Krätzebildung in Aluminiumschmelzen durch Rückstände der thermischen Vorbehandlung von Getränkedosenschrotten
von Jan SteglichPhD thesis about the Dross Formation in Aluminium Melts by Residues of Used Beverage Can Scrap with Thermal Pretreatment in German (116 pages) and extended abstract in Englisch (17 pages).
Dross formation of used beverage can scrap (UBCs) bales is investigated in laboratory scale experiments to understand the reactions with aluminium melts. Experiment conditions are chosen according to multi-chamber furnaces, which combine thermal pre-treatment and submerged melting of the scrap. Each process step is investigated separately, to describe dross formation excluding oxygen containing furnace atmosphere.
The results of thermal pre-treatment experiments have shown that the availability of oxygen (0,9 < λ < 1) has to be continuously adapted to the scrap oxygen demand. An effective material temperature between 550 °C and 570 °C is necessary for a treatment time of at least 30 min. It is clearly shown that adhering carbon containing pyrolysis char, as well as oxidised can sheet surfaces decrease the coalescence of molten scrap, resulting in dross with a high metal fraction.
Further melting experiments with UBC bales of different scrap densities show that lowering the bale density decreases dross formation, even with untreated scrap. This result highlights the necessity of using shredded UBCs, preferably without closed porosity in salt flux free melting processes. A comparison of melting experiments und inert gas and air prove that the organic contamination of has to be understood as energy content of the scrap. By removing this content, exothermic combustion reactions of organics in the whole process are avoided and metal oxidation supressed. Hence, the causality between metal loss and increasing organic contamination is established.
