Answer / nihar ranjan

Dross is a mass of solid impurities, which forms during smelting of low-melting point metals viz, Aluminium, Tin, Lead . As metal is melted, it oxidizes, forming a layer of scum and impurities which float to the surface as the metal heats up.

Scaling is mainly due to the presence of calcium and magnesium salts (carbonates or sulphates), which are less soluble hot than cold, or to the presence of too high concentration of silica.

Why Slag comes on top of weld bead & if ur answer is related to density then think of overhead welding if slag is ligter than weld metal then in overhead welding firstly a laye of slag & then a layer of weld metal must be deposited.

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