Heating furnace, for glass materials for optical fibre - has heating elements around core tube which isolates heating atmos. from elements

摘要

In heating furnace a porous glass material which consists of fine quartz glass particles, is heat-treated in a fluoride-contg. gaseous atmos. to add fluorine to it and make it transparent and obtain a glass material for optical fibre. Heating furnace has heating elements and a furnace core tube provided on the inner side of the heating elements to isolate the heat atmos. and heating elements from each other. At least the inner layer of the furnace core tube is formed of high-purity carbon.