Major causes of roller bearing failure and prevention tools

 Today, roller bearing mechanisms are used in thousands of industrial, automotive, marine and aerospace applications. Whether cylindrical, spherical, gear, tapered or needle, roller bearings work to reduce rotational friction to support radial and axial loads (see Figure 1).

 

Figure 1. Bearing shapes: a) deep groove ball bearing, b) angular contact ball bearing, c) self-aligning ball bearing, d) cylindrical roller bearing, e) tapered roller bearing, f) spherical roller bearing, g) needle roller bearing, h) thrust ball bearing. 

 

Lubrication is critical to roller bearing life

Roller bearing failure has the potential to shut down running equipment and possibly entire plant operations. Roller bearings require lubrication to reduce the metal-to-metal friction between the rolling and sliding contact areas. Letting lubrication-related tasks lapse can ultimately mean catastrophic equipment failure.

Lubricating helps disperse heat from the bearing, remove wear particles and contaminants from the rolling contact areas, protect against corrosion and increase bearing seal bonds.

Four of the top reasons roller bearings fail results from poor lubrication or lack thereof.

 

Lubricant contamination

As shown in Figure 2, the prime reason roller bearings fail to reach life expectancy is due to lubricant contamination from particles. To the naked eye, a lubricant sample might look clean, but in fact, contains tiny wear-causing contaminants, including dirt, dust, sand, metal shards and other elements. Pollutants can damage bearings, thus wearing them prematurely. Furthermore, once the roller bearing sustains damage, the condition is usually irreversible, and no amount of maintenance, except replacement, can restore the bearing to its original state.

 

Figure 2. Top reasons roller bearings fail.

 

Particles can be introduced in countless ways, including during lubricant production. The amount of debris in newly produced oil or grease can differ by as much as a factor of 1,000. Large quantities can contain even higher amounts. Particles can also be introduced during maintenance or replacement, or because of wear, fatigue, aging and imbalance caused by leaks, worn seals and other breaches.

Four principal ways to avoid particle contamination include:

1. Purchase lubricants from a reputable company. Information about the product should be readily available including specifications. Depending on the application, evidence should show that standards, such as IEC, ASTM, ISO or DIN, are up to date.
2. Store lubricants indoors and keep them away from heat and other possible sources of contamination. Lay drums horizontally. Select lubricant usage based on the purchase date, i.e., oldest to newest.
3. Test equipment for imbalance, misalignment and other conditions. Use vibration analysis, thermography and other proactive maintenance methods to prevent wear.
4. Ensure lubricant is clean. When replacing grease or oil, equipment should also be clean.

 

Indicators of emerging bearing failure

Regular preventive maintenance (PM) and predictive maintenance (PdM) strategies can help keep bearings operating. Although designed to last, roller bearings cannot rotate forever. Sooner or later, they experience material fatigue.

Evidence of bearing issues appears in many forms, including:

• Grooving: Contaminants wedged in soft cage material can incise grooves in rolling elements. Generates improper rolling contact geometry. Reduces bearing service life.
• Noise: Bearing damage can be distinguished by unusual yet characteristic noise using sound detection instruments during operation.
• Peeling: Caused by hairline cracks. Condition consists of small areas of flaking due to insufficient lubrication or infiltration of foreign matter.
• Spalling: Pitting or flaking away of bearing material. Primarily occurs on races and rolling elements. Always accompanied by an increase in vibration. Condition will continue to spread with ongoing operation.
• Overheating: Ring discoloration of rolling elements and cages from gold to blue. Temperatures over 400°F can anneal ring and rolling element metals, reduce bearing capacity and cause early failure. High temperatures can also degrade or destroy lubricant.
• Pitting: Small areas of flaking or peeling caused by hairline cracks. Condition may be caused by foreign matter infiltration or insufficient lubrication.
• Vibration: Bearing irregularities can be analyzed by measuring the vibrations of an operating machine using a frequency spectrum analyzer to calculate the magnitude of vibration and frequency distribution. Test results help determine the likely cause of the bearing abnormality.