I. Overview of Coating Application Methods

Coating application methods generally include brushing, rolling, air-assisted spraying, and airless high-pressure spraying. This article will focus on the airless high-pressure spraying technology, as it has significant advantages in industrial coating.

II. Principles of Airless High-Pressure Spraying

Airless high-pressure spraying does not rely on air to atomize the coating but applies high pressure to the coating directly, causing it to atomize when sprayed. This application method consists of a power source, high-pressure pump, pressure accumulator filter, paint delivery hose, and spray gun.

1. Power Source

The power source usually consists of compressed air, electricity, and hydraulic pressure. Compressed air is the most commonly used power source because it is simple and safe.

2. Pneumatic Pump

The pneumatic pump is powered by compressed air, with a pressure typically between 0.3-0.8 MPa. The pressure is controlled by a pressure-regulating valve to adjust the pressure of the coating. The pressure of the coating can be multiplied by several times the input pressure, referred to as pressure ratio, such as 45:1, 65:1, etc.

3. Paint Delivery Hose

In airless high-pressure spraying, the pressure loss in the paint hose depends on the flow rate of the coating. Coatings of different viscosities are divided into low-viscosity coatings (such as shop primers), medium-viscosity coatings (such as alkyd resin coatings, water-based acrylic coatings, and topcoats), and high-viscosity coatings (such as most thick slurry coatings, high solid-content coatings, and solvent-free coatings).

4. Spray Gun

The choice and maintenance of the spray gun are crucial for the spraying effect.

Spray Nozzle Size Identification: Common nozzle sizes, such as GRACO’s 517 or 521, are identified as: the number 5 multiplied by 10, 5×10=50, indicating a spray angle of 50° with a nozzle size of 0.017 inches or 0.021 inches.

Replacement of Worn Nozzles: Nozzles experience different degrees of wear after spraying a certain amount of coating (100-150 liters). This is especially true for coatings containing heavy pigments such as zinc powder, mica iron oxide, etc. Typically, after spraying 500-1000 liters, nozzles may experience significant wear. When the nozzle becomes worn, it will become larger and rounder, which reduces the spray pattern. If the spray pattern becomes 25% smaller, the nozzle must be replaced.

III. Conclusion

Airless high-pressure spraying technology, with its unique working principles and equipment configuration, significantly improves coating efficiency and quality. Understanding and mastering this technology is essential to improve the efficiency and quality of coating operations.