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The Basics of Needle Roller Bearings

Needle bearings are a small cylindrical type of roller bearings which are used to prevent friction between moving surfaces which have low rotational speeds. Needle roller bearings are usually used when space is at a premium as needle bearings are much more compact than ball bearings. According to Marks' Standard Handbook for Mechanical Engineers ,quoted on Wikipedia “A Needle Bearing is a roller bearing with rollers whose length are at least four times their diameter”.

The high speeds which needle roller bearings can operate at means that they are usually lubricated with grease or oil and depending on the demands of the application, high-speeds or heavy loads may mean that the bearings would need regular coats of lubrication. As needle bearings can reach such high speeds, the retainers are vital to prevent any friction between the needles and they help to make the needles more stable.

Although there are a wide range of designs available for needle bearings, the typical bearing features an inner race and outer race, a cage which contains the needle rollers and the actual needle rollers. In some cases needle bearings can be used without an inner race or outer race or either as the needle rollers in the bearings can operate alone. For needle rollers to be effective, the hardness, accuracy and finish of the shaft needs to have exactly the same qualities as the bearing races.

Due to the small size of needle roller bearings and the high speeds they are able to rotate at, they are used in compact mechanisms such as gear boxes, for example in an average car the drive shaft will usually have eight or more needle bearings in it. Other uses for these bearings include small appliances, robotics, air craft control, farm equipment and construction equipment.