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Coreless Induction Melting of Iron.

The earliest of metalcasters could not have dreamt of the technologies that their 20th century peers would have at their fingertips. But never in their wildest dreams could they have conceived of a furnace, fed by snake-like electrical lines, that could quickly and cleanly melt and hold iron--of precise composition and temperature--until the foundryman was ready to pour. But then again, we must understand that the early furnaces were abandoned as fuel or ore ran low, at which time the foundrymen "built" another furnace near a better supply of materials.

Even at the onset of this century, it would have been difficult to conceive of how the foundries would be melting by the end of the millennium. The cupola had been introduced to the U.S. around 1815, and the nation's first electric company was only 21 years old in 1900.

The tidal wave U.S. adoption of coreless induction melting that began in the '60s had started as a "pond ripple" in a Princeton Univ. lab a half-century earlier. The primary "stone tosser" was a 50-year-old physics professor named Edwin Northrup.

In his '95 autobiography, The Fire Within, Inductotherm founder Henry Rowan described the "pull" of induction melting. "Dr. Northrup, with his 'fireless, wireless furnace,' had unlocked the secret to melting via electromagnetic fields, by which the process itself becomes its own heat source. If the old processes were awe-inspiring, induction was invisible dragon. A man could place his hand inside an electromagnetic field and feel no discomfort whatsoever, unless he was wearing a ring or a watch, which, if left in the field, would rapidly heat up and melt off, perhaps with a finger or a wrist."

When the induction furnace arrived on the iron melting scene in the '60s, it offered iron foundries with an entirely new melt choice. It promised better chemical composition and temperature control, fewer raw material headaches, flexibility in alloy changes, and reduced labor and downtime (by eliminating "dropping bottom," and preparing for the next day's melt). Plus, some early adopters of this new melting method later found it would place them a step ahead of others in the fiercely competitive and highly-regulated era that soon followed.

The Invention

A New York native, Northrup had been secretary of Leeds & Northrup before joining Princeton's physics faculty in '10. In addition to the coreless induction furnace, he held 103 other patents for new methods and instruments for the production and measurement of high temperatures. He also developed a method for surface hardening crankshafts, camshafts and other automotive parts by induction heating.

According to an article in a '27 Iron Trade Review, Ajax Metal Co.'s Guilliam H. Clamer (AFS President '23-24 and an AFS Gold Medalist '33) asked Northrup in '16 to report on phenomena occuring during metal melting in electric furnaces. "At first, he was inclined to believe that every possible principle in the application of electric current in melting already had been tried. But, he was led by making an exhaustive analysis, to see that there was one door still open. He soon developed a sort of three-legged hypothesis: that metal could be melted in crucibles by heating it by induction with a current of higher than normal frequency, that it could be melted without the use of any transformer iron and, what nobody had seen before, with the use of static condensers to maintain the power factor on the supply at unity."

Later that same year, Northrup developed a small practical induction furnace, and he and Clamer founded Ajax Electothermic Corp. (where Northrup worked until his death at age 74 in '40). The first furnace was sold to Corning Glass Co., a glass-melting operation in Corning, New York.

Induction melting works by the alternating electric current that flows into a furnace through a copper coil. This resulting electromagnetic field passes through the refractory and couples with the conductive metal charge inside the furnace, inducing electric current to flow inside the metal charge itself, producing heat that rapidly causes the metal to melt. Thus, induction heats the charge directly, rather than the furnace.

While it first garnered popularity for nonferrous melting, its acceptance for iron was much slower. It would take 40 years and the influence of a variety of outside factors (such as raw material issues, electricity availability, increased regulatory pressures and a new type of iron) before the furnace began to take of for iron melting.

A Climate Change

Northrup's furnace was ahead of its time. Among the many reasons for slower adoption was limited availability of suitable high-frequency power sources.

A '71 modern casting article, "75 Years of Progress...In Melting" reported that much of the refinement of the furnace for iron melting occurred overseas. "As Europe began to rebuild after World War II, there was a shortage of suitable pig iron and metallurgical-grade coke, and ample hydroelectric power was available. New regulations developed to control air pollution were aimed at foundries."

Brown Boveri claimed to have installed the first coreless line-frequency induction furnace for iron duplexing at Italy's Fiat foundry in '46. Germany's Otto Junker also developed a early line-frequency coreless furnace before building furnaces for other foundries.

Air pollution requirements began being felt in North America around '60. Several papers reported that the cost of a new induction furnace was nearly the same as a baghouse installation for the cupola. Savings in charge material cost, ease of control and improvement in quality all contributed to the growth of the coreless induction furnace.

Also, Rowan wrote in a '72 "Progress in Melting" paper, that one of the greatest boons in the induction furnace business was the use of up to 100% low-cost steel scrap--released by the basic oxygen steelmaking process--for making ductile, gray and malleable iron. He noted that a $10/ton reduction in charge material costs resulted in a 15% return on investment on a one-shift basis alone.

