The Iron Age 1930-02-13: Vol 125 Iss 7

THE New York, February 13, 1930 ESTABLISHED 1855 VOL. 125, No. Production Stoves machine shop appren- ticeship was served the Detroit plant the Olds Motor Works, long brick struc- ture, the walls which ran paral- lel those stove works. From bench could look across through the windows into the as- sembly floor the stove company. Here dark rooms, ill lit, black masses took shape and the prosaic business constructing various kinds heaters went on. boys working automobile shop, those days considered quite romantic the airplane today, looked with patronizing pride the stove business uninteresting laying brick. But progress the law. person nor thing can hope escape it. Prosaic though stove manufacture used be, tied vitally with our everyday life. helps supply food and comfort. Food and comfort are necessities, but when they were once obtained, what more was necessary? thought our *Mechanical engineer, New York. Virtual Elimination Hand Work Between Press Room and Assembly—Circular- Hearth Furnaces Enameling FAY LEONE FAUROTE* ancestors. Black drab clothes, colorless, weatherbeaten houses, dull lives! what value after the essentials were furbelows, colors and concealments? reasoned also some the stove manufac- turers. Their business receded ac- cordingly. Finally progress com- pelled change. The rising wave color, the demand for beauty form well substance, made change interior decoration im- perative. reached even the kitchen. Furthermore, due mass production, prices other things began come down and quality up. Still the stove business remained stationary except for nor- mal seasonal increases. Then something happened. had to. Today, how different! Step into modern stove fac- tory, the Detroit Vapor Stove Co., Detroit, for example, learn how all has been changed: color, light, electric fur- naces, automatic conveyors, straight-line production, stand- ardized models and attention niceties design and harmony form quite comparable the motor car. was expected that such revolution stove Straightening Caterpillar Conveyor Upper Floor No.3 Electric Electric Electric Chamber Furnace Conveyor Bench Here Belt Layout the Enameling Department. Material entering lower left passes through successive oper- ations shown arrows, leaving upper left for assembly department 493 ? 3 q Pickling Conveyor, Which Dips the Parts the Tanks Succession and Then Raises Them for the Next Move manufacture would occur Detroit, where everyone, even the boys the street, familiar with the principles mass production and straight-line manufacture, which are widely employed the manufacture motor cars there. Almost all the parts the modern stove—those not cast—are made sheet steel and enameled. Sections composing modern gas stove structure are pressed usu- ally from iron; some parts from Monel metal, account its non-corrosive character. First operations are course performed the usual manner. There nothing widely different this fabrication from that hundreds other parts made other shops. There the the Press Department, Which Immediately Precedes Pickling, the Various Sections Are Accurately Formed 494—The Iron Age, February 13, 1930 usual careful planning stock save waste, treatment stock with pressing compound before the draw, and the usual allowances for the proc- ess, etc. Beyond this point, however, straight-line mass production begins take hold. First, interest the con- sideration this process know that the porcelain-enamel used coating the sheet metal for stove manufac- ture the quality true porcelain. has the hardness, the difficult fusi- bility, translucency, and whiteness body which come only when Kaolin, very pure white clay, mixed with finely ground felspathic rock. Fur- thermore, its fusion requires high temperature and its integrity, dust- less oven. early the fifteenth century was found that enamel could ap- plied directly plates. After one coat had been fused the surface the metal, another could superim- posed and fused the first layer with- out any danger separation from each other from the metal ground. But this process has been still further refined. The metal here chosen for the base Armco ingot iron, metal which slightly porous and relatively free from alloys which would prevent proper fusion the enamel the base. was discovered that the final quality the surface was dependent also upon the skill with which the firing process was carried on, the length the burning time, the degrees temperature, the constancy temperature, and the fuel used. first the ordinary muffle type furnace was thought perfectly satisfactory. But later was realized that the firing process was largely the mercy the operator, who many times was ill fitted training experience perform the operation correctly. The type fur- nace, too, affected the result too much. The length time the door was kept open for charging and discharging disturbed the constancy tempera- ture. Furthermore, when this type furnace was used, the parts were brought too suddenly the intense heat necessary for fusing the enamel the metal and, conversely, was sub- jected too quick cooling process. Obviously, then, the type fur- nace used was one the great vari- ables—sources waste—in the proc- ess. So, after months careful ex- perimentation, the engineers the Detroit Vapor Stove Co., working with the Holcroft furnace experts, designed the rotating circular furnaces now use. Each furnace uses about 201 kwhr. hour pressure 220 volts. Their adoption automatically insured the regulation several im- portant factors, safeguarding the integrity the firing process. They make certain uniformity product deemed impossible under the old system. The length time fir- ing controlled not the operator al | t * but the speed with which the hearth revolves. The speed regulated according the thickness the metal which being fired, the heavier sheet steel requiring longer firing time than the lighter. The temperature can main- tained constant, this being controlled rather complex thermostatic arrangement. the hearth pins are not al- lowed cool, the parts can laid upon them without the damaging and buckling effects that otherwise might occur were necessary reheat them each time. Furthermore, End Pickling Conveyor (Be- low) Parts Are Removed and Dipped, Then Hung the Chain Conveyor (Left, Below) Pass Through Furnace. circle one the spray booths skilled furnace tenders are not needed, the variable fac- tors firing operations are controlled the shop fore- man, man trained the knowledge proper enameling Furthermore, was discovered that such type continuous furnace fits perfectly into continuous system conveyor production. When begun, this straight-line stove production was piece pioneer work, but today has passed its experi- mental stages and has fully justified its installation. This how operates: essential for proper enameling that all pieces absolutely clean. Hence, with the mechanization the process, became necessary arrange for the passing the parts they come from the press room through the several cleaning, acid, neutralizing and rinsing tanks, five all. The solutions the pickling tanks are: Oakite, hot- water rinse, muriatic acid, soda ash and cyanide, borax. These pickling and washing operations function automati- cally. The parts are hung suspended hooks baskets pendant from long steel rods, in. diameter and ft. long, which extend horizontally across between two heavy roller chains, forming conveyor. Like similar one the Ford Motor Co., the entire mechanism, tanks and trav- eling parts, are inclosed well ventilated, fully acces- sible, glass-sided corridor. The conveyor runs con- stant speed 140 ft. hour and has ample capacity take care present production schedules and more. The time that each the parts immersed the The Iron Age, February 13, ar fur- ari- with 201 220 im- the t the fir- 3 washing solution, acid neutralizing solution gaged the horizontal distance travels through the tank. When the part reaches the end the corridor, has been washed all over, its surface freed from grease spots and acid, thoroughly rinsed and dried. ready for its ground coat blueish enamel. Taken from the pickling conveyor, dipped imme- diately and set vertical rack, series which form the conveying units endless belt conveyor the monorail type. These pressed steel parts then pass, this conveyor, through drying chamber, circulating back and forth six times, distance about 180 ft. The temperature the drying chamber about 125 deg. Fahr. Emerging, they are given spray black edge, and having arrived the open hearth the first electric fur- nace are taken off and laid horizontal position upon Withdrawing Piece from Rotary Furnace. right operator the charging door. The piece cooled the conveyor the vertical pins extending upward the revolving hearth the furnace. For enameling metal work such that used for doors, sides and various other sections the mod- ern gas stove, three coats are specified, first ground coat and then two coats white colored porcelain enamel. fusing burning process required between each coat and the next. The porcelain-enamel made glass frit (providing the base), clay, tin oxide, magnesia, certain composition No. 19, and water. The oxide regu- lates the color the enamel. These unique furnaces are the electrically heated rotating type, similar some the heat-treatment fur- naces found many automobile plants. They consist eter, lined with firebrick and provided with two openings the front the furnace; one for the introduction recently coated part, the other for the removal the fused unit. Inside the furnace, supported steel framework, rotating table firebrick whose upper surface are projecting, vertical pins heat-resisting metal. Upon these the ware laid for burning. The outside diameter the hearth measures 175 in. and the inside 113 in. There burning area approximately 14,024 sq. in. The 496—The Iron Age, February 13, 1930 average time required for one revolution the furnace hearth min. for the finishing coats. Twelve sets chromel-ribbon elements, placed around the rear half the furnace directly above the parts fused, heat the interior temperature about 1650 deg. Fahr. This temperature pyrometically controlled. Using electricity for heating, temperature control simple and accurate. The speed the rotation the hearth also quite capable easy alteration and control. Such furnaces have proved great improvement over the old type muffle furnace, even the electrically oper- ated They have other advantages: cold parts are introduced into comparatively cool zone. They may heated toa maximum temperature without distortion buckling. After passing through the hottest area, where the fusing takes place, they can begin cool slowly until they reach the exit. Most the parts are flat. They lie placidly the tops the vertical pegs and are heated thoroughly and uniformly. the hearth continually rotating, these pins never change materially temperature. passing interesting note that such heat may escape through the mouth the novel form hood and forced blower into the drying chambers alongside, thus conserving much which otherwise might wasted. After the fusion one coat takes place the part taken out sliding long two-pronged fork under the flat piece and placing the surface corrugated metal caterpillar tractor conveyor table alongside. the time the piece has reached the end this mov- ing bench, the top which slightly below waist level, asbestos-gloved workman the other end. This man sets again one the pendant vertical racks second monorail conveyor. This pursues back and forth looping course about ft. and automatically delivers the part station where again inspected and sprayed. After passing the spraying booth the conveyor enters second drying room. Finally, after brushing, the sheet-metal part placed furnace No. and burned temperature 1550 deg. Fahr. Removed from the rotat- ing hearth, put through duplicate process, given second coat porcelain enamel, third drying journey, third furnace rotation, third cooling before, final inspec- tion, the part ultimately delivered belt conveyor which transports the finished components the assembly line racks upstairs. course, for some the smaller, irregularly shaped parts, small pieces sheet steel, also burners and grates, this conveyor system straight-line production not well suited. take care these economically requires that they handled separately. has been found more efficient treat them straight-line type muffle furnace, for