1.What are the steps in the processing procedure?
The process mainly consists of three steps: surface treatment → selection of suitable materials → coating application.
2.How to perform surface treatment?
Thoroughly clean weld slag and spatter: Use tools such as a slag hammer and wire brush to remove all welding residue.
Grind the weld area:
Purpose: To remove the heat-affected zone (often oxidized, discolored, or with damaged zinc) and all rust from both sides of the weld.
Tools: An angle grinder.
Method:
Use a cup-shaped wire brush to clean the flat surface and weld bead surface.
Use a grinding wheel or louvered blade for a more thorough grinding until a uniform, bright, and solid metal surface is exposed.
Scope: The grinding area should extend 50-100 mm to each side of the weld, ensuring all damaged zinc is removed.
Clean the surface: Blow away dust with compressed air, then wipe with a specialized cleaner (such as acetone or xylene) or an oil-free cloth to remove oil, fingerprints, and moisture, ensuring the surface is absolutely clean and dry.
3.How to choose corrosion-resistant materials?
Zinc-rich coatings (the most common and recommended method) are the best choice for repairing galvanized layers because they provide similar cathodic protection as the original galvanized layer.
Working principle: The coating contains a large amount of zinc powder (typically over 80% zinc powder in dry film). In the presence of an electrolyte (such as rainwater or moisture), zinc acts as the anode and corrodes preferentially over steel, thus protecting the steel substrate.
Cold-dip galvanizing coating / galvanizing repair agent
These products can be considered easy-to-apply "liquid zinc," and their main component is high-purity zinc powder.
Features: Easy to apply, like ordinary paint by brushing or spraying, forming a coating with a composition similar to hot-dip galvanized layers. It is specifically designed for repairing galvanized layers.
Supporting System (For Harsh Environments)
For harsh environments like floating bridges, which are constantly exposed to moisture, immersion, and UV radiation, a complete coating system is recommended:
Primer: Epoxy zinc-rich primer or cold-dip galvanizing coating. Provides cathodic protection and basic corrosion protection.
Intermediate Coat: Epoxy micaceous iron oxide intermediate coat. Effectively increases coating thickness, shields against moisture and corrosive media, and enhances overall corrosion resistance.
Topcoat: Polyurethane topcoat or fluorocarbon topcoat. Provides excellent weather resistance, UV resistance, and abrasion resistance, while also offering an aesthetically pleasing color.
4.What are the steps involved in painting?
Coating Method: Brush, roller, or airless spraying can be used. For weld areas, brushing ensures better paint penetration to every corner.
Coating Scope: The coating should not only cover the sanded weld area but also extend 25-50 mm into the surrounding intact galvanized layer to ensure a good overlap between the old and new coatings.
Coating Thickness:
If using only zinc-rich paint, the dry film thickness should be at least 70-100 microns.
If using a complete system, the total dry film thickness should be determined according to design requirements, typically 200-300 microns or higher.
Drying and Curing: Strictly follow the product instructions to ensure sufficient drying and curing time, especially for epoxy coatings, which cure more slowly in low-temperature, high-humidity environments.
5.What are the best practices?
Surface Preparation: Use an angle grinder with a louvered blade or wire brush to thoroughly grind the weld seam and both sides until a metallic luster is exposed and the surface is clean.
Primer: Apply 1-2 coats of epoxy zinc-rich primer to ensure the dry film thickness meets the specified requirements.
Intermediate Coat: Apply 1 coat of epoxy micaceous iron oxide intermediate coat to increase coating thickness and shielding properties.
Topcoat: Apply 1-2 coats of aliphatic polyurethane topcoat to provide excellent weather resistance and abrasion resistance.