Uses of Aluminium

USES OF ALUMINIUM The following is an indication of the main classes into which the applications of aluminium fall and shows upon what properties of the metal they depend.

Automobiles and Railway Carriages.

With increasing efforts to reduce the axle load of road vehicles and thereby to economize in upkeep, fuel and tyres, whilst improving acceleration, the uses of aluminium in the automobile industry grow continu ously. Such parts as crank cases, differential housings, radiator tops, magneto bodies, brake shoes, etc., are regularly made as castings. Innumerable small cast parts also find their way into motor-car construction and in some cases dashboards, doors and windshields are similarly produced. Connecting rods forged from duralumin are used in some automobile engines and the cast aluminium piston is now standard for many types, since not only does the reduced weight entail greater efficiency and reduced vibration at high speeds, but the higher conductivity entails more rapid dissipation of the engine heat.

In the form of sheet, aluminium is widely used for the panel ling of private automobiles and motor omnibus bodies, whilst mouldings, foot plates and floorings are largely of the same material.

With railway carriages, too, the tendency to reduce dead weight and so to increase effective loading is encouraging the use of aluminium. At present sheet metal panelling is the most usual form, but many small parts, such as brackets, door and window furniture, etc., are produced as castings, whilst in some cases seats and other larger parts are also made of light alloys, and the possibility of using special alloys for structural parts is being seriously explored by experts for this and automotive purposes. Aircraft, etc.—Aluminiumis essential in aircraft construction and, in 1918, the Allies used 90,00o tons for this purpose. As far as the engines are concerned the same remarks hold good as for automobile engines. For the construction of complicated cowls, for fairings, seats, wind shields, etc., aluminium sheet has proved in dispensable. For the petrol tanks of airships it has been used al most exclusively, whilst the frameworks of these machines have been built up of light aluminium alloys, chiefly duralumin (q.v.) and the same applies to some all-metal heavier-than-air machines.

For the moving parts of many small machines, such as gramo phones, piano-players, typewriters, etc., the lightness of aluminium castings makes them particularly suitable, whilst for instruments and equipment which have to be carried aluminium is used wherever possible. In this category may be named photographic cameras, camping and military equipment, etc. Aluminium house hold furniture is now made on a large scale and finds its chief but by no means exclusive use in the tropics.

Aluminium Paint.

Itspower of reflecting light to the ex tent of 65-75% determines the use of aluminium bronze powder as a paint. Suspended in a suitable vehicle, the minute flakes of which the powder consists have not only a great covering power but offer a brilliant and to many a pleasing surface. This is responsible for the great development in the use of aluminium paints, especially in America. The same property accounts for the use of aluminium powder for covering the fabrics used on aircraft. Sunlight is very destructive to such materials as also to the rubber gas bags of lighter-than-air machines. It has been found that the reflection of so large a part of this light by aluminium greatly lengthens their useful life. Aluminium bronze powder is also largely used in decorative printing. Upon this same property of reflecting light depends the use of aluminium leaf in decorative art. For this purpose it has almost entirely replaced silver leaf.

Electrical Industry.

Herealuminium plays a very large part today. For bare conductors and especially for overhead transmission lines, some of them hundreds of miles long, absorb ing a thousand tons of metal or more, aluminium has largely replaced copper. In such cases the low tensile strength of aluminium is compensated for by interweaving with it high tensile steel wires. But for insulated wires the heavier cost of insulation due to the larger wire needed for a given current leaves copper supreme. During the copper famine of 1916-18 many electrical machines were made in Germany with aluminium windings, the individual wires being insulated only by thickening the natural film upon them. A special electrical application of aluminium is for transforming alternating into direct current. Aluminium in an electrolytic cell allows current to pass in one direction only, the reverse impulses being entirely suppressed.

The casings and housings of many electrical machines are aluminium castings. In some cases the fact that aluminium and its light alloys are non-magnetic is here of importance.

Foodstuffs Industries.

Agreat many of the uses to which aluminium is put depend upon the fact that aluminium salts are in no way poisonous. First among these must be named its use for cooking utensils, probably the largest single use of the metal in sheet form. For this purpose its high heat conductivity also commends it, as does the fact that it is uniform throughout its thickness, so that there is no fear of a protecting coating wear ing off as is the case with tinned copper or enamelled iron. Upon the same properties depends the use of aluminium steam-jacketed pans in institutional kitchens and in the foodstuffs and chemical industries almost universally. For the wrapping of chocolates and other articles aluminium foil is now very largely used in place of tin foil; whilst in America aluminium collapsible tubes are made on a large scale for the packing of etc. The stamping of thin sheet into bottle and jar covers is alone an industry of no small importance.

The brewing industry makes wide use of aluminium in the form of vats and fermenting vessels, storage vessels for yeast and beer and tanks for the transport of beer by road and rail. In Europe, the dairy industry also uses aluminum widely in the form of tanks and vessels for the storage, pasteurization and transport of milk and cream and for the vats used in cheese-making. For many other foodstuffs which are weakly acid, aluminium finds rapidly extending use, since much closer attention is being paid now than in the past to the presence of minute quantities of copper salts in materials destined for human consumption. Here may be specially named jam-making, fruit-preserving and meat extracting and the production of high-grade gelatines.

Chemical Industry.

Theresistance of aluminium to nitric acid has played an important part in the production of this acid and nitrates from the air, as well as in explosives factories, and some of the more recent processes for the production of acetic acid have also depended upon the possibility of using aluminium apparatus.

Many fine chemicals are made in aluminium vessels because the metal imparts no colour to them. For the same reason the palest varnishes are made in aluminium boilers.

The position of aluminium in the electrochemical series and its consequent ability to displace more noble metals from solutions of their salts has been made use of. Copper is precipitated from solution in this way for analytical purposes and silver and gold have been recovered from cyanide solutions on a large scale.

Because sulphurous vapours do not attack aluminium it can be used to advantage where exposed to fumes and especially to furnace gases. Here, however, its low melting point is a factor to be guarded against. A special application of this property is the use of aluminium to coat other metals by the process known as calorizing. The parts to be coated are heated in aluminium powder (to which certain additions are made) in a non-oxidizing atmosphere. An aluminium alloy which is highly resistant to furnace gases forms on the surface of the metal object.

Its affinity for oxygen accounts for the use of aluminium in refining steel, small quantities being added with other ingredients as deoxidizers to the liquid steel. Its use in steel and iron weld ing depends on the same property. Aluminium powder, mixed with iron oxide and ignited, deprives the iron of its oxygen, devel oping so much heat that the resulting metallic iron is molten and may be cast round pieces of the same metal which it is desired to unite (see THERaIIT). Many refractory metals can be similarly reduced from their oxides. Mixed with ammonium nitrate as a source of oxygen, granulated aluminium forms the powerful explosive ammonal and flash powders used in photography, and pyrotechnics are similarly made.

BIBLIOGRAPHY.-J. W. Mellor, Treatise on Inorganic and TheoBibliography.-J. W. Mellor, Treatise on Inorganic and Theo- retical Chemistry, vol. v. (1922), with an extensive bibliography. This valuable treatise should be consulted for the history, chemical and physical properties of aluminium and aluminium compounds. R. J. Anderson, The Metallurgy of Aluminium and Aluminium Alloys (1926), contains detailed accounts of the aluminium industry and its distribution, the production and fabrication of the metal and its alloys, and an excellent bibliography. It is profusely illustrated. M. G. Corson, Aluminium and its Alloys (1926) deals thoroughly with the alloys of aluminium and their structure, more particularly from the theoretical point of view. Edgar T. Painton's The Working of Aluminium is a good practical handbook. (R. S.)