining of a bearing using an electrode tool, according to the first embodiment of the present invention; 
           [0023]      FIG. 4  is a schematic flowchart showing a method of manufacturing a hydrodynamic bearing, according to a second embodiment of the present invention; 
           [0024]      FIG. 5  is a schematic cross-sectional view showing compression and sintering processes in the method shown in  FIG.4 ; 
           [0025]      FIGS. 6 to 8  are cross-sectional views showing a process of forming hydrodynamic grooves on a bearing using etching, according to the second embodiment of the present invention; and 
           [0026]      FIG. 9 and 10  are schematic cross-sectional views showing a conventional process of manufacturing a hydrodynamic bearing. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Hereinafter, embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. 
         [0028]    As shown in  FIG. 1 , a method of manufacturing a hydrodynamic bearing, according o a first embodiment of the present invention comprises a process (S 110 ) of compressing and sintering metal powder, a process (S 120 ) of shaping the sintered material, a process (S 130 ) of electrochemical machining the shaped material, and a process (S 140 ) of post treatment. The respective processes of the method according to an embodiment of the present invention will now be described with reference to  FIGS. 2 and 3 . 
         [0029]    As shown in  FIG. 2 , metal powder  10   a  is compressed and sintered to prepare a bearing  10  of a hydrodynamic bearing. 
         [0030]    The metal powder  10   a , which is used in the formation of the bearing  10 , may be essentially composed of copper powder, copper alloy powder or a mixture of copper powder and iron powder, and may have an optional lubricant powder additive such as a stearin additive. 
         [0031]    For the compression and molding of the metal powder  10   a , metal powder  10   a  is loaded into a hollow space of a press unit  20  which is a combination of an upper press part  21  and a lower press part  22 , and the metal powder  10   a  is compressed at a predetermined pressure using the upper press part  21 . Thereafter, the metal powder  10   a  is sintered at a proper sintering temperature, thus preparing a sintered bearing  10 . 
         [0032]    Subsequently, a shaping process of removing unnecessary portions of the bearing  10 , thus tailoring the bearing to a desired size, is performed. If required, the shaping process may be repeatedly conducted. 
         [0033]    Thereafter, a deburring process is conducted in which unwanted portions, such as burrs which may be formed on external and internal surfaces of the sintered bearing  10 , are eliminated using a deburring device. The bearing  10  is fitted in a predetermined mold, and then a predetermined pressure and stroke are applied to the bearing  10  for the process of shaping the bearing  10 . At this point, the diameter of the external surface and the total height of the bearing  10  may be calibrated to the desired dimensions. 
         [0034]    In consideration of frictional and cooling properties of the bearing, the shaping process may be conducted after the bearing  10  is dipped into shaping oil. In the case of dipping the bearing into shaping oil, an additional process of clearing away the shaping oil from the bearing  10  using an organic cleaning agent may be required. In the organic cleaning process, an ultrasonic organic cleaning, which is capable of completely removing the shaping oil from the bearing  10  by continuous application of ultrasonic waves to the bearing  10 , may be employed. 
         [0035]    After the organic cleaning, in order to eliminate the organic cleaning agent from the bearing  10 , the bearing  10  is put into a separate oven and is sufficiently heated and dried at a temperature of 60° C. or higher for a period of one hour (S 120 ). 
         [0036]    Subsequently, as shown in  FIG. 3 , the bearing  10  is subjected to an electrochemical machining (ECM) process, which is a kind of chemical etching processes, in order to form hydrodynamic grooves  11  on the external surface of the bearing  10 . 
         [0037]    The electrochemical machining (ECM) refers to an etching process of removing a metal oxide which results from electrochemical dissolution of a metal workpiece, thus forming fine grooves on the metal workpiece. More specifically, in order to form fine hydrodynamic grooves  11  at predetermined locations on the bearing  10 , a positive current is applied to the bearing  10  while a negative current is applied to an electrode tool which is provided with a conductive pattern corresponding to the hydrodynamic grooves  11 . Under these conditions, electrolyte is forced to flow between the bearing  10  and the electrode tool  30 , thus forming the hydrodynamic grooves  11 . 
