The key equipment for metallurgical processing of aluminum scrap (waste) are furnaces. Once the metal has reached the liquid phase, it can be cleaned of dirt and foreign matter. In this state, it is possible to add the necessary alloying elements, mix them with the aluminum melt source and receive a predetermined aluminum alloy.
In order to obtain the specified aluminum alloy within specified tolerances, its chemical composition is necessary to melt aluminum scrap with a known content therein of various alloying elements, impurities and extraneous contaminants. Unfortunately, there is some kind of "universal furnace technology", via which to receive any aluminum alloy from aluminum scrap any.
Remelting aluminum scrap
Various types of aluminum scrap present their specific demands to melting furnaces. solid waste, for example, It requires far less protection from oxidation during melting, than fine. Scrap with a high content of organic substances needed to melt completely different, than, let us say, aluminum waste such as slag, which originally contains a large amount of oxides.
To get the most effective technology for aluminum smelting, especially in terms of economy and ecology, in recent years it has been developed, tested and implemented in the production of a variety of technologies. Therefore, the choice of equipment for the production and melting of aluminum scrap requires careful consideration. Consider:
- types of available aluminum scrap, which can be smelt on this equipment,
- types of alloys, you need to get to the exit,
- the availability of energy and other resources,
- main type of energy and type of fuel (gas or liquid fuel),
- future production infrastructure neighborhoods,
- necessary equipment performance, etc.. d.
In the first stage melting furnace must provide effective melting metal, as well as separation of unwanted components, which are attached to aluminum and were not removed during the preliminary mechanical processing of scrap. These furnaces are called smelters.
The second stage metallurgical smelting of aluminum scrap is a refining stage, cleaning and finishing aluminum melt, obtained in the first stage. At this stage, a predetermined aluminum alloy. The furnace is charged with alloying elements necessary and mix them with the aluminum melt source in a furnace. Therefore the oven for this stage production is commonly called "mixers".
Melt holding furnace
This oven should also be able to raise the temperature of the metal, reduce it to a predetermined temperature or withstand the melt at a certain temperature for refining (purification) of liquid metal. In this case the oven is called «holding furnace» – oven for aging aluminum melt.
There are other factors, which should be taken into account when choosing a furnace for the second phase. for instance, standard practice in the production of smelting aluminum scrap is loading at this stage - the stage of refining, cleaning and finishing of the melt - relatively clean its own technological waste and own defective aluminum products, as well as large pieces of scrap and ingots purchased. For, to melt a large-sized charge, the oven must have a definite melting capacity, and not just be a "thermos" to store molten aluminum.
The furnace and ladle treatment of aluminum melt
One of the indicators of quality of molten aluminum is its degree of pollution gases and metal particles. Therefore, the oven should allow melt processing of fluxes or blowing inert gases for, to reduce the content of gases and metal particles, for example, hydrogen and sodium or potassium particle, and in some cases, and magnesium.
While the aluminum industry are very effective-furnace continuous melt processing system, melt processing in the furnace can be more profitable. This happens at frequent change of melted aluminum alloys. In this case, each time you change the alloy of the equipment for secondary treatment is necessary to merge all of the melt. Moreover, such plants require continuous heating, which requires a large energy consumption. Therefore, they can hardly suitable for small plants for smelting aluminum scrap with low productivity.
Holding furnaces for aluminum
The next step is the process of production of aluminum casting. At this stage of the furnace requires the ability to perform additional functions.
slag formation in the oxidation of aluminum must be minimized during its casting, a metal flow velocity in the mold and the mold is well regulated. Generally speaking, mixing ovens (metal holding ovens) are exactly the same, as for melting aluminum casting - holding furnaces, and - with certain restrictions - and melting furnaces. From the ovens, mixers aluminum melt should arrive at a constant rate into molds and mold. Thus, in this case, the holding furnace gets a new name – holding furnace.
Aluminum melting furnaces: similar and different
Thus, furnace of the same structure and the thermal power can have different names, depending on its application. This circumstance does not depend on the furnace design, which may be rectangular or circular or rectangular reflective oven, rotary or oval furnace tiltable reflective. Industrial production of various types of furnaces are used for smelting aluminum scrap. Some of them are designed for a very specific application needs, for example, for some special type of aluminum scrap and aluminum scrap specific.
Source: Ch. Schmitz, Handbook of Aluminium Recycling, Vulkan-Verlag GmbH, 2006.