1. Main bearing temperature too high (>60°C)

Sign: Bearing temperature reading abnormally high, hot to the touch.
Solutions:

• Check if lubricant is degraded or insufficient; add or replace.
• Check if bearing clearance is too small or worn; readjust or replace bearing.
• Check if cooling water system is blocked or water flow low; clean piping.
• Check if shell deformation causes extra bearing load.

2. Motor current abnormally high

Sign: Ammeter reading continuously exceeds rated value, or current fluctuates sharply.
Solutions:

• Check if feed rate is too high; reduce feed.
• Check if grinding media charge exceeds limit; adjust filling ratio (typically 30–40%).
• Check if material moisture is too high causing pasting; adjust material or increase drying.
• Check if voltage is stable; troubleshoot power supply.

3. Severe vibration during operation

Sign: Obvious vibration of foundation or shell, sometimes with abnormal noise.
Solutions:

• Check if anchor bolts are loose; tighten.
• Check if shell connection bolts are broken or loose.
• Check gear mesh clearance and wear; adjust or replace.
• Check coupling alignment; realign.
• Check if grinding media or liner pieces have fallen off; stop and repair.

4. Abnormal noise (metallic impact or periodic loud sound)

Sign: Irregular steel ball impact sounds or regular loud noises from inside the mill.
Solutions:

• Check if material feed is too low or mill is running empty; adjust feed.
• Check if grinding media gradation is incorrect; add smaller balls or adjust mix.
• Check if liner bolts are loose or liners have fallen off; tighten or replace.
• Check if diaphragm plate is cracked or detached; stop and replace.

5. Significant drop in output

Sign: Finished product per unit time is more than 30% below normal.
Solutions:

• Check grinding media wear; add or regrade.
• Check if classifying equipment (screen, separator) efficiency has dropped; clean or adjust.
• Check if material hardness or size has changed; adjust process parameters.
• Check if ventilation (dry mill) or slurry flow (wet mill) is obstructed.

6. Product too coarse

Sign: Excessive coarse particles in discharge exceed specification.
Solutions:

• Increase grinding media charge or adjust gradation (increase small ball proportion).
• Increase grinding time or reduce feed rate.
• Check if diaphragm or discharge grate slots are too wide; replace.
• Check if dry classifier speed is too low; increase speed.

7. Product too fine (over-grinding)

Sign: Abnormally high fines content, even excessive sliming.
Solutions:

• Reduce grinding media filling ratio or increase large ball proportion.
• Increase feed rate or increase shell speed.
• Check if classifier is blocked or speed too high.
• For wet mill, check if slurry concentration is too low; increase appropriately.

8. Sudden molino stoppage (jamming)

Sign: Motor cannot start or stops suddenly during operation.
Solutions:

• Check if large metal pieces or debris entered the mill; remove manually.
• Check if slurry or material has agglomerated and blocked the diaphragm; clean.
• Check if main bearing has burnt; replace bearing bush and repair.
• Check power supply and motor protection devices.

9. Discharge contains many grinding media fragments

Sign: Broken steel balls or cylpebs found at discharge outlet.
Solutions:

• Check if grinding media quality is poor; replace with tougher media.
• Check if shell speed is too high causing excessive impact; adjust speed.
• Check if liner surface is uneven increasing wear; replace liners.
• Control feed size not too coarse.

10. Main bearing oil leakage or seal leakage

Sign: Lubricating oil seeping from bearing end cover or labyrinth seal.
Solutions:

• Replace aged sealing ring or felt.
• Check if oil level is too high; drain to specified level.
• Check if oil return hole is blocked; clear.
• Check if journal surface has scratches; polish.

11. Dust collector (dry mill) emitting dust

Sign: Visible dust emission from dust collector exhaust or shell leakage.
Solutions:

• Check if filter bags are damaged or detached; replace.
• Check if pulse jet cleaning system pressure is normal; adjust.
• Check if hopper has excessive accumulated dust; empty promptly.
• Check if ducting is damaged or leaking; weld repair.

