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  • The nondestructive determination of the aluminum content in pressed skulls of aluminum dross
    Kevorkijan, Varužan ; Škapin, Srečo D. ; Kovačec, Uroš
    During production of primary and secondary aluminum, various amounts (in some cases up to 200 kg) of aluminum dross, a mixture consisting of molten aluminum metal and different oxide compounds (the ... nonmetallic phase), are skimmed per tonne of molten metal. To preserve the maximum aluminum content in hot dross for further extraction, it is necessary to cool the dross immediately after skimming. One way to do this is to press the skimmed hot dross in a press. In this process, the skimmed dross is transformed into so-called pressed skulls, with characteristic geometry convenient for storage, transport, or further in-house processing. Because of its high aluminum content-usually between 30% and 70%-pressed skulls represent a valuable source of aluminum and hence are in great demand in the aluminum recycling industry. Because pressed skulls are generally valued on a free-metal recovery basis, which is influenced by the yield of recovery, or in other words, by the quality of the recycling process, it was recognized as important and useful to develop a method of fast and cost-effective nondestructive measurement of the free aluminum content in pressed skulls, independent of the technology of pressed skulls recycling. In the model developed in this work, the aluminum content in pressed skulls was expressed as a function of the pressed skulls density, the density of the nonmetallic phase, and the volume fraction of closed pores. In addition, the model demonstrated that under precisely defined conditions (i.e., skulls from the dross of the same aluminum alloy and skimmed, transported, cooled, and pressed in the same way and under the same processing conditions), when other parameters except the pressed skulls density remain constant, the aluminum content in pressed skulls can be expressed as a linear function of the pressed skulls density. Following the theoretical considerations presented in this work, a practical industrial methodology was developed for nondestructive prediction of the amount of free aluminum in pressed skulls wAl, based on nondestructive measurement of the density of the pressed skulls. The pressed skulls density is measured by a fully automatic gas displacement pyknometer with a working volume large enough to enable the insertion of the whole pressed skull sample. An additional integral part of this methodology is the set of experimentally determined linear graphs wAl-?, plotted in advance for all classes of pressed skulls existing in the plant, from the experimentally collected data on pressed skulls density and aluminum recovery by melting. After selecting the proper graph wAl-?, which is usually performed on an aluminum alloy basis, the pyknometric measured density of the pressed skulls can be routinely related to the aluminum content sought, within a relative error of 5%.
    Vir: JOM : The journal of minerals, metals and materials society. - ISSN 1047-4838 (Vol. 65, iss. 2, Feb. 2013, str. 284-293)
    Vrsta gradiva - članek, sestavni del
    Leto - 2013
    Jezik - angleški
    COBISS.SI-ID - 16580886
    DOI

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