title = "Powder Coating: Application and Cure Process"

content = """
Powder coating is an organic coating process in which dry thermosetting or thermoplastic powder is applied to a metal substrate electrostatically and then cured in an oven to melt, flow, and cross-link into a durable, attractive finish. At Ridgecrest Metalworks, powder coating is used for steel and aluminum components requiring a tough, attractive, corrosion-resistant finish as an alternative to liquid paint.

The powder coating process consists of five stages: surface preparation, powder application, oven cure, quality inspection, and packaging.

Surface preparation is the most critical step—adhesion, corrosion resistance, and coating life are determined almost entirely by substrate cleanliness and surface conversion. Steel parts are typically cleaned by shot blasting (producing a clean, angular surface profile that maximizes mechanical adhesion), or by multi-stage washer (alkaline clean, rinse, iron phosphate conversion coating, rinse, dry). The iron phosphate conversion coating provides a chemically bonded base for the powder and significantly improves corrosion resistance. For aluminum, a zinc phosphate or chrome-free conversion coating is used.

Electrostatic powder application uses a spray gun that imparts a high-voltage electrostatic charge (typically 50–100 kV negative) to powder particles as they are sprayed from a fluidized bed powder supply. The charged powder particles are attracted to the grounded (earthed) workpiece and adhere uniformly. Parts hung on ground racks travel past spray guns in a conveyor booth. Faraday cage areas (recessed corners, deep pockets) have poor penetration because the electrostatic field is shielded; these areas may require special application techniques or higher-voltage fluidized bed immersion.

Oven cure schedules are specified by the powder manufacturer: typically 350–400°F (177–204°C) for 15–25 minutes at metal temperature (not air temperature). Thermoset powders (epoxy, polyester, polyurethane, hybrid epoxy-polyester) undergo cross-linking reactions during cure—the powder melts, flows to form a smooth film, and cross-links into a chemically resistant solid. Thermoplastic powders (nylon, PVDF) melt and solidify without chemical cross-linking and can be re-melted.

Quality checks include: film thickness per ASTM D7091 (magnetic gauge on steel, eddy current on aluminum), adhesion by cross-cut tape test per ASTM D3359, hardness by pencil hardness test, impact resistance, and salt spray exposure per customer specification.
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