Recent Innovations and Improvements in Infrared Thermometry within the Aluminum Extrusion Industry

The three main locations for non-contact, infrared thermometers (IRTs) within the aluminum extrusion process are: on the incoming heated billets, at the die exit and following a quench. Each of these locations poses its own set of problems and requirements which have, until recently, limited the deployment and usefulness of IRTs within this industry. The previous generation of instruments required frequent recalibrations against thermocouple spot readings to maintain any sort of accuracy. Recent advances in measurement techniques however have made high accuracy routine and reduced operator input to a minimum. The deployment of these new instruments has been rapid. They have the potential to allow for improved product quality, press utilization and, therefore, material throughput. At the die and quench exits, the huge range of alloys and sections that are commonly encountered required the development of complex processing algorithms to represent the emissive behavior of the target. Once correctly established however, these facilitate instruments that offer 'from the box' usability and enable automatic compensation for the vast majority of extruded sections. This allows constant die exit temperature to be maintained as well as control of the quench rate, which is critical on certain alloys. Billets, however, are very different to fresh sections in their surface characteristics, being fairly rough, oxidized and of constant (cylindrical) form. Here the requirement is for a complete longitudinal thermal profile, or 'taper' along the billet. Correct taper permits 'isothermal extrusion' - i.e. allows the die exit temperature and press speed to remain constant throughout the process. The importance of this for both uniformity of mechanical properties and improvements in press efficiency is now widely appreciated. An instrument has been developed, specifically for this measurement, using the principle of emissivity enhancement by multiple reflections. It has a fast speed of response and has been shown to capture the complete end-to-end profile with high accuracy and without stoppage of the billet, thus preventing any additional loss of the applied taper. It has allowed press engineers to repeatedly perform isothermal extrusion and has proved its worth in revealing a number of previously undiagnosed heater faults and mis-settings.