PRODUCTION OF GLASS PREFORM AND DEVICE THEREFOR

摘要

PROBLEM TO BE SOLVED: To provide the production by which a high quality transparent glass article can efficiently be produced through an degassing operation that involves changing the degassing time correspondingly to the bulk density of a synthesized porous composite preform. SOLUTION: This production comprises: synthesizing a porous glass preform by a vapor-phase synthesis process; and subjecting the resulting porous glass preform to heat treatment in a vacuum or reduced pressure atmosphere to transparentize the porous glass preform and to form a transparent glass preform. More specifically, the production consists of three stages, namely: a first stage for degassing gases adsorbed on or contained in the synthesized porous preform; a second stage for subjecting the degassed porous preform to temporary shrinkage at a temp. higher than the temp. in the first stage and lower than the glass trasparentization temp.; and a third stage for transparentizing the shrunk porous glass preform at the glass transparentization temp. to form a transparent glass preform, wherein the degassing time of the degassing operation performed in the first stage is changed correspondingly to the bulk density of the synthesized porous glass preform.