Method to manufacture sealing nipples or plugs

A method of manufacturing sealing plugs comprising the steps of:

• cutting a disk-shaped element from a metal sheet;
• drawing said disk to obtain a hollow element of cylindrical shape, closed at one end by a cap;
• inserting said hollow element between a die including a movable part and a stationary counter-die part, said stationary counter-die having a hole housing a punch that defines with respect to the peripheral surface of said hole, an annular seating into which said hollow element is inserted with said cap turned outward;
• toward said movable die part, said counter-die also having a groove surrounding said hole, said movable die part also having a cavity with a prismatic profile into which said cap fits,
• moving said die parts relative to each other to press said hollow element so that said punch partially inserts into said movable die cavity to produce on said cap of said hollow element a series of facets with said prismatic profile, said pressing producing an axial compressing of said hollow element to fold said hollow element into said groove of said counter-die,
• continuing said pressing to close said fold to form an outwardly extending annular crown on the outer peripheral surface of said hollow element below said prismatic profile of said cap;
• and
• threading at least a portion of the free end of said hollow element below said crown starting from the open end of said hollow element.