Abstract: A preparatory molding roll 4 having a convex push surface 41 is pushed to an outer peripheral surface of a work 1A while the work 1A is chucked by a pair of molds 2 and 3 and is rotated by applying axial propelling force, to bend inward the outer peripheral surface of the work in a radial direction. The work is then chucked by the preparatory molding roll and the upper and lower molds. Next, the preparatory molding roll is moved back and the work is crushed in the axial direction to form a bent portion 1a. A molding roll 5 is pushed to mold the outer shape of the work. A grooved roll 6 is next pushed to the outer peripheral surface of the work and a groove 1b is formed on the outer peripheral surface.

Abstract: A preparatory molding roll 4 having a convex push surface 41 is pushed to an outer peripheral surface of a work 1A while the work 1A is chucked by a pair of molds 2 and 3 and is rotated by applying axial propelling force, to bend inward the outer peripheral surface of the work in a radial direction. The work is then chucked by the preparatory molding roll and the upper and lower molds. Next, the preparatory molding roll is moved back and the work is crushed in the axial direction to form a bent portion 1a. A molding roll 5 is pushed to mold the outer shape of the work. A grooved roll 6 is next pushed to the outer peripheral surface of the work and a groove 1b is formed on the outer peripheral surface.