EUGENE C. SULLIVAN and ROBERT G. GULIAN Corning Glass Works, Corning, N. Y.
Glass That's Photosensitive. . .
Glass That Can Be Shocked by Molten Metal and Ice. . .
Ceramic Ball Bearings. . .
These Are Some Examples of the Pattern for Progress in
GLASS, CERAMICS, A N D THE American glass industry of half a century ago was described by Robert Kennedy Duncan ("Chemistry of Commerce," p. 3, Harpers, 1907) first director of Mellon Institute, as the type of crude and wasteful traditional industry which implies that the art is mysterious, ultraknowledgeable and extra-scientific, and when things go wrong the trouble should be ascribed, as it was in the old days, to diabolical influence—a story of confusion and waste. Today, dianks to mechanization and to developments in which the chemist and chemical engineer have had a major role, glass manufac-
ANNIVERSARY 48 A
FEATURE
REFRACTORIES
ture stands among the enterprising industries. Not only have methods of preparing and shaping glass been revolutionized but also the material itself has emerged from a single undependable substance to hundreds of versatile materials comparable with metals in reliability and possessing a wide variety of useful properties. Fifty years ago, glass was a fragile material. In 1958 it is an intrinsically strong material. Fiber tensile strength was measured 1,000,000 p.s.i., about twice the highest published figure for steel wire. At 5 0 % greater thickness or 5 0 % less weight, glass equals steel in resistance to bending. Glass fiber impregnated with plastic has greater impact strength, weight for weight, than armor plate.
Mechanization in the glass industry has been dependent upon the chemist to a greater extent than other fields because of the very critical conditions under which the glass can be worked by machine. A definite working quality, uniformity of the mass, is required in hot glass as it is being shaped. Before the chemist's advent, the glass varied for lack of raw material analyses. Constant checking of raw materials and the melted glass has made possible day-to-day uniformity required by the machine. At the turn of the century, melting pot refractory blocks were clay which dissolved more or less rapidly in the molten glass. Where the attack was most severe, especially at the upper surface level of the molten glass, it was only a few
Photo at top, left, shows glass can be precision etched . . . Center photo shows ball bearings made from the newest member of ceramic family—Pyroceram . . . Right, 9 6 % silica glass can withstand extreme thermal shock
INDUSTRIAL AND ENGINEERING CHEMISTRY
months before the block was cor roded to a thin shell. In 1921, a chemist and a physicist, H. P. Hood and G. S. Fulcher work ing together produced an electrically melted aluminum silicate which was several times as resistant to molten glass attack as the clay block. The blocks were formed by pouring the molten refractory into molds, similar to castings poured in an iron foundry. The blocks, Electrocast, soon came into wide use in the glass industry. They not only made it possible to melt at higher temperatures and thus increase tank output, but also to improve glass quality and lower cost of melting and repairs. Temperature control 50 years ago was entirely dependent on the eye of the fireman or "teaser." The result was that furnaces were fre quently too cold, the glass was not properly melted, or too hot, and the tank or the pot was badly damaged. Fifty years ago platinum-rhodium thermocouples were installed by A. L. Day in furnace walls and shortly thereafter the optical pyrom eter was used to check tempera tures. Today temperature measure ment is universal. The development of the glass in dustry during the past 50 years can most easily be followed by tracing the separate courses of the three main branches—flat glass, contain ers, and specialty glass. Each of these industries had problems pe culiar to its own products as well as those shared by the industry as a whole—for instance, the de velopment of continuous melting techniques and of new refractories. The flat glass industry, the largest of the three, produces millions of square feet of sheet and plate glass for residential and industrial uses. Next in size is the container in dustry, manufacturing with high speed machinery every size and shape of bottle and jar. Third in size but far more formidable in number of glasses and products is the specialty glass industry. Light bulbs, fiber glass, electronic com ponents, process piping, television bulbs, laboratory ware, and kitchen and tableware are a few of the products manufactured by specialty companies. Flat and Container Glass Industries
Progress in this field during the past 50 years has been immense.
