When you buy fasteners (bolts, nuts, screws, etc.), you want to make sure they are high quality and will last for a long time. You depend on the durability and elasticity of the fastener. No matter what harsh environment they're in or what elements they come in contact with, they're expected to withstand it. Rusted fasteners can be dangerous and expensive to replace. To give you the durability your fasteners need, manufacturers rely on the results of salt spray testing.
in short
Salt spray testing is a method of checking the corrosion resistance of coatings and materials used to manufacture products such as fasteners. Surface coatings are used to provide a level of protection to the metal beneath them. During salt spray testing, an accelerated corrosion attack is created to better predict how well the coating will protect the metal. The purpose of the test is to assess the life expectancy of the surface coating.
utility
Salt spray testing is often used to make quick comparisons between expected and actual corrosion resistance. In fact, there is only a small correlation between how long a coating lasts in the test and its actual life expectancy. This is due to the fact that many external factors can affect corrosion - it is not a simple process. This is especially true for materials such as hot-dip galvanized steel, where drying cycles are an important factor in durability considerations.
Salt spray testing is therefore effective in determining the pass or fail grade of a sample and comparing it to expected values, usually in a quality audit or to test the effectiveness of a particular production process.
Salt spray testing is used on phosphate surfaces, zinc and zinc alloy plating, electroplating of tin, copper, nickel and chromium, organic coatings, paint coatings and non-electrolytic coatings.
Why do we use it?
Salt spray testing has long been the standard corrosion testing method because it is fast, repeatable and relatively inexpensive. The first internationally recognized test dates back to 1939. The ASTMB117 test is still the most widely used salt spray test in the world today. Today, ASTM B 117 and ISO 9227 tests are also standardized and used.
how does this work
The salt spray test is carried out in a closed test room. Saline is applied to the sample through a nozzle. This concentrated salt spray is used to simulate a corrosive environment. After a period of time (depending on the corrosion resistance of the product), evaluate the appearance of oxides. The more resistant the product, the longer it will take for oxides to appear. Test times can take anywhere from 8 to 20 hours to complete for materials like phosphate steel, up to 720 hours for zinc-nickel coatings, and even possible for some zinc flake surface coatings It takes 1000 hours or even longer.
Different Types of Salt Spray Tests
The neutral salt spray test (NSS) using a 5% NaCl solution is commonly used for steel-based materials. These solutions have a neutral pH of 6.5 to 7.2. On the other hand, decorative coatings such as anodized aluminum, electroplated copper-nickel and electroplated copper-nickel-chromium are tested with a solution containing acetic acid (ASS) or acetic acid with copper chloride (CASS ) and other chemicals. The pH of these acidified solutions was between 3.1 and 3.3.
The results of a material or coating's corrosion resistance in salt spray testing can help you determine whether a particular fastener is durable enough for your needs.