12. Wet mill overflowing coarse particles (overflow type)

Sign: Overflow slurry contains many coarse particles.
Solutions:

• Reduce feed rate or increase slurry concentration.
• Check if overflow weir is worn causing lower height; repair.
• Increase steel ball charge or adjust gradation.
• Check if speed is too low causing poor discharge.

13. Local overheating of shell (dry grinding)

Sign: One area of shell significantly hotter than others, hot to touch.
Solutions:

• Check if internal diaphragm is broken causing material short-circuit; replace.
• Check if material moisture is too high causing adhesion; reduce moisture.
• Increase ventilation or use water spray cooling (cautiously for dry mill).
• Stop and check if grinding media has piled up.

14. Pitting or scoring on large/small gear meshing surfaces

Sign: Metal chips in gearbox oil; pitting or burn marks on tooth surfaces.
Solutions:

• Replace lubricating oil and improve oil quality.
• Check if tooth tip clearance and backlash are excessive; adjust center distance.
• Check if overload or impact load is too high; smooth feed.
• Ensure gear cover sealing to prevent dust ingress.

15. Liner cracking or premature wear

Sign: Abnormal internal noise; inspection reveals cracks or reduced liner thickness.
Solutions:

• Select high‑toughness alloy liners or ceramic liners.
• Check if grinding media gradation is too heavy; adjust.
• Check liner bolt preload uniformity.
• Avoid running empty or starting without material.

16. Low lubrication system pressure or oil flow interruption

Sign: Oil pressure gauge below set value, or flow switch alarms.
Solutions:

• Check if oil pump has failed; repair or replace.
• Check if oil filter is clogged; clean or replace element.
• Check for oil line leakage; tighten.
• Check if oil tank level is too low; top up lubricating oil.

17. Mill difficult to start or starting current stays high

Sign: Motor speed rises very slowly after closing; current stays at peak.
Solutions:

• Use turning gear to rotate shell, eliminating inertial resistance.
• Check if mill door not opened or brake not released.
• Check if voltage is below rated value.
• Reduce grinding media charge or use staged start.

18. Water or slurry leakage at shell end flange connection

Sign: Water or slurry seeping from joint between end cover and shell.
Solutions:

• Tighten flange bolts evenly in diagonal sequence.
• Replace aged sealing gasket (e.g., rubber asbestos gasket).
• Check if flange face is deformed or scratched; repair or apply sealant.
• Check if bolt loosening due to shell vibration; add lock washers.

19. Insufficient air pressure in dry mill system

Sign: Air pressure gauge reading below normal; reduced fine product; material accumulation inside.
Solutions:

• Check if fan inlet screen is clogged; clean.
• Check if fan belt slips or blades are worn; adjust or replace.
• Check if air duct leaks or is blocked with dust; repair or clean.
• Check if airlock valve of classifier leaks; repair.

20. Slurry concentration too low or too high (wet mill)

Sign: Concentration meter shows deviation from process requirement, causing fineness issues or poor discharge.
Solutions:

• Adjust water feed or material feed to maintain optimum concentration (typically 65–80% solids).
• Check if water addition valve is out of control; repair.
• Check if cyclone return sand water amount has changed; stabilize process.

21. “Ball coating” phenomenon (dry mill)

Sign: High temperature and poor ventilation; fine powder sticks to media and liners forming a cushion; drastic reduction in fine powder discharge.
Solutions:

• Add small amount of grinding aid (e.g., kerosene, ethylene glycol).
• Reduce feed material moisture (should be <1.5%).
• Increase ventilation or reduce material temperature.
• Temporarily reduce feed to allow mill to discharge adhered material.

22. “Pasting” phenomenon (wet mill)

Sign: Slurry too viscous; grinding media stuck and unable to fall properly; current drops.
Solutions:

• Increase slurry temperature or add dispersant (e.g., sodium silicate).
• Reduce feed rate; adjust water addition ratio.
• Check if plastic materials (clay) have entered; change material source.

23. Circumferential cracks on shell

Sign: Fine circumferential cracks on shell surface; even water/slurry leakage.
Solutions:

• Stop immediately; grind cracks and use ultrasonic testing to confirm depth.
• For non‑penetrating cracks, weld repair and heat treat.
• If cracks are penetrating or too long, replace shell section.
• Check if long‑term overload or uneven liner bolt preload existed.

