The roof of a steel rolling heating furnace is divided into two types: arched roof and flat roof. The arched roof is built with refractory bricks. Generally, the inner layer is a 232mm or 300mm thick refractory brick layer, and the outer layer is covered with an insulation layer. This type is only used in small furnaces with a furnace width of less than 3m. Large furnaces all adopt flat roofs. The earlier flat roof was hung with special-shaped refractory bricks, but since the promotion and use of amorphous refractory materials, the roof of the steel rolling heating furnace is almost entirely made of refractory castables or refractory plastics.
There are two typical refractory castable roof structures. One is an integral casting structure. During construction, the formwork is first supported and the anchor is fixed to the furnace roof steel structure, and then the refractory layer is cast, and the expansion joint is left; the insulation layer above the refractory layer uses lightweight castables. The second type is the prefabricated block structure, which appeared in the early days of the use of amorphous refractory materials. Its advantage is that it is easy to construct and maintain, but it uses a lot of materials and the furnace top insulation is not good. It has gradually been replaced by the integral cast structure.
1.Application of refractory materials in heating furnaces
Application of refractory materials in regenerative heating furnaces. Since the late 1990s, quick-drying castables, quick-drying self-flowing castables and quick-drying slag-resistant castables have been used in heating furnaces. This type of material not only ensures the excellent performance of low-cement, ultra-low-cement and cement-free castables, but also allows for rapid construction, especially rapid baking, so that the furnace body of the integral castable can be baked within 3 to 5 days. In addition to the above characteristics, quick-drying slag-resistant castables also have excellent anti-oxidation iron sheet erosion characteristics.
2.Development of heating furnaces
Regenerative heating furnaces are a new type of heating furnace developed in recent years. The biggest feature of regenerative heating furnaces is high efficiency and energy saving. The average energy saving rate is increased by 30% on the existing basis, and the pollutant emissions, especially NOx emissions, are reduced. Therefore, this type of heating furnace has received great attention from the metallurgical industry. Regenerative heating furnaces mainly include channel heating furnaces, external regenerative heating furnaces and burner heating furnaces. Compared with general heating furnaces, the combustion mode, heat exchange mode, heat exchange medium and other aspects of the regenerative heating furnace have undergone major changes, and the furnace structure has also changed. There are many mutually isolated regenerative chambers and many criss-crossing gas pipes or air pipes in the furnace body of the channel heating furnace. The regenerative chamber casted with traditional vibration molding castables has the disadvantages of decreased medium-temperature strength, large linear shrinkage, and poor volume stability due to the unreasonable gradation of ordinary refractory castables and the use of cement. After a period of use, it is easy to crack, causing the regenerative chamber to leak during operation, affecting the heat exchange and energy saving effect. In particular, once the gas regenerative chamber leaks, it will bring safety hazards to production. Ordinary castables use vibration equipment to make the material flow during construction to achieve the required filling effect, but in the narrow and complex shape of the regenerative chamber furnace wall (the furnace wall is a multi-layer structure, layered construction, and each layer is only about 100mm thick), the vibration equipment cannot be used. The use of self-flowing castables can solve this problem well.
3.Application of castables
Self-flowing castables are low-cement or ultra-low-cement refractory castables that can flow, form, level and degas without vibration. Suitable raw materials and particle size grading are selected for different use parts, and composite ultrafine powder and high-efficiency dispersant are used to obtain better construction performance and high-temperature use performance. Self-flowing castables are suitable for narrow construction parts and complex shapes, such as the wrapping of the bottom water pipes of the steel rolling heating furnace and the furnace wall of the heat storage heating furnace with special structure. It is also convenient to use self-flowing castables for some parts that need local repair and filling. Quick-drying self-flowing castables are used for water-cooling pipe wrapping. Since the thickness of the water-cooling pipe wrapping part is small, generally 40 to 60 mm, if castables are used, it is difficult to vibrate fully, which affects the integrity and strength of the material. The use of quick-drying self-flowing castables can not only fill the material by itself and make it dense, but also ensure the integrity and strength of the material, and it is easy to construct and bake.
