Fig. 6 Straight-sided lined cupola introduced after the middle of the 19th century. The first commercial cupola in the United States was the Colliau cupola, which was introduced in 1874. This cupola was prefabricated insofar as possible and was built primarily as a commercial product. It was highly successful, being a fast and economical melting unit. When first introduced, it presented a number of improvements, such as a hot blast, and double rows of tuyeres. After the Colliau cupola, the Whiting cupola was developed. It is still sold by the company bearing the name of its inventor, John H. Whiting. In the 1880s, Whiting developed a cupola that employed two rows of tuyeres, with the lower row arranged to form an annular air inlet that distributed the blast around the entire circumference of the furnace. The tuyeres could also be adjusted vertically for changes in classes of work, type of fuel, and cupola diameter. This cupola permitted the use of either coal or coke as a fuel and was equipped with a safety alarm and blast meter. The Whiting cupola, with its standardized construction, soon proved a boon to foundrymen and was widely accepted. Connellsville Coke The story of the cupola and cast iron in this period would not be complete without reference to the development of Connellsville coke. Coke was in general use in Europe in 1750, but because of the heavy timber resources of the United States, it was not produced here until 1817. From that time until 1860, American foundrymen generally made coke for their own use; after 1860, coke became a commercial product. Connellsville coke was first produced in 1841 at Connellsville, Pennsylvania, in beehive ovens. The product proved so popular that the demand for Connellsville coke remained high until 1914, when by product coke came into greater demand. The use of coke and bituminous coal was made possible by the introduction of the hot-blast furnace in 1828 by James B. Neilson of Scotland. At first, the blast pipes ran through the furnace. The pipes were later run through a charcoal oven, and finally they were placed on top of the furnace itself. This device increased melting output from 10 to 40% so that by 1869 the production of coke and bituminous pig iron exceeded that of charcoal pig iron, and by 1875 the use of coke pig iron alone surpassed that of anthracite pig iron. Chilled Iron Another American development of the mid-19th century involved the introduction of chilled-iron railroad car wheels. Asa Whitney of Philadelphia obtained a basic patent in 1847 on a process for annealing chilled-iron car wheels cast with chilled tread and flange. They were satisfactory as long as cold-blast charcoal iron was used. However, trouble developed when melting practice changed from the use of anthracite coal to the hot blast. In 1880, an attempt was made to introduce manganese for the production of chilled iron, but the resulting product did not possess adequate wear properties. Finally, a small amount of ferromanganese was introduced directly into the ladle with good results. Thus originated one of the basic products of the foundry industry--chilled car wheel iron. The excellent performance of this foundry product, as well as its wear resistance and economical properties, made possible the long- haul, heavier railroad freight loads of today. Malleable Iron No discussion of iron would be complete without mention of American blackheart malleable iron, as contrasted with European whiteheart malleable iron. Although credit for the progress and growth of the American malleable iron industry belongs to many, its origin lies with Seth Boyden of Newark, New Jersey. Boyden's experiments, beginning in 1820, were primarily based on an attempt to duplicate the whiteheart European product developed by French scientist R.A.F. Réaumur. Boyden was endeavoring to lower the cost of harness hardware and wanted a strong iron that could be easily machined. Because of a larger percentage of silicon than was available in the Réaumur process, Boyden was able to produce the strength, but not the white color, of the European product. However, Boyden (either by design or accident) had shortened the annealing time to 6 or 10 days. This left free temper carbon graphitization as opposed to Réaumur's decarburization. Boyden first used a crucible and then an air furnace with a capacity of about 450 kg (1000 lb). His annealing furnace was a beehive unit into which pots loaded with castings were lowered through the top. The beehive was eventually replace with a continuous annealing furnace having a sloping floor. This unit was known as a shoving furnace because the pots and castings were shoved in from one end and out the other. Boyden's work was important, but the most significant advances in the malleable iron field were made by the men who developed the malleable industry to its level of prominence in the foundry picture. More information on the manufacture and properties of malleable iron is available in the article "Malleable Iron" in this Volume. Cast Steel Next in the chronological sequence of casting developments is steel. For centuries, the goal of manufacturing steel castings in large quantities was pursued, but inadequate equipment was the limiting factor. In addition, steel was well known centuries