Scope of this guide
Management version: this defect as cost and risk — the metrics, audit points and claim defence.
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 |
|---|---|---|---|
| Film wipes off, powdery | Bath too hot / too long | Time-temperature log | Cut dwell; check heater |
| Iridescent patchy colors | Uneven zinc surface from rinse drag | Pre-chromate rinse check | Fix counter-flow rinse |
| Bare spots after chromate | Oil/silicone on zinc | Water-break test before chromate | Pre-clean audit |
| Weak color, fades fast | Bath exhausted / pH drift | Titration + pH | Rebalance per TDS |
| Color varies by rack row | Drag-in concentration gradient | Position sampling | Dip discipline; agitation |
Cost, metrics and defence
| Cost line | Driver | Metric | Lever |
|---|---|---|---|
| Rechromate loops | Dwell by feel | Timer compliance rate | Timers at every station |
| Chemical spend | Over-dosing exhausted bath | Titration log completeness | One owner per bath |
| Claims | Fading film in field | Storage-test samples | Ship gate on color standard |
| EHS exposure | Hexavalent handling | PPE audit score | Trivalent conversion where possible |
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: hexavalent chromate is a known carcinogen and sensitizer. Gloves, apron, face shield, exhaust on; trivalent lines preferred wherever spec allows.
FAQ
What does chromate rework really cost?
Double handling of finished goods; timer compliance is nearly free.
Why keep storage-test samples?
Field fading claims settle with the kept sample, not with opinions.
Hexavalent to trivalent — business case?
EHS risk down, compliance simpler; qualify with customer salt-spray spec first.