which, because its cleanliness and heat con- trol, electricity used heat. | ij al | tL —— — we we er UFFLE- Type Fur- nace Used for Some the Work. Ade- quate tion provided the hood the use the continuous conveyor system and the electric furnaces the human element has been almost en- tirely eliminated. not necessary use skilled labor. The parts need little manual handling and hence come through with fewer defects. not necessary rack them between operations. time lost, transporta- tion and burning and transportation and drying are now combined operation. storage takes place until after the final inspection. the case some parts, the scrap and pieces requiring rewashing respraying has been reduced low per cent. rarely goes above per cent under any conditions. Five different sizes ranges are produced. pos- sible combinations, however, from these five sized designs there may assembled stoves with without heat con- trol, with right left ovens, etc., that some differ- ent types can supplied this way. once appar- ent that standardization manufacture and simplification design, based actual domestic requirements re- vealed house-to-house canvass, have made possible for the engineers this company introduce into their stove business form mass production fully efficient that vogue Detroit’s automotive plants—and the balance sheets show it. | RA The plant the Detroit Vapor Stove Co. two-story structure brick, steel and concrete, about 700 ft. long. The fabrication process just described occupies all the first floor, with the exception that devoted the machine shop, die-room and storage. The entire second story devoted the assembly and packing line, with small corner reserved for drafting room and offices. 1000- ft. conveyor track bent run two parallel sec- tions, with semi-circular roller table between, takes the greater part the second floor. The space between the arms the about ft., and racks and piles material extend either side the section where the assembly begins. Assembly jigs benches, upon which the first four progressive operations take place, head the line. Here the main elements the stove are brought together. Formed accurate benches, which insure trueness the base angles, and designed receive the five sizes, the “chassis” the stove here lined up, bolted together and started its final assembly journey. the final process line the Ford Motor Co., the needed components are stored immediate proximity the conveyor and are added the assembly passes. The conveyor the simple, moving-platform type and , Sub-Assemblies Doors and Fronts, Made Benches, Are Then Passed the Assembly Conveyor Right The Iron Age, February 13, 1930—497 le, ne 4 possible for the workman reach all sides the stove with ease. Each man performs two three operations and, although the track capable accommodating maximum production approximately 500 stoves hr., there crowding either stoves men. the time the growing stoves reach the roller cross- over the track, they are complete with the exception heat controls, grates, burners and oven linings. These are put later, after the stoves start down the other side. Finally, hose leading from gas main pulled down tester, fitted quick-connection device, all the burners lighted and the heat controls adjusted. soon the stove pronounced fit every detail, the crating begun. The base angles the stove are bolted the crate bottom, the burners wired the burner rods, the sides and top the crate nailed on. then stenciled, checked and carried truck the fast ship- ping conveyor that extends the length the factory. The sequence assembly operations follows: Base angle; burner box bottom; burner box back; drawer slide; burner box end; burner box bottom cover; lower oven side; oven back; oven end; flue pot; drip pan rests; side panel; back panel; top rail; bracket; oven top; shelf top; oven front (doors, manifold; oven linings; heat control; burners; testing operations; accessories (drip and broiler pans, grates, etc.); crating. flexible the method assembly that only about two weeks advanced planning needed insure contin- uous assembly standard models. Furthermore, special jobs short orders can handled adequately between. maximum two days required from the time any one large order received, until those stoves are com- pletely fabricated and loaded the cars, ready for ship- ment. admitted, course, that the best results por- celain-enamel plant come from the continuous production 1000 more identical parts. the press department lot 5000 more from the same die economical and desirable, yet flexible the process, both fabrication and assembly, that this stove company remarkable suc- cess has been achieved sales demands calling for wide EAVING the Third Ro- tary Furnace Parts Receive Final Inspection and Then Upper Floor Belt Con- veyor, for As- sembling. Final Assembly, Benches, Shown Circle diversity types, sizes and colors. Production and inven- tory controls, therefore, not offer such serious problems are found many other institutions where variety cannot easily controlled. Inert Materials and Coking Power Coal has been observed that pieces mineral matter coal charged into coke-oven often appear the coke their shape and can picked out from the coke without much trouble. This indicates that the coke or- ganic matter not firmly cemented the mineral matter. explanation suggested for this that the fused matter from the coal, which causes the whole mass become plastic during the early stages coking, does not “wet” the minerals thoroughly the infusible organic matter the mass, hence this inert matter coal would there- fore expected have greater weakening effect the Age, February 13, 1930 coke made therefrom than organic inert matter such mineral charcoal. Evidence support this reasoning has been obtained recently the Pittsburgh Experiment Station the United States Bureau Mines. the course work the agglutinating coking power test coal, wherein electrode carbon was compared with sand diluting agent, was found that cokes made with sand were weaker than those made with carbon the ratio 1.4; particles the same size were proportioned weight each case. q 7 on | d | q inven- oblems variety such btained the wherein diluting were 1.4; eight X-Raying Large Steel Castings First Large