Optimisation of plastohydrodynamic system of wire drawing using polymer melts.

A feasibility study carried out on the wire drawing system consisting of a reduction die preceded by a pressure tube and polymer melt lubrication, led to the introduction of the die-less wire drawing process. The conventional reduction die is altogether replaced by a die-less unit of stepped bore configuration. The deformation is induced by means of an effective die which is formed as a result of hydrodynamic pressures generated in the unit due to the motion of the wire and viscous action of the polymer melt. The dimensions of the unit are such that the smallest bore size is greater than the incoming wire diameter, metal to metal contact, therefore is eliminated, removing some of the disadvantages encountered in a conventional wire drawing process. An extensive experimental study has been under taken which showed that the deformation in the wire was much higher at slower drawing and the obsticle percentage reduction in area reduced at higher drawing speeds. However, use of a higher viscosity polymer melt and/or a multi-unit drawing system has resulted in higher deformation of the wire at higher drawing speeds. An analysis has been developed for predicting the length of the deformation zone, shape of die, effective die and percentage reduction in area based on an empirical expression relating shear stress and shear rate of the polymer melt. The theory incorporates the pressure coefficient of viscosity derived from the available data, the limiting shear stress which manifests itself as slip in the polymer melt and the strain hardening and the strain rate sensitivity of the wire material. Results from the analysis appears to under estimate the experimental results at slower drawing speeds and over estimate the experimental results at higher drawing speeds.