Baking is critical after blast furnace overhaul repair(1)

Blast furnace maintenance, bricklaying or overall pouring repair for hearth, replacement brick or spray repair for inner lining, all involve the oven before opening. The oven is a very important part, and it is not advisable to blindly shorten the oven time in pursuit of a short maintenance cycle. In order to improve the competitiveness of the maintenance period, some refractory product manufacturers have compressed the overall casting and baking of the hearth to less than 3 days, even without baking. This actually only focuses on the volatilization of water in the casting body, and ignores the blast furnace body's requirements for preheating. 

The blast furnace oven discharges the internal moisture of the refractory material, discharges the free water in the casting body by evaporation, and then converts the bound water into free water through medium temperature decomposition and volatilizes it. If the thickness of the casting body is ≤ 200mm, this process may only require It takes about 3 days; for the casting of recycled carbon bricks, the thickness of the bottom of the furnace is generally more than 800mm, the thickness of the elephant foot area is more than 600mm, and the thickness of the iron mouth area can even reach more than 2000mm. The thickness of the casting body lasts for 1 week The above can completely drain the water. If the baking time is insufficient, the water will continue to volatilize in the initial stage of the furnace, and the phenomenon of blast furnace iron splashing and gas channeling may occur, which will prolong the production cycle.

The blast furnace baking to discharge the moisture of the refractory is only one of the functions of the furnace, and the more important blast furnace preheating and uniform stress distribution are mostly ignored. For the hearth repaired by masonry, during the construction process, wooden wedges will be used to hold the carbon bricks to leave gaps, and then the ramming material will be used to fill them, so local stress will be left. When the baking time is sufficient, the stress will gradually and evenly distribute. Avoid uneven stress and local brittle fracture in blast furnace operation (except for the temperature factor of brittle fracture of carbon bricks); And the use of integrally cast blast furnace hearth, in the drying process, water evaporation is accompanied by stress concentration and stress release. Slowing down is conducive to dissipating the concentrated stress of the casting body, reducing local defects, eliminating concentrated cracks, and more guaranteeing the smooth production of the furnace.

For the blast furnace hearth cast with used carbon bricks, shortening the oven time means sharply increasing the oven temperature, and the casting body and the old carbon bricks will expand and shrink when the temperature changes rapidly. It will peel off. Even if it expands and tightens during high-temperature operation in the later stage, it cannot ensure that the cast body and the old carbon bricks fit tightly together, so there is a local hidden danger of gap insulation.

The above is based on the experience summed up by a large number of blast furnace maintenance practices. For refractories, full baking can exert 100% of the characteristics, while the effect of non-baking is less than 50%. The fast-baking performance of the material only improves its baking efficiency, but the fundamental principle will not change. Sufficient baking has a great effect. Blindly shortening the baking time or not baking the oven may lead to the failure of the "vigorous" blast furnace maintenance.