Better maintenance procedures, better tools help improve bearing health

Managing the life cycle of rolling bearings with expert maintenance procedures and tools designed specifically for the job can help to increase plant equipment uptime, cut energy costs and reduce component replacement expenses.

Paul Michalicka, SKF, USA Inc. -- Plant Engineering, 6/8/2009 10:48:16 AM

Managing the life cycle of rolling bearings with expert maintenance procedures and tools designed specifically for the job can help to increase plant equipment uptime, cut energy costs and reduce component replacement expenses. The strategy works in virtually every manufacturing industry, and has particular relevance in the food and beverage, steel making, chemical processing and mining sectors.
A typical bearing's life cycle divides into distinct stages, including bearing installation, alignment, lubrication, condition monitoring and dismounting. Each stage directly impacts bearing performance and life expectancy. According to reliability studies, lubrication-related errors, such as selecting the wrong grease or under-lubricating bearings, account for 36% of premature bearing failures. The remaining 64% of failures originate at diverse points in the bearing life cycle.
Following accepted maintenance procedures and using the right tools at each life cycle stage can avert failures and improve bearing health and performance.

Bearing installation
The choice of installation method depends mainly on bearing size. Small and medium-size bearings are often mounted cold, with mechanical force. Makeshift tools, such as sections of tubing or pipe, should not be used to drive bearings onto shafts, as they can transmit force to the bearing's rolling elements, damaging the bearing before it becomes operational.
Bearing fitting tools are the recommended option. A fitting tool consists of an impact resistant ring and sleeve. Available to accommodate a range of bearing sizes, fitting tools distribute mounting forces evenly to a bearing's inner and outer rings, preventing damage during mounting.
Larger bearings can be mounted using hydraulic force. An Alabama-headquartered mining company now employs a hydraulic nut to install bearings in mineral processing and handling machinery. A hydraulic nut consists of a threaded steel ring with a groove in one side face, and an annular piston that rests in the groove. When oil is injected, the piston is pressed out, providing sufficient force to mount large bearings. Using hydraulic methods, the mining company succeeded in reducing installation-related problems and associated downtime, valued up to $5,000 per hour. Installation time was slashed by 50% or more per bearing.
Temperature mounting using induction heaters is another option. Induction heaters accommodate bearings weighing just a few lbs. to more than 80 lbs., provide a safe, controllable heating cycle and complete the heating process in minutes. An added benefit: certain induction heaters, including those supplied by SKF, automatically demagnetize bearings following heating.
Shaft and belt alignment
After bearings are installed, shafts should be properly aligned.
Misalignment can increase vibration and friction, damage bearing seals and lead to breakdowns. It can also increase energy consumption.
To improve the operating performance of its bakery machinery, a major Ohio-based food manufacturer now makes use of a laser-equipped shaft alignment tool. The tool delivers greater accuracy than the previously used manual method, which employed straight edges. Since the change of alignment method, the manufacturer has increased bakery machine reliability and reduced labor costs related to alignment-related issues. Total annual benefits are estimated at $9,000.
Laser-equipped alignment tools are also available for belt-driven machinery, where pulley misalignment can increase wear on pulleys and belts. Highly effective laser belt alignment tools are those which align the pulley grooves in which the belts run, instead of aligning pulley faces. These tools increase alignment accuracy regardless of pulley type or thickness.
Lubrication
Bearing lubricants prevent metal-to-metal contact between bearing components, guard against corrosion and stop contaminants from infiltrating bearings. Because speed and performance requirements vary in different applications, a single all-purpose lubricant is not usually the best solution. Instead, lubricants should be selected based on application-specific criteria such as bearing type and size, speed, load and operating temperatures.
Most bearings are lubed with grease and require periodic relubrication. It can be difficult, however, to judge the optimum amount of grease when relubing. Automatic lubricators address this issue by supplying a consistent, regulated flow of grease to bearings, eliminating the labor and guesswork involved with manual relubrication. One popular type of single-point lubricator employs a gas cell that generates a large-molecule inert gas. When activated, the gas pushes grease from the grease canister at a predetermined rate. These units are also available with oil.
There are also multipoint lubricators available that pump grease from a centralized cartridge through feed lines measuring 15 feet or more. Grease can be supplied to eight or more separate lubrication points.
Condition monitoring
Monitoring bearings during operation enables plant management to assess
both bearing and machine conditions. Hand-held data collectors can be used to gather data on parameters such as operating temperature and vibration. The data can be analyzed and trended, allowing companies to identify problems in advance of failure and schedule maintenance for planned shutdown periods.
Dismounting bearings correctly is as important as properly installing them. This holds true even when the bearings being removed will not be reused because improper dismounting can damage components that are often reused, such as shafts and housings.
Specialized tools, like bearing pullers, simplify safe dismounting. When using pullers, always apply the withdrawal force to the bearing ring with the interference fit. Three-armed pullers, which offer greater stability than two-armed varieties, are recommended. Induction heaters and hydraulic methods are useful when dismounting larger bearings.
Maintenance audits
Companies seeking to improve their bearing maintenance procedures should consider the benefits of a comprehensive maintenance audit. These audits, usually conducted by expert rotating-equipment technology companies, such as SKF, or by consultants, review current practices in depth and suggest ways to improve them. They address relevant issues at each stage of the bearing life cycle. For more information contact your bearing supplier or authorized rotating-equipment distributor.

Paul Michalicka is North American area sales manager for maintenance products, SKF USA Inc., based in Kulpsville, Pa. He can be contacted at Paul.Michalicka@skf.com; phone: 416-299-2894.