Why Does the Coil Jam in the Uncoiler?

Coil won’t rotate / stalls on startup

A “jam” can mean different things, such as:

• Coil won’t rotate / stalls on startup

• Strip won’t pull off smoothly

• Coil binds against the hold-down or peeler

• Coil slips then suddenly grabs

• Coil expands unevenly and locks up

• Strip telescopes and wedges

The most common root causes are:

1. Coil damage or poor coil shape

2. Mandrel expansion or segment problems

3. Brake/tension set too high (or unstable)

4. Incorrect coil ID or width setup

5. Poor hold-down / peeler arm adjustment

6. Side guide / centering errors

7. Strip threading errors and edge catching

8. Bearing/rotation resistance in the uncoiler

1) Coil Damage, Telescoping, or Out-of-Round (Most Common Real Cause)

If the coil is not a clean, round “cylinder,” it will bind.

Common coil conditions that jam

• Telescoped coil (layers shifted sideways)

• Collapsed or oval core

• Buckle or edge kink

• Strapped too tightly and “set” in shape

• Coil set / crossbow causing uneven payout

What you’ll see

• Coil rubs hard on side plates or hold-down

• Strip pulls unevenly, then locks

• You can see side-to-side step between wraps

Fix

• Reject severely damaged coils

• Re-center and re-square coil on mandrel

• Use a coil car to load squarely

• If telescoped: carefully re-align wraps (with proper safety controls)

2) Mandrel Not Expanding Correctly (Grip + Geometry Issue)

If the mandrel expands unevenly or not fully:

• Coil can shift

• Coil can bind on one side

• Expansion segments can “dig” into the core

Causes

• Low hydraulic pressure

• Internal leakage in expansion cylinder

• Worn mandrel segments/wedges

• Debris/rust in sliding surfaces

Fix

• Verify full expansion pressure

• Inspect segments for uneven movement

• Clean/lubricate mandrel mechanism

• Repair hydraulic leaks / rebuild cylinder if needed

3) Brake/Tension Too High (Creates Binding, Especially at Startup)

Over-braking makes the roll former fight the uncoiler.

At startup, the strip tension spikes and the coil can “stick,” then release suddenly—this feels like a jam.

Signs

• Jam happens on startup or acceleration

• Coil “snaps” free with a bang

• Tension marks or edge damage

Fix

• Reduce brake tension

• Use smoother acceleration ramps

• If using a dancer/loop: stabilize loop control so the brake isn’t hunting

4) Coil ID / Adapter Mismatch

If the coil ID (e.g., 508 mm vs 610 mm) doesn’t match the mandrel range:

• Mandrel may over-expand, causing wedge/bind

• Or under-expand, allowing coil to cock sideways and jam

Fix

• Confirm ID and use proper mandrel sleeve/adapters

• Ensure the coil is centered and squared before expansion

5) Hold-Down Arm / Peeler / Snubber Misadjusted

Hold-down systems prevent coil “springing” but if set incorrectly, they cause friction and binding.

Common problems

• Hold-down pressing too hard

• Peeler angle incorrect and catching strip

• Snubber roller not aligned across strip width

Fix

• Set hold-down pressure just enough to control spring-back

• Align peeler so it guides strip cleanly into the table

• Ensure snubber rollers are parallel and free-rolling

6) Side Guides / Centering Set Wrong

If the coil or strip is not centered:

• Strip rubs hard on one side

• Coil can track into side plates and bind

Fix

• Center coil to the line center

• Align entry guides and feed table

• Ensure side guides steer, not clamp

7) Strip Threading Errors (Edge Catching)

During threading, the strip can catch on:

• Feed table edges

• Guide rollers

• Peeler tip

• Coil retaining plate

That edge catch can “lock” the coil and make it seem jammed.

Fix

• Deburr entry surfaces

• Ensure smooth lead-in radius on guides

• Use proper threading procedure (slow speed, controlled feed)

8) Uncoiler Bearing or Gearbox Resistance

If the uncoiler rotation is stiff:

• Coil won’t unwind smoothly

• Load spikes cause jamming sensation

Fix

• Inspect uncoiler bearings for heat/noise

• Lubricate and service gearbox (if geared)

• Check brake drag even when “off”

Fast “Jam Diagnosis” Checklist (Best Order)

1. Stop safely and secure coil (safety first).

2. Inspect coil shape: telescoping, collapsed core, edge damage.

3. Confirm mandrel expansion is even and correct ID.

4. Reduce brake tension and try slow jog payout.

5. Check hold-down/peeler alignment and pressure.

6. Confirm strip is centered and not rubbing side plates/guides.

7. Check uncoiler rotation: bearing drag, brake dragging, gearbox issues.

Pattern Guide

• Jams at startup → brake too tight, peeler catching, hold-down too tight

• Jams mid-coil → telescoping, coil set/camber, debris, side guide rubbing

• Jams only on one supplier’s coil → coil quality/ID/core issue

• Jams and coil shifts sideways → mandrel under-expansion or uneven segments

• Jams with loud snap → excessive back tension + coil spring-back

Final Expert Insight

Coil jams are usually caused by coil shape/core damage, mandrel expansion issues, or excess back-tension/hold-down friction. The fastest fixes typically come from:

• verifying coil condition and ID

• ensuring even mandrel expansion

• reducing brake/hold-down pressure

• centering the coil and strip path