According to the description of salt fog testing mechanism, salt fog testing can be divided into two categories: natural environmental exposure test and artificial accelerated simulated salt fog environmental test.
Compared with natural environment, chloride concentration in artificial salt fog environment can be several times or tens of times of salt fog content in general natural environment, corrosion rate is greatly increased, and the time of salt fog test for products is greatly shortened. If a product sample is tested under natural exposure environment, the corrosion may take one year, while under artificial simulated salt spray environment, the similar results can be obtained in 24 hours.
Artificial simulated salt spray test includes neutral salt spray test, acetate spray test, copper salt accelerated acetate spray test and alternating salt spray test.
1. Neutral salt spray test
Under normal circumstances, it uses 5% NaCl solution and the pH value is adjusted to neutral range (6.5 to 7.2) as a spray solution. The test temperature is 35 (?) C. The settling rate of salt spray is required to be between 1 and 3 ml/80 cm 2.h, and the settling amount is generally between 1 and 2 ml/80 cm 2.h.
2. Acetate spray test
It pours some glacial acetic acid into 5% sodium chloride solution, reduces the PH value of the solution to about 3, turns the solution into acidity, and finally forms the salt mist from neutral salt mist to acidity. Its corrosion rate is about three times faster than that of NSS test.
3. Accelerated Acetate Spray Test with Copper Salt
It is a rapid salt spray corrosion test. The test temperature is 50 C. A small amount of copper salt - copper chloride is added into the salt solution to strongly induce corrosion. Its corrosion rate is about eight times that of NSS test.
4. Alternating salt spray test
It is a comprehensive salt spray test, which is actually a neutral salt spray test plus constant humidity and heat test. It is mainly used for hollow machine products, through the infiltration of tidal environment, salt spray corrosion not only occurs on the surface of the product, but also in the interior of the product. It alternates the product under the conditions of salt spray and humidity and heat, and finally checks whether the electrical and mechanical properties of the whole product have changed.