After leaving the batch house, the mix is fed continuously into the furnace or tank where it is melted into glass. The glass depth must be controlled to within ±0.01 inch for proper forming machine operation.
Furnaces consist of three main parts, the melter, refiner and regenerators or checkers. Most furnaces are designed to use natural gas but are capable of using alternate fuels-oil, propane and electricity-if necessary. Furnaces range in size from about 450 to more than 1,400 square feet of melter surface.
A properly operated and well-maintained furnace will last for 10 years or more with just one partial repair and will produce over 1,000 tons of glass per each square foot of melter surface over the life of the furnace.
The Melter is a rectangular basin in which the actual melting and fining (seed removal) takes place. In a side-fired furnace, the batch is charged into the furnace through the doghouse, which is an extension of the melter, protruding from the back wall. Along each side of the melter, above glass level, are three to seven ports, which contain the natural gas burners and direct the combustion air and exhaust gases.
The melter basin is separated from the refiner by the bridge wall (throat end wall). Glass passes from the melter to the refiner through the throat, which is a water-cooled tunnel that extends through the bridge wall.
The Refiner acts as a holding basin where the glass is allowed to cool to a uniform temperature before entering the forehearths. The melter and refiner are covered by crowns to contain the heat.