GASES IN METALS

Most of the problems for producing sound metal castings are due to lack of control of dissolved gases or reaction gas in the casting during the period of solidification.

Gases are absorbed in molten metals due to the following sources.

(i) Furnace charge

(ii) Furnace refractories

(iii) Furnace atmosphere

Precautions to be taken to avoid gas absorption in melt are

(i) Using bigger pieces possible as metal charge because they are less susceptible to contamination.

(ii) Restrict the use of contaminated scrap as metal charge.

(iii) Using preheated charge specially in case of continuous melting process.

(iv) Melt the metal first and handle it with little agitation. Metal handling includes skimming slags or protective atmospheres.

(v) Alloys, fluxes to be added and all other items as laddles or furnace tools coming in contact with molten metal should be perfectly dry.

(vii) Gas solubility decreases with temperature. So molten metal should be at minimum possible temperature. Overheating of melt should be avoided.