Methods for manufacturing ring-shaped glass bases, ring-shaped glass bases, and methods for manufacturing glass bases used for magnetic discs

Abstract

The invention relates to a method for producing a ring-shaped glass substrate (1) consisting of the following steps: creating, on a glass blank (20), a separation line (Cl) which includes defects (D) along a predetermined circle (Cl) by illuminating the surface (20a) of the glass blank (20) with a Lia laser band (L) along the circle (Cl); and separate the (21) part outside the separation line (C1) of the glass blank (20) on which the separation line (Cl) is created from the (22) part inside the separation line (C1) by heating the (21) part outside the separation line at a higher temperature than the (22) part inside the separation line (Cl). The separation line (Cl) consists of: the first region in which defects are created evenly spaced and the distance between adjacent pairs of defects is the first distance; and the second region in which the distance between adjacent pairs of defects is shorter than the first distance.