Needle Bearings

Needle Bearings

Needle bearings are used in farm and construction equipment, automotive transmissions, gasoline engines, gear pumps, small appliance and tool motors, alternators, aircraft controls, pumps, compressors, pivots and most predominantly, in the drive shaft of rear wheel drive vehicles. The rolling elements of these bearings ride on tracks called races, and the typical structure of a needle roller bearing has an inner and an outer race; some types of bearings also have a cage that retains and orients the needle rollers. Bearings are made usually of stainless and hardened steel though some cages are made from aluminum. Individual needle rollers have rounded, flat or relieved (pin-like) ends that help to relieve stress and keep the rollers captive in the bearing. Because the needle rollers themselves are so thin, the diameter of the bearing is only slightly larger than the diameter of the inner hole, or bore.

Needle roller bearings can be assembled to precise requirements and range in size from 3 millimeters to 150. The basic style of a needle roller bearing is the drawn cup design which has a thin-walled outer ring with either an open or closed end. Drawn cup bearings are used when the exterior of the outer ring needs to be smooth and not act as a raceway. If the bearing does not have a drawn cup, the needle rollers will rotate smoothly on the inner race as well as the outer. Drawn cup or not, practically all needle bearings fit into two categories: the full complement bearing and the caged version. Full complement needle roller bearings have outer rings that retain a full complement, or maximum number, of rollers inside. They are able to withstand vibration and overloading because the rollers are held in place as long as the outer ring is intact. In caged needle roller bearings, rollers are held in place by guides called retainers or cages that prevent roller misalignment in the bearing. Because of the retainer, these bearings cannot fit a full complement of rollers, and they have a lower load capacity as well. Caged needles bearings are, however, able to run faster than full complement needle roller bearings and are used for heavy duty, high speed applications. Lubrication is critical because of the potential for friction between the surface area of the needle rollers and the inner race.