In 1908 glass was worked almost entirely by hand. An automatic bottle-making machine was in use but not perfected; another machine was drawing cylinders, later flat tened for window glass, from pots. Although continuous glass melting tanks had been introduced into this country 20 years earlier, inter mittent melting in pots was still widely used. Composition. Basic raw mate rials in the glass batch for plate and window glass have remained nearly constant over the past 50 years. The composition of window glass, about 50 years ago and now, is compared : Composition
1908
1958
S1O2
70.5 0.3 0.1 7.9 0.1 15.0
72.91 1.26 0.10 8.63 3.73 13.21 0.12 0.03
AlsOa Fe2Oj
CaO MgO Na 2 0 K2O
Ti02
The rate of mechanizing the flat glass industry has been phenomenal. Plate glass 50 years ago was pro duced by dumping a pot of glass on the table where a heavy roller was used to flatten it. Then the slab was ground and polished on a rotary table. Now the glass flows in a stream from the tank fur.iace between rolls and onto a continuous belt for grinding on both sides at the same time. Window glass, the surfaces of which are acceptable without grind ing and polishing, was formed by flattening of glass cylinders, first making the cylinders by hand, and until the late 1920s by machine. Then the present methods of me chanically drawing sheet directly from the molten glass achieved suc cess. New products in the flat glass field include laminated sheets and wire glass to prevent broken glass from flying, and tempered plate glass for added strength. In the container industry, mech anization in forming existed 50 years ago, although the greater number of glass containers were formed in individual molds tended by hand. The problem of getting molten glass from the furnace to the mold was solved in the Owens machine by cups which sucked up the required charges from the sur face of the molten pool.
The first successful flow device for the container industry was the Hartford suspended gob feed, by Κ. Ε. Peiler in 1911, in which the hot glass dropped from an outlet in impulses such that a series of com pact masses could be cut off in turn and fed to a mold. The gob feeder, greatly improved, is a stand ard feeder today. Containers low in cost and of accurate dimensions are now turned out by the billions (19-billion pieces in 1957) by such automatic machines as the Hartford individual section machine and the improved Owens bottle machine. New products of the container field are thin-walled one-use bottles, square milk bottles, and lightweight increased-strength containers. Specialty Glass Industry
The term, specialty glass, covers an extremely broad range of products and is defined as any glass product not considered flat or container glass. This can encompass as many as 35,000 different products, nu merous types of forming, special and unique types of melting, and special finishing techniques. Fifty years ago many specialty glass industries produced everything from hand-pressed highly decorative dinnerware to hand-blown light bulb blanks. Most of these industries were small family-run affairs, situ ated near supplies of sand for melting, natural gas or coal for heat, and ready to produce any number of products at an ins.tant's notice. However, it has been in this section of the industry that the most startling changes have occurred in glass—both in composition and prod ucts. From it have come heatresistant glass, mass-produced optical glass, fiber glass, silicones, elec trically conductive glass, ribbon glass, photosensitive glass, glass-ce ramics, and others. Many of these advances have resulted from the efforts of chemists engaged in glass research. Compositions. Until 1908, the United States was dependent on the glass factories of Jena, Germany, for its low expansion glasses. But, during this year, an American spe cialty glass factory produced its first low expansion glass. Again, the railroads were looking for a special glass—for their lanterns—one that could withstand the sudden shock of rain or snow and not break. This VOL. 50, NO. 4
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APRIL 1958
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glass, high in boric oxide (27.5%) and low in alkali ( 4 % N a 2 0 ) , lacked chemical resistance but served its purpose and hundreds of tons were marketed. Another low-expansion composition was later worked out by Sullivan and Taylor for household bakingware—a project originated by J. T. Littleton. The story of glass bakingware is an interesting one. In 1913, the wife of a young physicist, J. T. Littleton, who had just joined Corning Glass Works, baked a cake in the bottom of a glass battery jar. The cake was a success. He persuaded the small research staff that baking would be possible in glass, providing they could produce a stable heat-resistant glass. As a new culinary idea, glass for baking met with skepticism elsewhere. A prominent cooking expert wrote that glass in a kitchen oven did not appeal to her. She tried it for an ice cream and cake combination called baked Alaska and became an enthusiastic convert. As it turned out, cooking time in glass was shorter, food didn't adhere to the glass, nor did its flavor stick to glass after washing. The cook could also watch the food brown and know when to take it from the oven. In 1915 a new glass was marketed as Pyrex brand ovenware and, with very few composition changes, is still widely sold. This glass proved chemically resistant for laboratory use, and when World War I shut off imports from Germany, American-made beakers and flasks were put on the market. This ware, with its low expansion, could be made heavy-walled and more rugged without sacrificing thermal resistance. From this same borosilicate glass, thousands of new products have come into use. Coming's laboratory glassware catalog alone lists over 9000 items, made for the most part from Pyrex brand glass. Glassware for plant equipment in the form of piping, shell and tube heat exchangers, bubble cap columns, pumps, filters, electrically conducting glass heaters, Godet wheels and thread guides for the textile industry, and laboratory drainlines is made from borosilicate glass. Indeed, the chemical stability, thermal resistance, and toughness of this glass, as it has been developed for the past four decades, have been responsible 50 A
