1A NUMERICAL HEAT TRANSFER STUDY OF PROFILE CALIBRATION

A 3D numerical code, based on the finite volume method, developed to model the cooling stage along an extrusion line is presented and validated prior to being used for investigating the effect of various process and geometrical parameters onto the efficiency of calibration/cooling units. The code is able to tackle accurately various practical situations such as the presence of several individual cooling units and the existence of a thermal resistance between the plastic profile and the cooling medium. The code was validated through the comparison of the numerical predictions with the analytical solution of a simple problem and with results produced by a commercial software. The detailed investigation of the calibration unit has shown that most of the heat is removed at the calibrator via the cooling channels and that the contact resistance at the interface is the most important parameter affecting the performance of the unit. Additionally, it was shown that boundary conditions on the calibrator/extrudate outer surfaces have negligible impact. The effect of process and geometrical parameters on the cooling performance can be quite distinct. Often, when a higher reduction of the profile average temperature is imparted, lower temperature homogeneity is also obtained, which is undesirable; exceptions are variations in the extrusion velocity and splitting the calibrator into several units