High-Efficiency Electrostatic Painting Applications for Eyeglass Frames

Eyeglass frames are generally made of metal, plastic or resin, natural materials, or mixed materials. Automated electrostatic painting offers greater efficiency, environmental friendliness, and material savings.

IMLUCKY has focused on the coating industry for over 20 years, providing mature coating production configurations and customized complete solutions.

Spray Gun: Utilizes the American Graco Pro XP automatic air spray gun equipped with an 85 kV power supply and internal power. The intelligent spray gun model connects to a control module, enabling kV voltage control and displaying spray gun performance.

Gear Pump: Precisely controls paint output, solving the problems of overspraying and underspraying.

Mitsubishi Servo Motor
LOCAL Electrical Control Box
LOCAL Reciprocating Machine
SMC Three-Position Valve

Challenges Faced: In eyeglass temple coating, overspraying leads to oil accumulation, while underspraying results in color differences, irregular eyeglass frames, and missed areas at corners. Manual spraying is inefficient and difficult to control the amount of paint applied.

1. Overspraying & Insufficient Coating: Addressing Color Difference Issues

*Optimize fluid supply and spray gun parameters: Use a low-pressure, high-atomization electrostatic spray gun; reduce spray pressure and control paint flow to avoid excessive instantaneous paint output; set a stable paint supply pressure plate pump to ensure consistent paint output.

*Reduce flow rate and maintain a uniform gun speed; apply thin, multi-layer sprays instead of single thick coats; for thin eyeglass temple components, apply 2-3 thin coats to prevent oil buildup and drips from a single thick coat, ensuring uniform paint film thickness and eliminating color differences.

*Paint mixing control: Stabilize paint viscosity and solvent ratio; maintain consistent ambient temperature and humidity; excessively high viscosity leads to dry spray color differences, while excessively low viscosity causes oil buildup and drips; use viscosity cups for regular monitoring to reduce batch-to-batch color variations.

2. Irregular Supports and Corner Missing Points: Eyeglass temples have many bends and complex corner grooves, making straight-line spraying prone to missing areas.

*Workpiece Rotating Fixture + Self-Rotating Tooling: Custom-made special hanging fixtures allow the workpiece to rotate 360° while revolving with the chain, ensuring all corners, inner sides, and bends are aligned with the spraying surface, eliminating spraying dead spots and solving corner missing point issues. Eyeglass temples are small, so fixture positioning must not obstruct the spraying surface, minimizing obstruction points.

*Multi-Gun Staggered Layout: Instead of using a single spray gun, multiple spray guns are arranged vertically and diagonally, one facing the main body, and angled spray guns specifically covering corners and inner bends; electrostatic adsorption assists, utilizing the electrostatic coating effect to allow paint to adhere to the back and corners of the workpiece.

*Spray Gun Distance and Angle Control: Maintain a fixed safe distance between the spray gun and the workpiece, aligning the angle with the corner's bevel, avoiding perpendicular spraying to the flat surface; the robot/reciprocating machine uses a fixed spraying trajectory, specifically adding spraying trajectory points at corner locations.

3. Manual spraying is inefficient and difficult to control in terms of paint volume.

*Automatic reciprocating spraying line/robotic spraying: The biggest drawback of manual spraying is the fluctuation in paint output, gun speed, and distance, leading to paint accumulation, color differences, and missed areas.

- Reciprocating machine solution: Moderate cost, combined with a rotating fixture, suitable for large-volume eyeglass frames; fixed trajectory and fixed flow pressure ensure consistent spraying conditions for each piece, resulting in stable paint film thickness and significantly reducing human error.

- Six-axis robotic spraying: Suitable for various styles and irregularly shaped frames; independent spraying programs can be programmed for different models, and corner areas can be resprayed at reduced speed.

*Electrostatic spraying: Electrostatics improve paint coverage and reduce scattering and overspray; electrostatic coating at edges and corners improves missed areas while reducing paint waste. Note: The conductivity of the eyeglass substrate material must be confirmed; plastic frames require pre-treatment for conductivity to ensure the electrostatic effect is effective.

4. Pretreatment and Post-treatment Auxiliary Improvements

* Thorough degreasing during pretreatment is crucial. Oil stains on the workpiece surface can indirectly induce abnormal paint film, localized color differences, and poor adhesion.

* Add a flash-off zone: A flash-off zone is implemented after each coat of paint to allow solvent evaporation before applying the next layer, effectively reducing oil accumulation and runoff.

* Quality Control: Increase film thickness sampling to monitor the paint film thickness range. Excessive thickness leads to oil accumulation, while insufficient thickness causes color differences. This allows for the calibration of equipment parameters.

Results: The workpiece rotates 360° on the automatic coating line, and the reciprocating spraying results in a smooth, even, brush-mark-free, and dense coating.