Application of inorganic zinc-rich primer

Water-based inorganic zinc-rich primers are widely used due to their non-flammable and non-explosive properties, as well as their toxicity- and odor-free characteristics. They offer excellent electrochemical corrosion resistance, are hard and wear-resistant, and have good weather resistance. In particular, they provide good compatibility, and their overall performance is superior to that of ordinary inorganic zinc-rich coatings. Water-based inorganic zinc-rich primers can be applied to oil tanks, oil holds, solvent tanks, ballast water tanks, as well as marine steel structures exposed to harsh environments and conditions, bridges, chimneys, etc. It can also be used alone as an anti-rust and heat-resistant coating. However, due to its water-soluble nature, its application differs from that of solvent-based coatings, and the treatment of the substrate has a direct impact on the overall performance of the coating film.

The surface of the steel structure must be sandblasted to remove impurities such as oil, oxide scale, and rust; the rust removal level should meet the Sa2.5 standard, and the roughness of the substrate should be between 35–70 μm. The steel surface, after rust removal, should be coated with an undercoat within 4 hours. The inorganic zinc-rich primer is applied using a spraying method, with a film thickness of 80 microns being appropriate; it should not be applied too thickly to prevent cracking of the paint film. During the drying process of the paint film, a certain level of humidity is needed to facilitate the drying reaction; water can be sprinkled on the ground to increase the moisture content in the air. After the inorganic zinc-rich primer dries, an epoxy topcoat needs to be applied; its function is to seal the pores on the surface of the inorganic zinc-rich primer and prevent bubbling. The coating thickness of the epoxy sealant is around 30–50 microns; it offers good adhesion and serves as a transitional layer, providing excellent sealing properties for inorganic zinc-rich primers. An epoxy ferrochrome intermediate coat is applied to thicken the coating layer, thereby enhancing the overall protective and shielding properties of the paint film. The epoxy ferrochrome intermediate coat serves as a link between the primer and the topcoat; its mica-iron oxide structure provides strong shielding effects, preventing the entry of corrosive agents and offering excellent protection against external corrosive factors. Finally, apply the topcoat; options for this include fluorocarbon paint and acrylic polyurethane paint. The topcoat not only needs to have weather resistance, corrosion resistance, and aging resistance, but it should also possess good aesthetic qualities. The topcoat should provide good protection for the underlying coatings and the surface being painted; it is also the outermost layer of the entire coating system. The technical requirements for topcoats are evident, as their protective function is of utmost importance.

(1) Quality control of steel plate surface treatment before painting: Before painting, it is necessary to check and confirm that the rounding of the steel plate’s edges and corners, the treatment of surface defects, the removal of oil stains, and the elimination of salt deposits meet the required standards. (2) Quality control for sandblasting rust removal ① Before carrying out sandblasting rust removal, it is necessary to check the quality and pressure of the high-pressure air, ensuring that it is free of oil and water and that its pressure is at least 0.6 MPa ； ②Confirm that the particle size, shape, hardness, mixing ratio, and cleanliness of the sandblasting abrasive meet the requirements ； ③Before sandblasting for rust removal, the ambient temperature, relative humidity, dew point temperature, and steel plate temperature are measured to ensure that the environmental conditions meet the requirements of the sandblasting process ； ④After sandblasting for rust removal, the quality of the rust removal process is inspected in terms of the rust removal level and roughness, to ensure that it meets the required standards. (3) Quality control of paint spraying ① Before using the paint, it is necessary to first check whether the name, batch number, color, type of curing agent and thinner indicated on the packaging meet the required standards; paint that has passed its shelf life must not be used ； ②Before mixing the coating, first stir the main component evenly, then add zinc powder according to the specified ratio and stir thoroughly until the color is uniform and there are no precipitates at the bottom. Depending on the temperature and application conditions, an appropriate amount of thinner can be added to adjust the viscosity suitable for application ； ③Before spraying the coating, it is necessary to measure the ambient temperature, relative humidity, dew point temperature, and steel plate temperature to ensure that the environmental conditions meet the requirements for coating application. Additionally, the air pressure, spraying equipment, and nozzle type should be checked to confirm they meet the specified standards before starting the spraying process ； ④Since the zinc powder in solvent-based inorganic zinc-rich primers tends to settle, the coating should also be continuously stirred during spraying to prevent the zinc powder from settling ； ⑤During the coating spraying process, the spraying pressure, spraying angle, spraying distance, spraying speed, and overlap range must be strictly controlled to prevent sagging or dry spraying ； ⑥When spraying the coating, a wet film thickness gauge should be used to continuously measure the wet film thickness, in order to ensure that the dry film thickness meets the design specifications.