Method for making a plastic container adapted to be grasped by steel drum chime-handling devices

A method of forming a plastic container having a reinforced raised circular rim which has at its top a circumferential outwardly radially thickened portion defining a downwardly facing circumferential ledge adapted to be grasped by steel drum chime-handling devices which comprises

• blow molding a generally tubular plastic parison in a blow mold to produce a preform having a bottom end, a top end and a generally circumferential sidewall between said ends, wherein a rounded peripheral shoulder joins said top and said sidewall which first flares outwardly in the form of the frustum of a cone and subsequently flares inwardly in the form of a first inverted frustum of a cone, said frustum and said first inverted frustum being connected by a circumferential outwardly radially extending rib forming a downwardly facing circumferential ledge meeting the top of said first inverted frustum,
• and during and immediately after said blow molding differentially cooling the outer surface of the wall of said preform to form a relatively cool and rigid outer skin while maintaining the material between the wall surfaces of said container at a deformable temperature but maintaining the outer skin and interior of the wall of said shoulder and of said rib at a relatively warmer and more easily deformable temperature,
• removing said preform from said mold cavity, and without further blow holding reshaping said preform by the steps of
• (1) closing a split ring forming assembly around a portion of said preform to enclose and fit said first inverted frustum and the bottom and sidewall of said rib,
• (2) thereafter pressing a circumferential shaping ring against said top end in the direction of said bottom end in an area extending radially inwardly from the juncture of said top end and said shoulder,
• (3) continuing said pressing to reshape said preform by bending said preform (i) at the juncture of said frustum and said rib and (ii) at said rounded shoulder until (a) the curve of said rounded shoulder becomes reversed, (b) said frustum is repositioned inside said first inverted frustum and becomes itself a second inverted frustum parallel to and pressed against said first inverted frustum and (c) the top of said rib becomes the peripheral top of the thus reshaped preform,
• said reshaping steps (1), (2) and (3) forming a container with an upstanding ring of double-walled thickness having said ledge near its top adapted to be grasped by steel drum chime-handling devices,
• and cooling the resulting container to a rigid condition.