It is necessary to combine the use of the correct degassing filter equipment to properly manage the cleanliness of the molten metal. The cleanliness of molten metal is one of the main challenges for most foundries. They must produce slabs with a sufficiently low content of hydrogen, alkali metals (main sodium), and inclusions to make the final product suitable for its end-use. This is especially important when rolling slabs into sheets used to make beverage cans or foils.
Initially molten metal cleanliness: First, it must be ensured that the melting and holding practices used before casting are as close to best practices as possible. The higher the cleanliness of the molten metal before the degassing/filtering operation, the higher the cleanliness after treatment.
Degassing Filter Equipment
Depending on the product, the next key operation may be the degassing equipment. There are many different types of degassers, but most rely on rotating degassing units.
The rotor injects a chemically active reactant (usually chlorine or solid salt flux) mixed with a carrier gas (such as argon or nitrogen) into fine bubbles into the molten metal. The key to operating this type of equipment to obtain the best efficiency is the use of rotor design and practice, which can produce smaller bubble sizes and have a longer bubble subsurface residence time.
A well-functioning degasser should be able to reduce the incoming hydrogen concentration by at least 50%. In addition, the content of alkali metals and inclusions should also be reduced. However, although the degasser will remove some of the inclusions, filtration can remove most of the inclusions.
The final filtration step is usually a ceramic foam filter (CFF) filtering equipment. This is a single-use disposable filter, made of hard porous ceramic foam, and has a strictly controlled pore size. Due to their simple operation and short-term good results, these are usually the only filtration equipment in many foundries.