Anti-corrosion coating neutral salt spray test

       Neutral salt spray test is a commonly used artificial accelerated corrosion test. It simulates the coastal atmospheric environment. The warm sea surface evaporates from the cold air and the tiny droplets containing chloride ions are splashed into the space under the impact of waves, forming a fine mist. The corrosion conditions of the medium to the metal, using a certain concentration of sodium chloride solution, sprayed in a fine mist under pressure, because the mist particles evenly fall on the surface of the sample, and continuously maintain the liquid film renewal, so the corrosion of the coating In line with the basic principle of atmospheric corrosion, the accelerated corrosion of the coating can be measured.



After all, the neutral salt spray test cannot perfectly simulate the corrosion of the metal coating caused by atmospheric conditions. In addition, there are many factors affecting the corrosion, which makes the test conditions difficult to control, etc., and the reproducibility is often poor, so it can only be used as the same type of coating in the test. Comparison of relative corrosion resistance under this condition. Practice has shown that it has a better corrosion resistance effect on anodic coatings (such as zinc and cadmium layers on steel substrates), while for cathodic coatings, it can only reveal the degree of pores and defects of the coating, indirectly. Reflects the corrosion resistance of the coating.



The equipment, reagents and methods used in the neutral salt spray test are specified in the national standard GB 6458-86 "Neutral Salt Spray Test for Metal Coatings".



The number of samples is specified in accordance with the test, generally 3 pieces are taken from each batch. During the test, the sample is placed in the salt spray test box, the test solution is 5% NaCl (mass percentage) solution, the pH value is 6.5~7.2, the temperature in the spray box is 35℃+/-2℃, and the relative humidity is greater than 95% . The test surface is facing up, and the salt spray is allowed to freely settle on the tested surface. After 24h of spraying, the solution collected by each collector should be 1ml~2ml in terms of 80cm2, and the tested surface is 15°~20 in the vertical direction. 30°, the test surface cannot be directly sprayed. The specimens must not touch the box, nor each other. The distance between the samples shall not affect the free fall of the salt spray on the tested surface, and the droplets on the sample shall not fall on other samples. The test time should be determined according to the requirements of the tested covering layer or product standard. If there is no standard, the recommended time is: 2h, 6h, 16h, 24h, 48h, 96h, 240h, 480h, 720h. No heating when spraying is stopped, and the sample is sealed in the box to cool naturally. After the test is over, the sample is taken out. In order to reduce the shedding of corrosion products, the samples were placed in the room to dry naturally for 0.5h~1h before cleaning. Then use clean running water not higher than 40℃ to gently wash to remove the residue of the salt spray solution on the surface of the sample, and make an appearance inspection and rating after drying. According to the JB/Z 88-66 evaluation standard for tropical electrical products in my country, the corrosion degree after the salt spray test is 4 grades: 1 grade is good, 2 grades are qualified, and 3~4 grades are unqualified. In each level, as long as one item is satisfied, it will be assessed according to that level.