Fluid dynamic bearing, method of manufacturing fluid dynamic bearing, rotating device, and disk drive device
A fluid dynamic bearing includes a shaft to which a resin flange is fixed by insert molding. The process where the flange is fixed to the shaft by insert molding includes a flange forming process in which the flange, fixed to the shaft, is formed by injecting the resin into a filled portion in the lower mold through an upper mold, while cooling at least part of the shaft, arranged in a shaft arrangement portion in a lower mold, with cooling water circulating through a cooling pipe.
1. A method of manufacturing a fluid dynamic bearing comprising:
a shaft;
a flange fixed to one end of the shaft;
a shaft housing member configured to rotatably house at least part of the shaft;
a flange housing space provided at one end of the shaft housing member and configured to rotatably house the flange;
a counter plate configured to face the end surface of the flange in the axial direction and to seal the flange housing space;
a radial dynamic pressure groove formed on at least either the shaft or the surface of the shaft housing member, facing the shaft in the radial direction;
thrust dynamic pressure grooves provided on at least either the flange or the surface of the flange housing space, facing the flange in the thrust direction, and provided on at least either the flange or the surface of the counter plate, facing the flange in the thrust direction; and
a lubricant filled in the radial dynamic pressure groove and the thrust dynamic pressure grooves, the method of manufacturing a fluid dynamic bearing comprising:
forming the flange by fixing a resin to the shaft by insert molding while at least part of the shaft is being cooled.
2. The method of manufacturing a fluid dynamic bearing according to claim 1 , wherein, in the forming the flange, the part of the shaft to which the flange is fixed by insert molding is heated to a temperature lower than the glass transition temperature of the resin of which the flange is made by 20 to 70° C.
3. The method of manufacturing a fluid dynamic bearing according to claim 1 , wherein the heat conduction from the flange to the part of the shaft to which the flange is fixed by insert molding is suppressed by insulating an area between the part of the shaft to which the flange is fixed and the part of the shaft to be cooled.
4. The method of manufacturing a fluid dynamic bearing according to claim 1 , wherein the thrust dynamic pressure grooves are formed when the flange is fixed to the shaft by insert molding.
5. The method of manufacturing a fluid dynamic bearing according to claim 1 , wherein the resin is fixed to the shaft by insert molding such that the amount of the surface fluctuation of the flange is less than or equal to 3 μm during its rotation.
6. The method of manufacturing a fluid dynamic bearing according to claim 1 , wherein the coefficient of linear expansion of the resin of which the flange is made is the same as that of the shaft.
7. A method of manufacturing a fluid dynamic bearing comprising:
a shaft;
a flange fixed to one end of the shaft;
a shaft housing member configured to rotatably house at least part of the shaft;
a flange housing space provided at one end of the shaft housing member and configured to rotatably house the flange;
a counter plate configured to face the end surface of the flange in the axial direction and to seal the flange housing space;
a radial dynamic pressure groove formed on at least either the shaft or the surface of the shaft housing member, facing the shaft in the radial direction;
thrust dynamic pressure grooves provided on at least either the flange or the surface of the flange housing space, facing the flange in the thrust direction, and provided on at least either the flange or the surface of the counter plate, facing the flange in the thrust direction; and
a lubricant filled in the radial dynamic pressure groove and the thrust dynamic pressure grooves, the method of manufacturing a fluid dynamic bearing comprising:
forming the flange by fixing a resin to the shaft by insert molding; and
adjusting the fixed position of the flange by pressing the flange in an adjusting mold after the flange has been fixed wherein, in the adjusting the fixed position of the flange, the adjusting mold is heated to a temperature slightly lower than the glass transition temperature of the resin of which the flange is made.
8. The method of manufacturing a fluid dynamic bearing according to claim 7 , wherein, in the adjusting the position of the flange, the shaft and the flange are gradually cooled to approximately 120° C. and further more rapidly cooled to room temperature, after the fixed position of the flange has been adjusted.
9. The method of manufacturing a fluid dynamic bearing according to claim 7 , wherein the thrust dynamic pressure grooves are formed when the fixed position of the flange is adjusted.
10. The method of manufacturing a fluid dynamic bearing according to claim 7 , wherein the fixed position of the flange is adjusted such that the amount of the surface fluctuation of the flange is less than or equal to 3 μm during its rotation after the resin has been fixed to the shaft by insert molding.
11. The method of manufacturing a fluid dynamic bearing according to claim 7 , wherein the coefficient of linear expansion of the resin of which the flange is made is the same as that of the shaft.