Moorman, T. A.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  The Manufacture and Uses of Aluminum and Its Alloys Creators:  Moorman, T. A. Issue Date:  May-1923 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 6, no. 4 (May/June, 1923), 11, 28. URI:  http://hdl.handle.net/1811/34231  Appears in Collections: Ohio State Engineer: Volume 6, no. 4 (May-June, 1923)     THE OHIO STATE ENGINEER 11The Manufacture and Uses of Aluminum and its AlloysT. A. MOORMAN, A. B.Cincinnati University, 1916—Grad. Student Ohio State UniversityHE aluminum industry is frequently citedas one of the expansions of industries thathave marked the last three decades as anepoch in commercial exploits, and rightlyso, for in this time the manufacture of the metaland its alloys has grown to the extent of supply-ing many of our daily needs. At the presenttime, aluminum in the form of alloys is findingever wider application, and in the newer alloysor in improvements of some that are well knownwill find a field of usefulness that can not bedefinitely limited.HistoricalIn 1886, Hall in America and Heroult inFrance applied for patent processes very sim-ilar in principle for the electrolytic manufactureof aluminum; so successful was the commercialexploitation of these processes that the oldmethod introduced largely by DeVille in 1854,of preparation by reduction from aluminumchloride with metallic sodium became quiteobsolete. The cost of manufacture also droppedand made possible the competition that alum-inum offered to many other previously usedmetals.Process of ManufactureThe Hall electrolytic process consists in theelectrolysis of aluminum oxide dissolved in amolten bath of Cryolite, the double fluoride ofsodium and aluminum. The negative electrodeupon which the aluminum is precipitated elec-trically consists of a carbon lining in a largerectangular steel box, in which the fused bathcontaining the dissolved oxide is melted. Thenegative electrodes consist of solid carbon cyl-inders or blocks, suspended from a current car-rying support and immersed partly in the bath.The passage of a heavy current for the electro-lysis is sufficient to maintain the bath in amolten state, the addition at correct intervalsof an amount of aluminum oxide to replace thatused in the precipitation of the metal being allthat is required to make the process continuous.The molten metal that collects on the carbonlining is tapped into ladles and after freeingfrom any adhering bath, is poured into ingotmolds or made directly into alloys. During elec-trolysis the carbon cylinders of the anode areslowly burnt away by the oxygen, which is setfree on their surface and are accordingly slowlymoved downward or entirely replaced by newones.It appears remarkable that, aside from minoralterations and mechanical improvements in thelarger and more efficient installations, the Hallprocess of aluminum manufacture has not,beengreatly improved since its introduction. Effortsto render more efficiency from the standpoint ofpower consumption are, however, being madetoday as in the past, following, however, theindications of a research laboratory.The economies that might be effected inpower consumption can be obtained from a con-sideration of the power theoretically needed andthat which is actually consumed. The averagepotential used at present in successful manufac-ture is near 7 volts; theoretically only 2.8 voltsshould suffice for decomposition. It is seen thatif operation were possible at, say, 3.5 volts thepower used would furnish twice as much metalor the power efficiency would be doubled. Thecurrent consumption and aluminum oxide con-sumption are very good, and in good practicethe electrode consumption and wastage are nearto the practical limit of operations.The most expensive ingredient used in alum-inum manufacture is the oxide, which must bevery pure if the metal to be made should bepure. Aluminum oxide is prepared from Baux-ite, the only mineral containing aluminum in astate of combination that allows of a cheapenough chemical treatment for its separationfrom iron oxide, titanium oxide and silica. Baux-ite is found in various places in the UnitedStates, the deposits of Arkansas furnishing thebulk of the ore. In the chemical treatment thealuminum oxide must be brought into solution,freed from all insoluble and soluble impuritiesand again be precipitated and calcined at ahigh temperature to free it from any combinedwater. The expense of this elaborate treatmentis offset only by an installation of considerablesize, which must be operated at full capacity tobe of any usefulness; obviously the solution tothis problem will be of influence in lowering thecost of the metal.Properties and Uses of Aluminum and Its AlloysIn the commercially pure state, aluminumpossesses several properties which have war-ranted its use on a large scale, chief amongwhich may be mentioned its low density, itshigh electrical conductivity, its fair tensilestrength, its ductility and, under normal condi-tions, its resistance to corrosion. To a greateror less extent these properties are found to enterinto consideration in the use of the metal forany specific purpose. In alloys of high alum-inum content, the property of lightness is mostfrequently the desired property and alloys ofhigh strength, ductility, casting ability and rig-idity have been developed and fill a long-feltneed.Among the best known uses of the pure metalis that of its fabrication into cooking and otherutensils, where its light weight makes it con-venient to work with, and its high thermal con-ductivity increases the efficiency of heat trans-fer while lessening the danger of overheatingthe contents of the utensil. It has been foundthat the purest metal, known commercially asNo. 1, which contains 99% aluminum or more,( C o n t i n u e d o n p a g e 2 8 )28 T III-: O H I O S T A T E E N f l I N E E R( C o n t i n u e d f r o m p a g e 1 1 )is best