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1. Electrostatic Powder Coating Principle

Electrostatic powder coating operates on the principle of a high-voltage electrostatic corona field. The metal guide ring at the gun tip is connected to the negative high-voltage terminal, while the workpiece to be coated is grounded, serving as the positive electrode. This setup creates a strong electrostatic field between the gun and the workpiece.

Compressed air, acting as the carrier gas, transports the powder from the feed hopper through the hose to the gun’s guide ring. Since the guide ring is connected to the negative high-voltage terminal, it generates a corona discharge, producing a dense concentration of negative charges in its vicinity. This charges the powder particles negatively.

These charged particles then enter the intense electrostatic field. Under the combined action of electrostatic force and the carrier gas, the powder is propelled uniformly towards the grounded workpiece surface, forming an even layer. Subsequently, heating curing transforms this layer into a durable coating film.

2. Coating Application Process Flow

Pretreatment → Drying (moisture removal) → Spraying → Inspection → Curing → Final Inspection → Finished Product

3. Standard Powder Coating Application Requirements

(1) To fully realize the properties of the powder coating and extend the service life of the coating film, strict adherence to the process is necessary during pretreatment.

(2) During spraying, the workpiece must be thoroughly grounded to enhance powder deposition efficiency.

(3) Inspect immediately after spraying. Address any defects found promptly. If defects are discovered after curing:

* Minor, localized defects not affecting appearance: Repair using powder of the same color diluted with acetone.

* Major defects affecting surface quality: Sand down the coating, then respray, or use paint stripper to remove the coating before reapplying powder.

(4) Reclaimed powder must be sieved to remove contaminants before being mixed with new powder in a specific ratio for reuse.

4. Requirements for Textured (Artistic) Powder Coating

Textured powders offer aesthetic appeal, strong three-dimensional effects, and excellent decorative results. However, their application demands stricter process control.

(1) Spray Parameters:

* Air Pressure: Should not be too high; typically controlled within 0.5 – 1.5 kg/cm². Excessive pressure can reduce pattern definition or cause pitting.

* Voltage: Electrostatic voltage should not be excessively high; generally controlled around 60-70 kV. Excessive voltage can cause powder on the workpiece surface to rebound, leading to pitting, poor leveling, and other defects.

(2) Film Thickness: Coating thickness is critical and should generally be controlled between 70-100 μm to facilitate the formation of distinct, larger patterns. Insufficient thickness results in faint, small patterns and may cause pitting or exposed substrate.

(3) Curing: Must be conducted strictly according to the specified temperature and time.

* Insufficient temperature or time will prevent proper pattern formation and significantly reduce mechanical properties due to incomplete curing.

* Due to the specific production process of textured powders, using reclaimed powder often results in smaller or less distinct patterns. Therefore, it is generally recommended NOT to use reclaimed textured powder. If use is attempted, testing is essential.

While the application requirements for textured powders are more stringent, achieving ideal and satisfactory results is assured by adequately controlling the factors mentioned above during the coating process.