The salt spray test is a kind of environmental test which mainly uses the artificial salt mist environment conditions created by the salt spray test equipment to assess the corrosion resistance of the products or metal materials. It can be divided into two categories, one is natural environment exposure test, the other is artificial accelerated simulated salt spray environment test. The artificial simulated salt fog environment test is to use a test equipment with a certain volume space, salt fog test box, and use artificial method in its volume space to cause salt fog environment to evaluate the quality of salt spray corrosion resistance of the product. Compared with the natural environment, the salt concentration of the chloride in the salt fog environment can be a few times or dozens times of the salt mist content in the natural environment. The corrosion rate is greatly improved, the salt spray test of the product is carried out, and the time of the result is greatly shortened. If a sample of a product is tested in a natural exposure environment, it may take 1 years to corrode, and a similar result can be obtained for only 24 hours in the artificial simulated salt fog environment.
Corrosion of salt fog
Corrosion is the damage or deterioration caused by the material or its properties under the action of the environment. Most of the corrosion occurs in the atmospheric environment, the atmosphere contains oxygen, humidity, temperature changes and pollutants such as corrosion components and corrosion factors. Salt spray corrosion is a common and destructive atmospheric corrosion. The salt fog here refers to the atmosphere of the chloride, its main corrosion component is the chloride salt of the ocean - sodium chloride, which is mainly derived from the ocean and the saline alkali areas of the mainland. The corrosion of the salt mist on the surface of the metal material is caused by the electrochemical reaction of the oxidizing layer containing the chloride ions through the metal surface and the inner metal. At the same time, the chloride ion contains a certain amount of hydration energy, which is easily adsorbed in the pores and cracks on the surface of the metal and displaces the oxygen in the chlorination layer, and turns the insoluble oxide into the soluble chloride to turn the passivated surface into a lively surface. Cause a bad reaction to the product.
Artificial simulated salt spray test includes neutral salt spray test, acetate spray test, copper salt accelerated acetate spray test, alternating salt spray test.
(1) Neutral salt spray test (NSS test) is the earliest and most widely used accelerated corrosion test method. It uses 5% sodium chloride saline solution, the solution pH value is adjusted in the neutral range (6 ~ 7) as the spray solution. The test temperature is 35 C and the settling rate of salt spray is between 1 and 2 ml/80 cm_ H.
(2) Acetate spray test (ASS test) is developed on the basis of neutral salt spray test. It adds a number of glacial acetic acid to 5% Sodium Chloride Solution, reducing the pH of the solution to about 3, the solution acidity, and the salt fog formed from the neutral salt fog to the acid at the end. Its corrosion rate is about 3 times faster than the NSS test.
(3) the copper salt accelerated acetate fog test (CASS test) is a rapid salt spray corrosion test developed recently in foreign countries. The test temperature is 50, and a small amount of copper salt - cupric chloride is added in the salt solution, which induces corrosion strongly. The corrosion rate is about 8 times that of the NSS test.
(4) Alternating salt spray test 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 cavity type of whole machine products, through the infiltration of humid environment, salt spray corrosion not only occurs on the surface of the product, but also occurs inside the product. It is the product in salt spray and humid and hot two environmental conditions alternate conversion, the final test of the electrical and mechanical properties of the whole product has changed.
Standard of salt spray test and determination of test results
Standards are uniform provisions for repetitions and summaries. The standard of salt spray test is a specific specification for the test conditions of salt fog, such as temperature, humidity, Sodium Chloride Solution concentration and pH value. In addition, the technical requirements for the performance of the salt spray test box are also put forward. The salt spray test standard for the same product should be selected according to the characteristics of salt spray test, the corrosion rate of metal and the sensitivity to salt spray. The following standards for salt spray test are introduced, such as GB/T2423.17 - 1993 "basic environmental test specification test for electrical and electronic products Ka: salt fog test method", GB/T2423.18 - 2000 "second parts of environmental test for electrical and electronic products: test test Kb: salt fog, alternating (Sodium Chloride Solution)", GB5938 - 86 "light industrial product metal" Test Method for Corrosion Resistance of Coatings and Chemical Treated Layers, GB/T1771-91 "Determination of Neutral Salt Spray Resistance of Paints and Varnishes".
The purpose of the salt spray test is to assess the quality of the salt spray corrosion of the products or metal materials, and the results of the salt spray test are judged to be the judgment of the quality of the products. Whether the result is correct and reasonable is the key to the correct measurement of the corrosion quality of the salt spray of the product or metal. The judging methods of salt spray test results are: rating judgment method, weighing judgment method, corrosion occurrence judgment method, corrosion data statistical analysis method. The rating method is to divide the percentage of the ratio of the ratio of the area to the total area into several levels according to a certain method, which is based on a certain level as the criterion of qualification. It is suitable for the evaluation of the flat sample, and the weighing method is to calculate the loss of corrosion by weighing the weight of the samples before and after the corrosion test. Weight is used to judge the quality of corrosion resistance of the sample. It is especially suitable for evaluating the corrosion quality of certain metals. The determination of corrosion products is a qualitative determination method. After the corrosion test of salt fog, the product is corroded to determine the sample, most of the product standards are collected. |
