1.What are the characteristics and impacts of minor scratches?
Characteristics: The scratch is visible under light, but when run across with a fingernail, there is no noticeable unevenness, or it feels very slight. The scratch is silvery-white, with no visible base color.
Impact: The effect primarily affects aesthetics, with minimal impact on corrosion resistance, as the zinc layer is not fully penetrated and still protects the steel base through the sacrificial anodic effect.
2.What are the characteristics and effects of moderate scratches?
Characteristics: The scratch is clearly visible, with a distinct groove that can be felt with a fingernail. The base of the scratch reveals a gray-black steel substrate, or red rust has appeared.
Impact: Corrosion resistance has been lost. The exposed steel substrate becomes a starting point for corrosion, which can spread to the surrounding area and requires repair.
3.What are the characteristics and effects of severe scratches?
Characteristics: Very deep, wide scratches, likely caused by a violent collision or scraping, which not only remove the zinc layer but also a portion of the steel substrate.
Impact: Severe dimensional defects and corrosion protection failure, making repair difficult and typically requiring consideration for downgrading.
4.How to repair minor scratches?
Mechanical Polishing/Grinding
Tools: Use very fine sandpaper (e.g., >600 grit), a scouring pad (fine-grit side), or a wool wheel with a light polishing paste.
Method: Gently sand or polish along the direction of the scratch, smoothing any raised areas around the scratch and making them flush with the surrounding area. Important: Use gentle movements and sand a small area, as this will damage the intact zinc layer.
Follow-up: After polishing, clean the surface and, ideally, spray a layer of passivation solution to re-form a protective film on the repaired area.
Chemical Passivation
How it works: Apply a specialized chromate passivation solution or a chromium-free passivation solution to the scratched area. The solution reacts with the zinc to form a composite protective film. This film not only prevents zinc oxidation and white rust, but also, its color (e.g., color coating, blue-white coating) can partially conceal superficial scratches.
Method: Dip a cotton swab or soft cloth in the passivation solution and apply it evenly to the scratch and surrounding area. Allow it to dry naturally.
5.How to repair moderate and severe scratches?
Cleaning and Rust Removal (First Step, Critical)
Use a degreaser to thoroughly clean the scratched area, removing any oil and impurities.
If red rust has formed, it is imperative to thoroughly remove it with a pointed tool, a graver, or fine sandpaper until the metallic luster is exposed. Failure to do this step will render any subsequent repairs ineffective.
Spraying Zinc-Rich Paint (The Most Common and Effective Method)
How it works: Zinc-rich paint contains a high concentration of zinc powder. After application, the zinc particles connect with each other and contact the steel substrate, creating a "sacrificial anode" protection similar to hot-dip galvanizing.
How to Apply:
After cleaning and removing rust, carefully apply the zinc-rich paint to the scratch with a brush or small brush, ensuring that the exposed steel substrate is completely covered.
Apply several coats to ensure sufficient thickness.
After drying, the paint will have a matte gray color that matches the surrounding zinc layer.
Advantages: Excellent corrosion protection, simple application, low cost, and suitable for scratches of all sizes.