The Iron Age 1929-08-29: Vol 124 Iss 9

~~ a ee New York, August 29, 1929 ESTABLISHED 1855 ~ Heat Treatment Wel VOI 124, No. 9 Grounded in Experience But Not Yet a Science BY JOSEPH NDENIABLY, the earlier applications of heat treatment to metals were developed through trial and error. While it may seem from a review of the exactly formulated methods now followed in routine heat treatments that a scientific basis had been reached for the explanation and prediction of the results of heat- ing and cooling the metals, especially steels, upon their structure and properties, the fact remains that our formu- lations are based upon much experimentation and upon mathematical theory. Until we know more clearly the mechanics underlying the constitu- tion of matter, particularly the thermal principles, we shall hardly reach a strictly scientific basis for any opera- tions that deal with those mechanics so directly as do the operations in heat treating. little exact science or Case Similar to Colored Glazes in Ceramics ESIDES, the finer touches of real artisanship apply in many special treatments, as in the case of tool steels and special new steels, and on larger masses and complicated shapes in the more ordinary steels as well. The case is similar to that in the production of colored decorations and which science is able, through chemistry, to duplicate in a defi- nite quality. But how shall we matchless beauty of the glazes and enamels of Kang Hsi or Chein Lung, for these were the products of the clever glazes in ceramics present-day ever again attain the craftsman favored by friendly hills where he selected his materials. Shall we ever know those mixes? As did this ancient artificer in the porcelains, so the heat treater, in spite of his superior sources of information, must refer to the “log” book of his trade and see what has been done on similar work in the past, improve the method as he can, and, above all, keep a careful record of both his work and its results for future reference. He can trust best his own experience. He cannot, without experience, predict or formulate a process. He cannot, without re- serve, use the experience of another. This, of course, does not refer to routine treatments that are well worked out, for almost anyone can do these; they are neither art nor science, but simply formulas to follow. Rate of Cooling a Vital Factor HILE we know some of the essentials of the theory of the reorganization of metal structures when heated and cooled, knowledge of the subject is broadening. *Pittsburgh. MILLER From a large amount of experimentation it seems now to be fairly well determined that the point at which trans formation in the metal (steel) structure takes place is determined by the rate of cooling. It is not a fixed point. Also, it is indicated that certain microstructures hereto- fore thought to represent definite states of the metal are in reality different simply in fineness of structure; that is, if enough steps are taken in producing the differences, the change is a gradual one from a coarse to a fine structure of the same characteristics. Thus on the one hand a troublesome variable is intro- duced in the process, while on the other we are taught to study more carefully our technique in the use of the micro- scope. These two developments are merely an indication of others on the way. Better than ever do we recognize the incompleteness of our present information. The facts that we need to know are very imperfectly understood, and it may be a long time before they are understood. The limitations that surround the treatments of large masses are particularly a hardship to the heat treater. Experimentation on pieces of large size is expensive. Also costly work may be destroyed by wrong treatments and for these reasons progress is slow and results are not broadly published. Those in metallurgical charge of such work are wary in its doing and wary in what they say about it. Each approaches a new job with his records of former work before him and deviates as little as possible from what he has known to be successful on the nearest similar job. The successful conduct of such heat treat ments is an art of the highest order. X-Ray a Decided Aid N additional aid to the heat treater is the X-ray, for A with it we may sift out and observe a little more clearly the ultimate structure that is being trans- formed. This seems, so far, to have best application to treatments in connection with cold working, which at pres- ent give rise to some uncertainties. Just how much those incertainties are due to heat treatments and how much they may be due to imperfections and variations of the stee] itself is more difficult to determine than in similar with larger pieces not cold worked. How- ever, it is certain that the field of adaptation of heat treat- ments and cold working properly combined for superior re- compli ations sults has hardly been explored beyond the range of wire sizes. 513 = 914 Heat Treating Aluminum Alloys Recent Progress Has Been Rapid—Views on Theory of Quenching and Aging—Uses of Heat-Treated Aluminum and Alloys ANDERSON, D. SC. the solid solubility of one constituent (the solute n another (the solvent) is increased considerably by r ng the temperature. Precipitation on aging is accompa! strength, elastic is the cause limit, and hardnes of these and other chang‘ ind precipitation e\ theories have been advanced to explain why pré ation should cause hardening and other changes, these cannot be taken up here. Precipitation Involves Two Processes \ ! rk by Gayler and Preston indicates rom solid solution entails two processes: Re the ed metal f1 4 n ed by the p i. r f é nd » 2 gu tion [tt | +}5 , These two processes probably overlap. These invé lr t tors also find that the parameter of quenched-and ged duralumin is measurably less than that of the an ealed and slowly cooled alloy (which latter is the sam: luminum). In other words, the solution of iminum is attended by a (small) contraction we num lattice That this lattice disturbance ! ecipitatior shown by the broadening of tl he X-ray spectrum. Hardness is therefore said to be due to distortion of the matrix by the precipitatio1 = Moreover, f highly dispersed particles Maximum