ON THE DETERMINATION OF HEAT-TRANSFER COEFFICIENT BETWEEN PVC AND STEEL IN VACUUM EXTRUSION CALIBRATORS

The design of vacuum calibrators for the cooling of complex PVC profil es is central to the production of high quality extrudates. One import ant parameter governing cooling efficiency is the heat transfer coeffi cient at the interface between the stainless steel calibrator and the PVC extrudate, whose value is often taken as constant regardless of th e extrusion velocity and the applied pressure vacuum. In this paper, a method is proposed to evaluate the variation of the heat transfer coe fficient over the entire calibrator length. The idea is to use tempera ture measurements together with heat transfer simulation to derive a h eat transfer correlation that can be used in practical design cases.