Patent ID: 8931308
Filing Date: 2015-01-13
Classification: C03B

Abstract:
1. A method of manufacturing a glass blank for a substrate for an information recording medium, the method including steps of: cutting out a gob of a glass material from a molten glass material by cutting the molten glass material discharged from a glass material outlet at a predetermined timing, so as to separate the gob of the glass material from the molten glass material; causing the separated gob of the glass material to fall downwardly so that the separated gob falls into a space between a pair of molds of a press unit; catching the separated gob of the glass material between the pair of molds, and pinching and pressing the separated gob of the glass material by the pair of molds, the molds' surfaces facing to each other being press surfaces which are planes without an unevenness, so as to contact the falling gob of the glass material only to the press surfaces; and forming, from the gob of the glass material, a circular flat plate-shaped glass blank having a target flatness as a glass substrate for a magnetic disk such that a ratio between a diameter and a thickness of the glass blank is within range of from 50:1 to 150:1.