Engine Friction and Lubrication (Part 2)

Introduction:

In previous blog, we have discussed about basic of engine friction and lubrication. Here, we will discuss about various topics like Grading of Lubricating Oil, Grease Lubrication and additives.

 Link to Part 1. Click Here

Grading of Lubricating oil:

Lubricating oils are classified according to viscosity property possessed by them. The Society of Automotive Engineers (SAE), USA, has assigned a unique number code to oil and they are commonly used for grading the lubricating oil. SAE has assigned a number to oil whose viscosity at given temperature falls in certain range. There are two different temperatures used as a reference for assigning unique number code to oils -18° C and 99° C. SAE, 5W, 10W, 20W grades are defined in terms of viscosity at -18° C and they are lubricants which render starting of engine in cold weather easily. While SAE, 20, 30, 40 and 50 grades are defined at 99° C temperature in terms of viscosity and they are lubricants which work satisfactory in normal and hot climatic conditions.

The above mentioned numbers for lubricants are nearly used for their classification according to viscosity and do not indicate the quality of oil since these numbers do not consider some important factors such as, stability, oiliness, etc.

Multigrade oils:

It is possible; with the advent of additives such as viscosity Index improves, to develop lubricants with more than one viscosity at different temperatures. Thus lubricants in SAE-30 grade at 99⁰ C and in the SAE-10 W grade at -18⁰ C oils of this type are known as multgrade oils. Also other possible grades are 5W/20, 20W/20, 20W/40.

There are many advantages of multigrade oils. Some of them are listed below:

·        No need to change oil as per the ambient temperature,

·        Battery life is extended due to ease of cranking even at low ambient temperature,

·        Engine remains healthy for long and required viscosity is maintained under different operating temperatures,

·        It provides easy starting and short warming up period and reduced oil consumption,

·        It retard the build-up carbon inside the combustion chamber and promotes the mileage between the decarbonization,

·         They possess excellent thermal and oxidation stability. Hence, they protect the engine from rusting, corrosion and wear.

Grease Lubrication:

A heavily loaded, low speed and large clearance bearings, thin lubricating oil is not suitable due to high fluidity.

Grease are semi-solid materials manufactured by dispersing a thickening agent in lubricating fluid. The lubricating fluid is generally mineral oil and the thickening agent is usually a metallic soap. The soap dispersed in the oil forms a pattern of minute cris-crossing fibers which trap the oil and prevents the flow. The mineral component provides the lubrication while the soap component gives the body to the greases. The properties of greases mainly depend on the type of soap and lubricating fluids used. Some of the common base greases are:

·        Calcium soap greases,

·        Sodium soap greases,

·        Lithium soap greases,

·        Aluminum soap greases and

·        Non soap greases.

Additives:

Additives are used in greases in the similar manner as in lubricating oils to enhance certain properties for special purpose. The main types of additives used are:

1.     Anti-oxidant

They are used to increase oxidation stability.

2.     Anti-rust

Additives are used to enhance protection against rusting and wear.

3.     Extreme pressure solid additives

They are mainly used to increase the load bearing capacity; molybdenum disulphide is sometimes used to reinforce greases which have to lubricate sliding surfaces for prolonged periods without renewals.