History of Electric Induction Heating


By James Farol Metcalf

Part of Chapter 11 from The Fire Within

"How fast can you get here?"

Foundrymen call it a "run-out" and it's their worst nightmare. It occurs when molten metal eats through the refractory to the coil where it short circuits the copper tubing and arcs. In the "worst case" scenario, the furnace will explode as arc and the hot metal burn through the coils to the water inside, changing its state from liquid to steam, shooting liquid metal everywhere.

It is really not that bad. Water under steel really is dangerous but water on top of steel makes steam. In almost every case when the steel finds a way through the coil the power supply trips and most of the time just a little escapes. In most major run-out situation the un-melted on the top forms a bridge causing the metal under it to become hot enough for a bottom run-out. Anyway it is a mess and the coax had already been replaced in all furnaces Stokes/TOCCO installed before this date.

On February 14, 1957, Crucible Steel company in Syracuse, New York, called to tell me they'd suffered a run-out on the division's production furnace, a 2,000-pound vacuum unit built by Stokes in Philadelphia in cooperation with the Consolidated Vacuum Company in Rochester, and the National Research Company in Boston. "I've never seen anything like it," said Chris Houghton, manager of Crucible's vacuum melting section. The scratchy phone connection did nothing to disguise the shock in his voice. "There's metal everywhere. The furnace is shot and we're out of business. Hank, we need help desperately."

As he described what had happened the day before, I couldn't help recalling that day at the Mint, when I was courting a similar catastrophe.

Crucible hadn't been so lucky; its production furnace had run out and exploded, sending lumps of molten alloy smashing like dumdums against the walls of the vacuum chamber that contained it.

Since Rowan was there one must assume that water some how was under the molten steel AND this happened when no vacuum was applied to the chamber. EVEN MORE LIKELY he allowed his writer John Calhoun Smith some poetic license.

If there was a positive note to the episode, it was that the vacuum chamber contained the explosion when it happened; otherwise, the consequences could have been far worse. As it was, the company was in dire straits. Crucible Steel used this particular furnace to make aircraft-quality super-alloys, worth about $10 a pound. Each time the company tapped a heat from that 2,000pound furnace, it produced $20,000 worth of ingots. With four melts per day, the furnace could generate $80,000 in revenue.

Conversely, every day Crucible was out of business, it lost $80,000 worth of production, and, with fixed costs continuing, most of that $80,000 was red ink.

In early 1957 the whole industry was in trouble because the properties of superalloys had gone down and almost every ingot cracked when forged. The early success by Special Metals was because they were processing the mountain of scrap previously melted in arc furnaces in air. Soon afterwards Nick Grant of MIT made the link that an impurity of boron from the arc furnace linings was missing form the new virgin melts. EVERBODY WAS LOSING MONEY ON EACH MELT.

"We've got to get a new furnace in here, and we want to get Inductotherm involved," said Crucible's CEO. "How fast can you get here?"

"Oh, how about this afternoon," I said, as casually as I could.

"This afternoon?" he sputtered. "How do you plan to get here, fly?" he asked incredulously. Houghton knew how far Syracuse was from Delanco, and as it was then close to noon, he knew it would be impossible for anyone to cover the four hundred miles of road in time to get there that afternoon. But when he said "fly," commercial flights weren't what he had in mind; airline schedules and connections between southern New Jersey and upstate New York were few and far between. No, what his tone of voice said was, did I plan to grow wings and fly?

"That's exactly what I plan to do," I advised him.

"I'm going to fly." This was a day I'd been looking forward to for years; this was the day Inductotherm earned its wings. I'd bought my plane, an old Ercoupe that had caught my eye at the Moorestown Airport, the previous month, and I received my private pilot's license the day before getting Crucible's phone call.

I couldn't help feeling I was overdue in buying this plane. It was a sibling to the single-engine two-seater I'd hoped to buy four and a half years earlier, but had quit my job with Ajax Electrothermic instead. I still loved the freedom and the feeling of flight and the fact that flying could take me where I wanted to go faster than any other mode of travel. I was also keenly aware of the fact that flying could give Inductotherm a big advantage over our competition.

