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Abstract

A method and system of melting a charge of metal in a closed hearth wherein the metal has a first high thermal conductivity when solid, a second low thermal conductivity when liquid and a given melting temperature below about 1600.degree. F., such as aluminum. The method and system involves the use of a plurality of heaters having a total high heat capacity sufficient to melt the metal in a given time and sufficient to drastically increase the temperature of the metal when the metal is in the liquid state. This method and system comprises operating the burners at the high heat capacity until a control temperature associated with the hearth and separate from the metal reaches a given value, modulating the burners to maintain the control temperature generally at this given value, turning said burners to a minimum capacity drastically below the high heat capacity after only part of the metal has melted, then allowing the furnace to stabilize whereby thermal energy absorbed by the hearth is combined with the low heat capacity of the burners to finalize melting of the metal and modulating the burners to maintain the control temperature to another value between the first high value and the melting temperature of the metal but substantially closer to the melting temperature of the metal during at least the rapid heat equalization cycle and during at least the initial portion of the holding and/or conditioning cycle. After the equalization cycle, the method and system can control the capacity of the burners by a temperature in the molten metal itself. This molten metal temperature is just below the upper surface of the molten metal bath and prevents overheating of the molten metal and the hearth and compensates for temperature gradients.

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First Claim