In the production of galvanized tray bridges, the galvanizing process is the core step determining its corrosion resistance and service life. This process forms a dual physical and electrochemical protective barrier by coating the tray surface with a zinc layer, effectively isolating the substrate from oxygen, moisture, and corrosive media. The process flow encompasses three main stages: material pretreatment, galvanizing, and post-treatment. Each stage requires strict parameter control to ensure coating quality.
Material pretreatment is the foundation of the galvanizing process, directly affecting the adhesion between the coating and the substrate. Galvanized tray bridges typically use low-carbon steel plates as the substrate, requiring pickling to remove surface oxide scale, rust, and oil. After pickling, neutralization is necessary to thoroughly remove residual acid and prevent interference with subsequent processes. The cleaning stage uses high-pressure water guns or ultrasonic cleaning equipment to ensure the substrate surface is clean and free of impurities. Furthermore, some processes include surface activation treatment after cleaning, using chemical reagents to enhance the surface activity of the substrate and improve coating adhesion.
Zincizing is the core step of the process, mainly divided into hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing involves immersing the pre-treated cable tray into molten zinc, where a metallurgical reaction occurs between the zinc and the substrate at high temperatures, forming a dense zinc-iron alloy layer. This process is suitable for thicker cable trays, typically producing a thicker coating with excellent corrosion resistance. Electroplating, on the other hand, deposits a zinc layer on the substrate surface through electrolysis. This results in a more uniform coating, but a thinner layer, and is often used in applications requiring high dimensional accuracy. Regardless of the method used, strict control of the zinc bath composition, temperature, and immersion time is essential. For example, hot-dip galvanizing requires the addition of alloying elements such as aluminum and rare earth elements to the zinc bath to improve corrosion resistance; electroplating requires precise control of the current density to prevent defects such as peeling and blistering.
Post-treatment is crucial for improving the surface quality of the galvanized tray bridge. After galvanizing, zinc ash, zinc dross, and other impurities may remain on the surface of the cable tray. These need to be removed by sandblasting or shot blasting, which also increases surface roughness and improves coating adhesion. To further enhance corrosion resistance or aesthetics, passivation treatment can be performed. This involves using chemical agents to form a dense passivation film on the coating surface, effectively delaying the formation of white rust. Additionally, some processes include oiling or powder coating after passivation to create a composite protective layer, significantly improving the cable tray's adaptability to harsh environments.
Quality inspection is a crucial step in ensuring that galvanized tray bridges meet standards. Inspection includes coating thickness, adhesion, corrosion resistance, and surface quality. Coating thickness is measured using a magnetic thickness gauge or metallographic microscope to ensure it meets design requirements. Adhesion testing uses the cross-cut test or tensile test to verify the bonding strength between the coating and the substrate. Corrosion resistance testing typically uses a neutral salt spray test to simulate harsh environments and assess the coating's protective effect. Surface quality inspection relies on visual inspection or a high-magnification microscope to check for defects such as incomplete coating, peeling, and bubbles.
The galvanizing process for galvanized tray bridges must balance efficiency and environmental friendliness. During the production process, the emission of waste gas, wastewater, and waste residue must be strictly controlled. For example, zinc vapor generated during hot-dip galvanizing is treated through a flue gas purification system to avoid air pollution; wastewater must be treated through neutralization and precipitation to meet discharge standards and prevent heavy metal pollution of water sources. In addition, some companies have begun to adopt chromium-free passivation technology to reduce the use of harmful substances such as hexavalent chromium and promote the green transformation of processes.
