A brief talk about salt spray testers ①

Salt Spray Tester

Salt, arguably the most widely distributed compound on the planet, is ubiquitous in the ocean, atmosphere, land, lakes and rivers. Once salt particles are incorporated into tiny liquid droplets, a salt spray environment is formed. In such environments, it is almost impossible to attempt to protect items from the effects of salt spray. In fact, salt spray is second only to temperature, vibration, heat and humidity, and dusty environments in terms of damage to machinery and electronic products (or components).

Salt spray testing is a key part of the product development phase to assess its corrosion resistance. Such tests are mainly divided into two categories: one is the natural environment exposure test, which is time-consuming and labour-intensive, and is therefore less commonly used in practical applications; the other is the artificially accelerated simulated salt spray environment test, where the chloride concentration can reach several times or even tens of times of the salt spray content of the natural environment, and corrosion rate is therefore greatly increased, thus shortening the time to arrive at the test results. For example, a product sample that would take a year to corrode in a natural environment can be tested in an artificially simulated salt spray environment with similar results in as little as 24 hours.

1) Salt spray test principle

A salt spray test is a test that simulates the conditions of a salt spray environment and is primarily used to assess the corrosion resistance of products and materials. This test utilises salt spray test equipment to create a salt spray environment similar to that found in the seaside atmosphere. In such an environment, sodium chloride in the salt spray decomposes into Na+ ions and Cl- ions under certain conditions. These ions react chemically with the metal material to produce strongly acidic metal salts. The metal ions, when exposed to oxygen, reduce to form more stable metal oxides. This process can lead to corrosion and rusting and blistering of the metal or coating, which in turn can lead to a number of problems.

For mechanical products, these problems can include corrosion damage to components and fasteners, jamming or malfunctioning of moving parts of mechanical components due to obstruction, and open or short circuits in microscopic wires and printed wiring boards, which can even lead to component leg breakage. As for electronics, the conductive properties of salt solutions can cause the resistance of insulator surfaces and volume resistance to be greatly reduced. In addition, the resistance between the salt spray corrosive material and the dry crystals of the salt solution will be higher than that of the original metal, which will increase the resistance and voltage drop in the area, affecting the electrocution action, and thus affecting the electrical properties of the product.