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Generating Insights: Best practices for re-lubricating alternator bearings

Grease is a form of lubrication that is fundamental to the operation and longevity of rolling element bearings. This form of lubrication reduces direct metallic contact between the bearing’s raceways, rolling elements and cage. It also helps to prevent foreign material from entering the bearing while guarding against corrosion or rusting and helps to discharge frictional heat. In turn, this helps to extend the bearing life significantly. Therefore it is critical that an appropriate re-greasing regime is controlled, monitored and checked on a regular basis.

There are various methods and many types of re-greasing equipment currently used today. However, the accuracy and method of application varies drastically. In too many cases, lubrication methods are inadequate and result in either too little grease or too much grease. In either case resulting in reduced bearing life.

The best method to re-lubricate bearings is to use a calibrated battery powered grease gun such as the example shown below. This system provides mobility, accuracy of grease dispensed with digital meter reading and ease of operation.

Figure-1-Calibrated-battery-powered-grease-gun

If standard hand pump grease guns are to be used, it is vital to make sure the correct amount of grease has been dispensed. This can be done by weighing the complete grease gun before and after the re-grease.

For more complex and remote systems, there are various auto re-grease system available on the market today. However, it is vital that consideration of the type of grease used, the method of pumping, the condition/environment the grease is stored and the distance the system is from the bearings is reviewed and engineered correctly.

Bearing maintenance

All STAMFORD and AvK products that have re-greasable bearings will have a label fixed to the end plates above the bearings giving information about the bearing grease type, re-lubrication frequency and quantities.

It is recommended to have a dedicated grease gun for alternator bearing re-lubrication only.

Never mix lubricant types.

As per the Installation, Service & Maintenance manuals, it is vital that the grease, grease gun, grease nozzle and relubrication nipple are free from abrasive materials and other contaminants.

If the generating set is running, apply the specified quantity of grease via the grease nipple (All grease quantities can be found in the alternator manuals). It is recommended to keep the generator running for at least 60 minutes after applying the grease.

If the generating set is not running, apply the grease then start the generator and run for at least 60 minutes to allow excess grease to exhaust from the bearing assembly.

Clean the grease exhaust systems if required and inspect the colour of the grease expelled. Replace the bearing if the expelled grease is severely discoloured.

Never Mix Lubricant Types

Figure-2-Examples-of-a-typical-condition-monitoring-system

Avoid high humid atmospheric or wet conditions as this can cause the grease to emulsify causing corrosion and deterioration of the grease, leading to premature failure of the bearings.

The best way to understand the condition of the bearings is to use a health monitoring regime. Measuring and monitoring the vibration characteristics of bearings is a very good way to identify the condition of the bearings and predict more accurately when the bearings need to be changed. Best practice is to take initial readings as a baseline level and periodically monitor the bearing signature to detect a change in trend. Examples of a typical condition monitoring system can be seen above in Figure 2.

Maintaining bearing life during periods of storage

If the alternator will not be used immediately and is stored for significant periods of time, the alternator must be stored in a clean, dry vibration-free environment.

If the alternator can be rotated, turn the rotor a minimum of 6 revolutions every month during the storage period.

This is to help move the grease around the bearing raceways and rolling elements to help line the contact surface with a film of oil to prevent metallic contact. This helps to reduce the possibility of false brinnelling that can significantly reduce the life of the bearing after the unit has been commissioned.

As per the alternator manual, before commissioning the alternator, refer to the following table below.

Table

For more information please contact the Applications team