The Science of Melt Refining: An LMD Symposium in Honor of Christian Simensen and Thorvald Abel Engh: TAE/CJS II Degassing and Oxidation
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: John Grandfield, Grandfield Technology Pty Ltd; Anne Kvithyld, SINTEF
Tuesday 2:00 PM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Geoffrey Sigworth, retired
2:00 PM Invited
Overview of Ultrasonic Degassing Development: Dmitry Eskin1; 1Brunel University
Ultrasonic degassing attracts industrial attention as an alternative to Ar-rotary and Ar-lancing degassing, offering environmentally friendly, economical and efficient technology. This paper gives a brief historical overview of ultrasonic degassing development in the 1960s¬-2010s, discussed basic principles of cavitation-induced degassing and demonstrates various technological implementations of ultrasonic degassing technology in foundry and cast house. Batch versus continuous, gas- or vacuum-assisted versus purely ultrasonic variant of the technology are considered. Main advantages of ultrasonic degassing include rapid degassing without the use of a carrier gas, significantly reduced dross formation, absence of rotating brittle parts. There are also some technological issues associated with the ultrasonic degassing such as material selection of a sonotrode, requirement to process larger melt volumes with less ultrasonic sources, rapid re-gassing of hydrogen-depleted melt. The paper is illustrated mainly with own results.
Modelling of Hydrogen Removal in Gas Fluxing of Molten Aluminium: Dag Mortensen1; Jinsong Hua1; Arild Håkonsen2; Terje Haugen2; John Olav Fagerlie2; 1Institute for Energy Technology; 2Hycast AS
Rotary degassing is one of the most commonly used methods for removing dissolved hydrogen and solid particles from molten aluminium. In order to improve the removal efficiency of both hydrogen and inclusions together with possibly lower investment and operating cost for the degassing equipment, modelling is a method that can be applied to study the process in detail. The removal efficiency depends on bubble size distribution, level of turbulence, residence time of bubbles in the melt etc. A modelling approach is presented including multiphase flow and mass transfer of impurities between the phases dependent on the solubility of the impurities in the different phases. A finite element model is used to solve the conservation equations and the impurity transport. A detailed 3D model for the in-line Hycast I-60 SIR melt refiner unit is used and results from the modelling are compared with experimental results.
The Use of Nitrogen to Degas Molten Aluminium - Comparison of Metallurgical Results with Argon and Nitrogen Used in an ACD™: Florent Gougerot1; Bruno Maltais1; Etienne Tremblay1; 1STAS Inc.
The use of argon to degas liquid aluminium is a widespread practice in aluminium casthouses, and the removal of the hydrogen contained in the metal by using this noble gas is a proven method with no downside effect on the metallurgical quality of the resulting metal. However, because of the sometimes high cost of argon, some producers are looking for a cheaper gas. Nitrogen often comes as an alternative, but there are many who are questioning the degassing efficiency of this gas or the risk of metal contamination by nitrides. STAS Inc. has carried out a series of comparative tests, successively using argon and nitrogen in an ACD for degassing liquid aluminium. This paper presents the results obtained during this test campaign carried out in an industrial environment.
3:25 PM Break
Oxide Skin Strength on Molten AA5XXX Aluminum Alloy – Effect of Beryllium and Alternatives: Martin Syvertsen1; 1SINTEF Materials and Chemistry
Aluminium alloys AA5XXX containing 4 - 5% magnesium is frequently used for marine applications due to its corrosion resistance in seawater. However, with the this amount of magnesium, the molten metal surface is much more likely to oxidize so the cast ingots may get a rough and uneven surface with a thick segregation layer. By adding a few parts per million of beryllium the surface properties are changed and better surface quality is obtained on the ingots. Previous oxide skin strength measurements have shown large impact of trace elements. In this paper, measurements of oxide skin strength with various Be/Mg-ratios are presented.
Understanding of Interactions between Pyrolysis Gases and Liquid Aluminum and Their Impact on Dross Formation: Regina Dittrich1; Bernd Friedrich1; Georg Rombach2; Jan Steglich3; Anne Pichat4; 1IME Process Metallurgy and Metal Recycling, RWTH Aachen University; 2Hydro Aluminium Rolled Products GmbH; 3TRIMET Aluminium SE; 4Constellium Technology Center
Organic contaminated aluminum scraps have to be recycled in an economical, effective and ecological way. It is state of the art to remove organic coating by thermal pre-treatment under reduced oxygen atmosphere, which can be achieved in multi chamber furnaces. If the organic coating is not removed completely during pre-treatment, gasification can continue while the scrap is submerged into the melt. Subsequently, undesirable gas-melt reactions cause an increase of dross formation and a decrease of metal recovery. This work aims to improve the understanding of interactions between pyrolysis gases and liquid aluminum to reduce oxidation losses. Experiments were performed in a lab-scale furnace with injection of pyrolysis gases into molten aluminum. Thermochemical calculations, off-gas analytics and dross structure analysis were performed to support the evaluation of the experimental findings. The paper presents qualitative and quantitative results on the impact of reactive gases on oxidation of aluminum melts.
Effects of 2 ppm Beryllium on the Oxidation of a 5XXX Aluminum Alloy at Temperatures between 500 °C and 750 °C: Nicholas Smith1; Gabriella Tranell1; Anne Kvithyld2; Brian Gleeson3; 1NTNU; 2SINTEF Materials and Chemistry; 3University of Pittsburgh
The oxidation of molten aluminum has been thoroughly studied, and it is established empirically that beryllium has an inhibiting effect on the oxidation behavior. The aim of this work was to increase the fundamental understanding of this inhibiting effect. Two 5XXX aluminum alloys (4.7% Mg), one with 2ppm of beryllium and one without beryllium, were oxidized in a tube furnace under a dry air atmosphere.Samples were oxidized at temperatures from 500 °C to 750 °C for 10, 30 and 120 minutes. The composition and morphology of the oxide layers were examined with FIB and EDS, revealing the differences between the samples. The results showed up to a tenfold reduction in mass gain in samples containing beryllium.Significant differences in the oxide layer morphology were found for the two alloys at all times, including from 10 minutes. Thus, beryllium plays a significant role from the onset of high temperature oxidation.
4:55 PM Concluding Comments