EXTRUSION, ROLLED PRODUCT,
CASTING, CONDUCTOR
Symbol: Al
Atomic Number:
13
Atomic
Weight: 27
Density: 2,7
gr/cm3
Melting Temp.: 660 deg.
Celcius
Boiling Temp.: 2300 deg.
Celcius
Thermal Comductivity(K): 2,37
W/cm/K (25 deg. Celcius)
Electrical Conductivity: 64,94%IACS
(Pure Al, at 25 deg Celcius)
CONTENTS
Aluminium-The Newest Metal| Properties Of Aluminum| Production Of Aluminum|Aluminium Products| Extruded Products|(Shapes, Bars, Rods, Tubes)
Rolled Products| (Sheet, Foil)) Castings|Conductors|Industries Using Aluminum| Buildings|
Packaging| Vehicles|Electrical Conductors| Engineering With Aluminium|
Aluminum And Energy Saving|Aluminum
Recycling| Aluminum And Enviroment| Sources Of
Aluminum|
Aluminum And Future| Aluminium And Quality| Statistics|
Timur
Ulucak
Metallurgical Engineer (M.Sc.)
E-Mail
Although aluminium is, after oxygen and silicon, the third most abundant element in the Earth's crust, it is by far the youngest of the major industrial metals, first produced on a commercially significant scale only just over a hundred years ago. Like lead, tin, iron aluminium exists naturally only in the form of compounds. Sir Humphrey Davy was the first, in 1807, to separate it from its oxide, alumina, though only in the form of an aluminium- iron alloy, and it was he who gave the metal its name.
A Frenchman, Henri St. Claire Deville, developing earlier work by the German scientist Friedrich Wohler, used a complex thermo-chemical method to produce small quantities of metallic aluminium in 1855. The strange new metal enjoyed a modest vogue in jewellery and cutlery, but, although the price dropped considerably over the next thirty years, it remained far too expensive for commercial use.
The breakthrough came in 1886 when, working quite independently, Paul-Toussant Heroult in France and Charles Martin Hall in the USA published patents for the molten electrolytic process of producing metallic aluminium from alumina. Shortly afterwards, Dr Carl Josef Bayer in Austria patented his technique for converting bauxite ore to alumina.
The basis was laid for the methods used in aluminium production all over the
world today, and still known as the Bayer Hall-Heroult process.
(Another useful website : http://www.aluminum-production.com
)
The Unique Properties Of Aluminum
Only a remarkable combination of useful properties could bring a new material so quickly from nowhere to a top position with a wide range of applications.
The advantages of aluminium are so wide-ranging that they deserve to be specially listed:
l. Lightness: On a volume basis, aluminium is only about one-third the
weight of steel. Significant weight savings can be made in almost every type of
mechanical application.
2. Durability: Because aluminium quickly forms
an impervious oxide skin on exposed surfaces, it is highly resistant to
atmospheric corrosion, even in marine conditions. So it does not require
painting for protection.
3. Conductivity: The specific electrical
conductivity of aluminium makes it indispensable for electronics and electrics.
Aluminium cables carry twice as much current as copper of the same weight. High
thermal conductivity makes it very suitable for heating and cooling
applications.
4. Workability: Aluminium can be formed by all the
common metal-working techniques, more easily than most. It is easy to cast, or
die-cast to precise and complex shapes. It can be forged, rolled to a superfine
foil, and extruded into intricate sections, or pressed. Superplastic alloys can
be worked almost like vacuum-formed plastics. Aluminium is also one of the
easiest and fastest materials to machine.
5. Versatility: Aluminium
alloys can be stiff or supple, especially strong or particularly
corrosion-resistant. It is easy to tailor the metal, by alloying and heat
treatment, to meet a wide range of needs.
6. Attractiveness: Aluminium
is a "clean" material. It looks good without further finishing, but takes kindly
to a wide range of applied coatings, from paints to coloured anodising.
7.
Recyclability: Aluminium is easily reprocessed using 5% of the energy needed
for primary smelting: almost one third of all the aluminium used today is
produced from scrap, either from production processes or from recycled
products.
Bauxite, found in parts of the world where high temperatures are combined with heavy rainfa.ll, is a mixture, produced by weathering, of chalk and rock containing aluminium hydroxide. It has the highest concentration of aluminium of the easily accessible compounds found in the Earth's crust, producing about one tonne of metal from every four tonnes of ore.
The complex Bayer process uses high temperature and pressure to convert the crushed bauxite to pure aluminium hydroxide, which is then roasted to drive off the water and convert it to aluminium oxide, or calcined alumina, a white powder.
The next step is the electrolytic smelting process, where the alumina is mixed with a molten cryolite electrolyte in a pot lined with pitch and coke which acts as a cathode. A carbon anode is lowered to the surface of the mixture from above, and a heavy direct electrical current at 4-5 V is passed between anode and cathode. The Aluminium Smelting Process (Hall Heroult Process)
The alumina breaks down by electrolysis, and molten aluminium falls to the bottom of the pot, where it is regularly tapped offto be cast into ingots or slabs weighing up to 20,000 kg.
Generally speaking, 2 tons of alumina is obtained from 4 tones of bauxite and one ton of aluminum is obtained from 2 tones of alumina.
