Secondary aluminum

aluminum recycling

Secondary alumina receive processing of aluminum scrap. More precisely, this process reflects a foreign word “retsikling” – really completes one cycle of life of aluminum and another begins. Aluminum scrap can not be obtained primary aluminum – it is obtained only from the primary producers of aluminum by electrolysis directly from bauxite. However, secondary aluminum producers may well be derived from scrap valuable and workable alloys, that meet the requirements of standards. At various stages of the secondary production of aluminum aluminum is separated from most related materials, and then remelted and subjected to further purification and processing.

Aluminum scrap

Aluminum melting

Since aluminum has a very high affinity with oxygen, it reacts spontaneously with ambient air to form alumina. In the solid state of aluminum is not a problem, since this oxide forms very dense film on the aluminum surface, which stops further oxidation. This film acts as a corrosion protection. In the liquid state, an oxide film is also formed, but it is constantly under the influence of the perturbation of the thermal power, that leads to a constant oxidation of all new aluminum. This oxidation is particularly intense, when the molten metal has a large specific surface area. Clear, the reaction oxidation of aluminum during melting should be limited, since mass transition aluminum oxide thereof leads to loss of aluminum during processing.

secondary aluminum melting furnace

Melting processes developed, which suppress the oxidation of aluminum during its melting. In the production of secondary aluminum is widely used kiln, in which scrap immediately immersed in a bath of liquid aluminum. there furnace, in which melting occurs at complete isolation of the melt from the surrounding air. Heavily contaminated aluminum scrap is melted under protective flux layer in special rotary kilns. Flux applied not only protects the aluminum melt from oxidation, but also helps to separate the oxide film from the liquid aluminum and purify it from the melt. In addition to use of flux in the aluminum melt, Additives used for melt purification or added small quantities of alloying elements.



Rotary furnace for melting down contaminated aluminum scrap

The production of secondary aluminum scrap

There are other inevitable losses of secondary aluminum throughout the production process. Some of these losses arise in the processing of liquid aluminum, others - resulting from marriage. Part of the metal is lost during the melt in the casting furnace cleaning, as well as aggregates of degassing or filtration of liquid aluminum. Certain metal part is lost when starting or stopping casting equipment. All production of secondary aluminum waste may be subjected to re-melting.

Production of secondary aluminum

Production of secondary aluminum alloys usually start with scrap, the chemical composition of which is close to the, that is specified in the order of the consumer. This can be easily, if it rejects a uniform scrap aluminum castings or scrap aluminum beer cans. And it is much more difficult, if it accidentally collected aluminum scrap.

In most cases, scrap, charged into the melter, It does not fully meet the requirements of the final chemical composition of a given aluminum alloy. It is therefore necessary to introduce into the melt more dopants. They may be from the existing scrap, pure elements or special alloys - ligatures. Typically the doping is performed in the part of the melting furnace, final doping - a casting furnace. Therefore, these furnaces must be adapted for such operations.

The aluminum melting furnaces using special additives for protecting molten metal from oxidation, removing impurities or grinding grains in the finished bars. Moreover, in itself produce the melt processing of such gases in the melting furnace or molten time of transmission to the casting equipment, how argon, chlorine or nitrogen, as well as mixtures of these gases.

Application of secondary aluminum

In the good old days of processing aluminum it was much easier. Scrap collecting good - and then there was little scrap - and just melted. Obtained in this secondary alloys are more or less arranged customers. They diluted casting alloys for casting castings at foundries. Problems with energy savings was not yet. With the growth of aluminum consumption and the use of its processing has become more complex. Now, customers want to get ready secondary aluminum alloys, each having a predetermined chemical composition, because many of these equipment allows only ready to melt the alloy and pouring it, and not to handle or to dope it.

Secondary aluminum for steel deoxidation

The preferred use in the production of secondary aluminum ingots and granules GOST 295-98 - there is a lot of room for impurities, which are contained in the aluminum scrap. These ingots and pellets are used for deoxidation of steel and other needs of the steel industry. GOST 295-98 directly indicates the application is recycled aluminum. This standard only three alloy - AV97, AV91 and AB87. The numbers indicate the minimum content of the alloy the total amount of aluminum and magnesium.

The purest alloy - alloy AV97. It allows the magnesium content of not more 0,1 %, obtained, that aluminum in it - at least 96,9 %. However, this alloy allow increased iron content - right up to the theoretically 2 % and therefore does not pull, for example, on wrought alloys AD1 and AD0 GOST 4784-97.

The most "dirty" alloy – alloy AV87. It allows the following impurity content: copper - up to 3,8 %, zinc - up 3,3 %, silicon - up 5,0 %, lead - up 0,3 %, tin - to 0,2 %. Iron, manganese and nickel may be included in the alloy composition in any amount, provided the total content of impurities not more than 13,0 %.

GOST 1583-93 – secondary aluminum casting alloys

Cast alloys allow increased compared to deformable alloys contents of impurities, for example, gland. In AK12 alloy during injection molding is the maximum iron content 1,5 %, in AK5M2 alloy - up 3,0 %. Therefore, the secondary aluminum is widely used in the preparation of foundry alloys.

The secondary deformable aluminum alloys according to GOST 4784-97

In these alloys, the content of impurities, including iron, much, below, than, let us say, in casting alloys. Therefore their preparation from secondary aluminum - a difficult task. Usually, diluted secondary aluminum or pure primary aluminum production waste to limit the content of impurities, permitted by the requirements of the standard or order.