Recycled steel can scrap is a proven iron foundry charge.
One man's trash is another man's charge material. OK, so it's not as catchy as the original adage, but it's nonetheless true-particularly in the case of the 1.5 million tons of steel cans discarded each year by private consumers and businesses that end up as industrial raw materials. Soup, vegetable and other food containers, along with pet food, paint and aerosol steel cans, make the journey from the curbside recycling bin to the steel mill all the time. However, more and more of those cans are being diverted from that journey, landing at iron foundries around America.
As the recycling push in the U.S. has intensified, new materials have headed for the scrap yards, opening up opportunities for alternative foundry charges. That is fortunate for foundries, as the proliferation of scrap-consuming steel minimills has in recent years greatly impacted the price and availability of conventional steel scrap. Since pioneering research in 1991, several large iron foundries, and probably an unknown number of other, have been adding quantities of post-consumer steel cans as a significant part of their charge material. Steel cans have proven to be a reliable, beneficial and, above all, cost-effective steel charge for iron melters.
Considering the nature of scrap, coming as it does from from various sources and various uses, steel cans provide a priceless quality: metallurgical predictability. They are uniformly made from high-grade steel and carry the added attraction of having generally less rust than other steel scrap.
According to Carl Loper, Jr., material science and engineering professor at the Univ. of Wisconsin-Madison, who orchestrated the early studies into steel can scrap's charge viability, the metallurgical implications of adding the tin-containing steel cans to the iron foundry melt were not harmful, and even proved beneficial. "For gray iron, tinned steel can scrap has worked out well, particularly in cupola melting," he said. "The levels of tin have had no detrimental effect when using the cans as up to 15% of the charge.
"Can scrap also seems to do well for ductile iron. You probably can't use as much of it as in gray iron-anything above 0.3% may cause trouble with annealing. Also, ductile iron metal-casters seem to be more reluctant than others to use it; they tend to stick with a more pure charge source."
The can scrap also improves mechanical properties of cast irons, including tensile strength, hardness and wear resistance. But while the steel cans themselves are a benign addition, they sometimes bring with them contaminants in the form of plastics and, particularly, aluminum cans.
"For the most part," Loper said, "aluminum content in the form of contaminants is not really a problem in cupola melting because the aluminum enters the slag and is removed with it. With electric melting, however, the aluminum may build to high levels. But even those foundries that have seen that happen in testing did not really have the pinholing problems that aluminum causes in iron castings."
One foundry with experience in that area is J.I. Case Co., Racine, Wisconsin. The foundry, melting 225 tons of gray iron per day, was one of the first to adopt steel can charging nearly five years ago. "The only thing you have to watch for is aluminum contamination," said Chief Metallurgist Charlie Shirvani.
The foundry continuously monitors the fluctuating aluminum level in the molten metal, taking steps to reduce it when necessary. "Only once did we have a significant problem with pinholing in the castings," Shirvani said. "That was due to a massive aluminum contamination in the melt."
Price and Procurement
Shirvani is a staunch proponent of steel cans. "I would charge up to 20% if I could get that much," he said. Right now, however, Case's suppliers are unable to provide enough cans for that type of ratio. Like other forms of scrap, steel cans fluctuate in availability as well as price.
Lisa Hirsch, superintendent of materials at Dalton Foundries, Warsaw, Indiana, has seen wide variances in availability since the foundry began using steel cans as a significant addition to its charge more than four years ago. "It is sometimes hard for us to acquire, mainly because recycling laws vary so much," she explained, saying that Indiana lacks a strong state-wide steel can recycling effort, and a lot of potential charge material is still being landfilled. "Our steel can scrap comes from as far away as West Virginia, Iowa, Michigan, Ohio, and some closer to home here in our state.
"What I find amazing-and a little sad-is that these steel cans can come all the way from West Virginia and still be cost-effective for both parties. If recycling laws were tighter and more comprehensive, it would be better for all of us from the supply side, the price side and the environmental side."
