Needle Roller Bearings | Construction, Advantages and Applications

Needle roller bearings are characterized by cylindrical rollers of very small diameter and relatively long length. Needle bearings are also called as “Quill bearings”. The length to diameter ratio of needles is more than four. That means if the diameter of the needle of needle bearing is 2 mm then the minimum length of the needle is 8 mm.
Rolling Contact Bearings, Their Types, and Applications.

Construction of Needle Roller Bearing

Needle bearings are used with or without inner and outer races. Very often, needle bearings are used without the races as shown in fig.

Needle Bearing diagram
Needle Bearing diagram

In this case, the needles run directly on the surface of the shaft. The shaft is hardened and ground with a surface hardness of 50 HRC. This type of construction is suitable where limited radial space is available.
Materials for Sliding Contact Bearing.

Needle bearings advantages

  1. Needle bearings have a smaller outer diameter. It is due to this reason that they are often used to replace sleeve bearings. This allows replacement with little or no change in design.
  2. They are compact and lightweight compared with other types of bearings,
  3. They have a large load-carrying capacity, particularly at low peripheral speeds.

Applications of Needle Roller Bearings

Needle bearings are ideally suited for applications involving oscillatory motion such as piston pin bearings, rocker arms, and universal joints. They are also suitable for a continuous rotation where the load is variable or intermittent.
Bearing Materials and Their Desirable Properties.

Although needle bearings are considered as a variety of cylindrical bearings, they have altogether different characteristics. Short roller bearings can be manufactured with a high degree of accuracy. the needles, which are considerably longer than their diameter, cannot be manufactured with the same degree of accuracy. Short rollers are accurately guided in their cage and race. Needles are not guided to that extent. This results in high friction in needle bearing. The coefficient of friction in the cylindrical roller bearing is 0.0011. On the other hand, the coefficient of friction in needle bearings is 0.0045 or almost four times that of cylindrical roller bearing.

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