in large part for transforming glass into an engineering material. The famous 200-inch disk, weighing over 20 tons, for the Hale telescope mirror at the Palomar Mountain observatory, came about through the known low expansion of borosilicate glass. Cast and annealed in 1934, this is the largest single glass object in existence, enabling man to peer into space four times farther than ever before. In the early 1930's, two chemists, H. P. Hood and M. E. Nordberg, discovered a method to manufacture a low expansion glass containing 9 6 % silica. By leaching with acid a chemically unstable high boric oxide glass, they produced a glass that was like a rigid sponge, full of submicroscopic holes. When this glass was heated it produced a hard clear glass, shrinking more than 1 5 % in the process. This new glass, Vycor, had great resistance to heat and sudden temperature change. Used for many years in chemical and laboratory applications, it was recently discovered that Vycor brand glass, specially treated, had amazing infrared transmission. Now this material is used extensively in infrared detecting missiles as the nose cone. Also, during the 1930's an organic chemist, J. F. Hyde, probably the first to conduct intensive research in glass, an inorganic material, was given the task of combining hard, heat-resistant silica with malleable plastics. From his studies came silicones and a new industry. This same chemist passed siliconcontaining gases through a flame and formed boules of extremely low expansion, high heat-resistant pure fused silica. This new material was not practical until 1950 when extremely low ultrasonic attenuation of fused silica made it an ideal material for radar delay lines. Fiber glass (G. Slayter), the dollar sale of which in 20 years has grown into nine figures, is produced by steam—or air—blasting thin streams of molten glass, or by drawing continuous filaments of molten glass from tiny orifices. In form of wool it serves for heat or sound insulation, filters, and other purposes. The fine textile fiber goes into draperies, wire and cable insulation, plastic-reinforced boats, and automobile bodies. In the early 1940's, another Corn-
INDUSTRIAL AND ENGINEERING CHEMISTRY
ing chemist, R. H. Dalton, discovered that glass could be made photosensitive. This has led, in the past decade and a half, to some wonderful new materials. At first, photosensitive glasses were used exclusively to develop latent images in the glass (S. D. Stookey)—by precisely controlling these images, such products as louvered glass panels for lighting and architectural glass panels decoratively mottled were formed. Not long after this, a method of chemically etching photosensitive glass came about. Now precise patterns could actually be chemically machined in the glass. By this process, it eventually became possible to etch as many as 750,000 evenly spaced holes in one square inch of glass. For centuries glassmakers had fought crystallization in glass, and yet it has been through this very crystallization (controlled, to be sure) that they have produced some of the more astounding new glasses. By increasing the heat cycle for the photosensitive glasses, a new semicrystalline glass, Fotoceram, was discovered. This glass was harder and stronger than ordinary glass. S. D. Stookey, a chemist discovered that by adding certain nucleating agents to an ordinary glass batch, growth of crystals could be carefully controlled, and by varying both nucleating agents and heat treatments, properties of this new material, Pyroceram, could also be varied. An entire family of these new materials was developed, some with strengths running five to eight times that of glass, others with electrical properties comparable to those of the best electrical ceramics. This crystalline material had the same physical properties as cast iron, yet weighed less than aluminum. Certain Pyroceram materials were harder than tool steel; and all the Pyroceram glass—ceramics had the tremendous advantage of formability—they could be formed by any of the high speed glass manufacturing machines. Melting a n d Forming. Sporadic attempts had been made in the 1900's at melting optical glass, some successful on a small scale, but it took World War I, with its sudden need for optical glass, to spur American glass industries to move ahead in the field. Some 700,000 pounds of
