Bearing Lubrication 201- The Differences Between Oil & Grease

In our post Lubrication 101 we took a brief overview of bearing lubrication and quickly outlined the importance that proper lubrication plays in promoting bearing life and performance. Now we are going to get a little more in depth and discuss some of the differences in properties and performance characteristics associated with both oil and grease.

Lubricant Type- Oil

Oil is going to be the best choice in the following circumstances/applications:

-applications that require extremely low torque or a narrow range of torque variation
-applications that exhibit high speeds and high operating temperatures

Lubricant Type- Grease

Grease is a mixture of fluid lubricant and a thickener dispersed in oil. As a lubricant for bearings, grease is going to be the best choice in the following circumstances/applications:

-systems or applications where an oil product would not be retained
-applications with slower operating speeds
-applications that require an added seal of protection from contamination and moisture

The composition of grease and its counterparts can be found in any arrangement of the following percentages.

Thickener        4- 20%

Base Oil           75- 96%

Additives         0- 8%

In order to decide which additive is right for your application or system, consider the following:

Additive Type              Capabilities

Antioxidant                  Prolongs life of base oil

Antiwear (EP)              Chemically active protection of loaded metal surfaces

Antirust                         Slows rusting of iron alloys

Anticorrosion               Slows corrosion of non-noble metals

Filler                              Thermal/electrical conductivity, special physical properties

Fortifier (EP)                Solids burnish into loaded surface under extreme pressures

Lubricity                        Reduces coefficient of friction, starting torque or stick/slip

Pour Point                    Improves lower temperature limit

Dye                                 Visual/UV markers as inspection/assembly aids

Viscosity Index            Reduces rate of change of viscosity with temperature

Advantages of Grease over Oil

There will be instances when oil will be a better choice of lubricant for your application. We discussed those circumstances at the beginning of the post. However, at VNC, we find that grease tends to be a better fit for an application due to the following reasons:

1. Ease of retention – stays in place
2. Minimal application – reduced maintenance cost
3. High reliability – historical reliability in electric motors
4. Protection – helps keep out moisture and contaminants
5. Clean – minimal leaking/dripping
6. Greased for life – ideal for inaccessible bearing applications

Whatever lubricant you choose, make sure you’ve considered all of the characteristics of your application and how it will need to perform. Bearings that are properly lubricated will have increased immunity to contamination, overloading, and premature failure.

If you have questions about what lubrication to use, contact us today! Our team can help you choose the right type and amount of lubrication for your application.