Rate of zone formation in magnesite-chrome roofs of open-hearth furnaces

Conclusions

The amount of melt dust absorbed by the working surface of the roof of a large-capacity open-hearth furnace averages 70 g/m² · hour. According to the period of the melt (temperature of the roof), the intensity of the absorption may vary from a very slight degree during charging and soaking to a maximum value (>100 g/m² · hour) during the final melting.

The slagging of the surface through the effect of melt dust and the splashing of the roof during intensive boiling of the bath and blasting of the bath with oxygen all help the absorption.

The rate of migration of the iron oxide into the deeper layers of the roof bricks, all other things being equal, depends on the concentration gradient and temperature, and drops from 150 to 40 g/m² · hour or less, as the iron oxides accumulate in the working zone.

The slowing down of the migration of the melt dust components helps the iron oxides to accumulate on the working surface and helps the surface to sweat, which increases the specific amount of dust settling and leads to a considerable reduction in refractoriness (to 1780°) [2] in the peripheral zone with the formation of beads and incrustation.

The variegation in the mineralogical structure (recrystallization of periclase) takes place slowly and is intensified only when the bricks are saturated with 30% iron oxide or more. During the course of the tests (14 melts) we did not observe the formation of a zone with an increased silicate content.

Our experiments confirm our assumptions with regard to the length of the process of zone formation in magnesitechrome brick in service. The period over which the zones develop is about 25 to 30 melts.

The rate of migration of iron oxides in the periclase contained in the brick requires further study in accordance with its initial properties.