The rust removal and anti-corrosion treatment of steel supports is a key process to extend their service life and ensure structural safety. It is necessary to follow the principle of "thorough rust removal, primer adhesion, and topcoat protection". The specific steps are as follows:
1、 Preparation: Surface cleaning and inspection
Clean surface attachments
Use a wire brush, shovel, or high-pressure water gun to remove floating rust, welding slag, oil stains, concrete residues, and other debris from the surface of the steel support, ensuring that there are no obvious lumps of dirt.
Polish the splashes and burrs on the welding area to avoid puncturing the subsequent coating; If there are dents or holes, putty (such as epoxy putty) should be used to fill and level them, and then polished smooth after drying.
Inspect for damage and defects
Inspect the steel support for structural damage such as cracks, bending, and cross-sectional deformation. These components need to be repaired or scrapped first and cannot be directly treated with anti-corrosion.
Record the degree of rust: Mild rust (surface spot rust) can be directly removed; Moderate rust (rust layer thickness ≤ 0.1mm, local peeling) requires special attention to rust removal; Severe rusting (rust layer peeling off in patches, with pockmarks appearing) requires evaluation of whether to replace the rod.
2、 Rust removal treatment: remove rust layer and oxide scale
Select appropriate methods based on the degree of rust and construction conditions to ensure compliance with Sa2.5 level (near white level) or St3 level (thorough manual and power tool rust removal) standards (refer to GB/T 8923 "Rust Grades and Preparation Grades of Steel Surfaces before Coating"):
Mechanical rust removal (preferred, efficient and thorough)
Sandblasting rust removal: By using high-pressure sandblasting (quartz sand, steel shot) to impact the steel surface, all rust layers, oxide scales, and old coatings are removed, forming a uniform rough surface (roughness of 50-80 μ m) and enhancing the adhesion of the coating. Suitable for batch processing or heavily corroded parts.
Angle grinder rust removal: equipped with steel wire wheels or sandpaper discs, manually polish rusted areas, suitable for local rust removal or small components, pay attention to the grinding direction being consistent with the steel texture, and avoid excessive grinding causing thinning of the section.
Manual rust removal (auxiliary, suitable for small areas)
Use a wire brush, sandpaper, and scraper to manually remove visible rust layers until a metallic luster is exposed; Parts that are difficult for machinery to reach, such as corners and nodes, need to be cleaned carefully to ensure that there is no residual rust.
Chemical rust removal (used in special scenarios)
For components with complex shapes, acid washing (such as hydrochloric acid solution) can be used for rust removal. After removing the rust layer, rinse with clean water, then neutralize the residual acid solution with a neutralizing agent (such as sodium carbonate solution), and finally dry it. Attention: Acid washing is prone to environmental pollution and requires proper wastewater treatment. It is only suitable for small components.
3、 Anti corrosion coating: layered protection and drying curing
Apply primer (adhesion layer, rust proof core)
Within 4 hours after rust removal, the primer should be applied (to avoid secondary rusting). Commonly used primers are epoxy zinc rich primer (with a zinc content of ≥ 80%) or red lead anti rust paint (in a dry indoor environment).
Painting requirements: uniform and no leakage, with a thickness controlled between 60-80 μ m (measured with a thickness gauge); Use brushing or spraying, and apply 1-2 more coats at corners and nodes to ensure complete coverage.
Apply intermediate paint (reinforcement layer to enhance durability)
After the primer dries (usually 24 hours, according to the coating instructions), apply an intermediate coat (such as epoxy mica iron intermediate coat) with a thickness of 50-70 μ m, which is used to isolate water vapor, enhance coating toughness, and reduce the risk of topcoat cracking.
Apply finish paint (protective layer, anti-aging and aesthetic)
After the intermediate paint dries, apply the topcoat (such as polyurethane topcoat, chlorinated rubber topcoat). For outdoor environments, choose polyurethane paint with strong weather resistance and a thickness of 60-100 μ m.
The topcoat should be uniform and smooth, without any sagging or bubbles. The color should be a prominent yellow or red (for easy identification of damage), and two coats of coating will yield better results.
Curing and maintenance
After painting, avoid exposure to rain and direct sunlight, and maintain in a ventilated and dry environment for 7-10 days (fully cured). During this period, collision or load-bearing is prohibited; After curing, the coating adhesion (≥ 5MPa) should be tested using the grid cut method, and any non-conforming areas should be reworked.
4、 Post maintenance: Regular inspection and repainting
In daily use, the coating condition should be checked every 3-6 months. If local rust or peeling is found, sandpaper should be used to polish and remove rust, and the "primer+topcoat" steps should be followed for local touch up coating.
Steel supports for long-term storage should be elevated at least 30cm above the ground and covered with rainproof cloth; The support used outdoors should be cleaned of accumulated water in a timely manner after rain and snow to avoid accelerated rusting of the damaged coating.
By following the above steps, the steel support can be effectively isolated from contact with air and water vapor, significantly reducing the corrosion rate and extending its service life to 5-8 years (under normal working conditions).
