In this article, you’ll learn what are the different properties of Lubricants (lubricating oil) with Explanation.
Lubrication is necessarily required in vehicle maintenance. To supply lubrication oil between the moving parts is termed as lubrication. lubrication of all moving parts (Other than nylon, rubber bushed or pre-lubricated components) is necessary to reduce friction, wear and to prevent seizure.
An engine lubricating oil must have some satisfactory properties or characteristics, which are as follows:
Properties of Lubricants
Following are the 18 properties of lubricants:
- Fire point
- Cloud point
- Pour point
- Physical stability
- Chemical stability
- Sulphur content
- Specific gravity
- Neutralization number
- Film strength
Viscosity is a measure of the resistance to flow or the internal friction of an oil. The viscosity essentially means the body a heavy oil has viscosity, a light oil low viscosity and medium oil medium viscosity. The viscosity of an oil is usually as the time in seconds that it takes for a given amount of the oil to flow by gravity through a standard sized orifice at a given temperature.
Viscosity is one of the most important properties of engine lubricating oil. It is used universally to grade lubricants. Viscosity is inversely proportional to temperature. It decreases as the temperature rises and increases as it falls. This is the reason why light oil is recommended for automobile engines in winter as compared to summer.
It also explains why engines are so hard to start in very cold weather. The viscosity of an engine lubricating oil should be just sufficient to ensure hydrodynamic lubrication. If it is more than this value, it will involve higher power losses due to the increased oil resistance.
The viscosity is measured by viscosimeter. There are many types of viscosimeters, the most important types are as follows:
- Saybolt Universal viscosimeter
- Redwood viscosimeter
- Engler viscosimeter
- Barbey viscosimeter
The unit of viscosity is given as “seconds say bolts” or “seconds redwood” etc. Temperature is also specified with the viscosity. For example, if an oil has a viscosity of 50 at 210°F, it means that 50 seconds were required for the measured volume of oil to flow through the standard tube under gravity at 210°F.
2. Flash Point
The flashpoint is defined as the lowest temperature at which the lubricating oil will flash when a small flame crosses its surface. When the oil is heated, it reaches a temperature at which, if a small flame is brought near it, a flash spreads across the oil.
It happens due to the volatilization of the light particles in the oil. The flashpoint of the oil should be sufficiently high to avoid flashing of oil vapours at temperatures in common use.
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3. Fire Point
If the oil is heated further after the flashpoint has been reached, the lowest temperature, at which the oil will burn continuously is called the fire point. The fire point also must be high in lubricating oil, so that the oil does not burn in service.
4. Cloud Point
The oil changes from a liquid state to plastic or solid-state when subjected to low temperature. Temperatures in some cases the oil starts solidifying which makes it appear cloudly. The temperature at which this occurs is identified as the cloud point.
5. Pour Point
This is the lowest temperature at which lubricating oil will be pour. The pour point of an oil use lubrication of its ability to move at low temperatures. This property must be considered because of its effect on starting an engine in cold weather and on the free circulation of oil through exterior feed pipes when pressure is not applied.
Oiliness is the characteristics property of oil. Oil is said to be oil when it has oiliness. This property highly desirable in helping the lubricant to adhere to the cylinder walls.
Corrosion has been defined as the destruction of a solid body by electro-chemical action which starts unintentionally outer surface. A lubricant should not occur the working parts and it must retain its properties when in the presence of foreign matter and additives.
Colours of lubricating oil are not of so much importance for its properties aspect as a test for checking the uniformity of any given grade or brand of oil.
During the combustion, petrol vapour may accept past the piston ring if the rings are worn or broken. A considerable amount of such fuel is mixed with the crankcase oil and dilutes it, thus affecting its lubricating property.
The test to determine the amount of dilution in crankcase oil indicates how far oil could be used when mixed with petrol vapour. Crankcase ventilation is forever, adopted to escape the petrol fumes.
A lubricating oil, when mixed with water, loses its lubricating properties. The emulsification number is an index of the tendency of an oil to emulsify with water.
11. Physical Stability
Lubricating oil must be stable physically at the lower and the highest temperature between which the oil is to be used. At the lowest temperature, there should not be any separation of solids, and at the highest temperature, it should not vaporise beyond a certain limit.
12. Chemical Stability
A lubricating oil should also be stable chemically. There should be no tendency for oxide to form. The oxidation products, being sticky, clog the working parts, cause the faulty piston rings and valve action. Oil should not decompose even at high temperatures to form carbon, which makes the spark plugs and valves defective to function.
13. Sulphur Content
It sulphur is present in a considerable amount in the lubricating oil it promotes corrosion. The corrosion test explains the amount of sulphur content.
14. Specific Gravity
Specific gravity is a measure of the density of oil. It is determined by a hydrometer which floats in the oil, and the gravity is read on the scale of the hydrometer at the surface of the oil. The scale used is the one recommended by the American petrol institute, and the result is called the API gravity.
15. Neutralization number
An oil may contain impurities that are not removed while refining. It may contain alkaline or acid products. The neutralization number test is a simple procedure to determine acidity or alkalinity of the oil. This is the weight in milligrams of potassium hydroxide necessitated neutralizing the acid content of one gram of oil.
It has the property of lubricating the oil, causing the oil particles to stick to the metal surfaces.
17. Film Strength
It has the lubricating properties of the oil due to which this oil maintains a thin film between the two surfaces even at high speeds and loads. The film does not break and the two surfaces do not come in direct contact.
Due to the adhesion and strength of the film, the lubricant penetrates the metal pores and clings to the surfaces of bearings and journals by keeping them wet when the journals are at rest and preventing metal to metal contact until the film of lubricant is built up.
Lubricating oil must be clean. It should not contain dust and dirt particles. These impurities may either the filtered out or removed with the change of oil at periodic intervals. Further, the oil must contain agents, called detergents which remove the impurities from the engine parts during oil, circulation.
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