After nearly a quarter century powering Acheson Foundry’s iron melting, everyone agreed that the Inductotherm 400-kW Power-Trak® induction power supply was ready to be replaced. In this case, “everyone” was the Rigsby family, fathers and sons, who have owned and operated the jobbing foundry in Chattanooga, TN, for over 100 years.
“We ran the heck out of our old Inductotherm system. It paid for itself many times over,” explained Jimmy Rigsby, vice president. “But, we needed to increase our production and update our technology. Inductotherm had done a great job keeping our old power supply running. However, many of the parts they needed were no longer in production, like a fast-acting circuit breaker that GE had stopped making years ago.” He went on to explain that Inductotherm retrofitted another type of system to replace the breaker. “It was getting to the point where our retrofits had retrofits,” Rigsby joked.
While it was time to replace its old power supply, the Acheson Foundry’s existing Inductotherm Dura-Line® furnaces still worked well. So, the foundry decided to continue melting with both the 1,000-lb furnace, installed with the original power supply in 1980, and the 1,500-lb furnace installed a few years later.
New power supply -- To replace the older unit, in 2004 Acheson Foundry purchased a new Inductotherm 600-kW Dual-Trak® induction power supply with built-in Melt-Manager® computer controls for its melt shop. “This new unit was set up with a limit of 400-kW so we would not exceed our electric demand,” Rigsby noted. “It was all the power we needed, but the full 600 kW remained available to power future growth.”
Acheson also installed a new Inductotherm closed-loop evaporative water-cooling system to replace its original open water-cooling system.
The system replacement proceeded quickly. “We needed to build a metal stand for the Dual-Trak unit and modify the bus trench,” Rigsby said. “Much of the work, however, could be done while we continued production with our old unit. There were only 10 days of downtime needed to complete the installation.” He pointed out, “We did not have to do anything to our existing furnaces to use them with the Dual-Trak unit.”
Being able to use its existing furnaces with its new power supply was a notable advantage for Acheson Foundry, producing significant cost savings for capital-equipment purchases and installation, Rigsby said. Also, Acheson was able to use its existing incoming power transformers, resulting in additional savings.
Regarding the new cooling system, Rigsby noted, “The closed cooling system solved our water issues. The old, open system required a lot of maintenance, and when it was removed we could see how build-up over the years had clogged many of the pipes. The new system with water and glycol is much cleaner and runs much cooler. It does not require nearly as much maintenance,” he said.
New melting system -- Unlike the previous single-output power unit, the new dual-output power supply is able to send power to both of Acheson’s furnaces at the same time for melting and holding. “We melt a complete charge in one furnace while we pour from the other.” Rigsby explained. “About 90% of the power goes to the melting furnace, while 10% is used to maintain the temperature in the pouring furnace. With our single-output power system, we were losing 20 minutes of melting time while were pouring. Now, with the Dual-Trak system we keep the melt ‘rocking and rolling’ while we are pouring. So when the pouring furnace is empty, the melting furnace is ready to pour,” he said.
Rigsby said that dual-output melting operations make it possible for Acheson to pour 3,000 lb more metal per day than was possible with its old, single-output system, at the same 400-kW demand level. “Our average daily production is 7,500 lb,” he said. This means that the additional metal represents 66% more daily production, without increased demand charges.
“In the past, the molders waited for metal.” Rigsby said. “Now, it’s the melters waiting for the molders to catch up.”
“There is not much a small foundry can do about increasing power rates,” he continued. “In our area, power rates were relatively flat until last year when they went up 7.5%. This year they are going up another 10%. Increasing production while keeping a cap on demand is one of the few ways a foundry can help to control its power cost per ton of metal melted,” he said.
Acheson melts gray and ductile iron, Ni-hard, and some steels. Induction batch melting gives the operators “great metal flexibility,” according to Rigsby.
Also, the dual-output power supply has allowed Acheson Foundry to increase the size of the castings it produces. “Now we can melt and hold the metal in one furnace at pouring temperature while we melt in the second furnace,” he explained, allowing Acheson to pour molds as large as 2,500 lb. “This has proven to be very useful for us and has brought us a lot of new business,” he said.
The built-in computerized operator assistance system has been productive for Acheson. “With the Melt-Manager system on our Dual-Trak unit, the learning curve for the operator was not bad,” Rigsby said “Melt-Manager really is user-friendly. We use it to preheat the furnaces in the morning. We especially like the sintering feature and the alarm history. The Melt-Manager’s control of sintering gives a much better sinter, and the lining lasts longer than it did when we ran the sinter ourselves,” he said.
Updating its melt shop was first step in Acheson’s capital improvement program, the goal of which is to upgrade the equipment to meet Acheson’s increasing production demands. “Melting is the heart of the foundry. If you don’t have melting, you don’t have anything,” Rigsby observed. “With the way our business is growing, we soon will need to remove the 400-kW power limit and use the new unit’s full 600-kW capacity.”
100 Years of Casting Iron
As related by Randy Rigsby, one of Acheson Foundry’s owners, the operation was founded in 1899 by Leonard Acheson at the same Chattanooga location it still maintains. The foundry was built to serve the coal industry, casting parts for mining equipment and later for steam engines. When it was established, it had just six employees.
Today Acheson Foundry has 30 employees. It is primarily a short-run jobbing operation specializing in producing prototypes and more complex castings involving core work. It also produces castings for historic battlefield equipment, such as parts for the cannons displayed at many of national and state parks and historic sites commemorating Civil War and Revolutionary War events. Similarly, it produces castings for many steam railroads operating around the country, including Chattanooga’s Tennessee Valley Railroad Museum.
“We have many talented pattern people around this town and they are able to build patterns from old drawings or simply from sample parts.” Randy Rigsby noted. “When I see many of the antique castings that come in to be recreated, I often am amazed by the skillful work of the early foundrymen. Our industry has a great heritage that we at Acheson Foundry are working to continue.