Low Friction Bearings

 

 

        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.

 

        Fluid bearings use a thin layer of liquid or gas fluid between the bearing faces, typically sealed around or under the rotating shaft.

 

There are two principal ways of getting the fluid into the bearing:

 

        In fluid static, hydrostatic and many gas or air bearings, the fluid is pumped in through an orifice or through a porous material.

        In fluid-dynamic bearings, the bearing rotation sucks the fluid on to the inner surface of the bearing, forming a lubricating wedge under or around the shaft.
Hydrostatic bearings rely on an external pump. The power required by that pump contributes to system energy loss just as bearing friction otherwise would. Better seals can reduce leak rates and pumping power, but may increase friction.

 

       Hydrodynamic bearings rely on bearing motion to suck fluid into the bearing and may have high friction and short life at speeds lower than design or during starts and stops. An external pump or secondary bearing may be used for startup and shutdown to prevent damage to the hydrodynamic bearing. A secondary bearing may have high friction and short operating life, but good overall service life if bearing starts and stops are infrequent.

 

        Low-friction cylindrical roller bearings LSL and ZSL are single row, self-retaining and correspond to dimension series 23. The bearings have solid outer rings with two ribs, while the inner rings have one rib. The inner ring can be removed and this gives easier fitting of the bearings. Disc cages or spacers prevent the cylindrical rollers coming into contact with each other during rolling.