Quick answer
If a ball‑mill trunnion shows a consistent temperature difference between the left and right bearings, start by confirming sensor accuracy, then verify lubrication flow, alignment, and load distribution. Isolate the mill, check bearing oil temperature and pressure, inspect for contamination or wear, and compare the readings to the OEM‑specified limits. Correct the root cause before returning the mill to service.
Problem / Job
During routine monitoring a ball‑mill trunnion bearing temperature sensor on the left side reads higher than the right side. The variance may indicate bearing distress, lubrication deficiency, mis‑alignment, or uneven load. The goal is to diagnose the cause, verify safe operating conditions, and implement corrective action.
Evidence
Typical data set: left bearing 85 °C, right bearing 70 °C, oil pressure within normal range, vibration within baseline, no recent maintenance. Sensor diagnostics show no fault codes. The mill is operating at rated speed and load.
Decision
Proceed with a structured isolation, inspection, and verification sequence. If the temperature differential exceeds the OEM‑defined acceptable delta, schedule corrective maintenance; otherwise, continue monitoring while confirming sensor integrity.
7‑Step Diagnostic Workflow
- Secure Isolation and LOTO
Verify that the mill is stopped, power is isolated, and lock‑out/tag‑out (LOTO) procedures are applied according to site safety standards. Depressurize hydraulic circuits and bleed residual energy from the trunnion drive. - Confirm Sensor Integrity
Disconnect the temperature transmitters and perform a bench calibration using a calibrated thermometer. Compare the sensor output to the reference temperature. Replace any sensor that fails calibration. - Review Operating Data
Pull the last 24‑hour trend for bearing temperature, oil pressure, vibration, and mill load. Note any spikes, gradual drifts, or correlation with load changes. Verify that the OEM‑specified temperature delta is not exceeded. - Inspect Lubrication System
Check oil temperature at the supply point, flow rate, and pressure gauges. Sample oil for contamination, water ingress, or metal particles. Ensure that the oil filter is clean and that the circulation pump is operating within its design parameters. - Examine Bearing Condition
With the mill still isolated, remove the bearing housings according to the manufacturer’s disassembly procedure. Visually inspect raceways, rollers, and cages for wear, scoring, or discoloration. Measure clearance and compare with OEM tolerances. - Assess Alignment and Load Distribution
Use a dial‑indicator or laser alignment tool to verify that the trunnion shaft is concentric with the bearing housings. Check that the mill shell is evenly supported and that any hydraulic or mechanical load‑balancing devices are functioning correctly. - Document Findings and Implement Corrections
Record all measurements, observations, and corrective actions in the maintenance log. Replace faulty sensors, replenish or replace oil, re‑align the trunnion, or replace worn bearings as required. Remove LOTO only after a full functional test confirms normal parameters.
Diagnostic Matrix
| Evidence | Likely Direction | Next Check / Action |
|---|---|---|
| Temperature delta > OEM‑specified | Potential bearing overheating | Validate sensor accuracy (Step 2) |
| Oil temperature normal, pressure low | Insufficient lubrication flow | Inspect pump, filters, and line blockages (Step 4) |
| Oil temperature high, pressure normal | Oil degradation or excessive heat load | Sample oil, replace if contaminated (Step 4) |
| Vibration increase on left side | Mis‑alignment or bearing wear | Perform alignment check (Step 6) and visual bearing inspection (Step 5) |
| Uneven shell support pressure | Load imbalance across trunnion | Verify hydraulic load‑balancing devices, adjust as needed (Step 6) |
| Metal particles in oil sample | Early bearing wear or cage failure | Disassemble bearing, inspect raceways, replace if wear exceeds limits (Step 5) |
| No abnormal data, sensor calibrated | Transient operational condition | Continue monitoring for at least two full production cycles |
Verification & Acceptance Criteria
After corrective actions, the following measurable conditions must be satisfied before the mill is returned to service:
- Both left and right bearing temperatures are within the OEM‑specified operating range and the temperature differential is less than the OEM‑defined delta (verify against the latest OEM data sheet).
- Oil temperature at the bearing inlet is stable and does not exceed the OEM‑recommended maximum for the operating load.
- Oil pressure at each bearing meets the minimum design pressure specified by the bearing manufacturer.
- Vibration amplitude at the bearing locations returns to baseline levels recorded during normal operation.
- Oil analysis shows no increase in wear metals, water, or contaminants compared with the previous acceptable sample.
- Alignment measurements are within the tolerance band defined by the trunnion design (typically a few thousandths of an inch over the bearing span).
- All LOTO devices are removed only after a functional test confirms that temperature, pressure, and vibration remain within the accepted limits for at least one full production cycle.
Common Mistakes & Repeat‑Failure Traps
- Skipping sensor verification – Replacing a bearing while a faulty temperature transmitter remains in service can mask the real problem and lead to premature failure.
- Ignoring oil quality – Continuing operation with degraded oil can accelerate bearing wear even after alignment is corrected.
- Partial LOTO removal – Re‑energizing any part of the drive system before the bearing temperature stabilizes can cause a rapid temperature surge.
- Over‑tightening bearing housings – Excessive preload can generate heat unrelated to lubrication, leading to false diagnosis of oil flow issues.
- Failing to rebalance load – After replacing a bearing, neglecting to verify hydraulic or mechanical load‑balancing devices can recreate the original temperature differential.
- Inadequate documentation – Not recording oil sample results or alignment measurements makes trend analysis impossible, increasing the risk of repeat incidents.
- Relying on a single data point – A one‑time temperature spike may be a transient event; decisions should be based on trend data and corroborating evidence.
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