Bearing

This topic explains the types of basic bearing such as friction bearing, fluid coated bearing, rolling bearing. This topic also explains the method of

selecting suitable bearing based on calculation of dynamic and life load ratio.

1By: M. Hamdi Bin Khosran JKM, PMM

� A bearing is any of various machine elementsthat constrain the relative motion between two or more parts to only the desired type of motion. This is typically to allow and promote free rotation around a fixed axis or free linear movement; it may also be to prevent any motion, such as by controlling the vectors of normal forces. Bearings may be classified broadly according to the motions they allow and according to their principle of operation, as well as by the directions of applied loads they can handle.


� A plain bearing, also known as a plane bearing[1] or a friction bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements.

� Therefore the journal (i.e., the part of the shaft in contact with the bearing) slides over the bearing surface.

� The simplest example of a plain bearing is a shaft rotating in a hole. A simple linear bearing can be a pair of flat surfaces designed to allow motion; e.g., a drawer and the slides it rests on or the ways on the bed of a lathe.

� Plain bearings, in general, are the least expensive type of bearing. They are also compact and lightweight, and they have a high load-carrying capacity.


� A rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing round elements between the two pieces. The relative motion of the pieces causes the round elements to roll with very little rolling resistance and with little sliding.


� Fluid bearings are bearings which support the bearing's loads solely on a thin layer of liquid or gas.

� They can be broadly classified as fluid dynamic bearings or hydrostatic bearings. ¡ Hydrostatic bearings are externally pressurized fluid

bearings, where the fluid is usually oil, water or air, and the pressurization is done by a pump. Hydrodynamic bearings rely on the high speed of the journal self-pressurizing the fluid in a wedge between the faces.

¡ Fluid bearings are frequently used in high load, high speed or high precision applications where ordinary ball bearings have short life or high noise and vibration. They are also used increasingly to reduce cost. For example, hard disk drive motor fluid bearings are both quieter and cheaper than the ball bearings they replace.


Bearing

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