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
| Observation | Likely cause | Confirm by | First move |
|---|---|---|---|
| Rate drops late in bath life | Orthophosphite build-up | Turnover count + rate log | Plan rebuild at 5–6 turnovers |
| P content unknown, spec dispute | No assay routine | Lab assay per rebuild | Set assay schedule |
| Dark deposits, slow plate | pH low / stabilizer drift | pH + Hull cell | Hold pH 4.4–4.8 per TDS |
| Plate stops on recesses | Gas sticking, agitation dead | Position pattern | Work the agitation, not the bath |
| Bath decomposes (black rain) | Overload or palladium contamination | Load history | Strip load; discipline on make-up |
Cost, metrics and defence
| Cost line | Driver | Metric | Lever |
|---|---|---|---|
| Bath dumps | No turnover ledger | Turnovers per dump vs limit | Plan rebuilds, don't crash them |
| Assay fees | Random sampling | Assay per rebuild compliance | Fixed schedule with the lab |
| Scrap | Decomposition events | Incidents per year | Loading band + filtration |
| Claims | Wrong P-class shipped | Spec-to-assay match rate | Assay gate on release |
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: EN baths run hot and acidic with nickel salts and reducing agents. Heat gloves, face shield, ventilation; never add chemistry to a decomposing bath.
FAQ
ENP cost per part — what moves it?
Turnovers achieved per dump and assay-planned rebuilds; crash dumps double chemistry cost.
Which spec risk do we carry?
Wrong phosphorus class shipped: assay gate on release closes it.
Is ENP worth it vs electrolytic for our parts?
Geometry with recesses and uniform-thickness specs favor ENP; cost it per family.