Q:What are the common types of defective surfaces on galvanized steel that can be repaired?
A:1. Missing plating/exposed iron (partial zinc plating)
2. Zinc nodules/zinc slag adhesion (surface raised particles)
3. White rust (white powdery corrosion on the surface)
4. Dirt/oil on the surface (grease, passivation liquid residue, etc.)
5. Minor scratches/scratches (no exposed substrate)
6. Insufficient plating thickness (partial or overall thinness)
Q:What types of defects on galvanized steel surfaces cannot be repaired or must be treated with caution?
A:Large area of missed plating/exposed iron
Plating peeling/flaking
Severe surface roughness/porous
Plating problems caused by substrate defects
Missed plating caused by weld defects
Q:How to repair missing plating/exposed iron (partial zinc plating)?
A:Zinc-rich paint repair: Use cold-dip galvanizing paint (such as epoxy zinc-rich paint) with a zinc content of ≥90% to paint the missed areas, and form an alternative protective layer after drying. Suitable for non-critical anti-corrosion scenarios (such as indoor structures).
Hot-spray zinc: Use arc spraying or flame spraying of zinc alloy to form a coating with performance close to that of hot-dip galvanizing, suitable for outdoor or highly corrosive environments.
Welding galvanizing: For extremely small missed points (such as diameter <5mm), you can first use zinc welding rods for repair welding, then grind it flat and apply passivation liquid.
Q:How should zinc nodules/zinc slag attachment (raised particles on the surface) be repaired?
A:Mechanical grinding: Use fine sandpaper, file or electric grinding wheel to gently grind the zinc nodules. Pay attention to control the strength to avoid grinding through the coating and exposing the steel. Suitable for workpieces with thicker galvanized layers.
Chemical dissolution: Apply dilute hydrochloric acid (5%~10% concentration) or special zinc nodule cleaning agent to the zinc nodules. After a moment of reaction, rinse with clean water and dry, then apply passivation liquid.
Heating and softening: For larger zinc nodules, local heating can be performed to near the melting point of zinc (419℃), and lightly pressed and leveled with tools, and polished smooth after cooling.
Q:How to repair white rust on galvanized steel?
A:Physical removal: Use a dry soft cloth or copper wire brush to gently wipe off the white rust (avoid damaging the coating with a steel wire brush), and then clean the surface with anhydrous ethanol or acetone.
Chemical treatment: Mild white rust: Wipe with a 3%~5% chromic acid solution or a special zinc layer cleaning agent, react for 1~2 minutes, then rinse and dry, and then apply chromium-free passivation liquid.
Severe white rust: First neutralize the corrosion products with a 10% citric acid solution, rinse and dry, then apply zinc-rich paint or re-passivate.