A hot ball-mill slide-shoe bearing is usually the result of lubrication-film loss, cooling deterioration, abnormal shell/bearing geometry, contamination or excessive local loading. Diagnose the trend before adjusting anything: compare inlet and return oil condition, bearing temperature pattern, lubrication pressure and flow, cooling-water performance, shell axial position, pad contact and recent maintenance history. Do not treat temperature alone as proof of bearing damage; confirm whether the oil film and mechanical position are stable.
Find why one slide shoe, one side of a bearing, or the whole support is heating without damaging the pad, shell or lubrication system.
Use temperature trend, oil pressure/flow, supply-return temperature, cooling water, shell position, pad contact, vibration and oil cleanliness together.
Separate lubrication, cooling, geometry, load and contamination causes before changing alignment, viscosity or oil-system settings.
Fast diagnostic order
- Map the heat, do not chase one number: compare every shoe/pad temperature with load, oil supply/return temperature and the known healthy pattern.
- Prove lubrication circulation: verify pump state, oil level, pressure, flow/return behavior, filters and valve line-up.
- Separate common cooling from local loading: check cooler-water performance, then compare local hot spots with shell position and pad contact.
- Inspect oil and surfaces when evidence points inside: look for contamination, debris, wiping, scoring, blocked oil grooves and edge loading.
- Verify under rising load: trend temperature, oil condition, vibration and axial position until the thermal pattern stabilizes.
Capture the thermal and lubrication pattern before intervention
Record: each shoe/pad temperature and trend; oil supply and return temperature; lubrication pressure and available flow indication; pump and filter status; cooler-water inlet/outlet condition; mill load and product rate; shell axial position; recent start/stop sequence; vibration; any metallic debris or discoloration in the oil; and whether the temperature rise is sudden, gradual or load-dependent.
Compare with a known-good operating period at similar mill load. A single temperature number without the operating context can mislead the diagnosis.
1. Verify oil supply, pressure and actual circulation
Confirm the correct lubrication pumps are running, suction and discharge paths are open, filters are not in abnormal bypass, and the oil level is correct. A pressure indication alone does not prove adequate circulation through the bearing. Compare pressure with flow indication, return-oil behavior and the temperature response of the pad. If a pump changeover recently occurred, check valve positions and rotation. Inspect flexible lines and distribution manifolds for restrictions or leakage.
2. Check oil condition and viscosity state
Oil that is contaminated, oxidized, aerated or diluted can lose effective film strength even when the nominal grade is correct. Review laboratory trends for viscosity, water and wear debris where available. Inspect the reservoir for foaming, sediment and discoloration. If oil temperature has risen significantly, effective viscosity may fall; if the oil is abnormally cold, flow distribution can also change. Use the mill supplier’s lubricant specification rather than substituting a generic oil grade.
3. Verify the cooler and cooling-water path
A fouled oil cooler, low cooling-water flow, hot cooling-water supply or bypassed cooler can make both bearings run warmer. Compare oil temperature before and after the cooler and inspect water-side condition. If only one shoe is hot while common supply oil is normal, the problem is less likely to be the common cooler and more likely to be local flow, pad contact or mechanical loading.
4. Compare temperature across all shoes and bearing sectors
A localized hot sector is valuable evidence. One shoe heating more than the others may indicate uneven load sharing, restricted local oil distribution, pad damage or geometry change. Map the temperature pattern instead of reporting only the highest point. Where the bearing design provides individual temperature sensors, trend them together during load changes and after startup.
5. Check shell axial position and bearing geometry
Slide-shoe systems depend on the designed contact relationship between the shell/riding surface and the support pads. Abnormal axial movement, foundation settlement, shell deformation or maintenance-induced geometry changes can redistribute load. Review axial-position indication and recent alignment work. Do not move a bearing or foundation support based only on temperature; first confirm repeatable geometry evidence and compare with the OEM alignment procedure.
6. Inspect the pad and running surface during a safe shutdown
Where inspection is permitted, look for wiping, scoring, discoloration, embedded particles, edge loading and abnormal contact marks. Inspect oil grooves and feed holes for blockage. Check the shell/riding surface for scoring or pickup. Preserve photographs and identify the circumferential/axial location of the damage. A polished or overheated edge can indicate load concentration that will return if only the surface is dressed.
7. Correlate temperature with mill load, vibration and process events
If temperature rises only at high feed, heavy circulating load or after upset conditions, investigate whether the mill is carrying abnormal mechanical load. Compare motor current, vibration and process stability. If temperature remains high even at reduced load with normal oil conditions, a local mechanical or lubrication defect becomes more likely. Use cause-and-effect evidence rather than lowering production permanently without finding the cause.
Slide-shoe overheating diagnostic matrix
| Observed pattern | Likely direction | Priority check |
|---|---|---|
| All shoes warm together; supply oil also hot | Common cooling/oil-system issue | Cooler, water flow, reservoir temperature, pump circulation |
| One shoe rises while common oil remains normal | Local flow/load/contact issue | Local feed path, pad surface, geometry, load sharing |
| Temperature rise plus metallic debris | Active wear risk | Oil inspection, pad/running surface, controlled shutdown review |
| Temperature changes with axial position | Geometry/load redistribution | Axial movement, pad contact, alignment history |
| High temperature after lubrication maintenance | Oil/valve/flow configuration error | Grade, level, valve line-up, filter, pump rotation and flow |
Common mistakes
- Changing oil grade before proving a viscosity or contamination problem.
- Assuming pressure equals adequate oil flow.
- Moving the bearing to correct temperature without confirming geometry.
- Ignoring cooler-water deterioration when both supports heat together.
- Resetting alarms repeatedly without preserving the as-found trend.
Return-to-service verification
After corrective work, restart under the plant/OEM procedure and trend all shoe temperatures, supply-return oil temperature, lubrication pressure/flow, vibration and shell axial position as load increases. Acceptance means the repaired bearing reaches a stable repeatable thermal pattern consistent with the plant baseline, oil circulation remains healthy, no new debris appears, and temperature differences do not continue to diverge with load. If the pattern deteriorates again, stop treating it as a transient and reopen the mechanical diagnosis.
Frequently asked troubleshooting questions
What usually causes a ball-mill slide-shoe bearing to run hot?
Typical directions include inadequate oil circulation, hot or degraded oil, local flow restriction, cooling problems, pad/contact issues and abnormal shell or bearing geometry.
Does normal oil pressure prove the slide shoe has enough lubrication?
No. Pressure alone does not prove adequate flow through the pad. Compare pressure with flow indication, return-oil behavior and the local temperature pattern.
Why would one slide shoe heat while the others remain normal?
A local oil-feed restriction, pad damage, uneven load sharing or geometry change can create a single hot sector. Map all shoe temperatures rather than relying on one alarm point.
Related Infinity technical guides
References
Use the installed mill OEM documentation for slide-shoe pad clearances, lubrication-system settings, alarm/trip values, lubricant grade and alignment limits. Trend-based diagnosis should be compared with the plant’s known-good baseline under similar load.