In terms of metal material adaptability, high-pressure airless spraying can treat a variety of metal surfaces, including carbon steel, stainless steel, aluminum alloys, and zinc alloys. For severely corroded steel surfaces, after sandblasting to Sa2.5, high-pressure airless spraying of an epoxy zinc-rich primer ensures a good bond between the primer and the substrate, enhancing corrosion protection. High-pressure airless spraying offers even greater advantages when spraying high-viscosity coatings (such as high-build epoxy and polyurethane coatings), achieving excellent atomization without requiring large amounts of thinner, thus avoiding issues such as slow drying and decreased adhesion caused by excessive thinners.
Process control for high-pressure airless metal spraying requires careful attention to several parameters. Paint viscosity should be controlled between 20 and 100 seconds (applying 4 cups). Excessively high viscosity can lead to poor atomization and sagging, while low viscosity can result in insufficient dry film thickness. Spraying pressure should be adjusted according to the paint type, typically 15-20 MPa for primer and 10-15 MPa for topcoat. The distance between the spray gun and the workpiece is generally 30-50 cm. Too close can result in excessively thick coatings and sagging, while too far can lead to poor coating uniformity. Furthermore, ambient temperature and humidity must be controlled. The optimal application temperature is 10-35°C, with a relative humidity not exceeding 85%. Avoid application in rainy or condensing environments to prevent defects such as pinholes and blistering. By properly controlling these parameters, high-pressure airless metal spraying can provide high-quality protective coatings for metal components .
Metal electrostatic spraying
Metal electrostatic spraying is a coating technology that uses a high-voltage electrostatic field to charge paint particles and then directionally adsorb them onto the surface of metal workpieces under the action of the electric field force. The basic principle is to ground the metal workpiece as the anode and the spray gun as the cathode, and apply 60-100kV high-voltage direct current between the spray gun and the workpiece to make the sprayed paint particles carry negative charge. Under the combined action of electrostatic attraction and compressed air thrust, the paint particles are adsorbed to the surface of the workpiece to form a uniform coating. This technology can significantly improve paint utilization and coating uniformity, and is especially suitable for metal parts with complex shapes. It is one of the mainstream coating methods in the automotive, home appliance, hardware and other industries.
The electrostatic metal spraying system primarily consists of a high-voltage electrostatic generator, spray gun, powder (or paint) supply system, recovery system, and drying equipment. The high-voltage electrostatic generator is the core component for generating the high-voltage electric field. It converts industrial-frequency AC power into stable high-voltage DC power, ensuring uniform electric field strength and preventing spark discharges. Spray guns are categorized into air-atomizing and airless-atomizing types. Air-atomizing spray guns use compressed air to atomize the paint and are suitable for liquid coatings; airless-atomizing spray guns rely on high pressure to atomize the paint and are primarily used for powder coatings. The powder (or paint) supply system must ensure uniform paint delivery. Powder coatings are typically supplied using a fluidized bed, while liquid coatings are delivered using a diaphragm pump. The recovery system collects unabsorbed paint, achieving a powder coating recovery rate exceeding 95%, saving materials and reducing pollution.
The process characteristics of electrostatic metal spraying give it unique advantages in metal coating. First, coating uniformity is excellent. Due to the electrostatic field, paint particles are evenly adsorbed to all parts of the workpiece, including difficult-to-coat areas such as grooves and corners, solving the problem of overly thin coating in these areas with traditional spraying. For example, after electrostatic spraying, the coating thickness of the complex curved surface of an automobile wheel hub can be controlled within ±5 microns, far superior to the ±20 microns of air spraying. Second, paint utilization is high, with liquid paint utilization reaching 60%-80% and powder paint utilization exceeding 90%, significantly reducing coating costs and waste emissions. Furthermore, this technology has a high degree of automation and can be combined with robots and conveyor lines to achieve fully automated coating, reducing manual intervention, improving production efficiency, and ensuring consistent coating quality.
Electrostatic spraying is suitable for a variety of metal substrates, including cold-rolled steel, galvanized steel, aluminum alloys, and magnesium alloys. For refrigerator and washing machine housings in the home appliance industry, electrostatic powder spraying can achieve a coating adhesion (cross-hatch method) of Class 0, salt spray resistance exceeding 500 hours, and a smooth, flat surface with a strong decorative effect. In the automotive component sector, cast iron parts such as engine blocks and transmission housings are electrostatically sprayed with high-temperature-resistant coatings, capable of withstanding temperatures exceeding 200°C while resisting corrosion from engine oil and coolant. For metal workpieces requiring grounding, simply ensuring a good connection between the workpiece and the grounding device ensures smooth electrostatic spraying, without the need for additional processing.
Process control for electrostatic metal spraying requires careful attention to several key parameters. Electrostatic voltage is a key parameter influencing paint adsorption. A voltage that is too low results in insufficient paint adsorption and reduced coating efficiency. A voltage that is too high can easily cause edge effects (overly thick coating on the edges of the workpiece) or even spark discharges, posing a safety hazard. Therefore, the appropriate voltage must be set based on the paint type and workpiece shape. The spraying distance is generally 20-30 cm. A distance too close can lead to excessively high local charge density, resulting in uneven coating. A distance too far weakens the electric field and increases paint loss. Paint atomization is also crucial. Powder coating particle size should be controlled between 10-100 microns, and the viscosity of liquid coatings should be adjusted to 15-30 seconds (applying 4 cups) to ensure good charging performance and uniformity. Furthermore, ambient humidity must be kept below 60%. Excessive humidity can reduce the charge of paint particles, impairing adsorption. By precisely controlling these parameters, electrostatic metal spraying can provide high-quality, high-performance coating protection for metal products.
