English
I. Development History
1. In 1742, Melouin pioneered the protective method of immersing iron in molten zinc;
2. In 1836, Sorel obtained the hot‑dip galvanizing patent, specifying pickling and ammonium chloride fluxing processes;
3. In 1836, similar patents were issued in the United Kingdom, launching industrial‑scale production;
4. In 1850, the annual output of galvanized steel structures in the United Kingdom reached 10,000 tons. Continuous process iteration yielded a mature technical system.
II. Two Major Process Categories
1. Continuous Hot‑dip Galvanizing: Steel strips, steel wires and steel pipes pass through the zinc bath at high continuous speeds up to 200 m/min. It is applied in automotive, construction and civilian sectors. Derivative processes include the solvent process and Sendzimir process.
2. Batch Hot‑dip Galvanizing: Steel structural components are immersed in the zinc bath in batches, used for transmission towers, guardrails, bridges, mining machinery and other products.
Complete procedures for batch galvanizing: Pre‑galvanizing treatment (degreasing, pickling for rust removal, solvent fluxing, drying) → Hot‑dip galvanizing → Post‑galvanizing treatment (cooling, passivation, trimming, optional painting).
III. By Fluxing Method: Wet‑process Galvanizing vs Dry‑process Galvanizing
1. Wet‑process Galvanizing
Fluxing solvent floats on the surface of the zinc bath. Workpieces pass directly through the solvent layer into and out of the zinc pot.
Advantages: Suitable for thin coating layers; suppresses zinc spatter; fewer hoisting operations; less zinc ash.
Disadvantages: Solvent residues may contaminate workpieces; high workpiece loss during solvent replacement; high operating costs.
2. Dry‑process Galvanizing
A separate flux tank is provided for fluxing. After degreasing and pickling, workpieces undergo fluxing in the dedicated tank, are dried, and then immersed into the zinc bath.
Advantages: High production capacity, low zinc dross‑related costs, clean workshop environment.
Current status: The mainstream process for modern enterprises; the wet‑process is rarely used today.
Process selection: Trade‑offs are made according to workpiece types and practical requirements. Industry debates persist regarding the respective merits of the two processes.