Coat Thickness in Wire-Coating Process With Corrugated Die

Effects of die wall corrugation on coat thickness t in the wire-coating process are investigated numerically, using non-isothermal viscous fluids of a Newtonian type as coating material and a finite element method. Corrugation is assumed to be in the form of sine waves near die exit. It can be seen that shorter wavelength or larger wave amplitude depresses t, whereas higher Nahme-Griffith number Na increases it; however, the changes in t are only very small. t is also depressed slightly when die wall’s exit angle θ is large and negative; but in general it is insensitive to variation in θ when this is small. That t is only slightly affected by Na and θ is in stark contrast to extrudate’s swelling behaviour in simple extrusion through annular dies under comparable conditions. Furthermore, wire speed does not affect t over the ranges of Na value considered here. One interesting aspect relating to isothermal smooth-wall situation is that the ratio t/ΔR, ΔR being annular gap size, is nearly constant and equal to 0.5, independent of wire radius ratio R_wire/R_die. This constancy is in contrast to the variation in coat thickness that results from a pure drag flow in the annulus.