Electroplastic rolling of refractory metal strips: mathematical modelling of the process

Abstract

In order to analyze the electroplastic deformation process, the authors developed a mathematical model that simulates strip rolling with high-density electric current going through the deformation zone. The model consists of two main parts: a model for determining the strip temperature beyond the deformation zone; and a model of the deformation zone. The paper describes temperature fields calculated for a tungsten strip rolled out of a 200 μm thick and 200 μm wide workpiece at the electric current power W equal to 0.2 and 0.4 kW and rolling speeds V equal to 8.5, 28 and 50 mm/s. It was established that the maximum temperature of the strip Tmax is reached inside the deformation zone, the length of which is taken equal to the length of the contact arc ld. In the section located at a distance of more than 3·l d before the rolling stand, the temperature of the strip is equal to 25 оC, which corresponds to the ambient temperature. After the rolling stand, the strip cools down due to heat dissipation. How quickly the strip will cool down is dictated by the cooling conditions, rolling speed and strip size. Obviously, a thinner strip transfers heat more intensely. A drastic temperature increase was observed in the deformation zone of the rolling stand. After exiting from the deformation zone, the strip, heated to the deformation temperature, gradually cools down as a result of heat dissipation. The intensity of the lengthwise temperature decrease rises as the rolling speed and the heat transfer coefficient go down. The results obtained with the help of the mathematical model were used to revise the technical data of the electroplastic rolling mill (the spacing between its key components, roll design, rolling speed, electric current density, etc.) and to elaborate recommended thermomechanical rolling regimes for micron thin molybdenum and tungsten strips.