Understanding the type of salt spray test - Database & Sql Blog Articles

Corrosion of a salt spray

Corrosion is the destruction or deterioration of a material or its properties caused by the environment. Most of the corrosion occurs in the atmosphere, which contains corrosive components and corrosive factors such as oxygen, humidity, temperature changes, and pollutants. Salt spray corrosion is a common and most destructive atmospheric corrosion. The salt spray mentioned here refers to the atmosphere of chloride. Its main corrosive component is the chloride salt in the ocean, sodium chloride, which is mainly derived from the ocean and the saline-alkali areas in the interior. The corrosion of the surface of the metal material by the salt spray is caused by the electrochemical reaction between the oxide layer containing the chloride ions penetrating the metal surface and the protective layer and the internal metal. At the same time, chloride ions contain a certain hydration energy, which is easily adsorbed on the pores of the metal surface, and the cracks are displaced and replace the oxygen in the chlorinated layer, turning the insoluble oxide into a soluble chloride, making the passivated surface active. surface. Causes a bad reaction to the product.

Second, the salt spray test and the actual connection salt spray test is an environmental test that mainly uses the artificial simulated salt spray environmental conditions created by the salt spray test equipment to assess 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, to artificially use the salt spray environment in the volume space to assess 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.
(1) Neutral salt spray test (NSS test) is one of the earliest applications in the field of accelerated corrosion test. It uses a 5% aqueous solution of sodium chloride solution, and the pH of the solution is adjusted to a neutral range (6-7) as a solution for spraying. The test temperature is taken at 35 ° C, and the sedimentation rate of the salt spray is required to be between 1 and 2 ml / 80 cm 2 · h.
(2) The acetate spray test (ASS test) was developed on the basis of a 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.
(3) Copper salt accelerated acetate spray test (CASS test) is a rapid salt spray corrosion test developed recently in foreign countries. The test temperature is 50 ° C. 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.
(4) The alternating salt spray test 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.

III. Salt Spray Test Standards and Judgment of Test Results The <br> standard is a uniform regulation of repetitive things and overviews. The salt spray test standard specifies the salt spray test conditions, such as temperature, humidity, sodium chloride solution concentration and pH value, and also sets technical requirements for the performance of the salt spray test chamber. The salt spray test standard for the same product is selected according to the characteristics of the salt spray test, the corrosion rate of the metal, and the sensitivity to salt spray. The following describes several salt spray test standards, such as GB/T2423.17-1993 "Basic environmental test procedures for electrical and electronic products test Ka: salt spray test method", GB/T2423.18-2000 "Electrical and electronic products environmental test part 2 : Test test Kb: salt spray, alternating (sodium chloride solution), GB5938-86 "corrosion resistance test method for metal plating and chemical treatment layer of light industrial products", GB/T1771-91 "color paint and varnish resistant Determination of salt spray performance.
The purpose of the salt spray test is to assess the salt spray corrosion quality of products or metal materials. The salt spray test results are judged on the quality of the product. The judgment result is correct and reasonable. It is a correct measure of the product or metal salt spray resistance. The key to corrosion quality. The methods for determining the salt spray test results include: rating determination method, weighing determination method, corrosion occurrence determination method, and corrosion data statistical analysis method. The rating judgment method divides the percentage of the ratio of the corrosion area to the total area into several levels according to a certain method, and uses one level as the basis for the qualification judgment. It is suitable for the evaluation of the flat sample; the weighing determination method is adopted before and after the corrosion test. The weight of the sample is weighed, and the weight of the corrosion loss is calculated to judge the corrosion resistance quality of the sample. It is especially suitable for assessing the corrosion resistance of a certain metal; the determination method of corrosion occurrence is a qualitative judgment. The method determines the sample after the salt spray corrosion test, and the sample is judged by the corrosion phenomenon. Most of the general product standards use this method; the statistical analysis method of the corrosion data provides a confidence in designing the corrosion test, analyzing the corrosion data, and determining the corrosion data. Degree method, which is mainly used to analyze and count corrosion conditions, rather than specifically used for quality judgment of a specific product.

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