Grease Compatibility (PDF)
Too often the presumption is that “grease is grease” which leads to ignoring compatibility issues. All greases are not created equal – there are dozens of options to choose from, each type is designed to work better in a specific application.
Grease Compatibility: Base Oils, Additives and Thickeners
When taking a look at grease compatibility, you need to consider: base oils, additive packages and thickeners.
Base Oils
It is absolutely critical to take into consideration the base oil when determining the compatibility of greases. Greases are manufactured from both mineral oil and synthetic oil bases. Some grease manufactured with synthetic base oils are not compatible with mineral oils of other types of synthetics, similar to mixing lubricating oils. Additionally, while thickeners may be compatible, if the base oil is not, it can lead to issues with insufficient lubrication resulting from incorrect viscosities. Since viscosity is the most important part of your lubricant, if the wrong base oils are selected, the resulting mixture will not be optimized for the application.
Additives
As with oils, incompatible additives can result in poor properties with the lubricant. Incompatible additives will not settle out in grease as it would in oil. The changes in the grease properties can impact on additive effectiveness may cause undesired conditions in the grease. This affects the grease itself and how the additives react with the metallurgical components of the asset being lubricated.
Thickeners
Mixing greases with incompatible thickeners usually results in one of two conditions: the thickener either solidifies in place, or thins to the point where it will leak out if the bearing housing. In either case, the equipment will not receive the necessary lubricant and a failure is eminent.
Grease Compatibility Best Practices
Conditions for equipment can change leading to changes in grease types and re-greasing schedules. Consult with your equipment manufacturer to see what they recommend when determining which grease to use in your specific application.
If introducing a new grease to your equipment, try to completely remove all of the old grease before applying new grease. If that’s not possible, request a grease compatibility test. This test will evaluate the changes in properties for the mixtures at different mix ratios according to ASTM D6185.
Grease Compatibility Guidelines
Following good grease protocols can overcome many concerns about compatibility. Grease compatibility charts can also provide an initial reference point. We recommend you consult with your equipment service manuals and/or conduct a grease compatibility test when in doubt.
Grease Compatibility Testing
Grease compatibility is not a single test but a set of tests. The number of tests will vary depending on how many different mixtures are being tested and which tests are applied to each mixture.
Typically, the lab will test each combination of greases at 100%, 50:50 and 90:10 which corresponds to 5 mixtures for two greases. This number of tests/combinations will increase with each additional grease (Ex. With one existing grease and two new greases it would be 8 mixtures, with two existing greases and one new grease you would need 10 mixtures).
For example if you have two greases a typical test program (ASTM D6185 mod.) might look like the following:
- Prepare 5 Samples (100% Grease A, 100% Grease B, 50:50 mix, 10:90 mix, 90:10 mix)
- Test High Temp Stability (Dropping Point on 5 samples)
- Test High Temp Storage Stability (Worked Penetration x 2 on 5 samples) = 10 total.
If you require grease compatibility testing, contact us for a quotation based on your specific scope of work.