Thermal aspects of the calibration of extruded profiles
Jose Covas, Joao Nobrega, Olga Carneiro
University of Minho
Portugal

Keywords: extrusion profiles, calibration, thermal aspects

---

Calibration of the cross-section of a profile before intensive cooling of the material is an unavoidable stage of profile extrusion. The viscoelastic behaviour of the melt upstream, together with the operating conditions and die design, make it very difficult to produce the required cross-section. As the profiles progresses along the line it is subjected to a variety of external forces. Hence, the calibration stage ensures that the incoming melt is properly shaped, and the the outgoing profile is strong enough to withstand the any erternal forces.
From a thermal point oif view, the calibrator(s) must ensure uniform of cooling of the extrudate at a fast rate, as these determine the final profile morphology, shrinkage and level of residual stresses. The parameters influencing its performance include the geometry of the system (number of calibrators, their length and relative distance separating them, the layout of the cooling channels - number, diameter, orientation relative to the extrusion direction, distance to the extrudate surface), the cooling conditions (temperature of the inlet water, flow rate, flow direction) and the extrusion conditions (flow rate, cross-temperature profile at the die exit).
In this work, a 3D code based on the finite volume method is used to model the calibrating/cooling stage of profile extrusion, with a view to designing calibration systems. For a number of different initial conditions (throughput, average temperature and thermal gradients of the extrudate at the die exit), the relative influence of the main process variables is identified.