1.What are the principles and standards of salt spray test chambers?
Principle: A continuous, high-humidity, high-salt corrosive environment is created by spraying a sodium chloride solution of a specific concentration into a sealed chamber, accelerating the corrosion of the galvanized layer.
Main Standards:
Neutral Salt Spray Test (NSS): The most basic standard, such as ISO 9227 and ASTM B117.
Acetic Acid Spray Test (AASS): Acetic acid is added to salt water to lower the pH value, accelerating corrosion. Used to evaluate decorative coatings.
Copper Accelerated Acetic Acid Spray Test (CASS): Copper chloride is added to AASS, resulting in the strongest and fastest corrosion. Commonly used for high-requirement coatings in the automotive and electronics industries.
Test Result Evaluation: After testing, the sample surface is checked for white rust (a corrosion product of zinc) or red rust (a corrosion product of the base iron), and the time it takes for rust to appear is recorded. The longer the time for white/red rust to appear, the better the corrosion resistance.
2.What are the principles and advantages of a cyclic corrosion test chamber?
Principle: It's not just continuous spraying; it simulates the natural wet-dry cycle. A typical cycle might include multiple stages: salt spray → drying → wetting (high humidity).
Advantages: Compared to traditional continuous salt spray tests, cyclic testing correlates better with actual outdoor corrosion because it simulates the different states materials experience in reality (e.g., dry during the day, condensation at night).
3.What are the principles and standards of a damp heat test chamber?
Principle: Simulates a high-temperature, high-humidity environment (e.g., temperature 85°C, relative humidity 85%) to evaluate the stability of the galvanized coating in a humid environment and whether problems such as coating blistering and decreased adhesion will occur.
Standards: Such as GB/T 2423.3, IEC 60068-2-78.
4.What are the methods and characteristics of natural exposure testing?
Method: Galvanized coil samples are placed in typical natural environments, such as:
Urban environment
Industrial environment (heavily polluted)
Marine environment (high salinity)
Characteristics: Provides the most realistic results, but is extremely time-consuming, typically requiring years or even decades to obtain convincing data. The purpose of accelerated laboratory testing is to predict the long-term performance of materials in natural environments within a short timeframe.
5.What are the key takeaways from the testing process?
Substrate Testing: Salt spray testing is conducted on bare galvanized coils to assess the corrosion resistance of the zinc layer itself, which is fundamental for rust prevention.
Finished Product Testing: Finished sheet metal that has undergone all surface treatments (such as powder coating) is tested for:
Cyclic Corrosion Testing: This assesses the overall protective performance of the entire coating system under simulated real-world conditions.
UV Aging Testing: This evaluates the weather resistance of the surface coating, checking whether the color and physical properties are maintained.
Adhesion Testing: Before and after the aging test, a cross-cut adhesion tester is used to check whether the coating peels off due to aging.