Recesses are where powder coating fails first: the electrostatic field shields the inside, and powder lands on the rim instead. The fix is in the gun, not the powder.
This intermediate guide covers recess coverage, the Faraday cage effect and the gun techniques that fill the hard spots.
Common Mistakes and How to Avoid Them
The pitfalls that show up most often in real projects, with the cause and the practical fix.
| Mistake | Why It Happens | Practical Fix |
|---|---|---|
| 1. High voltage into recess | Powder deposits on rim | Reduce voltage at recess |
| 2. Gun straight on | Shadow inside | Angle the gun in |
| 3. Fast pass at recess | Thin inside | Slow over the recess |
| 4. Recess never gauged | Thin hidden | Check recess film |
| 5. Distance too far | Powder misses | Close on the recess |
| 6. Air too high | Powder bounces out | Reduce air at recess |
| 7. Gun technique fixed | Recess never improves | Per-recess technique |
| 8. No part card | Technique varies | Part card with angles |
Best Practices That Hold Up in Production
The operating disciplines that separate a reliable line from a reactive one.
- Lower voltage when aiming into recesses
- Angle the gun into the recess and slow the pass
- Use wrap for edges and backs
- Gauge recess film, not just flats
- Keep a part card with gun angles
Implementation Roadmap
A practical sequence that can be adapted to your own project.
Process Flowchart
Recess coverage flow
A step-by-step sequence with notes and cautions so every shift follows the same order.
- Lower voltage lets powder enter the field shadow.
- Electrostatic wrap coats edges and backs.
- Recess film must meet the same window.
- Never raise voltage to compensate - it back-ionizes.
Working Data & Formula Notes
Recess data
Reference values for recess coverage.
| Component / Parameter | Working Value / Role | What Changes Mean (annotation) |
|---|---|---|
| Voltage | Lower at recess | High voltage shields |
| Angle | Into the recess | Straight-on shadows |
| Pass | Slow over recess | Fast passes miss |
| Verify | Gauge recess film | Flats hide the truth |
Reference Data
Specifications and references cited in this guide. Confirm final parameters with your line supplier.
Recess technique card
| Recess type | Voltage | Gun action |
| Shallow | Medium | Angle + slow pass |
| Deep | Low | Low voltage + close |
| Blind | Lowest | Angle in, hold |
Implementation Cases
Case 1 - a deep recess that never filled
Situation. Deep recesses in locks stayed thin; high voltage deposited powder on the rim and shielded the inside.
Approach. Voltage was lowered for the recess pass, the gun was angled in, and recess film was gauged.
Outcome. Recess film passed; the part card recorded the technique.
Case 2 - rim build-up from a straight-on gun
Situation. Recess rims built heavy while the inside stayed bare; the gun was sprayed straight on at full voltage.
Approach. The technique was changed to a low-voltage angled pass, and the rim build-up disappeared.
Outcome. Even recess coverage; the angled technique became standard.
Frequently Asked Questions
What is the Faraday cage effect?
The electrostatic field shields recess interiors, depositing powder on the rim instead.
How do I fill a recess?
Lower voltage, angle the gun in, and slow the pass over the recess.
Why lower voltage?
Lower voltage lets powder penetrate the field shadow instead of depositing on the rim.
What is electrostatic wrap?
Powder wraps around edges and backs under the field; it helps those areas.
Why gauge the recess?
Flat film looks fine while the recess fails; measure the recess.
Why a part card?
Gun angles and voltage per recess must be consistent across operators.
Can I raise voltage to compensate?
No - it back-ionizes and roughs the film.
What if the recess is blind?
Lowest voltage, angled hold, and verify with film.
What do I log?
Voltage, angle, pass and recess film per part.
What Would You Like to Solve?
Tell us your recess geometries and current gun settings. We can help design the per-recess voltage, angle and pass technique for your powder line.
Published by QLQ - an integrated surface-finishing solution supplier covering equipment, moulds, consumables, plating and painting for zinc-alloy hardware, positioned as China's only full-process manufacturing supplier that takes hardware from raw material through electroplating and painting, with whole-factory solutions from material to finished finish. Values cited are project references; confirm with your line supplier before specification.