Scale Attempt the Examination High-Pressure Steam Fittings DR. ANCEL ST. JOHN AND HERBERT ISENBURGER* industrial field, applications which were carried out Dr. St. John’s laboratory Long Island City, Y., have been discussed former the purpose this article give further information, includ- ing some about the X-ray inspection heavy cast steel pipe fittings for high pressure service, some which were recently examined the job” instead the labora- tory. useful applications X-ray inspection the Castings for 1200-Lb. Pressure Steam Plant order sure sound steel castings for 1200- lb. pressure steam plant, the owners new station and their engineers decided have these castings X-ray in- spected before putting them into service. several the fittings weighed more than tons each was decided carry the inspection place better equipped than the home laboratory for handling such heavy objects. Ac- cordingly, the high potential power plant was transferred suitable location near the steam plant. After comple- tion the inspection, the equipment was returned the home laboratory. This the first time the history Fifth Avenue, New York. tAncel St. John, Ph.D.: “X-Ray Examination Irregular Metal Objects,” Mining and Metallurgy, August, 1923; “Steel Castings and THE IRON Sept. 24, 1925; “X-Ray Inspection Fuels and Furnaces, September, Herbert Isenburger: “X-Ray Inspection the Machine Shop,” Machinery, May, 1928; “X-Rays and X-Ray Inspection Piping,” Heating, Piping and Air Conditioning, June, 1929. Temporary Installation the Plant for Examining Large Steel Castings Incorporated 1200-Lb. Pressure Steam Plant the art that X-ray equipment, powerful enough examine steel 3-in. thick, has been used transportable unit. One illustration depicts the temporary installation the plant “on the job.” The X-ray tube lead- lined box within sheet iron case directly over the cast- ing under investigation. The photographic films are placed special cassettes carrier which can seen projecting from the end the casting. The X-rays thus pass through the wall and make shadow picture which shows the location and nature any serious defects. During exposure the casting surrounded lead- covered housing prevent X-rays from going where they are not wanted. The casting and housing travel along tracks under the tube. How the Current for X-Rays Was Produced The 200,000-volt direct current produced special transformers and rectifiers within sheet iron room just behind the control stand. The high potential equipment thus completely surrounded grounded metal shield. The high potential power plant, within the sheet metal house, shown another illustration. Still another de- picts large manifold mounted for examination re- gions indicated the white stripes, with the lead housing rolled back out the way, while further illustration shows the housing position for exposure. For the complete examination fitting this size approximately 125 X-ray pictures are required, consuming The Iron Age, February 13, q m- a or- ion ind ion uc- ide the Ro- eive tion loor As- ibly, ircle q (Above) X-Ray Picture the Shrinkage Crack Shown Above Illustration. (At Left) Clear-Cut “Shepherd’s Crack” 3-In. Ell Casting. represents cold crack starting from small inclusion, developed hydrostatic test which had been passed successfully. (At Right) about hr. actual exposure time and least hr. for arranging the casting and placing the films. The development films and the loading cassettes are done while exposures are progress. Smaller fittings require correspondingly shorter times. For instance, the 6-in. tees averaged about hr. each. X-Ray Pictures Hard Reproduce Very few X-ray pictures sound steel have been pub- lished, probably because they usually show nothing special interest. attempted reproduction one rep- resents such picture made “on the job.” The rectan- gular dark patch with the number 3.5 lead marker identifying the area examined. The parallel bands are screw threads cut the inner surface. The light spot the lower right-hand corner not defect but the inner end hole drilled through the wall. X-ray tests, confirmed sectioning other collateral analyses, indicate that undesirable internal conditions fall into relatively few classes, all traceable Reproduction X-Ray Picture Flawless Casting. Light spot one corner the inner end hole drilled through the wall (at Left); Double Exposure Sand Pocket (at Right) 500—The Iron Age, February 13, 1930 4 ~~ ‘ 4 - 4 “a - 7 | definite and simple causes. Most these causes, not The principal undesirable conditions are the following: all them, can eliminated proper foundry practice. Gas, slag and sand pockets due loose dirt the Experience shows that when chronic defects have been mold. corrected making the indicated changes casting Gas cavities due imperfectly deoxidized metal. technique, they tend stay corrected. possible thus Sand inclusions due cutting mold runners. eliminate from per cent the major defects. Pipe primary shrinkage caused failure risers *Much valuable information about X-ray inspection con- function intended. Metal Castings,” 15-29, published recently the American Secondary pipes caused flow viscous metal Society for Testing Materials. The authors will glad sup- through constricted channels the casting during ply copy any one specially interested. the final stages solidification. ARGE Manifold Steel Casting Mounted for Exami- nation with X-Rays. White stripes indicate regions for examination (Upper Left). Manifold Position for Examination (Above) Shrinkage cracks starting from cavity de- veloped during cooling. Rupture developed during hydrostatic test. Some typical pictures, selected chiefly from work the home laboratory, illustrate some these. Cause Hardness Steel Professor Albert Sauveur Harvard University has published American Philosophic Magazine (Vol. 66, page 267) statement his beliefs the cause hardness quenched steels, which may summarized follows: Austenite supercooled solid solution iron carbide carbon gamma iron. Troostite supersaturated solu- tion iron carbide alpha iron. Martensite inter- mediate form where troostite precipitated along the octahedral planes the austenite crystals, thus forming true Widmanstatten structure. Hardness martensite due inherent