Bearings Classification – Types, Examples, and Applications
Bearings are essential machine elements that support rotating shafts and reduce friction between moving parts. They are widely used in mechanical systems such as pumps, compressors, automobiles, turbines, and industrial machinery. Understanding bearing classification helps engineers, technicians, and students select the right bearing for specific applications.
Main Categories of Bearings
Bearings are classified into two main categories:
1. Plain or Sliding Contact Bearings
2. Rolling or Anti-Friction Bearings
1. Plain or Sliding Contact Bearings
In plain bearings, the rotating shaft slides directly over the bearing surface. Since the contact area is large, friction is higher, and proper lubrication is essential.
Sub-Classification of Plain Bearings
- Metallic Sliding Bearings – Made of materials like bronze, brass, or white metal.
Example: Bronze bushings used in electric motors.
- Non-Metallic Sliding Bearings – Made of materials like wood, graphite, or plastics.
Example: PTFE (Teflon) bearings used in chemical industries for corrosion resistance.
Based on Loading
- Axial Loading Bearings – Support thrust loads along the shaft axis.
Example: Bearings in vertical pumps.
- Radial Loading Bearings – Support loads perpendicular to the shaft axis.
Example: Bearings in fans and blowers.
Based on Configuration
- Solid Bushing Bearings – Simple cylindrical bushings.
- Split Bushing Bearings – Split into two halves for easy assembly and maintenance.
Based on Lubrication
- Hydrodynamic Bearings – Oil film separates shaft and bearing surface.
- Self-Lubricating Bearings – Made of materials like graphite or composites.
- Hydrostatic Bearings – External pump supplies pressurized lubricant.
2. Rolling or Anti-Friction Bearings
Rolling bearings use balls or rollers between the shaft and bearing races. Since the contact area is small, rolling friction is much lower than sliding friction, making them highly efficient.
Sub-Classification of Rolling Bearings
2.1 Ball Bearings
Ball bearings are widely used due to their versatility and ability to handle both radial and thrust loads.
- Radial Ball Bearings
- Single Row Deep Groove Ball Bearings – Common in electric motors.
- Single Row Angular Contact Ball Bearings – Used in gearboxes.
- Self-Aligning Ball Bearings – Handle misalignment in shafts.
- Double Row Angular Contact Ball Bearings – Used in machine tool spindles.
- Duplex Angular Contact Ball Bearings – Provide rigidity in precision applications.
- Four-Point Contact Ball Bearings – Handle combined loads.
- Thrust Ball Bearings
- Single Direction Thrust Ball Bearings – Used in automobile steering systems.
- High-Speed Duplex Angular Contact Ball Bearings – Found in turbines.
- Double Direction Angular Contact Thrust Ball Bearings – Used in heavy-duty presses.
2.2 Roller Bearings
Roller bearings use cylindrical, tapered, spherical, or needle rollers to carry heavy loads.
- Radial Roller Bearings
- Single Row Cylindrical Roller Bearings – Used in electric generators.
- Single Row Tapered Roller Bearings – Common in automotive wheel hubs.
- Double Row Tapered Roller Bearings – Found in heavy trucks.
- Double Row Cylindrical Roller Bearings – Used in large gearboxes.
- Spherical Roller Bearings – Handle misalignment in conveyors.
- Needle Roller Bearings – Compact design for gear pumps.
- Thrust Roller Bearings
- Cylindrical Roller Thrust Bearings – Used in crane hooks.
- Tapered Roller Thrust Bearings – Found in rolling mills.
- Spherical Roller Thrust Bearings – Handle high axial loads in marine applications.
- Needle Roller Thrust Bearings – Used in automotive transmissions.
Practical Example – Bearing Selection in a Pump System
Imagine a centrifugal pump used in an industrial plant:
- The motor shaft uses deep groove ball bearings for smooth rotation.
- The pump shaft uses sleeve bearings (plain bearings) to handle radial loads.
- The thrust load from impellers is managed by thrust ball bearings.
This combination ensures efficiency, reliability, and long service life.
Conclusion
Bearings are the backbone of rotating machinery. From plain sliding bearings in simple machines to advanced roller bearings in heavy industries, their classification helps engineers choose the right type for performance, durability, and cost-effectiveness.
