The spraying process flow of powder coatings mainly includes the following steps:
1. Surface Pretreatment
Surface pretreatment is the first step in the electrostatic powder coating process, aiming to remove oxides, oil stains and other dirt on the workpiece surface, so as to improve the adhesion of the powder coating. Surface pretreatment generally follows these steps:
- Degreasing: Remove oil stains on the workpiece surface by chemical or physical methods. Common methods include solvent cleaning, alkaline cleaning, etc.
- Rust Removal: Use mechanical methods such as sandblasting and shot blasting to remove rust and corrosion products on the workpiece surface, so as to expose a clean metal substrate.
- Cleaning: Wash away the residues on the workpiece surface to ensure that the surface is clean and free of impurities.
- Phosphating (or Chromating): Generate a layer of anti - corrosion phosphating layer (or chromating layer) on the workpiece surface, which can increase the adhesion of the coating. This is a key step to improve the coating quality.
- Drying: Dry the treated workpiece to remove surface moisture and prepare for the next step of electrostatic spraying .
2. Electrostatic Spraying
Electrostatic spraying is the core part of the electrostatic powder coating process. The powder coating is evenly sprayed onto the workpiece surface by the principle of electrostatic adsorption. The specific steps are as follows:
- Powder Coating Conveyance: Transport the powder coating to the front end of the electrostatic spray gun.
- Electrostatic Adsorption: A high - voltage electrostatic generator is installed at the front end of the spray gun. The high - voltage corona discharge generated makes the area near the spray gun charged. When the powder is ejected from the gun nozzle, it forms charged coating particles and is attracted to the grounded workpiece with the opposite polarity.
- Coating Formation: As the powder continues to be adsorbed, a powder coating with a certain thickness is gradually formed on the workpiece surface. When the coating reaches a certain thickness, due to electrostatic repulsion, the powder will no longer be continuously adsorbed.
During the electrostatic spraying process, the following points should be noted:
- The moving speed of the spray gun should not be too fast or too slow to avoid thin coatings or sagging phenomena.
- The spray gun should be kept perpendicular to the substrate surface to avoid the spray pattern being skewed to one side, resulting in paint shortage on the other side.
- The distance between the spray gun and the substrate surface should be appropriate. The optimal distance for siphon - type spray guns is 15 - 20 cm, and for pressure - fed spray guns is 20 - 30 cm .
3. Curing
Curing is the process of melting, leveling the sprayed powder coating at high temperature and making it closely adhere to the workpiece surface. The specific steps are as follows:
- Heating and Curing: Put the sprayed workpiece into a high - temperature curing oven and bake it at a high temperature of 180 - 200°C to make the powder melt and level. The curing time depends on the quality of the selected powder and the thickness of the workpiece, and is generally about 20 minutes.
- Constant - Temperature Curing: After melting, enter the constant - temperature curing stage to ensure that the coating is cured evenly.
During the curing process, it is necessary to keep the curing temperature and time consistent to avoid color differences caused by temperature differences or paint film peeling due to insufficient curing .
4. Coating Inspection
After the spraying and curing process is completed, the coating needs to be inspected to ensure that the coating quality meets the requirements. The inspection contents include:
- Whether the coating thickness is uniform, without missed spraying, sagging, etc.
- Whether the coating surface is smooth and shiny, without orange peel, pinholes and other defects.
- Whether the coating adhesion is good, without peeling, blistering and other phenomena.
For coating defects such as bumps, scratches, orange peel and pinholes, timely repair or re - spraying is required .
Through the elaborate process flow and strict quality control, the coating quality can be ensured to be stable and reliable, and the corrosion resistance and aesthetics of the product can be improved. In actual applications, it is necessary to make flexible adjustments and optimizations according to specific product requirements and process conditions.
HLM(holyme) Powder Coating CO,.Ltd a leader in high-temperature resistant powder coatings, can professionally customize the production of high-temperature resistant powder coatings.