earlier as the Damascus and Toledo sword blades of legendary fame, but this steel was forged from the pasty masses of iron produced in the Catalan forge. The first reliable record of steelmaking was the work of Huntsman in England in 1750. Huntsman's developments in crucible refractories (the crucible process) first produced steel that could be poured as a liquid. Steel castings are also said to have been discovered by Jacob Mayer, Technical Director of the Bochumer Verein, Bochum, Germany, sometime before 1851. Records of the Bochumer Verein Company, which is still engaged in producing steel castings, indicate that cast steel church bells were produced in 1851. Some of these bells weighed as much as 15 Mg (17 tons). Cast steel guns were also made at the Krupp Works in Germany in 1847. In all probability, much smaller steel castings were made before the bells were cast, because it is difficult to believe that such large castings would be attempted without considerable previous experience. The steel church bell castings were displayed at various expositions throughout Europe and created quite a sensation because of their fine, clear tones and the fact that their selling price was about half that of the bronze bells formerly in general use. In a park outside of Bochum, one of the early steel church bells is enshrined as a marker of steel casting history. This bell even escaped the desperate need for scrap steel in Germany during World War II. Steel produced by the crucible process remained expensive, and it was not until the converter, the open hearth furnace, and finally the electric arc furnace were introduced that steel was produced commercially in quantities that were economically feasible. The steel for these early castings, in addition to being made in crucible furnaces, was poured in loam molds. It was not until 1845 that steel castings (steel cast to final shape) appeared on the scene. On July 14 of that year, Swiss metallurgist Johann Conrad Fischer exhibited various small castings produced from crucible steel. On July 23, 1845, Fischer applied to the British Patent Office for priority rights to a new method of making horseshoes that consisted of casting steel in sand molds. In the United States, cast steel was produced by the crucible process in 1818 at the Valley Forge Foundry, but difficulties resulting from the lack of adequate materials--principally refractories for crucibles--caused the experiment to be abandoned. In 1831-1832, high-quality clay from Cumberland, West Virginia, enabled William Garrard of Cincinnati, Ohio, to establish the first commercial crucible steel operation in this country. It is interesting to note that the first commercial steel castings from the Garrard plant sold for 18 to 25 cents per pound and were first used as blades and guards for the McCormick reaper. The history of steel castings in the United States begins with the Buffalo Steel Company of Buffalo, New York (later known as the Pratt and Letchworth Company). The foundry was built in 1860, and in 1861 it produced the first crucible steel made in the district. Records indicate that these first crucible steel castings were for railroad applications. Some of the first commercial steel castings produced in the United States are believed to have been made by the William Butcher Steel Works (later the Midvale Company) near Philadelphia in July of 1867. These castings are said to have been crucible steel crossing frogs car wheels, probably for the Philadelphia and Reading Railway. In 1870, William Hainsworth of Pittsburg began the manufacture of cast steel cutting parts for agricultural implements using a two-pot coke-fired crucible furnace. In 1871, Hainsworth founded the Pittsburg Steel Casting Company, which is reputed to have been the first company in the country devoted exclusively to the manufacture of steel castings. Some of the early steel foundries established in this country before 1890 are listed in Table 1. Table 1 Partial listing of early steel foundries in the United States Original Location Date of incorporation Now known as Buffalo Steel Co. Buffalo, NY 1861 Discontinued operations Wm. Butcher Steel Works Nicetown, PA July 1866 Discontinued operations Pittsburgh Steel Casting Co. Pittsburgh, PA March 1871 Discontinued operations Chester Steel Casting Co. Chester, PA 1872 Discontinued operations Otis Iron and Steel Co. Cleveland, OH Circa 1874 Discontinued operations Isaac G. Johnson and Co. Spuyten Duyvil, NY Circa 1850 (a) Discontinued operations Eureka Steel Castings Co. Chester, PA 1877 Discontinued operations Hainsworth Steel Co. Pittsburgh, PA Circa 1880 Discontinued operations Old Fort Pitt Foundry Pittsburgh, PA Circa 1881 MacIntish-Hemphill Div., E.W. Bliss Co. Solid Steel Casting Co. Alliance, OH August 1882 American Steel Foundries Alliance Works Standard Steel Castings Co. Thurlow, PA Circa 1882 Discontinued operations Johnson Steel Street Ry. Co. Johnstown, PA March 1883 Johnstown Corp. Pacific Rolling Mills Co. San Francisco, CA 1884 Discontinued operations S.G. Flagg and Co. Philadelphia, PA 1882-1885 Discontinued operations Cowing Steel Castings Co. Cleveland, OH 1882-1885 Discontinued operations Sharon Steel Casting Co. Sharon, PA February 1887 Discontinued operations (a) Began making steel castings in 