The article studies the issues involved in refining aluminium alloys when introducing small gas bubbles. A good level of dispersion throughout the entire volume of the degassing unit is achieved by using appropriate rotor geometry and selecting optimal process parameters. This study uses physical modelling employing a water model of a foundry degassing unit. Three pump-type rotors of different designs were tested. Variants A and C with a circular cross-section and cylindrical shape differ in the design and arrangement of the gas flow control blades, while variant B with the shape of a truncated cone is a kind of monolith with control blades placed in the lower part of the rotor. These rotors with were studied, with gas flows ranging from 13 to 21 l/min and rotor speeds ranging from 275 to 425 rpm. Tests included visualisation of the gas injection process and measurement of oxygen removal from water as an analogy of hydrogen removal from liquid metal. Then a mathematical model for the quantitative interpretation of research results was developed, in which the dimensionless parameter of degassing efficiency a was determined, which allows for a simple comparison of its value for all rotors, both new and used. The highest values of parameter a are observed for rotor C, only slightly worse values occur for rotor A, and the most significant differences are visible for rotor B. The research results were validated under industrial conditions - the Dichte Index was calculated for all rotors for selected process parameters and illustrated with porosity samples.

Department of Material and Engineering Metallurgy Faculty of Mechanical Engineering University of West Bohemia Univerzitní 22 Plzeň 301 00 Czech Republic

Die casting Division MOTOR JIKOV Slévárna Kněžskodvorská 2277 26 České Budějovice 370 04 Czech Republic

Environmental Research Department Institute of Technology and Business in České Budějovice Okružní 517 10 České Budějovice 370 04 Czech Republic

Faculty of Materials Engineering Silesian University of Technology Krasinskiego 8 Katowice 40 019 Poland

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