As a core support structure for cable laying, improving the fire resistance of galvanized tray bridges requires a comprehensive approach encompassing four dimensions: material processing, coating technology, structural design, and system integration. Through process optimization, the high-temperature resistance of the trays during fires can be significantly enhanced, slowing the spread of fire and providing more reliable protection for cables and equipment.
Strengthening the heat resistance of the galvanized layer is fundamental. Traditional galvanized tray bridges use a hot-dip galvanizing process to form a zinc-iron alloy layer on the steel surface. While this provides some corrosion resistance, the melting point of zinc is only about 419°C, making it prone to oxidation and failure at high temperatures. To improve fire resistance, a high-temperature resistant zinc-based alloy coating can be used. By adjusting the proportions of elements such as zinc, aluminum, and magnesium, the melting point of the coating can be increased to over 600°C. For example, a zinc-aluminum-magnesium alloy coating forms a dense oxide film at high temperatures, effectively isolating oxygen from contact with the steel and slowing down the oxidation process. In addition, the coating thickness must be strictly controlled. Too thin a coating makes it susceptible to penetration by high temperatures, while too thick a coating may peel off due to differences in thermal expansion coefficients. A minimum coating thickness of 80μm is generally recommended.
The composite application of fire-retardant coatings is a key technology. Spraying fire-retardant coatings onto a galvanized layer creates a double protective barrier. Intumescent fire-retardant coatings should be selected, with core components such as expanded graphite and ammonium polyphosphate. These rapidly expand at high temperatures to form a char layer, which can be dozens of times thicker than the original coating. This char layer has extremely low thermal conductivity, effectively blocking heat transfer while releasing non-combustible gases to dilute the oxygen concentration. During application, attention must be paid to coating uniformity to avoid localized thinning that could lead to protective failure. The curing environment must be kept dry and well-ventilated, with temperatures controlled between 5-35℃ and humidity not exceeding 85% to ensure full curing. For high-risk areas, a composite coating system of "primer + fire-retardant coating + topcoat" can be used. The primer enhances adhesion, and the topcoat improves weather resistance, resulting in an overall fire resistance limit of over 1.5 hours.
Optimizing the airtightness of the structural design is an important supplement. The fire resistance of galvanized tray bridges is closely related to their structural airtightness. While open tray bridges are easier to install and maintain, flames can easily penetrate through gaps; trough-type tray bridges, due to their fully enclosed design, effectively block the spread of flames and smoke. In practical applications, fireproof covers can be installed on top of the tray bridges, or covered tray structures can be used. A fireproof sealing strip must be installed between the cover and the tray body to prevent the penetration of high-temperature smoke. Furthermore, the connections between the tray bridges and building walls and floors should be filled with fire-resistant sealing materials, such as inorganic fireproof putty or fireproof boards, to ensure no gaps allow fire to spread. For long-distance cable bridge installations, fireproof partitions are also required to divide the tray bridge into multiple independent sections, limiting the range of fire spread.
System-integrated active defense is the ultimate guarantee. Improving fire resistance depends not only on the cable bridge itself but also on its integration with fire alarm and automatic fire suppression systems. For example, linear thermocouples can be laid inside the cable tray to monitor temperature changes in real time. When the temperature exceeds a threshold, an alarm is triggered and the fire extinguishing system is activated. Alternatively, an intelligent monitoring module can be integrated to upload data such as cable tray temperature and smoke to a management platform via IoT technology, enabling remote monitoring and early warning. Furthermore, cable selection must match the fire resistance rating of the cable tray, prioritizing flame-retardant or fire-resistant cables to reduce the risk of the cables themselves igniting.
Improving the fire resistance of galvanized tray bridges requires a comprehensive approach, including heat-resistant coating enhancement, composite application of fire-retardant coatings, optimized structural airtightness, and integrated active fire protection systems. These measures not only significantly enhance the fire resistance of the cable trays but also extend the normal operating time of cables during a fire, buying valuable time for personnel evacuation and fire rescue.