1880 William Kelly, whose invention of the converter clearly anticipated the work of Sir Henry Bessemer (although the latter gave his name to the unit), first operated his converter in 1851, a full 5 years before Bessemer's patent was obtained. Neither man realized that his efforts were being paralleled by the other, but it has been well established that Kelly was the first to use the converter. Kelly developed his idea out of experiments on the refining of pig iron as a result of his inability to obtain high-quality ore at his works in Eddyville, Kentucky. His theory was that the iron in ore is not metallic but a chemical compound of oxygen and iron. He came to the conclusion that, after the metal was melted, additional fuel would not be required but that the heat generated by the union of the oxygen in air with the carbon in the metal would be sufficient to decarburize the iron. Kelly's associates, fearing for his sanity, sent him to a doctor for treatment, with the result that the doctor agreed to back Kelly in his venture. In 1851, he was able to produce a rather soft steel, but had difficulty with high carbon. In the meantime, in England, Sir Henry Bessemer was working along almost identical lines. However, he had metallurgical assistance. Robert Mushet of England developed an alloy of iron, carbon, and manganese that purified the metal and ensured the presence of enough carbon to make steel. Although Bessemer obtained American patents, Kelly proved his patent priority in 1857, and in 1866 Kelly and Bessemer joined forces. A Kelly converter was first used in 1857-1858 at the Cambria Works at Johnstown, Pennsylvania. Later, Kelly obtained the rights to use Mushet's patent. Bessemer's first converter in the United States was installed at Troy, New York, in 1865. This converter was introduced into foundries and was further improved in 1891 by the Tropenas converter (Fig. 7), which blew over the surface of the metal rather than through it. The lower-pressure blast and resultant deeper metal bath produced better results. Fig. 7 The Bessemer and Tropenas converters. The converter had scarcely gained acceptance when another furnace came into use and gave the steel industry the capacity it required. This was the Siemens-Martin open hearth, a development dating back to 1845, plus the succeeding experiments of J.M. Heath. However, this unit did not become successful until the great heat of the open hearth regenerative furnace could be supplied to it. This became possible in 1857 as a result of the invention of the gas producer, which was patented that year. Because of its high initial cost, the first open hearth furnace was not installed in the United States until 1870. However, with its tremendous capacity, it soon surpassed the converter in tonnage until it was in turn challenged by the electric are furnace. The electric arc furnace (Fig. 8) was invented by Sir William Siemens, who developed an electric arc in 1878. However, it was little used until improved by Girod, Heroult, Keller, and others in 1895. An electric arc furnace was first installed in the United States in 1906 at the Holcomb Steel Company (later the Crucible Steel Company) at Syracuse, New York. Fig. 8 Cross section of an electric arc furnace. Induction electric furnaces were not introduced from Sweden until 1930, and many of the American developments of this furnace were made by Dr. E.F. Northrup and Dr. G.H. Clamer of the Ajax Metal Company, Philadelphia, Pennsylvania. Information on electric arc and induction furnaces is available in the articles "Melting Furnaces: Electric Arc Furnaces" and "Melting Furnaces: Induction Furnaces" in this Volume. Cast Alloy Steels. In 1888, the first manganese cast steel was made in the United States at the Taylor-Wharton Iron & Steel Company in High Bridge, New Jersey, under license from Robert Hadfield of England. This was also the first cast alloy steel to be produced in America, and it was used for railway crossings and switch frogs. In 1903, A.L. Marsh, an American, made an alloy of 80% Ni and 20% Cr. He was studying alloys for use as thermocouples, and he observed that this alloy had high electrical resistance and could sustain operation for extended periods at high temperature without excessive oxidation--an ideal combination for electric heating elements. This and similar high nickel-chromium alloys later became the standard for electrically heated equipment and appliances. Before World War I, E. Maurer and B. Strauss in Germany and H. Brearley in England were considering the alloys of iron with chromium and nickel for use as pyrometer tubes and gun barrels. They noted resistance to etchants by certain compositions and realized the potential utility of such steels as stainless or rust-free in corrosive environments. By 1912, the German firm of Krupp had obtained patents on a martensitic, hardenable 14% Cr alloy and on an austenitic, nonhardenable 20Cr-7Ni alloy, which they called VM and VA, respectively. By 1916, Brearley had received patents in the United States and Great Britain on cutlery made from hardenable steels containing 9 to 16% Cr with 0.70% max C. Thus, the major classes of heat-resistant and corrosion-resistant alloys were all discovered and patented from 1905 to 1915. The use of these materials in