         [0038]    In this embodiment, the electrode tool  30  comprises an electrode matrix  31  to which the negative current is applied, and a nonconductive insulating layer  32  surrounding the electrode matrix  31  and having grooves corresponding to the hydrodynamic grooves  11 . In other words, the electrochemical machining does not affect the region of the electrode tool  30  covered with the nonconductive insulating layer  32  but affects only the region of the electrode tool  30  which is exposed through the grooves of the nonconductive insulating layer  32  (S 130 ). 
         [0039]    Finally, the bearing  10 , which includes the hydrodynamic grooves  11  formed thereon, is subjected to a post treatment process. In the post treatment process(S 140 ), various successive processes are sequentially conducted, which include a cleaning process of removing electrolyte adhering to the bearing  10 , an antirust process to prevent corrosion of the bearing  10  using antirust agent, a water washing process of removing electrolyte and other substances remaining on the surface of the bearing  10  using water, a vacuum drying process of removing moisture and oil remaining in pores of the bearing  10  by subjecting the bearing to vacuum drying at a temperature of 80° C. or higher, an organic cleaning process of clearing away oil and the like exuding from the surface of the bearing  10  using organic cleaning agent, and a drying process of removing the organic cleaning agent by drying the bearing  10  at a temperature of 60° C. or higher (S 140 ). 
         [0040]    As described above, since the method according to this embodiment of the present invention is conducted in such a manner that the bearing is sintered and then the sintered bearing  10  is subjected to the electrochemical machining to form hydrodynamic grooves  11  on the bearing  10 , the method can enhance the durability of the bearing  10  itself and can prevent the breakdown of the hydrodynamic grooves  11 . 
         [0041]    As shown in  FIG. 4 , a method of manufacturing a hydrodynamic bearing, according to a second embodiment of the present invention comprises a process (S 210 ) of compressing and sintering metal powder, a process (S 220 ) of shaping the sintered material, a process (S 230 ) of etching the shaped material, and a process (S 240 ) of post treatment. The respective processes of the method according to a second embodiment of the present invention will now be described with reference to  FIGS. 5 to 8 . 
         [0042]    As shown in  FIG. 5 , metal powder  10   a  is compressed and sintered to prepare a bearing  10  of a hydrodynamic bearing. 
         [0043]    The metal powder  10   a , which is used in the formation of the bearing  10 , may be essentially composed of copper powder, copper alloy powder or a mixture of copper powder and iron powder, and lubricant powder such as a stearin additive may be optionally added thereto. 
         [0044]    For the compression and molding of the metal powder  10   a , metal powder  10   a  is loaded into a hollow space of a press unit  20  which is a combination of an upper press part  21  and a lower press part  22 , and the metal powder  10   a  is compressed at a predetermined pressure using the upper press part  21 . Thereafter, the metal powder  10   a  is sintered at a proper sintering temperature, thus preparing a sintered bearing  10 . 
         [0045]    Subsequently, a shaping process of removing unnecessary portions of the bearing  10 , thus tailoring the bearing to a desired size, is conducted. The shaping process may be repeatedly conducted, if required. 
         [0046]    Thereafter, a deburring process is conducted in which unwanted portions, such as burrs, which may be formed on external and internal surfaces of the sintered bearing  10 , are eliminated using a deburring device. The bearing  10  is fitted in a predetermined mold, and then a predetermined pressure and stroke are applied to the bearing  10  for the shaping of the bearing  10 . At this point, the diameter of the external surface and the total height of the bearing  10  may be calibrated to the desired dimensions. 
         [0047]    In consideration of frictional and cooling properties of the bearing, the shaping process may be conducted after the bearing  10  is dipped into shaping oil. In the case of dipping the bearing into shaping oil, an additional process of clearing away the shaping oil from the bearing  10  using organic cleaning agent may be required. In the organic cleaning process, an ultrasonic organic cleaning, which is capable of completely removing the shaping oil from the bearing  10  by continuously applying ultrasonic waves to the bearing  10 , may be employed. 
