Glass Furnace

a furnace designed to melt glass and provide the preparation for forming. Upon heating in a glass furnace, usually to 1500°-1600°C, the charge (raw materials) passes through the stages of silicate formation, mutual solution of silicates and residual silica, and fining (removal of gas bubbles). It is then converted into a glassy mass suitable for the forming of articles.

Glass furnaces of the batch type include pot furnaces and small tank furnaces. They are used for the production of such special glasses as optical glass, colored glass, crystal glass, and the glass used in illuminating engineering, the treatment of which is carried out primarily by hand. Pot furnaces usually contain six to eight pots, which are refractory vessels made of grog, kaolin, or quartz and which hold 100–1,000 kg of molten glass; less often, the furnace may have 12 to 16 pots, for example, when a casting process is used. Operation involves heating the furnace, filling the pots with raw material and scrap glass, and melting the charge. The glass is then subjected to forming, and the process is repeated. Although pot furnaces have an efficiency of only about 8 percent, they permit the simultaneous melting of glass with different compositions. Also, since mixing is comparatively easy in the pots, the homogeneity necessary in producing, for example, optical glass, can be readily achieved. Batch-type tank furnaces, used primarily in the production of hard glass and colored glass, are more economical.

In the large-scale production of glass (sheet glass, container glass), melting is carried out in continuous tank furnaces, and forming is done by machine. In continuous furnaces, melting occurs in certain sections, and the molten glass then moves the length of the furnace. The melting section also includes zones for fining and homogenization, and the forming section also includes a zone for cooling. The design of tank furnaces may differ in the path followed by the flame (transverse path, horseshoe-shaped path), the method of separating the melting and forming sections in the glass melt (floating grog pieces), and the method of dividing the space under the crown of the furnace occupied by gas (using a screen, lowering the roof). For example, in the production of sheet glass, continuous tank furnaces are used in which the flame is directed transversely. The length of the tank may reach 60 m, the width 10 m, and the depth 1.5 m. The tank can hold up to 2,500 tons of molten glass. Continuous tank furnaces have a melting capacity of up to 300 tons per day. They are made of refractory materials.