TL;DR
Strip thickness deviation despite AGC means the hydraulic capsule position sensor is drifting or the capsule is leaking. Verify sensor calibration and capsule pressure before blaming the rolling schedule.
What you might see
- strip thickness outside tolerance
- AGC system at its correction limit
- roll bending force asymmetric between operator and drive side
- strip camber developing during rolling
Likely causes
Hydraulic screwdown capsule position sensor uncalibrated or drifted
Hydraulic capsule seal leaking, causing position to drop during rolling load
Roll thermal crown different from the model assumption requiring schedule adjustment
Roll wear exceeding the allowable limit changing the actual roll gap
Required tools
- Position sensor calibration tools
- Strip gauge verification (calibration foils)
- Hydraulic pressure gauge
- LOTO kit
Safety first
- High-pressure hydraulic screwdown system. Bleed pressure before any capsule work.
- Hot strip hazard in the hot rolling mill. Aluminized PPE required near the rolling line.
Procedure
- 1
Read the actual strip gauge from the X-ray or laser gauge and compare to the AGC setpoint. Quantify the magnitude and direction of the deviation.[1]
- 2
Check the hydraulic capsule position feedback on the operator and drive sides. A side-to-side difference indicates asymmetric capsule behavior.[1]
- 3
Verify the zero calibration of the capsule position sensors. Zero calibration should be done with the rolls at a known reference position.
- 4
Check the hydraulic capsule pressure. A capsule that loses pressure under load has a seal leak.
- 5
If the capsule and sensor are healthy, review the roll thermal crown model. After a long rolling campaign without a roll change, the thermal crown may have changed.
- 6
If deviation persists, conduct a roll change and compare the new roll gauge against the old. Excessive roll wear confirms the rolls must be changed more frequently.
Sources
SMS group SMS X-Roll Hot / Cold Rolling Mill general technical documentation, SMS group
SMS group rolling mill AGC and hydraulic screwdown system documentation (general)
More guides for SMS group SMS X-Roll
How to diagnose roll chock bearing overheating on a SMS X-Roll rolling mill
Chock bearing overheating on a rolling mill is usually caused by low oil film bearing pressure or flow restriction. Check the oil supply pressure at the chock inlets and pull an oil sample before changing out the roll.
How to diagnose spindle coupling vibration on a SMS X-Roll rolling mill
Spindle vibration at roll speed frequency is usually worn coupling cross-pins or unequal coupling balance from worn elements. Inspect the coupling teeth or cross-pins during the next roll change stop.
Stop fixing the same fault twice.
Dovient turns guides like this into your team's shared playbook, with AI that catches recurring issues before they break the line.