Bearing inspection and maintenance are important not only to extend bearing life but to avoid any operational downtime, which promotes cost savings and lowers the total cost of ownership for your business. This is especially true if the operating environment is exposed to harsh conditions or is in a remote area. But no matter where your operations are, the measures you put in place to protect your bearings will pay dividends as you prevent premature fatigue and increase their length of service.
Early bearing failure is mostly attributable to inadequate handling or maintenance. Most failures are due to a relatively small number of issues that often are preventable, including lubrication, mounting, bearing handling and installation, and environmental issues. Here are the main countermeasures any operator should implement to prevent downtime and bearing failures in mission-critical equipment.
Handle bearings with care — Because bearings are precision components, they need special handling and storage to prevent the entry of airborne contaminants. Packaging should be kept intact when in storage, because even a tiny speck of dirt or dust in a raceway can cause tremendous damage.
Do not apply any direct force on a bearing or its outer ring, as this can cause rolling elements to misalign. But, even slight damage caused by dropping bearings can result in poor performance issues and subsequent failure.
Use the correct tools — Avoid using general purpose tools for handling or mounting or dismounting bearings. There is specific equipment associated with tasks like mounting bearings with cylindrical bores, which require a press fit method (mounting by pressing the bearing on the shafts) or a shrink fit (heating the bearing to expand its diameter.) Some of these tools include bearing pullers, bearing fitting tool kits, hydraulic nuts, oil injector kits or induction heaters.
It is a false economy to try to use standard tools, as many of these will do irreparable damage to bearings and will replacing them cost even more in labor and downtime.
Prevent corrosion — Bearings should not be exposed to water, as over time rust and corrosion may occur. Make sure that you wear gloves when handling bearings, as perspiration on your hands, water or other contaminants may cause corrosion. A water-resistant grease is a good choice for lubricant in damp environments, as it acts as a protective barrier.
In extremely corrosive operating conditions, special bearings may be recommended, and there are specific bearings designed for use in food-and-drink processing plants where frequent wash-downs are required.
Lubrication — It’s estimated that about 40% of premature bearing failures are due to lubrication issues, so getting this right is almost half the battle. The main purpose of lubricant is to separate the metal surfaces of the bearing’s components to reduce friction and wear.
At the same time, lubricants may result in power dissipation, reducing energy consumption. Choosing the right lubricant from the start is critical, and recommendations from the bearing manufacturer should be followed.
Criteria for selecting the right lubricant include bearing load, operating temperature as well as ambient temperature, speed range and possible contamination. Even more important is to ensure that bearings are re-lubricated on schedule. Like the oil in your car, delaying lubrication can lead to catastrophic failure of the entire system.
Operating environment — Despite proper handling, installation and design, failures may occur if issues in the operating environment aren’t taken into consideration. Here are some of the important details to consider:
• Airborne contaminants such as dust and dirt, which can contaminate a bearing over time. Proper sealing techniques are essential in these cases.
• Aggressive incursions of media or water. Sealing is critical to proper operation, and specialty seals that do not score the shaft are recommended.
• External heat will dictate many factors, such as a high-temperature lubricant, the radial internal clearance, intermittent or continuous running and other choices that will affect bearing life.
• Electrical current passage. In power-generating equipment it is important to be alert to current flows through the rolling elements, and a bypass circuit installed or by insulating the bearing. Otherwise pitting or fluting might occur on bearing surfaces.
Watch for danger signs — To maintain the optimal performance of a bearing, regular inspections should be performed. During operation, the crew should always check for abnormal bearing noise and/or vibration. Vibration analysis is part of condition monitoring that may include thermography, vibration analysis with tools such as a vibration pen, and oil analysis, which can compare current bearing states with historical data and provide an assessment of the remaining life of the bearing.
When conducting an inspection, the bearing should be thoroughly monitored and removed immediately if conditions worsen before a failure becomes catastrophic. If conditions stay the same, then the bearings can remain in operation and examined in detail as soon as time permits. Over time, studying and logging the type of failure and its possible causes will help to justify the types of bearing solutions mentioned above, leading to fewer failures of both the bearing and related equipment in the future.
Matt Nagel is a senior applications engineer with NSK Americas in Ann Arbor, Mich., and specializes in gearboxes and other industrial applications. He holds a BSME degree from the University of Toledo and has over 28 years’ experience in the bearing industry.
