Farm Power

LESSON 28 PROPERTIES OF LUBRICANTS

Viscosity

Viscosity is the property of the oil which refers to the resistance it has to flow due which two surfaces are kept apart from each other. The viscosity of the lubricants oil should be sufficient to ensure hydrodynamic lubrication. Higher viscosity is also not desirable as it increases the friction and power loss. The oil viscosity decreases at higher temperature and looses it efficacy, so the lubricants should have resistance against the temperature. High viscosity lubricating oils also hampers the initial starting of the engine. Viscosity Index (VI) is a measure of the change of viscosity of oil with temperature. A high viscosity index means less change of oil viscosity with temperature rise. Petroleum lubricating oils general have viscosity index from 100 to 110, which may be increased to 120 to 130 by means of additives.

Clean and stable

The lubricating oils should be sufficiently clean and stable for the smooth and prolonged trouble free operation of the engine. Lubricating oils should be stable at lowest and highest temperature as the oil particles should not get separated at low temperature and get vaporised at high temperature.  Generally, it is observed that at high temperature  oils get oxidized which become sticky and damages the engine components, sometimes form carbon, which damages the piston rings causing compression loss. So the lubricating oils should be chemically stable also which do not change their properties at high temperature. 

Pour Point

It is the minimum temperature at which the fluid/oil pour and the liquid/oil below this temperature will not be able to flow. Hence the lubricants below this temperature can not used and function for its desired purpose.  Thus, the lubricating oil with pour point less than the lowest temperature encountered in the engine is selected.

Flash Point

The flash point of the fluid/oil refers to the temperature at which it gets sparked  and it should be sufficiently high so as to avoid flashing of oil vapours.

Corrosion Resistance

The lubricating oil used in the automobile engines should have sufficient resistance to corrosion of the engine components like pipe lines, crank case etc. which are in regular contact with each other.