Failure mode
Burr on Slit Aluminium Strip
The slit edge is sharp to the touch. In transformer winding it threatens the interlayer insulation; in fin stock it jams the forming tool; in any manual process it is an injury risk.
What it actually is
The slit edge is sharp to the touch. In transformer winding it threatens the interlayer insulation; in fin stock it jams the forming tool; in any manual process it is an injury risk.
Mechanism
Why it happens
Four causes account for most of it. They are not equally common, and they are not equally within the mill's control.
Knife clearance and overlap
The relationship between blade clearance, overlap and material thickness decides whether the edge is sheared clean or torn. It is a setup value, not a fixed machine property.
Blade wear
Worn blades roll the edge over instead of cutting it. Burr height grows gradually with run length.
Temper
Softer tempers tear rather than shear. O-temper strip produces more burr than H-temper at the same knife setting.
Speed and tension mismatch
Running faster than the tension system can stabilise lets the strip move laterally during the cut.
Verification
How it is measured
Burr height is measured perpendicular to the slit edge, by feeler gauge, dial indicator or optical comparison against a reference. Many buyers express the limit as a percentage of thickness — commonly around 5% — or as an absolute value in hundredths of a millimetre. Agree which one applies.
Specification
How to specify around it
Most of these cost nothing to write into an order and are difficult to enforce afterwards. This is the part worth copying into your next RFQ.
1
Set a burr height limit
Give a number, and say whether it is absolute or a percentage of thickness.
2
Ask for deburring or edge conditioning
Where the edge is functional — transformer winding is the classic case — specify the edge treatment, not just the width.
3
State the width tolerance
Slitting width tolerance is a separate figure from burr and is usually quoted in hundredths of a millimetre.
4
Say what the strip is for
Transformer winding, cable shield, radiator fin and lamp caps each have a different tolerance for edge condition.
On slitting enquiries we ask what the strip feeds, because transformer winding and general-purpose trim are not the same specification. Burr is checked on the production sample and photographed, and where the application is electrical we flag the edge-conditioning question before the order runs.
We do not claim this never happens. Metal is rolled, shipped across an ocean and unloaded by someone else. What we do is ask the question before the order runs, put the answer in writing, and be the single party that answers for it afterwards.