In the design of furnace furnaces, the main attention is paid to the structural design, the operation of individual components of the structure and the provision of the smoke exhaust function. Initially, materials are also calculated for the manufacture of the structure, since the specificity of its operation determines stringent requirements for the characteristics of the unit. At the same time, the basic material is far from always able to cope with the thermal effects that a particular furnace is designed for. Lining, as a technological operation of additional processing, allows minimizing thermal negative factors and preventing mechanical damage to the structure.
In what cases is lining performed?
The initial choice of building material for the technical implementation of the design is made taking into account its ability to cope with operational loads. As noted above, basic characteristics are not enough. The use of additional thermal insulation materials is necessary in some cases, associated with an increase in temperature loads on the surface of the structure. In particular, this applies to furnaces designed to operate in continuous furnaces. High-calorific fuel also gives elevated temperatures, although such units are rarely used and mainly in enterprises.
As for domestic furnace structures, they, as a rule, do not require additional protective coatings, but only if we are talking about structures of small and medium sizes. The situation is different if a massive Russian stove is considered. Lining in this case allows you to provide protection functional areas that can also be used for cooking.
Basic materials for lining
Refractory chamotte bricks are considered a classic material for lining stoves. With its help, an external shielded protection is formed. This option is suitable for bath stoves, which in some way require complete thermal insulation. In the usual version, the chamotte refractory lining is a lining of the furnace part in order to protect it from elevated temperatures.
With the development of technology, other means of ensuring the protection of furnace structures have also appeared. So, if concrete solutions were previously prepared, from which ordinary plaster was later laid, then in the modern form the same method looks somewhat different. The main difference is that the mixture is applied to a hot surface using shotcrete technology. That is, heat-resistant concrete is applied to the target surface in layers, using pneumatic means based on compressed air.
Roll lining
A fundamental difference from classic coatings and masonry with a heat-insulating function are roll coatings. Firstly, they are easy to apply. Secondly, the coating takes up a minimum of space, increasing the thickness of the structure by no more than 1 cm. For comparison, heat-resistant concrete in the form of plaster increases the thickness of the walls of the furnace structure by 1-2 cm, and brick by this indicator can reach 10 cm. Roll material It is presented in several forms, as a rule, on a paper fire-resistant basis.
The most widespread in this segment was mullite-siliceous kaolin wool, which is obtained as a result of melting of silicon and oxide in an electric furnace. In practice, it is noted that this material has low thermal conductivity and at the same time increased heat resistance. Also, kaolin thermal insulation materials are not destroyed by the action of chemicals, for which they are appreciated in industrial production.
Features of protection of induction furnace
To begin with, it should be noted that the need for lining induction furnaces arises not because of the weakness of the structure before thermal shocks, but because of the specifics of their application. Such units are used for melting metals at high temperatures, therefore, special means in the form of dry mixtures are used to protect them. In essence, this is a classic coating, but the composition for the mass is fundamentally different from concrete mortars. So, the lining of induction furnaces that melt low alloy and carbon steel involves the use of spinel-forming masses. The latter, by the way, are resistant to slag formation. Units for cast iron smelting are treated with quartzitic compounds, and if non-ferrous grades with steel are added to this metal, technologists add lining and mullite-forming components to the recipe.
Execution technology
There are different techniques and approaches to lining, which differ in surface coverage and the method of applying insulating material. The protective lining can be external and internal. External lining is usually applied over the entire height - from the bottom to the crowning edges. Interior decoration may include the protection of working surfaces in direct contact with the flame, as well as with smoke in the form of high-temperature exhaust gases. The greatest effect is given by protection schemes that comprehensively isolate the furnace. Lining is carried out only on cleaned surfaces. The preparation of the material, as a rule, involves dilution of the active substances in solvents. Thus, a coating mixture is formed, which is applied on the surface of the structure using traditional facing tools. Brick, in turn, is laid according to standard schemes in accordance with the requirements for the protection of structures.
Conclusion
Outer coatings of furnaces should not only provide resistance to thermal influences, but also provide protection from other factors. For example, in industrial premises, the risk of mechanical stresses to which the furnace can be exposed increases. The lining in this case also involves the fulfillment of the tasks of physical protection of the structure. Therefore, special plasticizers can be added to the mixture, modifying the strength properties of the composition. But this applies only to means of creating external thermal insulation, and internal coatings are fully oriented towards the formation of effective temperature screens.