First and foremost, it is essential to understand the standard for thermal galvanizing corrosion prevention process in photovoltaic support structures. The process begins with the workpiece and involves multiple stages: degreasing → water washing → acid washing → water washing → immersion in auxiliary galvanizing solvent → preheating → hot galvanizing → sorting → cooling → passivation → rinsing → drying → inspection.

De-fatting

Oil can be removed using chemical degreasing or water-based metal cleaner until the workpiece is fully wetted.

Passivation

Acid cleaning can be performed using 15% H2SO4, 0.1% thiourea, at temperatures of 40-60°C, or with 20% HCl and 1-3g/L of hexamethylenetetramine, at temperatures of 20-40°C. The addition of a corrosion inhibitor helps prevent excessive corrosion of the base material and reduce the amount of hydrogen absorbed by the iron substrate. Poor degreasing and acid cleaning can result in poor adhesion of the coating, failure to apply zinc, or the shedding of the zinc layer.

Three: Immersion Plating Agent

Also known as a binder, it maintains the workpiece's activity before dipping, enhancing the bonding between the coating and the substrate. NH4Cl 15% to 25%, ZnCl2 2.5% to 3.5%, 55 to 65°C, 5 to 10 minutes. To reduce the volatilization of NH4Cl, it is appropriate to add a small amount of glycerin.

Four: Preheating of Drying

To prevent deformation of workpieces due to rapid temperature increase during dipping and to remove residual moisture to prevent zinc explosion, the preheating temperature is generally set between 120 to 180°C.

Five: Hot-Dip Galvanized

To control the zinc liquid temperature, dipping time, and the speed of removing workpieces from the zinc bath. Low temperature results in poor zinc fluidity, thick and uneven coatings, prone to sagging, and poor appearance quality; high temperature improves zinc fluidity, reduces the occurrence of sagging and skinning, enhances adhesion, produces thinner coatings with better appearance, and improves production efficiency; however, excessive temperature leads to severe iron loss in the workpiece and zinc pot, generates a large amount of zinc slag, affects the quality of the galvanized layer, increases zinc consumption, and may even prevent coating application.

At the same temperature, longer immersion time results in thicker coatings. At different temperatures, a longer immersion time is required to achieve the same thickness. Generally, manufacturers to prevent workpiece deformation at high temperatures and reduce zinc slag due to iron loss, use temperatures of 450-470°C, 0.5-1.5 minutes. Some factories use higher temperatures for large workpieces and cast iron, but avoid the temperature range with peak iron loss. To improve the fluidity of the hot-dip galvanizing liquid at lower temperatures, prevent excessive coating thickness, and enhance the coating appearance, it is common to add 0.01%-0.02% pure aluminum. Aluminum should be added in small quantities multiple times.

VI. Organize

Post-plating workpiece preparation mainly involves removing excess zinc and zinc lumps, which can be done through vibration or manual methods.

Seven: Passivation

The objective is to enhance the atmospheric corrosion resistance of workpiece surfaces, reduce or extend the appearance of white rust, and maintain a good appearance of the coating. All are passivated with chromates, such as Na2Cr2O7 at 80-100g/L, and sulfuric acid at 3-4ml/L.

Section 8: Cooling

Generally, water cooling is used, but the temperature should not be too low to prevent cracking of the matrix structure in the workpieces, especially castings, due to receding from rapid cooling.

Nine: Inspection

The coating surface is bright, fine, free of drips and skinning. Thickness inspection can be done using a coating thickness gauge, which is a relatively simple method. The coating thickness can also be calculated by converting the zinc adhesion amount. The bonding strength can be tested with a bending press, bending the sample 90-180°; there should be no cracks or coating detachment. A hammer test can also be used for inspection.