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.

Abstract: A vertical glass melting furnace provided with a material entrance at the uppermost portion and a molten glass exit provided at the lowermost portion. A resistance heating element 6 is provided over the substantially entire part of the horizontal section of the furnace at at least one level which is immersed in the molten glass.

Abstract: Glass fibers having a low dielectric constant composed of a glass having a dielectric constant of not more than 5 and comprising:SiO.sub.2 45-65% by weight,Al.sub.2 O.sub.3 9-20% by weight,B.sub.2 O.sub.3 13-30% by weight,CaO+MgO+ZnO 4-10% by weight,Li.sub.2 O+Na.sub.2 O+K.sub.2 O 0-5% by weight,Based on the total weight of the glass, the total proportion of SiO.sub.2, Al.sub.2 O.sub.3, B.sub.2 O.sub.3, CaO, MgO, ZnO, Li.sub.2 O, Na.sub.2 O, and K.sub.2 O being at least 95% by weight.

Abstract: A furnace for cooling molten glass, which comprises a cooling tank for slowly cooling the molten glass while the average temperature of the molten glass is within a certain range extending below and above the temperature at which the speed of absorbing bubbles is highest, and cooling it rapidly when the average temperature of the molten glass is outside said range.

Abstract: A method for producing glass bubbles, which comprises heating a glass powder containing a gas-blowing agent in an atmosphere containing steam having a partial steam pressure of at least 0.2 atmosphere to foam it.

Abstract: A method of cooling molten glass, which comprises slowly cooling the molten glass while the average temperature of the molten glass is within a certain range extending below and above the temperature at which the speed of absorbing bubbles is highest, and cooling it rapidly when the average temperature of the molten glass is outside said range.

Abstract: A process for the manufacture of glass raw material granular pellets is provided.The process comprises:(a) forming a mixture of powdered raw glass material with an aqueous solution of a binder, which can be converted into a solid upon exposure to an elevated temperature gas stream, said binder not adversely affecting the glass subsequently formed of said material,(b) directing a stream of gas at an elevated temperature upwardly through a substantially erect straight pipe having the upper end thereof connected to a solid-gas separator;(c) feeding said mixture into an opening in said pipe and into said upwardly flowing heated gas stream to disperse said mixture,(d) drying said dispersed mixture in said gas stream and bonding the particles in said dispersed mixture with said binder to form granular pellets thereof, and(e) separating said formed granular pellets from said gas stream in said separator.