Waupaca Foundry's Plant No. 1, Waupaca, Wisconsin, deals with brokers and municipal recyclers for its steel can scrap. "We get all the post-consumer steel cans in central Wisconsin," said metallurgist Mike Nikolai. The gray iron operation has been using the cans since Waupaca's Metallurgical and Melt Manager Bill Powell, who was interested in finding alternative steel charges as the new minimills began to gobble up scrap supplies, approached Waupaca County's solid waste disposal department about the idea in 1990.
A recurring theme among foundries buying steel can scrap is that availability is sometimes hampered by the foundry's own necessary selectiveness. While quality is important to everyone, steel scrap headed for steel mills has less buyer-imposed requirements. Residual elements in the scrap pose less of a problem for them, while they can and do accept very large bales of the material. Most foundries, however, need smaller sizes of bale (Shirvani said Case purchases 2x2 ft bales weighing about 80 lb), which many scrap processors aren't set up to provide.
The condition of incoming cans also makes a difference. Waupaca Melt Superintendent Len Jansen said the foundry asks suppliers that cans have only painted labels, "mostly because paper labels leave kind of a mess in the scrap yard. If we get some paper labels it's not a big deal."
Unlike Case's situation, Waupaca has voluntarily limited the amount of cans it charges. "We've run as much as 78%," said Jansen. "We've found that as iron demand increases, steel can charges decrease. That's because when you charge loose cans in the cupola, they tend to lay across the surface in a fish scale effect, which impedes air flow and builds up back pressure. When that happens you don't get the amount of iron you need out of the cupola. We're down to about a 3% can charge now."
Waupaca recently began obtaining its scrap from a processor who mixes the cans with shredded conventional steel in a 50/50 blend. Charging the steel cans this way is expected to raise the can charge ratio up to 4-5%. Jansen explained Waupaca's attitude toward the alternative charge: "It's a good, clean source of steel. Although we always have enough cane scrap for our requirements, the best thing about it is that you can add it if you have it, but you don't need it. We can charge tin pellets if necessary, so we aren't completely dependent on the steel can scrap."
Tin is one of the keys to steel can scrap's cost effectiveness. While cans are cheaper to buy than conventional steel scrap (at the time of this writing, conventional plate and structural steel scrap cost about $165 per ton in Wisconsin, with steel cans at about $125), an unexpected cost benefit arose from the original research. At 3-4 lb of tin per gross ton of steel cans, the tin level in can scrap is, if used in the proper ratios, sufficient to reduce or even eliminate the need to add copper for pearlitic formation in gray iron. Greg Crawford of the Steel Recycling Institute, Pittsburgh, said that 1 lb of tin has the same effect on pearlitic formation as 10 lb of copper.
Tin's price, however, is largely prohibitive. According to Shirvani, the steel cans charged at Case replace 30-40% of the necessary copper, without spending a cent on tin.
`The Three Ps'
According to Crawford, "A foundry using steel can scrap gets the benefits of 'The Three Ps': Pricing, Predictability and PR." He noted that "a few environmental buzzwords can make a foundry a local hero," and that if one can claim it is recycling-particularly recycling things people see and use everyday-it will go a long way toward building the company's image within its community.
There are other opportunities besides steel cans, Crawford said, citing automotive radial tire wire (average tires contain 2.5 lb of steel) and used oil filters as potential charge materials. "With the oil filters," he said, "cupola melters not only get the steel. but the oil-impregnated paper provides extra carbon. If carefully added in a metered fashion, oil filters can be a real benefit to the melt."
Like steel cans, however, these products aren't easy to find in a foundry-ready form. "We've looked at a lot of alternate scrap sources, including steel tire wire and crushed oil filters," Hirsch said. "Any conscientious foundry is doing that. We found they were usable if we could get them processed a certain way, but nobody seems to be doing that processing."
For the present, Hirsch said Dalton is satisfied charging its cupola with steel can scrap. "It's a pure, predictable charge material," she said. "As long as it's cost-effective, we'll continue to use it."
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|Author:||Philbin, Matthew L.|
|Date:||Sep 1, 1996|
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