The difference between hot-dip galvanizing and cold galvanizing



1. Cold galvanized anti-corrosion

1.1 What is cold galvanizing

Cold galvanized paint is a one-component new type coating with extremely high zinc content, which is composed of high-purity and high-activity zinc powder, special binders, additives, and solvents. With a zinc content of over 96%, it has electrochemical protection comparable to hot-dip galvanizing and excellent long-term anti-corrosion performance, low VOC content, room temperature drying, energy saving and environmental protection; simple construction, one-time thick coating, and good recoatability.

1.2 Principle of cold galvanizing anticorrosion

Long-lasting performance: zinc film with pure zinc content ≥96%, salt spray resistance ≥3000 hours, coating system with more than 25 years of anti-corrosion cycle, and its similar products have more than 50 years of successful examples abroad; environmental protection: no isocyanate , Benzene and other toxic chemical components; radiation resistance: this product is an inorganic substance, with strong UV resistance; anti-slip: anti-slip coefficient ≥0.55, can be used for anti-corrosion of high-strength bolt joints; welding resistance: coated welding is not Affect the quality of welding, and the coating is not damaged by cutting and welding; high temperature resistance: continuous high temperature resistance of 400℃, instant heat resistance of 1200℃; low temperature resistance: -60℃; fast drying: surface drying time at 23℃ 15 Minutes, 2 hours of hard work.

2.Hot-dip galvanized anti-corrosion

2.1 What is hot-dip galvanizing

What is hot-dip galvanizing? Hot-dip galvanizing (galvanizing) is also called hot-dip galvanizing and hot-dip galvanizing. It is the purpose of immersing the derusted steel parts in a molten zinc solution at about 500°C to attach a zinc layer to the surface of the steel parts, thereby achieving the purpose of anti-corrosion. It is an effective metal anti-corrosion method, mainly used in metal structure facilities in various industries. Hot-dip galvanizing is developed from the older hot-dip method. Since France applied hot-dip galvanizing to industry in 1836, it has a history of 170 years. However, the hot-dip galvanizing industry has been developed on a large scale with the rapid development of cold-rolled strip steel in the past 30 years. The production process of hot-dip galvanized sheet mainly includes: original board preparation → pre-plating treatment → hot-dip plating → post-plating treatment → finished product inspection, etc. According to the custom, the hot-dip galvanizing process is divided into two categories: off-line annealing and in-line annealing, namely, wet method (single steel plate hot-dip galvanizing method) and off-line annealing (single steel plate hot-dip galvanizing method). Galvanizing method), hot-dip galvanizing wheeling method (continuous hot-dip galvanizing method of strip steel), in-line annealing Sendzimir method (protective gas method), modified Sendzimir method, American steel union method (same as Japan’s Kawasaki method), Selas method and Sharon method.

2.2 Principle of hot-dip galvanizing

The hot-dip zinc layer is formed in three steps when zinc is in the liquid state. The surface of the iron base is dissolved by the zinc solution to form a zinc and iron alloy phase layer; the zinc ions in the alloy layer further diffuse to the base to form a zinc and iron mutual dissolving layer; alloy layer The surface is covered with a zinc layer.

2.3 Characteristics of hot-dip galvanizing

How does hot-dip galvanizing prevent rust: hot-dip galvanizing has a thick and dense pure zinc layer covering the surface of the steel fasteners, which can avoid the steel substrate from contacting any corrosive solution and protect the steel fastener substrate from corrosion. In the general atmosphere, a thin and dense zinc oxide layer is formed on the surface of the hot-dip galvanized zinc layer. It is difficult to dissolve in water, so it has a certain protective effect on the base of steel fasteners. If zinc oxide forms insoluble zinc salt with other components in the atmosphere, the anti-corrosion effect is more ideal; it has a zinc-iron alloy alloy layer, which is densely combined, and exhibits unique corrosion resistance in marine salt spray atmosphere and industrial atmosphere; due to the combination Strong, zinc-iron is mutually soluble, and has strong wear resistance; because zinc has good ductility, its alloy layer is firmly attached to the steel matrix, so hot-dip galvanizing can be cold punched, rolled, wire drawn, bent, etc. The forming process does not damage the coating; after the steel structural parts are hot-dip galvanized, it is equivalent to an annealing treatment, which can effectively improve the mechanical properties of the steel matrix, eliminate the stress during the forming and welding of the steel parts, and is beneficial to the turning of the steel structural parts; The surface of the fasteners after dipping galvanized is bright and beautiful; the pure zinc layer is the most plastic galvanized layer in hot-dip galvanizing. Its properties are basically close to pure zinc and have good ductility.

3.What is the difference between hot-dip galvanizing and cold-dip galvanizing

3.1. The difference in process flow

Cold spray zinc paint process: In terms of construction process, you only need to follow the normal paint spraying method (brushing, roller coating, spraying). It is recommended that the Yangtze River high-pressure airless spraying reaches the minimum film thickness of 40 microns and the maximum film thickness With a thickness of 120 microns, a complete coating system can protect the steel structure for more than 25 years. Hot-dip galvanizing process: Hot-dip galvanizing is to immerse the derusted steel parts in a molten zinc solution at 500°C to make the surface of the steel parts adhere to the zinc layer.

3.2 Future trends

The comparison between the two is also the anti-corrosion effect on steel. Why should the cold spray zinc paint spray method be preferred? With the country’s three orders and five applications for energy conservation and environmental protection, more and more people pay attention to environmental protection. Hot-dip galvanizing is usually accompanied by high pollution. Industrial waste gas and industrial waste water have a great impact on the environment and human health. Under the advocacy of environmental protection policies, cold galvanized paint products appeared. Cold spray zinc paint has a high solid content, low organic volatile VOC emissions, and will not cause major energy consumption problems. The anti-corrosion effect is equivalent to that of hot-dip galvanizing, making galvanizing as easy as painting, considering the overall cost , Cold spray zinc paint will have great market prospects.

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