castings for industrial applications awaited the next decade. During World War I, urgent demands for expanded production from the infant automobile and aviation industries created the need for improved heat- treating procedures. In 1916, a patent was issued on the use of high nickel-chromium-iron electrical resistance alloys in cast carburizing boxes. These were supplied at first by foundries set up by the producers of the electrical resistance wire, and later by independent foundries formed to specialize in heat-resistant castings. At the same time, the increased output of the munitions and synthetic dye industries was making the corrosion resistance of the iron-chromium alloys attractive for handling strong oxidizers, such as nitric acid. As a result, the foundries that were making pumps and valves in carbon steel were asked to make these parts in rustless iron and stainless steel. With the end of the war and the industrial expansion that followed, the demand for both heat- and corrosion-resistant castings increased substantially. The growth of high-alloy casting consumption has been stimulated by the continuing research objective of providing users with the materials and data needed to solve process design problems. Since 1930, there has been considerable development of new alloys and refinement of old ones as detailed in the articles found in the sections on ferrous casting alloys and nonferrous casting alloys in this volume. Foundry Mechanization With gray iron, malleable iron, and steel added to the foundrymen's metals for casting to shape, it follows that equipment and methods for the rapidly growing castings industry were also being given increasing attention. Molding, coremaking, sand preparation and conditioning, and metals and materials handling methods also progressed during the 1800s. To complete the story of the development of the art and science of casting, it is only logical to trace the early progress of the tremendous mechanization of the industry. Actually, sand casting is a relatively recent development (in terms of the antiquity of casting technology), and it occupies an indispensible place in the industry. As with the development of the molding machine, foundrymen soon realized that a mixed molding material was essential. With the use of loam, the early machines for the treatment and preparation of sands aimed at compounding or grinding rather than mixing and mulling. Early in the 1870s, machines began to appear that were essentially paddle mixers. In the 1890s and early 1900s, manufacturers began to adapt equipment used by the ceramic industry. In 1912, the first muller, with individually mounted revolving mullers of varying weights, was placed on the market. Since that time, mullers that effectively coat the sand grains have been successfully used in the preparation of sand for both cores and molds. This same period saw the first steps taken toward the development of sand screening machinery, which eventually resulted in the riddle, the magnetic separator, and the complete sand preparation plant. Mold-conveying methods, introduced about 1890, originally involved a continuous series of moving cars that looped at a steady speed from molder to pouring station and then to cool and shakeout. Core manufacture was also standardized and equipment made available for mass production in American foundries. Long rooms filled with workers producing cores could be seen as early as 1888. All cores were racked and dried in kilns and then placed on racks to be carried to the foundry. The importance of core production soon sparked the development of baking ovens specially adapted for foundry use so that cores of different types could be baked for longer or shorter times as required. An early developer of the foundry core oven was Eli Millett in 1887. Today, coremaking, like sand molding and conveying, is a complex and highly specialized division of every foundry (see the article "Coremaking" in this Volume). Early credit for the tumbling mill must be given to the W.W. Sly Company of Cleveland, Ohio. The Sly cleaning machine was a boon to foundrymen because it enabled them to offer their customers a finished product. In addition to tumbling mills for small castings, the sand blast was developed for larger work by R.E. Tilghman of Philadelphia, Pennsylvania, in 1870 (see the article "Blast Cleaning of Castings" in this Volume). The use of such equipment did not begin to broaden, however, until about 1900, when it was installed at the Logan Manufacturing Company at Phoenixville, Pennsylvania. Of the rapid improvements made since then by equipment firms, mention should be made of the American Foundry Equipment Company (now the Wheelabrator-Frye Company of Mishawaka, Indiana, and the Pangborn Corporation of Hagerstown, Maryland), whose constant innovations and engineering technology, have added much to the ease and efficiency with which foundries handle many cleaning room operation. In the 19th century, it was common for the pouring ladle to be hoisted by a jib crane located beside the furnace. The molds, arranged in a semicircle, were poured by swinging the crane from mold to mold. Modern overhead cranes have revolutionized the handling of the molten steel. Geared safety ladles (Fig. 5) were designed and built by