Martin Syvertsen

Wetting behavior of aluminium and filtration with Al2O3 and SiC ceramic foam filters

The wetting behavior between liquid aluminium and substrates made from industrial Al2O3 and SiC based ceramic foam filters (CFF) was investigated. The same CFF filters were also tested in plant scale filtration experiments. The wetting experiment results show that the SiC based filter material is better wetted by liquid aluminium than the Al2O3 based filter material. This indicates that the improved wetting of aluminium on a filter material is an advantage for molten metal to infiltrate the filter during priming. Also, better wetting of Al-filter might increase the removal efficiency of inclusions during filtration due to better contact between filter and metal. Non-wetted inclusions are easier to be removed.

A Comparative Study of Porosity and Pore Morphology in a Directionally Solidified A356 Alloy

Hydrogen in aluminum alloy melts leads to porosity, generally considered to be the most serious defect affecting both static and dynamic properties of structural aluminum castings. In order to study these effects, an investigation has been undertaken to examine the A356 alloy that is gravity die cast and directionally solidified. Castings were produced with as-molten metal and degassed metal, and with metal up-gassed by various treatments. Hydrogen content during melt treatment was measured with ALSPEK H,® a device based on electrochemical principles. Porous disc filtration apparatus (PoDFA) and reduced pressure tests (RPT) were performed in parallel with casting experiments to assess melt quality. The effect of hydrogen content and melt cleanliness on the amount, size, shape, and location of porosity was characterized, and the results show that amongst all the up-gassing methods used, up-gassing with wood and Ar-water vapor mixture is the most efficient. Pore size and shape factor increased with increasing distance from the chill.

Removal of Na and Ca from Aluminum Scrap through Filtration

Removal of Na by an “active” AlF3 filter seemed to be so efficient that all the sodium was removed in the present experiments. The removal of Na is considered to be limited by the resistance in the melt boundary layer only. However this is not the case for calcium. For calcium to be transfered into the AlF3, resistance in the filter grains has to be taken into account in addition to the resistance in the melt boundary layer. This was indicated by the total mass transfer coefficient of only 4x10-5 m/s. A kinetic model was derived that can describe the removal of Ca from molten aluminum in an “active” AlF3 filter by deep bed filtration following first order kinetics.

Plant Scale Investigation of Liquid Aluminum Filtration by Al2O3 and SiC Ceramic Foam Filters

Plant scale filtration experimentsof 10〝 × 10〝 × 2〝, 30PPi Al2O3 and SiC industrial filters were carried out. Wetting experiments show that the SiC filter wets better with molten aluminium than Al2O3. The assessments by LiMCA II and laser were employed to study the behaviour of the two filters. The Al2O3 filter shows improved time dependent behaviour, increasing filtration efficiency, during one hour filtration. This is not the case for the SiC filter. It decays faster than the Al2O3 one. The SiC filter requires less pressure drop to infiltrate the metal. The result suggests that the SiC can be a new filter choice in the aluminium industry.

Solubility of Fluorine in Molten Magnesium

The solubility of fluorine in molten magnesium was measured at temperatures between 700°C and 950°C. The experimental approach involved equilibrating molten magnesium in a MgF2 crucible under argon. Samples of the equilibrated melt were taken using alumina tubes and a syringe. The fluorine solubility was determined employing the “Sintalyzer method”, an electrochemical method developed at SINTEF, Norway. The fluorine content in liquid magnesium was described by an exponential function of inverse temperature and varied between 10 and 100 ppm by weight in the measured temperature interval. The standard Gibbs free energy of the fluorine dissolution reaction: 1/2 F2 (gas) = F (in mass %), in the temperature range 700°C to 950°C, was determined to:

Discussion of Bi-Film Index and LiMCA Data in Industrial Aluminum Remelting Trials

\Delta {G^ \circ }_3/2 = ( - 473 000 \pm 3250) + (53 \pm 3)T

Oxide Skin Strength Measurements on Molten Aluminum – Manganese Alloys with and without Salt on Surface

Today, aluminium dross is normally recycled by melting in a gas fired rotary furnace. Salt is partly used for protection against oxidation of aluminium metal and partly to enhance agglomeration of molten aluminium drops by breaking the oxide layers between them. The separated aluminium metal is then either retuned to the supplier of the dross, or sold to another costumer. The oxide on the other hand, which is mixed with salt and has to be further processed before it is sold as a low grade oxide. This paper describes how aluminum metal and oxide is separated in a plasma heated rotary furnace without the use of salt. The clue is that the plasma gas is a mixture of Ar + H2 and hence giving a reducing conditions. The oxides separated from the dross have been characterized with respect to chemical purity and physical properties, and compared to required properties for use in electrolysis.