Controlling shear thinning property of lime silica based mold flux system with borate additive at 1623 K

Abstract We have studied the shear thinning property of mold flux with borate additive using a rotational type rheometer at various shear rates. Mold flux at 1623 K is currently used in the steel industry as a lubricant to reduce the shear force exerted on a solidifying steel shell in an oscillating mold. In an actual casting process, the enhancement of shear thinning property might be beneficial for a casting process. Therefore, the present study is designed to control the shear thinning property of mold flux at 1623 K by changing a borate concentration. For the first step of the present study, Raman spectroscopy is used to identify structural change of mold flux with increasing a borate concentration. The second step is to conduct viscosity measurement by changing shear rates with a rotational rheometer. The degree of shear thinning has been successfully estimated by the flow behavior index of Oswald–de Waele's power law. In doing so, we successfully achieved the strong shear thinning property of mold flux and discovered the rationale behind this. In order to maximize the shear thinning property of lime silica based glass forming liquid, it is essential to understand the degree of polymerization (DP) and stiffness of entire mold flux structure.