Selecting the Best High-Temperature Grease for Your Application
In heavy-loaded industries such as construction and agriculture, special care must be taken when selecting a high-temperature grease for machinery. Ensuring you select the best lubricant fit possible, several factors must be analyzed. Those factors include a lubricant's viscosity, oxidation, and thermal degradation. In this article, we'll talk about the ideal grease properties to look for when choosing the best grease for your site's needs.
Viscosity
When looking for a quality high-temperature grease, one of the first factors to consider is its viscosity index. A quality grease will have a wide operating temperature range, allowing it to be pumpable at lower temperatures while offering protection at higher temperatures without thermally degrading. This means that at high temperatures, the grease won't "cook" onto your machine surfaces and leave harmful deposits.
Oxidation
You also need to consider the rate of oxidation, or the process by which lubricants age and begin to chemically break down. For example, in harsh environments, you wouldn't want to choose a grease formulated with mineral oils that can oxidize at high temperatures.
Thermal Decomposition
Finally, you need to consider thermal decomposition, or the rate at which the oil will break down at higher temperatures. You can test for the thermal decomposition temperature of the base oil, a component in the lubricant, by using an ASTM D2879 test. Although the thermal decomposition temperature can't be improved, you can lessen the effects by including different additives.
Dropping Point
When looking at the upper-temperature limits of a grease, you must also consider the thickener, another component of a quality lubricant. At certain higher temperatures, grease can reach a point where the structure destabilizes, and the grease becomes a liquid. This temperature point is referred to as the "dropping point". This chart shows the different dropping points for more stable, conventional grease thickeners.
| Grease Thickener | Dropping Point, °F |
|---|---|
| Lithium Complex | 500+ |
| Lithium 12-Hydroxystearate | 350 to 400 |
| Anhydrous Calcium | 275 to 290 |
| Calcium Sulfonate | 500+ |
| Polyurea | 470+ |
| Aluminum Complex | 500+ |
Although these thickeners can't withstand temperatures over 400°C, a potential solution is a solid lubricant and composite. Although it is not a perfect solution, the compromises and benefits will allow for better performance regarding certain properties.
In total, there are a limited number of high-temperature greases that can successfully handle extreme temperature environments, making your decision much easier.
By properly identifying your grease needs and comparing them against available lubrications, you give your grease and machines a fighting chance at optimal performance in extreme environments.
