Corrosion phenomenon that occurs around us refers to the damage of various materials under the action of the environment (the combination of chemical, electrochemical, and several physical factors), performance degradation, or deterioration of the state. Spray painting on metal surfaces is a very important means of metal corrosion protection. A good spray paint protection layer is continuous, intact and well-integrated and can act as a barrier against the invasion of corrosive media. However, since corrosion is an irreversible spontaneous process, it is difficult to protect the metal from corrosion even if it is a high-quality paint painting and maintenance layer, especially when the metal surface painting coating layer is poorly bonded, damaged, or has pinholes and blisters. , Cracking, falling off and other defects, the protective effect of paint coating will be greatly reduced, and even cause the consequences of metal corrosion. Therefore, it is very necessary to carefully analyze the factors of metal corrosion of spray painting and take effective countermeasures.
Paint coating metal corrosion mechanism
In general, corrosion of metals is the result of a combination of factors, and one of these factors plays an important role in the corrosion process. The metal surface is painted to form a protective coating layer. The area where the metal is corroded is the interface area between the paint film and the metal surface, and continues to erode and expand into the deep metal substrate.
If the metal surface painting coating can effectively separate the infiltration of water, oxygen and electrons, stray ions, etc., it can greatly reduce or avoid the corrosion of the coating metal. If the isolation effect is not good, the coating is kept to the metal. The anti-corrosion and anti-corrosion protection is not good. Production practice shows that the penetration rate of the spray coating protective layer on water seriously affects the adhesion of the metal spray coating surface layer, and the oxygen permeability greatly affects the metal corrosion performance. The corrosion of spray-painted metal is varied, but the root cause and the occurrence of corrosion are closely related to chemical and electrochemical effects.
Analysis of Corrosion Factors and Preventive Measures of Spray Painted Metals
Metal material and other factors
Corrosion of spray-painted metal has a lot to do with the corrosion resistance of the metal material itself. The metal used for painting is iron and steel materials, aluminum alloys, copper alloys, or magnesium alloys. Undoubtedly, metal materials are different, and the corrosion resistance of metal spray painting is not the same. The difference in the surface state of metallic materials, after spray painting, has a markedly different effect on the corrosion protection and corrosion protection of the coating. For example, the sandblasted steel plate parts and the naturally corroded steel plate parts of the same brand are protected by the same type of paint coating. Due to the adverse effects of corrosion, the natural corroded steel plate parts have higher corrosion rates than sandblasted steel plate parts. Times, its anti-corrosion protection effect is significantly lower than the latter. Defects on the metal surface such as inclusions, microcracks, stress, etc., and the adsorption of moisture and active ions (Cl-, Br-, etc.) in the atmosphere will affect or even accelerate the corrosion of the paint-spraying metal to varying degrees.
The application of pre-treatment such as degreaser degreasing, activated rust removal, and surface treatment before spray painting on metal surfaces can effectively improve the anti-corrosion and anti-corrosion properties of spray-painted metal. The production practice proves that the quality of the anticorrosive properties of spray-painted paint and the quality of the pre-treatment of the substrate prior to coating have a great influence. The effective degreasing, derusting or spray application of the metal (especially the casting) before surface painting is performed. Sand shot peening can cause the purification and activation of the surface, ensure the good adhesion of the coating film and the base metal, and it is very beneficial to improve the corrosion resistance of the paint coating metal.
The phosphating treatment of the steel material coating prior to the coating process is widely used as the bottom layer of the paint coating, and it is irrefutable to improve the adhesion of the coating layer and improve the anti-corrosion performance of the coating metal.
Phosphating, chemically oxidizing, anodizing, etc. of aluminum alloys can be used as the bottom layer of the paint coating, and it is undoubtedly excellent to improve and improve the anticorrosion performance of the coating metal.
In short, a good surface treatment process for metal substrates is an important and reliable basis for improving the corrosion resistance of paint-coated metals.
Metal spraying paint construction technology and environmental impact
The degree of cleanliness of the metal surface seriously affects the binding force of the painting and painting layer, and the remaining or adsorbed water, oil and other foreign materials on the surface of the workpiece are not completely eliminated, and pinholes, nodules, peeling or poor bonding are often caused.
After the phosphating of steel parts, after the chemical oxidation or anodization of aluminum alloy parts, the chemical oxidation treatment of magnesium alloy parts, etc. shall be carried out in no more than 24 hours in time, and the steel parts shall be subjected to sandblasting and shot peening. It must also be painted within six hours. This process measure is a good way to help improve the adhesion of the coating film to the substrate and enhance its corrosion resistance.
The separation of oil and water in the compressed air used for spraying is not complete enough, so that the compressed air contains excessive amounts of water and oil, which will inevitably affect the quality of the paint coating film layer, resulting in various fault defects. Therefore, adhering to the regular cleaning of the filter material in the replacement oil and water separation facilities to keep the compressed air clean is beneficial to improving the performance of the paint spray coating.
The temperature and humidity of the spray painting site have a significant influence on the quality of the paint coating film. Care should be taken to maintain the temperature of the painting construction site in the range of 10 to 30°C, and the relative humidity is not to exceed 80%. The construction site must be kept clean and tidy and orderly.
The temperature is too high, the relative humidity is large, the paint layer of the paint is easy to whiten, and the orange peel is present. However, if the temperature is too low, the paint layer is easy to flow, adversely affecting the quality of the surface coating of the metal coating.
Spray painting operations on metal surfaces are usually air sprayed. Pay attention to keep the distance between the spray gun and the sprayed surface in the range of 200-300mm, and the compressed air pressure is controlled at 2～4kg/cm2, so as to be able to effectively protect the paint coating quality.
Effect of paint performance
The performance of the coating has a great influence on the anti-corrosion performance of the coating metal. The high-quality coating can effectively protect the metal even in harsh conditions. Different types of paint have different properties. The factors affecting the performance of the protective coating are mainly determined by the synthetic resin, filler, etc., and the degree of crystallinity and solubility of the coating film.
Depending on the properties of the coating, the applicable environment, and other factors that may cause loss of the selected coating, the anti-corrosion protection of the coating layer can be more effectively demonstrated.
The choice of lacquer base, solvent and auxiliary agent should be appropriate. The mixing ratio must be strictly in accordance with the process requirements, and it must be ensured that the stirring is sufficiently uniform to ensure that it is diluted to the specified working viscosity.
The extensive application of rust-preventive rust-preventing coatings developed and developed in recent years has made it possible to further improve the range of application and corrosion protection of spray-painted metal, and it is necessary to promote and improve it.
Conclusion
All in all, strengthen the specification of pretreatment and surface treatment process of metal spray painting, strengthen the control and management of painting process, ensure that the paint coating protective layer and the base metal have a good bonding force, overcome and avoid pinholes in the coating protection layer Bubbling, wrinkling, cracking, detachment and other fault defects make the painting and protective layer an excellent barrier against the intrusion of corrosive media. It is undoubtedly an effective measure to improve the anti-corrosion and anti-corrosion performance of spray-painted metal.
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