A needle bearing is a type of bearing that features roller elements which are longer and thinner than traditional roller bearing elements. Due to its considerably smaller roller diameters, the needle bearing is ideally suited for applications where reduced overall bearing heights are required. Notwithstanding the small roller diameters, needle bearings have good load bearing capacities and are often used in large numbers in automotive engines and other high stress, precision applications. Needle bearings are available in a wide range of designs including caged or full compliment bearings and sealed or open bearings. There are also angular contact varieties of this bearing available which combine needle roller and ball bearing elements.
Roller bearings use sets or cylindrical roller elements instead of the more traditional balls. Needle roller bearings follow the basic design principles of a normal roller bearing with an inner and outer race which contain and orient a set of roller elements between them. The inner race is pushed onto the shaft of the machine and the outer race is held captive in an end cap or outer frame. The rollers then offer low friction support for the shaft when it rotates. The main difference between conventional roller bearings and needle bearings is the roller diameter.
The needle bearing features roller elements of a greatly reduced diameter than a normal roller bearing element. This means that a needle roller bearing has a far lower profile than that of a conventional type. This characteristic allows the needle bearing to be used in applications where small inner to outer surface tolerances are required. The use of needle bearings allow machine designers to keep overall design dimensions down, thus saving space and weight in applications such as automobile engines. The reduced height of needle bearings does not have a negative impact on their performance; they exhibit good load bearing qualities.
There are many different configurations of needle bearings available to suit a wide range of applications. These include sealed or open bearings and examples which include flanged outer races for increased lateral stability. Caged needle bearings feature steel or brass “cages” which hold a reduced number of rollers in constant positional orientation that results in reduced friction. Full compliment bearings are also available which have the race area fully filled with rollers. This increases the friction co-efficient of the bearing but also increases its stability and load bearing ability.
Some needle bearing designs include an additional set of ball bearings which run on the outside of the roller set and allow for improved angular load bearing. Self aligning needle bearings have two outer races with mating, cupped inner surfaces which gives this variant a degree of axial misalignment absorption. Needle type thrust bearings are also fairly common and feature roller sets arranged radially in a fan formation.