You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Casting flux is used to and explain in detail?
Fluxes are specifically used

To remove gas or prevent its absorption into the melt.
To reduce metal loss.
To remove specific impurities and nonmetallic inclusions
To refine metallic constituents, or to lubricate and control surface structure in the semi-continuous casting of metal alloys.

Key concept
Flux powder may be sprinkled over the molten metal to reduce the oxides and increase fluidity for casting.