Influence of process parameters in drawing of superconducting wire

Superconducting wire is often produced by the powder-in-tube method involving a number of different mechanical processes, among these is multi-step drawing operations of single filament wire. A silver tube is filled with ceramic powder (BiSrCaCuO). This composite is drawn in up to 100 steps, from an initial diameter of 20 mm to the final one of 1 mm. The present paper shows how two of the main parameters, the reduction and the semi-die angle, influences the drawing stress and the powder compaction of the single filament wire during drawing. The optimum die angle and the largest acceptable reduction per drawing step are determined. In powder compaction tests a linear relationship between microhardness and powder density is determined. This relationship is applied for determination of the density distribution in the cross section of drawn single filament wire. It is found that the drawing process causes an increase of the powder compaction near the interface between the silver and powder, whereas the density increase near the centre axis of the tube is smaller. The average density determined in this way corresponds well with the one determined by geometrical measurements.