![]() If this slag is not quickly removed from the surface or treated with a flux to separate the metal from oxides and contaminants, then this metal, will quickly oxidize and this will lead to additional loss of usable metal. It can contain up to 80 or even 90 % good metal. This slag is a "liquid" mixture of oxides and metal entrained in the slag. It happens, if slag, which formed on the surface of the melt, then exposed directly to the flame of the burners. Loading of lightweight scrap directly into the melt of reverberatory furnaces of the bath type can be a source of an additional increased increase in melting losses of metal. If we allow the development of this reaction, the temperature in the oven may exceed 1650 oC, which can lead to melting of the refractory lining and complete failure of the furnace. ![]() This thermite reaction can have serious consequences. Therefore, the high temperature of the melt causes the risk of ignition of the slag and spontaneous combustion of metallic aluminum. Usually the temperature of the slag layer is about 50-85 ºС above, than the melt temperature. For this reason, in smelting furnaces, the thickness of the slag on the surface of the melt is usually not allowed to exceed 40 mm.įigure 4 - Influence of the thickness of the slag layer on the reduction of the melting rate of the reflective smelting furnace (in percent).4, which is confirmed by most aluminum smelters. The effect of increasing the slag thickness on the melting rate is shown in the figure. As a result, there is a logarithmic increase in the loss of metal during melting. In this case, the temperature in the slag layer rises and, respectively, the rate of metal oxidation increases, which enters the slag from the surface of the melt. Slag layer thicknessĮxcessive thickness of the slag layer above the melt can have a thermal insulating effect and cause increased burner operation., to maintain the desired melt temperature. This will give a sharp increase in aluminum oxidation., what, as a result, will lead to an increase in the thickness of the slag layer. Consequently, heat, shown in Figure 1, can be achieved at the surface of the melt. It is impossible to measure the temperature directly on the uppermost surface, which can be significantly hotter, than the temperature in the depth of the melt. Need to keep in mind, that thermocouples in a bath of molten aluminum actually measure the temperature in the depth of the bath. With increasing holding temperature (in percent) Temperature rise only by 25-55 ºС can have a very large impact (figure 3).įigure 3 Logarithmic increase in the rate of aluminum oxidation Second, and also an important factor, is the holding temperature of the melt after melting. The situation is getting worse, if the burners "hit" directly on the surface of the melt or on the aluminum charge. Excessive air supply leads to an increased rate of slag formation, if a fresh aluminum surface appears as a result of any movement of the melt surface. The first factor is the gas / air ratio on gas burners. These furnaces are characterized by the following technological factors, which have a great influence on the technological losses of metal in the furnace.įigure 2 - Cross section of a reflective melting furnace:ġ) transfer of heat to the surface of the melt by radiation Ģ) heat transfer deep into the melt by convection Gas / air ratio on gas burners The overwhelming proportion of aluminum is melted in gas reflecting furnaces (Figure 2). Under an electron microscope Influence of melting technology on slag formation If proper measures are not taken to prevent excessive slag formation, as well as maximum extraction of metal aluminum from it, then this can lead to significant losses of potentially usable metal.įigure 1 - Kind of aluminum slag with high aluminum content This is because, that the slag, in addition to oxides, often contains a large amount of usable metallic aluminum, which is captured by these oxides (figure 1). In solid form, the slag is all the more undesirable., as it is a valuable by-product, which greatly depends on the profitability of production operations. Dross, which forms on the surface of the aluminum melt, is an inevitable by-product.Īluminum slag is a source of problems in all industries, who are engaged in melting aluminum and aluminum alloys. ![]() Slag is a physical mixture of oxides and other solid compounds, as well as molten metal, which is inside them.Slag is formed on the surface of melts as a result of interaction with air gases, primarily, with oxygen.Dross is a surface layer on a metal melt, which has a high oxide content.
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