Page 78 - Welding of Aluminium and its Alloys

Removal of thin oxide film for fusion welding Removal of thick oxide film for all welding and brazing operations Removal of films and stains from heat treating and oxide coatings Removal of anodic coatings

Purpose

Container material Stainless steel Mild steel Stainless steel Antimonial lead lined steel tank Stainless steel

Procedure Immerse 15min Rinse in cold water Rinse in hot water Dry Immerse 10 to 60s Rinse in cold water Immerse 30s Rinse in cold water Rinse in hot water Dry Dip for 2 to 3min Rinse in cold water Rinse in hot water Dry Dip for 5–10min Rinse in cold water Rinse in hot water Dry
Chemical treatments for cleaning and oxide removal

Temp (°C) 18–24 70 18–24 70–80 95

Concentration 50% water 50% HNO 3 (technical grade) 5% NaOH in water Concentrated HNO 3 5 litres H 2SO 4 1.4kg CrO 3 40 litres water 1.98 litres of 75% H 3PO 3 0.65kg of CrO 3 45 litres of water

Table 4.4 Solution Nitric acid Sodium hydroxide followed by nitric acid Sulphuric – chromic acid Phosphoric – chromic acid