hardness ha + Se p isly been ascribed to a critical dispersion of th« I rhea nee nitated articles _ rh d solubility of many metals in aluminum as af _ , te yy temperature has been thoroughly investigate na tw! ! rmation made available by recent research ha Theor 1f Quenching and Aging Heat Treatment * ene we WaUee me the development of alloys =" better understanding of the heat-treating processes. Th H 1 ust tec] ipplication of dilatometry to the study of aging has beer derable attention recently. finnealing Governed by Certain Principles lt us | PRIN! IPLES governing the annealing of cold-worked I ent ger iluminu im and id aluminum alloys are the same as thos« ngt applying to metals in general. The object of annealing ni ed by aging ld-worked metal is ordinarily to effect softening so that material may e subjected further deformation. Thus, « mercial aluminum is furnished in the form of lead-soft circles for utensil drawing and as sheet and rming and stamping. The demands of consun minum ne¢ capable of resisting severe cold ’ rawing pera ms have become increasingly severe. Con- i equently, the uminum sheet mill operator has had to pay : pecial attention to the control of his annealing methods ing tur' h sheet to grain-size specifications. Continuous Annealing for Aluminum Metal Continuous methods . of annealing have been developed n recent years for aluminum circles, sheet, and coil. Con- 3 nuous, or so-called flash annealing, has been found ad- “va ) fugust 29, 1929, The Iron Age oF aa eh Be SS re vantageous. With this process, individual pieces (or pieces stacked a few high) are passed through a heated chamber at such a rate of speed that the metal is exposed to the heat for only a short time. practical and simple with continuous annealing. In mass Grain-size control is (bulk) annealing, the question of stacking has received much attention with a view to permitting uniform and thorough circulation of the heat. Load temperatures ars rrelated with furnace temperatures in mass annealing. lime and temperature of exposure in annealing are now sely regulated. Mass annealing has been replaced to msiderable extent by continuous methods. Quenching Heat Treatment for Alloys \ J ARIOUS aluminum alloys possess only ordinary m« chanical properties as rolled or cast, but they can bs heat treated to yield a wide range of properties. The ten le strength obtainable in some alloys by heat treatment is nothing short of remarkable. This also applies to the du tility and hardness. There has been considerable devel: ment of recent years in special aluminum alloys to be heat treated, both for cast and wrought manufacturers S far, in alloys for working, nothing has been brought that excels ordinary duralumin in all-around mechanical properties and usefulness. Leading Proprietary Alloys Most of the aluminum alloys used for parts to be heat treated contain copper or magnesium silicide, or both {mong the alloys claimed to be proprietary may be men oned the following: Lautal, Carbium, Almelec, Scleron, Montegal, Aldrey, Constructal, 25S, and 51S. Lautal has attained considerable use abroad for both cast and wrought parts. The nominal composition is 94:4:2 aluminum-cop- per-silicon. Aldrey, also known as Wire Alloy No. 3, is typical of the compositions which have been developed abroad for use as cable for electric power transmission. This alloy contains 0.4 per cent magnesium, 0.5-0.6 per cent silicon, 0.3 per cent iron, and the remainder alumi num. There has been an influx of special heat-treated alloys for cable conductors in Europe. Mention should be made here of so-called Alclad. \lelad consists of duralumin sheet coated with a thin layer of pure (Hoopes) aluminum. The material combines the good mechanical properties of duralumin with the corrision-resisting qualities of pure aluminum. In the case of casting alloys, the following may be mentioned: 95:5, aluminum-copper: 95.8:4:0.2, aluminum- copper-magnesium, 94:5:1, aluminum-copper-silicon: 88.5:- 10:1.25:0.25, aluminum-copper-iron-magnesium: and 92.5: Dr. Robert J. Anderson OR many years Doctor Anderson has been an investigator of aluminum. days as well as with other branches of the non-ferrous industry He is the author of numerous technical articles and papers, and of a book on aluminum. he has given in the accompanying article a review of recent de velopments in the rapidly expanding field of aluminum alloy heat treatment, as well as some ideas as to the future As usually supplied, He has been identified with At the invitation of THI 4:1.5:2, aluminum-copper-magnesium-nickel. The fore- going are nominal compositions, the alloys being made from aluminum containing say 0.2 to 0.3 per cent silicon and 0.3 to 0.6 per cent iron. While many aluminum alloys are suitable for the pro- duction of cast or wrought parts to be heat treated, the uulk of present commercial requirements can readily be met with a relatively few compositions. One reason for .e large number of alloys which have been developed lies in the attempts of competitors to get around patent claims ] There is a demand for alloys to be used in castings production, which, without quenching heat treatment, will age spontaneously to yield enhanced mechanical proper es pome de eiopme! work has already been done in this direction. A wider field could be found for aluminun ] wala: hicl wld alle castings vs could developed which would harden and rengther i ntial simple alr aging ratew davs r by W n iture fe ne I i ew t I ite. is ARLY equipment used for heat treating aluminum alloys was generally crude, inefficient, and poorly ; irnaces designed for steel reating were used. Today, with a more comprehensive inderstanding of the theoretical aspects of aluminum al y heat treating, furnace equipment is designed to meet the special requirements of the operations to be carried out. Various types of heating equipment are still used n practice for annealing, soaking, and aging processes Irrespective of the design of the equipment and method of heating, the chief requirements are accuracy of tem- perature control and uniformity of heat distribution. In the writer’s opinion, the supremacy of electric heat- ing can hardly be questioned except on the grounds of t ‘ tallation