1.What is the mechanism of sun aging?
Ultraviolet rays (UV) damage the zinc protective film. Consequence: the dense protective film is powdered and peeled off → the zinc layer consumption rate increases by 3~5 times
Temperature difference stress between day and night (>40℃ fluctuation)
Zinc layer cracking: difference in thermal expansion coefficient between zinc and steel → accumulation of interface shear stress → microcrack expansion
High temperature catalytic corrosion Temperature effect: For every 10°C increase in temperature, the electrochemical corrosion rate doubles
2.What is the difference in lifespan under different exposure environments?
Temperate cities: 30-40 years
Subtropical coastal areas: 15-20 years
Tropical deserts: 8-10 years
3.What are the characteristics of sun aging?
Initial stage (1-3 years)
Surface gloss loss → grayish white powdery layer (ZnO)
Local light yellow spots appear (FeOOH begins to form)
Mid-stage (5-10 years)
Zinc layer cracks appear (width < 0.1mm)
Red rust seeps out from corners
Late stage (> 10 years)
Large area of red rust and white rust coexist
Zinc layer blistering and peeling (loss of bonding strength)
4.What are the optimization solutions for anti-exposure?
Upgraded coating, enhanced surface protection, design protection, avoid water accumulation on flat surfaces, and add sunshades above galvanized parts
5.What are the post-exposure repair techniques?
Mild powdering: high pressure water gun washing (pressure ≤ 150 bar)
Brushing silane impregnation agent (penetration depth > 5 mm)
Moderate cracking
Sandblasting to Sa2.5 (abrasive: garnet G80)
Spraying arc zinc layer (thickness 150μm)
Severe rust (zinc layer <20μm)
Cut and replace + use stainless steel/weathering steel instead