James Nasmythe in 1867. Prior to this, bull ladles were tipped by a number of men applying leverage on large horizontal arms. Hand- shanked ladles made their appearance about the same time as the geared tilt ladles. In the final quarter of the 19th century, industrial growth in the United States exceeded all previous experience. The mass production of machines, the new consumerism, the proliferation of steel-framed buildings, and the spread of electric power and telegraph networks all created an appetite for metals and in turn placed increasing demands on the casting industry. The 20th Century The 20th century began without any indication of the dramatic changes that computers and automation would bring about by the 1960s. The changes in equipment and methods would be quite obvious. As the 20th century began, the average U.S. foundry poured more tonnage than was cast throughout the world when the Nation was born. Despite so striking a transformation in the industry, man was called upon to expend far less energy. With minimal physical effort, workers produced increasingly sophisticated shapes in less time for increasingly intricate machines. As automation took over, production rates climbed until one automated foundry in the automotive field in 1967 was able to established a consistent production figure of 6 man-hours per ton of castings. Machines replaced the labor of man and horse, and with the sudden impetus given metal manufacturing in World War I, machinery became a necessity. Without cast metal parts, the machine age could never have existed. The metal casting industry adopted automation and did so rapidly. Characteristically, the first fully automated plant in the United States (one of the first in the world) was a Rockford, Illinois, foundry that cast hand grenades for the U.S. Army in 1918. The history of metal casting shows that the foundryman is as eager as any manufacturer to take full advantage of inventions and even to inspire them. America's first commercial metal caster, Joseph Jenks, was awarded the first patent in America. Thomas Edison called Seth Boyden one of America's greatest inventors, for Boyden established two basic industries in America--patent leather and malleable iron. In 1851, James Bogardus's factory in Chicago, which was constructed with cast iron supports, opened the way for what many art historians considered to be America's only original contribution to the arts of the world--the skyscraper. By 1960, less than 1% of the foundries in operation were a century old. The trend continued as huge conglomerates entered the picture. American metal casting was big business. After a walking tour, Walt Whitman described the Nation: "Colossal foundry, flaming fires, melted metal, pounding trip hammers, surging crowds of workmen shifting from point to point, waste and extravagance of material, mighty castings; such is a symbol of America." In the first year of the new century, foundries in the United States poured more open hearth steel than those in the United Kingdom--almost as much as the rest of the world combined. As far back as 1864, the military foundry at Old Fort Pitt (Pittsburgh) had cast a 510 mm (20 in.) smooth-bore Rodman cannon weighing 52 Mg (115,000 lb). This was a hundred times bigger than the famed Urban Gun of Muhammad II that was used to fell the walls of Constantinople in 1453. Three years later, the Krupp plant in Essen, Germany, poured a 45 Mg (50 ton) cast steel cannon, and the fate of the French army in the War of 1870 was sealed. Casting Markets. The largest consumer of metal castings, however, was not the military but the automobile industry, which in 10 years provided a greater incentive to metal casting than cannons, bells, and the steam engine had in a century and a half. Approximately 25% of all castings produced in this century have been component parts for automobiles, trucks, and tractors. In 1924, Henry Ford made 1 million automobiles in 132 working days. Casting knowledge and the world's first mass production concept were vital to this phenomenal production increase. Automobile output in the first 10 years of the 20th century increased 3500%, with a corresponding increase in demand for castings. The mass production of trucks, tractors, and other mechanized farm and industrial equipment also heightened the demand for castings. This was followed in rapid succession by parts for such mushrooming industries as refrigeration (1930s); aviation (1940s); air conditioning (1950s); and data processing, electronics, and aerospace technology (1960s). Cast metals played a vital role in each. Major markets for castings are reviewed in the following article "Casting Advantages, Applications, and Market Size" in this Volume. Foundry Organizations. Metallurgy began to achieve prominence in 1889 when nickel was alloyed to make a stronger steel. Although the science of metallurgy is now recognized as the basis of sound metal casting technology, in the beginning it was welcomed only by the more advanced foundry owners interested in the continuing benefits to be achieved by accepting a new technology. A group of these enterprising foundry owners arranged to form a number of industry-sponsored organizations dedicated to metal science and research and development, which, its leading