and power operating costs. These higher costs may be outweighed by several advantages not obtainable with other methods of heating. The writer prefers electrically heated and automatically controlled equipment for annealing, soaking, and aging processes, semi-continuous) are be Car-ty pe irnaces (batch or ¢ avored over the older pan-type furnaces for the In the case of continuous ing mass annealing of aluminum pment for annealing sheet and circles, the usual equ construction involves a continuous moving belt or con vevor made of woven wire screen or separate wires, 01 bands, driven by variable speed mechanism. Such a bel nasses through a relatively long chamber of restricted height The continuous coil annealing furnace is a recent from its early IRON AGpr, j The Iron Age, August 29, 1929—5I15 velopment of importance. In the operation of this, alum- alloys have come in the transportation field, including ( s unwound from a drum, passed through the aircraft, motor cars, trucks, and buses. Interesting us« ber of the furnace, and wound up at the other have been made of heat-treated alloys in the constructior \ similar furnace has been developed of street railroad cars, steam railroad passenger cars, an num f parts of locomotives. Certain of these applications a1 n the experimental stage. Substantial increase in the u Continuous Electric Furnaces Preferred of heat-treated aluminum alloys is seen in the moder: Lilt tendency to save weight and increse speed in all kinds to tl ench transport. For highly stressed parts, the unheat-treat ! sto Contin- aluminum-alloy casting has passed out of the pict nit. cast Increasing use of duralumin-type alloy sheet and shay ‘ fF thy s seen with the tendency toward all-metal construction reraft, while the modern Zeppelin-type ship could not built without the use of this material. ng ! e tl heat treat Future Trend Outlined f { ire ised ¥ T is significant to the future business welfare of met I producers and manufactures that the heat treatme: aluminum alloy parts is not only here to stay, but heat causing radical departures in practice. While possil tortioy n future developments are difficult to predict, the writ at the progress of the past will be overshadow ntace nn mai? in the next ten years. The number of alloys for uss .eat-treated manufactures will doubtless increase. It quite unlikely) that these alloys will be found accidenta ses Which Heat-Treated Alloys Are Put but rather will be developed by systematic research. Al] . i with more alloys available, it will be possible to sel reatment process« as ay = . e r | ‘pe Ae pe ES: material especially suited for particular purposes. TI at-treated structural shapes and forgings xpected to increase greatly. tel oe With the development of heat treatment and new allo} a the future a large proportion of the aluminum-alloy s castings consumed by the engineering trades will be of nd nz . the type once regarded as special, namely, special compo roduction of sition and heat-treated. Heat-treatment plant is now a } er mechar ecessary adjunct of the modern aluminum alloy foundry now used f Commercial heat-treatment plants are being called on t ngil es whet t was for heat treat aluminum alloy parts, both cast and wrought nu illo: it a If the price of aluminum should be reduced appreciabl; re 1 ! g mpe there would be a large increase in the use of heat-treated aluminum alloy manufactures, particularly in competitior Correct Wrapping Prevents Spots on Plated Ware W ea ite t! 4 rica ting, (c) the application of a thin film of a grease, suc! > Societv at the Burea f Stand natrolatum. to ¢ ireau i and aS petrolatum, to the lacquered surface, and (d) the us¢ tain if wax paper for wrapping. H Stain spots are caused by acid or a chemical con ir P 5 uu of pound absorbed in minute cavities in the metal during the plating proces In a humid atmosphere, these chemicals nde! absorb moisture and exude upon and stain the surface UI ty Alkaline substances are especially difficult to remove fron t hat the metal, once it is there, and it is not practicable t ppe phid eliminate alkaline substances from the cleaning and I ers rt ne tall lating solutioz ! Sometimes porosity of the metal may be reduced by a . rregular are ISU th a hange in pattern or in casting conditions. No method of the cent nsing or neutralizing was found entirely effective t growl! lean the surface; baking at high temperatures befor: I i I lacquering 1s sometimes helpful. I i r torn I The two most effective remedies are to induce the n eve! nute ic] ction by exposing the articles to a high humidity before ma m rubbe1 final finishing, or to use a lacquer which retards spotting. r or cal rd cartor rT Phenol-condensation lacquers are less permeable to mois- ) ¢ ! r from the sw ture than nitrocellulose lacquers, and are also more effec- pot tive in retarding stain spotting. 916 dugust 29, 1929, The Iron Age A Year’s Progress in Steel Treating From the Viewpoint of the Testing Engineer—wNitriding, High-Test Iron, Bridge Wire and Gas Carburizing Among Features BY H. F. MOORI HE testing engineer is not among the pioneer work piece, and a wide range of possible heat treatments of the ers in heat treating. His viewpoint, then, is that of re without much disturbance f the surface hardness one who observes tendencies as to general agre: eem t be features f the nitriding procs which will as to theory and technique among pioneer workers, render it very valuable to the maker of steel parts which the tendencies to the formation of “current practice” have to withstand abrasive action heat treating. What further possibilities (and limitations) of the ocess will develop a is used in practice are matte! General Agreement Exists as to Principles ee Seah a 1] tee] ne nterest » al isers f eel, \n outstanding feature of the past year has been the ndency to a fairly general agreement as to principles idvances Made in Heat-Treating Gray oe treating, especially heat treating of iron and .