Furnace for melting aluminum
The figure 1 general classification shown furnaces for melting aluminum [1]. Schematically shown, both were born, evolved and how the different types of ovens are interconnected - hearth (reflective), Crucible and rotor.
Figure 1 - Classification of designs of furnaces for melting aluminum [1]
Hearth furnaces are classical and metallurgical furnaces oldest. They were used by our ancestors, which melted his bronze, and later - iron. many different designs have been developed over the past century, since even the Millennium, which have been used for a variety of special purposes. Thus the more specific structure of the furnace is, the more narrow area it is applied.
Reverberatory hearth furnace
Modern hearth furnace for melting aluminum - is reflection oven. They are so called because, that in these furnaces the metal is melted mainly under the influence of radiant energy, which comes from the hot furnace roof.
Development of design reflecting smelter has been pushing the need for industry to recycle scrap metal various types, for example, with a high specific surface, like chips. Such materials cannot be efficiently remelted in conventional reverberatory (hearth) furnaces.. In order to somehow overcome this problem with a reverberatory furnace smelters cover the surface of the molten protective flux. However, the melt is sharply reduced heating efficiency of the radiation furnace roof, necessitating its intensive mixing. Since the aluminum melt to mix by hand is very tiresome, then came the idea to move the furnace itself, and not melt. So, for example, rotary furnaces for melting aluminum scrap were born (Figure 1.1).
Figure 1.1 – Rotary furnace for remelting contaminated aluminum scrap [2]
Stationary ovens
The stationary reflective hearth furnace (1.00) is the basic design for all reflective aluminum melting furnaces. The use of reverberatory ovens as holding ovens led to the birth of tilt ovens (1.21). The slope of the furnace at a controlled rate required to ensure constant feed velocity of the metal during its casting into molds or molds.
Figure 2 - Stationary reverberatory furnace (1.00) [1]
Figure 3 - Tilting Reflective Furnace (1.21) [1]
Round and oval ovens
The rectangular shape of the oven is not optimal from the standpoint of reducing the heat losses through the walls. In particular, if the furnace only task to maintain a predetermined molten aluminum temperature, then the round furnace (1.22) will better and more efficiently cope with this task. Such a - circular - design combines low heat loss through the furnace walls with good conditions for refining molten metal. Due to the circular shape of the furnace door sizes for removal of the slag obtained in very small, and this makes it difficult to service the furnace. To solve this problem, the cross section of the furnace is made "flattened" and the furnace becomes oval (1.23). Both types of furnaces - round and oval - always make tilting.
Figure 4 - Round Reflective Furnace (1.22) [1]
Figure 5 - Oval reflective oven (1.23) [1]
Furnace top loading
Standard reflective oven is loaded through a door in one of the walls. However, in the production of aluminum rolling mills often domestic waste - technological waste - fed to a melting furnace in the form of "ragged" packs of metal profiles and various trimmings. Download these packs through the doors of the oven is very inconvenient. Therefore, in this case, furnaces with a top loading are useful (1.11). Typically, such furnaces have perimeter one or more windows for removing slag. On the other hand, stricter environmental regulations and rising energy prices limits the use of such furnaces with a charge load from the top on some special steel plants.
Figure 6 - Reflective oven with top loading [1]
Shaft furnaces
The high cost of energy is the main reason for the design of the shaft melting furnace (1.17). These furnaces use a relatively large amount of heat of exhaust gas, which leave the furnace through the flue. Material for melting - batch - before loading directly into the furnace enters the so-called mine, through which a stream of hot furnace off-gas. Melting capacity and speed of such furnaces is relatively small. Therefore, they are used mainly in the production of aluminum casting plants.
Figure 7.1 - Shaft reflective furnace (1.17) [1]
Figure 7.2 – Scheme of a shaft furnace for remelting aluminum scrap [2]
Oven with a dry floor
A similar approach is used in the so-called dry hearth furnaces (1.15). These furnaces are used, when it is necessary to separate the aluminum from other metals with higher melting, than aluminum, such as brass, copper or iron. furnace combustion products is first melted aluminum in the charge, which lies on an inclined "dry" hearth. The molten aluminum flows down the slope in the oven compartment, which is called the forehearth. Then the furnace operators removed from the dry hearth peeled more refractory metals aluminum.
Figure 8 - Reflective dry hearth furnace (1.15) [1]
Figure 8.1 – Slant-hearth furnace for remelting aluminum scrap [2]
The design of the furnace 1.16 It is a combination of the shaft furnace and the furnace hearth dry. It also uses waste heat to heat the charge. Such furnaces are also used in essentially only at factories producing aluminum castings.
Figure 9 - Reflective dry hearth furnace (1.16) [1]
Furnaces with pit
Standard hearth furnace is very well suited for the melting of large ingots and billets, briquetted scrap, linked aluminum profiles and similar batch. However, in such batch melting furnaces with a large specific surface inevitably leads to large losses of metal because of its high oxidation. If this "trifle" – These "seeds" – download directly into the molten metal, the contact of the metal with the exhaust gases and the ambient air is reduced to a minimum. Therefore, hearth furnaces are often equipped with an external side loading well (1.13). However, even if such a boot well has a good cover, energy losses therethrough are too large and therefore the melting speed is quite low.
Figure 10 - Oven with an external loading well (1.13) [1]
Figure 10.1 – Reflective furnace with open loading well [2]
Double chamber ovens
To escape from the drawbacks of the outer boot well designed furnace construction with an inner well of. For this, the furnace was simply divided by a partition into two chambers: one chamber - loading - for loading the charge, the other chamber - heating - for its melting. These two chambers are connected through a common bath of liquid aluminum. Aluminum while freely flows from one cell to another. Such furnaces are called two-chamber (1.14).
The charge loaded through a side window in the boot well and melted by contact with the liquid metal. Molten aluminum is poured from the furnace through the hole in the bottom of the heating chamber.
Figure 11 - Reflective two-chamber oven (1.14) [1]
Source:
1. Ch. Schmitz, Handbook of Aluminium Recycling, Vulkan-Verlag GmbH, 2014.
2. TALAT 1102
Additional Information:
Reflective and shaft furnaces // ASM Handbook- Volume 15: Casting
