1.How to choose the base material type for galvanized skeleton?
Commonly used Q235B low carbon steel (low cost) and Q355B low alloy high strength steel (high strength, suitable for heavy snow load areas). The lower the carbon content and impurities (such as sulfur and phosphorus) of the base material, the better the corrosion resistance.
Structural form: round tube, square tube or special-shaped tube. The larger the cross-section and the thicker the wall, the stronger the deformation resistance, but the more difficult it is to cover with coating.
2.What is the core difference in galvanizing process?
Hot-dip galvanizing
Process: Immerse the steel in molten zinc to form a zinc-iron alloy layer + pure zinc layer, with a total thickness of 20~80μm.
Advantages: The coating is dense and has strong bonding strength. The corrosion resistance is 3~5 times that of cold galvanizing. It is the mainstream process for greenhouse frames.
Electrogalvanizing
Process: The zinc layer is formed by electrochemical deposition, with a thickness of 8~15μm, and passivation treatment is often required.
Application: Only suitable for short-term greenhouses or non-critical components, and the cost is about 1/3 of hot-dip galvanizing.
Zinc-aluminum-magnesium alloy coating:
A new process, aluminum and magnesium are added to the zinc layer, the corrosion resistance is 2~3 times that of ordinary hot-dip galvanizing, and it is gradually promoted in coastal or high-humidity areas.
3.What is the coating thickness and standard?
Hot-dip galvanizing refers to GB/T 13912-2020. The coating thickness of greenhouse frames is usually ≥55μm, and can be increased to 65~80μm in extremely cold areas or areas with heavy acid rain.
Zinc-aluminum-magnesium coating refers to ISO 14713. The salt spray resistance time can reach more than 200% of hot-dip galvanizing at the same thickness.
4.What impact do humidity and condensation have on lifespan?
The humidity inside the greenhouse is ≥80% all year round, and condensation water is easily formed on the surface of the frame. If the drainage is not smooth (such as the slope of the frame design is insufficient), local water accumulation will accelerate the electrochemical corrosion of the coating.
5.What impact do temperature and UV rays have on lifespan?
In summer, the temperature inside the greenhouse can reach 50~70℃, and high temperature accelerates the oxidation of the zinc layer. Although ultraviolet rays have limited direct impact on the zinc layer, they will accelerate the aging of the sealant on the surface of the frame (such as the seal of the connection parts), causing water corrosion in the gaps.