Grease contamination is a leading cause of machinery failure. It impairs the grease’s ability to control friction, wear, and corrosion, which makes control of contaminant entrance vital to avoid destruction of the lubricant and internal machinery surfaces. Once contamination occurs, lubricants begin to degrade, and the equipment’s internal components deteriorate prematurely. However, by identifying and reducing contamination, lubricant and machine life can be greatly extended.
A successful lubricant management program focuses on contamination sources and contamination control. Proper filtration, clean handling, and storage solutions are critical to reducing particulates and leads to dramatically extending grease life and decreasing the number of lubricant-related failures.
To learn how your lubricants become contaminated, perform an inventory of the contamination sources and the primary points of entry. Review covers, containers, storage, handling, and dispensing. You may find some drums without covers or containers used for more than one type of lubricant, because proper identification is missing. These problems alone can lead to equipment failures, not to mention time and money spent in repairs and downtime.
A lubrication computer program can be another step toward reducing contaminate entrance. This program contains a comprehensive list of all plant equipment, the type of lubricant for each piece of equipment, and historical data. It tracks time intervals for lubricants, oil filters, and air filters.
Lubricant handling and dispensing procedures must keep contaminants from entering equipment and should be reviewed. Open metal containers used to store and transport lubricants to the machines are also at risk for contamination and must be properly labeled.
The Other Enemy…Water
Water is another contaminant of grease that is discussed less often but needs to be controlled.
We know the operating life of a bearing is determined by the performance of the lubricating grease. The consistency of the grease prevents it from leaking out of the bearing and providing a good seal. Ingress of water into the bearing will not only have a significant impact on consistency, but also on the lubricating ability of the grease. Industries in which water entrance is more likely to occur are the steel, food, pulp, and paper industries.
Some greases are less sensitive to water than others. No specific guidelines are available to select the proper grease for bearings subjected to water entrance. Water strongly influences rheological properties such as zero shear viscosity, yield stress, and storage modules. Calcium sulfonate greases may become stiffer after absorbing a considerable amount of water, leading to an increase in yield stress and zero shear viscosity [(ZSV) is the viscosity measured in shear deformation at a shear rate approaching zero]. Lithium, lithium complex, and polyurea greases have been found to soften with considerable changes in measured rheological properties. Therefore, it’s important to keep grease away from locations where water will enter.
A Word About ContainersOpen containers create a high risk for spills and allow foreign particles such as dust, debris, and water to easily contaminate the oil. Metallic containers can cause problems due to their potential for rust (and subsequent lubricant degradation). Some metal containers are painted, presenting a risk of contamination from paint chips. Also, painted containers are difficult to label, creating more problems with mixed lubricants.
Like any good maintenance practice, the earlier a problem is detected, the less expensive it is to correct. Investing in ways of keeping contamination out of equipment is a better practice than removing the contamination after entrance. It has been said that the cost to prevent the entrance of contamination may only be 10 percent of the eventual cost once the contamination is allowed to enter lubricating greases.