Cleaning All Dirt, Oils, and Greases from the Surface

1 Cleaning All Dirt, Oils, and Greases from the Surface 

Initial cleaning can be accomplished by using solvents or alkaline solutions. 

Solvents. Mineral spirits, naphtha, alcohols, ethers, chlorinated solvents, and so on, are applied by dipping, brushing, or spraying. One such solvent is Stoddard solvent, a petroleum base mineral spirit with a flash point of 40-55°C (100-130°F), sufficiently high to minimize Are hazard, and it is not particularly toxic. 

Chlorinated solvents, on the other hand, although nonflammable, are relatively toxic and contribute to pollution. In addition, they may leave chloride residues on the metal surface that can later initiate corrosive attack. They are used largely for vapor degreasing (tri- or perchlorethylene), in which the work is suspended in the vapor of the boiling solvent. Care must be exercised in the vapor degreasing of aluminum, ensuring that adequate chemical inhibitors are added and maintained in the chlorinated solvent in order to avoid catastrophic corrosion (see Section 21.1.4.1) or, in the extreme, to avoid an explosive reaction. 

If the metal is free of mill scale and rust, a final rinse in water and in a dilute chromic-phosphoric acid ensures both removal of alkali from the metal surface. 

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