The difference between artificial simulated environment corrosion test and reality

The purpose of the salt spray test is to assess the salt spray corrosion resistance quality of the product or metal material, and the judgment of the salt spray test result is the judgment of the product quality. Whether the judgment result is correct and reasonable is to correctly measure the product or metal resistance to salt spray. The key to corrosion quality.

How many hours does the salt spray test of electroplated parts (such as zinc, nickel, chrome, etc.) reach, and their service life can reach 15 years? If the service life is required to reach 20 years or 25 years, how much is the salt spray test qualified? What is the saturator temperature and test temperature for the salt spray test?

1. Corrosion of salt spray：

Corrosion is the destruction or deterioration of a material or its properties under the action of the environment. Most corrosion occurs in the atmospheric environment, which contains corrosive components and factors such as oxygen, humidity, temperature changes and pollutants. Salt spray corrosion is a common and most destructive atmospheric corrosion. The salt fog mentioned here refers to the atmosphere of chloride, and its main corrosion component is the chloride salt in the ocean - sodium chloride, which mainly comes from the ocean and inland saline-alkali areas. The corrosion of salt spray on the surface of metal materials is caused by the electrochemical reaction of the chloride ions contained in the metal surface through the oxide layer and protective layer of the metal surface and the internal metal. At the same time, chloride ions contain a certain amount of hydration energy, and are easily absorbed by pores and cracks on the metal surface to displace and replace oxygen in the chlorinated layer, turning insoluble oxides into soluble chlorides, and making the passivated surface active. surface. Cause very bad adverse reactions to the product.

2. Salt spray test and its connection with practice

Salt spray test is an environmental test that mainly 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 natural environmental exposure test, and the other is artificial accelerated simulated salt spray environmental test. The artificial simulated salt spray environment test is to use a kind of test equipment with a certain volume space - the salt spray test box, in its volume space, use artificial methods to create a salt spray environment to assess the product's salt spray corrosion resistance performance and quality . Compared with the natural environment, the salt concentration of chloride in the salt spray environment can be several times or tens of times that of the general natural environment salt spray, which greatly increases the corrosion rate. The salt spray test is carried out on the product to obtain the result. time is also greatly shortened. For example, if a product sample is tested in a natural exposure environment, it may take 1 year to wait for it to corrode, while in the artificial simulated salt spray environment, it only takes 24 hours to obtain similar results.

The artificial simulated salt spray test also includes the neutral salt spray test, the acetate salt spray test, the copper salt accelerated acetate salt spray test, and the 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 salt solution, and the pH value of the solution is adjusted in the neutral range (6-7) as the solution for spraying. The test temperature is 35℃, and the sedimentation rate of the salt spray is required to be between 1～2ml/80cm².h.

(2) Acetic acid salt spray test (ASS test) is developed on the basis of neutral salt spray test. It is to add some glacial acetic acid to the 5% sodium chloride solution, so that the pH value of the solution is reduced to about 3, the solution becomes acidic, and the finally formed salt spray also changes from neutral salt spray to acid. Its corrosion rate is about 3 times faster than the NSS test.

 

(3) Copper salt accelerated acetic acid salt spray test (CASS test) is a kind of rapid salt spray corrosion test recently developed abroad. The test temperature is 50 °C. A small amount of copper salt - copper chloride is added to the salt solution, which strongly induces corrosion. . It corrodes about 8 times faster than 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 complete machine products. Through the penetration of the tidal environment, salt spray corrosion occurs not only on the surface of the product, but also inside the product. It is to alternately convert the product under two environmental conditions of salt spray and damp heat, and finally check whether the electrical properties and mechanical properties of the whole product have changed.

3. Salt spray test standards and determination of test results

A standard is a uniform specification of repetitive things and overviews. The salt spray test standard is a clear and specific regulation for the salt spray test conditions, such as temperature, humidity, sodium chloride solution concentration and pH value, etc., and also puts forward technical requirements for the performance of the salt spray test chamber. The salt spray test standard used for the same product should be selected according to the characteristics of the salt spray test, the corrosion rate of the metal and the sensitivity to salt spray. Several salt spray test standards are introduced below, 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 "Test Method for Corrosion Resistance of Metal Coatings and Chemically Treated Layers of Light Industrial Products", GB/T1771-91 "Middle Resistance of Paints and Varnishes" Determination of salt spray performance.

 

The judgment methods of the salt spray test results include: rating judgment method, weighing judgment method, corrosive substance appearance judgment method, and corrosion data statistical analysis method. The rating judgment method is to divide the percentage of the ratio of the corrosion area to the total area into several grades according to a certain method, and a certain grade is used as the basis for qualified judgment, which is suitable for the evaluation of flat samples; 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 quality of a certain metal; the judgment method for the appearance of corrosion is a qualitative judgment. It judges the sample by whether the product has corrosion phenomenon after the salt spray corrosion test. This method is mostly used in general product standards; the statistical analysis method of corrosion data provides the confidence of designing corrosion test, analyzing corrosion data and determining corrosion data. It is mainly used to analyze and count the corrosion situation, rather than to determine the quality of a specific product.

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2022-04-29 12:20