Q:What pretreatment of the substrate is required before galvanizing?
A:1. Degreasing and cleaning: remove surface oil (alkaline solution or electrolytic cleaning);
2. Pickling and rust removal: soak in hydrochloric acid or sulfuric acid to remove iron oxide scale;
3. Water washing and drying: avoid residual acid contamination of zinc liquid;
4. Annealing (optional): annealing in a reducing atmosphere to eliminate stress and enhance the adhesion of the zinc layer.
Q:How to ensure the uniformity of the galvanized layer during the production process?
A:To ensure the uniformity of the galvanized layer, the key lies in strictly controlling the air knife parameters and substrate pretreatment, while maintaining the stability of the zinc liquid temperature, composition and production line speed, and coordinating with the online X-ray thickness gauge for real-time monitoring and adjustment, regular maintenance of the air knife and cleaning of zinc slag to avoid defects such as zinc nodules or streaks.
Q:What is the role of annealing process in galvanized coil production?
A:1. Eliminate work hardening：
Recrystallization annealing can eliminate the internal stress of the cold-rolled substrate, restore the ductility of the material, and avoid cracking or deformation during subsequent galvanizing.
2. Enhance the adhesion of the zinc layer：
Annealing in a reducing atmosphere removes surface oxides, forms an active clean surface, and enables the zinc liquid to achieve metallurgical bonding with the substrate.
3. Regulate mechanical properties：
Controlling the annealing temperature and time can adjust the substrate strength to match the needs of different uses.
Q:What is the difference between the production processes of hot-dip galvanizing and electro-galvanizing?
A:1. Coating formation method
Hot-dip galvanizing: The steel is immersed in 450℃ molten zinc liquid to form a metallurgically bonded thick coating.
Electrogalvanizing: The electrolyte is electrified to deposit zinc ions to form a non-metallurgically bonded thin coating.
2. Production efficiency and cost
Hot-dip galvanizing: fast speed, low cost, suitable for mass production.
Electrogalvanizing: slow speed, high energy consumption, but better precision.
3. Product characteristics
Hot-dip galvanizing: obvious zinc flowers, strong corrosion resistance, suitable for outdoor structural parts.
Electrogalvanizing: uniform surface without zinc flowers, suitable for precision appearance parts (need to be matched with painting).
Essential difference: hot-dip galvanizing relies on high-temperature metallurgical reaction, and electrogalvanizing relies on electrochemical deposition.
Q:What is the impact of the cooling process of galvanized coils on the performance of the final product?
A:The cooling process of galvanized coil directly affects the three major properties of the product:
1. Mechanical properties: rapid water cooling can improve strength, while slow cooling can enhance ductility;
2. Zinc layer structure: the cooling rate determines the thickness of the Fe-Zn alloy layer;
3. Surface quality: uneven cooling can easily lead to zinc flowers of different sizes or warping.