Patent ID: 9328012
Filing Date: 2016-05-03
CPC Classification: C03B,Y02P

Claim Text:
1. A glass base material elongating method comprising: holding, with a pair of chucks, longitudinal ends of a glass base material that has a trunk portion and a tapered portion, which is located on one end of the trunk portion and has an outer diameter that changes along a longitudinal direction; heating, with a heat source, a heated region that is a portion in the longitudinal direction of the glass base material held by the pair of chucks; and elongating the glass base material by increasing distance between the pair of chucks in the longitudinal direction of the glass base material, with a portion of the glass base material being in a softened state due to the heating by the heat source, wherein the elongating begins from a state in which a position of the heat source indicated by a center of the heated region is at an elongation start position, which is a position in the tapered portion at which the outer diameter of the glass base material is set in a range from no less than 95% to no more than 98% of an average outer diameter of the trunk portion, the glass base material elongating method further comprises, before the heating, preheating while moving the heat source from a preheating start position, which is farther from the trunk portion than the elongation start position, toward the elongation start position, wherein the preheating start position is distanced from the elongation start position by a distance greater than or equal to 50% of the average outer diameter of the trunk portion.