property the Widmanstatten type structure, its fineness, and the hardness both the alpha and gamma phases. Severe internal strains may also High Potential Power Plant for Gener- ating X-Rays, Surrounded Grounded Metal Shield contributory cause. The Iron Age, February 13, 4 dq Alloy Steel Sheets for Aircraft Chrome-Molybdenum Thin Sheets for Heavy Airplanes— How They Are Made—Physical Properties and Heat Treatment—Effects Welding JOHNSON* HEET steel one the very important materials used the airplane manu- facturer. can fabricated into practically any form for the main structural members well for fittings join these members to- gether. Sheet steel for structural members must thin—often less than 0.030 in. thickness. Its use has been retarded the lack suitable methods joining. The development mechanical methods welding means the oxy-acetylene flame electric resistance welding may assist overcoming this difficulty. material for highly stressed fittings sheet steel pre-eminent. Plain carbon steel satisfactory for low- powered, light airplanes, but alloy steel with its high physical properties will show worth while saving weight for the larger types. The alloy sheet steel which has been used most generally chrome-molybdenum steel conforming the analysis the alloy steel tube which has been adopted standard the airplane in- dustry. Three Types Are Used considerable quantity this steel has been used the cold-rolled condition. The average physical properties for this grade are shown Table has also been used the annealed condition where the only physical re- quirement bend 180 deg. over one thickness. third type hot-rolled normalized sheet with ten- sile strength 85,000 100,000 per sq. in., but with ductility which varies considerably and, consequently, the fabricating qualities are poor. order meet the need for sheet steel which can fabricated into fittings (Figs. and and then welded without serious loss tensile strength, special grade chrome-molybdenum steel has been developed which has several advantages over those grades now use. The chrome-molybdenum sheet, after welding, should have physical properties equivalent the tube the same analysis. The unit strength chrome-molybdenum tube the annealed zone distance in. from the seam has minimum value 80,000 lb. per sq. in. fine-grained annealed sheet steel with minimum tensile strength 90,000 lb. per sq. in. will not lose more than per cent this strength after welding; therefore, will meet this minimum re- The steel must also have satisfactory fabricat- ing qualities and high resistance vibration. These properties are determined the ductility indicated the tensile and bend tests. The chrome-molybdenum sheet steel which has been *Chief, branch, War Department Air Corps, Dayton, Ohio. 502—The Iron Age, February 13, 1930 developed hot-rolled product. made rolling 20-in. ingots into bars about in. wide and from thick. These bars are cut the length required roll the size sheet specified. They are hot-rolled side- ways sheet with thickness about 5/16 in. This sheet then reheated and hot-rolled the finished dimen- sions. This final rolling done with the sheet angle deg. the previous rolling. This cross-rolling gives approximately equi-axed grain and therefore gives equal physical properties both lengthwise and crosswise the sheet. After the final roll- ing, the sheet may heat-treated short annealing operation just above the critical temperature, longer box annealing below the critical temperature. The physical properties are dependent both the amount reduction and the subsequent heat treatment. surface finish obtained pickling satisfactory for laying out fittings. Before electroplating applying enamels lacquers advisable sand-blast. Average Physical Properties Average physical properties and chemical analysis for sheets varying from 0.039 0.250 in. thickness are given Table II. The analysis the finished sheets con- forms closely the heat analysis. designated X-4130 inasmuch the manganese and chromium requirements are lower and higher, respectively, than specified for S.A.E. 4130. The tensile strength sufficiently high meet the re- Fig. 1—Sheet Metal Lugs Welded Tubular Structures # te Fig. 2—Typical Welded Fittings quirements for large number fittings and will permit considerable saving weight over carbon steel with tensile strength 55,000 per sq. in. The proportional limit was obtained from stress-strain curve plotted from points taken with Ewing extensometer graduated 0.0002 in. The extensometer was attached the specimen with one point and one disk opposite sides the sheet. The load was applied the rate 0.05 in. per min. the yield point. The yield point was taken observing the lag the pointer hydraulic testing machine. This material has sufficient plastic flow that this method gives satisfactory results. Elongation partial measure the fabricating properties, but must combined with the bend test. The quenched and drawn alloy steel with per cent elon- gation may crack bend test, whereas the same steel the annealed condition and with the same elongation will not crack. The elongation will also vary considerably with the thickness the sheet and the form test speci- men. 0.040-in. sheet with elongation per cent the crosswise direction will fabricate well 0.250- in. sheet which has elongation per cent. The relationship between three test specimens shown Fig. and Table III. These data were obtained that would possible interpret specification requirements the terms the test specimen which may conve- nient use. desirable have one standard form test speci- men and the aircraft industry has generally adopted that shown Fig. 4-a for thin sheet metals. Since only ma- chines with large capacity are available some mills, may necessary use large specimen with greater area order obtain more accurate readings the beam. The general relationship between the elongation gage length and area given Bertella’s equation for the logarithmic curve shown Fig. The form this curve is: where: Percentage elongation from the curve from the curve L=Gage length cross-section the elongation specified for certain test specimen, comparatively easy calculate the required elonga- tion any other form test specimen using this equation. The bend test