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HaiGang Yunyi
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Tianjin Haigang Steel Coil
Service first, quality assured. More dedicated and focused on crafting even better boards.
13
2020
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Introduction to Hot-Dip Galvanizing
What is hot-dip galvanizing?
Hot-dip galvanizing, also known as hot-galvanizing, involves immersing rust-prevented cast iron parts into a molten zinc bath heated to around 500°C, thereby causing a zinc coating to adhere to the surface of the steel prefabricated components and achieving the purpose of corrosion protection. It is an effective method for protecting metal materials against corrosion and is widely used in metal structural components across various industries. Hot-dip galvanizing evolved from earlier hot-plating techniques; since the Netherlands first applied hot-dip galvanizing to industrial production in 1836, this process has a history of over 170 years. However, the hot-dip galvanizing industry has experienced substantial growth only in the past three decades, driven by the rapid development of cold-rolled strip steel. The production process of hot-dip galvanized sheets mainly includes: preliminary preparation of the entire sheet → pre-galvanizing treatment → hot-dip galvanizing → post-galvanizing treatment → quality inspection, and so forth. By convention, based on differences in the pre-galvanizing treatment methods, hot-dip galvanizing processes are typically categorized into two types: off-line quenching and on-line quenching—namely, the wet-process (single-sheet hot-dip galvanizing method) and the off-line quenching (single-sheet hot-dip galvanizing method).
Basic Principle of Hot-Dip Galvanizing
The hot-dip zinc coating is formed in three stages as zinc melts into the liquid: First, the iron-based surface dissolves in the molten zinc, creating a zinc-rich, non-ferrous phase layer. Next, zinc ions from the aluminum alloy layer further diffuse outward into the substrate, forming a zinc-iron interdiffusion layer. Finally, the surface of the aluminum alloy layer is encapsulated by the zinc coating.
How Hot-Dip Galvanizing Prevents Rust: Hot-dip galvanizing provides a thick, dense layer of pure zinc that completely covers the surface of steel fasteners. This zinc coating effectively prevents the steel substrate from coming into contact with any corrosive solutions, thereby protecting the steel fastener substrate from corrosion. In normal atmospheric conditions, a very thin yet highly compact layer of active zinc oxide forms on the surface of the hot-dip galvanized zinc coating. Since this layer is hardly soluble in water, it offers considerable protection to the underlying steel substrate. If the active zinc oxide further reacts with other components in the air to form insoluble zinc salts, the anti-corrosion effect becomes even more pronounced. The galvanized coating also features a zinc-aluminum alloy layer that is highly dense and exhibits exceptional corrosion resistance in marine and industrial atmospheres. Thanks to its strong bonding and the mutual solubility between zinc and iron, the zinc-aluminum alloy layer boasts excellent wear resistance. Moreover, due to zinc’s outstanding ductility, the alloy layer adheres firmly to the steel substrate, allowing hot-dip galvanized parts to undergo various forming processes—such as cold stamping, cold rolling, wire drawing, and bending—without damaging the coating. After hot-dip galvanizing, steel components essentially undergo a preliminary annealing treatment, which significantly improves the physical properties of the steel substrate, relieves residual stresses generated during casting, welding, and other fabrication processes, and facilitates machining operations on the steel parts. The surface of fasteners after hot-dip galvanizing is bright and aesthetically pleasing. The pure zinc layer is the most ductile among all hot-dip galvanized coatings; its properties closely resemble those of pure zinc and exhibit excellent ductility.
The Basic Principle of Cold-Spray Zinc Corrosion Protection
High Efficiency: The zinc coating contains ≥96% pure zinc, with a corrosion resistance of ≥3,000 hours. The spraying system boasts an anti-corrosion lifespan of over 25 years, while similar foreign products in the same industry have demonstrated successful performance for more than 50 years. Environmental Friendliness: This product contains no toxic chemical components such as acrylates or n-hexane. Radiation Resistance: Being an inorganic compound, this product exhibits strong resistance to ultraviolet radiation. Load-bearing Capacity: The load-bearing index is ≥0.55, making it suitable for corrosion protection of high-strength bolted joints. Weldability: Coating does not compromise weld quality when welded, and the coating itself remains undamaged by laser cutting or welding processes. Heat Resistance: Continuous high-temperature resistance up to 400℃; short-term heat resistance up to 1,200℃. Cold Resistance: Down to -60℃. Quick Drying: At 23℃, the surface dries within 15 minutes, and full curing takes 2 hours.
Production process differences
Cold-spray zinc coating process: From a construction technology perspective, you only need to follow standard painting procedures—whether by brush, roller, or spray. We strongly recommend using Xiangjiang high-pressure airless spraying to achieve the required minimum film thickness of 40 μm and a maximum film thickness of 120 μm. A comprehensive coating system can protect steel structures for over 25 years. Hot-dip galvanizing process: Hot-dip galvanizing involves immersing rust-prepared iron or steel parts into molten zinc at 500°C, causing a zinc layer to adhere to the surface of the parts.
Future Development Trends
Both methods share the common advantage of providing corrosion protection for steel. So why is cold-spray zinc coating the preferred choice? With China’s repeated and stringent emphasis on green and environmentally friendly practices, environmental protection has attracted increasing attention from people. The hot-dip galvanizing process typically involves significant environmental pollution—emitting organic gases and chemical wastewater—which pose serious risks to both the environment and human health. Driven by increasingly stringent environmental policies, cold-spray zinc coatings have emerged. Cold-spray zinc coatings feature a high solid-content formulation, low volatile organic compound (VOC) emissions, and do not generate substantial energy consumption. Their corrosion-protection performance is comparable to that of hot-dip galvanizing, yet they are as easy to apply as spray painting. Considering the overall cost-effectiveness, cold-spray zinc coatings hold tremendous potential for future industry growth.
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We primarily produce various products including galvanized strip steel, pickled strip steel, and cold-rolled strip steel. These products are widely used in industries such as construction, mechanical manufacturing, automotive, and household appliances.
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