What Is a Salt Spray Tester?
A salt spray tester is an experimental device used to perform salt spray tests on metal materials, parts, and products that have been plated, painted, or otherwise coated.
Using the salt spray tester creates an atmospheric environment of a specific temperature and humidity, including salt in the space inside the tester, defined by industrial standards such as ISO. The process of corrosion is checked by placing a test specimen in this test environment.
Uses of Salt Spray Testers
The salt spray tester is a specialized testing device for salt spray testing. The main test objects for the salt spray test are metallic materials, plated or painted coatings, and products coated with these coatings.
Industrial standards require evaluation using test specimens of a specified size, but in product development and quality control, actual products are used for testing. Specific uses of salt spray testers are as follows:
1. Automotive Field
Salt spray testers are used in the automotive field to evaluate the corrosion resistance of plated and surface-treated parts. Specifically, it assesses the corrosion resistance of screw parts, various bracket parts, and transmission oil pans.
Especially in regions with heavy snowfall, the snow-melting salt sprinkled on roads to melt snow can cause significant corrosion on automobile exteriors and suspension parts. Salt spray tests evaluate corrosion resistance to such external environments.
2. Construction
The architectural field evaluates corrosion resistance to natural environments such as wind and rain. For example, in coastal areas with strong sea breezes, metal houses’ parts will rust relatively quickly.
It is not uncommon to see rust on tin sheets used for roofs and walls of old houses and on storage sheds for general household use. The salt spray test checks how long it takes for such rust to form.
Principles of Salt Spray Testers
In the salt fog & spray tester, the test object is placed in the instrument’s chamber, and an acidic solution that promotes corrosion is misted into the chamber and continuously sprayed on the sample. The acidic solutions include sodium chloride, calcium chloride, and magnesium chloride. The solution is spread evenly over the test sample by misting the acidic solution, and corrosion can be promoted without local bias.
Salt spray testers maintain and control the atmospheric environment to meet the specified conditions.
Judgment Methods for Salt Spray Tests
When evaluating salt spray testing on products, it is also essential to clearly define the occurrence of rust. Evaluation is carried out by periodically checking the test products visually or otherwise for the presence or absence of rust. Salt spray test equipment is a device that creates a test environment and cannot detect or determine the occurrence of rust.
In industrial standards, rust is determined as a percentage of the surface area using a test piece of a specified size to determine that rust has occurred. Therefore, when conducting tests on actual products, it is essential to agree in advance with the companies concerned on “which condition is judged as rusting” and “the area where rust is generated and the percentage of surface area.”
Furthermore, in the case of plating that prevents rusting of the base metal by self-sacrifice, such as galvanizing, red rust, which indicates that the base metal has rusted, usually occurs after white rust, which is self-sacrifice. For this reason, salt spray tests are also evaluated based on the time taken for both white and red rust to occur. For example, white rust must not appear within 72 hours, red rust within 240 hours, etc. Two evaluation criteria are used in operation.
Other Information on Salt Spray Tests
Equivalent Time for Salt Spray Test
The salt spray test verifies the quality of plating, coating, and industrial products to prevent rust from occurring in the daily environment where they are used as products. It is one of the accelerated tests to evaluate corrosion resistance in terms of time, which is required in years. However, various industrial standards do not specify the correlation between natural and test environments.
Each product manufacturer has its standard for the correlation between the test time of the salt spray test and the amount of elapsed time in the natural environment. Test methods and conditions follow various industrial standards, and each company or industry defines the evaluation time under the specified conditions.