Two salvaged laminations can share the same outline and have different engineering histories. One may have retained its coating and shape; the other may have been overheated, bent during removal or mixed with another steel grade. Pooling them destroys the information needed to decide where either belongs. [1]
Restacking begins with traceable populations. Keep steel from different cores, packets and damage zones separate until the assessment supports combining them. Matching dimensions is necessary for a particular arrangement, but it cannot establish magnetic grade, coating compatibility or equivalent condition.
Sort before the stack hides the evidence
Record original packet position and orientation where recoverable. For grain-oriented electrical steel, rolling direction is a functional property. Preserve the relationship between material direction and the intended magnetic path; a geometric fit cannot correct an unsuitable orientation.
Inspect edges, flatness, surface condition and identifiable coating damage in the state received. Cleaning or flattening can alter the evidence and may introduce new damage. Any proposed treatment needs material-specific qualification rather than an assumption that salvaged steel can be restored indefinitely.
| Population attribute | Why it matters | Sorting record |
|---|---|---|
| Known grade or material lot | Magnetic behavior may differ | Original identity or explicit unknown status |
| Original core/packet location | Wear and fault exposure differ | Source packet and damage-zone tags |
| Rolling direction | Relates to the designed flux path | Orientation marking retained |
| Coating condition | Affects interlaminar contact risk | Condition category and examined area |
| Edge and shape condition | Affects fit, contact and joint assembly | Mapped defects and disposition |
| Handling/treatment history | Can introduce stress or surface changes | Actual process applied to that population |
Design the stack around the retained populations
If populations are combined, document the reason and the implications. A mixed core may need a different magnetic assessment from one rebuilt using a single identified material. Avoid assigning all steel the best known grade just because some pieces carry that identity.
Preserve joint layout and packet distribution in the restacking record. Changes in joint arrangement, clamping and flatness can affect assembled behavior independently of the steel’s original material properties. This is why a favorable measurement on a salvaged specimen cannot establish the finished core’s loss or noise.
Budget an identified mixed steel population
Nippon Steel specifies maximum new-strip loss of 0.85 W/kg for 23ZH85 and 0.90 W/kg for 23ZH90 at 1.7 T, 50 Hz. [2] Assume the grade-planning population is 1,000 kg with 600 kg identified as 23ZH85 and 400 kg as 23ZH90. Its catalogue-only basis is 600×0.85 + 400×0.90 = 870 W, versus 850 W for all 23ZH85. With an assumed catalogue planning budget of 860 W, the higher-loss grade may contribute at most (860 − 850)/(0.90 − 0.85) = 200 kg. The proposed mix exceeds that planning allocation by 200 kg; revise the mix or budget before restacking. Recovered pieces require their own condition/magnetic verification: these new-strip limits establish neither aged-steel performance nor finished-core loss. Unknown steel receives no grade assignment by appearance.
Rolling direction, retained coating, edge burr, packet order and joint alignment determine what the rebuilt assembly adds to the steel basis. Sorting by wear history must survive cutting and restacking; the weighted catalogue figure does not qualify the assembled core.
Measure the rebuilt object on a declared basis
The completed-core verification should record excitation, frequency, waveform and assembly condition relevant to the claim. Compare with a credible reference only when its basis is sufficiently aligned. A reference from another core with a similar rating is not automatically an original-performance target.
References
- IEC, IEC 60404-11:2021, Magnetic materials — Part 11: Methods of measurement of the surface insulation resistance of electrical steel strip and sheet.
- Nippon Steel Corporation, Grain-Oriented Electrical Steel Sheets, catalogue D004je, April 2020, specification and typical-property tables.