Lubrication properties

Question 1

Viscosity

Answer 1

Viscosity: Is the resistance to flow or shear of a lubricant and must be taken into
account when selecting a lubricant. The viscosity at low temperature must be low
enough to allow machines to start and let the oil flow. The viscosity must be high enough to ensure adequate film thickness at high temperatures. An example where viscosity would be important is in an internal combustion engine lubrication system

Question 2

Viscosity index

Answer 2

Viscosity index: The rate of change of viscosity with temperature is known as the viscosity index. It is normally desirable for the viscosity to remain the same over a wide range of temperature. A high viscosity index indicates such a property where a low index indicates the oil tends to thin out rapidly with increasing temperature.

Question 3

Emulsion:

Answer 3

Emulsion: An emulsion is a mixture of water and oil, which is undesirable because it has poor lubricating properties. Emulsifeation is a measure of the tendency of oil to mix intimately with water. This is a problem with steam turbine lubrication systems.

Question 4

Foaming

Answer 4

Foaming: Due to air bubbles that form foaming occurs normally in gearbox lubrication systems. This can be a problem in hydraulic systems because air is compressible.

Question 5

Compatibility

Answer 5

Compatibility: Care must be taken when selecting seal materials to ensure there are no adverse effects on the materials by the lubricating oil. Consideration must also be taken where oils could be mixed with other oils and the type of bearing material.

Question 6

Pour point

Answer 6

Pour point: This is the low temperature at which the lubricant becomes so thick that it ceases to flow. This is a consideration that has to be taken in refrigeration units and in any other low temperature conditions.

Question 7

Flash point

Answer 7

Flash point: This is the temperature at which the vapour of a lubricant will ignite. This is important in steam turbine lubrication.

Question 8

Additives

Answer 8

Additives: The large variation in the requirements of modern machinery is beyond the ability of straight oil and greases to handle, and a range of additives has been developed to improve lubrication properties.

Question 9

common types of additives

Answer 9

 Anti-foam agent
 Emulsifiers and emulsifier breakers
 Oxidation inhibitors
 Detergents and dispersants
 Pour point depressants
 Extreme pressure agents
 Viscosity index improvers