Electric arc furnace refractory lining

Electric arc furnace refractory lining

What is an Electric Arc Furnace Refractory Lining and Its Characteristics?

1.What is an Electric Arc Furnace Refractory Lining?

An Electric Arc Furnace Refractory Lining is a layer of refractory material applied or applied to the inside of the EAF shell. It is the core protective component of the EAF. Its primary function is to isolate the high-temperature molten steel and slag from the furnace shell, withstand the extreme temperatures, chemical attack, and mechanical impact during the smelting process, protect the furnace structure, and maintain a stable smelting environment.

2.Characteristics of Electric Arc Furnace Refractory Lining

High-Temperature Resistance: It must withstand temperatures of 1500-1800°C (higher temperatures in ultra-high-power EAFs), and remain resistant to softening or melting under prolonged high temperatures. For example, magnesia-carbon bricks have a refractoriness of over 2000°C.

Chemical Corrosion Resistance: Direct contact with slag containing SiO₂, FeO, and CaO requires resistance to chemical corrosion from the slag (e.g., preventing the formation of low-melting-point compounds). Magnesium-based materials are commonly used for alkaline slag, while high-aluminum materials can be used for acidic slag. Thermal shock resistance: Severe temperature fluctuations occur during the smelting process (such as rapid cooling and heating during charging and tapping), requiring resistance to repeated thermal expansion and contraction to prevent cracking and spalling (e.g., magnesia-carbon bricks use graphite to buffer thermal stress).

High mechanical strength: Materials in key areas such as the furnace bottom and slag line must possess high compressive strength and wear resistance to withstand mechanical forces such as scrap impact, molten steel erosion, and furnace vibration.

Structural adaptability: Differentiated designs for different areas (e.g., lightweight materials for the furnace cover to reduce heat dissipation and corrosion-resistant materials for the slag line) meet the demands of complex operating conditions.

How can we improve the service life of electric arc furnace refractory linings?

Extending the life of refractory linings requires comprehensive optimization of multiple aspects, including material selection, construction quality, smelting operations, and maintenance. Specific measures are as follows:

1.Rationally Select Refractory Materials

Match materials based on the type of steel being smelted and the properties of the slag. For smelting high-carbon steel, alloy steel, and other alkaline slag-based applications, magnesia-carbon bricks (with their strong alkali resistance and thermal shock resistance) are preferred. For small and medium-sized electric arc furnaces or those using acidic slag, high-alumina bricks or alumina-magnesia spinel bricks can be used to balance cost and performance.

Reinforce Key Areas: High-density, high-purity refractory materials (such as low-carbon magnesia-carbon bricks) should be used in susceptible areas such as the furnace wall slag line and the taphole to reduce slag penetration and chemical reactions.

2.Strictly Control Construction Quality

Standardize Masonry Techniques: Ensure uniform brick joints (generally ≤ 2mm) to avoid misalignment or loosening. Use high-quality refractory mortar for masonry to ensure a tight bond between bricks and reduce slag penetration through gaps.

Ensure Standardized Construction of Unshaped Materials: When using ramming materials or castables in areas such as the furnace bottom and slope, strictly control the water addition ratio and vibration compaction to avoid air holes and delamination, thereby improving structural integrity. Reasonable baking system: New lining or repaired lining needs to be baked slowly according to the temperature rising curve (gradually from room temperature to above 1000℃) to remove moisture and volatiles and prevent cracking due to rapid evaporation of moisture at high temperature.

3.Optimize smelting operations.

Control temperature fluctuations: Avoid frequent rapid cooling and heating (e.g., reduce unnecessary furnace door opening time and allow for slow cooling after tapping) to minimize thermal stress damage to the lining.

Reduce mechanical impact: Avoid large scrap pieces directly impacting the furnace bottom or walls during charging. Layered charging or the addition of buffering materials (e.g., lime) can be used to reduce impact loads.

Optimize slag composition: Adjust the ratio of slag-forming agents (e.g., CaO and MgO) to control slag alkalinity (generally maintained at 1.2-1.5) to minimize chemical slag attack on the lining (e.g., high-alkalinity slag reduces SiO₂ attack on magnesia).

Shorten smelting cycle: Reduce the duration of high temperatures and the lining’s exposure to extreme temperatures, while also avoiding overheating (excessive temperatures accelerate softening and oxidation of refractory materials).

4.Strengthen routine maintenance and repair.

Regular inspection and local repair: Inspect the lining after each tapping. Repair any minor erosion or spalling with gunning material (e.g., magnesia-based gunning material) to prevent further damage. Taphole Maintenance: The taphole is a vulnerable part and can be replaced regularly with precast bricks or amorphous materials to prevent damage to the taphole, which could result in molten steel eroding the furnace walls.

Preventing Secondary Oxidation: For carbonaceous refractories (such as magnesia carbon bricks), deoxidizers (such as SiC and Al) can be added in the later stages of smelting to reduce the oxidizing atmosphere within the furnace and slow carbon oxidation loss.

5.Other Auxiliary Measures

Furnace Cooling Technology: Install water-cooled plates or jackets on the outside of the furnace shell to lower the operating temperature of the lining and minimize high-temperature softening and erosion (avoid excessive cooling that could cause localized low-temperature cracking of the lining).

Regular Slag Removal: After tapping, promptly remove any remaining slag and scrap steel from the furnace to prevent slag from eroding the lining surface during the next smelting cycle.

Through the above measures, the erosion, wear and thermal damage of the refractory lining can be significantly reduced, its service life can be extended, thereby improving the operation rate of the electric arc furnace and reducing production costs.