In a cupola furnace, which materials are added to reduce excess carbon and refine impurities?

• A. Pig iron, coke and limestone are added to refine impurities
• B. Scrap steel is melted and refined
• C. Limestone is the only additive
• D. Iron ore and coke are used

Answer: (A)

In a cupola furnace, refining impurities and controlling carbon content is achieved by a charged mix that includes a carbon source, iron-bearing material, and a flux-forming agent. The combination of pig iron, coke and limestone provides these essential roles. Coke supplies heat and carbon, helping melt the charge and set the burn-off conditions; limestone acts as a flux, reacting with silica and other impurities to form a slag that floats on the molten metal and carries impurities away from the bath; pig iron adds iron to the melt and helps balance the overall chemistry, contributing to the final composition and aiding in diluting impurities as the slag scavenges them.

This trio is chosen because it accomplishes both impurity removal and carbon management in a single charge: the slag formed by limestone removes unwanted elements, while the coke-driven oxidation and the presence of iron from pig iron help adjust the metal’s carbon level and chemistry. Other options lack one or more of these critical functions—limestone alone wouldn’t provide the carbon and metal balance; iron ore would change the process to a different smelting path with different impurities; relying on scrap alone or omitting the flux wouldn’t effectively refine impurities or control carbon in the cupola melt.