Bearing problems rarely happen without warning. Before a failure actually occurs, the bearing usually gives clear signals – a rise in temperature, a change in vibration, or a new noise. If you can spot these clues early and interpret them correctly, you can move from reactive repair to planned maintenance and avoid costly shutdowns.
Condition monitoring does not have to be complicated. With a simple routine of measuring temperature, vibration, and noise, and recording the data systematically, your maintenance team can detect deterioration at an early stage. The cost of an intervention at that point is usually a fraction of what a full breakdown would cost.
Understanding the three key indicators
1. Temperature
Temperature is a broad indicator of friction and heat dissipation. Under normal conditions, the bearing temperature should level off and stay within 40°C above the ambient (or the limit specified for your equipment).
If the temperature keeps climbing with no sign of stabilisation, suspect poor lubrication, excessive preload, overload, or blocked cooling paths.
You can check surface temperature with an infrared gun or a fixed thermocouple. The important thing is the trend – a steady rise of 8–10°C above the usual baseline, even if it is still below the alarm threshold, warrants further investigation.
2. Vibration
Vibration reflects the mechanical condition of the rotating assembly. A healthy bearing produces a steady, low‑level vibration with no spikes.
If the amplitude increases notably, or if you see sudden impulsive shocks, there may be surface wear, spalling, fatigue cracks, looseness, or misalignment.
For daily checks, a simple vibration pen or hand‑held meter can give you velocity or acceleration readings. If you have access to a spectrum analyser, you can identify characteristic frequencies (ball‑pass frequency, outer‑race frequency, etc.) to pinpoint the defective part. Again, watch the trend – a single high reading might be a fluke, but a consistent upward drift is a red flag.
3. Noise
Acoustic signals carry a wealth of information. A healthy bearing makes a smooth, uniform "rustling" sound as the rolling elements pass.
A high‑pitched metallic squeal usually means the oil film has broken down due to lack of lubrication.
A periodic "clunk" or "thump" suggests a localised dent or pit on the raceway or a rolling element.
A low‑frequency rumble often indicates excessive internal clearance or a loose fit.
Use a stethoscope or a listening rod placed directly on the bearing housing. For a more advanced approach, record the sound and compare it to a baseline recording made when the bearing was new.
Building a practical monitoring routine
1. Establish a baseline
After installing a new bearing or commissioning a new machine, take readings for a week under normal operation. Record the average temperature, vibration level, and sound character. This becomes your reference.
2. Stick to a fixed route and schedule
Classify your machines by criticality – daily checks for key units, weekly for the rest. Always measure at the same marked points on the housing so the data stay comparable.
3. Follow the "look‑listen‑feel‑measure" approach
Look at the grease colour, any leaks, or discolouration.
Listen with a stethoscope for changes in pitch or rhythm.
Feel (carefully) the housing temperature with the back of your hand or an infrared device.
Measure the vibration and temperature precisely with your instruments.
4. Keep trend charts
Log every reading in a spreadsheet or a dedicated software. Plot temperature and vibration against time. If you see three consecutive increases, schedule an inspection even if the absolute values are still within limits – the trend is more important than the number.
Quick comparison table
| Parameter | Normal condition | Red‑flag change | Likely cause |
|---|---|---|---|
| Temperature | Stable, below limit | Continuous rise >5°C above baseline | Lubrication failure, overload, tight clearance |
| Vibration (velocity) | Steady, low level | 20% above baseline | Wear, pitting, looseness, misalignment |
| Noise | Smooth "rustling" | Squeal, periodic thump, deep rumble | Dry running, fatigue spall, excessive clearance |
Final remarks
Condition monitoring is all about trends, not absolute numbers. A disciplined routine of regular checks and data recording will give you a feel for the "health signature" of each bearing. Cross‑checking temperature, vibration, and sound against each other helps avoid false alarms. Catching a problem early and acting on it is always cheaper – and safer – than waiting for the bearing to destroy itself and take the machine down with it.