* AST iron foundrymen seem to have awakened to th + Cal \n excellent example of this is seen in the stat possibilities of their product This was shown by ent of “Pr ait _ > , i Tin ne . ' 599 . nt of “Principles of the Heat Treatment of Steel” pn a special session of the American Foundrymen’s Asso red by the metallurgical staff of the United States Bun ciation in April [THe IRoN AGe, April 18, page 1072}, eau of Standards and issued in the Transactions of the devoted to high-strength cast iron, and by the symposium \merican Society for Steel Treating. In the 90 pages of ’ ist on at the meeting of the American Society for = pamphlet there is presented a concise statement, in Testing Materials in June [THE IRON AGE, July 4, page 6]. telligible to the beginner in the study of heat treatment Heat treatment and alloving f grav cast iron have Of course this statement, like all similar ones of physical een f i ipable of giving a much better structural laws” is not to be regarded as final, but the fact that naterial than the ordinary gray iron of former days. The such a statement can be made is evidence not only of the r tructure-weakening flakes of graphite found in or skill of the authors, but also of the growing degree of linary st iron can apparently be induced to take unto stabilization of ideas on the subject. thems ves more globular and less damaging forms. Of alla she Ae . : urse, this has been possible by the malleabilizing proce \ itridin 5 a Si inal f P ‘eC ig j e ‘ d ‘ eat . 1 s £ ure vr a long time, but heat treatment by other, and quicker, A NOTHER outstanding feature of heat-treating prog nethods give promise of usefulness, although their useful ress during the year is the develonment of the 1 ness and limitations are not yet clearly defined triding process for hardening the surface of steel Che , ; a = yer of hard material produced by current process¢ Ges Carherising » Tempting ii ems to be very thin, and the use of the proce f Progress in ise carburizing, a seen by the testing engthening steel parts seems not to have encroache: engineer, has been mainly along the lin of improved erlously as yet on the field of the case carburizing pro technique, and in the development of gas carburizing. Gas However, surface hardness without distortion of a irburizing, in which ther no need of expensive and : frequently-renewed carburizing boxes, is indeed a tempt . Ur Po a lacie ne field fon tudy The neces f heat treatment of Prof. H. F. Moore N authority on fatigue testing, Professor Moore is widely > { ' known among steel treaters and materials engineers. At the invitation of THe [Ron Act . he has reviewed in the accom panying article the more recent events in heat treating steel. He is a past-president of the American Society for Testing Mate- ; ; ee rials and active in the work of the American Society for Steel Treating, as well as in research organizations and other technical societies. The Iron Age, August 29, 1929—517 irburized steel pieces, is more and more being recog The year has not passed without some costly lessor and the fields of carburizing, nitriding, and of heat Perhaps the most dramatic of these has been the tro f ating without alteration of chemical content are grad- bles which have shown up in heat-treated wire for cable ning ined Evidently here is a field requiring much study, with th , possibility of the emergence to prominence of new f Lal tors which may weaken steel. The writer has heard 1D DT 4 gf) f “2 an lain pari several conflicting theories of the cause of this trou ROGRESS in the field he reating plain carbon ' 4 4] with wire for he a) eels ha Heer ess e¢ ‘ular. but the vr cables, is not going to advance ar cA CALs t Urit ic : treating 1 Ce es and of measurement theory, but to urge that the progress of the investigat rane stead -d. The behavio1 f this trouble, an investigation carried on by a nun be close L\ watched by every steel treat laity iaiiealaaiaieilieases Future of Tungsten Carbide progress would be com thout a mention of the appearance of the new ingste! irbide, as a cutting tool although this is n steel at all It was several years ago that Rosenha addresses predicted the development of tungste1 rbon alloys along lines roughly parallel t Designers Using Steel Must Know Heat Treating ; . =i velopment of the iron-carbon alloys. The tungster ( I } Y ‘ Y ‘ w used are a cutting-tool material rath« in a structural material. What the future will bring The di n and ¢ gr enst interesting uncertainty. £ £ I tar I Io the work and prospects of the steel treater th ! I words of E. E. Slosson, spoken to the industrial chemist f ! ire very true In this field the progress of the past, i nt n tead of discouraging the hope of future progress, ind f t that tl ites numerous opportunities for it. In the field of hea i treat t tment “there are as good fish in the sea as ever ha Navy Uses Color Markings for Identifying = a es F Metals aot ote ig tp ict { ‘ ! ne “ 1) : ; Q Q Catalor B Reds W Ste reat . — desig : ari ae a rahe king i ( ot y WW} St, | t-treater ! t , no ' | St Gi finished f \ Cy ; HG. heat-treatet WI s Grade W, semi-finishe ~~ a i per ne S , nell t S ( ( é finished Hh leat I Ste ( S, semi-finished é ‘ | S ( B, bolt-mater v, witl i pe l . } t! S ‘ A old-rolled These colors have been used by the Navy for about ; fifteen years and presumably will be adopted by all de , partments and establishments of the Government afte1 . the 1 iance of the sheet of the Federal Standard Stock Latalog This method of identification, which represents a step in the simplification and standardization program of thé Government, may be found applicable, by industry, 01 ervé basis for a similar program. 5 ( Austenitic chrome-nickel steel has been used in Eng > | ae ; nd for numerous seaplane parts. Cold worked wire of ype of material makes excellent springs, which hav: } added’ advantage of resisting the corrosion due to marine conditions. It also appears to be a satisfactory) material for obtaining not only rustless rivets but also nuts nd bolts, split pins, spar and hull fittings, skin plating ind struts for floats. A modification in the composition the austenitic nickel-chromium steels has resulted in : the production of extremely satisfactory materials for ; exhaust manifolds and pipes. 