The effect of melt compressibility on a high‐speed wire‐coating process

The effects of melt compressibility on a wire‐coating process have been investigated, assuming that the compressible behavior of a polymeric melt obeys the Spencer‐Gilmore equation of state. The compressible model is distinctly different from the incompressible model in two ways: (1) it has substantially lower pressure build‐up within the die, and (2) the location of the maximum velocity is closer to the traveling wire position. As a result, the velocity profile within the die may change from a parabolic shape to a shape somewhat similar to that observed in a drag‐flow case; and the shear stress generated by the fluid on the moving wire is no longer constant. Calculations indicate that the effect of melt compressibility during wire coming may not be neglected if the wire speed Ls greater than 50 cm/s (100 ft/min). In addition, the relationships between processing parameters and product coating thickness for both compressible and incompressible fluids are quite different.