Method of Manufacturing Sheet Metal Back Face Pulley

Abstract

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 expansion ( 40 ) that is radially outward expanded is formed in the cylindrical portion ( 3 ), and the annular expansion ( 40 ) and the cylindrical portion ( 3 ) are clampingly pressed by a rotary lower mold ( 5 ) and a flat-face forming rolling roller ( 16 ) to a degree at which the annular expansion ( 40 ) disappears, whereby the outer circumferential face ( 30 ) of the cylindrical portion ( 3 ) is flatly formed. Therefore, the axial length (h 4 ) of a sheet metal-made back face pulley ( 11 ) is increased, and the increased axial length (h 4 ) can be used as the effective length.

1 . A method of producing a sheet metal-made back face pulley wherein a sheet metal-made cup-shaped material com-prising: a circular base plate portion; and a cylindrical portion which extends from an outer peripheral edge portion of said base plate portion in one direction along an axis of said base plate portion is prepared, an annular expansion is formed in said cylindrical portion, and said annular expansion is clampingly pressed by a rotary inner mold and a flat-face forming rolling roller to a degree at which at least said annular expansion disappears, whereby an outer circumferential face of said cylindrical portion is flatly formed.  
   
   
       2 . A method of producing a sheet metal-made back face pulley according to  claim 1 , wherein said annular expansion is formed by expansion in a radially outward direction of said cylindrical portion.  
   
   
       3 . A method of producing a sheet metal-made back face pulley according to  claim 1 , wherein an upper end portion of said cylindrical portion is pressed by a groove-forming protrusion disposed in a roll-forming roller, to form an annular groove in an upper end portion of said cylindrical portion, and an annular projection that projects in a direction opposite to a direction along which said cylindrical portion extends is formed above said annular groove.  
   
   
       4 . A method of producing a sheet metal-made back face pulley according to  claim 2 , wherein an upper end portion of said cylindrical portion is pressed by a groove-forming protrusion disposed in a roll-forming roller, to form an annular groove in an upper end portion of said cylindrical portion, and an annular projection that projects in a direction opposite to a direction along which said cylindrical portion extends is formed above said annular groove.