1. Lubrication Failure

According to a recent study, up to 80 percent of bearing failures are caused by improper lubrication. This includes insufficient lubrication, use of improper lubricants or excessive temperatures that degrade the lubricant.

What to Look for

Look for discoloured rolling elements (such as blue or brown) and rolling-element tracks as well as overheating or excessive wear in the bearing.

How to Fix it

Use the appropriate type and correct amount of lubricant, avoid grease loss, and follow appropriate relubrication intervals.

2. Contamination

Contamination is caused by foreign substances getting into bearing lubricants or cleaning solutions. These include dirt, abrasive grit, dust, steel chips from contaminated work areas and dirty hands or tools.

What to Look for

Watch for denting of rolling elements and raceways that cause vibration.

How to Fix it

Filter the lubricant and clean work areas, tools, fixtures and hands to reduce the risk of contamination.

3. Improper Mounting

In most instances, bearings should be mounted with a press fit on the rotating ring.

What to Look for

A number of conditions can cause denting, wear, cracked rings, high operating temperatures, early fatigue and premature failure of bearings. These include mounting bearings on shafts by applying pressure or blows to the outer race, mounting bearings into a housing by pressing on the inner ring, loose shaft fits, loose housing fits, excessively tight fits, out-of-round housings and a poor finish on the bearing seat.

How to Fix it

Follow proper mounting instructions and provide training to ensure all employees understand the difference between a properly and improperly installed mounting.

4. Misalignment

Bent shafts, out-of-square shaft shoulders, out-of-square spacers, out-of-square clamping nuts and improper installation due to loose fits can cause misalignment, which may result in overheating and separator failure.

What to Look for

A wear path that is not parallel to the raceway edges of the non-rotating ring should be noted.

How to Prevent it

Inspect shafts and housings for runout of shoulders and bearing seats, and use precision-grade locknuts.

5. Corrosion

Moisture, acid, low-quality or broken-down grease, poor wrappings and condensation from excessive temperature reversals can cause corrosion that is abrasive to the finely finished surfaces of ball and roller bearings.

What to Look for

Look for red and brown stains or deposits on rolling elements, raceways or cages, as well as increased vibration followed by wear, an increase in radial clearance or loss of the preload.

How to Fix it

Divert corrosive fluids away from bearing areas. Select integrally sealed bearings and consider external seals for particularly hostile environments. Using the proper bearing material, such as stainless steel, can help if you cannot avoid a corrosive environment.

6. Electrical Damage (Fluting)

Constant passage of alternating or direct current, even with low currents, can lead to electrical damage.

What to Look for

Brownish marks may be observed parallel to the axis on a large part of the raceway or covering the entire raceway circumference.

How to Fix it

Prevent electrical currents from flowing through the bearing by grounding or using insulated bearings.

7. Overheating

Overheating is generally the result of excessive operating temperatures and improper lubrication. High temperatures can cause grease to bleed (purge the oil), which reduces the lubricant’s efficiency. In elevated temperature conditions, oxidation can lead to the loss of lubricating oils from the grease, leaving a dry, crusty soap that can seize the bearing. Higher temperatures also reduce the hardness of the metal, causing early failure.

What to Look for

Note any discoloration of the rings, rolling elements and cages. In extreme cases, the bearing components will deform. Higher temperatures can also degrade or destroy the lubricant.

How to Fix it

Thermal or overload controls, adequate heat paths and supplemental cooling are among the best options to mitigate overheating.

8. Excessive Loads

Putting too much load on a bearing is another common cause of failure.

What to Look for

You may see heaving rolling-element wear paths, evidence of overheating and widespread fatigue areas.

How to Fix it

Reduce the load or consider a redesign using a bearing with greater capacity.

9. Improper Storage and Handling

Improper storage exposes bearings to dampness and dust. Storing bearings in excessively high temperatures can also degrade a grease’s shelf life, so always check with the grease manufacturer for storage specifications. Handling bearings by opening boxes and tearing wrappings prematurely can let in dirt and expose bearings to corrosive elements.

What to Look for

Watch for dampness and temperatures that can cause rust and/or uncovered bearings in a storage area.

How to Fix it

Store bearings in a dry area at room temperature. Always cover bearings to keep them clean while in storage and take them to the installation site before unwrapping.

10. Fit

A tight fit can be caused by excessive loading of the rolling element when interference fits exceed the radial clearance at operating temperatures. Micro-motion between fitted parts where the fits are too loose in relation to the acting forces may result in a loose fit.

What to Look for

For a tight fit, look for a heavy rolling-element wear path in the bottom of the raceway, overheating or an inner-ring axial crack. For a loose fit, note any fretting (generation of fine metal particles), which leaves a distinctive brown color. Wear at the fitting surfaces can cause noise and runout problems.

How to Fix it

Make sure a proper clearance is selected to avoid fit issues. Refer to the manufacturer’s installation guide.

Preventing Failures

By becoming aware of the different problems that can cause a bearing failure and the signs to look for, you have already taken a big step toward limiting machine failures. Of course, you don’t have to wait for the symptoms of a bearing failure to take action. 

Regular preventive measures can keep your bearings at peak performance for as long as possible, saving your business, time and money.