The salt spray test is an environmental test that uses artificial simulated salt spray environmental conditions created by salt spray test equipment to evaluate the corrosion resistance of products or metal materials. It is divided into two categories, one is the natural environmental exposure test, and the other is the artificial accelerated simulated salt spray environment test. The artificial simulated salt spray environment test uses a test equipment with a certain volume space--the salt spray test chamber, and uses artificial methods in its volume space to cause the salt spray environment to evaluate the salt spray corrosion resistance quality of the product.
Compared with the natural environment, the salt concentration of the chloride in the salt spray environment can be several times or several times higher than the salt spray content of the general natural environment, so that the corrosion rate is greatly improved, and the product is subjected to a salt spray test to obtain a result. The time is also greatly shortened. If a product sample is tested in a natural exposure environment, it may take 1 year to corrode, and in a simulated simulated salt spray environment, as long as 24 hours, similar results can be obtained.
The artificial simulated salt spray test includes a neutral salt spray test, an acetate spray test, a copper salt accelerated acetate spray test, and an alternating salt spray test.
Neutral salt spray test
It is the most widely used accelerated corrosion test method in the earliest applications. In general, it uses a 5% aqueous solution of sodium chloride solution, and the pH of the solution is adjusted to a neutral range (6.5 to 7.2) as a solution for spraying. The test temperature is 35 °C, and the sedimentation rate of salt spray is required to be between 1~3ml/80cm2.h, and the settlement is generally between 1~2ml/80cm2.h.
Acetate spray test
It was developed on the basis of the neutral salt spray test. It is to add some glacial acetic acid to the 5% sodium chloride solution, the pH value of the solution is reduced to about 3, the solution becomes acidic, and the salt spray finally formed is also changed from neutral salt spray to acid. Its corrosion rate is about 3 times faster than the NSS test.
Copper salt accelerates acetate spray test
It is a rapid salt spray corrosion test developed recently in foreign countries. The test temperature is 50 °C, and a small amount of copper salt-copper chloride is added to the salt solution to strongly induce corrosion. Its corrosion rate is about 8 times that of the NSS test.
Alternating salt spray test
It is a comprehensive salt spray test, which is actually a neutral salt spray test plus a constant damp heat test. It is mainly used for cavity-type machine products. Through the penetration of the tidal environment, salt spray corrosion is generated not only on the surface of the product but also inside the product. It converts the product alternately under the two conditions of salt spray and hot and humid, and finally checks whether the electrical and mechanical properties of the whole product are changed.