Double crucible for a glass drawing method and method of making glass fiber or a preform with the double crucible

摘要

The double crucible for a glass drawing method has a heatable outer crucible ( 1 ) and an inner crucible ( 2 ) surrounded by the outer crucible ( 1 ), which is heatable separately from the outer crucible ( 1 ). Both crucibles ( 1,2 ) have an outlet nozzle ( 1 a, 2 a) for the glass to be drawn. To make glass fibers from heavy metal oxide glass (HMO-glass) with higher quality and comparatively simple crucible features, the outlet nozzle ( 1 a) of the outer crucible ( 1 ) extends a certain distance beyond the outlet nozzle ( 2 a) of the inner crucible ( 2 ). Surfaces of the outlet nozzles coming in contact with the glass melt are polished and are provided on a material, which has a reducing action on heavy metal glass in the melt in all cases. These surfaces also have sufficient mechanical strength for and chemical inertness to heavy metal oxide glass.