Patent ID: 8800320

Claim:
A manufacturing method of a sheet glass material for magnetic disk, the method including a dropping process for dropping a lump of molten glass, and a pressing process for sandwiching simultaneously the lump from both sides of the dropping path of the lump with surfaces of a pair of dies facing together, and performing press forming to the lump to obtain the sheet glass material, at least one of the pair of dies having a convex shape with respect to the dropping path of the lump, and the die having the convex shape with respect to the dropping path of the lump is formed by bonding a plurality of plates or thin films made of materials, each of which coefficient of thermal expansion is different, and a coefficient of thermal expansion of a plate or a thin film that contact the lump is the lowest of those of the plurality of plates or thin films so that the die having the convex shape becomes flat by pressing the lump with the pair of dies.