Needle Bearings

Needle bearings are defined as a type of cylindrical rolling-element bearing in which the length of the elements is at least four times their diameter. They are arranged parallel to the axis of the shaft, which results in a long bearing housing, improving the bearing's load bearing capacity, and a very small clearance between the outer diameter of the housing and the inner diameter of the bearing. This small cross-sections means the bearing is often found in mechanisms which require a combination of both compactness and a capacity for managing large radial loads and high operational speeds that is not readily provided for by a typical deep groove or angular contact ball bearing.

In its most compact and economical form, the needle bearing design does not use an inner race. Instead, the needles make direct contact with the equipment shaft, reducing both the total friction in the system and the thickness of the bearing. However, for this to work, the shaft must meet high manufacturing standards of roundness, durability and surface finish, as it is essentially fulfilling the role of a component that would otherwise be precision engineered to fit the bearing. Needles often taper to a point, in which case they are held in place by lips or flanges at the edge of the bearing housing, or even by the shaft itself.The number of needles used in cageless designs is such that mechanically significant slippage or clustering is impossible, eliminating the need for a needle cage as found in a typical ball bearing and reducing the overall thickness of the design. However, heavier-duty needle bearings often use both a needle cage and an inner raceway, sacrificing compactness for robustness and durability when operating with high loads and speeds. These may also use more than one outer race, depending on their specific application.

Needle bearings find application is tightly engineered mechanisms such as engines where they are of course favoured for their compactness.They find a number of other applications in the automotive industry, particularly in transmissions and some gearboxes.Four needle bearings are often found at every universal joint in a drive shaft, and they have additional applications in steering and braking systems. Heavier vehicles such as trucks must use correspondingly heavier bearings, in order to manage the high radial stresses they are likely to encounter. Lighter varieties are also found in some highly compact domestic or office mechanisms, such as power tools, exercise equipment, printers, copiers, scanners and fax machines.