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Modern Induction Melting Improves Process and Productivity

July 31, 2005
With a new Inductotherm dual-output melt system D&L Foundry and Supply cut operating costs and raised its performance level, to compete in the global market for municipal castings.

D&L Foundry and Supply Co., in Moses Lake, WA, casts manhole covers and frames, utility covers, and other municipal and utility castings. It is a good example of a municipal casting producer that is meeting worldwide competitive challenges head on.

In the 1980s, producers of municipal castings were among the first U.S. foundries industry to feel the impact of overseas competition, because their products were so basic enough that they could be matched by the less sophisticated foundries in places like China and India. Foundries in such places had difficulty offering technically sophisticated castings (e.g, automotive castings), but they could and did send municipal castings to the U.S. at exceptionally low prices. Municipal castings were especially vulnerable to price competition because most government agencies and utilities awarded contracts primarily on a low-cast basis.

Municipal casters got relief through the Intermodal Surface Transportation Act of 1991. This legislation explicitly required that only iron castings made in U.S. foundries could be used for federal transportation infrastructure projects, and effectively stopped American taxpayers from unknowingly subsidizing overseas producers of municipal castings. It gave U.S. foundries serving that market the opportunity to take steps to compete against foreign if they wanted to stay in business, i.e. increasing productivity and reducing costs.

New look foundry

D&L Foundry and Supply was founded in 1991 as a direct result of that legislation. Now, it is using advanced technologies to reduce its overall costs, including a new induction melt shop, mold lines and cleaning systems designed to lower man-hours and to consume less energy.

When it opened, D&L Foundry was melting with a 1,500-kW, 6,000-lb. induction melting system of European design. Soon, an identical system was added for a total connected load of 3,000 kW. But, by the end of the 1990s, these furnaces could no longer keep pace with the foundry’s increased demand for metal when a new molding line was added. More molten metal was needed.

Jason McGowan, D&L Foundry plant manager, explained that adding a third, 1,500-kW, 6,000-lb. furnace system was not an attractive option for several reasons. “We were up against a 5,000-kW limit from our power utility. If we used more power than that, we would need to build a new power substation and there was no way for us to justify that cost,” McGowan noted. “Also, our power utility had experienced harmonic problems caused by our original induction equipment, and we had to add filters to our lines.

“These filters, however, did not solve the problem,” McGowan said, “and we were facing further costs for even more power filtering. Finally, at best, we were only able to achieve 50% utilization of our induction power equipment and, therefore, not getting full value from our power company load factor charges,” he said. “We knew we needed a melting system that would be more efficient and more productive. Also, it needed to be cleaner, both in terms of harmonics-free power usage and reduced fume emissions.”

To meet the need for higher melting capacity without exceeding its 5,000-kW cap, D&L Foundry installed a single, modern, solid-state 3,250-kW dual-output induction power supply, connected to two four-metric-ton furnaces in place of the two European design furnace systems. (One of the original furnaces was retained to provide some supplemental capacity under strict power demand control.)

Inductotherm Corp. supplied the new melting system. Of the former installation, McGowan recalls “that system was characterized as the ‘Cadillac of melting systems,’ but we didn’t need a Cadillac.

“What we wanted was a pickup truck,” McGowan observed. “And that’s what we configured the system to be, a great pickup truck. It was the right tool for the right job.”

New melting process

As configured by D&L Foundry, the new melting system came equipped with several important options: close-capture fume-collection covers; an automated computer system built into the power supply with input from furnace load cells; and a hydraulic lining push-out system. Also, an automated charging system with a preheater/dryer and vibratory conveyors replaced the charging buckets used with the old furnace system.

With its new dual-output induction system, D&L Foundry was able to change from the heel melting process with its previous system to more efficient and safer batch melting.

“With the dual-output power supply, we are able to melt in one furnace at 3,000 kW and simultaneously use the remaining 250 kW to maintain temperature on the furnace being poured,” McGowan explained. “In a normal operating cycle, we melt 9,000 lbs. of iron in one furnace in about 40 minutes and it takes about 35 minutes to empty the pouring furnace. With the time needed to slag and adjust chemistry, we are able to achieve power-supply utilization of 90%, compared to 50% with our old systems,” he reported. “This lets us take advantage of the full value of our load factor power charges while increasing production 80% at no increase in demand charges.”

