Investigation of internal defects formation reasons in copper billet obtained at rotary continuous casting machine (CCM)

A physical model has been created that simulates the cross section of a continuous casted trapezoidal copper billet. The results of physical modeling of continuously cast copper billets solidification process are presented. The features of the trapezoidal continuously casted copper billet crystal structure formation during the casting of metal on a rotary caster are shown. During physical modeling, it was found that the solidification mechanism of the model substance in the study of the formation of the crystalline structure of the copper trapezoidal billet has significant differences from the "classical" crystallization mechanism, in which the crystals grow parallel to each other. The main feature of the copper billet crystal structure formation is that in most cases dendrites growth direction is chaotic relative to the surface of the heat flow, and the growth rates of individual crystals differ by 25–35 %. In this case, the development of nearby crystals ceases due to a collision with the secondary branches of more intensively developing dendrites. It was also established during the modeling process that during crystallization of the melt according to the described above mechanism, a collision of the most intensively developing crystals growing on neighboring faces is possible, in which the closing main axes of the dendrites separate part of the liquid phase from the total volume. This isolated volume of the liquid phase cannot be feed by the melt from the axial part of the billet. The shrinkage of such areas during solidification is the reason for the formation of pores inside the billet. The disordered arrangement of internal pores in the cross section of a trapezoidal copper billet is explained by the randomness of the dendritic crystals growth directions and of the difference in their growth rates.