During the production of hot-dip galvanized bridges, zinc splash is a key factor causing surface defects and impacting coating quality. Its root cause is closely related to process control, equipment status, and operating procedures. Splash can cause surface defects such as zinc nodules, missing plating, and roughness, and can even pose safety hazards. Therefore, coordinated control at multiple levels is crucial to prevent these defects.
Precise control of the zinc bath temperature is paramount for preventing splash. Excessively high zinc bath temperature reduces viscosity and increases fluidity, leading to splashing caused by violent surface fluctuations during bridge immersion or withdrawal. Excessively low temperatures result in insufficient zinc bath fluidity, resulting in uneven coating on the bridge surface and potentially causing sudden splashing due to localized overheating. During production, the temperature must be maintained within a reasonable range based on the bridge material, specifications, and zinc bath composition. Automated temperature control equipment should be used for real-time adjustments to avoid temperature fluctuations caused by manual operation.
Standardized bridge immersion and withdrawal speeds directly impact the dynamic equilibrium of the zinc bath. If the bridge is immersed too quickly, the zinc solution will be rapidly displaced, forming vortices and causing the surface to churn violently. Excessive withdrawal speed will cause zinc adhering to the hot dip galvanized bridge surface to fall off due to inertia, both of which can cause splashing. Operators require professional training to master the "slow entry and slow exit" principle and adjust the speed based on the bridge structure. For example, for complex hot dip galvanized bridges with elbows or tees, the speed should be appropriately reduced to ensure smooth zinc adhesion.
Optimizing the zinc solution's composition can reduce the tendency to splash. Excessive impurities (such as carbon black, zinc ash, solvent residue) or harmful elements (such as lead and tin) in the zinc solution can alter its surface tension and fluidity, increasing the likelihood of splashing. Regular zinc purification is required during production to remove impurities through methods such as slag removal and filtration. The proportion of alloy additives must be strictly controlled to ensure that the zinc solution meets standard requirements. Furthermore, the mixing ratio of new and old zinc must be appropriate to avoid abnormal fluidity due to uneven composition.
Quality of the bridge pretreatment is fundamental to preventing splashing. If grease, rust, or scale is present on the bridge surface, these impurities can react violently with the zinc solution during zinc dipping, producing gaseous or explosive spatter. Pretreatment requires multiple steps, including pickling, water washing, and flux treatment, to thoroughly remove surface contaminants and form a protective film within the flux to prevent secondary oxidation of the bridge. Furthermore, ensure that the bridge welds are free of pores, residual welding slag, or spatter, as these defects can become sources of spatter.
Equipment maintenance and tooling design are crucial for spatter control. Galvanizing tanks, preheating furnaces, and other equipment require regular inspections to ensure proper sealing to prevent oxidation or leakage of the zinc solution. Tooling, such as hoists and supports, must be compatible with the bridge specifications to prevent unstable mounting, which can cause spatter. For example, using adjustable clamps to secure the bridge can reduce movement during zinc dipping. Installing baffles within the galvanizing tank can buffer the flow of zinc solution and reduce spatter height.
The operating environment's humidity and ventilation conditions must also be controlled. High humidity accelerates zinc oxidation, forming scum and increasing the risk of spatter. Poor ventilation can lead to zinc vapor accumulation, which not only harms operator health but can also cause spatter due to airflow disturbances. Production workshops should be equipped with dehumidification equipment and exhaust systems to maintain humidity within a reasonable range and ensure that no visible vapor layer forms on the surface of the zinc bath.
Preventing zinc spatter in hot-dip galvanized bridge production requires a comprehensive approach encompassing temperature control, standardized operating procedures, component optimization, pretreatment, equipment maintenance, and environmental management. Standardized process flows and refined process control can significantly reduce spatter defect rates and improve the surface quality and corrosion resistance of hot-dip galvanized bridges, thereby meeting the long-term, stable operation requirements of bridges in the chemical, power, and rail transportation sectors.
