Method and master-die for casting a bifocal contact lens in a si

Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Including step of mold making

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Details

249135, 249184, 249187R, 264219, 425808, B29D 1100

Patent

active

046055240

ABSTRACT:
A bifocal contact lens has a distant-vision portion of a diameter between 3 and 5 mm either located in the center of the lens or offset about 2 mm above the center. The anterior surface of the lens is cast in an injection molding machine from a working die which itself is made from a master-die composed of two pieces of steel, a plug portion being tightly fitted in an aperture in the carrier portion so that the boundary of the different prescription curvatures of the plug and carrier portion will meet as closely as possible. The plug portion is shrink-fit inside the carrier portion. No further finishing procedures are necessary after casting the bifocal lens in one piece from the working dies, and the working dies are so cheap to cast that they may be melted down after one or a few uses to make new working dies from the steel master-dies.

REFERENCES:
patent: 285058 (1883-09-01), Nickerson
patent: 2254440 (1941-09-01), Moulton
patent: 2424235 (1947-07-01), Hoffer
patent: 3579805 (1971-05-01), Kast
patent: 3649236 (1972-03-01), Rosenbauer
patent: 3946982 (1976-03-01), Calkins et al.
patent: 4025751 (1977-05-01), Wright
patent: 4169119 (1979-09-01), Covington
patent: 4190621 (1980-02-01), Greshes
patent: 4279401 (1981-07-01), Ramirez
patent: 4425699 (1984-01-01), Nordin

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