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Thursday, 11 August 2011

How to lubricate a bearing?

How often do you re-pack bearings? Ever wondered whether you’re doing it right? Well here are four important considerations when deciding to lubricate a bearing:
• Lubricant selection
• Application method
• Volume of lubricant to be delivered
• Application Frequency.

There are many different ways to lubricate a bearing, and opinions vary concerning which approach is best. Therefore, the best approach may be to use several methods to develop a strategy that defines default values, which can then fine-tuned, based on feedback from visual inspections, operating temperature, ultrasonic instrumentation and other factors. Due to the variability of operating conditions and machine design, it could be impossible to be precise without introducing the condition-based component to the
formula.

Condition-based lubrication should form part of any world-class program.

Grease Selection to lubricate a bearing
When it’s time to lubricate a bearing, a good starting point is selecting the correct grease. Simply choosing the best-quality grease is not as important as choosing the correct grease for a given application. Too often, grease selection is oversimplified and the key properties to effectively lubricate a bearing overlooked.

Grease selection is far more complicated than lubricating oil selection. Due to the lack of specificity in most grease recommendations, it is important to understand how to select greases for specific applications.

Proper grease specification to lubricate a bearing, involves all of the components of lubricating-oil specification. These include:
• Base oil viscosity
• Additive requirements
• Base oil type
• Thickener type and concentration
• Consistency
• Dropping point
• Operating-temperature range.

While most users acknowledge grease quality, many don’t stop to make sure the right lubricant is being used to ensure effective lubrication
.
How to apply the grease when you lubricate a bearing
There are various methods of applying grease when you lubricate a bearing.
• Using centralized application systems,
• Single-point auto application systems
• Hand packing
• The manual grease gun.

A compelling argument can be made for the superiority of continuous application systems to lubricate a bearing, but unfortunately, they are impractical for most applications. Therefore, the manual grease gun is the most common application method and is the focus of this article
.
Manual grease application, when performed correctly, is an effective method and provides several advantages over automated systems.

The manual application process used to lubricate a bearing requires the technician to be in close proximity to the lubricated component. This allows for inspection using sensory observations such as sight, smell and sound. Instrument inspections, such as ultrasonic monitoring and temperature readings, are also helpful in providing component condition information while fine-tuning the lubrication strategy.

How much grease to use when you lubricate a bearing
One of the more important but frequently botched steps of the greasing strategy is how much grease to use to lubricate a bearing. “However much it takes” is not best practice to lubricate a bearing! There are many ways of estimating the appropriate relubrication volume.

SKF have the following advice to define the correct volume to lubricate a bearing:
Gp = 0.005 * D * B

where
Gp = grease replenishment amount (gm)
D = bearing outside diameter (mm)
B = total bearing width (mm)

This method provides positive results, but does but you need to be aware that it does not account for differences in bearing housings and application points; assuming the grease is added at the optimum location. It is also not always possible to know the amount and condition of old grease in the housing at the time of reapplication.


For these reasons, it may be advantageous to modify the calculated values with a condition-based approach when you lubricate a bearing. The most advanced condition-based technique is ultrasonic instrumentation, which optimizes the relubrication volume. By establishing a baseline value and determining a statistically appropriate limit, the volume of grease added to lubricate a bearing can be optimized.

Determine the correct application frequency to lubricate a bearing
Determining the correct intervals to lubricate a bearing is one of the more difficult steps. Many factors must be considered to be reasonably accurate in determining the best application frequency. Factors to consider when looking at the correct frequency to lubricate a bearing are:
• Operating temperature
• Seal type and condition
• Particle contamination
• Moisture
• Vibration
Industrial grease type

For accuracy, feedback is needed from the lubricated components to verify the proper frequency to lubricate a bearing has been chosen. For frequency, as with volume, ultrasonic instrumentation might be the best tool available. A conservative approach is to use a frequency generation method as a starting point, and continuously refine that value based on feedback from the ultrasonic equipment and other physical observations.

Summary
Optimizing a grease lubrication strategy to lubricate a bearing can be difficult. The best tactic is to combine the latest technology with proven traditional observation methods. Put simply, just remember to use the right lubricant in the right place, and use the right application method in the right amount at the right time when you lubricate a bearing.

5 comments:

Dick Olson said...

Good tip, so this method allows you to see when the new grease is starting to ooze across the top of the bearing? babbit bearings

John Harbaugh said...

Great informative site. I'm really impressed after reading this blog post. I really appreciate the time and effort you spend to share this with us!
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Elina Maria said...

Thanks for sharing this great information. I liked it. It has a useful and important info of greasing.
Lubrication Equipment

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