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Quality inspection of mechanical joint of rebar
Continuous hot dip galvanized sheet steel
Continuous hot dip galvanized sheet steel

Characteristics of the surface treatment of the galvanized layer 

1. The galvanized layer is oiled

The coating is designed to prevent rust from the steel plate. Oil products should not deteriorate within a year under normal temperature dry stock conditions; It can be easily removed in the alkaline coating before painting. For some finished parts of the workpiece need to paste is not allowed to have oil, and the partial removal of oil on the workpiece is not reasonable in economy, safety and preservation, so the general selection of oil-free plate production. However, oil-free galvanized sheet is extremely produced, requiring its storage conditions to be more demanding. That is, ventilation, no harmful gases and dust, relative humidity is not more than 70%.
Oil, commonly used mineral oil anti rust oil (solvent), storage, plate weight honey fold, not easy to volatile. Made into stamping parts, natural hair clean.

galvanized layer 
  • Improve the surface structure and gloss of galvanized layer

  • Improve the corrosion resistance and service life of galvanized layer.

  • Prevent “white rust” in transportation and storage

  • For brushing other coatings as a good substrate.



under certain conditions, when the metal’s potential is shifted in a positive direction by an applied anode current or a local anode current, the state of the previously dissolved active metal surface is changed in a certain way (oxide film or membrane form). Because of this mutation, the regularity of anodic dissolution process also changes, and the dissolution rate of metal decreases sharply. This sudden change in the state of the metal surface is called passivation.

4. Chromate passivation film

Its main components are zinc chromate (ZnCrO4) and chromium chromate (CrO3•Cr2O3•nH2O). In passivation film, chromium 3 is the most, followed by water, followed by chromium 6, in the form of colloidal material chromium chromate exists on the surface of galvanized layer. Zinc chromate is attached to the membrane. It is soluble in water, is harmful ingredients, should be rinsed clean.
As a large amount of chromium 3 in the passivation film is difficult to dissolve in water, it is isolated from the infiltration of oxygen and water in the air, and closes the pores of the galvanized layer (especially the electrogalvanized layer). A small amount of chromium 6 is distributed in the film, which can repair the passivated film that has been erased and make the slightly torn film complete again.
Passivation film thickness about 0.5~1μm, stable, fine structure, transparent metal color. The conductivity of the film is slightly poor, which is not conducive to the welding operation. Passivation film has poor corrosion resistance when drying above 70℃. The thick passivation film is orange yellow. The thin passivation film is iridescence. The color changes from thick to thin film are: reddish brown – rose red – golden yellow – olive green – green – purplish red – light yellow – bluish white. Passivation film darkened after a period of storage. Become dark brown or brownish black.

5. Passivation film self test method

The color is bright yellow as normal standard; Its mechanical strength, with finger hard rub test, wipe not qualified.


6. phosphating

The purpose of phosphating galvanized galvanized sheet is to prevent rust and facilitate the next coating operation. The shelf life of phosphating board is much shorter than that of passivation board. The thickness of passivation film treated with zinc (or iron) passivation agent is about 0.5~0.2μm, and scratches can be seen with fingernail. The main coating components are Zn2(PO4)2•4H2O or Zn2Fe(PO4)2•4H2O zinc phosphate and iron phosphate. In the drying temperature of 160℃, the water of crystallization precipitates and the film is destroyed. Gray scaling film is subgray, only used for immediate coating of the workpiece galvanized sheet.

7. Fingerprint-free processing

Galvanized plate without fingerprint processing is to make galvanized plate made of electrical appliances, such as operation panel, not by fingerprints pollution, and good electrical conductivity, good corrosion resistance.
Fingerprint-free treatment agent is made of polysilicate lithium film. This film in the process of stamping and stretching, will also be scratched, damaged in the curing furnace at 220℃ will appear small bubbles, small particles, affect the appearance of the coating quality. This film in the process of coating pretreatment, basically will not phosphating film, is not conducive to the adhesion of powder spraying.

8. Composite surface treatment

Simple galvanized sheet after chromate passivation, phosphating galvanized sheet, can be coated with anti-rust oil, to enhance the anti-rust effect.

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