The elecrical energy consumption per ton of aluminum produced has decreased from 42,000 kwh to an avarage value of 16,500 kwh today. The state-of-the-art plants consume 13,000 kwh per ton of aluminum smelted. Aluminum obtained from the electrolysis cell is named as "primary aluminum".
Aluminum products and semi-products are produced by shaping processes such as Extrusion, Rolling, Casting and Drawing.
Extruded Products of Aluminium
Extrusion is the process of shaping a metal, such as aluminum, by forcing it to flow through a shaped opening in a die. The metal emerges as an elongated piece with the cross-sectional profile of the die opening. The process also gives its' name to the product obtained hence.
Aluminum extrusions can be made with almost any kind of cross-sectional shape. They can be further fabricated with ease by cutting, drilling, puching, machining, bending, finishing and other conventional methods.
Hot and cold rolling processes are used to obtain flat products such as sheets and foil.
Casting methods, such as pressure, die, sand, and investment are used to produce castings in different shapes and size. Those parts are employed generally in vehicle manufacturing industries.
The specific electrical conductivity of aluminium makes it indispensable for electronics and electrics. Aluminium cables carry twice as much current as copper of the same weight. Also, high thermal conductivity makes it very suitable for heating and cooling applications.
That is why aluminum conductors have replaced copper for the transmission of electrical power from the generator plants to the cities.
The European building industry uses about 1.2 mill. tons of aluminium every year, making it the second biggest user of the metal. Japanese and American building industry use about 915,000 ton and 1,05 million tons of aluminum per year, respectively. It is found everywhere, in roof and wall cladding, windows and doors, stairs and railings, roof frames, scaffolding, greenhouses and home extensions.
The lightness of aluminium not only makes it much easier to handle, but can also allow considerable savings in supporting structures. Its self protecting and self renew- ing oxide film means that it needs no further defence against the elements. At the same time, it can be anodised in an unlimited choice of colours, or given a wide range of durable factory applied coatings so that no finishing or repainting is required on site. Rolled sheet in attractive profiles is the principal form of cladding, pressed and superplastically formed panels offer distinctive and individual facades for important buildings. Aluminium's virlually unique ability to be extruded into complex sections makes it especially suitable for window frames, accounting for up to 80 per cent of the market in some countries. Aluminium tubing is increasingly used in clad structures, often in dramatic yet economical geodetic systems, to be seen in domes, concert halls, arenas, reservoir covers and other shell structures. A growing and highly significant trend in Europe is the local manufacture of small quantities of individually designed components for building. This is often economical because aluminium's ease of working means that expensive tooling can be dispensed with, and it helps add distinction in a field where unifomity is all too common.
Aluminium is probably the most versatile packaging material available today. It makes strong, light, secure shipping containers, and it encapsulates pills. Tooth-paste is squeezed from it, left-overs preserved. It is probably more commonly seen on supermarket shelves than any other product, and it is equally at home in the heat of oven and the cold of freezer. The metal owes its success as a packaging material to a number of features shared by no other substance. It is exceptionally homogeneous, so that it can be rolled to the thinnest of foils. Its ductility makes it easy to wrap, and to re-seal once opened.
Aluminium foil is totally opaque to
ultra-violett light, which can quickly cause deterioration of many foods. It is
completely airtight, in laminated form it is ideal for vacuum-packing and it is
impervious to fluids, gases, dust and bacteria. It keeps good flavours in and
contamination out, and imparts no taint of its own. Laminated with plastics,
aluminium is widely used as heat-sealed closures for bottles containing anything
from yoghurt to pharmaceuticals. Heavier foil containers are used by the million
every day for convenience foods, ready to pop in the oven, and for countless
take-away meals. It is certain that aluminium prevents wastage far beyond its
own cost. As an example, the foil in which a 100 g bar of chocolate is sold is
worth about one hundredth of the cost of the product it keeps fresh.
One of the fastest growing uses of aluminium is in beverage cans for both soft drinks and beer World- wide, of the 125 billion drink cans sold in 1988, 80% were aluminium. The aluminium can is popular because it is light, easy to open, tamperproof unbreakable, it is quick chilling, and the most recyclable package. Since 1980 the weight of a standard 33 cl aluminium can has fallen 38% from 21 g to 13 g. Lightweight cans produce fewer emissions during production and require less energy for cooling and transportation. (A typical 33 cl glass bottle weighs 210 g (16 times heavier than an aluminium can and 10 times heavier than a steel can (20 g)).
Above all, the high scrap value of the used beverage can justifies collection systems before the package enters the waste stream. A cash incentive motivates the consumer to return cans rather than to throw them away With an energy saving of 95% the used cans can be remelted up to 100% and used again for the production of new cans.
Can recycling is a commercially viable business for
the collectors and the industry and is not something undertaken reluctantlyto
satisfy environmental pressuregroups. These advantages explain why almost 50% of
the world wide consumption of aluminium cans were recycled in 1988. The average
recycling rate of all aluminium cans in Western Europe reached 57% in 2006. In
Western Europe per capita consumption of aluminium beverage can is 38 units per
year. Scandanavian countries recycle 90 % of all cans. About 50% of
beverage cans in Europe are now of aluminium, and successful recycling systems
have been established and are being expanded in those countries where the
aluminium share justifies viable collection programmes. The aluminium beverage
can has enormous growth potential in Europe and its incomparable recyclability
is what will make it the predominant beverage package of the
future.
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