GLASSIFICATION OF POROUS SUBSTANCE MADE FROM GLASS SUIT AND FURNACE FOR CARRYING OUT SAME

摘要

A method of vitrifying a porous cylindrical article made out of glass soot, especially for manufacturing a preliminary blank for optical fibers. The article is heat-treated in a furnace in a vacuum or in an atmosphere that contains helium. The porous article is placed in a horizontal graphite tube in the furnace, is sintered therein for 20 to 40 minutes in a vacuum or in a helium atmosphere with reduced pressure at 1250 DEG to 1400 DEG C., and is subsequently vitrified by heat-treating the sintered article at first in the sintering atmosphere, while slowly rotating it in the hot graphite tube for 20 to 40 minutes at approximately 1450 DEG to 1600 DEG C. and then while rotating it in the graphite tube more rapidly than in the first stage for 10 to 30 minutes at approximately 1650 DEG to 1750 DEG C.