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Glass-Melting Furnaces

Glass-Melting Furnaces

Date posted: November 10, 2017 // Glass Melting

In the wake of mankind’s newly found ability to produce fire on demand, it was not long before humans learned to adapt its unique properties for use in applications other than keeping warm, cooking their food, providing light in the darkness, and keeping wild animals at bay. Among the most significant of these additional uses was the process we now refer to as smelting. The discovery enabled them to work with metals and glass, melting and forming them for a variety of uses, despite lacking the sophisticated furnaces in use in the foundries of today.

During the heating process, the raw materials or “charge” undergo a series of changes that results in a mixture of silicates and residual silica. In a modern foundry, the mixture is then “fined” to remove any gas bubbles present. The result is a transparent, molten mass that may then be formed into finished items using a variety of techniques, such as moulding and extrusion.

During the process, it is required to generate a temperature of between 1500 and 1600 °C, which means that, in order to preserve the integrity of glass-melting furnaces, any material used to line them must have a significantly higher melting point. In smaller operations, it is common practice to load the raw materials, which will often include scrap glass, into pots. For obvious reasons, the latter also need to be made of a suitable refractory material, such as kaolin or quartz.

In most cases, the heat required to melt the raw materials is obtained by burning oil or gas and distributing it throughout the enclosing structure so as to ensure rapid and uniform heating. In some cases, however the heat is provided electrically and, given that molten glass is a conductor, heat is delivered directly into the charge by means of metal electrodes in the more specialised types of glass-melting furnace.

This type of operation, of course, would not be possible unless the electrodes used were made of a suitable refractory metal and, in this case, the element of choice is molybdenum. With a melting point that is more than a thousand degrees above that of silica, at 2623 °C, the metal provides a wide margin of safety. In addition, the use of molybdenum has the further advantage that it is highly resistant to the corrosive effect of prolonged immersion in the molten silicate mixture.

Glass-melting furnaces have undergone vast improvements since they first appeared on the scene. Regardless of how they may be powered, today’s models are essentially of two main types. Both the pot and tank designs are available in sizes suitable for the production of smaller batches. However, for use in a large-scale operation, the entire manufacturing process can, if required, be conducted with the use of a single long tank. The tank is divided into separate zones in which the melting, fining, homogenization, forming, and cooling processes take place sequentially and continuously.

Whether for its inherent beauty or the more practical qualities, this product of molten silica has become an important component of modern living. Consequently, those who operate glass-melting furnaces aim to maintain the highest possible quality standards. To support them, LIT Africa supplies a range of related products including crucibles, mandrels for shaping, hoppers, and molybdenum electrodes.