Refractory Lining of the Electric Arc Furnace - Part 10

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... hearth shown on the refractory drawing of the furnace is to be carefully followed to leave sufficient room to add the monolithic hearth material at the appropriate thickness.

For the EBT furnaces, it is even more critical to follow the refractory bottom drawing exactly. There are partial rings of brick with varying radii extending out into the nose section of the furnace which is to be kept level. One way to facilitate this is to drill a hole in the top flat course of bottom brick in the exact centre of the furnace and then utilize a broomstick with a nail on it extending up from this centre brick as a mandrel to draw circles and arcs for the stadium rings and partial rings extending into the nose.

If a monolithic hearth material is not used, the final course or final two courses in the all-brick hearth are laid in rowlock (on edge) or soldier (on end) construction. Rowlock or soldier construction gives much greater brick-to-brick contact and minimizes heaving of the hearth in service. Again, all courses in the hearth and stadium are laid dry and swept with magnesite mortar to fill the joints.

Once the stadium rings are completed, the slag line bricks are installed course by course using the same keying up concept utilized for the stadium rings. The slag line is also to be installed in excess of 25 mm away from the steel shell to permit thermal expansion without spalling or heaving the brick. Brick rings or partial rings are to be continued up into the sidewall and hot spots until the water-cooled panels or the top of the furnace is reached.

The door jambs are a critical design area for the refractory lining. Several designs simply utilize regular key shapes in interlocked courses as their door jamb, and these designs are quite successful. Other designs use special door jamb shapes which have greater surface area for better interlocking between courses and a sharper angle which opens up the door opening and eliminates or reduces refractory damage when slagging off. Still other door jamb designs involve brick or precast shape assemblies which are welded or bolted to the steel shell. These are generally installed first and the slag line and side wall brick is laid directly against these assemblies, with side wall rings keyed up halfway between the door and the taphole.

Conventional tilting EAFs generally use taphole module shapes set with a crane at the proper elevation prior to bricking the slag line and side walls. One alternative is to leave an opening in the side wall rings and then ram or gunite around a steel pipe forming the taphole. This pipe is then melted out on the first heat. Refractory taphole shapes can also be used in this same manner with monolithic material holding them in place at the proper elevation and angle..