Design Interview Questions with Answers

 

Design of machine Elements Interview Questions with Answers

(Shafts, Keys, Bolts, Nuts, Screws, fasteners, Bearings, Flywheel & Governor)

1. Define the term critical speed.

The speed, at which the shaft runs so that the additional deflection of the shaft from the axis of rotation becomes infinite, is known as critical or whirling speed.

2. Factors considered designing a shaft?

Strength and Stiffness

3. What is a key? What are the types of keys?

A key is device, which is used for connecting two machine parts for preventing relative motion of rotation with respect to each other.

The different types of keys are

1. Saddle key
2. Tangent key
3. Sunk key
4. Round key and taper pin

4. What is the main use of woodruff keys?

A woodruff key is used to transmit small value of torque in automotive and machine tool industries. The key-way in the shaft is milled in a curved shape whereas the key way in the hub is usually straight.

5. What are the various failures occurred in sunk keys?

Shear failure and Crushing failure.

6. What is the function of a coupling between two shafts?

Couplings are used to connect sections of long transmission shafts and to connect the shaft of a driving machine to the shaft of a driven machine.

7. Under what circumstances flexible couplings are used?

They are used to join the abutting ends of shafts when they are not in exact alignment.

They are used to permit an axial misalignment of the shafts without under absorption of the power, which the shafts are transmitting.

8. What are the purposes in machinery for which couplings are used?

Couplings are used

1. To provide the connection of shafts of units those are manufactured separately such as motor and generator and to provide for disconnection for repairs or alterations.
2. To provide misalignment of the shafts or to introduce mechanical flexibility.
3. To reduce the transmission of shock from one shaft to another.
4. To introduce protection against over load.

9. What are the main functions of the knuckle joints?

It is used to transmit axial load from one machine element to other.

10. How is a bolt designated?

A bolt is designated by a letter M followed by nominal diameter and pitch in mm.

11. What factors influence the amount of initial tension?

The factors influence the amounts of initial tension are

1. External load
2. Material used
3. Bolt diameter

12. What is bolt of uniform strength?

A bolt of uniform strength has equal strength at the thread and shank portion.

13. What are the ways to produce bolts of uniform strength?

The ways to produce bolts of uniform strength are

1. Reducing shank diameter equal to root diameter.
2. Drilling axial hole

14. What stresses act on screw fastenings?

Stresses act on screw fastenings are

1. Initial stresses due to screwing up
2. Stresses due to external forces
3. Combined stresses.

15. What are the different applications of screwed fasteners?

The different applications of screwed fasteners are

1. For readily connecting & disconnecting machine parts without damage
2. The parts can be rigidly connected
3. Used for transmitting power

16. What are the advantages of screwed fasteners?

The advantages of screwed fasteners are

1. They are highly reliable in operation
2. They are convenient to assemble & disassemble
3. A wide range of screws can be used for various operating conditions
4. They are relatively cheap to produce. 

17. Define pitch.

Pitch is defined as the distance from appoint on one thread to the corresponding on the adjacent thread in the same axis plane.

18. Define lead.

Lead is defined as the distance, which a screw thread advances axially in one rotation of the nut.

19. What are the different types of metric thread?

The different types of metric thread are

1. BSW (British standard Whit worth)
2. BSE (British standard End)

20. Define welding.

Welding can be defined as a process of joining two similar or dissimilar metals with or without application of pressure along with or without addition of filler material.

21. What are the types of welded joints?

The types of welded joints are

1. Butt joint
2. Lap joint
3. T – joint
4. Corner joint
5. Edge joint.

22. What are the two types of stresses are induced in eccentric loading of loaded joint?

The two types of stresses are induced in eccentric loading of loaded joint are

1. Direct shear stress.

2. Bending or torsional shear stress.

23. Define butt and lap joint.

Butt joint: The joint is made by welding the ends or edges of two plates.

Lap joint: The two plates are overlapping each other for a certain distance and then welded. Such welding is called fillet weld.

24. When will the edge preparation need?

If the two plates to be welded have more than 6 mm thickness, the edge preparation should be carried out.

25. What are the two types of fillet weld?

Two types of fillet weld are

1. Longitudinal or parallel fillet weld
2. Transverse fillet weld 

26. State the two types of eccentric welded connections.

Two types of eccentric welded connections are

1. Welded connections subjected to moment in a plane of the weld.
2. Welded connections subjected to moment in a plane normal to the plane of the weld.

27. What are the practical applications of welded joints?

It has employed in manufacturing of machine frames, automobile bodies, aircraft, and structural works.

28. What is bearing?

Bearing is a stationery machine element which supports a rotating shafts or axles and confines its motion.

29. Classify the types of bearings.

The types of bearings are

A. Depending upon the type of load coming upon the shaft:

1. Radial bearing
2. Thrust bearings.

B. Depending upon the nature of contact:

1. Sliding contact
2. Rolling contact bearings or Anti-friction bearings.

30. What are the required properties of bearing materials?

Bearing material should have the following properties.

1. High compressive strength
2. Low coefficient of friction
3. High thermal conductivity
4. High resistance to corrosion
5. Sufficient fatigue strength
6. It should be soft with a low modulus of elasticity
7. Bearing materials should not get weld easily to the journal material.

31. What is a journal bearing?

A journal bearing is a sliding contact bearing which gives lateral support to the rotating shaft.

32. What are the types of journal bearings depending upon the nature of contact?

 The types of journal bearings are

1. Full journal bearing
2. Partial bearing
3. Fitted bearing.

33. What are the types of journal bearing depending upon the nature of lubrication?

 The types are

1. Thick film type
2. Thin film type
3. Hydrostatic bearings
4. Hydrodynamic bearing.

34. What is known as self – acting bearing?

The pressure is created within the system due to rotation of the shaft; this type of bearing is known as self – acting bearing.

35. What is flywheel?

Flywheel is a machine elements used to minimize the fluctuation of speed in a engine.

36. What is the function of flywheel?

A flywheel used in machine serves as a reservoir which stores energy during the period when the supply of energy is more than the requirement and releases it dulling the period when the requirement of energy is more than the supply.

37. Define the term ‘fluctuation of speed’ and ‘fluctuation of energy’.

The ratio of maximum fluctuation of speed to the mean speed is called co efficient of fluctuation of speed. The ratio of fluctuation of energy to the mean energy is called coefficient of fluctuation of energy.

38. State the type of stresses induced in a rim flywheel?

The stresses induced in a rim flywheel are

1. Tensile stress due to centrifugal force
2. Tensile bending stress caused by the restraint of the arms and
3. The shrinkage stresses due to unequal rate of cooling of casting.

39. What are the stresses induced in flywheel arms?

The stresses induced in flywheel arms are

1. Tensile stress due to centrifugal force.
2. Bending stress due to torque.
3. Stress due to belt tension.

40. How does the function of flywheel differ from that of governor?

A governor regulates the mean speed of an engine when there are variations in the mean loads. It automatically controls the supply of working fluid to engine with the varying load condition & keeps the mean speed with contain limits. It does not control the speed variation caused by the varying load. A flywheel does not maintain constant speed.