24. Feed or discharge chute blockage

Sign: Material accumulation at feed or discharge opening, unable to flow normally.
Solutions:

• Stop and clear blockage.
• Check if material moisture is too high; increase drying or adjust process.
• Check if chute slope is too small; modify angle.
• Install vibrator or air cannon to assist material flow.

25. Frequent motor overload protection tripping

Sign: Thermal relay or overcurrent protection trips during operation; resets and runs briefly.
Solutions:

• Check if grinding media charge is excessive; reduce filling ratio.
• Check if voltage is too low; stabilize power supply.
• Check if motor bearing is damaged; replace.
• Check for frequent large lump feeding; improve screening.

26. Abnormal vibration or noise from reducer

Sign: Reducer housing vibrates noticeably; internal gear impact or bearing noise.
Solutions:

• Check reducer oil level and quality; replace with new oil.
• Check gear wear; replace if necessary.
• Check bearing clearance; adjust or replace bearings.
• Check coupling coaxiality; realign.

27. High differential pressure across baghouse dust collector (dry mill)

Sign: Inlet‑outlet differential pressure exceeds 1500 Pa; exhaust flow drops.
Solutions:

• Check pulse jet cleaning pressure; adjust.
• Check if bags are blinded; perform off‑line cleaning or replace.
• Check for condensation; add insulation or heating.
• Check if hopper dust discharge is timely.

28. Coarse overflow from hydrocyclone (wet mill)

Sign: Coarse particle fraction in cyclone overflow exceeds specification, affecting downstream separation.
Solutions:

• Increase cyclone feed pressure.
• Reduce apex diameter.
• Check if cyclone is severely worn; replace liner.
• Reduce mill feed rate; improve grinding fineness.

29. High‑pressure oil pump (hydrostatic bearing) cannot establish oil film

Sign: High‑pressure oil pressure fails to reach set value before mill start; main bearing may run dry.
Solutions:

• Check if high‑pressure oil pump rotates backward or lacks oil; correct.
• Check if check valve or relief valve is stuck; clean.
• Check if clearance between bearing bush and journal is excessive; adjust or repair.
• Check for oil line leakage.

30. Slurry/dust leakage through shell bolt holes

Sign: Slurry or dust seeping from bolt holes securing liners.
Solutions:

• Tighten nuts and apply sealant.
• Replace aged or damaged sealing gaskets.
• Check if bolts are broken; replace.
• Add rubber sealing ring between bolt head and shell.

31. Pneumatic clutch slipping or overheating

Sign: Mill start‑up time too long; clutch has burnt smell or smoke.
Solutions:

• Check if air pressure is insufficient; increase to rated pressure.
• Check if friction plates are excessively worn; replace.
• Check for air line leakage.
• Avoid frequent starting/stopping.

32. Low efficiency of dry classifier (separator)

Sign: Excessive fines in return (coarse) material; lower finished product yield.
Solutions:

• Adjust classifier speed or air volume.
• Check if distribution plate and guide vanes are worn; replace.
• Check if seal clearance is too large.
• Clean dust adhering to vanes.

33. Insufficient feed due to slurry pump wear (wet mill)

Sign: Pump discharge pressure drops; mill feed rate insufficient; output decreases.
Solutions:

• Replace pump wear‑resistant lining or impeller.
• Adjust clearance between impeller and casing.
• Check if suction line is blocked or leaking air.
• Appropriately increase pump speed.

34. High oil temperature in lubrication station (>55°C)

Sign: Tank temperature exceeds 55°C; oil quality degrades faster.
Solutions:

• Check if cooler is fouled or cooling water temperature/flow insufficient; clean or adjust.
• Check if oil pump has excessive internal leakage; repair.
• Check if overheating due to overload.
• Increase tank heat dissipation area or add cooling fan.

35. High temperature of shell sliding ring (sliding shoe)

Sign: Sliding shoe bearing temperature exceeds 70°C.
Solutions:

• Check sliding shoe pad clearance and contact surface.
• Increase oil supply pressure and flow rate of thin oil lubrication station.
• Check if dust enters lubricating oil due to poor shoe cover seal.
• Temporarily use external spray cooling.