How to Select Rolling Bearings and Plain Bearings?

Bearings are indispensable key components in mechanical equipment, undertaking the critical function of supporting rotating shafts. Based on different friction characteristics inside bearings, 

they are classified into rolling friction bearings (rolling bearings for short) and sliding friction bearings (plain bearings for short).

These two types of bearings feature different structures, with respective advantages and disadvantages in performance. Comprehensive practical conditions shall be taken into account during selection. 

The following provides a comparative analysis of the performance between rolling bearings and plain bearings.

Comparison of Structure and Motion Mode
The most obvious distinction between rolling bearings and plain bearings lies in the presence or absence of rolling elements.
Rolling bearings: Equipped with rolling elements (balls, cylindrical rollers, tapered rollers, needle rollers). Rotating rolling elements support the rotating shaft, so contact occurs at discrete points. More rolling elements mean more contact points.
Plain bearings: Free of rolling elements. Smooth surfaces support the rotating shaft, forming surface contact.
Structural differences determine their motion modes: rolling bearings operate via rolling motion, while plain bearings rely on sliding motion. Accordingly, their friction mechanisms are fundamentally different.
Comparison of Load Capacity

Generally, plain bearings possess larger bearing areas, so their load capacity is usually higher than rolling bearings. Rolling bearings have limited capacity to withstand impact loads. Nevertheless, 

fully fluid-lubricated plain bearings can sustain heavy impact loads because the lubricating oil film delivers buffering and vibration absorption effects.

At high rotational speeds, the centrifugal force on rolling elements inside rolling bearings rises, reducing load capacity and easily generating noise. For hydrodynamic plain bearings, load capacity increases with rising rotational speed.
Comparison of Friction Coefficient and Starting Friction Resistance

Under normal operating conditions, rolling bearings have a lower and more stable friction coefficient. By contrast, the lubrication condition of plain bearings is susceptible to external factors such as rotational speed and vibration, 

leading to a wide variation range of friction coefficients.

During startup, stable oil film has not yet formed inside plain bearings, resulting in larger resistance than rolling bearings. However, hydrostatic plain bearings feature low starting friction resistance and low operating friction coefficients.
Comparison of Applicable Operating Speeds

Restricted by the centrifugal force of rolling elements and temperature rise, rolling bearings cannot operate at excessively high speeds and are generally applied for medium and low-speed working conditions. 

Due to heat generation and wear, non-fully fluid-lubricated plain bearings also have limited operating speeds.

Fully fluid-lubricated plain bearings exhibit excellent high-speed performance. In particular, when gas serves as the lubricant for hydrostatic plain bearings, the rotational speed can reach 100,000 rpm.
Comparison of Power Loss
Thanks to the low friction coefficient, rolling bearings generally have minor power loss, lower than that of non-fully fluid-lubricated plain bearings. Yet power loss will surge if lubrication or installation is improper.
Fully fluid-lubricated plain bearings have low frictional power loss. However, hydrostatic plain bearings involve power consumption of oil pumps, so their overall power loss may exceed that of hydrodynamic plain bearings.
Comparison of Service Life

Subject to material pitting and fatigue, rolling bearings are generally designed for a service life of 5 to 10 years or require replacement during major overhauls. 

The bearing shells of non-fully fluid-lubricated plain bearings suffer severe wear and need periodic replacement.

Theoretically, fully fluid-lubricated plain bearings have unlimited service life. In practice, cyclic stress may trigger fatigue failure of bearing shell materials, especially for hydrodynamic plain bearings.
Comparison of Rotational Accuracy

Rolling bearings generally achieve high rotational accuracy due to small radial clearances. Operating under boundary or mixed lubrication conditions, 

non-fully fluid-lubricated plain bearings run unstably with heavy wear and low precision. Supported by the damping oil film, fully fluid-lubricated plain bearings offer relatively high precision, 

and hydrostatic plain bearings deliver even superior rotational accuracy.

Other Comparative Points

Rolling bearings adopt oil, grease or solid lubricants with low consumption (higher consumption at high speeds). Strict requirements are imposed on lubricant cleanliness, 

so sealing structures are necessary. Rolling bearings are easy to replace, and crankshaft journals usually do not need repair.

For plain bearings (excluding non-fully fluid-lubricated types), liquid or gaseous lubricants are commonly adopted with large consumption and high cleanliness requirements for lubricants. 

Bearing shells need frequent replacement, and shaft journals sometimes require reconditioning.

Improper design will drastically shorten bearing service life and trigger various bearing failures.