A transformer core looks simple from the outside: sheets of CRGO steel cut, stacked, assembled, and clamped.
But the real performance is decided by small manufacturing details.
One of the most important details is burr height.
In transformer core production, burrs are formed during shearing. If the cutting blade is worn, the clearance is unstable, or the material feeding is not accurate, the burr becomes larger. This is not only a surface defect. It can directly affect the electrical performance of the core.
For high-quality transformer cores, burr height must be controlled strictly.
At Chenfan Electric, our target is:
Burr height: < 0.02 mm
This is not a decorative standard. It is a physical requirement.
Why Burrs Increase Transformer Core Loss
CRGO steel sheets are coated with insulation film. The coating separates each lamination and prevents current from flowing between sheets.
If the burr is too high, it can pierce or damage this coating.
The failure chain is clear:
Excessive burr → coating damage → metal-to-metal contact → interlaminar short circuit → circulating current → local heating → higher no-load loss
Once interlaminar short circuits occur, the transformer core no longer behaves as a properly insulated laminated structure. Local eddy currents increase. Hot spots may appear at joints or corners. The final transformer may show higher no-load loss, abnormal temperature rise, or noise problems.
This is why burr control must be managed at the cutting stage, not after assembly.
Burr Control Starts from Cutting Accuracy
Good burr control depends on several manufacturing factors:
- Sharp cutting blades
- Stable blade clearance
- Accurate feeding system
- Correct material support during shearing
- Regular inspection during production
- Proper handling to avoid edge damage after cutting
For thin CRGO materials such as 0.23 mm, 0.20 mm, or 0.18 mm, burr control becomes even more difficult.
The thinner the material, the smaller the tolerance margin. A small cutting error can quickly become a performance problem.
This is especially important for high-efficiency distribution transformers and low-loss transformer designs.
Stacking Factor Also Matters
Burr height affects insulation safety.
Stacking quality affects magnetic cross-section.
A high-quality transformer core also needs a stable stacking factor.
At Chenfan Electric, our preferred benchmark is:
Stacking factor: > 97%
A low stacking factor means more air gaps inside the core window. This reduces the effective magnetic cross-section and may increase excitation current, noise, and loss.
Good stacking factor depends on:
- CRGO thickness consistency
- Flatness of sheets
- Accurate cutting length
- Good step-lap alignment
- Stable clamping pressure
- Controlled burr height
Burrs and stacking factor are connected. Excessive burrs can create small gaps between laminations, reducing stacking density and increasing local stress.
Why Multi-Step Lap Structure Is Used
For modern transformer cores, Multi-Step Lap structure is widely used to improve magnetic flux transition at the joints.
Compared with simple butt joints or rough miter joints, MSL structure helps reduce flux crowding at the corner area.
The benefit is practical:
- Lower no-load loss
- Lower excitation current
- Lower noise
- More stable magnetic performance
- Better joint area distribution
But MSL only works when cutting accuracy is stable.
If step length is inaccurate, the magnetic joint will not align correctly. If burrs are too large, the joint area can still become a source of local heating.
So MSL is not only a design structure. It requires precise manufacturing control.
What Buyers Should Check Before Ordering Transformer Cores
When purchasing transformer cores, buyers should not only ask for material grade.
Material grade is important, but it is not enough.
A proper transformer core order should confirm:
- CRGO grade and thickness
- Core type and drawing dimensions
- Step-lap structure
- Burr height requirement
- Stacking factor requirement
- Cutting tolerance
- Core weight
- Clamping or frame requirement
- Packing method
- No-load loss target if required
Many purchasing mistakes happen because buyers compare only CRGO material price. But a finished transformer core is not raw steel.
A complete core price includes:
Material + cutting loss + slitting + shearing + stacking + assembly + inspection + packing + profit
Comparing raw CRGO coil price with finished core price is technically wrong.
Conclusion
Transformer core quality is decided before the transformer is assembled.
If burr height is not controlled, insulation coating may be damaged.
If stacking factor is unstable, the effective magnetic section may be reduced.
If MSL cutting accuracy is poor, the joint area may become a loss point.
A reliable transformer core must control these risks from the manufacturing stage.
For serious transformer production, burr height below 0.02 mm, stacking factor above 97%, and accurate Multi-Step Lap processing are not optional selling points.
They are the foundation of stable no-load loss, low excitation current, and long-term transformer reliability.