Material & testing
Engineering Question
Why can cores made from the same CRGO grade deliver different magnetic performance?
Key Data
- Mill certificate: evidence for the specified material and its recorded test results.
- Finished-core report: evidence for the assembled core under a stated test arrangement.
- Chenfan process parameters: burr height <0.02 mm; stacking factor >97%.
Technical Explanation
A mill test certificate identifies the starting material. Check the coil reference, grade, thickness and magnetic data against the order. The certificate does not describe the cutting, joint alignment, clamping or handling that takes place afterwards.
The finished core contains cut edges, overlapping joints and a mechanical stress state. Those conditions help explain why the same nominal grade and thickness can produce different loss and exciting-current results. A low burr reading and a high stacking factor are useful process indicators; neither is a standalone magnetic acceptance test.
Material tests on processed samples can support an investigation, provided sampling and specimen preparation are defined. Treatments such as stress-relief annealing can change what the comparison reveals. Finished-core testing must also have an agreed excitation method, calculation boundary and acceptance basis. It supports pre-shipment verification but does not replace the transformer manufacturer’s final testing.
Engineering Implications
- Link the material certificate and process records to the supplied core or lamination batch.
- Read no-load loss and exciting current together under comparable test conditions.
Procurement Implications
- Agree the inspection and testing scope before ordering, including which reports will be supplied.
- For critical designs, request evidence of repeatability across comparable production.
What to Confirm Before Ordering
- Material traceability and certificate requirements.
- Sample preparation, test frequency, flux density and reporting units.
- Finished-core test availability, acceptance criteria and responsibility for final transformer testing.
For CRGO material supply, agree the certificate and test basis; define any finished-core testing separately in the core order.