Two-roll Mill Troubleshooting: Causes & Fixes

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Problems on this page:

Sheet thickness uneven Compound sticking to the wrong roll or bagging Emergency stop or trip bar not stopping the rolls fast enough Roll temperature control failing Roll bearing problems Contamination in the compound Drive overload Stock blender faults

Sheet thickness uneven

Hits OEE: Quality

Symptoms: The milled sheet is thicker on one side or varies along its length.

Nip set unevenly across the rolls

Set the nip with feeler gauges at both ends and the middle.

Roll temperature uneven across the face

Check the cooling water flow and the roll temperatures.

Roll bearings worn, letting the gap open under load

Check the bearings for play.

Compound fed unevenly

Spread the compound evenly across the nip.

Prevention: Sheet thickness measured at both edges and the centre.

Compound sticking to the wrong roll or bagging

Hits OEE: Quality

Symptoms: The compound sticks to the back roll or hangs loose instead of banding.

Roll temperature difference wrong for the compound

Set the front and back roll temperatures for the compound.

Friction ratio wrong

Check the speed ratio between the rolls for the compound.

Nip too wide

Reduce the nip in small steps until the compound bands.

Compound too warm or too cold

Check the compound temperature coming from the mixer.

Prevention: Banding behaviour noted per compound.

Emergency stop or trip bar not stopping the rolls fast enough

Hits OEE: Availability

Symptoms: The rolls do not stop within the required distance when the trip bar is hit.

Brake worn or out of adjustment

Have the brake adjusted or relined; a mill that does not stop fast enough is a serious hazard.

Trip bar switch faulty or misaligned

Test the trip bar switch.

Brake control circuit fault

Have the circuit tested by qualified staff.

Stopping test not done

Do the stopping distance test at the interval the site sets.

Prevention: Stopping distance tested and recorded at the set interval.

Roll temperature control failing

Hits OEE: Quality

Symptoms: Roll temperatures drift and compound behaviour changes.

Rotary joint leaking or blocked

Check the rotary joints for leaks and blockages.

Cooling water flow low

Check the cooling water supply and clean the strainers.

Scale inside the rolls

Descale the roll water circuit and check the water treatment.

Temperature sensor fault

Check the roll temperature sensors against a surface probe.

Prevention: Roll temperatures logged each shift.

Roll bearing problems

Hits OEE: Availability

Symptoms: The roll bearings run hot or noisy.

Lubrication supply low or blocked

Check the oil or grease supply to each bearing.

Bearing wear

Check vibration and temperature on a route and plan the replacement.

Overload from milling cold or stiff compound

Check the compound temperature before it goes on the mill.

Bearing cooling not working

Check the cooling water to the bearing housings where fitted.

Prevention: Bearing temperature checked on a route.

Contamination in the compound

Hits OEE: Quality

Symptoms: Foreign material or residue from another compound turns up in the sheet.

Rolls not cleaned between compounds

Clean the rolls and the drip tray between compounds, as the colour or compound change requires.

Tools and knives left near the rolls

Keep tools in a holder away from the nip.

Residue falling from guards and the stock blender

Clean the guards and blender guides on schedule.

Dirty pallets or trays for the sheet

Check the trays used for sheet handling.

Prevention: Sheet inspected at take-off.

Drive overload

Hits OEE: Availability

Symptoms: The mill drive trips while milling.

Nip closed too tight for the batch

Open the nip and close it in steps as the compound warms.

Batch larger than the mill handles

Reduce the batch size to the mill rating.

Compound too cold

Let the compound warm up or check the mixer dump temperature.

Gearbox or coupling problem

Check the gearbox oil and the coupling.

Prevention: Drive trips recorded per compound.

Stock blender faults

Hits OEE: Availability

Symptoms: The stock blender stops or does not fold the compound properly.

Blender guide rollers worn

Replace worn guide rollers.

Blender drive fault

Check the blender motor and drive.

Traverse settings wrong for the batch

Check the traverse speed and stroke settings.

End position sensor faulty

Check the traverse end sensors.

Prevention: Blender checked weekly.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: internal mixer · calender · extruder · gearbox · chiller · compression moulding press

Stop the same fault coming back

Recurring two-roll mill stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover