Scope of this guide
Senior version: the fix set with parameter windows, boundary cases and the discipline that keeps them fixed.
Series: finishing.com recurring questions answered with platingclub line practice. Parameters are industry-standard starting ranges — confirm against your supplier TDS.
Triage: symptom → confirm → first move
| Symptom | Likely root | Confirm by | First move |
|---|---|---|---|
| Burnt, gray nodules on edges/high points | Local CD far above window | Position map vs rack layout | Cut total amps; add thieves |
| Bare spots in recesses while edges burn | Throwing power ceiling | Coverage vs position chart | Aux anode trial on recess |
| Burns after bath cools overnight | Temperature-CD coupling | Temp + amps log overlay | Interlock heat to line start |
| Burns only on new racks | Contact resistance low, current hogging | Contact check by rack age | Balance load across racks |
| Coverage loss with normal burn | Catalyst ratio drift | Hull cell + titration | Correct sulfate ratio 100:1 |
The fix set
- Fix 1 — amp staging — Start 20% under target CD for 30 s, then ramp; burns fade without losing coverage
- Fix 2 — geometry — Anode gap ≥ 150 mm; thieves/shields on corners; recesses get aux anodes, not more amps
- Fix 3 — temperature first — Decorative 45–50 °C ± 2 °C: cold bath burns at lower CD than operators expect
- Fix 4 — rack rotation — Retire high-mileage racks; new racks plate hotter at same setting
- Fix 5 — ratio discipline — Sulfate 0.8–1.2% of CrO3 by titration; coverage loss precedes haze
Case method
A rack chrome line burned every corner at set current. Adding thieves on the two hottest rack positions and staging the ramp (20% under for 30 s) cleared burns without losing recess coverage; total amps ended lower than before. (Method illustration: verify with your own position-mapped thickness data.)
Engineer notes
- One variable per corrective action; verify with the confirm-by column.
- Records beat memory: log every trial on the tank card.
- Two failed actions in a row is a senior call — escalate with your log.
Safety: chromic acid mist is a carcinogen and burns skin. Exhaust running before load-in, face shield, and immediate first aid for any chrome burn.
FAQ
How do I design thieves for a new rack?
Map burn positions over three loads, size thief wire to steal the excess, trial at staged amps.
When is aux anode justified?
Recess that must plate to spec but sits below throwing power: geometry revenue beats cycle loss.
Ramp or straight current for parts that burn?
Stage 20% under for 30 s then full: burns seed in the first seconds.