When applying anti-corrosion coatings to bridge embedded parts, ensuring complete corner coverage requires a systematic control plan encompassing four key areas: surface pretreatment, coating selection, optimized application processes, and quality inspection.
Surface pretreatment is fundamental to ensuring corner coverage. After installation, corners and edges require detailed treatment. First, use an angle grinder or sandpaper to chamfer the cut edges to remove burrs and sharp edges, reducing the risk of stress concentration. Next, use an electric cutter or wire brush to thoroughly clean welds and areas around bolt holes, where welds are prone to residual weld slag, to ensure complete exposure of the metal substrate. Finally, perform a secondary grinding of the corners to create a smooth transition surface and avoid coating buildup or sagging caused by right-angle structures. For example, when applying steel box girders to bridge embedded parts, the corner radius must be kept at least 2mm to improve coating adhesion.
The compatibility of the coating system directly impacts the effectiveness of corner protection. Primers should be highly permeable and highly adhesive epoxy zinc-rich or inorganic zinc-rich coatings. Their molecular structure penetrates deep into metal pores to form chemical anchors, providing electrochemical protection, particularly at stress-concentrated areas like corners. Epoxy micaceous iron oxide coatings are recommended as intermediate coats, as their flake-like micaceous iron oxide forms a dense barrier layer, effectively blocking the penetration of corrosive media. Topcoats should be selected based on the environmental level: For environments C3 and below, acrylic polyurethane topcoats are suitable, as their flexibility allows for micro-deformation at corners. For environments C4 and above, cross-linked fluorocarbon coatings should be used, as their amorphous structure provides long-term resistance to UV and salt spray corrosion. For example, in coastal bridge construction, a composite system of "inorganic zinc-rich primer + epoxy micaceous iron oxide intermediate coat + fluorocarbon topcoat" is often used at corners, achieving an anti-corrosion lifespan of over 20 years.
Refined construction techniques are key to ensuring corner coverage. During spraying, adjust the spray gun angle to 45°-60° to spread the paint in a fan-shaped pattern around corners. Maintain a spray distance of 25-30cm to avoid paint rebound from too close a distance or excessively thin coating from too far a distance. For three-dimensional structures such as grooves and bolt holes, a "pre-coat + overcoat" process should be employed: First, pre-coat the corners with a brush to ensure the paint fully fills the gaps; then, spray the entire structure to achieve a uniform coating thickness. For example, in the construction of embedded parts of cross-sea bridges, a "two-coat pre-coat + three-coat" process was used at corners, achieving a coating thickness of over 300μm without defects such as sags and pinholes.
Quality inspection must be carried out throughout the entire construction process. After each coat, the thickness of the corners must be checked using a magnetic thickness gauge to ensure it meets at least 90% of the design requirement. Adhesion should be tested using the pull-off method; adhesion at corners should be at least 5MPa. Visual inspection of the coating surface should ensure there are no defects such as missing coating, cracks, or bubbles at corners. Areas that fail inspection are sanded down to the metal substrate, then re-prepared and re-coated. For example, in a large bridge project, by establishing a closed-loop "construction-inspection-repair" management system, the coating pass rate for corner areas increased from 85% to 98%, effectively extending the service life of bridge-embedded parts.
Through the coordinated control of surface pretreatment, coating matching, process optimization, and quality inspection, the challenge of coating corners on bridge-embedded parts can be systematically addressed. This approach not only enhances the integrity and durability of the anti-corrosion coating but also provides long-term assurance for the safety of the bridge structure, significantly contributing to the high-quality development of infrastructure.
