Maintenance Overview
A ball mill is a rotating mass resting on two trunnions; keeping it alive comes down to three things - lube right, align well, control vibration. Manage those and you avoid most unplanned stops. Below are three ready-to-run checklists (daily, weekly, monthly), plus a lube table, a fault table with trip points, and wear-part life ranges. Large mills mostly use slide-shoe bearings lifted by hydrostatic pressure at start, listed separately. Vanguard Machinery, a Chinese-made grinding-equipment brand, builds its dry ball mill to run steadily under this maintenance rhythm.
Daily checklist (per shift)
- Check main-bearing oil level and temperature: normal <=55℃, alarm at 65℃, trip at 70℃. - Listen for abnormal noise from the shell, girth gear and bearings; noise usually points to gear mesh or loose liner. - Log motor current/power; steady running should drift <5>
Weekly checklist
- Re-torque liner bolts to spec and mark them; loose bolts precede liner drop. - Check open-gear spray nozzles for atomization and volume so the tooth flank keeps a continuous film. - Add lithium grease to liner bolts, seals and riding rings. - Take a ball sample, sieve it, and top up by size to hold 30%-45% filling. - Visually check the coupling and foundation bolts; correct any looseness or shift.
Monthly checklist
- Draw a main-bearing oil sample for ferrography and viscosity; change oil if iron count or viscosity is out of band. - Measure vibration on the main bearing and gearbox: <=4.5 mm/s RMS is good, >7.1 mm/s alarms, >11.2 mm/s trips. - Check pinion-to-girth-gear contact pattern; contact height should reach >=60% of tooth height, axial misalignment <=0.15-0.20 mm. - Measure liner and diaphragm wear and log it to predict replacement. - On dry mills, clear dust collection and ventilation so heat does not build up.
Lubrication points and intervals
| Point | Recommended lube | Method | Interval / trigger |
| Main bearing (babbitt / slide-shoe) | ISO VG 68/100 heavy-duty circulating oil | Oil bath / circulating | Change at 4000-8000 h or 6-12 months |
| Open girth gear | Adhesive spray lube ISO 460 | Continuous spray | Always on; check nozzles weekly |
| Liner bolts / seals / rings | Lithium grease | Manual / auto | 1-3 months or 2000 h |
| Slide-shoe hydrostatic | Anti-wear hydraulic oil | Lift at start | Check pressure and filter monthly |
| Motor / reducer | Gear oil per nameplate | Oil bath | 4000-8000 h |
Fault quick-reference
| Symptom | Likely cause | Fix | Trip point |
| High main-bearing temp | Low oil / bad oil / no water | Top up, change oil, open cooling | >=70℃ |
| Excess vibration | Loose liner / bad ball mix / gear wear / loose base | Tighten, re-ball, repair gear, anchor | >11.2 mm/s |
| Coarser product | Worn balls / low filling / low speed | Re-ball, raise filling, check speed | - |
| Lower output | Worn liner / wrong circulating load / feed change | New liner, tune classifier, steady feed | - |
| Gear noise / pitting | Low spray / bad alignment / poor mesh | Fix spray, align, repair teeth | Stop on broken tooth |
| Feed-end powder leak | Failed seal | Replace seal kit | Stop on trunnion erosion |
| Slide-shoe scoring | Hydrostatic not built / film lost | Check pump and oil cleanliness | Stop on sharp temp rise |
| Motor overload | Over-filling / feed overload / low voltage | Lower filling, control feed, steady volts | >10% of rated |
Wear-part life ranges
- Liner (Hadfield ZGMn13): 6-12 months on hard rock, 12-24 on soft; rubber liner resists corrosion and cuts noise. - Grinding balls: 0.3-1.5 kg/t of ore, topped up by hardness and size. - Diaphragm: 12-24 months; worn slots raise return and coarsen product. - Main-bearing bush: 3-8 years with good lube; a scored bush needs full replacement. - Open girth gear: 8-15 years; repair once pitting passes 25% of the flank. - Feed-end seal: 6-12 months.
How to extend service life
- Sieve balls by tonnage and top up by size to keep filling and mix; do not wait for output to drop. - Run oil analysis (ferrography + viscosity) every 3-6 months to catch wear early. - Laser-align the pinion and hold axial misalignment within 0.15-0.20 mm; gear life can double. - Hold the circulating load between 150% and 250%; too low over-grinds and wastes liner, too high chokes classification. - Use soft start and ramp the load up to spare the tooth flank and bush from shock. - Keep one set of liners, a spare gear, a bush and seals on hand so change-outs never wait on shipping.
FAQ
<=55℃ is normal, 65℃ alarms, 70℃ must trip; running on past that scores the bush.
Bearing-housing velocity <=4.5 mm/s RMS is good; >7.1 mm/s alarms, >11.2 mm/s trips - find the cause.
Sieve a sample regularly and add the right diameters by what remains, holding 30%-45% filling - not by guesswork.
Hadfield steel 6-12 months on hard rock, longer on soft; judge by measured wear, not by calendar.
Main bearing oil every 4000-8000 h with analysis; open gear spray always on; grease points every 1-3 months.
First check spray and alignment, then contact pattern below 60% tooth height; repair once pitting passes 25%.
It erodes the trunnion and foundation; replace the seal the moment you see it.
Usually the hydrostatic lift never built or the film broke; check pump pressure and oil cleanliness first.
One liner set, a spare gear, a bush, seals and common bolts - that covers most downtime waits.
Ball top-up by tonnage, periodic oil analysis, laser pinion alignment, circulating load 150%-250%, soft start - do these five and life stretches clearly.
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