Improved method for better temperature assessment in the contact of die bearing surface with profile surface in aluminium hot extrusion

The paper presents an improved technique of temperature measurement on the bearing surface of industrial die during hot extrusion of aluminium and an assessment of the heat transfer coefficient from the extruding profile on the bearing surface. The measurement was carried out by using a method of split die and three thermocouples (incorporation of the K type and welded at distances from 0.18 to 1.32 mm from the bearing surface) with high measuring accuracy. Extrusion exit speeds were increased to the extent that Mg2Si, with a known melting point, started to melt on the extruded profile. This state was determined by the phenomenon of oscillations of the measured temperature of the nearest two thermocouples and by the phenomenon of visually remarked deterioration of surface finish of the extruded profile. Insight into the temperature conditions on the "die bearing surface/extruded profile surface" contact, obtained in this way, enabled a more reliable calculation of heat transfer coefficients that is by one order of magnitude higher than data known until now in the literature and, in our case, amounts to 189 kW/km(2). The applied method of temperature measurements is good either from the point of economic effect of industrial technologies, i.e. for increased productivity and for looking for technological solutions, to cool industrial dies locally (close to the bearing surface of die) more intensively, or from the point of more accurate numerical modeling and optimizing the, process of hot extrusion.