Viscosity Measurements of Molten Metal Using an Improved Oscillating Crucible Method

We developed a simple viscosity measurement method to directly evaluate the period and logarithmic decrement of oscillation. The viscosity of a molten metal is an important thermophysical property for production at high temperatures. However, the viscosities of molten metals are relatively low and difficult to measure because of challenges involved in their handling. Among several methods available for measuring viscosity, the oscillating crucible method is generally used with molten metals. The conventional method involves an approximation using a multistep iteration to determine the viscosity. The first step assumes that the oscillation period does not change and that only the amplitude decays. This method also assumes that the center of oscillation is close to the center of the array of photodiodes. Thus, it is necessary to consider whether the conditions are within a valid approximation range. In addition, it is necessary to determine the on/off thresholds to obtain binary data from the photodiode outputs. In this study, we developed a simple viscosity measurement method based on the principle of least squares to derive the period and logarithmic decrement of oscillation. To confirm the reproducibility of the proposed method, the viscosity of molten nickel was measured and found to be in good agreement with those reported in the literature. The measurement error was less than +/- 3 %. Further, the experimental data showed good reproducibility, and the measurements were obtained with high accuracies using the proposed method.