Non-oxidizing melting

Melt treatment preventing oxygen from entering the liquid metal which is specifically used for copper and copper alloys.

In this process, the molten bath is covered with a neutral or reducing melt additive and a low oxidizing flame is set for fuel-fired furnaces. This is to ensure complete combustion to keep the furnace atmosphere free of hydrogen. Hydrogen gassing, e.g. through the crucible wall, is therefore excluded.

The cover coating can be neutral (see Neutral cover coating) or reducing and protects the molten bath surface from oxidation, reducing weight loss by oxidation.

Non-oxidizing melting usually uses reducing cover coatings, e.g. charcoal. It must be absolutely dry and form a layer with a sufficient thickness of at least 100mm on the melt. The charcoal – which is already added to the crucible together with the cold batch – combusts at the molten bath temperatures to form carbon monoxide (CO) which has a reducing effect, preventing the ingress of oxygen from the low oxidizing furnace atmosphere.

The major benefits of non-oxidizing melting are the prevention of otherwise relatively high weight loss due to oxidation and the accurate deoxidation as long as the phosphorus content in the batch material is not overly high. The process can also be used in induction channels or crucible induction furnaces.

Additional references:
Oxidizing melting
Reduction melting
Oxidation
Degree of oxidation
Metal loss by oxidation
Smelting loss percentage

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