Galvanizing process : Hot dipping (Corrosion control)

Describes the galvanizing process/hot dipping. The types of hot dipping methods are listed. It discusses the surface treatment, galvanizing and post-treatment steps. It discusses how zinc is coated on iron or any other corrosive metal. Mentions the uses of this method. It also explains the users of this method. Why did stuffs cannot be stored in galvanized containers is also explained. Hot Dipping: Galvanizing You will be able to define hot dipping and discuss the two types. list out the surface treatment of galvanizing process. describe the process of galvanizing and post treatment steps. enumerate the uses this method. mention the drawback of using galvanized containers to store food stuffs. Hot dipping Hot dipping is a process of coating the base metal (metal with higher melting point) by dipping into a bath containing molten coating metal (metal with lower melting point) Types of Hot dipping Galvanizing : Anodic Coating- Coating of more active metal (less standard reduction potential) over less active metal (more standard reduction potential). eg. Coating zinc over copper, iron, steel etc. Tinning : Cathodic Coating- Coating of less active metal (more standard reduction potential) over more active metal (less standard reduction potential). eg. Coating tin over copper, iron, steel etc. Galvanizing process Galvanizing is a process of coating the base metal (metal with higher melting point) by dipping into a bath containing molten coating metal (metal with lower melting point). Surface preparation DEGREASING/CAUSTIC TREATMENT Caustic/Alkaline solution: Removes dirt, oil grease PICKLING Dilute HCl or H2SO4 : Removes oxides and scales FLUXING ZnCl2/NH4Cl : Protective layer to prevent oxidation of the base metal DRYING Hot air : Reduces splash and increases dip speed Galvanizing Galvanizing kettle Molten metal 98% Zn Temperature 438 – 460 oC (820-860 oF) Dipping Time ~10 minutes Galvanized Coating Post treatment Quenching Water and chemicals to form passivation layer to protect galvanized component Removal of zinc drips or spikes by grinding Uses of galvanisation/galvanizing Galvanized steel wires, pipes, nails, screws, nuts and bolts. Galvanized steel frames and roof tops for construction. Door frames, window frames and bars. Domestic applications such as washing machine, hair dryers, trimmers, computer parts, AC housings etc. Protective gears, high way signs, high tension electric towers Galvanized containers cannot used to store food stuffs, as zinc dissolves especially when acidic food is stored and poisons the food.