Failure mode
Telescoped or Loose Coil
The coil face is no longer flat — layers have slid sideways into a cone, or the coil has gone slack on the core. It will not sit properly on the decoiler, and handling it risks edge damage.
What it actually is
The coil face is no longer flat — layers have slid sideways into a cone, or the coil has gone slack on the core. It will not sit properly on the decoiler, and handling it risks edge damage.
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.
Winding tension profile
Tension has to taper as the coil diameter grows. A constant or wrongly tapered profile lets inner layers slip.
Core strength
A core that collapses under coil weight allows the whole package to shift. Paper cores behave differently from steel and aluminium ones.
Transport restraint
Coils that are not chocked and strapped properly move in transit. One hard brake is enough.
Soft temper and thin gauge
O-temper thin gauge has low structural stiffness and telescopes more readily than hard temper at the same thickness.
Verification
How it is measured
Telescoping is measured as the lateral deviation between the innermost and outermost wrap on the coil face. Also check coil inner diameter against the stated 508 or 610 mm, and confirm coil weight against what your decoiler is rated to carry.
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
State coil ID and maximum weight
508 mm or 610 mm, and a weight limit that matches your decoiler. This is equipment data, not a preference.
2
Name the core material
Steel, aluminium or paper — and say if a reinforced core is required for heavy coils.
3
Specify the packing orientation
Eye-to-sky or eye-to-side, with chocks and strapping described. The orientation decides how it travels.
4
Add protection for soft thin gauge
Inner liner paper and end-face protectors for O-temper thin material.
Coil faces are photographed before the container is sealed, and we confirm coil ID and weight against the decoiler rating before confirming the order — a coil your machine cannot lift is a problem created at the enquiry stage.
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.