sheet steel good one for determin- ing the ability fabricated fittings resist failure under vibrating stresses. examination several fittings carbon and alloy steel which had failed service has indi- cated that the bending properties were poor. The actual bend the fitting may have been only from deg. but, due the low bending qualities the steel, over- strained condition was caused the stretch the ma- terial the outside the bend, with the result that small cracks, invisible under ordinary visual inspection, were started and under vi- bration rapid failure re- sulted. sheet steel which will bend 180 over one thickness will not have this overstrained condition deg., which very often made fittings. The method making bend test quite important. The bend should full 180-deg. bend and made the following manner. strip cut from the sheet and the edges are rounded emery wheel with file prevent the formation edge cracks. The strip then bent machine, and strip the same sheet about in. wide placed the inside the bend. The bend then com- pleted forcing the two legs the test specimen flat the strip, illustrated Fig. The strip must show cracks the outside the bend. This test should made specimens cut with their axes parallel both the long and short edges the sheet. Microstructure and Heat Treatment The microstructure shows fine-grained structure com- paratively free from grain distortion due the hot-roll- ing. The heat treatment does not remove all traces the rolling, however, etching the surface the sheet with sulphuric acid solution shows the flow lines due the final rolling. There was surface decarburization. The changes structure due reheat treatment are Per Cent Elongation Per Cent n Elongation 0.050 0200 0250 the Percentage Elongation for Three Types Test Specimens. The lower graphs show the elongation and in., respectively, and the upper graph the elongation in. The Iron Age, February 13, Table I.—Physical Properties Cold-Rolled Sheet Proportional limit, Ib. per sq. 50,000 Yield point, Ib. per sq. in......... 65,000 75,000 Elongation in. per cent........ 25, depending upon thickness and amount Bend reduction cold-rolling. ness for sheets in. and 125 deg. for sheets and including in. Tensile strength, per sq. in..... 65,000 85,000 slight and scarcely detectable with the microscope. The microstructures shown Fig. were taken sheet be- fore and after annealing improve the bending proper- ties. slight grain refinement indicated the sheet annealed 1400 deg. Fahr., which just above the criti- cal temperature. Fig. 4—Dimensions Sheet Steel Test Specimens Length, in.—a........ 8.000 10.000 18.000 Length, in.—b........ 2.625 4.750 10.000 Length, 2.25 4.250 9.250 Gage length, in—d... 2.000 4.000 Width, in.—w........ 0.500 0.750 1.500 Width, in.—f......... 0.750 1.000 2.000 Radius, 0.500 0.500 0.750 Reduced approximately 0.005 in. width middle gage length. Chrome-molybdenum sheet steel has very satisfactory properties after heat treatment. The quenching tempera- ture varies from 1600 1650 deg. Fahr. The steel may quenched either oil water. Oil preferred where the parts are welded built parts different thick- nesses. thin sheets, such those used aircraft, the physical properties are not affected appreciably the dif- ference the quenching mediums. air quench will often give sheet which has tensile strength greater than 150,000 lb. per sq. in., but the results are not uniform with the liquid. Average physical properties after heat treatment are shown Table IV. The ratio yield point tensile strength practically constant about 0.92 for all thick- nesses and the three drawing temperatures. The ratio proportional limit tensile strength quite erratic, but general the water-quenched specimens show higher value than the oil-quenched. The tensile strength and yield point with various drawing temperatures are not af- fected the thickness. The elongation, however, again dependent upon the thickness and increases rapidly with sheets varying from 0.064 0.250 in. Welding Properties Satisfactory The heat the welding operation will cause decrease physical properties the zone which has been heated just under the critical and cooled air. This loss, how- ever, was confined less than per cent the original tensile strength for all thicknesses sheet. The average results several tests made welded specimens are shown Table These results are from both plain butt welds and welds. The welds were made with both low- carbon welding wire conforming the specification the American Welding Society, No. G-la, and with chrome- molybdenum steel welding wire the same analysis the sheet except for the carbon content, which was 0.15 per cent. For the unheat-treated welded joints the low-carbon wire entirely satisfactory and preferred inasmuch the weld metal more ductile than that deposited with chrome-molybdenum rod. the case heat treatment where high strength desired the weld metal, chrome- molybdenum rod gives good results. the case heat- treated welds care must exercised that there complete fusion the weld metal into the corner the abutting sheets case weld and that the fillet built that the shearing stresses the weld metal are not Table Analysis and Average Physical Properties for Special Chrome-Molybdenum Sheet Steel Lb. per Sq. In. 1000 Elongation In., Rockwell Chemical Analysis Propor- Per Cent Hardness Thickness, tional Yield Tensile Bend, Man- Phos- Molyb- In. Limit Point Strength Deg. Carbon ganese Sulphur phorus Chromium denum 0.039 105 180 0.33 0.58 0.018 0.017 0.91 0.24 0.062 100 101 180 0.31 0.58 0.017 0.017 0.92 0.2 0.124 101 180 0.30 0.58 0.015 0.015 0.96 0.25 0.250 180 0.31 0.59 0.016 0.018 0.98 0.21 Table Shape Specimen Tensile Properties Lb. Per Sq. Lb. per Lb. per In. 1000 Elon- In. 1000 Blongation, In. 1000 Average gation, Per Cent Per Thickness, Yield Tensile Yield Tensile Yield In. Point Strength Per Cent Point Strength In. Point Strength In. 0.039-L 88.0 102.0 14.0 87.0 106.0 15.5 12.0 95.0 109.0 18.0 14.0 10.5 0.062-L 80.5 100.0 16.0 80.0 99.0 17.5 12.5 81.5 101.0 21.0 16.5 12.0 0.124-L 76.0 98.0 19.5 78.5 99.5 22.0 15.0 72.5 93.0 25.0 18.0 13.0 0.250-L 61.5 94.5 26.5 61.5 94.5 29.5 20.0 60.0 91.0 34.5 23.5 17.5 0.039-X 87.0 99.0 12.0 93.0 107.0 9.0 7.5 89.5 104.0 14.5 11.0 8.5 0.062-X 87.0 102.0 14.5 81.0 101.0 15.0 12.0 79.5 102.0 18.0- 15.0 11.5 0.124-X 77.0 102.0 18.5 76.0 98.0 20.0 16.0 79.0 23.0 15.5 12.0 66.0 100.0 23.0 59.0 92.0 28.0 19.5 60.0 89.5 36.0 25.0 17.5 L—Lengthwise—Axis specimen parallel direction final rolling. specimen perpendicular direction final rolling. 