         [0048]    After the organic cleaning, in order to eliminate the organic cleaning agent from the bearing  10 , the bearing  10  is put into a separate oven and is sufficiently heated and dried at a temperature of 60° C. or higher for a period of one hour (S 120 ). 
         [0049]    Subsequently, as shown in  FIGS. 6 to 8 , the bearing  10  is subjected to an etching process, which is a kind of chemical etching processes, in order to form hydrodynamic grooves  11  on the external surface of the bearing  10 . 
         [0050]    The etching process refers to an etching process of removing a metal oxide which results from electrochemical dissolution of a metal workpiece, thus forming fine grooves on the metal workpiece. More specifically, in order to form fine hydrodynamic grooves  11  at predetermined locations on the bearing  10 , the bearing is covered with photoresist or a dry film  40  such that regions of the bearing  10 , at which the fine hydrodynamic grooves  11  are formed later, are exposed. The regions of the bearing  10 , at which the hydrodynamic grooves  11  are formed, are etched using etchant. 
         [0051]    As shown in  FIG. 6 , photoresist is applied to the bearing  10  such that the bearing  10  is completely covered with the photoresist  40 . In this embodiment, the photoresist  40  may be positive photoresist which is cured by exposure to ultraviolet rays. Prior to the exposure to ultraviolet rays, in order to remove the regions of the photoresist  40 , which correspond to the hydrodynamic grooves  11  on the internal surface of the bearing  10 , a masking member  50  is inserted into the internal space of the bearing  10  such that the regions of the photoresist  40  which correspond to the hydrodynamic grooves  11  are not exposed to ultraviolet rays. More specifically, the masking member  50  is configured such that the regions of the masking member  50 , corresponding to the hydrodynamic grooves  11 , remain uncut so as not to allow the regions of the photoresist  40  corresponding to the hydrodynamic grooves  11  to be cured by the exposure to ultraviolet rays whereas the other regions of the masking member  50  are cut away so as to allow the other regions of the photoresist  40  to be exposed to the ultraviolet rays. 
         [0052]    As shown in  FIG. 7 , after the photoresist  40  is exposed to ultraviolet rays and is thus cured, the regions of the photoresist  40 , corresponding to the hydrodynamic grooves  11 , i.e., the uncured regions of the photoresist  40  are removed, and the entire bearing  10  is completely immersed into etching solution  60 , with the result that the hydrodynamic grooves  11  are formed on the bearing  10 . Subsequently, as shown in  FIG. 8 , the bearing  10 , which includes the hydrodynamic grooves  11  formed on the internal surface thereof, is pulled out of the etching solution  60 , and then the photoresist  40  surrounding the entire bearing  10  is removed from the bearing (S 230 ). 
         [0053]    Finally, the bearing  10 , which is formed with the hydrodynamic grooves  11 , is subjected to the post treatment. In the post treatment, various successive processes are sequentially conducted, which include a cleaning process of removing electrolyte adhering to the bearing  10 , an antirust process to prevent corrosion of the bearing  10  using antirust agent, a water washing process of removing electrolyte and other substances remaining on the surface of the bearing  10  using water, a vacuum drying process of removing moisture and oil remaining in pores of the bearing  10  by subjecting the bearing to vacuum drying at a temperature of 80° C. or higher, an organic cleaning process of clearing away oil and the like exuding from the surface of the bearing  10  using organic cleaning agent, and a drying process of removing the organic cleaning agent by drying the bearing  10  at a temperature of 60° C. or higher (S 240 ). 
         [0054]    As described above, since the method according to this embodiment of the present invention is conducted in such a manner that the bearing is sintered and then the sintered bearing  10  is subjected to the etching to form hydrodynamic grooves  11  on the bearing  10 , the method can enhance the durability of the bearing  10  itself and can prevent the breakage of the hydrodynamic grooves  11 . 
         [0055]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.