8.1 Tribology
QUESTION 1 (5 marks)
Distinguish between static and kinetic friction.
QUESTION 2 (7 marks)
Under what circumstances does contact fatigue occur? What are the consequences arising out of this type of wear and how can it be limited?
QUESTION 3 (8 marks)
What is hydrodynamic lubrication? What are the parameters on which the shift from one lubrication regime to the other based on?
QUESTION 4 (10 marks)
What is the lubrication type encountered in worm wheel drives?
a) What is the chief consideration as far as the lubrication requirements for worm wheel drives go?
b) What type of lubricant is recommended for worm wheel drives?
QUESTION 5 (8 marks)
Name four basic factors that affect the choice of lubricant for any given application.
QUESTION 6 (10 marks)
Name two main disadvantages of semi-liquid lubricants.
QUESTION 7 (10 marks)
Given the following operating conditions for a rolling bearing, what lubricant would you select and what is the reason for your choice? Speed @ Bearing contact 10,000mm/s, Bearing pressure 1000KN/m².

8.2 Properties of Lubricants
QUESTION 8 (10 marks)
Two oils are tested to establish their viscosity index. Oil “A” and Oil “B” have their viscosity measured at temperatures of 40C and 100C. Oil “A” has a viscosity of 80Cst at 40C and 8Cst at 100C. Oil “B” has a viscosity of 90Cst at 40C and 15Cst at 100C.
Which oil has the higher viscosity index?
QUESTION 9 (15 marks)
A pump fitted with 50mm bore ball bearings uses oil whose viscosity ranges from 100cSt at cold pump start-up to 7.5Cst when running at maximum speed and load. If these viscosities are the safe limits for the oil, specify the maximum start-up speed and the maximum running speed you would recommend for the pump.
QUESTION 10 (4 marks)
Give two advantages and two disadvantages of vegetable oils.
QUESTION 11 (10 marks)
Explain the difference between mineral base oil and synthetic base oil manufacture?
QUESTION 12 (5 marks)
Explain the difference between the Flash Point and Fire Point of a liquid lubricant?
8.3 Characteristics and Application of Additives
QUESTION 13 (5 marks)
What are the consequences of oxidation in lubricants? List some of the commonly used anti-oxidant additives.
8.4 Failure Analysis
QUESTION 14 (10 marks)
Name two root causes of lubrication failure and their possible sources.
QUESTION 15 (10 marks)
A rolling bearing in an open gearbox fails. Lubricating oil is circulated by a gear pump from the cast iron sump through a galvanised steel pipe to the bearings.
Analysis of the bearing shows oil contamination to be the cause of failure. List four possible sources of the contamination.
8.5 Lubricant Storage
QUESTION 16 (5 marks)
List some of the important information that is contained in Material Safety Data Sheets of lubricants?
QUESTION 17 (4 marks)
What is the typical shelf life for the following categories of lubricants? What happens to the shelf life in case of outside storage?
a) Automotive
b) Aviation
c) Industrial oils
d) Greases
QUESTION 18 (5 marks)
Outline some of the measures by which lubricant contamination potential can be minimized.
QUESTION 19 (5 marks)
List some of the standard procedures that must be adhered to, for outside storage of lubricants.

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QUESTION 1 (5 marks)
Distinguish between static and kinetic friction
Static friction                                    Kinetic friction
It resists an object from moving.    It is the resistance force while moving.
Generally, for the same pair of       For the same pair of surfaces, this force is
surfaces, this force                           weaker than static force.
is greater than kinetic force.
No energy conversion.                   Conversion to heat, sound etc.
No erosion occurs.                           Generally liable to erosion.

QUESTION 2 (7 marks)
Under what circumstances does contact fatigue occur? What are the consequences arising out of this type of wear and how can it be limited?
Answer: The circumstances:
1. Where the contact area is very small.
2. Contact area seems a point or line that enlarges to an area with increase in loading.
3. Two curved surfaces are pressed together where a subsurface plastic strain is generated with increasing cycles until a crack is produced.
4. The higher the traction or tangential force, the more probable the occurrence of contact fatigue.
In general the consequences are:
1. Cracking.
2. Pitting.
3. Flaking of the surface material.
To limit these effects
1. Lubricants are applied.
2. Bearing loads are reduced or distributed among more elements.
3. Surface hardening treatments are used.
4. Scatter is reduced through ensuring the homogeneity of material microstructure, high quality surface finish, improving rolling element precision.
5. Compressive residual stress may be imposed by short peening, nitriding and burnishing.
QUESTION 3 (8 marks)
What is hydrodynamic lubrication? What are the parameters on which the shift from one lubrication regime to the other based on?
Answer: Hydrodynamic lubrication occurs when a shaft rotating in a bearing floats over a layer or thick film of the lubricant fluid existing between the bearing material and the shaft itself so that the shaft is not in contact with the bearing...

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