Bearing having arch-shaped recesses and method of manufacturing the same

A method of manufacturing an annular bearing having a steel backing metal on its outer surface and a porous metal layer impregnated with a resin on its inner surface, said porous metal layer comprising 6-24 recesses each with a uniform arch-shaped cross section of 20-110 .mu.m, which recesses extend axially on said porous metal layer and are formed adjacent to each other, said method comprising the steps of:

• mounting an annular wrapped bushing concentrically on an inlet of an inner hole of a molding die;
• inserting a mandrel into a center hole of said wrapped bushing with a sleeve being fitted around a periphery of said mandrel so as to abut an upper end of said wrapped bushing, said mandrel being provided with plurality of ridges each having an arch-shaped cross section having a height of 20-100 .mu.m and extending axially of the outer surface thereof in corresponding relationship with said recesses to be formed on said porous metal layer and having an outer diameter slightly larger than an inner diameter of said wrapped bushing;
• lowering said wrapped bushing together with said mandrel and said sleeve along said inner hole of said molding die to such a degree that said wrapped bushing reaches an ejector which is located on a bottom of said inner hole of said molding die, axially restraining said bushing, and applying an axial compression force to said restrained bushing by axially urging said sleeve and/or said ejector and thereby molding said wrapped bushing in a space defined by said molding die, said mandrel, said sleeve and said ejector and expanding said wrapped bushing inwards;
• and
• after said bearing is molded, raising said ejector above the top surface of said molding die, and then lowering said sleeve and extracting the molded bearing.