Molding arrangement to achieve short mold cycle time

Details Molding arrangement to achieve short mold cycle time Molding arrangement to achieve short mold cycle time

B - Operations, Transporting

29

C

B29C 33/38 (2006.01) B29C 33/30 (2006.01) B29C 33/56 (2006.01) B29C 45/37 (2006.01) B29C 45/73 (2006.01) B29D 11/00 (2006.01)

Patent

CA 2151327

An arrangement for molding a front or back polystyrene mold half which is used, with a second complementary back or front mold half, for subsequent molding of a soft contact lens such as a hydrogel soft contact lens. The arrangement is designed with heat flow considerations in mind to minimize the molding cycle time, while producing uniformly precise and accurate optical quality mold halves. Each mold half defines a convex curved surface and a concave curved surface spaced therefrom, with one of the surfaces defining an optical quality curved surface for the soft contact lens. A heated molding machine introduces molten polystyrene through a hot runner system to a plurality of mold cavities, each of which defines an optical quality curved surface and also a second noncritical surface. The optical quality surface of the mold cavity is positioned further away from the heated hot runner side of the mold than the second surface, which allows faster cooling of the optical quality surface of the mold cavity. This allows quicker setting and locking of minimal temperature residual stresses on the optical quality side of the mold half and a faster molding cycle time. Each mold cavity has a first insert on the optical quality side of the mold cavity and a second insert on the second side. Each of the first and second inserts has a circumferential cooling passageway defined therearound or in proximity for the first inserts, and also includes a bubbler positioned internally therein. Coolant is circulated in a turbulent mode through the circumferential passageways -39- 1 and also through the bubblers against inner surfaces of the insert to provide rapid cooling of the mold cavity.

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