Abstract: A glass composition of the present disclosure includes, in wt %, 50?SiO2?56, 20?B2O3?30, 10?Al2O3?20, 3.5?MgO+CaO?10, and 0?R2O?1.0, further includes Fe2O3, and has a permittivity of less than 5.0 at a frequency of 1 MHz. R is at least one element selected from Li, Na, and K. The glass composition of the present disclosure is a low-permittivity glass composition with which the occurrence of fiber breakage during fiber forming can be reduced even when glass fibers to be formed have a small fiber diameter, and the occurrence of defects such as fiber breakage and fluffing during processing of the glass fibers can be reduced.

Abstract: A glass composition of the present disclosure includes, in wt %, 50?SiO2?56, 20?B2O3?30, 10?Al2O3?20, 3.5?MgO+CaO?10, and 0?R2O?1.0, further includes Fe2O3, and has a permittivity of less than 5.0 at a frequency of 1 MHz. R is at least one element selected from Li, Na, and K. The glass composition of the present disclosure is a low-permittivity glass composition with which the occurrence of fiber breakage during fiber forming can be reduced even when glass fibers to be formed have a small fiber diameter, and the occurrence of defects such as fiber breakage and fluffing during processing of the glass fibers can be reduced.

Abstract: A glass composition of the present disclosure includes, in wt %, 50?SiO2?54, 25?B2O3?30, 12?Al2O3?15, 0.5?MgO?1.9, 3.0?CaO?5.5, 0?ZnO?3.5, 0.1?Li2O?0.5, and 0.1?Na2O?0.3, and has a permittivity of less than 5.0 at a frequency of 1 MHz. The glass composition of the present disclosure has a low permittivity. The use of this glass composition can reduce the occurrence of devitrification and the inclusion of bubbles in glass fibers to be formed or in a shaped glass material to be formed even when the glass fibers have a small fiber diameter or the shaped glass material has a small thickness.

Abstract: A vertical glass melting furnace of the type having an inlet for raw materials at the top thereof, an outlet for molten glass at the bottom thereof, and a tabular electric resistance heating element for melting which is immersed at some level in molten glass, has at least one opening, and covers almost entirely the cross-section of the furnace at that level, the vertical glass melting furnace comprising a stirrer which extends from above the furnace and passes through the batch layer and the tabular heating element so that the stirrer brings about forced circulation for homogenization of the molten glass which has passed through the tabular heating element and stays in the region below the tabular heating element.