Characteristics of lubricating oil
Characteristics of Lubricating oil:
The lubrication oil is used in automobile to reduce the friction between the two mating parts. In order to minimize the friction losses it is essential to use lubricating oil which has the desirable characteristics as per the operating conditions of vehicle. The main characteristics of lubricating oil are as follows.
Viscosity: It the property of fluid which offer resistance to its flow. Higher the viscosity, thicker is the fluid. The viscosity helps in maintaining the fluid film between the mating surfaces which separates the mating parts. If we use oil having very high viscosity, it can break the oil film, leaving the surfaces with dry friction. It can also results in power losses. So the viscosity of lubricants should be sufficient to maintain the film thickness between mating parts.
Volatility: The property of oil to vaporize at high temperatures is called volatility. Good lubricating oil should have low volatility.
Pour point: It is the lowest temperature at which the lubricant will flow. For better performance during winter time, the pour point should be low.
Cloud point: It is the temperature at which the wax and other substances in the lubricating oil crystallize, and separate out on cooling the oil. The cloud point should be as low as possible.
Chemical stability: It is the property which resists the oil against oxidation. Various additives can be added to oil to obtain chemical stability.
Corrosion property: Several additives are mixed in oils to make it corrosion resistant. The corrosion property of oil can be checked by immersing the metal strips in oil for a specified time under specified conditions.
Mechanical impurities: The lubricating oil should be free from mechanical properties such as sand, dust particles etc.
Fire point: The highest temperature at which oil vapors burn when brought in contact with flame. Oil should have high fire point.
Flash point: The lowest temperature at which the oil vaporizes and mix with air to form ignitable mixture.
Adhesion: The property of oil to stick with the surface is called adhesion. It provides the film thickness between the two mating surfaces.
Carbon residue: Lubricating oil is a hydrocarbon containing a high percentage of carbon. After decomposition, the oil leaves deposits of carbon, which is unwanted. These deposits should be least in good lubricating oil.