Throughout the industrial sector, machines like boilers, furnaces and kilns help drive material processing, manufacturing and energy production. One feature, vital yet easily overlooked, is common to all of these: the use of heat-resistant materials known as refractories. Many different materials fall under this class, but their use has been present since the earliest brick kilns and ovens. An understanding of what role refractories serve is important in maintaining the modern manufacturing processes that rely on them.
Properties of Refractories
In industrial contexts, a refractory is a non-metallic material that retains its strength and integrity at high temperatures, at least above 1000 °F (538 °C / 811 K). Traditionally, refractories were made in brick form, but modern refractories can exist as preformed shapes like interlocking tiles, aggregates or cements that are formed and fired where necessary or lightweight ceramic fibers. Most refractories are composed of ceramics or minerals, with various oxides and carbides being common components, and they vary in chemical reactivity and acidity/alkalinity.
How Refractories are Chosen
The ideal refractory to use in a given scenario or machine depends on the environment it’ll be exposed to—temperature, atmosphere, materials being processed, expected byproducts, etc. For instance, a given material may excel in high-temperature environments without oxygen, such as graphite, but would combust in the presence of oxygen. Similarly, coke oven door plugs, used to seal the interior atmosphere, contain refractories that must resist both carbon penetration and thermal shock caused by sudden changes in temperature to keep the seal from breaking.
Where Refractories are Used
Refractories are common anywhere where high temperatures are involved, both in and out of industrial settings. Clay kilns and fireplaces use simpler refractory materials, while high-grade alumina composites make up the heat shielding installed on space shuttles. Coke ovens, smelting crucibles, boilers and more remain structurally stable during operation thanks to various refractories lining or comprising their interiors.