Refractory materials: history and classification
The article deals with the history and classification of refractory materials.
Refractory materials: history and classification
Refractory materials (refractories) are materials manufactured on the basis of mineral raw materials and characterized by the ability to maintain without significant violations of their functional properties in a variety of service conditions at high temperatures.
They are used for metallurgical processes (melting, annealing, firing, evaporation and distillation), construction of furnaces, high-temperature units (reactors, engines, structural elements, etc.). Refractories used are called refractory scrap and are used in processing.
Most refractory products are produced in the form of simple products such as a rectangular parallelepiped weighing several kilograms. It is a universal form to carry out the lining of various configurations. At present, the refractory industry is reducing the production of refractories in the form of simple products and the corresponding increase in the production of refractory concretes and masses.
Refractory materials are characterized by high strength at high temperatures, chemical inertness. The composition of refractory materials is a ceramic mixture of refractory oxides, silicates, carbides, nitrides, borides. Carbon (coke, graphite) is used as a refractory material. Basically, these are non-metallic materials with a fire resistance of not less than 1580°C, are used almost everywhere where it is required to conduct any process at high temperatures.
Even at the dawn of human culture with the receipt of fire there was a need for refractory materials. As a result of millennia of development of human society and its culture, refractory materials have become the basis of modern blast furnaces, steelmaking, copper smelting, cement-roasting, glassmaking and other furnaces.
Refractories in the form of bricks made of refractory clays and kaolins began to be produced after the appearance of blast furnaces. In Russia — about the middle of the XVII century. Under Peter I a significant number of such bricks were made of clay near Moscow. During the first half of the XIX century, the production of refractories developed mainly at metallurgical plants, being an addition to the General direction. Of course, this adversely affected production, as it slowed down the work and sprayed the industrial potential, but because of the agricultural orientation of the country, this problem was not solved for a long time. Industrial Europe, which had undergone an industrial revolution by the 19th century, had at its disposal working refractory plants, founded in the period of the Napoleonic wars. The first specialized production of refractories was organized in Germany in 1810.
With the rapid development of industry and the advancement of the bourgeoisie class to decisive political and social roles, the Russian Empire is no longer interested in artisanal production of refractory materials, and a specialized branch, which should be the basis of the refractory industry. The first steps in this matter was the creation of the first plants: Belokamensky refractory plant in Bryantsevka (now Soledar) (1893) and refractory plant in Latna (1897) with a narrow refractory specialization.
Production of refractories in the former Soviet Union is concentrated in three main industrial areas: southern (white stone, Yar Clock), Central (Podolsk) and Ural (Pervouralsk, Bogdanovich).
At the moment, the presence of the refractory industry and the quality of refractories in a country characterizes the degree of its industrialization. Of the more than 212 countries in the world, the refractory industry is only available in 35 countries. More than half of the world production accounts for the CIS and the US.
Refractory materials are of single-piece products (blocks) and unshaped. The latter include welding materials, mertel, backfilling and other special printed and molded masses, including those used for the production of refractory concretes and shotcrete.
Refractories are divided into the following characteristics:
- shapes and sizes
- the method of forming
- chemical and mineral composition
Classification by shape and size
- straight and wedge normal size, small and large format;
- shaped simple, complex, particularly complex, large-block, weighing over 60 kg
- special: industrial and laboratory purpose (crucibles, tubes, etc.)
Classification by method of molding
- sawn from natural rocks or from pre - made blocks;
- castings, made by casting of a liquid slicker, foaming agent, etc.;
- plastic molding, made from a mass in plastic condition, machine molding, jolt squeeze, followed;
- semi-dry molding of powders;
- fused cast from the melt obtained by electric melting;
- thermoplastic pressed;
Fire resistance classification
- refractory (fire resistance from 1580 to 1770 °C)
- high-pressure (from 1770 to 2000 °C)
- highest fire resistance (from 2000 °C to 3000 °C)
- super-resistant (over 3000 °C)
Classification of porosity
- very dense (an open porosity of up to 3 %)
- high density (open porosity from 3 to 10 %)
- dense (open porosity from 10 to 16 %)
- compacted (open porosity from 16 to 20 %)
- medium density (open porosity from 20 to 30 %)
- low density (porosity from 30 % to 45 %)
- highly porous (total porosity from 45 to 75 %)
- ultrapurity (total porosity greater than 75 %)
Classification by chemical and mineral composition
It is necessary to distinguish between acidic, neutral and basic refractories. More detailed classification is made by their chemical composition:
Refractories have a lot of applications, but all of them can be divided into two main groups, these are refractories (refractory products, for example, brick) for General purpose, and refractories designed specifically for any thermal unit. Refractory materials used in metals, glass, sugar, engineering, chemical industry and all other industries, where the work with the application domain, shaft and rotary kilns.