Alkaline Cleaning


Alkaline cleaning may also be known as caustic cleaning. A hot alkali solution often is used to remove organic contaminants such as dirt, paint markings, grease and oil from the metal surface. Epoxies, vinyls, asphalt or welding slag must be removed before galvanizing by grit-blasting, sand-blasting or other mechanical means.

This is the most widely used industrial cleaning method. As its name indicates, alkaline cleaning employs an alkali to remove oils, grease, wax, and various types of particles (metal chips, silica, carbon, and light scale) from a metallic surface. Alkaline cleaning solutions consist of low-cost, water-soluble salts such as sodium and potassium hydroxide (NaOH, KOH), sodium carbonate (Na2CO3), borax (Na2B4O7), phosphates and silicates of sodium and potassium, combined with dispersants and surfactants in water. The cleaning method is commonly by immersion or spraying, usually at temperatures of 50‐95°C (120‐200°F). Following application of alkaline solution, a water rinse is used to remove the alkali residue. Metal surfaces cleaned by alkaline solutions are typically electroplated or conversion coated.

Electrolytic cleaning, also called electrocleaning, is a related process in which a 3‐12-V direct current is applied to an alkaline cleaning solution. The electrolytic action results in the generation of gas bubbles at the part surface, causing a scrubbing action that aids in removal of tenacious dirt films.

Alkaline cleaning is a type of chemical cleaning.