Scope of this guide
Intermediate version: symptom-to-cause triage with the confirm-by column — find the variable, run one change, verify.
This series answers a top recurring question from finishing forums with platingclub line practice. Parameters are industry-standard starting ranges — confirm against your supplier TDS.
Triage: symptom → confirm → first move
| Blister pattern | Likely root | Confirm by | First move |
|---|---|---|---|
| After plating bake only | Sub-surface porosity out-gassing | 200 °C re-bake test | Quarantine casting lot |
| Random single blisters | Oil or wax under deposit | Blister cross-section | Pre-clean audit |
| Edges and thin walls | Over-etch or acid dwell | Etch weight loss check | Cut acid time, verify strike |
| On flat faces in rows | Air trapped by rack angle | Position map | Re-rack angle 10–20° |
| Whole lot, every load | Casting gas content | Density / lot tag audit | Push back to foundry |
Engineer notes
- One variable per corrective action; verify by the confirm-by column.
- Records beat memory: log every trial on the tank card.
- Escalate when two consecutive actions fail — that is a senior call.
Safety: bake ovens hold hot parts and hydrogen risk from pickled parts is real. Heat gloves, face shield at door, and never load pickled zinc straight into a hot oven.
FAQ
Acid pickle or alkaline clean for zinc diecast?
Alkaline. Acid attacks the zinc surface and seeds blisters; acid contact should be seconds if ever.
How long is the standard bake gate?
100–110 °C for 1–2 hours before plating; the 200 °C test bake is for release of new lots.
Blister pattern moves with rack position — meaning?
Mechanical: trapped air or drag-over. Re-rack angle and check transfer wetness.