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Electric arc furnaces steal show.

In the Steel Division this year, the hot topic of discussion was how to better use electric arc furnaces.

S.A. Hornby-Anderson, Walnut Creek, California, and C.L. Bermel, Countryside, Illinois, both of Liquid Air Corp., discussed the new technologies and benefits of electric arc furnace (EAF) bottom stirring.

EAF bottom stirring has rapidly gained worldwide acceptance in large steel mills as a means to facilitate improvement in quality while reducing operating costs. The technology was designed to overcome concentration and temperature gradients as well as over-oxidized slags.

Today's EAF stirring is practiced using directional porosity plugs, multi-hole plugs or porous elements installed at the EAF bottom. Current techniques make it much more cost-efficient and practical than earlier models.

According to the authors, steel mills and foundries have found EAF bottom stirring reduces energy consumption, tap-to-tap time, operating costs and refining times while increasing productivity and yield. Bottom stirring also contributes to lower electrode and refractory wear as well as nitrogen pickup when using argon gas.

The authors evaluated costs for a 30-ton EAF bottom stirring installation. They concluded that it could save $113,900 a year and noted that the technology offers similar cost-saving benefits for foundries with smaller EAFs.

C.F. Pilliod, Keokuk Steel Casting Div., Keokuk, Iowa, discussed the variables controlling nitrogen content of steels produced in electric arc furnaces. He explained that excessive nitrogen contents in steel causes gas porosity and aluminum nitride embrittlement. Under normal conditions, gas porosity can be detected and repaired, but aluminum nitride embrittlement is virtually impossible to detect on a production basis in foundries.

To produce steel with minimum nitrogen levels, Pilliod suggested purchasing melting scrap with low nitrogen contents, using charge with adequate silicon, carbon-boiling, lowering voltage taps and recarburizing the bath. Each of these steps, he said, reduces nitrogen content.

To help control nitrogen and oxygen that can be introduced during melting, D. Lawrenz, LECO Corp., St. Joseph, Michigan, offered attendees an introduction to modern gas fusion oxygen and nitrogen instruments. He said many instruments provide precise oxygen and nitrogen determination in a variety of materials in less than a minute.

Advanced capability determinators offer controlled fusion and separation of the oxygen and nitrogen as they are released from a sample, allowing users to quantify existing oxide and nitride bonds.
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Title Annotation:96th AFS Casting Congress Milwaukee
Publication:Modern Casting
Date:Jun 1, 1992
Previous Article:Sand reuse heads discussion.
Next Article:Ductile iron properties and processes studied.

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