Sealing Treatment of Arc Spray Anticorrosion Coatings

       Arc spray coatings often have 2% to 15% porosity, which can be interconnected and can extend from the surface to the substrate. Sealing is a common post-processing method whose purpose is to fill the pores inherent in the coating. The purpose of sealing the arc spray coating is to prevent or prevent the corrosion at the interface between the coating and the substrate caused by the penetration of the liquid medium, prolong the service life of the zinc-sprayed aluminum coating on steel components, and prevent some mechanical parts in contact with high-pressure liquid media. .



Pores in coatings are detrimental in industrial atmosphere marine environments, chemically active substances, corrosive gases and high temperature environments. Since the corrosive medium may penetrate into the steel matrix through these pores, chemical or electrochemical erosion of the coating and the matrix may occur, resulting in the failure of the coating. In this case, the coating must be sealed.



Sealed thermal spray coatings deplete at a slower rate in corrosive environments and generally provide longer-lasting protection, even after the surface sealer fails, the underlying metal coating is more depleted than unsealed metal coatings slow. The inherent porosity and rough surface of thermal spray coatings allow sealers and coatings to bond firmly to their surfaces.



There are many types of sealing agents. In order to achieve a good sealing effect, the sealing agent must meet the following requirements:



It has sufficient permeability and high bonding strength with the coating; it has stable performance at working temperature, is resistant to the action of chemical solvents, cannot chemically or electrochemically react with the coating or substrate, and can interact with the coating under the working environment. and matrix to maintain chemical stability.



2. Construction points of sealer



Generally, sealants used in anti-corrosion coatings must be fully cured before being put into service. General sealants are not dangerous, but some sealants are volatile and flammable, so extra care should be taken during storage and use. Adequate ventilation so as not to affect the normal breathing of the builder.



Sealing agents are generally divided into two types: organic and inorganic. Organic sealing agents are mostly composed of resins, solvents and pigments in appropriate proportions. Usually the concentration of the sealer is low, and if pigment is added, the particle size of the pigment must be small enough to penetrate into the pores of the thermal spray coating. Suitable for thermal spray zinc or thermal spray aluminum. The sealant used in the coating is low-viscosity vinyl resin, nitro paint, acetic acid copolymer, phenol resin, modified alkyd resin phenolic resin, modified epoxy resin, etc. Sealers for metal coatings are fundamentally different from topcoat coatings. Coatings are used for coatings as a protective layer, while sealants are used to penetrate the pores of the coating with low viscosity substances and seal them without increasing the overall thickness of the protective layer. The main basis for the selection of sealant is the corrosion of the medium and the working temperature.



The organic sealing agent is mainly used for the sealing of zinc coating or aluminum coating. The working temperature is not high, and it is in the environment of atmospheric oxidation, industrial atmosphere, seawater, etc.; Some inorganic substances such as silicate chromate, the maximum working temperature can reach 980 ℃. Different sealants have different requirements, generally follow the following points.



(1) Sealing treatment should be applied to the metal coating as soon as possible after spraying to avoid surface contamination of the coating. The surface of the thermal spray coating to be painted and sealed should be free of dirt. It is best to use dry and clean compressed air to remove the dust on the surface of the coating before applying the sealer. It is best to pre-treat with an etch coating (usually phosphoric acid) to form a complex phosphate compound film that aids in the adhesion of the sealer.



(2) Most sealants require diluent dilution to reduce viscosity to ensure good permeability. For some applications in high temperature environments, flake aluminum powder can be added to the sealer to improve the temperature resistance and corrosion resistance of the sealer.



(3) The sealer is usually smeared with a brush. According to the needs, the sealer can be brushed once or several times. The most important thing is to ensure that the sealant can fully penetrate into the pores of the coating.