Method and apparatus for minimizing plug diameter variation in spin flow necking process

A method of spin flow necking-in an open end of a cylindrical container body, comprising the steps of:

• a) positioning inside the container body, in axial inwardly spaced relation from the open end thereof, an axially fixed roll engageable with an inside surface of the container body, said axially fixed roll having a sloped end surface which faces the open end;
• b) positioning inside the container body a slide roll which fits the inside diameter of the container body to support the same, said slide roll having an end facing the sloped end surface of said axially fixed roll, and said slide roll being supported for axial displacement away from said axially fixed roll, said slide roll end and said sloped end surface of said axially fixed roll defining a gap therebetween;
• c) positioning opposite said gap on an outside surface of the container body a form roll supported for axial displacement away from said axially fixed roll, said form roll having a trailing end portion and a peripheral portion;
• d) spinning the container body thusly supported by said slide roll and advancing said form roll radially inwardly relative to said gap so that said trailing end portion presented by the form roll and said sloped end surface of said axially fixed roll engage the container body between them while said trailing end portion of said form roll moves radially inward along said sloped end surface of said axially fixed roll to roll a neck into the container body;
• and
• e) continuing to spin the container body while the form roll moves inwardly and the slide roll retracts axially until the form roll has spun an outwardly extending portion on the end portion of the container body engaged between said slide roll and said form roll;
• and
• f) stopping the radially inward movement of the form roll in step (e) by first preventing further axial retraction of the slide roll at a predetermined location.

Apparatus for necking-in an open end of a side wall of a container body, comprising:

• a) a necking spindle assembly for rotating said container body;
• b) a slide roll and an eccentric roll mounted on said necking spindle assembly for engaging inside surfaces of the container side wall defining said open end;
• c) a form roll mounted for radially inward movement into deforming contact with an outside surface of said container side wall in a region of the open end overlying an interface between said slide and eccentric rolls, whereby contact between said form roll with said side wall causes the contacted surface of said container side wall to move by radially inward deformation into a gap formed at the interface caused by axial separation of said slide and eccentric rolls under the action of the radially inward advancing movement of the form roll into the gap to thereby neck-in said side wall;
• and
• d) at least one stop spacer mounted to the necking spindle assembly rearwardly from and within a region into which a rear portion of the slide roll axially moves for limiting further axial retraction of said slide roll by contacting said rear portion to thereby stop the radially inward advancing movement of the form roll.