Definition And Working of Plain Bearings Explained

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Plain bearings are basically the mechanical components that are charged with bearing load and allowing rotational and sliding motions between two parts of a machine. The main objective of Plain bearings is to prevent wear and tear of the point of support of the machine that usually takes place if the shafts roll directly into the structure. 

Plain bearings are made of two major parts. One is a fixed part that is known for bearing the loads and is also known as the support whereas the other part is the area that gets worn out and is also called a ‘the bush’. Bush is in contact with the moving element. 

Types of plain bearings

The types can be divided on the basis of various categories like - 

Type of contact between the parts 

  • Plain or friction bearings - The moving and fixed surfaces generally have sliding friction and are separated by an oil film. These are also known as friction bearings, bushes, and solid bearings. These have cylindrical shapes and no moving parts. 

  • Rolling bearings - Inside them, there’s a journal of the shaft along with the rolling surface for the support that’s separated with the rolling elements so that when the bearing or journal rotates, a rolling motion is generated instead of the sliding one. These are the ones that are composed of two rolling rings and are separated from each other equally by the rolling elements depending on the shapes and type of use. 

Based on the lubrication system 

  • Self-lubricating bearings: These are the ones that require no lubrication externally. They are manufactured with porous materials.

  • Regularly lubricated bearings: These are the bearings that require lubrication for a limited period of time.

  • Hydrostatic bearings: In this, the lubricant is pressure fed with the help of an external pump. 

  • Hydrodynamic bearings: These bearings do not require any external injection but their moving parts are the one that generates a hydrodynamic effect that makes oil lubrication easy in almost all the parts. 

Based on the position of the rolling bearing

  • Axial: These are the ones that take loads into the direction of the shaft. 

  • Radial: It takes loads perpendicularly to the shaft and not longitudinally. 

  • Thrust: These include radial and axial loads. 

Advantages and disadvantages of plain bearings

Plain bearings have both merits and drawbacks as compared to rolling bearings -


Plain bearings are lightweight, cost-effective, and less noisy. They have longer fatigue and a free service life of all its elements and features. It requires less maintenance, radial space as these are built with thin walls. The installation of Plain bearings is also very simple. The lubrication procedures are not retired with the self-lubrication bearings. These are allowed for various higher rotational speeds and come with a great shock resistance. 

Disadvantages of Plain Bearings

These bearings require more axial space and have higher friction during the startup or transient processes. The use of such friction-resistant material is indispensable. There’s greater wear and tear as compared to the rolling bearings because of the direct friction between the shaft and the bush. 

To briefly describe, plain bearings are used because of the mechanical advantage and cheaper shaft rotations which brings out the best solution and the most beneficial thing for the customer.