The metal melting industry isn't like many other businesses-textiles, advertising, or the garment trade--with multiple companies clustering together to form a district. Instead, the majority of our customers were dispersed around the East and Midwest, often 100 miles or so apart. These included companies like Curtiss Wright in Buffalo, New York; GE in Cleveland, Ohio; and now Crucible Steel in Syracuse, New York. By car--even if he left at the crack of dawn--a salesman would have had a tough time getting from Inductotherm to Syracuse and back in one day. But, as I had observed a decade earlier from the cockpit of a B-17, it would be a cinch to cover the circuit by plane.

Typically, however, acquiring that first plane was a gamble. "There's only one problem with flying, Hank," said Bob Hotchkin, the day I advised him of my plan.

"What's that, Hotch?" I asked.

"Corporate planes are an extravagance that a growing company like Inductotherm can ill afford," he complained. "It sends the wrong message to your employees, especially with you preaching the gospel of frugality, and it can be misinterpreted by your customers."

I sighed, resignedly, to myself. I understood what he meant, but at the same time, I felt Hotch was dead wrong. The issue he raised was one of perception and, like most people, Hotch didn't yet appreciate what flying could do for us. Still, there was a logic to what he said, and I was unwilling to ignore his advice, which had always been so right, and so valuable, in the past.

That didn't mean I was willing to abandon the corporate strategy I'd envisioned, in which flying would play a pivotal role. Inductotherm had reached that point in our development where time--especially the CEO's time--was precious, and personal mobility, invaluable. So much so that I couldn't afford not to fly, or so I rationalized. Thus, to appease Bob on the one hand, while still gratifying my yearning to fly on the other hand, I dug into what was left of my money from the sale of our home in Trenton, and for $1,600, I became the proud owner of a second-hand Ercoupe.

It wasn't a tremendous amount of money, and the plane, with a top speed of no more than 90 miles an hour, was a pretty poor excuse for a corporate aircraft. To look at it, nobody would have suspected that, on its first flight, that humble little Ercoupe was going to launch Inductotherm into the thick of the burgeoning jet aviation field.

Nobody had heard of jet aircraft until the previous decade, but the Cold War and then the Korean Conflict and the need for jet fighters and bombers had spurred military R&D, resulting in aircraft like the F-86 and B-52.

On the civilian side, commercial airlines were replacing piston engine aircraft with larger, faster, and more comfortable jetliners--DC-8's and 707's--as fast as Douglas and Boeing could move them down the assembly lines. The Sunday rotogravures spoke eagerly of a time when people would travel by air as routinely as they traveled by train.

On this page is Rowan sitting in his first executive aircraft--The Ercoupe 1955 with his young son.

At the same time that jet aviation was opening up a new era of flight, it was also creating a demand for a new induction melting technology, vacuum melting. Although jet engines were simpler and more reliable than piston engines, they ran at very high temperatures--as hot as 1,800 degrees Fahrenheit--at which point ordinary steels lose nearly all their strength. Moreover, jet engine parts had to withstand mechanical stresses far beyond those encountered in piston engines stresses that would rupture even the superalloys, if they contained microscopic impurities in the form of oxides resulting from exposure to air in their molten state. Superalloys for the new, more demanding engines could only be produced in furnaces in vacuum chambers free of oxygen or other gases.

For induction furnace manufacturers, vacuum melting brought a new, more stringent subset of criteria. The furnaces had to be more compact to fit into the vacuum tanks. Further, the porous materials used in air melting could hold moisture and gases which would "outgas" into the vacuum, and thus had to be kept to a minimum.

Coil joints and power connections were far more critical than in atmospheric melting because even the slightest water leak, insignificant in air melting, would expand 100 million times as water vapor in vacuum, spoiling the integrity of the vacuum environment. The refractories required in vacuum melting also allowed for less margin of error. They had to be thinner and of higher quality, since contact between the molten alloy and refractory, just as exposure to the air, created impurities.

I doubt that even today Rowan has taken the time to understand the effect of water in a vacuum system. First water expands about 1700 times when it becomes steam and although steam is not a gas the effect the volume is about 1,700 million. Something unexpected happens in a melting furnace. A small water leak from the coil expands to become steam and this takes energy. The location is where it can not see or use the heat of the melt and most of the time freezes at the point of the leak.

