OBRABOTKAMETALLOV Vol. 25 No. 4 2023 technology produced in this way, and complex shapes can be easily obtained [5]. This method was developed by Alcan international. According to this method, small amount of additives are required to increase the viscosity of the molten metal. Before adding the ceramic powder in the molten metal, preheating is required to increase the wettability between the ceramic particles and the molten metal. The molten metal in the furnace is then injected with inert gas, carbon dioxide, nitrogen, air or any other gas. Gas bubbles rise rapidly through the molten metal due to buoyant force of the molten metal. To stop the flow of gas bubbles inside the molten metal, some additives are added to increase the viscosity of the molten metal. These additives are aluminum oxide, magnesium oxide, silicon carbide. In addition, other parameters such as temperature need to be monitored [6]. It is necessary to continuously create small spherical gas bubbles using a rotating impeller or orifice. Yuan and Li studied the bubbles’ formation stages by using the orifice (1) nucleation stage (2) growth stages (3) detachment stages. Size of the bubbles depends on the wedge angle of orifice (wedge angle of orifice increases bubbles sizes decreases) and cell diameter also depends on the orifice diameter and chamber pressure. The gas flow rate also affects the size of the bubbles. In their opinion, the size of the bubbles increases as the gas flow rate increases [7]. Finer cell size makes the cell spherical, stable and decreases the chance of cell wall defects. Cell size of the metallic foam has not effectively controlled by the static gas injection method. Another method for controlling the pore size in metal was developed by Ningzhen Wang and is shown in fig. 2. In that method researcher used dynamic gas injection method. Dynamic gas injection is realized by adjusting the intensity of the vibrator in the range from (0 to 100 %). At 100 % intensity, cells with a diameter of 4 mm are obtained, which is smaller than with static gas injection [8]. In this method, the porosity of the metallic foam can vary from 50 to 90 % [9]. Foam, containing ceramic powder, is difficult to cut due to its hardness. Therefore, to obtain a complex-shaped product from foam metal, one should initially use a special mold. The molten metallic foam is collected from the furnace to be shaped. The production of metal foam by gas injection requires various steps. Fig. 2. Melt gas injection method [8] Producing metal foam by adding the foaming agent into molten metal According to this method, to produce metal foam, special foaming agents should be added to the molten metal. Foaming agents are titanium hydroxide (TiH2), calcium carbonate (CaCO3), zirconium hydride (ZrH2), manganese oxide (MnO2), dolomite (CaMg(CO3)), magnesium carbonate (MgCO3). Calcium carbonate and titanium hydroxide are most commonly used to produce metallic foam. The decomposition rate of titanium hydroxide is higher than that of calcium carbonate and hence it releases gas easily. To stabilize the molten metal in this case, additives are needed – Al2O3, SiC. Hence its manufacturing costs increase. To make this processes more economical M. Hiedari Galeh has used CaCO3 as foaming agent
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