504—The Iron Age, February 13, 1930 Table IV—Average Physical Properties After Heat Treatment Quenched Quenched Oil 1625 Deg. Fahr. Water 1625 Deg. Fahr. Thickness, In. D-650 D-900 D-1100 D-650 D-900 D-1100 Proportional limit, lb. per 160,000 140,000 130,000 170,000 130,000 125,000 Yield point, per sq. in...... 192,000 150,000 140,000 199,000 157,000 143,000 Tensile strength, per sq. in. 210,500 166,500 150,000 210,000 168,000 153,000 Elongation in., per cent... 2.5 5.5 7.0 2.5 5.5 6.5 Rockwell “B” 117 114 120 117 114 Proportional limit, Ib. per sq. 0.064 165,000 135,000 110,000 160,000 140,000 130,000 Yield point, lb. per sq. in..... 194,000 156,500 134,500 195,000 157,500 138,000 Tensile strength, per sq. in. 215,000 168,000 146,500 212,000 168,000 151,000 Elongation in., per cent... 4.5 6.5 9.0 4.0 6.5 8.5 Rockwell “B” hardness....... 118 117 114 120 117 114 Proportional limit, lb. per sq. 0.124 150,000 130,000 120,000 140,000 125,000 120,000 Yield point, per sq. in...... 206,000 156,000 139,000 191,000 157,000 134,000 Tensile strength, per sq. in. 222,000 169,000 148,000 202,000 170,000 146,000 Elongation in., per cent... 6.0 8.0 11.0 6.0 10.0 Rockwell hardness....... 122 118 115 120 117 114 Proportional limit, lb. per sq. in, 0.250 140,000 110,000 110,000 170,000 150,000 130,000 Yield point, lb. per sq. in...... 204,000 160,000 141,000 204,000 165,000 141,000 Tensile strength, lb. per sq. in. 222,000 175,000 150,000 229,000 178,000 149,000 Elongation in., per cent... 9.0 14.5 9.0 12.5 Rockwell “B” hardness....... 118 115 117 114 Oil and water about deg. Fahr. Time furnace, min. All specimens cut lengthwise. Standard 2-in. specimen. Proportional limits taken from stress-strain curves inspection. Table V—Average Tests Welded Specimens Tensile Strength, Lb. per Sq. In. Thickness Before After Welding Sheet, Welding In. Average Average Maximum Minimum 0.250 92,000 91,000 95,000 85,000 0.125 98,000 87,000 97,000 82,000 0.039 105,000 90,000 104,000 82,000 more than per cent the tensile stresses the base metal. specification for this material should include the fol- lowing technical requirements: The grain size shall fine and uniform all parts the sheet. The sheet shall not decarburized point that the physical properties are affected. The finished surface shall free from any scale that would interfere with the laying out fittings. The sheet shall conform the following chemical analysis: 0.040 The sheet shall have the following physical Tensile strength (min.), persq.in. 90,000 Yield point (min.), Ib. per sq. Elongation in. (min.), per cent: Sheet thicker than in.......... Elongation Per Cent Ratio Fig. Relationship Between Elon- gation Gage Length and Area Given Bertella’s Equation Sheet less than in............ Rockwell hardness “B” scale, Bend test: The sheet shall withstand bending cold without fracture the outside the bent portion angle 180 deg. for sheets less than in., and 135 deg. for sheets thicker than in., over diameter equal the thickness the material. The elongation specified for test specimen with gage length in. and width in. Fig. 6—Typical Bends Properly Treated Sheet Specimens (Left) Sheet 0.093 in. Mag: 500 Etch: Nital Hot-rolled, finishing temperature above critical. Tensile strength, per sq. in. 118,000 (Right) Annealed 1400 deg. Fahr.—5 Min. Tensile strength, per sq. in. ....... 106,000 Blongation, per 14.5 The Iron Age, February 13, — | Various Steels Are Used for Gears Oil-Hardened Gears Are Usually Chromium Steels; Case- Hardened, Nickel Treatment for Rapid Production Machine Line DEUBLE* REVIEW gear styles shows that practically all analyses are being used have been used the past. When one considers the large number gear applications, not surprising that many types steel have been used. know the history back some these applications. some cases certain analyses are adopted because the success competitor with that par- ticular analysis similar application. many in- stances the metallurgy well founded and apparent. This discussion will limited small gears such used the automotive industry for transmission and dif- ferentials. Gear steels can divided into two classes: (a) the full-hardening and (b) the carburizing grades. The former are usually chromium steels modification, while the carburizing grades are nickel steels modi- fication. Effect the Principal Alloys Chromium added iron forms solid solution, but upon the addition carbon, complex carbides are formed. Chromium raises the Ar, and points. Chromium steels also have the peculiar characteristic that the higher the initial temperature which the steel heated, the lower the critical points are depressed, hence the higher the tem- perature used, the easier the steel harden. However, this has its limitations because the narrow quenching ranges, which produce fine fractures. Chromium intensifies the action carbon, increasing the elastic limit and tensile strength. also increases the depth penetration and when heavy sections are involved this property very valuable. These steels are capable great hardness, and resist abrasion and deformation, but high hardness induces certain amount brittleness. Chromium carbide has slow solution rate, hence pro- longed times heat high temperatures are necessary when heat treating these steels insure thorough solution. Chromium steels have large economic value their favor and, would expected, are used extensively gear work. Chromium steels for carbon from 0.30 0.55 per cent, the largest proportion having 0.47 0.52 carbon and 0.80 1.10 chromium. Nickel also forms solid solution with iron and the presence carbon does not affect this solid solution forming carbides. Nickel increases the elastic limit and tensile strength well resistance shock. Each per cent nickel lowers the critical points between and *Metallurgical department, Central Alloy Steel Corporation, Canton, Ohio. THe IRON AGB, Dec. 1929, page 1513. 