Steel Tapping Hole Refractories
Ordinary electric arc furnace steel tapping is through steel spout, but this tapping method requires large electric arc furnace angle of inclination, refractory material corrosion rate is high, furnace lining life is low, steel smelting efficiency is affected. Besides, this tapping method also has great washing abrasion to steel ladle, the service life of steel ladle is also affected.
To overcome the shortcomings of spout tapping method, eccentric bottom tapping method is developed, it has these advantages: 1. Water cooling wall area can be increased, refractory material consumption and cost can be reduced; 2. Tapping speed is high, air oxidization is reduced, steel quality is improved; 3. Easy to leave slag in electric furnace, heat loss is and refractory material corrosion is reduced. Therefore, power consumption is reduced and furnace lining life is prolonged.
When shutter is closed, tap hole is filled with brasque, furnace charge can be loaded for smelting. Shutter is mechanical structure, brasque is usually magnesia refractory, silica refractory and olivine refractory. Tailing block is usually corundum-SiC-C and magnesia carbon refractories. Sleeve bricks are often magnesia and magnesia carbon refractories. Pocket bricks are usually impregnated rebonded magnesia bricks. The gap between sleeve brick pocket brick is often filled by magnesia crack filler. During using, tail brick and sleeve brick damages are the main reasons for tapping hole replacement.
Tapping Hole Refractory Damage Mechanism
For sintered magnesia sleeve bricks and tailing bricks, thermal shock stripping and steel washing are main damage reasons. For MgO-C sleeve bricks and pocket bricks, not thermal shock stripping, but carbon oxidization formed loose de-carbonized layer is the main reason. Sometimes, brasque is sintered or steel liquid permeates into brasque and welds together, tap hoe is blocked and should be burned open by oxygen blowing tube. It will cause local high temperature and overheat, sintered magnesia sleeve bricks will have thermal shock stripping and mechanical abrasion, magnesia carbon sleeve bricks will have high temperature chemical corrosion and mechanical wearing, so high quality alkaline brasque, lower tapping temperature and shorter smelting time should be adopted.
Tapping Hole Refractories
Tapping spout can be built by bricks, ramming mass or castable. Tapping spout refractory materials are magnesia carbon bricks, alumina carbon ramming mix, Al2O3-SiC-C refractory, pitch magnesite bricks, high alumina bricks and high alumina castable. Carbon containing refractory life has relatively longer service life. In Europe, magnesite ramming mass, magnesia chrome ramming mix, pitch impregnated magnesite bricks, Al2O3-SiC precast blocks are often used at tapping spout, while tapping hole part is often constructed by pitch impregnated magnesite bricks or magnesia carbon bricks.
Eccentric bottom tapping hole is initially built by magnesite bricks, or casted by refractory materials with steel tube at center, or consisted of 2~3 pieces of fused bricks. With the development of refractory technique, tube bricks usually adopt magnesia carbon bricks, outside tube bricks are tapping hole well bricks. When tube bricks are consumed, new sleeve bricks can be quickly installed, and the surrounding can be filled with jointing materials. Jointing materials are usually magnesia ramming mix or castable. Under normal circumstance, tapping hole pocket bricks are not easy to break, they are often pitch magnesite bricks, sintered magnesia bricks and magnesite carbon bricks.
Tail bricks suffers great thermal shocks and oxidization, so alumina silicon carbide carbon bricks with better thermal shock resistance is adopted in some steel mills.
To prolong tapping hole service life, maintenance and patching should be carried out. Patching method is: when tapping hole corrosion reaches to certain extent, magnesia carbon brick tube or steel tube can be inserted into tapping hole, then hot boiling castable is used to fill the gaps. Hot boiling castable mainly includes: hydrous magnesia chrome castable and magnesia carbon castable.
