Mold apparatus for making a closure cap

Claim 1

Apparatus for injection-molding of a cup-shaped closure cap having a skirt extending from a closed axial end to an open axial end, and with a radially inward retaining lug of relatively small arcuate extent formed integrally with said skirt near the open end and spaced from the closed end, said apparatus comprising: cavity-mold structure presenting at one face a cavity for determining the external contour of said skirt and closed end, and force-plug structure adapted to fit the cavity face of said cavity-mold structure for determining the internal contour of said skirt, lug, and closed end; said force-plug structure comprising: an outer-ring member, an inner-ring member longitudinally and coaxially guided within said outer-ring member and keyed against rotation with respect thereto, and an ejectorpin member longitudinally guided within said inner-ring member; said members in a retracted position having axial-end face formations coacting to determine the inside contour of the closed end of the cap, and said ring members having further generally cylindrical external surface formations coacting to determine the lug and other inside contour of said skirt; said external surface formations comprising a helical spline formation in said outerring member, whereby a molded cap will be characterized by spline-tracking formation, a concave generally V-shaped formation in said outer-ring member and characterized by increased arcuate extent in its divergence in the direction of said end-face formations, a convex generally V-shaped formation on said innerring member and matching said concave formation to an axial extent short of the axial inner limit of said concave formation, whereby in said retracted position a lug-defining cavity is established at the axially inner ends of said concave and convex formations; at least one pair of adjacent matched edges of said concave and convex formations being characterized by a net angular offset between axial inner and outer limits, said offset being in the direction of helical-spline advance and of magnitude exceeding the effective angular extent of the lug-defining cavity; whereby, upon molding with the force-plug structure positioned in said cavity-mold structure, the molded cap is removed with the force-plug structure and with the force-plug members in retracted position, and further whereby upon a first axially outward displacement of said inner-ring member with respect to said outer-ring member, the molded cap is cammed in partial rotation as it tracks said spline formation to the extent of clearing the lug from interference with said inner-ring member, so that in a second axially outward displacement of said ejector pin beyond the displaced inner ring, the molded cap will continue to track said spline formation until stripped of said outer-ring member and will thereafter strip readily from said inner-ring member.