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The surface coating of door and window anti-fall chains is an important barrier against rust. Its impact on rust resistance and identification methods are as follows:

• Impact: The coating can isolate air and water vapor from contact with the metal substrate. The thicker the coating (usually 8-12 microns is optimal) and the higher the uniformity, the better the rust prevention effect. If there are pinholes, bubbles, or peeling in the coating, water vapor will seep in through the defects, causing the substrate to rust (rust will further damage the surrounding coating). Among common coatings, chrome plating has better rust resistance than zinc plating, and nickel plating (combined with passivation treatment) has even better rust resistance.
• Identification methods:Visually inspect whether the coating is smooth and uniform, without scratches or bulges.Gently scratch the coating with your finger; high-quality coatings are not easy to leave marks (inferior coatings are prone to scratches).You can check the product's coating test report to confirm the coating thickness and salt spray test results (coatings that can pass the 48-hour neutral salt spray test are qualified).A simple test can also be conducted: spray a small amount of salt water on the coating surface, observe after 24 hours, and if there is no rust, the rust resistance is good.