Electric Arc Furnace Subhearth Refractory Construction

Articles

There are basically three types of sub hearth construction utilized today in the electric arc furnace industry – these being the stadium, dished, and the contoured (or flats on the shell).

The most commonly used types of brick for sub hearth applications are those in the 95% and 97-98% MgO burned class.

Electric Arc Furnace - Stadium Construction

The stadium construction is accomplished with the use of keys and straights. Before beginning installation, it is important to check that the furnace is level, that all foreign material has been removed from the furnace shell, and that all weep holes are open. When this has been done, that actual construction can commence in the following sequence:

Cover all weep holes to avoid loss of material through the holes.
Level flat of the bottom with Rescomag Mix to the desired elevation.
Locate the exact center of the furnace and lay the first course of flat with straights, making sure that brick is level in all directions.
After the first course is completed, fill the voids at the outer periphery with Rescomag Mix. Dry dust the first course and each succeeding course with dry Permanente mortar.
The best method of dry dusting is to sweep with a broom. Complete the remaining flat courses, in the same manner, bond every other course to minimize straight through joints; break joints horizontally and vertically.
Once the flats are completed, the step ring courses can be started. Scribe a circle from the exact center of the furnace to the inside of the first ring. Lay in the first ring, making sure that the brick is snug and conform to the scribed circle.
With the first ring in place, lay any outer rings working from the center of the furnace outward. This makes up the first step. Fill voids at the outer periphery with Rescomag Mix and dust brick with dry Permanente mortar.
Complete each successive step in the same manner until the vertical steel sidewall is reached. Always leave 1” void between the shell and the brick. In any direction, this void should be filled with dry Rescomag Mix.
Complete each additional step in the same manner until the lower sidewall is reached.

Electric Arc Furnace - Contoured Construction (Flats on Shell)

This type of construction is typically accomplished with the use of 9x4.5x3 & 9x6x3 straights laid flat.
When laying straights or flats directly on the shell, it is important that all foreign material be removed from the furnace shell and that all weep holes are open and clean. Then, the actual construction can commence in the following sequence:

If the bottom of the shell is not a smooth contour as in riveted construction, a layering of Rescomag Mix is recommended against the steel before beginning the brickwork.
Start the first course by laying the brick flat against the contour of the shell. Brick can be laid dry and dry dusted. Note: it is recommended that if cold face gapping at brick ends exceeds 1/8”, that the brick be laid with a buttered join.
Complete the first course, making sure that the brick farthest from the center of the furnace are at or below the prescribed mark denoting the lower sidewall.
With the first course in place, dust joint by sweeping in dry Permanente Mortar.
Complete each additional course following the procedures used for the first-course break bond with every other course to minimize straight through joints; break.
When all courses are in place, level outer periphery (lower sidewall base) with working hearth material.

Electric Arc Furnace - Dished Construction

This type of construction involves placing key and wedge (KAW) brick around a center plug directly on the shell. With a clean shell locate the center of the bottom and positive center plug. Around the center plug lay the designed KAW's per the supplied drawing. Keep the brick in-ring radial and periphery of ring round. Use Permanente mortar (wet) as required to achieve this goal. Lay the desired number of the ring until the desired elevation achieved to transition to the sidewall.