members realized, could be turned to commercial advantage. The American Foundrymen's Association (since 1948, the American Foundrymen's Society) was formed in 1896 out of the Foundrymen's Association of Philadelphia, itself only 3 years old. The New England Foundrymen's Association was formed that same year, and 1 year later the American Malleable Casting Association (changed 30 years later to the Malleable Iron Research Institute and in 1934 to the Malleable Founder's Society) was formed. In 1900, the Carnegie Research Scholarships of the Iron and Steel Institute were founded, followed by the Steel Founders' Society of America in 1902. The Foundry Equipment Manufacturers' Association (now the Casting Industry Supplier's Association) was founded in 1918, and the Gray Iron Institute was founded in 1928. Other casting associations included the American Die Casting Institute (1929), the Alloy Casting Institute (1940), the Nonferrous Founders' Society (1943), and the Foundry Educational Foundation and National Castings Council (1947). The Investment Casting Institute was founded in 1953, the Society of Die Casting Engineers in 1954, and the Ductile Iron Society in 1959. The goal of worldwide cooperation in metal casting prompted the formation in 1923 of the International Committee of Foundry Technical Associations (ICFTA, Zurich, Switzerland), which strives through 24 nations and an annual International Foundry Congress to exchange technical data. Permanent Mold Processes. Developments in molding logically included the use of permanent molds, although the permanent mold preceded the loam mold and the sand mold by centuries. Subsequent types of permanent molds gradually appeared, but for many years they were limited in application by the metal available. Permanent molding can be defined simply as the pouring of liquid metal into a preheated metallic mold. As described in the article "Classification of Processes and Flow Charts of Foundry Operations" in this Volume, currently used permanent mold casting methods include die casting (high-pressure, low-pressure, and gravity), centrifugal casting (vertical and horizontal), and hybrid processes such as squeeze casting and semisolid metal casting. The centrifugal casting process, which involves the pouring of molten metal into a rapidly rotating metallic mold, was developed by A.G. Eckhardt of Soho, England, in 1809. The method was soon adopted by the pipe foundries and was first used in Baltimore, Maryland, in 1848. Sir Henry Bessemer, famed for his converter, used centrifugal casting to remove gases and was the first to pour two or more metals into a single rotating mold. The centrifugal casting of steel was first attempted in 1898 at the plant of the American Steel Foundries in St. Louis, Missouri. Railroad car wheels were spun cast in 1901 at a rotation speed of 620 rpm. Slush Casting. Following the early development of the centrifugal method, a permanent mold method known as slush casting was introduced. Slush casting is a process in which molten metal is poured into a split metal mold (generally made of bronze) until the mold is filled; then, immediately, the mold is inverted and the metal that is still liquid is allowed to run out. The time required for this casting operation is sufficient to freeze a metal shell in the mold, corresponding to the shape of the cavity wall. The thickness of the wall of the casting depends on the time interval between the filling and the inverting of the mold, as well as on the chemical and physical properties of the alloy and the temperature and composition of the mold. Usually lead and zinc alloy castings are produced by slush casting. The process is limited to the production of hollow castings (lamp bases are the principal product). More detailed information on slush casting can be found in Volume 5 of the 8th Edition of Metals Handbook. Aluminum, the most abundant metal in the earth's crust, was a development of this century. Isolated in 1825, it derives its name from the Latin alumen, meaning bitterness. Aluminum was first exhibited in 1855, but for many years was so difficult to obtain that it was more costly than gold. In 1888, the Pittsburgh Reduction Company offered the metal in half- ton lots for $2 a pound and had difficulty attracting buyers and users until one manufacturer discovered it made good, inexpensive tea kettles. Within 5 years, the price decreased to 62 cents a pound, and by 1900 it was down to 32 cents per pound. In 1890, only 28,000 kg (62,000 lb) of aluminum was produced in the United States. Production was low until World War II, but by 1963, $635,934,000 worth of aluminum castings were shipped in the United States. In 1963, this industry, undreamed of in 1900, employed 35,970 people in 951 plants with a payroll of $221,567,000. In the first 7 months of 1968 alone, more than 412,000 Mg (450 tons) of aluminum were cast in the United States. The article "Aluminum and Aluminum Alloys" in this Volume contains more information on the processing and applications of aluminum alloys. Magnesium. The development of magnesium as a casting metal parallels the history of aluminum (see the article "Magnesium and Magnesium Alloys" in this Volume). During World War I, magnesium sold in the United States for $5 a pound, and by 1935 only 