Types of Mechanism of Lubrication
Lubrication is the process of reducing friction and wear between two moving surfaces by introducing a lubricant. The mechanism by which lubrication works can be classified into three main types:
1. Hydrodynamic Lubrication (Fluid Film Lubrication)
2. Boundary Lubrication
3. Mixed Film Lubrication
1. Hydrodynamic Lubrication (Discussed in Detail)
Definition
Hydrodynamic lubrication occurs when a thick film of lubricant is formed between the moving surfaces such that the surfaces do not touch each other directly. The load is completely supported by the pressure developed within the lubricant film due to the relative motion of the surfaces.
How it Works
- When a moving surface (like a rotating shaft) slides over a stationary surface (like a bearing), it drags the lubricant into the narrow space between them.
- Due to the viscosity of the lubricant and the relative velocity, a pressure is developed in the fluid.
- This pressure lifts the moving surface, forming a wedge-shaped lubricant film.
- This film separates the two metal surfaces completely, preventing any direct contact.
Conditions Required for Hydrodynamic Lubrication
- There must be relative motion between the surfaces.
- The lubricant should have suitable viscosity.
- The geometry of the surfaces should allow a converging wedge of lubricant.
- The surfaces should move at sufficient speed to build pressure in the film.
Diagram Description
You can draw:
- A shaft rotating inside a bearing
- A wedge-shaped lubricant film between them
- Arrows showing motion of the shaft
- Arrows indicating fluid pressure direction
📝 Caption: Hydrodynamic Lubrication between Shaft and Bearing
Advantages
- Complete separation of surfaces — no metal-to-metal contact
- Minimum wear and friction
- Can handle high loads and speeds
- Provides cooling effect due to circulation of lubricant
Applications
- Journal bearings in electric motors and turbines
- Crankshaft and camshaft bearings in engines
- Steam engine cylinders
- Gearboxes and compressors
Real-Life Example (Indian Context)
In Indian Railways, hydrodynamic bearings are used in electric locomotives to support high-speed rotating shafts. Also, automobile engine crankshafts in cars like Maruti Suzuki, Tata, and Mahindra use this principle for smooth functioning.
Other Two Types (Brief Overview)
2. Boundary Lubrication
- Occurs when the lubricant film is very thin and the surfaces are almost in contact.
- Common during starting or stopping of machines.
- Depends on the chemical properties of the lubricant, which forms a protective layer on the surfaces.
3. Mixed Film Lubrication
- A combination of hydrodynamic and boundary lubrication.
- Some areas of the surface are separated by the fluid film, and some are in boundary contact.
- Occurs in intermediate conditions, like medium load and medium speed.
Conclusion
Hydrodynamic lubrication is the most effective and desirable form of lubrication in high-speed machinery, as it provides complete separation of moving surfaces and minimizes wear. Understanding the lubrication mechanism helps in choosing the correct type of lubricant and designing reliable machines.