Even more critical was the coil construction. Coils had to be electrically insulated in order to avoid corona and arc-over in the ionized, rarefied gases in a vacuum furnace.

I was eager to establish Inductotherm as a major presence in this new field, but in terms of experience and volume, the established furnace makers held a clear advantage over us. Ajax and TOCCO and now National Research of Boston, which had built the 2,000 pound Crucible Steel furnace, had carved out a position for themselves in this industry. Nonetheless, perhaps because the technology was so new, or perhaps due to the highly cyclical nature of the vacuum melting industry, they had failed to make the commitment to this field, and no one held a dominant position in this technology. All too often, the burden of fine-tuning and upgrading the furnaces for successful operation in the harsh vacuum environment fell upon the vacuum melter.

So here was an opportunity to gain a foothold in this new and exciting industry. Our smaller size, our flexibility, and our willingness to operate in an "emergency" mode, made aviation alloy producers an ideal market for us.

Further, our first furnace customer, Stokes, was a leader in the manufacture of the vacuum systems, and that 30-pound vacuum furnace--Inductotherm's first ever--had been performing flawlessly for over two years, as had others we'd built for Stokes. Still, it was probably more desperation than confidence in our abilities that prompted Houghton and Crucible Steel to turn to Inductotherm.

The flight to Syracuse took about three hours, as air miles are a lot more direct than road miles. After landing, I rented a pickup from an airport employee for the drive to Crucible, where I found Houghton. We walked through the melting facility and into the melting chamber, a steel-walled chamber about 10 feet in diameter and 10 feet long. It was an eerie place; our footsteps echoed sharply against the artificial, tomb-like silence; the walls were splattered with lumps of solidified alloy--$20,000 worth of scrap.

The furnace, now a blackened hulk about three feet cubed, hung at the center of the vacuum chamber hinged about the axis of the coaxial power conductor that ran through the steel wall of the chamber. The 2,000-pound-capacity furnace was huge compared to anything we had ever built for vacuum. From the standpoint of either engineering or operating, the coax was a nightmare. It was comprised of two copper tubes, one 14 inches in diameter within another, about two inches larger, both water-cooled with complex and expensive sets of bearings and water seals where the coax connected to the furnace. All very fancy and all very expensive and far beyond the specialized capabilities of our still-nascent company.

For what must have seemed ages to Houghton, I walked back and forth in front of the open chamber, occasionally stopping to gaze inside with much the same bedside manner as a physician confident he could get his patient up and walking around soon. But there was no use kidding myself; Inductotherm was not equipped to rebuild that coax. At the same time, it was against my nature to say sorry, maybe Ajax or TOCCO can help you, but Inductotherm can't. My stomach churned as I pondered these two alternatives, neither of them acceptable to me. This golden opportunity to thrust Inductotherm into vacuum melting technology now seemed to be slipping from my grasp. Why, I asked myself, did Crucible's furnaces have to have a coaxial power entry? Why were these coaxials so danged complicated and expensive to build. Rhetorical questions, I knew, but I was desperate.

Yet, the more I thought about it, the more I became convinced that these were good questions. In fact, if it were possible to substitute a standard flexible lead.

I stopped in my tracks; it just might work. It had to work. But first, I had to convince Crucible Steel of that. "Chris, we can build your furnace," I began, hoping that I sounded more confident than I felt, "but there's no way in the world we can replace that coax. Nor would we want to. It's far too complex, too expensive, and, in many ways, too fragile."

"Well, then, how do we bring the power in?" asked Chris, exasperated, knowing full well that, without a power connection, a new furnace was useless.

This was no time to hesitate, though a myriad of questions and answers raced through my mind even as I was talking. "What I would propose is a whole new approach to the power entry," I continued. "We can use standard airmelt flexible leads adapted for vacuum. It will be simpler, more reliable, and rugged. What's more," I was hoping this would be the clincher, "we can do it and get you back into business much faster than if you were standing around, waiting for somebody to build you another coax."

