Scope of this guide
This intermediate guide goes into diagnosis: reading symptoms, isolating the variable that changed, and fixing it with data you can collect on the line.
Process: Powder Coating. Figures in this guide are industry-standard starting ranges; confirm against your supplier TDS before locking settings.
Working ranges and control points
The table below is the daily reference for a powder booth. Set by the card, verify by the control point column.
| Parameter | Typical range | Control point | Watch out |
|---|---|---|---|
| Gun distance | 150–250 mm | Stand-off jig per part | Close range back-ionises |
| Powder output | Sharp 60–100 g/min | Feed pump pressure | Surging gives heavy spots |
| Booth airflow | 0.4–0.6 m/s at face | Anemometer weekly | Drafts blow powder off parts |
| Cure | Object 180 °C × 12–15 min | Data logger per batch | Under-cure chips easy |
| Film thickness | 60–100 µm | Comb gauge per rack | Edge falloff on sharp corners |
Diagnose It Fast: the intermediate view
Beyond the basic card, this is the layer that matters at your level:
| Symptom | Likely variable | Confirm by | First fix |
|---|---|---|---|
| Dull or hazy finish | Bath chemistry drift | Hull cell panel | Rebalance per test |
| Defects cluster on one rack position | Contact or current map | Position thickness map | Repair contact / re-map amps |
| Good-bad-good pattern | Loading or cycle drift | Time-stamped samples | Standardise load weight |
| Defect appears after maintenance | Work just done | Revert one change | Restore and re-verify |
Standard routine
- Ground-check every hook — conductivity is the first defect cause
- Pre-bake to drive off moisture
- Set gun stand-off by part geometry
- Log object temperature through cure
- Comb-gauge film at three points per rack
Engineer notes
- Poor grounding mimics Faraday cage rejection — clean hooks first
- Recycle ratio above 30% changes particle size and charging
- Colour changes: blow down booth fully to avoid speckling
- Sharp edges thin out; design radius or double-pass corners
- Store powder below 25 °C; caked powder throws chunks
Safety: Powder dust is combustible. Keep concentrations below the lower explosive limit, ground all equipment, and never smoke in the booth area.
FAQ
Why does powder repel from deep recesses?
Faraday cage effect. Lower voltage, add a second gun angle or touch-up with liquid paint.
How do I verify cure without a lab?
Solvent rub per batch plus logged object temperature in the cure window.
Why do hooks cause defects?
Ground loss. Burn off or replace hooks before charging changes.