optical glass were furnished the armed forces by three commercial firms under the direction of the Geophysical Laboratory of Carnegie Institution. While they were effective in devising new formulas for optical quality glass, the methods of melting optical glass remained primitive until World War II. U p to that time, optical glass was still made by traditional pot-melting methods. The pot of extremely pure molten glass was allowed to cool slowly until it hardened. Then it was chipped in large chunks from the pot. The chunks were heated and sagged into blocks; imperfect portions were broken out and the remaining glass heated and pressed into optical blanks. It was inconceivable that optical purity could be maintained in large, inass-production tanks, but the strenuous demands for optical blanks at the outbreak of World War II proved this theory wrong. By 1944 Corning was making the first massproduced optical glass, thanks to a method of melting and stirring by C. F. DeVoe. His method has gained wide acceptance among optical glass manufacturers in this country and abroad. Forming operations in the specialty glass industry have changed considerably in 50 years, going from hand work to automatic production of the highest degree. Many forming operations, concerned with filling small volume orders—such as railroad signal lenses, maritime lenses, large flasks—continue to revolve around the time-honored hand shop. But in 1908 the production of bulbs for electric lights presented staggering problems in the hand shop. One hand shop could turn out more than 1200 bulbs a day, but this wasn't enough to meet the demand. By 1911, a semiautomatic machine was turning out 10 bulbs a minute, and during World War I another fully automatic bulbblowing machine was developed capable of blowing 40 bulbs a minute. But the real story on mechanization did not occur until 1926 when a new machine, known as the Corning ribbon machine, began turning out bulbs at the rate of 250 per minute. By constant improvement, this machine today can produce as many as 2000 bulbs per minute, blowing them from a constantly flowing
molten ribbon of glass. Just after World War I, an ingenious automatic machine for drawing glass tubing was invented by Edward Danner. Until that time, all tubing had been drawn by hand ; Danner's machine was swiftly adopted throughout the industry. Another tube drawing machine, developed in Paris by L. S. Velio in the 1920's and perfected in the early 1930's, soon produced tubing at a rate of six times that of the Danner machine. Television brought about the first major change in glass forming in many years. As television bulbs began growing larger and larger, production problems increased. Larger face panels and funnels were extremely difficult to press, and glass engineers foresaw a limit of 15 inches on the size of T V bulbs. One man, J. W. Giffen, attacked the problem as if he were forming metal rather than glass. The result —the first glass-forming machine to use centrifugal casting. Using this new method, it became a simple matter to spin or cast T V funnels up to 27 inches in diameter. Conclusion
The space available is very inadequate to do justice to the many far-reaching developments in the past 50 years, such as fiber glass, glass blocks, electrically conductive glasses, glass-to-metal seals, tempering glass to make it stronger and more heat resistant—in which chemists and chemical engineers played major roles. As to the immediate future, the field of glass promises to continue to expand as its qualities as a versatile engineering material become more widely recognized. The degree to which energy is harnessed is the key to a civilization's progress. Whether this energy be electrical, nuclear, or solar, in our world's future, glass can conceivably perform a major function in capturing, carrying, and utilizing power. The electrical, chemical, and thermal properties of today's glasses are already superior to any other known material in many applications. For example, mammoth reflectors of glass could focus rays of the sun at temperatures now unattainable. These would revolutionize chemical and metallurgical manufacturing
ANNIVERSARY
FEATURE
methods as well as permit the development of new substances of unique and valuable properties. A segmented mirror, 200 feet in diameter, capable of producing a temperature of 5000° C. is under consideration. Malleable glass with the workability of plastics and the abrasion and heat resistance of glass is a foreseeable achievement. Through composition control, this glass might be made to remain as flexible as rubber, or to harden with heat or time. Perhaps one of the first uses of flexible glass will be in making replacement parts for body organs. Easily formed, light weight, inexpensive glass may become the principal structural material. Glass structural members could be cemented or fused together in place without nails or rivets. Their weight would be one third that of steel, their strength, at equal weight, many times that of aluminum. We might expect lighter weight buildings requiring less solid foundations, lighter automobiles, trains, bridges, and ships. Glass itself may be a source of light. Phosphorescent glass could be used as a wear-resistant road material, softly but distinctly outlining the highway at night and elastic enough to prevent disintegration by frost. Other glasses may be formulated that will directly transform electric power into visible light to serve as glowing ceilings or as hanging sheets on controlled intensity illumination. Perhaps all these materials will not be called glass. But the hope of their development and their expected benefits rest firmly on the work that glass scientists have done and are doing today. Acknowledgment
The writers are indebted for help to J. S. Gregorius of Pittsburgh Plate Glass Co., Donald E. Sharp of Libbey-Owens-Ford Glass Co., Karl E. Peiler of Hartford Empire Co., Games Slayter of Owens-Corning Fiberglas Corp., and to members of the Corning Glass Works. VOL. 50, NO. 4
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