Abstract: Up to date, a reasonable and adequate process to treat magnesium scraps in die casting factory is not yet achieved, especially for middle or small scale die casters. Actually, many existing methods of handling magnesium scraps have met the level of technology for practical utilization requirement. Now, what we have to do is to propose a systematic handling process according to factory suitability and cost consideration. In this paper, the classification of magnesium scraps will be introduced first. Then the complementary storage methods and treatment methods for each type of scraps and recycle policy for die casters will be discussed. Finally, we propose a management model of magnesium scraps that is possibly suitable to some die casting factories.
Abstract: Anhydrous magnesium chloride (MgCl2), the dehydration product from bischofite
(MgCl2•6H2O) and as industrial raw material for preparation of electrolytic magnesium, is now the most advanced and perfect technological process. For long, the detailed dehydration process was not known due to its dehydration complexity and lack of appropriate experimental conditions. In this paper, quantum chemistry method based on density functional theory (DFT) was used to study the whole dehydration processes. The molecular geometries of MgCl2•6H2O, MgCl2•4H2O, MgCl2 •2H2O, MgCl2•H2O and MgCl2 were all optimized at level of B3LYP/6-31G*, the optimized geometrical parameters and correspondent energies corrected by the second order Møller-Plesset perturbation theory (MP2) were thus obtained. Results show that the energy variations corresponding to the whole dehydration steps from MgCl2•6H2O via intermediates MgCl2•4H2O, MgCl2•2H2O and MgCl2•H2O, to anhydrous product MgCl2 are 35.55, 41.30, 28.55, 31.08kcal/mol, respectively. For steps of 2H2O removal, the energy variation from MgCl2•2H2O to MgCl2 is 59.63kcal/mol, bigger than the steps from MgCl2•6H2O to MgCl2•4H2O (35.55kcal/mol) and from MgCl2•4H2O to MgCl2•2H2O (41.30kcal/mol), which means the last two water molecules are the
most difficult to be removed. All these results are significant for mechanism study of bischofite dehydration and are helpful for industrial production of anhydrous magnesium chloride.
Abstract: Magnesium chloride hexammoniate (MgCl2·6NH3) is an intermediate product for
preparation anhydrous magnesium chloride by reaction crystallization method. An experiment study of a semi-batch reaction crystallization is presented. In a single feed operation, magnesium chloride solution is fed to a stirred methanol solution mixed with ammonia to crystallize magnesium chloride hexammoniate. The median crystal size of product increases with increasing stirring rate, reaches a maximum, and then decreases again. Decreasing feed rate or decreasing stirring time increases the crystal size significantly. The reaction temperature and concentration of magnesium ion can also influence the crystal size distribution (CSD). A double feed operation can create larger crystal size than that of single feed operation. The relationship between crystal size and the content of water of the product is discussed.
Abstract: Magnesium chloride hex-ammoniate (MgCl2·6NH3) is an intermediate to produce
anhydrous magnesium chloride (MgCl2) by method of reaction crystallization. MgCl2·6NH3 is decomposed at 670K to produce anhydrous magnesium chloride. The process of thermal decomposition and its non-isothermal kinetics of MgCl2·6NH3 is studied. Results show that the thermal decomposition process is made up of three stages, the thermal decomposition functions and the thermal decomposition kinetics parameters, such as activation energy (E), pro-exponential factor (A) of MgCl2·6NH3 for each step are obtained by means of the Acher differential, the Coats-Redfern integral and multi-accelerated heating rate method. This study provides a valuable theoretical basis for MgCl2·6NH3 decomposition process on industrialization.
Abstract: Optimum performance of metal in the die casting shop in terms of metal loss, sludge
generation, and high quality and consistency in mechanical properties of the die cast components are becoming increasingly important. In this context metal quality both from alloy producers’, die casters’ and end users’ perspectives is critical. The term metal quality can be defined to include 1) chemical composition, 2) inclusions and porosity inside the metal, 3) the surface appearance, and 4) consistency. This definition may apply to ingots as well as die cast parts. When the ingots are
remelted and processed in the die casting shop, the effect of ingot surface quality and porosity on performance and properties is usually overshadowed by the quality of the processes in the die casting furnace. The paper discusses how the alloy gradually loses its pre-history. If the metal quality becomes inferior, housekeeping may become notoriously difficult, affecting important performance indicators such as up-time of operation and scrap rate. In partnership with the individual die casters, Hydro Magnesium offers assistance and audits to further improve the die caster’s performance and products.
Abstract: Sulphur hexafluoride (SF6) is widely used by the magnesium industry as a protective atmosphere. It has been demonstrated that SF6 prevents molten magnesium from further oxidation by reacting with magnesium to make the surface film on the magnesium melt denser. However, due to its high greenhouse effect (GWP=23900), the alternatives of SF6 must be sought. In this paper, 1,1-difluoroethane (commercially named HFC-152a), whose GWP value is only 140 and far lower than that of SF6, was tested to check its capacity of ignition-proof and further-oxidation-proof. Similar to SF6, the melt’s surface film formed in the protective atmosphere containing HFC-152a has a shiny metallic appearance. The surface film’s microstructure has been characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD’s results showed that the film contains only MgO and MgF2 phases while SEM showed their morphologies are uniform.
Abstract: A new technique capable of on-line generating SO2+CO2+N2 shielding gas via thermal chemical reaction between compressed air and a mixture of C and S powder was introduced in the present study. The test results in both laboratory and foundry indicate that the on-line generated gas is able to provide effective protection to Mg melting bath up to 730 oC as SF6+N2 shielding gas does, while its running cost is 30% less than of the latter.
Abstract: The operating principle of and the calculating method of the key technology parameters of precise system for mixing the protecting gas of magnesium-Alloy smelting are described. This system adopts the “static-pressure mixing” technology, which has two gas vessels to provide the gas in turn. This technology, compared to the current “dynamic throttling commingle ” technology, enjoys higher
precision of mixing and stability of gas-providing. The economic precision of the mixing is 0.1 percent, which can obviously reduce of the commingling-ratio density of the valid elemental gas’ component and the operating cost of the equipment on the basis of ensuring the safety of segregation the oxygen during the magnesium- alloy smelting.
Abstract: The environmentally friendly alternatives are being examined by an R&D group funded by German Federal Ministry of Education and Research. The research goals of this group are to analyze the potential of known environmental friendly gases to serve as protective atmosphere, and also to develop and to evaluate new methods for protecting the surface of magnesium melts. One possible alternative is covering the magnesium melt with CO2-snow, which is deposited on the molten bath and decreases the surface temperature of the melt. On the other hand gas expansion is the result of the sublimation of the CO2-snow which displaces any oxygen at the surface of the molten magnesium.
Abstract: This paper covers information on salt melts, used in crucibleless electrical furnaces as a heating element, which interact with atmospheric air to form solid and gaseous products and mostly determine the furnace design, governing furnace maintenance conditions and its service life.