5 early signs of bearing failure

Catch bearing problems before they take a machine down — here's what to watch for.

Bearings are one of the most common causes of unplanned downtime — and one of the most predictable. A failing bearing almost always announces itself weeks before it seizes, if you know what to listen for.

Here are the five signals that show up first — ordered roughly by how early they appear.

The very first stage of bearing damage — microscopic fatigue and lubrication breakdown — is invisible to vibration analysis but loud in ultrasound. A bearing that's 'starting to go' produces a characteristic hiss or crackle long before it gets rough to the touch.

• 1. Ultrasonic noise

As spalls form on the raceways, they excite the bearing's characteristic defect frequencies. Overall vibration rises first; a spectral view shows the peaks that identify which component — inner race, outer race or rolling element — is wearing.

• 2. Rising vibration at defect frequencies

A bearing running dry or starting to break down generates heat. Temperature is a lagging indicator — by the time the housing is noticeably hot, damage is underway — but it's a reliable confirmation signal alongside vibration.

• 3. Temperature creep

• 4. Lubrication problems
• Grease that's darkened, dried or contaminated with metal particles
• Leaking seals — lubricant leaving and dirt entering at the same time
• Over-lubrication, which causes its own heat and churning losses

A deteriorating bearing adds friction, and friction costs torque. Intermittent current spikes on the motor driving the shaft are often the last early warning before the vibration becomes audible.

• 5. Current spikes on the driving motor

Each of these signals appears well before catastrophic failure. A bearing swapped on a planned stoppage costs hours; one that seizes takes the shaft, the coupling and the weekend with it. Continuous monitoring catches the earliest signals — ultrasound and vibration — while there's still time to plan.

• Why it matters