TL;DR
Elevated ball mill vibration is most often caused by girth gear or pinion alignment drift, incorrect ball charge, or a loose liner. Check the pinion backlash and ball charge level first.
What you might see
- vibration alarm on pinion bearing
- mill product fineness coarser than setpoint
- periodic impact noise from the mill shell
- girth gear grease thrown from the mesh zone
Likely causes
Pinion alignment drifted from the design position causing uneven girth gear tooth contact
Ball charge below the design fill level causing the balls to cascade rather than tumble
Loose or broken liner bolt allowing liner movement
Girth gear backlash outside specification from tooth wear
Required tools
- Dial indicator with magnetic base
- Precision level
- Torque wrench for liner bolts
- Confined-space entry equipment
- LOTO kit
Safety first
- Lock out both the main motor and the barring gear before any person works near the mill shell or girth gear.
- Confined-space entry into the mill shell requires a formal permit and rescue standby.
- Cement dust explosion risk. No hot work near the mill without a hot-work permit.
Procedure
- 1
Stop the mill and lock out the main drive and the auxiliary drive.
Warning: Lock out both the main motor and the barring drive before any person approaches the mill shell, girth gear, or trunnion. - 2
Measure girth gear to pinion backlash with a dial indicator on the tooth flank. Compare to the design specification.[1]
- 3
Check pinion shaft alignment to the mill axis with a precision level.[1]
- 4
Estimate the ball charge fill level by measuring the ball surface height inside the mill through the inspection port.
- 5
Inspect liner bolts for correct torque. Use the confined-space entry procedure if any bolt is inside the mill.
Warning: Confined-space entry into the mill shell requires a permit, atmospheric testing, and a rescue standby. - 6
Inspect the girth gear spray lubrication nozzles for correct spray pattern coverage.
- 7
If alignment is in tolerance and liner bolts are tight, adjust the ball charge to the design fill level and retest.
Sources
FLSmidth FLSmidth UMS / TMS Cement / Ball Mill general technical documentation, FLSmidth
FLSmidth ball mill operation and maintenance documentation, vibration diagnosis and alignment procedures (general)
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