218 dugust 29, 1929, The Iron Age eat Treating Aircraft Parts Large Electric Furnaces Handle Delicate Members Without Distortion—Exceptional Properties Obtained in Alloy Steels of Thin Section BY HORACE C. E A T 1 treat- ment of delicately e¢ structed on- aircraft members is one of he chief problems confronting the ndustry. The necorporation of steel, not heat treated, into wing spars, landing vear, struts, en- gine supports and the fuselage, has fre- sections ot quently necessi- tated > se : . — on ater the use of Tube A fairly thick tub- S.A.E. N ing—so thick, in Ultimate strength fact, that the re- een Surveunen. 06 Sth = . Size dia wall sultirg weight , ea Weight per ft., Ib 2.00 was unsatisfac- torily great, if not in some cases prohibitive. If these various successfully heat treated, a thinner section of tubing could be parts could be used with a saving in weight and an in- crease in strength and serviceability. To do this, however, without excessive distortion has hitherto been extremely) difficult or impossible. A method for successfully heat treating such delicate parts has recently been perfected and has resulted in larg: savings in weight and improvement in strength and safety of aircraft, at the same time opening the way for more extensive and high-grade alloys in more efficient use of the construction of aircraft. It is the aim of the present article to describe how this has been accomplished. Steel and Other Materia’s Compared TEEL is the lightest of all materials of construction, when strength and weight are regarded concurrently they should be in the design of aircraft and other struc ires Where weight and inertia are important factors One of the most important considerations in deté mining whether a certain material should be used in all raft construction is its strength-weight factor. This fa tor is obtained by dividing the ultimate strength of the material in thousand of pounds per square inch specific gravity. This result is, of course, purely ar stract figure, having no inherent meaning in itsell, but provides a “rating” which is easily obtained and sound 11 p! inciple. 0.06 lb. K NERR Table I the strength- gives weight factors of typical materials used in aircraft construction. Wood is virtu ally obsolete as a structural ma terial for aircraft. It is obvious, from the strength weight factors, that struction 1 metal con Chrome lighter than wood Mild ( Mi de where design is _ = such that the full B ’ = reo D strength of the . { \ metal is taken ad ( vantage of. aaa The table and 1.65 0.92 0.50 accompanying cut of tubes fore eful through give a illustra the The circles weight savings steel of use possible of heat-treated alloy high strength. represent sections through tubes of equal outside diameter, but having wall thicknesses selected so that all will have the same strength in tension or simple compression. of that table would A duralumin tube corresponding to those 0.40 in would be 20 would have a wall thickness of per ft. Therefore it than the heat-treated alloy steel tube. that steel vive as a material of construction for aircraft, except in and weigh per cent heavie It appears unheat-treated cannot long Sul those parts which act as long columns, and where stru tural strength is therefore determined by the modulus of elasticity of the material and not by its tensile strength. On the basis of strength-weight efficiency, it is plain that unheat-treated stee] cannot compete with duralumin it by heat treating a suitable alloy steel to even the mod rate value « 150,000 lb. per sa. in., it becomes relative. as light or lighter than duralumin. It seems certain that both aluminum alloys and heat- reated alloy steels will have an increasing use in aircraft n iction. neither one replacing the other, but each finding the application which its particular characteristics will best serve. Steel of high strength probably will b« employed for landing gear, engine mounts, wing beams ind fuselage structures, especially for aircraft of medium and large size, while duralumin will have its place in the structural parts of small ships and for wing surfaces, fuselage covering, engine cowling and boat hulls in gen The Iron Age, August 29, 1929—519 520 arKable ombination of properties, bdenum steel, No. 4130X, is rapidly be- ! uctural material for aircraft (Ta Il) is readily worked into seamless f red diameters and thin walls, as well as ar stock. When properly made and an- thstand severe cold forming as in the fittings, and can be readily hot worked as ng tubes or the production of forgings. It mat ne n the annealed state, and one of its ling characteristics is superior machineability in son th other alloy steels, after heat treatment to hig ngth and hardness. It has exceptionally Oil 60.000 lb t} an Better to ¢ ] -August 29, 1929, The Iron A ZSZSZS7SZSZ SZ WING Spar Made of Steel Tubing Heat Treated Successfully After Assembly. treated 135,000 Ib. per sq. in oxyacetylene flame, temperature, about 1600 free iy in alr, it develops a 95,000 lb. per sq. in. with a over, and an elonga- or over, per sq. in. or 2 per cent in 2 in Than Water for Quenching section near the weld has unavoidably i This anneall S0.000 ng temperature. portion lb. ies are satisfactory for cer- the something better than per rt where members act as “long tresses are determined princi llus of the material. sfactory charact ge steel, however, is its response to heat treatment, consist- ing of quenching from about 1600 deg. Fahr. followed by suitable tempering. It may be quenched either in oil or in water. Various authorities (including certain Government specifications) have heretofore recommended quenching in water, but experience at the Metlab plant has shown that il quenching is decidedly preferable for parts other than those of large or heavy cross section. Oil produces as good or better tensile strength tha water and gives a higher combination of strength and duc tility. It also appears to give a higher yield point o1 elastic limit for a given tensile strength. At the sam time there is little tendency to cause warping during the quenching operation and the liability to cracking in quenching is practically eliminated, whereas these are con- siderable when water is the quenching medium. Values given in Table III are typical of the results ob- tained in the heat treatment of this steel by the method described in this article. Vanufacturing and Treating Problems preteen of