The process and principle are as follows:
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1. Pretreatment: First of all, the surface treatment of galvanized products is carried out to remove impurities such as grease and oxides on the surface to ensure the adhesion and corrosion resistance of the galvanized layer. Pretreatment methods include mechanical treatment (such as grinding, polishing), chemical treatment (such as pickling, electrolytic polishing), etc.
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2. Zinc dipping: The pre-treated steel products are immersed in the molten zinc solution, and the galvanic cell effect formed by the potential difference between zinc and iron is used to migrate zinc ions to the surface of steel products and deposit to form a coating. It is necessary to control temperature, time and other parameters during zinc dipping to ensure the quality and thickness of the coating.
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3. Cooling and passivation: After removing galvanized products from the zinc solution, they need to be cooled and passivated. Cooling can be carried out by water or air to reduce the temperature of the zinc layer and prevent the quality of the zinc layer from being affected by excessive temperature. Passivation treatment is to form a passivation film on the surface of the zinc layer to improve the corrosion resistance of the zinc layer. Passivation treatment methods include immediate passivation after zinc immersion, natural passivation, etc.
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4. Inspection and finishing: Check the appearance, size and other aspects of galvanized products to ensure that they meet the quality requirements. If necessary, the galvanized products can be mechanical processing, welding, painting and other follow-up treatment.
Hot dip galvanizing is the process of soaking iron and steel products in molten zinc liquid, so that the surface is attached with a layer of zinc, in order to achieve anti-corrosion, wear-resistant, beautiful and other effects.
Hot-dip galvanizing process generally includes the following steps:
Surface treatment: The steel products to be galvanized are cleaned, pickling, hot leaching phosphorus and other treatment to remove the surface of oil, rust and oxide.
Soaking in molten zinc solution: The surface treated steel products are soaked in molten zinc solution, so that the surface is evenly plated with a layer of zinc.
Cooling: Remove the zinc plated steel products from the molten zinc liquid and cool them with water or air so that the zinc layer on the surface is solidified and firmly attached.
Protective treatment: Some protective treatment of zinc plated steel products, such as cutting, punching, marking, painting and so on.
The principle of hot dip galvanizing is to use the chemical properties of zinc, the zinc atoms in the zinc liquid and the iron atoms on the surface of iron and steel products to chemically react to form a zinc-iron alloy layer or pure zinc layer to play a role in anti-corrosion, anti-oxidation, beautiful and so on. The zinc layer will be intermetallic diffusion with the steel substrate, and the zinc and steel will be firmly combined to form a non-peeling, durable protective layer.
Principle of hot dip galvanizing
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Hot dip galvanizing layer is formed in three steps: 1, the surface of the iron base is dissolved by zinc liquid to form a zinc-iron alloy phase layer; 2, the zinc ions in the alloy layer further diffuse to the matrix to form a zinc-iron miscible layer; 3. The surface of the alloy layer is enveloped by the zinc layer.
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Raw material inspection → pickling → cleaning → zinc aid → drying → galvanizing → cooling → passivation → cleaning → finished product inspection → inspection packaging, etc. According to the habit, the hot-dip galvanizing process is often divided into two categories: off-line annealing and in-line annealing according to the different pretreatment methods.
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process
Workpiece → degreasing → washing → pickling → washing → Dip plating solvent → drying and preheating → hot dip galvanizing → finishing → cooling → passivation → rinsing → drying → inspection
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Hot dip galvanizing formation principle:
The process of forming an iron-zinc alloy between the iron matrix and the outermost pure zinc layer, the surface of the workpiece formed an iron-zinc alloy layer during hot dip plating, so that the iron and pure zinc layer is well combined, the process can be simply described as: when the iron workpiece is immersed in the molten zinc liquid, the first zinc and α-iron (body-centered) solid melt is formed on the interface. This is a crystal formed by the matrix metal iron dissolved with zinc atoms in a solid state, and the two metal atoms are fused, and the gravitational attraction between the atoms is relatively small. Therefore, when zinc reaches saturation in the solid melt, the two elements of zinc and iron atoms diffuse each other, the zinc atoms diffused into (or infiltrated into) the iron matrix migrate in the matrix lattice, and gradually form an alloy with iron, and the iron diffused into the molten zinc liquid forms an intermetallic compound FeZn13 with zinc, which sinks into the bottom of the hot galvanized pot, that is, zinc slag. When the workpiece is removed from the zinc leaching solution, the surface of the pure zinc layer is formed, which is hexagonal crystal. Its iron content is not greater than 0.003%.