What is Lubrication?
It is defined as a process/technique used for keeping two surfaces, which are working at close proximity to each other separated & carry load.
Or
It is technique used to reduce friction between two moving parts.
What is a Lubricant?
They provide a protective film that separate the two rubbing surface and reduce the level of friction between them.
e.g- Oil, Grease, etc.
Purpose of Lubrication
Below is the list of primary reasons to use lubrication:
- To keep moving parts apart.
- To reduce friction.
- Transfer Heat(cooling)
- To carry away contaminants & debris
- To transmit power.
- To prevent corrosion.
- To seal gases.
- To reduce the risk of smoke & fire objects.
Types of Lubrication👇
Boundary Lubrication
- Also known as Thin Film Lubrication
- Fluid film thickness is basically molecular usually one or two molecule thick.
- Depends on the molecular property of the lubricant ie its ability to adhere to the metal surface.
- It is independent of shape & velocity of the moving surfaces.
- Lubricants used should be able to maintain a strong attachment to the surface under high temp & load pressure. Hence, Greases are the most commonly used boundary lubricants, the sacrificial wear of the lubricant layers will reduce the metal wear and prolong the life of the machinery.
Hydrodynamic Lubrication
- Uses Liquid lubricant
- Relative motion between the surfaces is high.
- Viscosity of the liquid lubricant.( Optimum viscosity is very essential as too low a viscosity will jeopardize the lubrication & Too high a viscosity lead to power loss and heating.)
- Geometry of the surface (Convergent Wedge)
- The distance between the surface reduces with the increase in load.
- The Coefficient of friction is as low as 0.001& fluid film thickness is 1mm to 0.01 mm.
- Advantages of Hydrodynamic lubrication are
- Low Friction
- Zero Wear
- Low Cost
In this type of lubrication one surface floats on the other surface due to hydrodynamic lift.
Elasto-Hydrodynamic Lubrication
- Occurs when there is a point or a line contact with extremely high pressure.
- High pressure has a significant effect on the fluid viscosity in fact the oil at the contact point becomes semi-solid, similar to cheese. Thus allowing a very thin film
Hydrostatic Lubrication
In this type of lubrication, the hydrostatic pressure, supplied with the help of external pump, lifts the load on the bearing.
Advantages:
- Low friction- as the film thickness is not dependent on the relative motion between the surfaces.
- Unaffected by the discontinuous motion of running.
- Capable of supporting heavy loads.
- Little or moderate temperature rise of the lubricant - Due to thicker film & ample supply of lubricant.
- Continuous flow prevents accumulation of dirt/wear particles.
Disadvantages:
- Requires external pumping arrangement.
- Risk of lubrication failure due to failure of the pump.
- Requires continuous supervision.
- High initial cost.