Ladle refiner takes clean steel technology to new level.

Recently tapped at Maynard Steel, this refiner assures higher quality castings while saving nearly $180,000 per year.

Thanks to a cooperative effort between two industries, a new clean steel technology will propel foundries into meeting the quality demands of the 21st century--while significantly reducing costs.

On June 16, the world's first direct current (dc) plasma ladle refiner for a foundry application was tapped at Maynard Steel Casting Co., Milwaukee, Wisconsin. The project was funded by Maynard Steel; Wisconsin Electric Power Co., Milwaukee; the Electric Power Research Institute, Palo Alto, California; and the EPRI Center for Materials Production (CMP), Pittsburgh, Pennsylvania. This refiner represents a significant step forward in producing castings with fewer oxide inclusions while making steel foundry industry more competitive.

"It offers steel foundrymen the opportunity to increase productivity in the melting operation by 20-30%," said John Svoboda, Process Metallurgy International, Inc., and manager of the CMP foundry office. "This is achieved by performing a major portion of the total melting and refining cycle in a special, efficient vessel that is separate from the melting furnace."

The technology promotes clean steel technology--defined as low levels of sulphur, phosphorous and absorbed gas, as well as a minimal amount of nonmetallic inclusions.

Traditional refining is difficult in metalcasting because foundries use smaller ladles. Therefore, a smaller ladle refiner, capable of compensating for heat losses during refining, reducing nonmetallic inclusions, melting substantial alloy additions and controlling melt temperatures was needed.

The idea for the refiner was born about eight years ago when John Svoboda, Frank Kemeny, Nupro Corp., and Professor Alex McLean, University of Toronto, were discussing plasma arc furnaces in McLean's office. Since the technology is commonly used throughout the basic steel industry, Svoboda wondered aloud, "Why can't we apply this technology to a five-ton furnace and use it in foundries?" That day, the three men put their heads together and came up with a design that is very similar to what was installed at Maynard.

Ladle Design

Designed by Nupro Corp., the unit consists of a cylindrical graphite electrode mounted on a 4-1/2 ton bottom-pour ladle and fitted with a special three-plate slidegate nozzle system. In operation, molten steel is transferred from the electric arc furnace to the refiner, where the electrode strikes an arc with the molten bath.

Argon flowing through a small hole down the center of the electrode is used to form and stabilize the plasma arc. Because of the high heat capacity of the arc, the ladle closely controls the molten metal temperature and superheats the slag cover on the molten bath.

The steel is refined by the combined action of the superheating (which increases the slag metal reactivity) and the electric currents at the slag metal interface, which assist the electrochemical reactions. In addition, by passing argon through a bottom, porous plug, the entire bath of molten metal is stirred, improving chemical and temperature homogeneity.

The dc plasma ladle refiner is used to refine commercial grades of cast steel to very low levels of sulfur and oxygen, providing superior quality castings. The unit allows the production of two small heats of different alloy compositions from one larger melting furnace heat, providing additional production flexibility.

Benefits

The dc plasma ladle refiner offers several key benefits to foundries. These include:

* reduced melting energy use, precise chemistry control and improved shop logistics;

* improved steel cleanliness with increased productivity up to 30%;

* productivity improvements allow a portion of production to be shifted to off-peak periods, reducing energy demand.

Through the use of this electrotechnology, foundries can produce clean steel while increasing productivity.

Maynard's Application

Maynard Steel, a 500-man shop whose primary customers are the machinery and mining markets, began looking at how to reach new markets two years ago. "With the severe competition and excess capacity in the U.S., we knew we had to rise above commodity-based thinking," said Ed Wabiszewski, Jr., executive vice president.

Capital and installation costs for the ladle refiner were about $350,000. By processing 25 tons of clean steel through the refiner each day, Maynard will save about $30/ton in finishing costs, or about $187,000.

The refiner will enable Maynard to increase productivity by 20% for a product with a profit margin of $200/ton, yielding an additional $250,000 per year.

Factoring these numbers with total annual operating costs of $258,500, the foundry expects an annual savings of $179,000.

"Too often, R&D takes a back seat to short-term thinking," Wabiszewski said. "Innovation is the key. Not only does this type of effort ensure the future of Maynard, but also improves the steel casting industry."