Houghton nodded, and I went on. "What we'll do is build an insulating Micarta power port to seal on the coax's entry flange. Then we'll vulcanize rubber plugs to the power leads, and they'll plug into holes in the Micarta plate like corks in a bottle, forming a vacuum seal where they enter the chamber. We'll make the connection to the capacitor bank bus outside the vacuum chamber, and then we'll have only the four furnace connections to insulate and make leak proof."

The engineer thought about this for a moment or two before responding, "I don't see any reason why it wouldn't work, only ... "

Only what? I thought to myself, and held my breath. What if Crucible's chief engineer was simply unwilling to depart from the way his company had always done things? If that was so, my trip here was in vain. But, in fact, Houghton wasn't about to object; I breathed a sigh of relief as I heard what he had in mind.

"Instead of replacing the old furnace with one the same size," Houghton was saying, "what's the possibility of moving up to a bigger one? Say, a 3,000-pound furnace?"

My heart leapt! A 3,000-pound furnace would be the biggest vacuum furnace in the world. If we made it--and of course we wanted to make it--we'd position Inductotherm in the forefront of vacuum melting technology. Of course, I agreed with him.

"It sounds like a terrific idea, Chris. You'll be able to produce 50% more alloy with each heat. And we'll be pleased to build it for you."

Houghton smiled at the prospect of turning this misfortune into an opportunity to expand his capacity, and I had to admire his thinking; this was the way progress was made. Then, he came to the big question. "How much is it going to cost us?" he asked, warily.

Any astute businessman would have suggested that he'd have to return to his office, study the cost involved, and call back with a quote. But I was rarely astute, far too impetuous, too anxious to appear the expert, and too bent on closing the deal then and there.

So mentally I made a stab at weighing our probable cost against the market price, reminding myself of Roy's lessons on pricing, yet fully aware of how badly I wanted this job. "How does $5,300 sound, Chris?" I asked, tentatively. What if it was too high? But if I'd expected Houghton to play hard to get, I was wrong.

"Good. I'll take two," he said, happily. "As long as you can get the first to me within two weeks."

Two furnaces? This was turning out better than I had ever imagined it might. I agreed, and we shook hands on the deal. Yet, as we walked out of the Crucible plant I began to wonder how good a deal it was, and for whom.

Houghton was still chatting, expansively, as he walked me up to the truck I'd rented at the airfield. "Thanks for coming up. We're really desperate to get back into operation. I can't wait to work with our new 3,000-pound furnace," and so on.

Then, before I drove away, he said something that hit home. "You know, we paid $20,000 for that 2,000-pound furnace and $20,000 for the coax. So we were looking at a $40,000 problem, and you solved it, with two larger furnaces, for $10,000."

Fifteen minutes later, I had lifted off and was headed south, but I couldn't get Houghton's last words out of my head. As the section head had said, they were prepared to spend $40,000 for one 2,000pound furnace and coaxial, just to get back to work, and with anyone else they'd probably be shut down for six to eight weeks. But no, they were getting two 3,000-pound furnaces for $10,600 and in two weeks. Should I have charged $30,000 for them? Or, $60,000? Of course, I took pride in delivering value to our customers, but still, it gnawed at me, to think that I was selling Inductotherm short. And that I still hadn't learned Roy's lesson very well.

Sure, that $10,000 price would cover our costs and yield a modest profit, but we were providing more than equipment; we were providing solutions to complex, multi-million dollar problems. Either way, it was too late now. I tried to console myself by reminding myself that, with this one flight, my $1,600 investment in a second-hand Ercoupe had more than paid for itself.

Two weeks later, we installed Crucible's first 3,000-pound furnace with the radically different power connection, which performed every bit as well as I had hoped. In fact, it worked so well, it became the standard for vacuum induction melting, replacing coaxial power supplies not only in this installation, but in dozens of other future furnaces of various sizes and configurations.

This was the only furnace remaining with a coax at the time because furnaces at Cannon Muskegon, General Motors Research, Carpenter Steel, General Electric, and Cyclops were using standard pass through assemblies. I am not sure when Special Metals changed the earlier ones that led to this one being at Crucible

For Rowan the 3000 pound furnace with the improved coil, leads, and pass through system coupled with his already technically superior power supply allowed Inductotherm and Stokes to win every order in the market place until I started to sell for Ajax in 1961.