Whether it is the protection of steel structures in the construction industry or the corrosion protection of metal components in the automotive industry, coatings play a vital role. As a special equipment for testing corrosion resistance of coating, salt spray chamber has irreplaceable value for predicting the service life of coating.
The salt spray chamber is mainly composed of chamber, spray system, heating system and control system. Its working principle is to heat the brine atomization, so that it forms a high concentration of salt spray environment in the chamber, so as to simulate the Marine climate or other harsh salt environment. In this enclosed space, the salt spray spreads evenly to all corners and can fully contact the coating sample placed in it.
When the coating sample is placed in the salt spray chamber, the salt spray will rapidly adhere to the coating surface. At first, the coating by its own protective properties will play a protective role in isolating the internal metal substrate, but over time, chloride ion salt spray and other corrosive components will gradually penetrate the coating. This process is a slow and continuous erosion process in which tiny water droplets in the salt spray condense on the surface of the coating, and the chloride ions in it begin to react chemically with certain components of the coating, for example, potentially breaking the chemical bonds in the coating, making the coating gradually lose its integrity and density, and creating conditions for the chloride ions to penetrate further into the substrate surface.
In the process of salt spray testing, there are several key indicators that are closely related to the coating life. The first is the time of corrosion points on the coating, which is a very intuitive and important indicator. If the corrosion point of the coating appears in a short time, then obviously its life in the actual use environment will not be too long. For example, some poor quality coatings may begin to show tiny corrosion points after a few days in a cycle corrosion tester, meaning that it may only last a few months or less in an actual outdoor or industrial corrosion environment. Secondly, the rate of change of corrosion area is also a key factor. With the increase of salt spray test time, the corrosion area gradually expands. If the corrosion area expands faster, it indicates that the corrosion resistance of the coating is poor, and its life will be shortened accordingly.
In the salt spray test, the properties of different types of coatings are significantly different. Taking common paint coatings and electroplating coatings as an example, paint coatings mainly rely on organic resins and other components to form a protective film on the metal surface, which has the advantages of relatively low cost, convenient construction, and diverse color choices. However, in the salt spray test, the corrosion resistance of the paint coating is relatively weak. Due to the characteristics of its molecular structure, the paint coating is prone to foaming and peeling under the long-term erosion of salt spray. For example, on the exterior walls of some seaside buildings, after several years of wind and sun and salt spray erosion, the paint will fade and flake in a large area, and the metal substrate will also begin to rust. Electroplating coating is the deposition of a layer of metal or alloy on the surface of a metal by an electrochemical method, such as chromium plating, zinc plating, etc. The binding force between the coating and the metal substrate is strong, and the metal coating itself has good corrosion resistance. In the salt spray chamber, the electroplating coating can withstand longer salt spray erosion, and its corrosion time and corrosion rate are significantly better than that of ordinary paint coating. This is because the coating has a relatively dense crystal structure, which can effectively block the diffusion of invasive ions such as chloride ions in the salt spray to the matrix.
In actual industrial production and application scenarios, there are many cases to illustrate the effectiveness and limitations of salt spray chamber for coating life prediction. For example, in the automotive industry, the coating of the body needs to have good corrosion resistance to cope with various harsh environments that may be encountered in daily driving, including salt on the road, rain and so on. Automobile manufacturers often conduct salt spray tests on coatings produced by different formulations and processes. Some coatings verified by strict salt spray tests can provide effective protection for the car body for many years in actual use, and the car body is not easy to rust corrosion even when driving in high salinity coastal areas.
However, in some cases, the predictions of the salt spray test do not exactly match the actual life. This may be due to the existence of other complex factors in the actual environment, such as the impact of the stone during the driving of the car will destroy the integrity of the coating, so that the local coating is damaged, thus accelerating the corrosion process; Or because the composition of pollutants in the actual environment is more complex, not only salt spray, but also acidic substances in industrial waste gas, etc., these substances and salt spray synergistic effect, aggravate the erosion of the coating, and the salt spray chamber often can only simulate a single salt spray environment, can not fully reproduce all factors in the actual environment.
Salt spray chamber plays a very important role in the prediction of coating life, it can simulate the salt spray environment, quickly detect the corrosion resistance of the coating, and provide a scientific basis for the research and development of the coating, production quality control and product selection. However, we must also be aware of its limitations, the actual environment is far more complex than the simulated environment in the salt spray chamber. Therefore, when using salt spray chamber to predict coating life, it is necessary to comprehensively consider various factors, and constantly explore more perfect test methods and technologies to improve the accuracy of prediction, so as to provide a more reliable guarantee for the development and wide application of coating technology.
