A suspected lamination fault may no longer appear after a packet is unclamped. That can mean a conductive contact opened, debris moved, layer alignment changed or the observation method now sees a different geometry. It does not by itself establish that the original cause has been corrected.
Preserve the assembled state before authorized investigation changes it. Record restraint, support, alignment and accessible contact evidence. An instrument trace without those mechanical observations can become impossible to interpret once the packet is released.
Keep a state-transition log
For every significant investigation step, record the previous state, the change made, the new mechanical observations and the corresponding electrical or thermal result. Use common coordinates and timestamps. The aim is to connect disappearance of a signal to a specific state change.
As-found state
Retain the actual assembly configuration and the condition under which the finding occurred. Identify what is observed and what is inferred. If some evidence cannot be collected safely within the approved procedure, mark it unavailable rather than attempting an improvised test.
Partial release or movement
Record the approved transition and changes in sheet position, contact openings or debris. An electrical result collected after this transition belongs to the new state. It should not overwrite the original result.
Separated inspection
Map contact marks, coating damage and object positions with their layer identities. Separation can itself create marks or move material, so distinguish as-found evidence from changes introduced during inspection where possible.
Interpret a normal retest conditionally
Ask which required contact or return path is no longer present. If a model predicts that pressure closes the path, an open-path observation after release is consistent with that model. It neither proves the model correct nor proves the production condition repaired.
Other explanations need consideration. Probe standoff can change, reflected radiation can disappear with a moved surface, or a sensor can be remounted. Check the observation process alongside the contact hypothesis.
Investigate the cause through a representative comparison
Where a professional laboratory study is justified, use a representative construction to examine the suspected load-dependent behavior. Its procedure must be separately qualified. Do not attempt to recreate an abnormal conductive path in a deliverable transformer merely to make the original signal reappear.
Compare predicted and observed state dependence. A reproducible relation between contact geometry and the electrical response strengthens attribution. If the signal disappears without an identified transition, retain the cause as unresolved.
The final investigation record should show what changed and what remains necessary to prevent recurrence. Corrected geometry, controlled debris origin or a qualified insulation repair are different outcomes from a normal reading in a newly dismantled state. The transition log preserves that distinction when the fault’s most important evidence depends on the pressure that the inspection removes.
Quantify how one-sheet release can open a contact
Nominal sheet thickness is 0.23 mm [1]. Assume a clamped state has a 0.15 mm unbridged surface separation and a conductive projection reaching 0.18 mm. Geometric contact overlap is 0.03 mm. If release permits one nominal sheet thickness of normal movement away from the projection, separation becomes 0.38 mm and the path has a 0.20 mm opening. A normal electrical retest in that released state is consistent with an opened contact, even though the projection remains. Record uncertainty on the original gap, reach and movement [2]; this rigid-contact illustration does not infer the real compliance or a permissible repair condition.
Manufacturing controls. Clamp sequence, local flatness, packet springback, burr reach and debris restraint govern state-dependent contact. Inspect and document those parameters before disassembly changes them, then verify the final assembled state after corrective action.
References
- Nippon Steel Corporation, Grain-Oriented Electrical Steel Sheets, catalogue D004je_03_202004, 2020, Specifications; Size and Form Tolerances.
- JCGM, JCGM 100:2008, Evaluation of measurement data — Guide to the expression of uncertainty in measurement, 2008.