Why do salt spray experiments after screw plating?

Editor:Jiaxing UNITEK Machinery Technology Co., Ltd. │ Release Time:2021-11-11 

Salt spray test and connection with reality:

Salt spray test is an environmental test that mainly uses artificially simulated salt spray environmental conditions created by salt spray test equipment to assess the corrosion resistance of products or metal materials. It is divided into two categories, one is the natural environment exposure test, and the other is the artificial accelerated simulated salt spray environment 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, artificial methods are used to create a salt spray environment to assess the quality of the salt spray corrosion resistance of the product . Compared with the natural environment, the salt concentration of chloride in the salt spray environment can be several or tens of times the salt spray content of the general natural environment, which greatly increases the corrosion rate. The salt spray test of the product is carried out and the result is obtained The time is also greatly shortened. For example, if a product sample is tested in a natural exposure environment, it may take 1 year for its corrosion, while the test under artificial salt spray environment conditions requires only 24 hours to obtain similar results.

Classification of artificial simulated salt spray test

  The artificial simulated salt spray test includes neutral salt spray test, acetic acid salt spray test, copper salt accelerated acetic acid salt spray test, and alternating salt spray test.

(1) Neutral salt spray test (NSS test)

   is the earliest accelerated corrosion test method with the widest application field. It uses 5% sodium chloride salt aqueous solution, the pH value of the solution is adjusted in the neutral range (6-7) as the spray solution. 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)

   was developed on the basis of the neutral salt spray test. It is to add some glacial acetic acid to 5% sodium chloride solution to make the pH value of the solution drop to about 3, the solution becomes acidic, and the salt mist formed finally turns from neutral salt mist 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℃. A small amount of copper salt—copper chloride is added to the salt solution to strongly induce corrosion. Its corrosion rate is approximately 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 a constant damp heat test. It is mainly used for cavity-type complete products. Through the penetration of the wet environment, the salt spray corrosion is not only generated on the surface of the product, but also inside the product. It is to alternately switch the product under two environmental conditions of salt spray and damp heat, and finally check whether the electrical and mechanical properties of the whole product have changed.

The purpose of the salt spray test:

The purpose of the salt spray test is to assess the salt spray corrosion resistance of the product or metal material. The result of the salt spray test is the judgment of the product quality. Whether the judgment result is correct and reasonable is to correctly measure the salt spray resistance of the product or metal. The key to corrosion quality. The methods for judging the results of the salt spray test include: rating judging method, weighing judging method, corrosive appearance judging method, and corrosion data statistical analysis method. The grading judgment method divides the percentage of the corrosion area to the total area into several levels according to a certain method, and a certain level is used as the basis for qualified judgment, which is suitable for evaluation of flat samples; the weighing judgment method is through the corrosion test before and after The method of weighing the weight of the sample to calculate the weight of the corrosion loss to evaluate the corrosion resistance quality of the sample. It is especially suitable for assessing the corrosion resistance quality of a certain metal; the corrosion appearance judgment method is a qualitative judgment It uses the salt spray corrosion test to determine whether the product has corrosion phenomena. This method is mostly used in general product standards; the statistical analysis method of corrosion data provides the confidence of designing the corrosion test, analyzing the corrosion data, and determining the corrosion data. It is mainly used to analyze and count the corrosion situation, rather than to determine the quality of a specific product.

Therefore, based on the above, the corrosion resistance of screws is generally tested by salt spray test.