Needle roller bearings have relatively small diameter cylindrical rolling elements whose length is much larger than their diameter. Compared with other types of rolling bearings, needle roller bearings have a small cross-sectional height and significant load-bearing capacity and rigidity relative to their volume. Also, because the inertial force acting on them is limited, they are an ideal choice for applications with an oscillating motion.
Needle roller bearings have a greater surface area in contact with the races, so they can support a greater load. They are also thinner, so they require less clearance between the axle and the surrounding structure.
Needle roller bearings are heavily used in automobile components such as rocker arm pivots, pumps, compressors, and transmissions. The drive shaft of a rear-wheel drive vehicle typically has at least eight needle bearings (four in each U joint) and often more if it is particularly long, or operates on steep slopes.Needle roller bearings also work well in compact and lightweight machine designs and they serve as a ready replacement for sliding bearings.
Needle roller bearing utilize small, cylindrical rollers, referred to as needle rollers, to reduce friction between moving components. The needle rollers are the load-carrying components of the needle roller bearing. They are located between two races, between a single race and a shaft, or between a shaft and a housing, depending on the design of the bearing. Most radial needle roller bearings are designed to accommodate axial-oriented forces more than 5% of the radial load. Those which are used in radial applications have rollers that are parallel to the shaft. Thrust bearings, those meant for axial loads, contain rollers with axes that are perpendicular to the shaft and from which they extend radially.
All needle roller bearings require some type of lubricant to help dissipate heat and reduce friction. The amount of friction is resultant from the load carried, the type and size of the needle roller bearing, the speed at which the bearing rotates, and the characteristics of the lubricant used. Needle roller bearing, especially those with outer rings made of high-strength steels, can also suppress shock and vibration.Needle roller bearings are designed to operate under a minimum load. Not meeting this quota may damage raceways from low roller inertia. Furthermore, needle roller bearings are typically not suitable for static loads. Such loads can damage roller elements. This includes applications in which the bearing rotates at less than 10 rpm, has slow oscillations, or may experience points of rest.
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