An analysis of splitting failures during the drawing of tungsten wire

A model is proposed to describe crack formation (referred to as wire splitting) that can occur during wire drawing of commercial tungsten lamp wire. In the proposed model, wire splitting is said to occur in response to residual tensile hoop stresses that are generated during wire drawing. The resistance of tungsten wire to crack formation is said to be controlled by the degree of polygonization that has taken place during wire drawing. It was found that wire splitting did not occur when high wire drawing temperatures were maintained throughout the seven wire drawing passes that were studied. Previous work in which dynamic recovery mechanisms were quantified for various wire sizes and drawing temperatures allowed us to show that the drawing temperature, for a given wire size, above which wire splits were not detected coincided well with the onset temperature of dynamic polygonization.