Caring For Bearings In Extreme Environments
EP Editorial Staff | February 16, 2018
The old ‘give it more grease’ approach has been supplanted by safer, more cost-effective strategies.
Ensuring the reliability of equipment assets in extreme operating environments, such as those often found in food- and beverage-processing applications, isn’t easy. A well-planned and consistent best-practice approach to lubrication management is key in these demanding situations. Fortunately, there are better alternatives today than the “give it more grease” solution. Less resource-intensive than past solutions, they also reduce the chance of product contamination.
Technological advancements in those types of alternatives are changing the thinking about lubrication strategies and the way they are practiced in plants. In the process, they’re having a positive impact on food and human safety, cost, overall equipment effectiveness, and sustainability.
Consider these individual examples of extreme environments and the implications to bearings operating in those conditions:
• Subjecting bearings in ovens to temperatures exceeding 350 F and high levels of humidity increases maintenance requirements and costs. Limitations of available grease technology do not permit increased oven temperature that would allow faster throughput. High-temperature lubricants—those that are formulated to function at temperatures of 250 F and higher—are required for extreme conditions.
• Operating in cold environments, as found in chillers and freezers below 32 F, also has an adverse effect on bearings. Oil viscosity changes and appropriate grease consistency with an NLGI 0 or less is required. If the oil becomes too viscous, the all-important film separating the rolling elements and the race surface will not form. Subjecting bearings to sudden temperature shifts during washdowns increases the chances for moisture to seep into the bearing, emulsify the grease, and cause it to leak out.
• Pressure washing with hot water and caustic agents creates a variety of reliability problems. Lubricants can be washed out, resulting in the need for frequent re-lubrication. Corrosion may occur in areas with poor chemical resistance, creating flaking and possible contamination. These combined effects can lead to reduced service life of bearings, as well as increased costs for re-lubrication.
Many times those individual adverse conditions combine in the same application. In addition to causing potential bearing failures and downtime, such combinations can also pose risks in the areas of food contamination and operator safety.
The following types of lubrication and sealing solutions can reduce the critical control points in your HACCP (hazard analysis critical control point) process, as well as reduce the need to stop production lines for re-lubrication and frequent replacement of bearings:
Graphite-based lubricants: Advanced graphite-based lubricants contain minute quantities of graphite that lubricate the bearing during operation, preventing metal-to-metal contact. This NSF-approved technology allows bearings to perform optimally in humid and continuous operating temperatures as high as 660 F without re-lubrication.
Solid-oil lubricants: Solid-oil lubricants use an oil-saturated polymer matrix that effectively fills all of the free space within the bearing allowing the bearing to contain two to four times more oil than is possible with conventional greases. The porous polymer material is molded into the bearing, forming very narrow gaps around the rolling elements and raceways and enabling the bearing to rotate freely. These micro-pores hold the lubricating oil. In service, oil is released from the material into the narrow gaps between it and the bearing components, thus providing effective minimum-quantity lubrication that makes re-lubrication unnecessary. The micro-pores withstand the negative effects of high humidity and the breathing effect caused by air-volume expansion and contraction. These features make solid-oil work reliably, even when faced with rapid operating-temperature changes, such as those found in freezer applications.
More effective seals and housings: Specially designed housed bearings incorporating corrosion-resistant materials and an improved sealing system are a good choice for high-pressure washdown environments. Glass-fiber-reinforced polyester housings and insert bearings using a multi-lip seal design, coupled with end covers, to form an effective barrier to hazardous conditions. Stainless-steel balls and bolt-hole bushings prevent corrosion. The benefits of these re-lubrication-free solutions include:
• reduced foreign-body contamination
• no dripping grease or purge contamination
• decreased re-lubrication costs and environmental impact
• compliance with OSHA requirements
• no risk of missed lubrication points due to human error
• reduced risk of premature bearing failure and maintenance intensity.
These types of specialized lubricants and components can help plants overcome the challenges of harsh conditions and, ultimately, reduce downtime, extend bearing life, and increase cost savings. EP
Information in this article was provided by Stephen White of SKF (Gothenburg, Sweden), and Richard R. Knotek, of Motion Industries (Birmingham, AL). White is the SKF Food & Beverage industry portfolio manager. Knotek is a technical-training specialist with the Motion Institute, a division of Motion Industries. A former adjunct instructor with Northern Michigan University’s Industrial Maintenance Program, Knotek is the co-author of Mechanical Systems & Principles for Industrial Maintenance (Pearson, London and New York, 2005). For more information, visit MotionIndustries.com, or take a closer look at SKF’s Solutions Factories click here.