Lubrication Failure Cause Bearing Failure

Bearings fail for many reasons:

• Improper lubrication: 40% to 50%
• Improper mounting: 25% to 30%
• Other causes: approximately 20%
• Reaching the natural fatigue limit: less than 10%

Lubricant Selection

• Without lubrication, bearings can be expected to fail early and possibly cause other equipment to fail. The three main concerns with bearing lubrication are:
  • Specifying the right amount – Rolling element bearings operate at their optimum temperature when the minimum amount of lubricant is used.
  • Specifying the right type – Rolling element bearings can be lubricated with grease or oil. In special cases, solid lubricants can be used.
  • Keeping the lubricant clean.
• Choice of lubricant depends on conditions such as operating temperature, rotating speed, loads and the
• Grease lubrication should be used when the bearing operates under normal speeds and temperatures. Grease has several advantages over oil, including simpler and less expensive application procedures, better adhesion, and improved protection against moisture and contaminants.
• Oil is the preferred lubricant when speed or operating conditions preclude the use of grease or where heat must be transferred from the bearing.

Lubricant Viscosity 

• Required viscosity depends on operating temperature. Inadequate lubricant viscosity appears as a highly glazed or glossy surface. As damage progresses, the surface appears frosty and eventually spalls.
• Smearing is a form of surface damage caused when two surfaces slide and the lubricant cannot prevent adhesion of the surfaces. Minute pieces of one surface are torn away and rewelded to either surface.
• Grooving also results from inadequate lubrication. The areas subject to sliding friction, such as locating flanges and the ends of rollers in a roller bearing, are the first parts affected.
• Inadequate flow in a circulating oil system can cause failures of tapered roller bearings. The area between the guide flange and the large end of the roller is subject to sliding motion and is more difficult to lubricate than areas under rolling motion. Therefore, some of the rollers can weld themselves to the guide flange.

Leaky Seals 

• Bearing seal leaks can be traced to three basic causes:

1. Condition and size of the shaft and housing bore
2. Poor installation practices
3. Contamination

• The most common cause is a worn or scored shaft, most often the result of abrasion caused by contamination. The shaft should be replaced or repaired to prevent seal damage.