suited for this purpose, because of itshigh resistance to corrosion. Lower grades aresubject to pitting, which lowers their durability.There exist today utensils made from the purermetal, which have given service for more thantwenty years, and are still as useful as whenfirst made, showing only mechanical wear.As a conductor for electricity, in transmissionlines and all wiring in general, the high con-ductivity of aluminum, coupled with its lowspecific gravity, has led to its extensive appli-cation as a metallic conductor. In this case it isdisplacing copper, which weighs more thanthree times as much and has only about one-third greater conductivity. For cross sectionsof equal conductivity the ratio of copper toaluminum is 1:1.59, and in weight per unitlength for equal conductivities, the aluminumconductor is less than 50% of the weight of thecopper conductor (commercially 48.33'%).This advantage in favor of aluminum is offsetby its greater cost per pound; indeed, the costof aluminum in cable is largely determined bythis factor, the cost of aluminum being suchthat it can compete with copper on an equalfooting, and with the new designs in cable con-struction at an advantage. Aluminum has ahigh coefficient of expansion, which causes con-siderable sagging of cables in warm weather,and its tensile strength in the hard drawn condi-tion as used in cables is such that a greatercross section than that necessary for obtainingequal conduction with copper is required. Tomeet these conditions aluminum cables are nowmade with a steel wire core, which has giventhe aluminum cable properties far in advanceof any other commercial cable. Because of theincreased strength much greater spans are pos-sible, eliminating towers and reducing in addi-tion thereto the hazards from insulator sup-ports. Large spans are becoming more com-mon, the largest to date is probably that erectedby the Knoxville Power Company, which thewriter had the opportunity of seeing some timeago. This high tension transmission line has aspan of over 5000 feet at the point where itcrosses the gorge of Little Tennessee River, andis a part of the line running from the Cheochpower house to Alcoa, Tennessee.The largest use for pure aluminum is in themanufacture of alloys to be used for certainpurposes. The addition of other metals onlypartly affects the density, while the mechanicalproperties can be altered at will and made toapproach those of mild steel. Aluminum formsthe basis of the common "light alloys," whichin recent years have come into prominence intheir application to automobile and aeronauticindustries. For casting purposes the main al-loys are those containing copper, and zinc withsmall amounts of copper. Many special alloysto meet particular casting requirements havebeen developed, literature for which is quitevoluminous. For general forging purposes thealloy "Duralumin," presents the maximum at-tained to date for lightness combined withstrength and ductility. It contains generallyfrom 3 to 5 per cent copper with 0.2 to 1.0 percent magnesium in addition to the commercialimpurities of iron and silicon in the metal asmade. The properties can be altered by furtheradditions of other metals, such as manganese,nickel, iron, even excess silicon finding somevalue in this respect. A newly published Dur-alumin having a tensile strength of over 90,000pounds per square inch and an elongation of 9per cent contains, in addition to the magnesiumand copper, 20 per cent zinc. The castings andforgings of Duralumin are capable of beingheat treated in a manner similar to steel, thusthey can be worked in an annealed condition,then by heat treatment be brought into the con-dition of greatest strength. Uses of these lightalloys, which are still somewhat expensive, arerestricted to those parts that are subject torepeated stress, which these alloys seem to with-stand to a large degree, for example in connect-ing rods, forged pistons and as heat treatedcastings for very light motors such as the "Lib-erty Twelve" and other automobile parts. Theuse of Duralumin in construction of airshipsand to replace the customary fabric of aero-planes is well known.For equal volumes aluminum alloys arecheaper than brass or bronze, and its machiningability being far in excess of as regards speedto that of cast iron, has led to its wide use forthe purpose of sheer econcmy.The heat of combustion of aluminum is rela-tively high in comparison to that of the othermetals. Advantage is taken of this fact in thealumino-thermic process used for preparing car-bon free metals and alloys of purity by directreduction of the oxides with aluminum. Thisprocess is also used in welding, in raising thetemperature of melts of metals and in the deox-idation of steel for the production of sound in-gots.T TT E 01T T 0 S T A T E E N 0 I N E E R 2!)9o men who beginat the bottom - nextmontPublished inthe interest of Elec-trical Development byan Institution that willbe h$lped 1y what-ever helps theIndustry.for big men.big field there's always roomThere is room up here. In anation you can reach the top.energy, experience and imagi-strength to climb. With addedcollege training will give youfacturing and commercial. Yourgraduates — engineering, manu-divisions of the industry open toThere are three ever-broadeninglarge, and finally the whole world.town are the state, the country ator communication. And after theelectrified—in heat, light, power,your own home town is completely3s now only in its youth. Not evenmanner remember that the industryits infancy. As you begin in a likewhen the electrical industry was inHERE is where the executives beganSince 1869 makers and distributors of electrical equipmentNumber 30 of a series

The Manufacture and Uses of Aluminum and Its Alloys

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The Manufacture and Uses of Aluminum and Its Alloys

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