Refractory Lining of the Electric Arc Furnace - Part 7

... If the operating practice of the EAF limits the introduction of slag into the taphole and the runner, then high strength, high alumina castables are used for the precast runner. The high alumina runner generally has a higher life because of improved thermal shock resistance and higher strength as compared to the magnesite precast runner.

Bottom tapping EAFs need specially designed taphole sleeves and an end block for the taphole design. The taphole sleeve sits within the hearth in a taphole seating assembly. The assembly can be made up of either brick shapes or precast shapes which results in an around 450 mm diameter hole through the furnace hearth refractories. The taphole sleeve is centred within the taphole seating assembly and a basic castable or ramming mix is packed in the annular opening between the sleeve and the seating blocks. Taphole sleeves are Mag-C blocks made from high purity magnesia or fused magnesia grain with 10 % to 15 % of C content. Metal powders are used as a strengthening agent for maximizing erosion and oxidation resistance. The bottom of the taphole extends beyond the furnace shell utilizing a shape called an end block. The end block is a similar Mag- C brick which is held in place by an end block casting attached to the EAF. The end block is exposed to the outside environment and is required to have very good oxidation resistance as well as a high erosion resistance for withstanding the erosive action of the taphole stream. The end block is quite often the limiting factor for the taphole performance. As the refractory erosion occurs, the tapping stream begins to flare, increasing the reoxidation of the liquid steel. It is essential then to carry out a hot repair to replace the end block and taphole sleeve.

Roof and Delta – EAF roof refractories for both the AC and the DC furnaces are normally high alumina (70 % Al2O3 to 90 % Al2O3) precast shapes having high strengths. Since, the roof lifts and swings away from the furnace body during the charging process, refractories in the roof are subject to extensive thermal shock. The lesser thermal expansion of high alumina castables compared to the basic castables offer an advantage in withstanding thermal shock. Further, high alumina castables have higher strength than the basic castables. Hence, high alumina roofs are better able to resist the stresses developed as the roof is lifted and moved during the furnace operations. EAF roof refractories normally last for a longer time.

The roof also enables the furnace exhaust gases to leave the furnace through a duct. While the immediate exit from the furnace is normally water cooled, there is a refractory lined zone in the duct system. Refractories in the exhaust ductwork are capable of withstanding the slag carryover and slag abrasion from particulate laden exhaust gases moving at high velocity. Refractories in the ductwork are alumina bricks (To be followed)#graphiteelectrode #الکترود گرافیت #Grafitelektrot #Графитовыйэлектрод