Bearing Wear Identification and Prevention

Proper selection, handling, installation and maintenance are needed for reliable bearing operation. Based on industry published data and Regal Power Transmission Solutions compiled data, short bearing life is most often the result of issues related to lubrication, contamination, installation, misalignment, shaft lock or other application factors. The information provided is meant as a general guide to identify typical forms of wear that can occur in bearings. The causes and preventions listed are not a comprehensive list but address common examples for each wear type. Wear may occur from a single cause, or from multiple causes, therefore review all items listed. Experience is needed to correctly identify and resolve root cause especially when multiple types of wear are present.

Frosting

Also known as micro-spalling, it is a common form of wear that is typically observed in bearings over time. The frosted appearance can be due to either adhesive or abrasive wear to the material surface caused by insufficient lubrication film thickness and/or fine contamination. Continued use may result in surface initiated spalling.

Possible Causes

  • Inadequate Lubricant Properties
  • Lubrication Breakdown
  • Ineffective Re-lubrication
  • Contamination

Prevention

  • Review Lubrication Selection
  • Review Re-lubrication Frequency, Amount and Procedure
  • Review Seal Selection



Debris Denting

Plastic deformation of a material surface due to hard particles getting caught between the rolling elements and raceway. Particles could be from external contamination or from internal wear, such as metal fatigue spalling.



Possible Causes

  • External Contamination
  • Internal Wear
  • Ineffective Re-lubrication

Prevention

  • Review Seal Selection
  • Resolve Source of Internal Wear
  • Review Re-lubrication Frequency, Amount and Procedure





Surface Initiated Spalling

Metal fatigue that develops at a material surface that has worn, deformed, or been damaged. The metal flaking that occurs is a secondary form of wear due to stress concentrations at existing wear locations.                                                                                                     

Possible Causes

  • Wear or Debris Denting
  • Brinelling or False Brinelling
  • Inadequate Lubricant Properties
  • Ineffective Re-lubrication

Prevention

  • Determine Initial Source of Wear
  • Refer to Appropriate Prevention For Source of Wear
  • Review Lubrication Selection
  • Review Re-lubrication Frequency, Amount and Procedure 
See also Spalling




Fretting

This form of wear is initially an adhesive wear between two surfaces in contact (such as the inner ring bore and shaft) experiencing movement or vibration. As the surfaces wear, continued movement or vibration results in adhesive and abrasive wear. Oxidation or corrosion may occur on the worn surfaces.

Possible Causes

  • Vibration
  • Minute Relative Movement of Surfaces
  • Excess Clearance Between Bearing and Mating Components

Prevention

  • Reduce System Vibration and/or Imbalance
  • Review Shaft and Housing Fit-up





Loss of Lock

Scratching, gouging and general wear observed in the bore of an inner ring and outside diameter of a shaft are indications of loss of lock. Often times the set screw tips will also be worn. Fretting wear can sometimes be present on the surfaces and a precursor form of wear prior to the loss of lock.

Possible Causes

  • Improper Tightening of Locking Mechanism
  • Shafting Undersized, Worn or Damaged
  • Hardened or Stainless Shafting Reducing Set Screw Penetration or Holding
  • Frequent Start Stop Operation

Prevention

  • Refer to Installation Instructions
  • Use Calibrated Torque Wrench
  • Verify Shaft Tolerance, Replace Worn Shafting
  • Consider Alternate Locking Mechanism



Spalling

A form of metal fatigue due to cyclical high sub-surface stress conditions between the rolling elements and raceway. Spalling is typically caused by high loading conditions, pinching of the rolling element due to improper installation or alignment, or reaching the fatigue life of the material.

Possible Causes

  • High Load Condition
  • Loss of Radial Clearance
  • Misalignment or Distortion
  • Improper Bearing Selection

Prevention

  • Reduce Load
  • Use Bearing With More Capacity
  • Review Installation Method
  • Review Bearing Selection See also Surface Initiated Spalling



False Brinelling

A form of wear observed as single or multiple lines at rolling element spaced intervals. Similar to fretting, this form of wear is caused by vibration or minute relative motion between the rolling elements and raceways (Typically occurs when the bearing is not rotating). As the surfaces wear, continued movement or vibration results in adhesive and abrasive wear.

Possible Causes

  • Vibration
  • Minute Relative Movement of Surfaces
  • Small Oscillation Angle
  • Excess Bearing Clearance
  • Inadequate Lubricant Properties

Prevention

  • Reduce System Vibration and/or Movement
  • Review Bearing Selection
  • Review Lubrication Selection 
See also True Brinelling




True Brinelling

A form of wear observed as single or multiple lines at rolling element spaced intervals. This form of wear is caused by permanent metal deformation due to excessive loading that occurs when the bearing is not rotating. The depth and width of the lines can vary but are typically visible and can be felt.                                                                                                             

Possible Causes

  • Impact or Excessive Loading
  • Hammering Bearing Onto Shaft
  • Improper Equipment Handling

Prevention

  • Determine and Eliminate Source of Impact or Excessive Loading
  • Review Bearing Selection
  • Do Not Hammer Bearings Onto Shaft
  • Review Handling Procedures to Reduce Load on Bearing





Smearing

Surface smearing, peeling and skidding are forms of adhesive wear that occur during operating when lack of sufficient oil film thickness is present. Under these conditions sliding occurs between the rolling elements and raceways causing surface deformation, cold welding and/or material transfer.

Possible Causes

  • Inadequate Lubricant Properties
  • Lubrication Breakdown
  • Ineffective Re-lubrication
  • Mixing of Incompatible Lubricants
  • Insufficient Load at High Speeds
  • Sudden Acceleration / De-Acceleration

Prevention

  • Review Lubrication Selection
  • Review Re-lubrication Frequency, Amount and Procedure
  • Verify Lubrication Compatibility
  • Review Bearing Selection 




Thrust Load

For a single row bearing, wear would be observed offset from the center of the raceway to one side. For a two row bearing, wear would be predominantly on one raceway. Most bearings are designed to support some thrust load. Excessive thrust load can cause wear on the edge of the raceway or spalling.

Possible Causes

  • Thrust Load Applied to Bearing
  • Linear Shaft Expansion
  • Frame Distortion or Flexure
  • Preload During Installation

Prevention

  • Reduce Amount of Thrust Load
  • Review if Expansion Bearing is Needed
  • Review Installation Procedure to Eliminate Source of Preload
  • Review Bearing Selection 




Misalignment

Wear present on the raceways traveling from side to side due to improper alignment at installation or machine operating characteristics. Static misalignment creates a fixed skew between the inner and outer rings. Dynamic misalignment creates a variable skew due to system imbalances.

Possible Causes

  • Shaft or Housing Misalignment
  • Uneven Mounting Surfaces
  • Frame Distortion or Flexure
  • Bent or Deflecting Shaft
  • System Imbalance

Prevention

  • Review Alignment at Installation
  • Mounting Surfaces Should be Clean and Flat
  • Replace Damaged Shafting
  • Review Bearing Selection




Corrosion

Deterioration of material properties due to a chemical reaction. The rate and type of corrosion depends on many factors such as material, chemical, temperature and contact method. Proper bearing selection should balance corrosion resistance with material strength, durability, sealing and lubrication.

Possible Causes

  • Insufficient Sealing
  • Inadequate Lubricant Properties
  • Ineffective Re-lubrication
  • Material Selection

Prevention

  • Review Seal Selection
  • Shield or Cover Bearing To Minimize Contact With Moisture
  • Review Lubrication Selection
  • Review Re-lubrication Frequency, Amount and Procedure
  • Review Bearing Selection
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