2016 Volume 102 Issue 4 Pages 187-195
The formation and extinction behavior of cavity bridges has been experimentally evaluated by allowing the cylindrical particles simulating inclusions to approach and separate off in mercury and in molten steel. An interaction model of spherical alumina particles close to the actual inclusion shape due to cavity bridge force has been developed on the basis of the experimental results. Using this interaction model, the processes of agglomeration and separation of alumina inclusions in molten steel have been analyzed, and the agglomeration force due to cavity bridge force has been discussed in comparison with different agglomeration forces that are derived from the van der Waals force in molten steel and the capillary force on the surface of molten steel. When two isospherical alumina inclusions are approaching each other in molten steel, a large agglomeration force of 1.54 d·σFe (d: the diameter of alumina inclusions, σFe: the surface tension of molten steel.) is generated by the cavity bridge formation from the interparticle surface distance of 0.07 d, and then the agglomeration force also gradually increases to reach the maximum value of 1.88 d·σFe in complete contact state. Conversely, when two isospherical alumina inclusions in molten steel are separated from the contact state, a large agglomeration force of 0.92 d·σFe and above is maintained until the cavity bridge extinction in the interparticle surface distance of 0.12 d, whereas the agglomeration force gradually decrease from 1.88 d·σFe. In addition, it is assumed that alumina inclusions in aluminum deoxidized molten steel principally agglomerate and coalesce on the basis of the agglomeration force derived from very strong cavity bridge force in comparison with the van der Waals force in molten steel and the capillary force on the surface of molten steel, and coarse alumina clusters are thus formed in molten steel.