1. The surface of the ventilation duct is coated with a thin layer of zinc, which is immersed in a molten zinc bath. At present, the main production method is continuous galvanizing, which involves immersing the coils in a molten zinc plating bath to make galvanized sheet air ducts;
2. Alloyed galvanized air duct. This type is also manufactured using the hot dip method, but immediately after leaving the tank, it is heated to around 500 ℃ to form an alloy coating of zinc and iron. This galvanized sheet has good coating adhesion and weldability;
3. Galvanized sheet air duct. The use of electroplating method to manufacture this type of zinc plating has good processability, but the coating is thinner and the corrosion resistance is not as good as that of hot-dip galvanized sheet;
4. Single sided and double sided galvanized air ducts. Single sided galvanized sheet air duct, which refers to products that are only galvanized on one side. In terms of welding, painting, rust prevention treatment, processing, etc., it has better adaptability than double-sided galvanized sheet air ducts. To overcome the disadvantage of not coating zinc on one side, there is another type of galvanized sheet coated with a thin layer of zinc on the other side, namely double-sided differential galvanized sheet; Galvanized air duct
5. Alloy and composite galvanized air duct, which is made of zinc and other metals such as lead and zinc, and even composite plated air duct. This type of galvanized air duct has both rust prevention performance and good coating performance.
（1） The body, frame, and solid materials, as well as sealing gasket materials of the fire resistant air duct must be non combustible materials, and their fire resistance rating should be in accordance with the plan.
（2） The splicing of galvanized or colored coatings should accept biting or riveting, and there should be no cross shaped splicing joints. The plastic coating surface of the color coating should be located on the inner side of the air duct. During processing, damage to the plastic coating layer should be restrained, and the damaged department should be repaired.
（3） Welding of air ducts can accept three types of situations: overlap, corner joint, and butt joint. Before welding of air ducts, rust and oil should be removed. The welding seam should be well fused and flat, and there should be no defects such as cracks, overlap, penetrating slag friendly holes in the appearance. The deformation of the welded plate should be corrected, and the welding slag and splashes should be cleaned up.
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