170 Mg (375,000 lb) had been cast. By 1944, however, the industry was producing more than 39,000 Mg (43 tons) a year, a good portion of which was cast. Die Casting. Manually operated casting machines were patented as early as 1849 (Sturgiss) and 1852 (Barr) in an effort to satisfy the insatiable demands of a growing reading public by way of rapidly cast lead type. These early inventions led to Ottmar Mergenthaler's Linotype, an automatic casting machine in which molten lead is forced by piston stroke into a metal mold. The first die casting machine bearing the Linotype name was patented in 1905 by H.H. Doehler. Two years later came E.B. Wagner's casting machine, a prototype of the now familiar hot chamber die casting machine. It was first used on a large scale during World War I for binocular and gas mask parts. Zinc alloys were used for die casting as early as 1907, but were not competitive until Price & Anderson developed the Zamak die casting alloy in 1929. Additional information on die casting machines can be found in the article "Die Casting" in this Volume. Investment (lost wax) casting, one of the oldest casting techniques, was rediscovered in 1897 by B.F. Philbrook of Iowa, who used it to cast dental inlays. Industry paid little attention to this sophisticated process until the urgent military demands of World War I overtaxed the machine tool industry. Shortcuts were then needed to provide finished tools and precision parts, avoiding time-consuming machining, welding, and assembly. Molding Sands and Equipment. The 20th century saw the refinement of processes and materials used in the foundry for over 400 years. Until the 1920s, sand testing consisted of squeezing a handful of sand to judge its ability to compact and stick together. Early in that period, a sand research committee of the American Foundrymen's Society began to develop sand test methods. By 1924, standards were established that covered the various properties of molding sands. A better understanding of molding sand technology has resulted in sands of a higher degree of uniformity being prepared for the repetitive green sand (clay-bonded) molding sand. This high degree of achievement could only be possible with the great advances in sand testing produced by the foremost researchers and developers of sand testing instrumentation. The current understanding of the fundamentals of clay mineralogy, sand preparation, sand compaction, and the physical properties of molding and core sands all contribute to the success of the modern foundry industry. Ductile Irons and Austempered Ductile Irons. Continuing technological advances that seek to fulfill the need for materials capable of providing greater thermal, chemical, and mechanical properties have brought forth the development of new alloys and properties never believed possible. During World War II, the inoculation of gray iron became common practice, because high-quality cast irons replaced the scarcer steel in many castings. Shortly after the war, a new type of iron, variously known as spheroidal graphite cast iron, nodular iron, and (more universally) ductile iron, was patented and announced by the International Nickel Company. It was a major breakthrough in metallurgy because its high strength and ductility allow it to compete with malleable iron and, in certain applications, with steel. If ductile iron is austenitized and quenched into a salt bath or a hot oil transformation bath at a temperature in the range of 320 to 550 °C (610 to 1020 °F) and held at that temperature, transformation to a structure containing mainly bainite with a minor proportion of austenite takes place. Irons so transformed are referred to as austempered ductile irons (ADI). Austempering generates a range of structures depending on the time of transformation and the temperature of the transformation bath. The properties are characterized by very high strength, with some ductility and toughness, and often an ability to work harden, giving appreciably higher wear resistance than that of other ductile irons. See the article "Ductile Irons" in this Volume for an extensive review of the properties of ductile irons and ADI. Organic Binders. Since World War II, experimentation has been accelerated in organic and chemical sand binders for the thermosetting of molds and cores (see the article "Resin Binder Processes" in this Volume). Beginning with the Croning process (shell process), phenolics led the way to urea and the dielectric process and then to furans and urea-free resins. The continued development of binders for the production of chemically bonded cores and molds in being directed toward increasing productivity as well as achieving the dimensional repeatability necessary to meet the new challenges of net shape and near-net shape casting requirements (Table 2). Many patterns were made of epoxy resins and polyurethane and other expendables such as polystyrene. Table 2 Development of core and mold processes . information on die casting machines can be found in the article "Die Casting& quot; in this Volume. Investment (lost wax) casting, one of the oldest casting techniques,. currently used permanent mold casting methods include die casting (high-pressure, low-pressure, and gravity), centrifugal casting (vertical and horizontal),