U.S. Introductaon/Pioneers

According to Hans G. Heine, the 48year induction melting veteran who was instrumental in Brown Boveri's penetration of the U.S. market, the first line-frequency coreless furnace was sold to Outboard Marine in '60 for melting magnesium. "The magnesium market soon showed (due to price volatility) that there wouldn't be enough business to survive on. With iron, we were 300% off on our market analysis," said Heine, remarking that it's always better to err on the conservative side in such forecasts.

According to Heine, the first installation Brown Boveri Co. (today's ABB) sold for the melting of iron was to Detroit's Budd Co. in '61,an 800 kg,900 kW, 6O Hz furnace for superheating gray iron.

The second installation (two 4.5-ton, 800 kW, 60 Hz furnaces) was at Wagner Castings (now an Internet foundry), Decatur, Illinois, which represented the first U.S. installation for cold-melting ductile iron. Don Lawson, Wagner's retired vice president-manufacturing, recalled that metallurgist Lyle Jenkins had set up a pilot coreless furnace operation in the foundry, and produced electric-melt ductile iron for a year and a half. As a result, said Lawson, Jenkins had complete confidence how the coreless-produced ductile iron would perform out on the floor.

"We were entering the production of as-cast ductile iron," said Lawson. "It wasn't cheap. We decided we'd only produce the highest quality iron. If customers wanted to buy ductile cheaper, we said 'go ahead.' We figured if we were to stay in the automotive market, we'd need to be equality conscious."

He added: "Within a year, nearly all the big AFS-member foundries and their presidents walked through our place--it was a showcase installation. The Japanese came over with recorders and cameras." In '71, the foundry removed its cupolas and went 100% electric melt for its malleable iron as well.

Other early adopters ('62) included Albion Malleable, Bowmanville Foundry and Claw Corp. Longtime AFS Vice President-Engineering Services Ezra Kotzin said "The move to electric melting upset the existing foundry mindset, which included vast floor space dedicated to the cupola and enormous charge yards."

Because it had been proven to a degree overseas, induction melting was better understood and accepted than some other industry revolutions. But it was not a nobrainer. Recalls Consultant Roy Lobenhofer, who worked at Clow and several other iron foundries in melt control and metallurgy: "During those days, ACIPCO installed a large cupola, Caterpillar's Mapleton Foundry put in a large induction shop and John Deere's East Moline foundry went to electric arc melting, so you can see that there was a clear choice of what was best."

While Heine noted that the pioneering Budd installation came after 234 other iron installations globally, W. Fischer of Birwelco, Ltd. in a '67 paper reported that "it took only a few successful installations in the U.S. to start a virtual stampede to induction melting...American foundrymen had unmistakenly taken over the pioneering role--that of putting in bigger and more powerful furnaces than had ever been built, often in applications new for the induction furnace."


Besides the promise of moving toward a smokestack-free industry, the assurance that the melt foreman and customer would receive the same product every time was a significant improvement. This quality improvement, said Lobenhofer, was substantial, particularly for the small foundry. Kotzin, who has seen the steady disappearance of true casting talent, confirmed that the technology (which "marvelously improved productivity") provided an "excellent opportunity for step-by-step process control."

"Cupola operators were the masters of the melt--dedicated students who monitored every heat," Kotzin said. "With coreless induction melting, you could essentially provide a reciPe to follow." Lobenhofer added: "It'd take 2-3 years to properly train a good cupola operator, and you might still be a little wary," said Lobenhofer. "In 2-3 months on an induction furnace, your operator could be well-trained."

By no longer relying on the chemical control of a process that also involved coke and limestone, careless induction offered a process in which foundrymen "got out exactly what they put in." Lobenhofer also noted that furnace's entrance also spurred anew, largescale industry education on iron metallurgy and inoculation.

Driven primarily by the change in furnace repair schedule, foundries reported man-hour/ton reductions that approached 50%. As reported in Rowan's '72 paper, the new induction furnaces could be continually operated and tapped every 20-60 mm., vs. the cupola that was tapped in batches once a day. "This permitted foundry operators to adopt assembly-line concepts to run molds down a pouring line, resulting in far superior utilization of the floor space and people."

Further, in a time when automakers first began looking seriously at aluminum, Heine credited the new melting method with "giving the iron foundries a boost by making their castings more competitive."

Lobenhofer said that an oft-overlooked improvement was work conditions, particularly in smaller shops. He recalled the story of a foundry president stopping by to see his melt operator 2 months after switching to careless induction. "Just to pull his chain," said Lobenhofer, "he told the melter that he was considering a cupola for an expansion. 'You do that,' the melter replied with the point of his finger, 'and I quit!'"

Changing an Industry

Development has been steadily increasing in this sector of the foundry, with changes that include medium-frequency power supplies for greater flexibility and reliability; greater melt capacities; batch melting processes (which increased production by 10%); digital control systems; and the ability to power multiple furnaces at once. Others include the many improvements in furnace safety, lining wear prediction and automation of the melting/ pouring process.

According to Stratecasts, Inc., induction melting will be used for 35% of all domestic casting shipments this year, and will grow to consume nearly another 5% over the next 10 years.
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Article Details
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Author:Lessiter, Michael J.
Publication:Modern Casting
Date:Mar 1, 2000
Previous Article:The Basics of Feeding Steel and Ductile Iron Castings.
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