TL;DR
VRM vibration almost always means the material bed on the grinding table is too thin. Increase the dam ring height or reduce the separator speed to build the bed before increasing feed rate.
What you might see
- mill vibration alarm active
- vibration level above automatic trip setpoint
- grinding noise with periodic impact
- product fineness fluctuating
Likely causes
Material bed too thin on the grinding table, allowing metal-to-metal roller contact
Dam ring height too low for the current material and moisture, reducing bed depth
Feed interruption causing the bed to empty and triggering roller contact
Foreign material or tramp metal on the grinding table causing an impact
Required tools
- Access to DCS vibration trend display
- Dam ring adjustment tools
- LOTO kit
Safety first
- Lock out the mill drive and gear unit before any person enters the mill housing for inspection.
- Cement dust explosion risk inside the mill housing. Use confined-space entry procedure with atmospheric testing.
Procedure
- 1
Reduce the mill feed rate immediately when the vibration alarm activates. Do not wait for the automatic trip.[1]
- 2
Increase the dam ring height if the vibration correlates with low bed depth, use the adjustment mechanism without stopping the mill.[1]
- 3
Check the feed chute and weigh feeder for flow interruptions. Restore a continuous, steady feed flow.
- 4
Reduce the separator rotor speed slightly to allow coarser material to remain on the table, building up the bed.
- 5
If vibration persists after bed depth correction, stop the mill and lock out the drive.
- 6
Inspect the grinding table and roller tires for cracks, embedded tramp metal, or excessive wear.
- 7
After any tramp metal removal or roller inspection, restart with reduced feed and step up gradually while monitoring vibration.
Sources
Loesche Loesche LM Series Vertical Roller Mill (VRM) general technical documentation, Loesche
Loesche vertical roller mill operation and maintenance manual, vibration diagnosis and material bed procedures (general)
More guides for Loesche Loesche LM Series
How to diagnose hydraulic tensioning faults on a Loesche LM Series VRM
Low roller grinding force means the hydraulic tensioning system has a leak or the accumulator nitrogen charge is low. Check the accumulator pre-charge before looking at the cylinder seals.
How to assess roller tire wear on a Loesche LM Series VRM
Worn roller tires increase specific power consumption and degrade product fineness. Measure the tire profile with a profile gauge during a planned stop and schedule replacement when wear reaches the minimum profile depth.
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