Why do corrosion-resistant coatings need to be sealed and what sealing agent to use

       Thermal spray coatings always have a certain porosity. The shape, size and distribution of pores vary with the thermal spray process and spray materials. The distribution can vary from less than 1% to more than 15%. These pores may They are interconnected and have porosity from the coating surface to the substrate. However, when the thickness of the coating meets certain requirements, the pores will not penetrate the entire coating and erode the substrate. In order to prevent or prevent corrosion at the coating/substrate interface and prolong the service life of the coating, the corrosion-resistant coating is often sealed to fill such pores.



As the material for the sealing treatment of the corrosion-resistant coating, it should have the following characteristics:



1) Sufficient permeability.



2) Resistant to chemical or solvent action.



3) Certain mechanical properties.



4) Certain temperature resistance.



5) Does not affect the performance of the coating or substrate.



6) Safe to use.



In actual operation, after thermal spraying, the coating should be pre-treated with etching paint (usually phosphoric acid) before sealing to form a layer of composite phosphate film on the surface, which is helpful for the bonding of the sealing agent. .



The test results show that the anti-corrosion performance of aluminum and zinc coatings can be improved by using low-viscosity sealing agent to seal the steel substrate. These sealants include: vinyl, silicone, phenolic, modified epoxy novolac, and polyurethane.



Different sealing agents should be selected for different ambient operating temperatures. Among them, the maximum use temperature of vinyl resin is 65 ℃. The use temperature of phenolic resin is 150 ~ 260℃. The use temperature of the silicone resin sealant with aluminum as the pigment can reach 480℃, and it is mainly used for the sealing treatment of exhaust pipes, mufflers and other parts; the use temperature of the coal tar sealant containing aluminum can be as high as 870~980℃ ℃, mainly used for sealing of aluminum and nickel-chromium coatings working at this temperature.



When paraffin wax is used as a sealing agent, it is not only resistant to seawater, fresh water and most acids and alkalis, but also is often used for sealing and lubricating surface coatings of mechanical parts in food and chemical industries to solve the existing pollution problems.