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revolutions, that 90 percent of a group of bearings will complete at a given load and speed before fatigue failure occurs -This life can also be given in hours of operation -The basic load rating can be used to predict the L10 life of a bearing under specific load and speed conditions-Prediction of bearing life -Bearing life is inversely proportional to bearing load and speed -Thus, reducing the load or speed or increasing the bearing size can substantially increase the bearing life -Safety factors -Because it is virtually impossible to predict the exact life of a bearing, a safety factor should be used to minimize the possibility of premature or unexpected failure -Bearing replacement and machine downtime may cost fat more than that for installing a larger bearingApplication and Selection -Bearing application and selection-Bearing application and selection is based on three major factors: load, speed and life-Consideration must also be given to other operating and environmental conditions, as well as installation and operating costs
-Here are some factors to consider:-Load: is it radial, thrust, or a combination of both? What is the magnitude?Is the load uniform or does it pulse causing the bearing to operate under shock? -Speed: what is its magnitude? Is it constant or variable? Bearing speeds are limited by tolerance grade, lubricant used, retainer cage design and type of bearing seal-Required life: how long must the bearing of operate? This is usually expressed as the number of hours of operation reuqired at a given load and speed? -Noise and vibration: will the bearing operate where noise is undesirable or in high-speed equipment where balance is essential to prevent vibration? -Selecting a bearing -Misalignment: is it present? To what degree? -Temperature: what are the ambient and operating temperatures? Speed, load and external heat affect operating temperature -Environmental conditions: are contaminants or corrosives present? To what degree and what types -Once you have identified and evaluated these application constraints, compare the capabilities of various bearing types with the application requirements-Consider both operating and maintenance requirements, as well as cost -Selecting rolling element bearings -Here are various considerations when selecting rolling element bearings-Rolling-element bearings can handle heavier loads and higher speeds-They have the lowest friction and require the last energy to turn -Load requirements usually determine the type of rolling-element bearing to use for a specific application -For example, predominant thrust loading requires either thrust, angular contact, or tapered roller bearings -Ball bearings are typically applied in hihg-speed applications, whereas roller bearins are best suited for high loads -Spherical roller bearings offer high radial load capabilities with moderate thrust capacity and dynamic alignment capability-Tapered roller bearings have high radial and thrust load capability but do not allow for misalignment-Selected mounted bearings -