Problems and causes of surface treatment before prepainted galvanized steel coating

Problems and causes of surface treatment before prepainted Galvanized Steel coating

The paint coating will have scratches, scratches, cracks and other problems during the covering process. First check whether the chromium content of the chemical conversion coating is controlled between 30 and 34mg/m2. In addition, since the defects in the chemical conversion treatment section mainly include several phenomena such as complete lack of film, partial lack of film, yellowing of the film quality, and ash hanging, the inspection should also be carried out in a targeted manner. The sampling method for inspection: during the production process A small amount of chemically-coated panels not covered with organic coatings shall be kept as samples for inspection at the head and tail of the volume, and shall be regularly sent to the chemical coating manufacturer to detect the chromium content of the chemical coating. X-ray fluorescence, diffraction, plasma, atomic absorption or chemical Analytical method for determination of chromium content.

In addition, the prepainted galvanized steel coating may be mechanically damaged. The possible cause is that part of the coating surface has been removed. In severe cases, organic matter is exposed through contact with another object, such as cargo, fenders, or a ship's metal chains. The solution is to use the effect of mechanically damage-resistant coatings based on special resins and pigments.

Prepainted galvanized steel coating will appear blistering. This is a dome-like protrusion due to localized loss of adhesion and jacking up from the underlying coating. Blistering can result from a variety of causes and mechanisms. Include osmotic gradients related to soluble salts, soluble pigments, corrosion products, residual solvents. Non-permeable blisters are associated with cathodic disbondment, thermal gradients from the cold wall effect, and compressive stress. The precautionary measure is to apply an appropriate coating system after testing for soluble salts.

If there is a crumbly, powdery layer on the surface of the paint film, the paint is chalked. Chalking rate is related to pigment concentration and binder selection. This situation is generally a problem of formula and technology.