The roof of an electric arc furnace is typically designed in an arched, dome-like shape. Depending on the furnace type and size, the weight of the roof can vary significantly—but it is generally very heavy. For example, the roof of a 5-ton brick-lined electric arc furnace may weigh nearly 5 tons, while a water-cooled one can exceed 10 tons.
Roof Structure and Material Selection
The central portion of the furnace roof—commonly referred to as the small furnace cover—is often made from prefabricated refractory blocks, or it may be designed as water-cooled or semi-water-cooled. In ultra-high-power electric arc furnaces, this section near the electrodes frequently uses high-alumina prefabricated blocks with outer-ring water cooling to enhance durability and thermal performance.
Since the furnace roof is continuously exposed to extremely high temperatures and frequent thermal cycling, the refractory materials must meet high performance standards. Initially, silica bricks were widely used, offering a refractory temperature of around 1690–1710°C. However, with the rise in furnace intensity and internal temperatures, the poor thermal shock resistance and weak resistance to alkaline slag of silica bricks led to their gradual replacement.
Today, high-alumina bricks are the mainstream choice, providing a higher refractory range of 1750–1790°C along with better resistance to thermal shock. However, high-alumina bricks are still vulnerable to erosion by lime powder and iron oxide-containing basic slag, often resulting in surface peeling or even melting. Once incorporated into the slag, these materials can significantly thin the slag consistency. As a solution, many steel plants now construct the main sections of the roof with alumina-magnesia bricks, which offer superior resistance to both high temperatures (up to 2100°C) and slag corrosion. High-alumina bricks are still retained around the electrode holes and charging ports.
Advantages of the Arched Design
Brick-lined furnace roofs are usually built with a domed arch, where the inner surface is slightly smaller than the outer surface. This allows for the use of wedge-shaped bricks (larger on top, smaller on the bottom) that fit tightly together, greatly improving the structural stability of the arch.
In real-world operations, the central roof section—located above the high-temperature electrode area—is often the most prone to damage. By designing a proper arch, the central section is positioned further away from the furnace’s hottest zone, which helps to extend the roof’s service life. However, the arch must be carefully proportioned; excessive curvature can lead to falling bricks during tapping operations.
