Method of manufacturing glass substrate for information recording medium

A method of manufacturing a glass substrate for information recording medium, comprising the steps of:

• forming a molded body having a cylindrical shape and provided with a through hole at a central part thereof by press-molding molten glass by a metallic die in which a cylindrical body is provided in a vertically standing manner at a central part of a bottom surface of a hole having a cylindrical shape;
• cutting the molded body perpendicular to an axial direction to be divided into preforms having a predetermined thickness;
• and
• molding the preform in a metallic die having a first molding surface having a chamfered shape in contact with an outer peripheral edge surface and a second molding surface having a chamfered shape at an inner peripheral edge surface of the preform.

A method of manufacturing a glass substrate for information recording medium in which an outer peripheral edge surface has a chamfered shape, said method comprising the steps of:

• forming a glass substrate precursor circumferentially provided with a groove having a substantially V-letter shape on one surface of the glass substrate precursor wherein a pair of metallic dies in which protruding parts corresponding to the chamfered shape and having a wedge shape in section are formed in one of the metallic dies is used to press-mold molten glass;
• cutting the glass substrate precursor at an apex of the substantially V-letter shaped groove to remove an outer peripheral portion so that one side of an outer peripheral edge surface has the chamfered shape;
• heating an other side of the outer peripheral edge surface not having the chamfered shape;
• and
• pressing by a metallic die having a molding surface corresponding to the chamfered shape onto the glass substrate precursor to form a chamfered shape on the other side of the outer peripheral edge surface.

A method of manufacturing a glass substrate for information recording medium in which an inner peripheral edge surface has a chamfered shape, said method comprising the steps of:

• forming a glass substrate precursor circumferentially provided with a groove having a substantially V-letter shape on one surface of the glass substrate precursor wherein a pair of metallic dies in which protruding parts corresponding to the chamfered shape and having a wedge shape formed in one of the metallic dies is used to press-mold molten glass;
• cutting the glass substrate precursor at an apex of the substantially V-letter shaped groove to remove a central section so that one side of the inner peripheral edge surface of the glass substrate precursor has the chamfered shape;
• heating an other side of the inner peripheral edge surface not having the chamfered shape;
• and
• pressing by a metallic die having a molding surface corresponding to the chamfered shape onto the glass substrate precursor to form a chamfered shape on the other side of the inner peripheral edge surface.

A method of manufacturing a glass substrate for information recording medium in which an outer peripheral edge surface and an inner peripheral edge surface has a chamfered shape, said method comprising the steps of:

• forming a glass substrate precursor circumferentially provided with two concentric grooves having a substantially V-letter shape on one surface of the glass substrate precursor wherein a pair of metallic dies in which two concentric protruding parts corresponding to the chamfered shape and having a wedge shape formed in one of the metallic dies are used to press-mold molten glass;
• cutting glass substrate precursor at an apex of the substantially V-letter shaped grooves to remove an outer portion and a central section so that one side of an outer and an inner peripheral edge surfaces of the glass substrate precursor has the chamfered shape;
• heating an other side of the outer and inner peripheral edge surfaces not having the chamfered shape;
• and
• pressing by a metallic die having a molding surface corresponding to the chamfered shape onto the glass substrate precursor to form a chamfered shape on the other side of the outer and inner peripheral edge surfaces.