Why an MTC is more than a purchasing attachment
When purchasing silicon steel, a material name on the invoice is not sufficient evidence of its measured magnetic properties. An electrical steel mill test certificate (MTC) can help a buyer verify which material was supplied, which tests were performed and whether the documented values match the purchase specification.
Certificate layouts vary by mill, market and product grade. Some orders include a mill document, while additional inspection or traceability records may be required from the processor. Buyers should agree on the exact documentation rather than assume a particular certificate format will automatically be provided.
Start with identification and traceability
First check the mill name, product designation, grade, coil or heat identification, manufacturing lot where used, thickness, width and ordered quantity. The key question is whether the certificate can be linked to the label on the delivered coil and, later, to the laminations produced from that coil.
If a supplier slits one parent coil into several narrower coils, the receiving system should be able to connect the daughter coils back to the parent identification. A clear labeling process reduces the risk of using an incorrect grade during stamping and helps manage a quality claim after delivery.
Compare magnetic values under the same conditions
The certificate may list specific total loss, magnetization or polarization-related information, depending on the grade and applicable specification. A value of core loss in W/kg is meaningful only together with the test frequency, induction or polarization condition, test method and any relevant tolerances.
For example, two reported loss values should not be compared merely because both are expressed as W/kg: one may have been measured at a different magnetic condition. Testing of electrical steel and strip is addressed by the IEC 60404 series, including the relevant magnetic measurement methods. Buyers should refer to the grade’s product standard to decide which values must appear on the certificate.
Mechanical and surface data also matter
A certificate can include thickness and other material properties, but it may not demonstrate the geometry of a slit coil or stamped EI lamination. After processing, inspect dimensions, edge burr, coating condition, camber and damage under a separately defined quality plan.
IEC 60404-9:2018 provides methods for characteristics such as edge wave, residual curvature, edge camber and burr height in electrical steel strip and sheet. Those checks are especially important when coils are used in high-speed stamping or a precision stacking process.
A practical seven-point certificate review
- Identification:Does the grade and coil number match the purchase order and packaging label?
- Dimensions:Are thickness and material form correct, with any required tolerances?
- Magnetic properties:Are the reported values relevant to the intended application?
- Test conditions:Are frequency, magnetic condition and method stated adequately?
- Coating:Is the agreed surface treatment identified or supported by another record?
- Traceability:Can processed slit coils and production batches be connected to the material record?
- Exception handling:Is there a process for missing fields, substitutions and nonconformities?
A reliable review ends with a simple decision: accept, request clarification, or quarantine pending engineering approval. Re-labeling a grade without authorization is not an acceptable solution to a missing document.
Applying the certificate to a lamination RFQ
For silicon steel strip coils, specify the steel grade, intended magnetic properties, coil format and required documentation. For custom laminations, add the drawing revision, stack requirements and quality plan. Consider incoming inspection samples for the first order, then adjust sampling only after process confidence is established.
Frequently asked questions
Is a mill certificate the same as a finished-core test report?
No. A mill certificate addresses supplied material, while a finished-core report addresses a processed or assembled component under its own measurement conditions.
Can magnetic loss figures be compared across different frequencies?
Not directly. Always compare like-for-like testing conditions and relevant material grades.
What if the certificate uses a different grade naming system?
Request a documented equivalence assessment. Names that look similar may not impose the same acceptance limits.
Is a certificate enough to approve incoming slit coils?
Usually not by itself. Dimensional, surface and packaging inspection may still be needed, depending on application risk and the purchase agreement.
Request material documentation before purchasing
Tianxiang supplies strip coils and manufactures EI laminations. Send an inquiry stating the material grade, test data required, delivery form and traceability expectations so the documentation scope can be confirmed during quotation.
Technical references: IEC 60404-9; IEC 60404-11.
