After cutting galvanized fireproof iron sheet, the edges lose their dual protection due to the shearing of the original galvanized layer and the cracking of the fireproof coating, becoming a major entry point for rust. Therefore, edge treatment requires a complete, closed-loop process encompassing pretreatment, galvanizing repair, fireproof coating reapplication, and subsequent protection to ensure consistent performance with the main sheet. Edge pretreatment is crucial. Burrs, oxidized slag, and oil stains generated during the cutting process can directly affect the adhesion of subsequent coatings. First, gently grind the edges with an angle grinder and a fine-grit grinding wheel to remove sharp burrs and uneven slag, creating a smooth transition and preventing stress concentration that can cause cracking in the coating. Next, clean metal debris from grinding with a wire brush or compressed air. Wipe the edges and surrounding areas with a volatile solvent to remove any residual oil and dust, ensuring a clean, rough surface. This creates a good adhesion foundation for subsequent galvanizing repair and fireproof coating reapplication.
Galvanizing repair is a key step in preventing edge rust, and the appropriate repair method should be selected based on the specific application scenario. If corrosion protection is critical, a hot zinc spraying process can be used. First, preheat the edge substrate to an appropriate temperature. Then, using specialized equipment, melt the zinc wire into atomized form and evenly spray it onto the edge surface, forming a metallic protective layer with a composition similar to the original galvanized layer. During spraying, the angle and speed of the spray gun must be controlled to ensure complete zinc coverage. Particular attention should be paid to easily missed areas, such as right angles and bevels, to avoid exposing the base. If site conditions are limited, cold zinc spray paint or a high-zinc-content anti-corrosion primer can be used. After stirring thoroughly, apply multiple thin coats with a specialized brush or spray gun. After each coat dries, lightly abrade the surface to enhance interlayer adhesion and ensure that the zinc content reaches the specified protection standard. This creates a continuous electrochemical protective layer that, together with the original galvanized layer, provides cathodic protection, preventing the intrusion of corrosive media.
Fire retouch coatings must maintain compatibility with the original coating to avoid degradation of protective performance due to material differences. First, confirm the type (e.g., intumescent, non-intumescent) and composition of the original fire retardant coating and select a fire retardant with the same system. Before re-applying, test-apply to a small area around the edge to observe any adverse reactions such as wrinkling or flaking. When re-applying, extend the coating 2-3 cm from the edge toward the main metal sheet, creating a gradual transition zone to avoid a noticeable step at the junction of the edge and the main sheet, which could lead to cracks in high-temperature environments. For intumescent fire retardant coatings, the coating thickness should be consistent with the original coating to ensure simultaneous expansion in the event of fire, forming a dense insulation layer. For non-intumescent fire retardant coatings, ensure uniform coverage without pinholes or bubbles. After re-applying, fully cure under specified temperature and humidity conditions. Avoid touching or contaminating the coating during the curing process to ensure that fire protection performance meets standards.
Follow-up protection and regular inspections are equally important and can further extend the life of the edge protection. For galvanized fireproof iron sheets exposed to humid, high-temperature, or corrosive environments for extended periods, an additional layer of weather-resistant sealant can be applied to the repaired edges to enhance the coating's aging and penetration resistance. During installation, if the edges need to be connected to other components, anti-corrosion gaskets or sealant should be installed at the joints to prevent rainwater and moisture from seeping in through the joint gaps. During routine maintenance, the edge coating should be regularly inspected. If localized peeling, bubbling, or rust is observed, the damaged area should be cleaned promptly and repaired according to the pretreatment, galvanizing repair, and fireproofing recoating process to prevent the spread of rust. Furthermore, after edge treatment is completed, care should be taken to avoid mechanical damage to the edge coating during subsequent processing or handling. If necessary, protective strips can be used for temporary protection to ensure the edge protection structure remains intact, working together with the main iron sheet to achieve both fire and corrosion protection.
