Method of molding using gated dies

Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Changing mold size or shape during molding or with shrinkage...

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249 82, 2643282, 2643287, 2643289, 26432811, 425557, 425808, B29D 1100

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048391107

ABSTRACT:
A method and apparatus for molding and casting ophthalmic lenses includes a front surface die and a back surface die slidably and removably received in the bore of a molding or casting apparatus. Molding or casting compound is introduced by conventional means between the two dies, and the dies are urged together to impress the die surfaces on the compound as the compound is cured by thermal or chemical means. At least one of the dies includes at least one gate channel formed in the edge thereof parallel to the axis of the bore and extending from the optical forming surface to a point adjacent to the opposite, external die surface. In compression molding, the gate channel comprises a vent through which excess molding compound is discharged from the molding cavity as the dies are urged together. As the gated die is fully inserted in the bore, the gate channel opening to the exterior is sealed, thus limiting the discharge effect and controlling the thickness of the molded part. In casting, the dies are partially inserted in the bore, and the gate channel serves as an injection channel to introduce the casting compound into the casting cavity. The dies are urged together in the bore, the gate channel first serves to vent excess casting compound from the casting cavity. Full die insertion in the bore causes the gate channel opening to the exterior to be sealed, thus limiting the discharge effect and controlling the thickness of the cast part.

REFERENCES:
patent: 4569807 (1986-02-01), Boudet
patent: 4664854 (1987-05-01), Bakalar

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