Protect Bearings In All Five Life Stages
Ken Bannister | January 21, 2019
Compare lubrication and handling factors that affect bearing performance with your practices, and implement these improvement tips.
Poor lubrication practice has long been used as a standard scapegoat for bearing failure. While ineffective practices significantly contribute in as much as 70% of all lubricated-bearing failures, the root cause(s) of failure is rarely investigated and often misunderstood.
There are many elements that affect the bearing lifecycle as it transitions from the drawing board to its working environment. While design, storage, installation, and set up play an important part in a bearing’s early life, effective lubrication throughout a bearing’s working life has the greatest positive impact on longevity, performance, and equipment uptime. Being aware of a bearing’s needs in early- and working-life stages will determine maintainability requirements and assure maximized reliability. The following synopsis follows a bearing throughout its lifecycle stages and highlights influences and elements that can affect reliability. Each stage offers easy maintenance tips to mitigate chances of premature failure.
Stage 1: Manufacture
Bearings are manufactured to the highest tolerances and assembled and packaged in a contamination-free, environmentally controlled process. These components can be ordered and readied for sale with only assembly lube, pre-lubricated with standard bearing-manufacturer grease or oil, or pre-lubricated with a customer-specified lubricant. Lubricated bearings are usually shipped with between a 20% and 30% cavity fill.
Tip: To avoid initial lubricant cross contamination and ensure the bearing is filled with the correct viscosity and lubricant type from the onset, consider purchasing non-lubricated bearings for inventory spares.
Stage 2: Equipment-Design Engineering
Original equipment manufacturers (OEMs) design machines based on client specifications. Bearing type, style, and size are chosen based on operating speed, design load, temperature, and working-condition factors. These factors, along with financial considerations (grease nipples are much cheaper than centralized lubrication systems), determine whether the machinery is to be lubricated by oil or grease. OEMs will often work you to accommodate your requirements.
Tip: If possible, provide your internal engineering and/or purchasing department with an OEM maintenance-specification list of preferred automated lube-delivery systems similar in design to in-house systems (if available), and provide a list of current lubricants used in the plant.
Tip: Request an OEM schematic that locates and lists all lubricated bearings used on the equipment by type, style, bearing-identification number, and bearing-fit classification.
Stage 3: Inventory
When a bearing reaches its end-of-life stage, it will require a maintenance replacement. To offset equipment downtime, most maintenance departments choose to pre-purchase and inventory replacement bearings.
Poor quality of care afforded to inventoried bearings due to handling issues (open wrapping, touching bearing surfaces, dropping on the floor), exposure to moisture and dirt, and exposure to floor vibration (leading to false brinelling and flat spots on bearings) can cause a bearing to significantly deteriorate prior to first-time use.
Tip: Store bearings in a clean, humidity-controlled environment.
Tip: Always store bearings flat in their original packaging materials in a vibration-free cabinet.
Stage 4: Installation, Machine Setup
During installation, future bearing life relies greatly on the skill and knowledge of personnel responsible for fitting such components and setting up the machinery. Forcing bearings into place using blunt-strike tools can cause immediate surface brinelling. Bearings that fit too loosely or too tightly can cause surface scoring, rapid wear, and fatigue failure.
Where belt- and chain-drive systems are used, accurate motor, pulley, and gear alignment is essential if bearings are to survive for any length of time. Angular and offset misalignment excessively and unevenly loads a bearing, causing wide ball-path wear on the inner race, and non-parallel wear on the outer race.
Tip: Ensure maintainers have the proper training and tools to install bearings correctly.
Tip: Invest in a laser-alignment tool for use on all machine driver-assembly setups.
Stage 5: Working Life
Assuming a bearing has successfully arrived at its working-life stage in good operational condition, it is now ready to provide service. At this point, it is the operating conditions and quality of the lubrication-management program that will dictate the lifecycle of each and every bearing. For example, a standard 6206-RS sealed bearing employed in a pharmaceutical manufacturing plant is likely to survive longer than its counterpart in a food-processing facility or foundry. This is due to the white-room controlled environment and light-duty cycle of the pharmaceutical plant in comparison to those of food-processing operations, in which equipment is water washed every day, and a foundry that uses lots of heat and sand (silica) in its manufacturing process. To combat these conditions, a formal lubrication-management program must ensure that the right lubricant is placed in the right bearing, in the right amount, at the right time. If no program is in place, follow these three tips.
Tip: Introduce a lubricant-consolidation program that reviews your current catalog with the intention of updating and streamlining the number and types of lubricants used. This will reduce cross-lubricant contamination and provide better management of current lubricant stocks.
Tip: Introduce a contamination-control program that examines maintenance cleanliness habits when handling lubricating bearings and lubricant storage, handling, and transfer practices. In more-severe process industries this program can be expanded to investigate opportunities to mitigate lubricant and bearing contamination due to process fluids, moisture, dirt, and production-solids fallout.
Tip: Provide lubrication-awareness training for all maintenance and supervisory staff and lubrication certification training supported by ICML (International Council for Machinery Lubrication), Broken Arrow, OK (icmlonline.com), and STLE (Society of Tribologists and Lubrication Engineers), Park Ridge, IL (stle.org).
If installed correctly, operated within its design specification, and lubricated in a knowledgeable manner, a bearing will deliver a long, reliable service life. If a bearing fails within its first six months of operation on a new piece of equipment, suspect the design or OEM installation as the root cause. Similarly, if a replacement bearing on an existing machine fails in the same time period, look internally at your inventory methods and installation techniques. Bearings failing after their warranty period usually require detailed analysis of the lubricant and the failed item.
As your lubrication-management program matures, bearing failure should drop dramatically, allowing time to assess future failures through lubricant and forensic analysis. When your next bearing fails, don’t throw it away. Instead, photograph, tag, and bag it and send for analysis. Then, perform an internal review to see how you compare to the analysis report. EP
Contributing editor Ken Bannister is co-author, with Heinz Bloch, of the book Practical Lubrication for Industrial Facilities, 3rd Edition (The Fairmont Press, Lilburn, GA). As managing partner and principal consultant for Engtech Industries Inc., Innerkip, Ontario, he specializes in the implementation of lubrication-effectiveness reviews to ISO 55001 standards, asset-management systems, and training. Contact him at firstname.lastname@example.org or telephone 519-469-9173.