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Chemistry key to optimizing use of turnings, borings in electric furnace charge

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The use of turnings and borings varies from mill to mill, depending on the melter's experience and preference. But for all mills, chemistry is key.

Some mills might use only a small fraction in their melt, or they'll specify alloy-free turnings in the scrap purchased from outside suppliers. Still others have different ways of buying, storing and charging turnings and borings into their electric-arc furnaces.

There are two different types of briquetting. One is specifically for borings, while the other can be used for combinations of borings and turnings. Hot briquettes are made at Ferrous Processing & Trading Co.'s Zalev yard in Windsor, Ontario. Louis Padnos Iron & Steel Co. also makes both hot and cold briquettes at its facility in Holland, Mich. Many more scrapyards and industrial plants make the cold-pressed briquettes.

Some melters prefer the hot briquette over the colder puck because it has better physical properties, holds together much better and is a more robust product, travels better and doesn't disintegrate and fall apart as easily as the cold briquette. But many of the cold briquettes are made at steel mills and, thus, don't have far to go to the melt shop.

What they give up with the hot briquetting process is some part of the carbon, one scrap buyer said. It is oxidized in the process, so while loose borings typically have a 2- or 2.5-percent carbon content, hot briquettes of borings range from 1.9- to 2-percent carbon. "That's one of the key reasons we melt borings," he said. "We are after the carbon."

What separates iron from steel is the carbon level. Borings come from cast iron, so typically they are 2.5 percent or higher in carbon than steel turnings. By using the more carbon-rich borings, mills hope to reduce some of the charge carbon that must be added to meet specifications. Also, the carbon combines with oxygen and creates energy, thus saving the melt shop a little on its fuel wattage consumption.

But borings and turnings in loose form are lower yielding, according to Rob Whistle, purchasing manager at Gerdau Ameristeel Corp.'s recycling division in Whitby, Ontario. "The melters gain some advantages with the briquette, but it is just minimal. It is nothing like what the scrap dealers suggest," he said.

Not all steelmakers and scrap processors are fond of hot briquettes. Some, like Fort Wayne, Ind.-based Steel Dynamics Inc. (SDI), use cold briquettes, and avoid the problem of keeping the hockey puck-sized briquettes from falling apart by using a binder to hold the material together.

Some mini-mills used to be big users of both briquetted borings and turnings and loose turnings, but have cut back consumption of those grades. In some instances last year, better industrial steel scrap grades like No. 1 bundles and No. 1 bushelings were available at lower prices while some briquetters were being offered higher prices for their products.

Where were those turnings and borings going? The dealers found homes among mills in the United States, where some paid prices that were close to those of plate and structural scrap. Plate and structural scrap normally commands a premium of at least $10 per long ton over No. 1 heavy melting steel and a $50-per-ton premium over the more common grades of turnings and borings.

But the idea of marketing briquettes as a plate and structural scrap substitute doesn't make much sense to Whistle and other scrap buyers.

"The chemistry is still just mixed machine shop turnings, so you are never sure what the chemistry is in those briquettes," one Ohio-based scrap buyer said.

One explanation for the price spike was an apparent short supply of turnings and borings, one SDI manager said. "The manufacturing economy got so slow that the output of turnings and borings was way down. Most of the turnings SDI uses come from industrial plants like screw and bolt makers."

Gerdau Ameristeel stopped using briquettes and sacrificed the density its melters desired. The primary benefit of using briquettes at its Canadian mills was the density, particularly at the Cambridge, Ontario, operation, where it has a small 50-ton-per-heat electric-arc furnace.

But for all the mills, chemistry is the most critical problem. SDI uses turnings and borings only at its bar-making plant in Pittston, Ind., and not at its flat-rolled mills. Still, it carefully separates the turnings and borings into bins that represent different dealers and industrial sources. Others, like ArcelorMittal's mill in Coatesville, Pa., have been doing the same for years. Both mills have separate bins in the mill scrapyard and a clear idea of the chemistries in each bin.

Moisture content is less of a problem. When turnings and borings are sitting in a dealer's yard the cutting fluids drain off or evaporate. Also, some scrapyards have installed large centrifuges that further dry out the turnings and borings.

Moisture is often more of a problem at some industrial plants and might be as high as 5 or 6 percent of the weight in the collection hopper. That's where the economics of a smaller briquetting machine can make a difference, Whistle said, noting that a wise scrap dealer will explain to the plant manager that they should put in a small briquetter. First, the plant can recapture and possibly reuse some of the cutting fluids; second, the turnings and borings will be worth more because the scrap dealer will reduce the discount for moisture in each load; and lastly are the idiosyncratic decisions that melters make for charging turnings and borings into the furnace. Some that use loose turnings put them at the bottom of the charge bucket to serve as a cushion and protect bottom refractories in the furnace. Still others layer the charge and put the briquettes between two other grades of heavier scrap. A few put the briquettes on the top of the charge, but one scrap buyer said most melters avoid that practice because the briquettes loosen up and the smaller turnings can be blown out into the baghouse and start a fire.

"That's a major reason why a lot of shops turn away from turnings because there is a major potential for that," one scrap buyer said.
MICHAEL MARLEY


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