PURPOSE: To solve easiness to unscrew and advanced tamper-proof properties at the same time by applying preforming to the tamper-proof ring provided to the lower part of a screw cap by using a mandrel provided with an annular peripheral cam.
CONSTITUTION: A cylindrical mandrel M provided with an annular peripheral cam C is introduced into the tamper-proof ring 3 provided to the lower part of a screwed cap 2 so that the undersurface 13b of an inner annular projection 13 comes into contact with the cam C. Subsequently, support stresses E, E' are applied to the cap 2 and/or the mandrel M to relatively move the mandrel M to a preforming position within the cap 2 to hold the same for a predetermined time to curve a strip 18 outwardly in a cooperative manner. Residual deflection is generated in the inner annular projection 13 by this controlled deformation and the upper surface 13a of the projection 13 remains in an inclined state having an angle δ with respect to the perpendicular N to the axial line 1a of the cap 2. The residual angle δ of inclination is set 25° or less, preferably to be within a range of 10-15°.
GUERRAZZI VINCENT (FR)
PELLERANO PIERRE BATISTE (FR)
