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What are Lubricants exactly ? How do Lubricants work ?

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What are Lubricants exactly ? How do Lubricants work ?

So, Let’s start discussing

First of all,

What is Lubricant !!

Lubricants

A lubricant is basically a substance introduced between two moving surfaces to reduce friction. Before going into what a lubricant is and how it functions, we need to know what friction is.

So, what is friction !!

Friction is the force that resists the relative motion between two bodies in contact. The surfaces of all material, no matter how smooth they appear, are not truly smooth on an atomic scale. They are rough, with sharp and rugged projections called asperities.

 

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When two surfaces come in contact with each other, initially, they only touch at a few of these points. A small load is applied on a metal surface, local high pressure develops at these points (asperities) of contact, which then tend to interlock, thus developing a resistance to motion.

Lubricants

When a metal slides, the peaks get broken resulting in wear and tear of the surfaces. Further, if the pressure is high, the asperities deform plastically increasing the contact area between the two surfaces.

A sufficiently high pressure leads to the formation of a welded junction between asperities. Additional force is then required to break these junctions. This further adds to the frictional resistance.

Now we come to the point, How lubricants work or what is the role of lubricants !!

 

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Functions of Lubricants

  • A lubricant reduces frictional resistance by keeping the moving surfaces of a system apart and prevents their direct contact so that the asperities do not interlock.
  • It reduces surface deformation and wear and tear by keeping the moving surfaces apart.

Lubricants

  • The lubricating oil absorbs the generated heat and acts as a coolant.
  • Lubricants increase the efficiency of the machine.
  • They reduce maintenance cost of machines and increase their life.
  • Lubricants also act as sealants for gases.
  • They reduce noise of the machine.
  • Lubricants prevent corrosion and rust.

Mechanism of Lubrication

  1. Fluid film or thick film or hydrodynamic lubrication
  2. Thin film or boundary lubrication
  3. Extreme pressure lubrication

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  1.  Fluid film or thick film or hydrodynamic lubrication

Hydrodynamic lubrication occurs when the load is low and the speed is high. In this type of lubrication, the two sliding metal surfaces are separated by a thick, continuous unbroken film or layer of the lubricant.

    2.  Elasto-hydrodynamic lubrication

It occurs when the surfaces are in rolling motion relative to each other, like in ball bearings and roller bearings. In it the pressure is higher and the thickness of the film is much less than hydrodynamic lubrication At here, the film elastically deforms the rolling surface to lubricate it.

    3.  Extreme pressure lubrication

Lubricants

When the moving surfaces are subjected to very high pressure and speed, heat is generated causing some harmful effects –

  • The lubricants fail to stick to the metal surface. They vaporize or decompose.
  • Surface deformation and seizure takes place.

To overcome these difficulties due to extreme pressure conditions, extreme pressure additives are added to the lubricant. The commonly used extreme pressure additives are organic compounds having active radicals or groups such as chlorine (as in chlorinated esters), sulphur (as in sulphurized oils) or phosphorus (as in tricresyl phosphate). Extreme pressure lubricants find use in aircrafts and spacecrafts.

 

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