“Another advantage of batch melting is better metal quality,” McGowan said. “It’s easy to produce metal with its chemistry right on spec. With heel melting, it was difficult to maintain the desired chemistry for each tap. It was a moving target.”

Overall, with its new dual-output system running on a three-shift melting schedule, D&L normally runs at 100 tons of castings per day with a top capacity of more than 120 tons per day.

McGowan reported that the new melting equipment eliminated problems with power line harmonics. “The new equipment operates inherently “clean” without power-robbing and unreliable harmonics filters. Complaints from our power utility have stopped.”

Emissions control — Anticipating more rigorous foundry emissions standards, D&L Foundry ordered its new furnaces with integral fume-collection covers. “We knew we had to significantly reduce emissions, but we also did not want to incur significant new expenses,” McGowan explained. “Our competitors in the Third World certainly weren’t burdened with such costs,” he pointed out. “That’s why we were pleased to learn that our existing dust-collection system would work with the new furnace close-capture covers. When we connected everything together, virtually all furnace emissions were taken care of and removed,” McGowan reported.

Melting Control — While D&L foundry did not anticipate the need for a separate melt-control computer system, the advantages provided by computerized controls built into the power supply were compelling enough for it to be selected for its new melting system. “Computerized controls offered us the same equipment operation and safety advantages as a separate computer, without the ‘bells and whistles’ we didn’t need,” McGowan said. “These automated controls, with accurate input from the furnace load cells, enable our furnace operators to control temperature precisely while melting and holding, reducing wasteful and dangerous overheating of the bath. They also allow the melting system to be operated remotely from the safer environment of the control room.”

Maintenance — Both routine maintenance that takes any longer than absolutely needed, and unplanned downtime, can rob a foundry of its productivity. That’s one reason D&L Foundry specified its new furnaces be supplied with hydraulic lining-removal systems. “The lining push-out system for our new furnaces allows us to remove a worn lining quickly while the dual-output power supply lets us maintain more than half our production during the process,” McGowan said. “Also, hydraulic removal requires less labor, produces less dust, and is less likely to damage the back-up lining than manual lining removal,” he noted. “Our offshore competitors can throw lots of man-hours at manual lining removal with little cost: we have to do it better and faster.

“In terms of unplanned downtime, we have not lost any production time since the new melting system was installed almost five years ago,” McGowan reported. “It has proven to be highly reliable.”

Manpower Savings — With its new equipment, D&L Foundry was able to reduce its melt deck crew from three furnace operators to two, a significant savings. “But that wasn’t the most important effect involving personnel,” McGowan noted. “Thanks to our new melt shop, turnover virtually disappeared. With our old system, workers typically quit after six months in the melt shop as a result of the poor working conditions brought about by metal splash, ineffective fume collection, and the excessive slag removal required. This was an enormous drain on human resources and productivity,” he said. “Now, with the addition of an air conditioned control room (made possible by the computerized furnace controls), the higher freeboard of the U.S.-designed furnace, the effective fume-collection system, and the automated charging system, working conditions are much improved. Melt shop turnover is nil.”

Looking ahead

D&L Foundry planned its new melting system for future growth. Its current system has a 3,250-kW power rectifier connected to two 3,000-kW power inverters, one for each furnace. This allows the 3,250 kW to be allocated in any proportion between the two furnaces. Also, the system has been configured so that an additional 3,250-kW rectifier and inverter with an additional furnace can be connected at any time, creating a three-output power system. “A three-output, 6,500-kW melting system would give us the ability to double our melting capacity,” McGowan said.

In a global market for castings, foundries in developing countries have competitive advantages: low labor costs, lack of pollution control costs, and government subsidies. But, this should change as living standards improve in these countries. Wages will increase and governments will recognize the need for more regulation and less subsidization. And, emerging automation technologies will offset the economic advantages of low-cost labor.

A number of U.S. foundries in the municipal casting market have proven they can succeed globally — with some transitional government protection and by applying automation technology to foundry operations. D&L Foundry and Supply Co. has demonstrated that automation and efficient power usage in the melt shop can play an important part in reducing costs and raising productivity.