506—The Iron Age, February 13, 1930 deg. Fahr., which very advantageous, results low quenching temperatures with less scaling and volume change. Typical Treatment Chromium Steel Gear blanks are forged under supervised control, the temperature being maintained under 2250 deg. Fahr. regulating the production that bar stock heated over this temperature, overheated forgings are eliminated. Lower initial temperatures result less scaling and hence forging with fewer scale pits. The majority the gear manufacturers prefer up- set gear blank, because the uniform grain Some metallurgists claim that flat forged gear per cent weaker transverse the direction rolling than the longitudinal direction. also felt that less distortion that the machining properties vary more flat forged gear than upset gear. One Microstructure “Best” hammer shop cannot maintain uniform finishing temperature necessary anneal normalize the forgings prior machining. With the oil-hardening steel this absolutely necessary because the blanks are too hard machine forged. preliminary work, various structures should produced which can put into the machine shop determine which one machines the most satisfactorily. This one place where proper metallurgy often offset shop practice. Gears must machined satisfactorily and economically and the best structure for final hardening may not the most easily machined. This particularly true the full-hardening grades. After the proper structure determined, annealing cycle must set produce this structure. chromium steels three distinct structures can produced with Brinell hardness 187. These are pearlitic, sorbitic and spheroidized, and are illustrated the accompanying micrographs. mixture these will result unless the annealing carefully regulated. Each these will have dif- ferent machining char- acteristics, and what satisfactory one shop not always suitable for another making the same product. These structures will also have effect the hardness and charac- teristics the final product. The big problem be- fore the metallurgist produce conditions | | | that uniform product always obtained. This im- possible box type furnace, because the cooling rate varies from the center outside pile gears. special annealing furnace can built and from this uniform product can obtained both regard structure and hardness. Machine Line Controls Details Production After the proper an- nealing cycle set and maintained, specific number gears should machined size. These should checked and marked for proper identi- fication before heat treat- ing. The gears should then heat treated under very carefully controlled and uniform conditions. The gears should re- checked for size, using the same procedure meas- uring the green gears, and all changes dimensions should noted. the sections are uniform the changes should regular. This regular change should not called distor- tion, because always ex- ists. uniform section changes dimensions irregular manner, this can termed distortion, and undoubtedly the re- sult non-uniform condi- tions somewhere during previous operations. the proper precau- tions are used keep con- ditions uniform the aver- age change all dimen- sions can obtained and allowed for machining upon production basis, but doing this work absolutely essential provide uniform conditions and accurate inspection dimensional changes. When heat treating the full-hardening gears con- siderable scale and decar- burization encountered; these retard quenching and the maximum hard- ness not obtained. Salt baths containing per cent more cyanide are very suitable pre- 2: DEAL Microstructures, Sorbite, Perlite, and Spheroidized Cementite, Respectively. All 100 diameters, etched with nitric acid vent scaling; long the cyanide content excess per cent decarburization occurs. Gears treated *Approximate analyses are follows: 5150 6150 3150 3250 2345 Carbon ...... 0.50 0.50 0.45 Manganese ..... 0.65 0.65 0.45 0.65 Chromium ...... 1.0 0.60 1.0 salt bath are clean and usually have superficial skin hardness which very advantageous for resisting wear. Immediately after hardening, all gears should drawn. ¢ “a + Temperatures between 475 and 700 should avoided chromium steels, gears drawn within this range are more brittle. This brittleness probably due the struc- tural changes, the austen- ite decomposing mar- tensite. uniform drawing tem- perature will also elimi- nate certain variables, be- cause steel contracts certain temperature and then expands. This ex- pansion also due de- composition austenite martensite. Are Transmission Gears Subject Shock? Chromium steel and its modifications, such chrome-nickel and chrome- vanadium, are used exten- sively. These full-harden- ing steels have fair re- sistance wear de- signed properly; this wear resistance further in- creased cyanide bath treatment. For light gears for pleasure cars, straight chromium steel gears are very satisfactory, but they not have great resist- ance impact shocks. About this point hinges very heated discussion, that is, “Are gears this type subjected impact?” For heavier work such truck and tractor gears, chromium steels are not suitable. carburizing grade should used be- cause the high tooth pressures, large amount gear work and the shock stresses service. “large amount gear work” meant the large percentage slow speed and second speed the to- tal mileage. pleasure cars this factor low. the full-hardening steels the following are 5150, 6150, 3150, 3250 and 2345,* the straight chromium steel 5150 being most extensively used. The chrome-vanadium steels (6150) have broad quench- ing range and slightly better resistance shock. The low chrome-nickel steel 3150 does not show better physical properties than the straight chrome steel, and increase the depth hardening and resistance shock the chro- mium and nickel must increased. The 3200 series nickel steels gives excellent results, but difficult The Iron Age, February 13, 1930—507 4 Wal 3 a a ene AQ q handle. Some manufacturers are using S.A.E. 2345, which has the highest impact values the full-hardening steels but better resistance wear. The latter two are used for large gears outside the automotive field. Advantages Carburized Gears Against the school which desires use the oil-harden- ing full-hardening steel