Bearings are critical components of machines and with proper performance monitoring, imminent failures can be identified and corrected. However, without a monitoring program in place, and subsequent corrective actions taken, a single bearing failure can result in full machine shutdown and countless hours of lost production.

Bearing monitoring is guided by three main senses: sight, sound and touch. Basic monitoring is conducted through elemental observations. However, many highly sensitive tools are available that amplify these observations so they are more noticeable, recordable, and include basic logic to assist with warning identification.

Visual Monitoring
Monitoring bearings visually through classical methods include observing lubricant condition, corrosion, and deterioration. Mounted bearings that are lubricated properly will purge grease from their seals. The condition of the grease upon purging can indicate improper relubrication intervals and/or contamination. Dark, cakey or milky grease are visual signs that relubrication intervals and procedures may be improved.

Evidence of corrosion is a valuable monitoring tool as well. High levels of corrosion can degrade material strength and performance. Deterioration of the surface, seals, or obvious physical dimensional characteristics should also warrant further investigation. These observations are often signals of wear, heat and other abnormal performance prior to total bearing failure.

Several monitoring tools commonly available to leverage visual observations include site gauges for oil lubricated bearings, and thermal imaging guns. Bearings that are lubricated by oil rather than grease are often fitted with site gauges, which will give an indication of the presence of oil and the quantity of oil available to the bearing. These gauges are practical and inexpensive.

Audible Monitoring
Traditionally, audible monitoring is one of the most common methods of monitoring machinery because odd noises are obvious indicators of improper operation, even to the untrained user. It is conducted quickly through an operator’s daily routines. After all, if a bearing within the machine doesn’t sound well it usually isn’t well.

The main problems with bystander audible observations is that (1) it usually identifies the later stages of bearing failure, when planning downtime for bearing replacement is impractical and (2) when audible feedback of a single bearing is masked by the overall noise of its environment. That’s when instruments such as stethoscopes (with amplification) and decibel level meters are advantageous. Both tools are available with a wide range of features that include quantified readings and recording features so bearing performance can be trended. These tools are also more useful at identifying improper operation at a less threatening stage of failure.

Bearings should run quiet and smooth; anything different will likely reflect a flaw or a problem with the bearing itself. Noises such as grinding or banging should be investigated quickly. These noises may indicate complete bearing failure and continued use may lead to catastrophic failure and/or damage to neighboring equipment. Bearing noises such as light clicking and squealing may indicate looseness, faults or skidding and should be inspected for cause and remedy.

Audible evaluation is not as sensitive as other monitoring techniques. It is primarily a method of identifying a failure more so than identifying poor performance. Additionally, audible monitoring in the early stages of failure is more noticeable at higher operating speeds than lower speeds.

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