1. Rust Removal: Clean the Cut Surface First
Mild rust (thin, powdery): Use wire brushes (manual or electric) or sandpaper (80–120 grit) to scrub the cut surface. This is suitable for small plates or localized rust spots.
Moderate rust (thick, adherent): Use mechanical tools like angle grinders with wire wheel attachments, or sandblasting (dry/wet) for larger areas. Sandblasting ensures thorough rust removal and creates a slightly rough surface, which improves subsequent coating adhesion.
Post-removal cleaning: Wipe the surface with a clean cloth dipped in ethanol or acetone to remove dust, oil, or residues. Ensure the surface is completely dry before the next step (moisture accelerates re-rusting).
2. Corrosion Protection: Protect the Cut Surface
Method 1: Passivation (Enhance Inherent Weathering Resistance)
Process: Apply a weathering steel passivator (commercially available, e.g., chromium-free passivators compliant with environmental standards) to the cleaned cut surface. Use a brush or spray to ensure uniform coverage.
Principle: The passivator accelerates the formation of a stable, dense oxide film (similar to the steel's natural weathering layer) on the cut surface, restoring its corrosion resistance.
Curing: Allow the passivator to air-dry for 24–48 hours (depending on ambient temperature/humidity) before exposure to the environment.
Method 2: Coating (Long-Term Sealing Protection)
Primer: First apply a weathering steel-specific primer (e.g., epoxy zinc-rich primer) to the passivated surface. It provides cathodic protection and enhances coating adhesion.
Topcoat: Once the primer is dry (follow manufacturer's instructions), apply a weathering-resistant topcoat (e.g., acrylic polyurethane topcoat or fluorocarbon topcoat). Choose a color close to Q235NH's natural patina for aesthetic consistency.
Note: Ensure the coating is free of bubbles or gaps-these can trap moisture and cause localized rust.
3. Post-Treatment Inspection and Maintenance
Inspection: After rust removal and protection, check the cut surface for missed rust spots or uneven coating. Touch up any defects with additional passivator or coating.
Regular maintenance: For outdoor applications, inspect the cut surface every 6–12 months. If minor rust reappears, repeat the wire brushing + passivation process to maintain protection.
