Grease compatibility is a straight forward concept when armed with the correct knowledge. Too often the presumption is that “grease is grease”. This leads to an oversight with compatibility issues. Greases are not created equal – there are dozens of options to choose from, each type is designed to work better in a specific application. Keep in mind that the various types of greases have different strengths and weaknesses. Mixing two greases together to observe changes may not give any obvious indication of a concern.
Grease Compatibility: Base Oils, Additives and Thickeners
When taking a look at grease compatibility, you need to consider: base oils, additive packages and thickeners.
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.
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.
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
A strong greasing program includes documentation of all greases in-use, by each piece of equipment, and required re-greasing frequencies. Since grease is not universal, different equipment may require different greases to be applied at different frequencies.
However, 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.
Try to completely remove all of the old grease before applying new grease if a grease change is required. 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.
Ultimately, the safest practice is to avoid mixing of greases.
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.
Interested in learning more? Contact our team of reliability specialists and find out how we can help you with your lubrication program.
Article by Drew MacRae