Turnings, whether the smaller machine shop item or the short shoveling variety, are often seen as the dregs of industrial ferrous scrap. They were rarely, if ever, used by integrated mills in their open hearths and basic oxygen furnaces. And while they have become more desirable as melt materials since the development of the electric-arc furnace, they still don't get much respect.
The material charged into most mini-mill furnaces normally includes only between 2 and 5 percent turnings, much lower than the 30 to 40 percent of bushelings and shredded material used to fill the charge buckets. This scrap, however, has found a home in the electric furnace shop—well, more like a back bedroom or an efficiency apartment.
While turnings might not be the most desirable scrap, they still require sorting and checking, according to Mitch Padnos, executive vice president of sales and marketing at family owned and operated Louis Padnos Iron & Metals Co. in Holland, Mich. "We check all the inbound loads to make sure it isn't getting mixed (with alloy or stainless turnings)," he said.
In the past, Padnos and many scrap processors used to briquette the turnings, which makes them easier to ship and reduces the loss in the furnace. But today, fewer mini-mills want briquetted turnings. In some instances they distrust the materials in briquettes in much the same way they question what might be inside No. 1 or No. 2 dealer bundles, Padnos said. The big question often is chemistry. "People would wonder what was in it" because often the briquettes were made of turnings from 50 or 60 different industrial plants, he said.
Some melters layer charges in the furnace and prefer to use loose turnings at the bottom of the melt vessel. At the bottom, the turnings can serve as a sort of cushion for heavier scrap, like No. 1 heavy melt and No. 1 bundles, in part helping to protect the refractory at the bottom of the furnaces. Putting them at the bottom of the charge also helps keep the turnings from flying out the top of the furnace and into the melt shop's baghouse.
Turnings come in different sizes and configurations. Machine shop turnings are short and curly, while the short shoveling turnings are heavier. If turnings are dumped into the top of the charge, some might fall through and fill up the empty space in the furnaces, but the smaller turnings are likely to be blown out during the melting process.
One key to handling turnings goes back to the source—the industrial plants. Processors have to supply the right size dumpster or loading box, depending on the volume of turnings and borings generated at the plants, and make sure that only ferrous turnings go into the dumpster, said Chris Ochoa, an account executive at Tube City IMS' Fairfield, Ala., facility.
Dumpsters filled with ferrous turnings that come through the gates at Tube City IMS yards are checked for alloy, stainless and aluminum materials, he said. All three are seen as contaminants by melt shops, but they're also more valuable than carbon steel turnings and thus are wasted when simply tossed into a dumpster with steel turnings.
Still, turnings are a lot better to work with than tire wire, which in many instances still has chunks of rubber clinging to it and spews clouds of smoke throughout the melt shop, Ochoa said.
Some mills have made a careful study of turnings and have devised ways to separate them by source and know the chemical content. The former Lukens Steel Inc., an eastern Pennsylvania plate producer that is now part of ArcelorMittal, was able to use a furnace charge that contained as much as 15-percent turnings—but that required careful sorting in the mill's scrapyard.
Most electric furnace steelmakers make certain they aren't getting contaminants in the turnings, preferring to leave them loose to prevent contaminants from entering the stream. Fort Wayne, Ind.-based Steel Dynamics Inc. relies on its scrap processing arm, OmniSource Corp., to carefully inspect the turnings, but then—unlike many other steelmakers—they are briquetted and charged into the furnace. OmniSource briquettes both steel turnings and cast iron borings in one type of briquette, and just cast iron borings in another. It doesn't make a briquette that uses only steel turnings, according to Daniel Dray, manager of the Southern Indiana division of OmniSource.
There are other processors that, like OmniSource, briquette turnings and borings, but there is a challenge in purchasing the briquetting equipment and the operating process. At present, it's not a good time to justify spending on equipment, he said.
Chemistry is a problem because many machine shops have streamlined their production processes. One minute workers are cutting and machining aluminum, and the next they're doing steel. It's not worth their time and effort to dump that hopper every time.
None of the mills wants copper, chrome and stainless in their charge materials. The key to controlling such pollution is dilution, Dray said. In other words, the melters will use only sparing amounts of those materials in the furnace to keep the chemistries within limits. "Some of the metals, like copper and chrome, may have been very pricey when new, but they are at the bottom of the food chain when you get this kind of contamination," he added.