aircraft parts consists primarily in the cutting to size and shape of sheet and tubing, bending and forming, and assembly by welding. Machin- ing operations in the ordinary sense are restricted to a few parts requiring accurate surfaces and fit, such as axles, end fittings for struts and engine mounts and the like. Where a moderate strength is sufficient, the steel may be fabricated in the normalized condition and left so For important structural parts which are subjected to Length 10 ft. Heat A delicate member which can be handled in a vertical furnace high stresses, shock, fatigue and overload, this steel is icated in the annealed state, and heat treated after welding. fabr In some cases, it is desirable to heat treat parts before assembly and then assemble by means of (tubular) rivets, instead of welding. The good machining qualities of chrome-molybdenum steel make it possible to cut, drill and otherwise machine parts prior to assembly which have Table Il Chrome-Molybdenum Steel. ¢ omposition Ni 1130X Army-Nai Standard Per Cent Carb 0.25 to 0.35 Manga 0.40 to 0.60 P} phe I x 0.040 Suly ir (max.) 0.045 Chi un 0.80 to 1.1! Mol lenur 0.15 to 0.25 been treated to a strength of 150,000 to 200,000 lb. per sq. in. Heat treatment of aircraft parts is in a class by it- elf. Made, as they are, of tubing and sheet ranging in thickness from about 0.035 in. to ™% in. and varying in size, shape and length from small fittings to axles 6 or 8 ft. long, ] iengten, engine mounts 3 ft. sq. and wing spars 25 ft. in they are extraordinarily delicate at the quenching temperature and exceedingly liable to distortion. They are likely to cool prematurely and irregularly during transfer from the furnace to the quenching tank. Be- cause of their thinness, a small amount of scale or de- carburization has a large effect in reducing the strength of the members. They are often of complex form. Typical parts are shown in some of the illustrations. Attempts to heat treat parts the h methods and in the ordinary furnaces are generally disas- heat-treated aircraft by usual ‘ ep RENEE: GREE) EEE EE EEE NE ee trous. During heating through the critical range they sag under their own weight. On lifting out of the furnace for quenching they sag again, in other directions. Upon quenching horizontally they warp again due to side con- tact of the quenching medium. There are therefore three chances for distortion. Attempts to straighten after heat on Is Furnace 11 Ft. High and 33 in. Sq. In- side. Quench tank is directly | under furnace in position it would be in for quenching. The charge is shown almost in the oil with the alloy spider just appearing below the fur- nace eerie rere aa aeieae ares treatment usually result in denting or crushing, because of the thinness of the walls. Difficulties encountered were so serious, and the fail- ures so costly, that many aircraft engineers became dis- couraged and gave up the idea of using alloy steels wher: heat treatment was required, sacrificing lightness or using more costly or less satisfactory means of construction. The author’s contact with these problems as chief metallurgist of the Naval Aircraft Factory, Philadelphia, convinced him that the difficulties could be solved only by suspending the parts vertically during heating, in such a Way as to avotd all tendency to distortion, in a furnace permitting close control of both atmosphere and tempera- ture, and arranged for quenching the charge without re- handling it, by lowering it without other movement into a quench tank placed directly beneath. Furthermore, the charge must be kept under control during quenching, be- ing lowered rapidly, but without swinging, out of the fur- nace into the quenching tank, where it must be brought to rest beneath the surface without shock. Quenching should be in oil. The advantages of oil as a quenching medium’ have | T HE General View of 10-Ft. Furnace. Fur- | nace resting on framework in centre of pic- | ture (above). Quench tank is seen just to right | of legs of furnace. A charge has been hung on | the alloy spider which is resting on the rack at- | tached to the quench tank. The next operation | would be to lower the door, roll it to one side and | move the tank so that rack is directly under fur- | nace opening and pull the charge up into the furnace. The automatic controllers and recorder are seen to the left on the wall. The control relays are mounted in front of the furnace. The | winch for raising and lowering the work is directly to the left of the furnace been outlined, but its use entails a serious fire hazard which must be guarded against. When the oil enters hot tubular members at the moment of quenching, there is a tendency for it to break down into its more volatile con- stituents. These are superheated on passing upward through the tubes and issue from the open end as a mass of flame. Should a charge become stuck part way out of the oil bath, or be lowered too slowly, a very large amount of flame may be produced, with serious consequences. In obtaining the advantage of the use of oil as a quenching medium, it is necessary to overcome this danger. Aircraft parts may be divided roughly into four classes: gs and ott par B p ] é tier g gear « \ I A traight I aing ixXié t ind g } K ind | d ift I it ent For economical operation these call for three furnaces f different size and shape. A small furnace for class 1, a furnace of large section and moderately great length for lass 2, and a furnace of moderate section but great length The Iron Age, August 29, 1929—521 lA died 1, — ees meee " ae ses 3 and 4 Small parts may, of course, be ted in either of the furnaces intended for parts of 2 or 3, when the quantity warrants. Necessity for close and automatic temperature control, ertical position of the heating chamber favo! electrical heating. Electrical furnaces of the to handle aircraft parts of classes 2, 3 and p t ecessal temperature regulating equip m<¢ I the mechanism for handling the charge are They must have a reasona ly large capacity i er hour to avoid an excessive labor cost pet rk heat treatec I inything like continu oO I é lid there re ive in output far i é ‘ 1 requirements of eve the largest I rer ft i I me me to come oO S cos ntenan¢ epreciat n ana narges, tnere ust he added the bur- erhead of a highly trained staff. The heat treat I iit parts Calls 1 pe alized metallurgica e part of the management and carefully 1 ne tur lhe answer to the proble1 s believed to be found in a central plant with specially designed fur- erated by specialists and fully equipped in every ng laboratory facilities, to which aircraft mar end their parts for heat treatment. 