Why bearings fail early (and what the technician controls)

Every bearing leaves the factory with a calculated life. In practice, many of them are replaced long before that. The reason is rarely a manufacturing defect: almost always, the life was cut short by something that happened during lubrication, mounting or operation. And almost all of that is in the hands of the people doing the maintenance.

The five most common causes

1. Wrong lubrication

It's the most frequent cause, and people get it wrong in both directions.

• Too little grease: the lubricant film breaks, there's metal-to-metal contact and the raceway starts to wear.
• Too much grease: the bearing churns the grease, heats up, the grease breaks down faster and the seal can blow out. Packing the housing to the top isn't care, it's a problem.
• Wrong or mixed grease: greases with different thickeners can be incompatible. Mixed, they soften or harden. Use the specified grease and label the lubrication point with it.

To know how much to add when relubricating, a rule of thumb widely used by manufacturers is:

Grease quantity (g) = 0.005 × D × B

D is the outside diameter and B the width of the bearing, in millimeters. For a 6310 (D = 110 mm, B = 27 mm): 0.005 × 110 × 27 ≈ 15 g. Now find out how many grams your grease gun delivers per stroke: give it 10 strokes into a plastic bag and weigh it. If it comes to 15 g, each stroke is 1.5 g and the 6310 takes 10 strokes. Write that in the plan; don't leave it to "judgment".

2. Contamination

Dust, water and process residue act like sandpaper between the balls and the raceways. The most common ways in come from the job itself:

• Grease fitting not wiped before greasing: the dirt on the fitting goes in with the grease.
• Grease stored open, or a dirty spatula.
• A new bearing taken out of its packaging long before mounting and left on the bench.
• A cleaning water jet aimed straight at the bearing housing.
• A reused seal or lip seal.

3. Mounting

Many failures in the first weeks of use are blamed on a bad part, when the problem was the mounting:

• Hammering the bearing directly, or force passing through the balls (pushing the outer ring to fit the inner ring on the shaft), dents the raceways.
• Heating with a torch creates overheated spots and changes the material. Use an induction heater with temperature control; in general, don't go above 110 to 120 °C.
• Wrong fit on the shaft or in the housing: too tight removes the internal clearance; too loose lets the ring spin and wear the seat.
• Damaged shaft or housing: measure before mounting. An out-of-round seat kills the new bearing.

4. Misalignment and unbalance

The bearing suffers for the whole assembly. A misaligned coupling, a pulley out of line, an overtightened belt, an unbalanced rotor and soft foot (a base that doesn't sit evenly) all raise the load and shorten the life fast. Alignment with a dial indicator or laser, after every motor or pump replacement, is part of the job, not an extra. Often the bearing is the victim and the cause is in another component.

5. Electrical current

In motors driven by a variable frequency drive, voltage can build up on the shaft and discharge through the bearing. Each discharge melts a microscopic spot on the raceway. Over time, regular ridges appear, like a washboard (what's called fluting), and the bearing gets noisy. Solutions include a shaft grounding brush or ring, an insulated or hybrid bearing, and proper grounding of the motor and drive.

Read the bearing that came out

The replaced bearing is the best clue to the cause. Don't throw it away before you look at it. Clean it, open it if you can and compare:

What you see	Likely cause
Bluish or darkened raceways and balls, dry or burnt grease	Lack of lubrication or overheating
Marks spaced exactly like the balls	Impact during mounting, or vibration while the equipment was stopped
Regular, fine, parallel ridges on the raceway	Electrical current passing through
Wear band off-center or slanted on the raceway	Misalignment or excessive axial load
Small craters and scratches, grease with particles	Contamination
Rust, dark corrosion stains	Moisture or water
Shiny or worn ring seat	Loose fit: the ring spun on the shaft or in the housing

Take photos and record what you found on the work order. Three replacements with the same mark on the same bearing housing call for a recurring failure analysis, not a fourth bearing.

Checklist for a good replacement

• Confirm the bearing and grease part numbers before you take anything apart.
• Measure the shaft and housing; reject a damaged seat.
• Open the new bearing only when it's time to mount it.
• Mount with the proper tool: induction heater or mounting sleeve, never a hammer directly.
• Add the right amount of grease, not "until it's full".
• Replace seals and lip seals.
• Align the coupling or pulley and check for soft foot.
• Run it, watch temperature and noise, and only then release it.
• Keep and photograph the bearing that came out; record the cause on the work order.

In taskfield, the lubrication plan can record the point, the grease and the quantity in grams or strokes, and the technician attaches photos of the removed bearing to the work order itself, from a phone.