Scope of this guide
Junior version: what you will see, what you record, and what you never touch. Recognise early, escalate fast.
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 |
Recognise, record, escalate
| You see | You do | You never do |
|---|---|---|
| Bath turning dark | Stop loading, call senior immediately | Keep parts in and hope |
| Rate seems slow | Log pH and temperature first | Dump extra reducer in |
| New spec arrives | Ask which phosphorus class it needs | Assume same as last job |
| Any addition due | Record product, amount, time | Add by memory |
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
Why is the bath getting dark?
Possible decomposition starting — stop loading and call the senior now. Do not add anything.
What phosphorus class is this job?
It is on the job card (low/mid/high). If missing, ask before plating.
Why log every addition?
Rate and stability follow the chemistry history; the log is the bath's memory.