Forming small diameter opening for aerosol, screw cap, or crown cap by multistage necking-in of drawn or drawn and ironed container body

Method for reducing the diameter of the sidewall at the open end of a single-piece sheet metal can body comprising

• providing a seam-free unitary can body having a sidewall disposed about a longitudinal axis and a unitary endwall at one longitudinal end of the sidewall, the unitary can body sidewall having a peripheral edge defining an open end at the remaining longitudinal end of the sidewall opposite to the unitary endwall,
• reducing the diameter of the sidewall contiguous to the open end of the unitary can body by a plurality of die forming operations in excess of two to form a truncated cone configuration portion at the open end of the can body,
• the truncated cone configuration portion having a stepped configuration in longitudinal cross section with the total reduction in diameter at the open end of the can body being at least one-third of the original diameter of the sidewall portion at the open end,
• the stepped configuration comprising a plurality of reduced diameter gradations starting with a reduction in diameter portion which is of curvilinear configuration in longitudinal cross section and located to form a juncture with the original diameter portion of the sidewall and progressing with further reduction in diameter portions toward the open end of the can body,
• the plurality of die forming operations forming such stepped configuration being carried out in sequence, the initial die forming step forming
• the curvilinear configuration reduction in diameter juncture at the original diameter portion of the sidewall,
• a longitudinally extended cylinder of substantially-uniform reduced diameter corresponding to the reduction in diameter at the curvilinear configuration juncture, and,
• an inflection in the sheet metal of the reduced diameter cylinder out of its cylindrical configuration at the open end periphery, such inflection of the sheet metal forming a strengthening rim in such open end peripheral metal, and
• each next sequential die forming step being carried out on such reduced diameter cylinder of the next preceding die forming step utilizing die means of reduced diameter characteristics in relation to die means of the next preceding die forming step,
• with each separate die means utilizing a loose-fitting inner pilot-type die means for maintaining such cylindrical configuration without otherwise supporting the can body internally by maintaining clearance for ease of removal of such pilot-type die means after each reduction in diameter,
• the initial die forming step reducing the diameter a selected percentage of the original diameter with each subsequent percentage reduction in diameter being less than the next preceding previous percentage reduction in diameter.