Mechanical (Rotary) Common Questions -5

EPC-School 2012

M for Mechanical 

Topic - Lubrication

1. What are the main functions of lubrication?

2. What can be the reasons for rise in lubrication temperature?

3. What are the advantages and disadvantages of lubrication grease and lubrication oil?

4. What are the advantages of synthetic oils? What are its typical applications?

5. What is viscosity index?

6. How does viscosity vary with temperature?

7. What is the effect of lowering of lubricant viscosity?

8. What is the oil viscosity of servo prime 46?

Answers to Above Questions-

1. Reduce wear & friction, Provide cooling

2. Lubricating oil contamination due to Hydrocarbon, gas or process dilutants, water & sediments, improper cooling, insufficient flow

3. Grease:

Advantages: Simpler / cheaper installation, better adhesion, protection against impurities, less frequent application reqd, reduces starvation risks

Disadvantages: Reduced cooling capacity, low speeds, contamination control is difficult, risk of over greasing

 Lubrication Oil:

Advantages: High Speed and temp conditions, excellent cooling, cleaning and flushing characteristics, can be used in recirculative systems, can serve better in excessive dirt environment, more stable than greases

Disadvantages: Needs separate circulating, filtering, cooling system, expensive, formation of emulsion, oxidation, vapour formation, foam formation risks, viscosity comes down drastically at high temp

4. Can be used for very low & very high temperature applications, need not be replaced for a long time, has uniform viscosity at elevated temperatures, has higher load carrying capacity

5. The viscosity index (V.I.) of an oil is a measure of a fluids change of viscosity with temperature 

It is the ratio of change in viscosity of the lubricant at normal temp to 100 degrees to the change in temperature

A low V.I. signifies a relatively large change of viscosity with changes of temperature. In other words, the oil becomes extremely thin at high temperatures and extremely thick at low temperatures. On the other hand, a high V.I. signifies relatively little change in viscosity over a wide temperature range.

6. Viscosity reduces with increase in temperature.

7. Reduces friction and hence the load carrying capacity.

8. Kinematic viscocity @ 40°C is 43~48 cst.