Bearing (1)

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Bearing Failure: Causes and CuresBearing Failure: Causes and Cures

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Excessive LoadsExcessive Loads

• Excessive loads usually causepremature fatigue. Tight fits,brinelling and improperpreloading can also bring aboutearly fatigue failure.

• The solution is to reduce theload or redesign using a bearingwith greater capacity.

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OverheatingOverheating

• Symptoms are discoloration of therings, balls, and cages from gold toblue.

• Temperature in excess of 400F cananneal the ring and ball materials.

• The resulting loss in hardnessreduces the bearing capacitycausing early failure.

• In extreme cases, balls and ringswill deform. The temperature risecan also degrade or destroylubricant.

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TrueTrue Brinelling Brinelling

• Brinelling occurs when loads exceedthe elastic limit of the ring material.

• Brinell marks show as indentations inthe raceways which increase bearingvibration (noise).

• Any static overload or severe impactcan cause brinelling.

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FalseFalse Brinelling Brinelling

• False brinelling - elliptical wearmarks in an axial direction ateach ball position with a brightfinish and sharp demarcation,often surrounded by a ring ofbrown debris - indicatesexcessive external vibration.

• Correct by isolating bearingsfrom external vibration, andusing greases containingantiwear additives.

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Normal Fatigue FailureNormal Fatigue Failure

• Fatigue failure - usually referred to asspalling - is a fracture of the runningsurfaces and subsequent removal ofsmall discrete particles of material.

• Spalling can occur on the inner ring, outerring, or balls.

• This type of failure is progressive andonce initiated will spread as a result offurther operation. It will always beaccompanied by a marked increase invibration.

• The remedy is to replace the bearing orconsider redesigning to use a bearinghaving a greater calculated fatigue life.

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Reverse LoadingReverse Loading• Angular contact bearings are

designed to accept an axial loadin one direction only.

• When loaded in the oppositedirection, the elliptical contactarea on the outer ring istruncated by the low shoulderon that side of the outer ring.

• The result is excessive stressand an increase in temperature,followed by increased vibrationand early failure.

• Corrective action is to simplyinstall the bearing correctly.

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ContaminationContamination• Contamination is one of the

leading causes of bearingfailure.

• Contamination symptoms aredenting of the bearingraceways and balls resultingin high vibration and wear.

• Clean work areas, tools,fixtures, and hands helpreduce contamination failures.

• Keep grinding operationsaway from bearing assemblyareas and keep bearings intheir original packaging untilyou are ready to install them.

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Lubricant FailureLubricant Failure• Discolored (blue/brown) ball tracks

and balls are symptoms of lubricantfailure. Excessive wear of balls,ring, and cages will follow, resultingin overheating and subsequentcatastrophic failure.

• Ball bearings depend on thecontinuous presence of a very thin-millionths of an inch - film oflubricant between balls and races,and between the cage, bearingrings, and balls.

• Failures are typically caused byrestricted lubricant flow orexcessive temperatures thatdegrade the lubricant’s properties.

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CorrosionCorrosion• Red/brown areas on balls,

race-way, cages, or bands ofball bearings are symptoms ofcorrosion.

• This condition results fromexposing bearings to corrosivefluids or a corrosiveatmosphere.

• In extreme cases, corrosioncan initiate early fatiguefailures.

• Correct by diverting corrosivefluids away from bearingareas and use integrallysealed bearings wheneverpossible.

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MisalignmentMisalignment• Misalignment can be detected on

the raceway of the nonrotating ringby a ball wear path that is notparallel to the raceways edges.

• If misalignment exceeds 0.001in./in you can expect an abnormaltemperature rise in the bearingand/or housing and heavy wear inthe cage ball-pockets.

• Appropriate corrective actionincludes: inspecting shafts andhousings for runout of shouldersand bearing seats; use of singlepoint-turned or ground threads onnon hardened shafts and groundthreads only on hardened shafts;and using precision grade locknuts.

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Loose FitsLoose Fits• Loose fits can cause relative

motion between mating parts. Ifthe relative motion betweenmating parts is slight butcontinuous, fretting occurs.

• Fretting is the generation of finemetal particles which oxidize,leaving a distinctive browncolor. This material is abrasiveand will aggravate thelooseness. If the looseness isenough to allow considerablemovement of the inner or outerring, the mounting surfaces(bore, outer diameters, faces)will wear and heat, causingnoise and runout problems.

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Tight FitsTight Fits• A heavy ball wear path in the

bottom of the raceway aroundthe entire circumference of theinner ring and outer ringindicates a tight fit.

• Where interference fits exceedthe radial clearance atoperating temperature, theballs will become excessivelyloaded. This will result in arapid temperature riseaccompanied by high torque.

• Continued operation can leadto rapid wear and fatigue.

• Corrective action includes adecrease in total interference.

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