Sources of aluminum scrap
Raw materials for the production of secondary aluminum – aluminum scrap – includes:
- technological waste from the production of aluminum products;
- expired service life of aluminum products;
- aluminum shavings and
- Aluminum foundry slag.
The chemical composition of aluminum scrap depends on the final chemical composition secondary aluminum alloy and, Consequently, industry sector, wherein it can be used.
Secondary aluminum alloys
Casting aluminum alloys with a high content of silicon can "absorb" is much more diverse scrap aluminum, because of their tolerance for various impurities are much wider, than wrought aluminum alloys.
Casting alloys are given less value added, than wrought alloys. Therefore, for their production does not fit all types of aluminum scrap - not only on the chemical composition, but also for reasons of economic benefits. for instance, all aluminum-silicon foundry alloys can be smelt from the extrusion scrap with addition of silicon, copper and other alloying elements. However, the lower cost of casting alloys makes it impractical.
A large share of aluminum scrap, which is remelted by manufacturers of secondary wrought aluminum alloys (remelters), is domestic production of technological waste, as casting slab for rolling-pillars or ingots for extrusion, and waste production of extruded sections.
Aluminum scrap categories: GOST 1639 and ISRI
All aluminum scrap, which is collected from different sources, sorted, treated and separated into different categories to be sold to processors in the country or for export. Supplies of scrap aluminum on the world market produce according to international specifications. These conditions are supervised by a special institute (The Institute of Scrap Recycling Industries (ISRI)). These specifications include about 40 grades of aluminum scrap. Each variety has its short name, for example, «Tata». domestic Standard 1639 as amended 2009 year partly include these categories in its classification of aluminum scrap and waste.
Important factors, on which the scrap value, include the following:
- Does the scrap contain only one aluminum alloy? - This allows the recycled aluminum manufacturer to know exactly, any chemical composition, he will receive, When the melt the scrap.
- Does the scrap contain impurities (contaminants)? - Metallic impurities will affect the chemical composition of the resulting aluminum melt and may lead to its non-compliance with the specified technical requirements. Non-metallic impurities can lead to negative environmental consequences, as well as lower product yield.
- Whether the hazardous waste items, such as sealed reservoirs, which could lead to an explosion in the oven?
- Is the scrap ready for direct loading into the furnace or does it need to be subjected to some kind of preliminary preparation?
Process aluminum waste
scrap advantage of manufacturing technology in the waste, that they can be easily divided into individual alloys. Moreover, this scrap does not contain any so-called "pridelok", i.e, for example, steel bolts, nuts and studs, which can contribute to unwanted impurities in aluminum melt. This scrap does not require additional processing prior to loading to the melting furnace, or require it in a minimal volume. In most cases, this scrap has no paint coating and therefore provides maximum metal yield.
Possible pre-treatment may include this type of aluminum scrap can include briquetting, grinding and in a more "advanced" factories - Paint removal. This type of aluminum scrap and waste includes foundry, such as a foundry mold and casting cull.
Examples of typical ISRI categories are: "Tough" and "Tata".
«Tough» ̶ Mixed technological waste aluminum alloys
It must contain pure, without cover, unpainted aluminum residues of two or more alloys, thickness of at least 0,4 mm
- without wire bundles,
- without wire screens,
- no polluted and non-metallic objects.
The content of oils and lubricants should not exceed 1 %. It should not contain aluminum waste perforation size less than 1,3 mm.
«Tata» – Wastes from the production of extruded aluminum profiles
Must contain one alloy (usually 6063). May include press residues from press (extrusion) production, but should not contain any impurities. Anodised material allowed. Colored material or alloys, other than 6063, You shall be agreed between buyer and seller. Example «Tata» category briquetted aluminum scrap is shown in Figure 1.
Figure 1 - Waste from the press production ("Tata")
Scrap aluminum products after a lifetime
This category includes aluminum scrap aluminum products, which may have a lifespan:
- a few weeks, such as, in aluminum beer cans,
- to 12 years, for example, automotive castings, or even
- more 30 years in the case of construction products, for example, aluminum windows.
This type scrap can be collected from many different sources. Before loading to the melting furnace it normally requires sorting. This scrap is inevitably contaminated with one or more kind of paint, mud, plastic, oils, greases and various metallic and non-metallic "pridelkami". For effective use of this type of aluminum scrap can require more sophisticated methods of pretreatment, including grinding and magnetic treatment, as well as various sorting methods.
For this type of aluminum scrap ISRI include categories such as, for example, taint/tabor, tense и taldon.
«Taint / tabor» - Pure mixed scrap b / a sheet of aluminum
Must keep clean, a used aluminum sheet of two or more aluminum alloys, but:
- free of oil contamination;
- without window blinds;
- without castings;
- without wire bundles;
- without wire screens;
- without cans of beer and drinks;
- without heatsink plates;
- without aircraft sheets;
- without bottle caps;
- no plastic;
- without dirt;
- no other non-metallic contaminants.
The content of oils and lubricants in general, no more than 1 %. Permission is granted to 10 % aluminum scrap category "Tale" (painted siding). The figure 2 Shown is an example of pure mixed sheet aluminum scrap (Taint / tabor).
Figure 2 – Mixed aluminum sheet (Taint / tabor)
«Tense» - Mixed aluminum castings
It must contain a clean aluminum castings, which may include automotive and aircraft castings, but peppers. Must not have iron, brass, dirt and non-metallic objects. The total content of oils and greases must not exceed 2 %. Mixed aluminum castings are shown in Figure 3.
Figure 3 - Mixed aluminum castings ("Tense")
«Taldon» – Briquetted cans of beer and beverages
Must have a density of about 225 kg / m3 for not flattened aluminum cans and 325 kg / m3 - for flattened.
Dimensions: minimum volume 0,85 m3 with the dimensions of the sides of the briquette (61-100 cm) x (76-132 cm) x (102-213 cm).
Briquetting method: from 4 to 6 steel belts (1.6 cm x 5 cm) or from 6 to 10 rows of steel wire (# 13). Allowed to use aluminum strips and wire strength and the equivalent amount of. The use of any shims or plates of any material not allowed. The material must be magnetically processed and must not contain:
- bottle caps,
- plastic cans and other plastic products,
- garbage and
- other foreign substances.
Any other aluminum items, other than cans of beer and drinks are not allowed.
An example of briquetted aluminum cans ("Taldon") is shown in the figure 4.
Figure 4 - Briquetted aluminum cans ("Taldon")
Aluminum shavings produced mainly when machining cast and rolled blanks. Normally it contains a considerable amount of oils and moisture, which must be removed before loading into the melting furnace. The advantage of aluminum scrap in the form of chips is often the, it consists of one aluminum alloy. Mixed shavings, on the other hand, is a problem, because it may comprise a number of aluminum alloys - cast and wrought - or zinc alloys.
ISRI category for mixed aluminum chips - «Telic».
Aluminum dross is formed during the melting process and is composed of aluminum metal and aluminum oxide. Slag treatment by specialized companies. Slag is considered a hazardous material and, in contact with water liberates ammonia and other gases. Industry for the production of secondary aluminum processing large amounts of slag, which are formed during the production of primary aluminum. there are plants, are engaged exclusively aluminum slag from the primary isolation.
Figure 5 – aluminum dross
Source: G. Wallace, in “Fundamentals of aluminium metallurgy. Production, processing and applications” / ed. R. Lumley, 2011.