Department of Casting and Strengthening Techniques, Institute of Novel Materials and Technology, Ural Federal University named after the First President of Russia B. N. Yeltsin, Yekaterinburg, Russia:

A. B. Finkelstein, Professor, Doctor of Technical Sciences, e-mail: avinkel@mail.ru

S. N. Zlygostev, Associate Professor, Candidate of Technical Sciences, e-mail: zgres@bk.ru

The process of making replicated aluminium foarm includes wetting of watersoluble NaCl space holder with molten aluminium alloy. Items made of porous cast aluminium have a porosity range of 40 to 70% and a high cost. As structural material, they can hardly compete with aluminium foams considering the low cost and the porosity of 80 to 95% of the latter. At the same time, porous cast aluminium has proven to be an effective functional material for moving fluids and gases. Thus, items made of porous cast aluminium are used as filters. The service life of a filter element is an important operational parameter determined by its porosity, which can be raised through the use of multi-size space holder. For the purpose of predictability of filter characte ristics, the number of sizes was limited to two, which helps raise the porosity by 10–15%. Space holders of the following small sizes were used: 200–400, 400–630 and 1000–1600 μm – in the proportions of 30, 50 and 70% to the volume of a 2500–4000 μm space holder. Two fractions of the space holder get mixed together in a certain proportion, then the mix is heated up in a box-type resistance furnace, transferred into a metal mould, and a molten AK7 alloy is poured over it. Application of vacuum suction provides the infiltration process. After solidification, the casting was subjected to machining. Thus, a cylinder-shaped specimen was cut out of the bottom section of the composite casting and the space holder was dissolved in water. In the course of a dynamic experiment, the permeability coefficient was determined of the porous cast aluminium produced with a double-granular space holder. The authors demonstrate an additive dependence of the permeability coefficient on the percent of single fractions and their permeability coefficients. The permeability coefficients of single fractions were calculated using a single resistance concentration model. The authors overviewed the existing permeability models for double-granular space holders and demonstrated that Kazemi model has the most accurate correspondence to the experimental data obtained. A discrepancy between the model and the experimental data only occurs when the difference between the two fractions is too high (in particular, when the share of the finer aggregate is low), which can be attributed to the opening effect. Using the obtained results, one can design high-porosity filter elements.

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