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In this blog we will see about lubricants that we use in our automobiles. So lubricant is a substance such as grease that is capable of reducing friction, heat, and wear when introduced as a film between solid surfaces.


What are objectives of lubricants?

The primary purpose of lubricants is to reduce friction between moving parts in order to minimize power loss and to reduce wear of the moving parts as far as possible. Beside this we can also comment on secondary objectives of lubricants that include cooling effect and cushioning effect. The lubricating oil takes heat from the hot moving components and delivers it to the surrounding during its circulation. Apart from this lubrication oil serves as cushion and prevents damage to engines against shocks.


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Lubrication Circuit


What are requirements of lubricants?

In order to get a reliable lubricant we have to go for some properties that define good lubricants. These properties or requirement for good lubricants are viscosity, physical stability, chemical stability, resistance against corrosion, pour point, flash point and resistance against extreme pressure. Let see what are these properties.


Viscosity: It can be considered as the resistance of the lubricant oil to flow. And due to this property two bearing surfaces are kept apart. The viscosity of lubricating oil should be low at the time of starting engine otherwise engine may not start if sufficient viscosity is maintained.


What is viscosity index (VI)?

Viscosity index is an indication which shows how viscosity of oil changes with temperature. A high viscosity index means less change of oil viscosity with temperature rise. Viscosity is the most important property of lubricants and they should be selected on the basis of viscosity and viscosity index.


Physical stability: This property indicates the stability that is, with change in environmental condition it should not go under physical changes. Or in simple words it should vaporize at higher temperature and should not be solid at lower temperatures. 


Chemical Stability: At higher temperature a lubricant should be chemically stable. There should be no tendency for oxide formation. It should not decompose at higher temperatures. Chemically instability could severely affect the vehicle performance, for instance in an engine, if a oil decompose at higher temperature then it will form carbon and this formed carbon lowers rings efficiency and thus reduces engine compression.  The sparkplugs and valves also don’t function efficiently due to sticking of these carbon particles.


Resistance against Corrosion: The lubricating oil should not have tendency to corrode the pipe lines, crank case and other engine parts with which it comes into contact.


Pour Point: The minimum temperature at which the oil will pour is called its pour point. As the oil will not be able to flow below the pour point, the pour point of the oil should be less than the lowest temperature encountered in the engine.


Flash point: The Flash point of the oil should be sufficiently high so as to avoid flashing of oil vapors at the temperatures occurring in common use. A flash point higher than the minimum desired value will not serve any useful purpose.




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