This post is the first in a three-part series analyzing the importance of a grease’s upper operating temperature and which testing methods are best for gauging a grease’s actual high temperature performance.
Upper operating temperature, or the maximum temperature at which a grease will provide adequate lubrication, is one of the most important characteristics to consider when selecting a grease.
This is because high temperature environments present a number of lubricant challenges.
When a grease is heated, it generally becomes softer and flows more readily. As a result, its performance can be impacted in a number of ways, including:
- Loss of base oil due to excessive bleeding or separation from the thickener;
- Loss of base oil due to evaporation resulting from excessive volatility;
- Degradation of base oil or thickener due to oxidation; and,
- Irreversible fluidization at or above the dropping point temperature.
Further, the collective impact of oxidation, evaporation and oil separation can shorten a grease’s lifespan, making it even more challenging to accurately predict the life of a grease in a given application.
So, to ensure optimal equipment performance in high temperature environments, it’s important to understand what kind of temperature conditions a grease can withstand when being used in a given application, and testing is the best way to do so.
However, there is no single accepted industry standard used to determine a grease’s recommended upper operating temperature.
In fact, the range of methods used by manufacturers to test grease high temperature performance varies widely. These methods include everything from rule-of-thumb guidance based on thickener types, to static tests measuring properties under stationary conditions, to dynamic testing which attempts to simulate performance under an actual operating condition.
Obviously, some testing methods are less thorough and comprehensive than others, which can lead to results that do not provide an accurate depiction of a grease’s real-world performance. This, in turn, means that end users might struggle to make accurate comparisons between various greases or fully understand which grease product is most appropriate for a specific application.
So, because of the impact that high temperatures have on grease performance, sales and field engineers must understand the various types of test methods used so they can characterize a grease’s expected real-world performance and provide the customer with the best product recommendation.
In my next post, I will take a closer look at the advantages certain tests offer when it comes to accurately predicting a grease’s high temperature characteristics.
"Assessing High Temperature Grease Claims: Part I" by, Chris Decker used with permission of the Mobil SHCTM Club (all rights reserved.)