In the EAF, 2 / 3 of the arc power transfers heat to the bath through the furnace lining. The effect of furnace cover on the heating of the bath is much greater than that of the furnace wall. The heat required in the non high temperature zone of the bath almost depends on the radiation heat transfer of the furnace cover.
The working conditions of furnace cover are very bad, especially when the furnace is calm in the reduction period of electric furnace, a large amount of heat energy is reflected from the liquid level and furnace lining to the furnace cover, which makes the temperature of furnace cover as high as 1700 ℃. The rapid change of temperature, erosion of furnace gas, slag and dust, and mechanical vibration also accelerate the destruction of furnace cover brick.
The furnace cover materials of alkaline electric arc furnace are generally made of first and second grade high alumina bricks, and some are made of alumina magnesia bricks. The refractoriness, load softening temperature and resistance to FeO slag of alumina magnesia brick are higher than those of high alumina brick, but the thermal conductivity and thermal expansion coefficient of alumina magnesia brick are large, which makes the furnace cover deform seriously. At present, alumina magnesia brick is mainly used in vulnerable parts of furnace cover (electrode hole, smoke exhaust hole, center part), and other parts are still made of high alumina brick to form composite furnace cover.
The masonry of the furnace cover is carried out on the fixed arch mold. The center of the furnace cover net must correspond to the center of the three electrode circles. The furnace cover built with high alumina brick is generally wet laid. Brick joint filler is made of high alumina fireclay, brine and purified water. The connection between bricks is tight to prevent gas passing through and slag penetration.
Fireclay clinker plays a key role in the slurry and prevents volume shrinkage. Raw meal plays a bonding role in the mud and adjusts the plasticity. The particle size should not be large to prevent the expansion of brick joint. The density of the mixture is 1.2 ~ 1.25. If the density is too high, the mud will dry easily and the joint of firebrick will increase. If the density is too small, the fire resistance of fireclay will be reduced.
When magnesia brick or alumina magnesia brick is used for furnace cover, it is suitable to use dry masonry, which will lead to pulverization of brick body at high temperature.
The masonry method of furnace cover brick is usually "herringbone" (as shown in the figure). Firstly, build "t" beam, then build three electrode holes, so as to avoid cutting bricks when building electrode holes, and then build upward from the arch angle beam. Brick laying shall be conducted according to herringbone shape between three large frames, and the joint shall be ≤ 3mm. One end of brick shall be reserved every 7-8 bricks to facilitate wedging down, and grouting shall be conducted from the furnace cover surface after laying.
