Key takeaways
- Measure before adjusting — unrecorded adjustments mask original causes and introduce new problems.
- Cover width errors start at the entry guide — check the guide width before touching forming stations.
- Length variation is almost always a measurement wheel or encoder fault, not a cutter fault.
- Burr severity at the cut is set by shear clearance as a percentage of material thickness — adjust for each gauge.
- Overload trips must be investigated before resetting — resetting without finding the cause trips again immediately.
How to diagnose problems systematically
Most roll forming problems fall into four categories: dimensional problems (the profile is the wrong size or shape), surface problems (marking, scratching, coating damage), cut problems (length errors, burrs, distortion at the cut), and drive problems (the line stops, trips or runs unevenly). Identifying the category first narrows the cause quickly.
Before adjusting anything, measure. A profile that looks wrong may be within tolerance; a profile that looks right may be outside it. Record the actual measurement and the nominal dimension before touching any setting. Adjustments made without measurements tend to introduce new problems while masking the original cause.
Dimensional problems
Incorrect profile width or flange length usually means a forming station is out of position or the entry guide width is wrong. Check the entry guide first — it is the most commonly overlooked cause and the easiest to correct. If the guide is correct, use a profile gauge at each forming station to find where the dimension first deviates.
| Symptom | Most likely cause | Check first |
|---|---|---|
| Cover width too wide | Entry guide set too wide, or first station open | Measure entry guide width against spec |
| Cover width too narrow | Entry guide too tight, strip edge lifting | Check strip is flat entering the first station |
| Flange too short or too long | Station roll gap incorrect on one side | Measure roll gap at suspect station with feeler gauge |
| Profile twisted along length | Rolls not level across width, or strip has edge bow | Level rolls across both sides; check coil for camber |
| Profile bowed upward (camber) | Exit rolls set too high relative to forming exit | Lower exit guide or straightening roll |
| Profile bowed downward (sweep) | Exit rolls set too low | Raise exit guide or add upward correction |
| Springback more than expected | Material yield strength higher than specified | Verify coil certificate against tooling design |
Surface defects
Scratching and marking on the top surface usually come from contamination on the forming rolls or a roll that has developed a burr. Stop the line, clean the rolls with a solvent-soaked cloth and inspect under good light for nicks or embedded material. A single metallic particle trapped in a forming groove will scratch every metre of material until it is removed.
Coating damage on pre-painted material is often caused by roll speed mismatch — if any station runs slightly slower than the strip speed, the strip drags across that roll surface rather than rolling cleanly. Check that all station drives are engaged and that drive chain or belt tension is correct.
Oil staining on painted material comes from excess forming lubricant migrating forward. Reduce lubricant flow to the minimum needed to prevent pick-up, and verify that any oil wiper before the entry guide is clean and correctly positioned.
Cut problems
Length variation beyond tolerance is almost always a measurement wheel or encoder issue, not a cutter issue. If cut lengths drift longer over a production run, the measurement wheel is slipping on the strip — clean the wheel surface and increase spring pressure. If lengths are randomly scattered, check the encoder cable for intermittent continuity.
Burrs on the cut edge indicate a worn or incorrect shear clearance. Shear clearance is set as a percentage of material thickness — typically 5–8% for mild steel, closer to 10% for high-strength grades. A clearance that was correct for 0.8 mm will produce heavy burrs on 2.0 mm material. Check that the blade gap matches the current material thickness.
Distortion at the cut end (the profile 'opens' or 'closes' after cutting) is caused by residual stress in the strip being released when the constraint of the forming line is removed. This is a tooling design issue and cannot be corrected by adjustment alone — discuss with the manufacturer.
Drive and control problems
Overload trips are the most common drive problem. Before resetting and restarting, identify why the overload occurred. Common causes: material jammed in the entry guide, strip edge caught on a forming roll shoulder, coil binding on the decoiler mandrel, or a blade that has seized in the closed position. Resetting without finding the cause will trip again immediately.
Speed variation between stations is felt as strip buckling between stations or intermittent tearing at the edges. On chain-driven lines this usually means a worn chain or sprocket. On gearbox-driven lines it means a shaft coupling has slipped. On servo-driven lines it means the synchronisation parameters have drifted and need re-tuning.
Encoder or sensor faults on the control panel are usually caused by vibration-loosened connectors or condensation on sensor faces. Tighten all connectors at the control cabinet and clean sensor faces with a dry cloth before calling for service.
Preventive checks to run every shift
A five-minute start-of-shift inspection prevents most unplanned stoppages. Check: lubrication levels on gearboxes and forming stations; condition of the entry guide and first two forming stations; shear blade gap against the scheduled gauge; any loose bolts on roll housings (vibration works them loose in heavy-gauge lines); encoder wheel cleanliness.
Record the first profile produced in each shift and measure it. A dimension that is drifting gradually over days or weeks indicates tooling wear. Catching this trend early means a planned tooling change rather than an emergency shutdown.