3 g the production in this way, the cost of treatment uught down to a reasonable tigure. Such een established in Philadelphia, a location near the center of production of the air- and otherwise favorably situated. The plant he following Design of the New Furnaces 10 ft. high, for the treatment of parts of large at such as landing geal nt rie nt I i « age sect ons and the like. The otne. ndling parts up to 25 ft. long and 2 ft. wing beams, spars and straight tubing Sn parts handle y quantities ! S T ( I T na opera- é eTterre is neat-treating nace it ’ 7 ’ ‘ ‘ nis eve 1) , mu rT n prec ( sa fa to tT y ) e’{ ‘ i } tht) ‘ n? l t ther ( 4 ace ENTER Sec tion Cros Tube on Bottom ot Fuselage, Hea Treated to 200,001 Lb. per Sq. In. to turn out 57,600 lb. of work in either furnace in a 6-da week. This is equivalent to more than 5,000,000 Ib. a yea for both furnaces together, which presumably would ample capacity for the needs of the entire aircraft indu try for some time to come. At the present time, when the demands are smal] comparison with the furnace capacity, each furnace is us¢ for quenching on one or two days only of each week. A the power stand-by charge is high, and is determined the peak load in any month, the two furnaces are co! nected with the same main power switch, and used a ternately, never simultaneously. The temperature cor trollers and recorders are arranged so that they may connected with either one furnace or the other and that one set suffices for both. When production increass to a point warranting the extra stand-by charges involv: n operating both furnaces at once, this can easily be a ranged by adding another main switch and control pan and making a few changes in wiring. The furnace heating elements consist of nichrome 1 bons suspended upon General Electric refractories. T} lining is of supersilocel brick and is backed up by 13 ir or more of silocel powder insulation. The heating ele- ments are divided into horizontal zones, the 10-ft. furnac: having 4 zones and the 25-ft. furnace 6 zones. The zones nearest the top and bottom are of shorter length than the intermediate zones, in order to take care of end losses. Each zone is automatically controlled by a Wilson- Maeulen controller. It is possible to maintain temperatur uniformity throughout the heating chamber within plus o minus 10 deg. Fahr. at any temperature up to 1700 deg Fahr. The temperature at various points in the furnac« is recorded continuously on a Leeds & Northrup multip| point recorder. The recorder and controllers are on en tirely independent thermocouple circuits so as to afford a check and warning should any part of either system get out of order. A fan is provided to circulate the furnacs atmosphere and insure uniformity at low as well as higl operating temperatures. The two furnaces have about the same power demand, about 90 to 95 kw. and are connected with a 220 volt, three-phase line. Radiation losses are about 30 kw. at 1600 deg. Fahr. They are placed vertically side by side ipon structural steel columns, and having a working spac« between them. The quench tanks are mounted directly beneath the furnaces on small cars having ball-bearing wheels which run on tracks attached to the columns, pet mitting the tanks to be moved laterally. The bottom each furnace is fitted with a door or plug, which is first lowered and then moved to one side when charging or d charging the furnace. + The furnaces are elevated to such a height 01 RONT Landing Gear, Fabri cated and Heat Treated by Metlab Heat treated t 180,000 Ib. sq. in Overall height, 5 ft., 6 in. » Gries ‘qalmeias —<——-—<—<—_- TO Pe +e.a" the structural steel framework as to be conveniently operated from the second floor of the building, thus avoiding the necessity for a large excavation in order to accommodate the quenching tanks. The tank for the 10-ft. furnace together with its sump tank is entirely above ground level; the lower part of the tank for the 25-ft. furnace, itself 27-ft. deep, moves in a concrete lined well 12-ft. deep, the remainder being above ground. Both furnaces are in a small building separated by a brick wall from the main building and reached through a fire door. The work is prepared in the main building and passed through the fire door for loading and back again after treatment. This arrangement removes the fire haz- ard from the main building, which is utilized for manufac- turing purposes. All openings in the furnace, such as power and thermo- ‘ouple leads, are sealed, so that no draft occurs and the atmosphere of the heating chamber can be closely con trolled. Oxidation of the work is thereby avoided. A sump tank, which is stationary and provided with water-cooling coils, is placed on the ground directly be- neath the quench tank of the 10-ft. furnace. By means of a entrifugal pump the oil is pumped from the sump tank an inlet in the bottom of the quench tank and allowed overflow through a manifold at the top of that tank, rom where it returns through a down pipe to the sump especially for the purpose will be installed for tempering. These will be of different and simpler construction. Some Results Obtained HESE furnaces have been used for about a year, in I the heat treatment of a great variety of aircraft parts. The percentage of loss due to unsatisfactory treat- ment, including warping, has been nearly zero. The physi- cial properties obtained are usually far in excess of the specified values (see Table III) and in fact exceeded ex- pectations for this grade of steel. Examples of high-ten- sile properties of test specimens of parts are shown in ANDING 4 Gear, Heat Treated to 180, 000 Lb. per Sq In Center Section Spars, Front and Rear Heat tank. The hottest oil therefore overflows immediately and is cooled while new oil replaces it in the tank from below. This