| 摘要 |
In the invention, a sheet metal-made cup-shaped material ( 4 ) comprising: a circular base plate portion ( 2 ); and a cylindrical portion ( 3 ) which extends from an outer peripheral edge portion of the base plate portion ( 2 ) in one direction along the axis of the base plate portion ( 2 ) is prepared, an annular groove ( 13 ) is formed in an upper end portion of the cylindrical portion ( 3 ), whereby an annular projection ( 15 ) that projects in a direction opposite to a direction along which the cylindrical portion ( 3 ) extends is formed in the cylindrical portion ( 3 ), and the annular projection ( 15 ) and the cylindrical portion ( 3 ) are clampingly pressed by a rotary lower mold ( 5 e), a rotary upper mold ( 6 d), and a flat-face forming rolling roller ( 18 ) to a degree at which the annular groove ( 13 ) at least disappears, whereby the outer circumferential face ( 15 a) of the projection ( 15 ), and the outer circumferential face ( 30 ) of the cylindrical portion ( 3 ) are formed to be flush with each other. Therefore, the axial length (h 4 ) of a sheet metal-made back face pulley ( 11 ) is increased, and the whole of the increased axial length (h 4 ) can be used as the effective length.
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