Sintered bearing

A method of manufacturing a sintered bearing for supporting a shaft inserted into an inner periphery so as to be freely rotatable relative to the sintered bearing, the sintered bearing comprising a cylindrical portion having a constant diameter on an inner peripheral surface of the sintered bearing, a one-side increased-diameter portion having an inner diameter gradually increased in a direction away from one side of the cylindrical portion in an axial direction of the sintered bearing, which is arranged adjacent to the cylindrical portion on the one side in the axial direction, and an another-side increased-diameter portion having an inner diameter gradually increased in a direction away from another side of the cylindrical portion in the axial direction, which is arranged adjacent to the cylindrical portion on the another side in the axial direction, the method comprising, when sizing is performed on a sintered compact having a tubular shape:

• primary sizing for molding the another-side increased-diameter portion on an inner peripheral surface of the sintered compact by pressing an another-side increased-diameter portion molding surface of a first sizing core comprising the another-side increased-diameter portion molding surface corresponding to a shape of the another-side increased-diameter portion against the inner peripheral surface of the sintered compact under a state in which an outer peripheral surface of the sintered compact is retained by a first die having a tubular shape;
• and
• secondary sizing for molding the cylindrical portion and the one-side increased-diameter portion on the inner peripheral surface of the sintered compact by press-fitting a cylindrical portion molding surface of a second sizing core comprising the cylindrical portion molding surface corresponding to a shape of the cylindrical portion and a one-side increased-diameter portion molding surface corresponding to a shape of the one-side increased-dimeter portion, which are provided so as to be continuous in the axial direction, into the inner peripheral surface of the sintered compact from the one side in the axial direction, and then by pressing the one-side increased-diameter portion molding surface of the second sizing core against the inner peripheral surface of the sintered compact under a state in which the outer peripheral surface of the sintered compact is retained by a second die having a tubular shape,
• wherein a metal structure of the another-side increased-diameter portion has a higher density than a metal structure of a core portion of the sintered compact due to the another-side increased-diameter portion comprising a surface compression-molded without ironing with the first sizing core,
• wherein a metal structure of the cylindrical portion has an expansion along a direction of ironing by the second sizing core and a higher density than the metal structure of the another-side increased-diameter portion due to the cylindrical portion comprising a surface molded by ironing with the second sizing core, and
• wherein a metal structure of the one-side increased-diameter portion has an expansion along a direction of ironing by the second sizing core and a higher density than the metal structure of the cylindrical portion due to the one-side increased-diameter portion comprising a surface compression-molded through ironing with the second sizing core.