1. What is the loss mechanism?
Generally, magnesia carbon bricks are made of high-quality magnesia sand, high-purity graphite, silicon, silicon carbide and other additives, and are pressed with phenolic resin as a binder. The basic requirements of electric furnaces for magnesium carbon bricks are:
(1) Low thermal conductivity to ensure less heat loss and improve the thermal efficiency of the electric furnace;
(2) High resistance to thermochemical and thermophysical erosion coefficients, that is, good volume stability is required;
(3) Anti-slag, anti-stripping, anti-oxidation and high compressive strength, so as to obtain low consumption and high life.
When baking a new furnace lining, the following main reactions will occur when the furnace lining temperature reaches 750℃:
MgO(s) + C(s)→→Mg(g)+ CO (g)
Mg(g) +Rn0m→MgO ・R„О (m-1)(s)
Reaction 1 is mainly the migration of magnesium gas and carbon monoxide gas along the pores to the high temperature zone. Reaction 2 is that the magnesium gas on the surface of the furnace wall is oxidized again by oxides to magnesium oxide, and forms a high melting point petrographic compound with other trace compounds in the magnesia carbon bricks. Therefore, controlling the temperature system of the furnace to prevent the occurrence of reaction 1 in large quantities is the key to maintaining the volume stability of magnesium carbon bricks. This is very important whether in converters or electric furnaces. The direct consequence of furnace failure is the collapse of the furnace lining or a significant reduction in the life of the furnace lining. Most domestic manufacturers have a lot of experience and lessons in this regard.
2. What are the causes of erosion?
During normal smelting, the furnace lining is in direct contact with high-temperature molten steel and slag, and the working conditions are very harsh. The causes of lining damage are:
(1) Thermal spalling caused by arc radiation and chemical erosion in high temperature state.
(2) The scouring effect of slag, molten steel and furnace gas on the furnace lining.
(3) The slag on the furnace lining Chemical erosion.
(4) Peeling caused by temperature changes.
(5) Layer cracking caused by the decomposition of the mineral composition of the furnace lining bricks themselves.
(6) Mechanical impact and scouring of the furnace lining when adding scrap steel and molten iron.
3. What is the effect on slag resistance?
Magnesia carbon bricks react with slag to form a dense reaction layer, and their slag erosion resistance will also be improved. The slag erosion resistance of the material is poorer than its oxidation resistance. After use, the organizational structure must be loose, and the slag will invade the interior of the material, damaging the original brick layer and completely destroying the material.
After understanding the damage mechanism of the refractory material of the electric furnace lining, we can choose suitable durable and long-life refractory materials based on this. The furnace wall of the electric furnace is generally made of magnesia carbon refractory materials, and the furnace bottom of the electric furnace is generally built with ramming materials, mostly magnesium calcium dry ramming materials, and must have the characteristics of rapid sintering, forming a solid working layer, being able to prevent slag penetration to the maximum extent and keeping the deep material moderately loose.
