What is Powder Coating | powder coating process | types of powder coating | uses of powder coating | their advantage & disadvantage . - Chemical and Paint technology Study Notes

What is Powder Coating?

Powder coating is a dry finishing process in which a powdered paint (free-flowing and electrostatically charged) is applied to a surface and then cured under heat to form a hard, protective layer. It’s widely used for metal, automotive, appliances, and industrial equipment.

The powder is made from Resins, Pigments, Flow Modifiers, Leveling agents, and other Additives.
It is applied using an Electrostatic spray gun and then cured in an oven.

Powder Coating Process: Step-by-Step Explanation:-

The powder coating process involves preparing the surface, applying the powder, and curing it to form a durable, protective, and decorative finish.

1. Surface Preparation (Pre-treatment):-

✅ Purpose: Remove oil, dirt, rust, and other contaminants to ensure proper adhesion.

Methods:

Degreasing/Chemical Cleaning: Removes grease and contaminants.
Etching/Phosphating: Enhances corrosion resistance (zinc or iron phosphate used).
Sandblasting/Shot Blasting: Abrasive cleaning for rust or heavy scale.
Drying: Ensures no moisture is left before coating.

2. Powder Application

✅ Purpose: Apply the powder using electrostatic charge.

How it works:

The powder is sprayed using an electrostatic spray gun.
The gun gives the powder a negative charge.
The workpiece (usually metal) is grounded, attracting the charged particles.

Application method:

Electrostatic Spray Gun (Corona method) – most common.
Fluidized Bed Coating – for dip-coating large, simple-shaped items.

⚙️ Powder Coating Gun Parameters:-

Setting the correct parameters on a powder coating gun is critical for good coverage, adhesion, and finish quality. Below are the key parameters and their typical ranges:

🔑 Main Parameters for Powder Coating Gun:-

Parameter	Typical Range	Purpose / Effect
Voltage (kV)	40 – 100 kV	Determines the strength of the electrostatic charge applied to the powder particles.
Current (μA)	10 – 100 µA	Function: Controls the amount of current flowing to the part.. Lower current helps avoid Faraday cage issues.
Powder Flow Rate	50 – 200 g/min	Adjusts how much powder is delivered per minute.
Air Flow (CFM)	5 – 15 CFM (cubic feet/min)	Controls the atomizing and conveying air. Too high can blow powder off.
Spray Distance	6 – 12 inches (15–30 cm)	Distance from gun to part; too close may cause back ionization, too far leads to weak adhesion.
Gun-to-Work Voltage Control	Automatic or Manual	High-end guns use dynamic adjustment based on part geometry.

🎯 Best Practices

Use lower voltage (40–60 kV) for recessed areas (to reduce Faraday cage effect).
Use higher voltage (80–100 kV) for flat and open surfaces.
Adjust air flow and powder flow together to maintain a smooth, even spray.
Maintain consistent gun angle (~45–90°) to the surface for uniform coverage.
Always ground the workpiece properly to ensure electrostatic attraction.

3. Curing

✅ Purpose: Melt the powder and chemically bond it to form a hard, durable finish.

The coated part is moved into a curing oven.
Temperature: 160°C to 220°C
Time: 10–30 Minutes, depending on powder type and thickness.

Thermoset powders chemically cross-link, while thermoplastic powders simply melt and harden on cooling.

4. Cooling

✅ Purpose: Allow the part to solidify and stabilize after curing.

The part is slowly cooled in ambient air or with fans.
Ready for handling, packaging, or assembly.

🔄 Summary of the Powder Coating Process

Step	Description
1. Cleaning	Removes dirt, grease, and contaminants
2. Pre-treatment	Improves corrosion resistance and paint adhesion
3. Application	Powder sprayed using an electrostatic gun
4. Curing	Heat applied to melt and harden the powder coating
5. Cooling	Coating stabilizes and becomes fully durable

Types of Powder Coating:-

Thermoset Powder Coatings :-
- React chemically when cured to form a solid, irreversible layer.
- Common types:
  - Epoxy - Known for good adhesion, corrosion resistance, and impact resistance.
  - Polyester - Offers good weatherability, low cure temperatures, and a wide range of colors. Ideal for outdoor applications and heat-sensitive products.
  - Epoxy-Polyester Hybrid - Combine the strengths of both epoxies and polyesters, offering a good balance of performance and aesthetics .
  - Acrylic - It’s known for its excellent UV resistance, high gloss retention, and weatherability.
  - Urethane - Its excellent durability, chemical resistance, and aesthetic finish.
Thermoplastic Powder Coatings:-
- Melt and flow when heated but do not undergo chemical change; They can be Re-melted.
- Common types:-
  - Polyethylene
  - Polyvinyl Chloride (PVC)
  - Polyamide (Nylon)
  - Polypropylene

Uses of Powder Coating

Automotive parts (Lever Kick Starter , Brake Pedal, wheels, frames, bumpers)
Appliances (Refrigerators, Washers, Dryers)
Architectural (Window frames, Railings)
Furniture (Metal chairs, Tables)
Industrial equipment
Bicycles
Electrical enclosures
Home décor and hardware

Advantages of Powder Coating:-

Advantage	Description
Durability	Resistant to chipping, scratching, and corrosion
Eco-friendly	No solvents or VOCs (Volatile Organic Compounds); minimal waste
Even Coating	Electrostatic process ensures uniform layer without runs or drips
Cost-effective	Overspray can be recycled; high material utilization rate
Variety of finishes	Glossy, matte, textured, and metallic finishes available
Quick curing time	Faster turnaround compared to liquid coatings

Disadvantages of Powder Coating:-

Disadvantage	Description
High initial setup cost	Equipment for application and curing can be expensive
Material limitations	Best suited for metal; some plastics or wood can’t withstand curing temperatures
Difficult touch-up	Hard to repair small defects compared to wet paint
Thick coating limitations	May have issues with very thick layers or fine detail
Color change is time-consuming	Cleaning equipment between colors can be labor-intensive