Abstract
High shear melt conditioning technology refines the as-cast structure of light alloy melts, thereby improving the mechanical properties of the casting and reducing the occurrence of defects, without requiring chemical grain refiners. To upscale the technology and apply it to processes involving larger melt volumes, a computational fluid dynamics study is conducted with three rotor–stator mixers operating in both batch and continuous modes. Analysis of the results show that rotor–stator mixers with smaller stator holes outperform those with larger ones because of larger shear rates—increasing the deagglomeration rate—and larger volume flow rates—increasing the dispersion of the intensively sheared melt in the bulk liquid. Compared with batch mode, continuous operation results in lower mass flow rate through the mixer and reduced mixing, although the mixer design has a larger impact on both measures.
Highlights
High shear melt conditioning (HSMC) technology results in improved thermophysical properties, extrudability, and machinability and reduces the occurrence of defects in the treated light alloy melt,[1,2] without the addition of chemical grain refiners
The velocity contours are plotted on horizontal slices along the following selected planes: z 1⁄4 13 mm for mixer A and z = 8.7 mm for mixers B and C
The performances of three rotor stator mixers were assessed via numerical modeling
Summary
High shear melt conditioning (HSMC) technology results in improved thermophysical properties, extrudability, and machinability and reduces the occurrence of defects in the treated light alloy melt,[1,2] without the addition of chemical grain refiners. HSMC consists of submitting a bulk volume of melt to an intense shearing field through a rotor– stator mixer. Melt is ejected at high velocity through stator holes, with the shear rate being larger at the stator hole surface facing the leading edge of the rotor.[7] The effect of the rotor–stator mixer operation is two-fold: (1) The large shear rates result in particle deagglomeration, thereby reducing the size of oxide films and other inclusions in the melt.[8] (2) The large flow rate through the rotor–stator mixer redistributes the intensively sheared melt in the bulk of the mixing vessel.[9,10]. Since deagglomeration and mixing both depend on the flow conditions around the rotor–stator region, the velocity field, turbulent viscosity, shear rate, and flow rates through the mixer in both operating modes are compared. Each simulation was run for a minimum of 65 rotor revolutions before analyzing the results
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