| CPC C03B 23/037 (2013.01) | 9 Claims |
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1. An elongating method for elongating a glass base material by heating the same while moving the same downward within an elongating apparatus, the glass base material including a transparent tapered section, wherein the transparent tapered section is located at an upper end of the glass base material and has an end face to which a suspension dummy formed from a glass pole is welded, the elongating method comprising steps for:
starting elongating of the glass base material by heating the same, starting from a lower-end side thereof, by causing the glass base material to pass through a range of a heating furnace within the elongating apparatus in which a preset elongating process temperature or higher is maintained; and
after the transparent tapered section enters the range, ending the elongating of the glass base material once the following condition is met:
(X/2)<Y<{(X/2)+Z},
where X is a length of the range in an up-down direction of the elongating apparatus [mm], Y is a length of an area extending from a central position in the range in the up-down direction to the end face [mm], and Z is a length of the transparent tapered section in the up-down direction [mm].
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