produces an ideal circulating arrangement Addi tional and quite strong circulation is produced in the quench tank by means of stirring devices. The same sump tank is used for both furnaces, being connected with the circulating system of either quench tank by means of three-way valves. Quenching and Tempering HE work to be heat treated is hung on a rack 01 spider of heat-resisting alloy, by means of nichrome wires or hooks. It is suspended in such a way as to be free from all tendency to sag under its own weight while hot. The spider and charge are now raised into the heat ing chamber where they remain suspended until ready to be quenched. The quenching tank is then brought into position directly below the opening in the bottom of the furnace, and the charge is lowered straight down into it, without other motion. While the production demands are not great, a furnace is used for quenching on one day and for tempering on the following day. The temperature of the heating chambet has by then dropped to that required for tempering (600 to 1100 deg. Fahr.), so that only a small amount of cur- rent is needed for the latter. The operations during tem pering are similar to those during quenching, except that the oil is drained from the quenching tank. When it be- comes necessary to run the furnaces continuously for quenching at 1600 deg. Fahr., separate furnaces designed treated to 180,000 Ib. per sq. in. Length, 8 ft. Table IV. This steel is in no sense “brittle,” as specimens can be bent nearly double without cracking Distortion has been reduced to a negligible point. The first wing beam treated was 10 ft. long. After treatment the deformation was less than 3/16 in. in 10 ft. and this has been bettered in the considerable number of such beams treated to date. Parts of complex form, such as shown in illustrations, have been treated without notice- able distortion. Duralumin Treated in These Furnaces HESE furnaces are suitable also for the heat treat- ‘ae of duralumin and other aluminum alloys, eithe: cast or wrought. These alloys, when made up into deli cate and complex parts such as bulkheads for flying boats, fuel tanks, etc., have a persistent tendency to distortion ble 1\ ] vical } imples of Physical Properties Obtained by ‘ He 7 D ye Elong I Yield ma |’ Cent I nt 5 ngth J \ Lb Lb I ne Sq. Ii per Sq. Ir per Sq. Ir Max. M Aver x ; 106 p20 l rf) 6.0 ) + x } 7 201,000 my ; 1 ) 211,000 7.4 % ‘ ‘i 191 26.000 ( 1 { ) x 12,0 »g OOO ( ,On a pene ' ‘ 7 4 * Tube ed ‘ I ‘ flat specime rom gare ct t rt 1 hig A f thinne of I mer The Iron Age, August 29, 1929-—523 ent when treat n the ordinary wa ties are a part of the plant equipment. Tensile test speci ! igh the te eratu s . because of the grea mens representing the material are introduced with each n¢ mperature charge and are tested immediately after heat treatment. . eat t t ( furnace Aircraft manufacturers located at a distance from ths ant usually find the delay incidental to shipping thei treatment and return interferes with pro dules and adds an item of expense. In con q ! ha te nection with the heat-treating plant, a fabricating sho} rait part has therefore been established in whic} nding gear and other parts requiring heat de up to the aircraft manufacturer’s bl nt nd specifications, heat treated and shipped to the Ninal assembD(y. Surface of Drilled. Reamed and Press- Finished Holes erlol nish OL drilled, reamet has bet tudied by Dr. O. Sc! J 12, 1929, page 33). The qual ! rilled hole depends pon the meta I ; i! ed in harder teeis and cast 1ro1 tl I I pper on ithness ul mall feed Reamers ma iff I care Lye a Se | not é ! Cc! e! ined in the cutte1 \ nding ar lishing, the best hols finishir I a polished stee indersize hole, already drilled a ed his gives a work hardened surface, smoot! ? n aspect to a cleaned gun-barre]l Doct Schlippe’s studies were made on gelatine Ace ind ar¢ immarized in the table. T} ( es, 7 2 much smoother than the drilled ones, nave til and arp corrugations which scatter the light ( ste) Press finishing obviously cannot I out t regula n drilled holes in a singl nie the increase in radius is of the same orde1 ‘ een r} t Nel ral D Sg Vit ncreasing A ! fore this end is reached M i G ; ; Depth in M : f 4 A] 2 } ' A eT ? al ? ra , = : Sed il B nz el I Cla I I ! : . . \ t \ ! is herefore be de i hing i1 g being done it 2 , to avoid the ad Revises Specification For Manganese Steel ee ae . Welding Rod Chemical specifications for manganese steel welding 5 Other Uses for the Furnaces re have been revised by the American Welding Society e £ é y r ? 4 +hy e rie ! I i l ee <a a per cent vhere e) part , "4 it ely thir p ~ pe 11 to 14 per cent 0.09 per cent T } tT pe ne t tre ted tl tT dist ? a“ - a A ‘ ] } Y Hon te 0.04 per cent - t { é cent ‘ e¢ , ict as iré sec ) “ pel n ind linoleum industries; arbors; blad Such rods are intended for use in building up surfaces n paper machinery; shafts, both hollow where an extremely hard, tough metal is required, such as h as are used in the oil industry track frogs, crossing centers, switch points and dredge ‘ } 17 1 i I are itisrat ! r carburizing long ucKets } } no ne n tut ] ; ; f Al ‘ ‘ ai AWUIL l re OT ‘ Heating while suspended vertically avoids the Strip or open-pit mining is adapted to minerals of laily occurs during carburizing in horizonta low market value. For instance, anthracite averages $5.60 in value a short ton and bituminous coal $2.20; laboratory facili copper, $2.80 to $4.40 a long ton: iron, $4.55 a long ton; bauxite, $6.15 a short ton; and pebble phosphate, $3 a K long ton. 524 fugust 29, 1929, The Iron Age Making a Whirlwind Crankcase Successive Steps in Machining the Castings for a Nine-Cylinder Wright Engine—Multiple Operations Performed Simultaneously or in Sequence BY FAY LEONE FAUROTI ANUFACTURE of the Wright crankea bevit ast astings, which are performed on a 36-in. Bullard \ in the foundry with the act of making an as vertical turret lathe, are as follows: sembly of the cores in the mold. Due to th tricate form of some of these aluminum-alloy ca } ; } } | ’ ce re ‘ { n flat ( ) ) % of the utmost importance that all cores be prope poug ; Ax SCCUON Te AD In. 1FO™ } 1 é r } ( (eh } ' thickne laced and the molds be well ve