Inverse problem-based analysis on non-uniform profiles of thermal resistance between strand and mould for continuous round billets casting

The thermal resistance between the billet and mould, which is determined greatly by the solid and liquid films thickness, the air-gap size and the interfacial thermal resistance between the solid slag and mould, has strong influence on the mould thermal behavior, further the billet quality. In the present paper, a two-dimensional (2D) transient finite element model is developed, and the unknown thermal resistance between the billet and mould is identified by solving appropriate inverse problem from the measured temperatures by the thermocouples buried at various locations in the mould wall. The calculations of the mould heat flux, shell thickness, the distributions of solid and liquid slag films thickness and the air-gap size are also carried on. The calculation results show that the non-uniform distributions of solid and liquid slag films and air-gap around the mould circumference can better reflect the real casting conditions of round billet, that is the characteristics of non-uniform heat transfer. The profile of thermal resistance between the billet and the mould is corresponding to that of the mould heat flux, which is parallel to that of shell thickness. In the coexistent region of solid and liquid slag the profiles of them are similar with each other to some extent. In the upper mould the distribution of solid slag film thickness is similar with that of the thermal resistance between the billet and mould, whereas in the lower mould the distribution of thermal resistance is strongly influenced by that of air-gap size after it appears.