Efficient cooling of extruded Aluminium
Extrusion of Al alloys is accomplished by forcing a hot billet of Al through a shaped die and quenching or cooling it as it emerges to produce a long piece. The extruded Al can be used as is, cut in smaller pieces or used as feedstock for other processes. Scientists are developing a controlled quenching and heat-extraction system for high-grade heat recovery at the profile cooling stage. This will be reused in the energy-intensive heat-ageing process with EU funding of the project ECOQUENCH . The technology is expected to recover 50 % of energy wasted during spray quenching and to reduce scrap produced at this stage by 25 %. During the first project phase, researchers established the optimal cooling rates for various extruded Al profiles. They investigated a number of oils to be used in the spray quenching process. The selection of candidates was complicated by a number of factors, including the high temperatures to be withstood. This meant that substances with low flash points (temperatures at which they can be ignited in air) such as mineral oil were unsuitable. The team finally determined that synthetic esters were the best candidates and selected one with high flash point, high self-ignition temperature, inertness and safety. Scientists also conducted thermodynamic analyses of spray quenching and developed a test rig to evaluate both the nozzle design and the spray quenching thermodynamics. The entire spray system has now been designed, including air cooling, oil spraying, recirculation and removal of oil from the piece. Investigations of energy recovery during the spray quenching process have begun and will continue during the next project phase. ECOQUENCH plans to deliver an energy-efficient and cost-effective technology for cooling extruded Al that will drastically reduce emissions and material waste. The end result will be an enhancement in the competitive position of EU industry and a decrease in the impact of its activities on the global environment.
Keywords
Extrusion, aluminium alloy, spray quenching, synthetic ester, cooling, heat recovery
