charge materials. Steel thickness largely determines the amount of iron oxide that will be generated in the cupola, which leads to silicon loss. Te frag steel used in the cupola charge for these trials was 0.125- 0.25-in. thick. Coke composition and size were
2
measured, as well as the composition of the limestone. Te cupola was 233 in. in height with an unlined hearth diameter of 72 in. and a well depth of 29 in. Prior to the cupola’s weekly startup, the coke bed height measured 42 in., resulting in an overall coke column height of 71 in. Te iron dam height was 7.5 inches. Te two grades of briquetted SiC,
coke and limestone were analyzed by both vendors and an independent commercial lab (Auburn Analyti- cal Labs). All other charge materials were analyzed by vendors only. Bri- quetted SiC was examined for silicon carbide, combined carbon, free car- bon, sulfur and moisture. Coke was analyzed for carbon, ash, moisture, volatile matter and sulfur. Limestone was tested for CaO, MgO, SiO2 Al2O3
, , total carbon, lesser constitu-
ents and loss on ignition. Te researchers established a method of adding carbon and silicon outside the cupola to correct iron that was out of specification. Cor- rections to iron composition were made in a holding furnace or ladle. Te critical cupola output responses during the performance of each SiC trial were measured and recorded. Te following cupola operating
data acquired during the melt trials were used for the analysis of the results: • Cupola charge records and weights of all charge materials for every individual charge at each point in time (typical time between cupola charges was three to five minutes).
• Continuous electronic cupola data, including blast rate, blast tem- perature, windbox back pressure,
Procedure Te researchers measured
the carbon, silicon, manga- nese and sulfur concentra- tions of the selected metallic
oxygen enrichment flow rate and spout iron temperature.
• Comprehensive spout slag analyses every 15 minutes, including SiO2
,
• Cupola spout/trough iron tem- perature by continuous infrared pyrometer and immersion pyrom- eter (target spout iron temperature was 2,700F [1,482C]).
TiO2, sulfur and carbon. CaO, Al2O3
• Cupola thermal analysis by tellurium cups for carbon, silicon and carbon equivalent every five minutes with matching spout and holding furnace spec- trometer samples.
• Stack gas analyses, including %CO, %CO2 and temperature every 15 minutes.
• Tuyere back pressure and tempera- tures of water-cooled cupola shell measurements.
• Climatic data from the Kings- ford (Iron Mountain), Mich., National Weather Service station every hour.
• Cupola iron thermal analysis by plain cups for metallurgical thumbprint every 15 min- utes (eutectic point was the primary metric). Slag analyses were a crucial
component of the mass balances used to calculate melt yields and elemental recovery. Slag samples were collected in real-time but analyzed later by an outside laboratory. A time lag of 45 minutes between cupola charging and spout iron was used for the data analysis.
, MgO, MnO, FeO,
ONLINE RESOURCE
For an additional article on SiCin melting, visit
www.moderncasting.com.
Grede Holdings LLC’s Iron Mountain, Mich., facility uses a cupola to melt the iron used in its castings. In 2007, 60% of the liq- uid iron produced in the U.S. was melted in a cupola.
June 2012 MODERN CASTING | 37
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