hot-dip galvanizing treatment process
Hot galvanized sheet production process Brief
HDG production process
Feeding → → pinch unwinding, straightening → welding → washing → entry looper → annealing → galvanizing → (alloyed) → cooling → middle Looper → flat → straightening → reprocessing → exit looper → Check reeling .
Galvanizing cleaning process
Cleaning typically include alkali scrubbing and electrolytic degreasing, it can clear the iron and oil and other impurities on cold-rolled steel sheet, the production of high surface quality and coating adhesion force is essential for high galvanized products.
Galvanizing annealing process
Continuous hot galvanized steel using a continuous annealing line. Annealing process is the key to high-strength dual-phase steel production of galvanized steel, for Mn, Si and other elements have a great impact on the steel surface enrichment, which in turn will affect the high-strength steel can be coated and its surface quality. Galvanized steel sheet annealing process generally comprises preheating, heating, soaking and cooling. The use of waste gas pre-heating the strip can not only save fuel, but can be avoided by heating the strip too fast and cause deformation of the strip of thin plate-shaped product specifications are very favorable. Some units use cooling process slow cooling rapid cooling after the first segment cooling, both to avoid cooling too fast adversely plate shape, and dual-phase steel, high-strength steel to meet the cooling speed requirements. Some manufacturers in the cooling section after section also set up a balanced, objective is to provide a buffer area between the galvanizing and cooling section, so that the strip has a better shape and more uniform temperature into the zinc pot galvanizing, improve plating Zinc quality.
Alloyed galvanizing process
Alloying refers to the hot-dip zinc coating was immediately plated pure diffusion annealing at 450 ~ 550 ℃, get the iron content of between 7% and 15% of zinc alloy plating process. The main factors affecting the alloying zinc was effective aluminum content, zinc pot temperature, the strip into a zinc pot temperature, alloying temperature, strip speed, the chemical composition of the substrate and coating thickness. High quality alloy plating products often want sheet and plated alloy coating suitable annealing process, the heating rate, soaking time and cooling rate is strictly controlled.
Galvanizing formation process
To eliminate strip yield plateau, get a good strip flatness and strip surface roughness suitable to be leveled for hot dip galvanized sheet. Smooth process parameters include rolling force, bending force, flat and smooth entrance tension by tension. In improving the shape and improving the quality of the strip surface four roller mill was better than the two-roll mill. At present, Japan has developed a work roll can be replaced by a different roll diameter of four roller mill, can better control the different sizes and shape and surface hot dip galvanized steel products roughness.
After the hot-dip galvanizing treatment process
After treatment includes a passivation pre phosphate and oiled. By passivation, zinc coating can improve the surface structure and gloss, improve zinc coating corrosion performance and service life, and can improve the adhesion of the coating and the base metal. Currently the main use chromate passivation treatment. Add some activators such as fluoride, phosphoric acid or sulfuric acid in the passivation solution such that the resulting thick chromate passivation film. When there is fluoride passivation solution can reduce the surface tension of the strip to accelerate the film-forming reaction, and can increase the chemical polishing effect, so the passivation film delicate light.