Design of Machine Elements: Shafts, Keys, Bolts, Nuts, Screws, Fasteners, Bearings, Flywheel & Governor

Question No. 01
Define the term critical speed.
Answer: 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.



Question No. 02
Factors considered designing a shaft?
Answer: Strength and Stiffness

Question No. 03
What is a key? What are the types of keys?
Answer: 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 pins

Question No. 04
What is the main use of woodruff keys?
Answer: A woodruff key is used to transmit small value of torque in automotive and
machine tool industries. The keyway in the shaft is milled in a curved shape whereas the key
way in the hub is usually straight.


Question No. 05
What are the various failures occurred in sunk keys?
Answer: Shear failure and Crushing failure.

Question No.06
What is the function of a coupling between two shafts?
Answer: 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.

Question No. 07
Under what circumstances flexible couplings are used?
Answer: 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.


Question No. 08
What are the purposes in machinery for which couplings are used?
Answer: 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.


Question No. 09
What are the main functions of the knuckle joints?
Answer: It is used to transmit axial load from one machine element to other.

Question No. 10
How is a bolt designated?
Answer: A bolt is designated by a letter M followed by nominal diameter and pitch in mm.

Question No. 11
What factors influence the amount of initial tension?
Answer: The factors influence the amounts of initial tension are
1. External load
2. Material used
3. Bolt diameter

Question No. 12
What is bolt of uniform strength?
Answer: A bolt of uniform strength has equal strength at the thread and shank portion.

Question No. 13
What are the ways to produce bolts of uniform strength?
Answer: the ways to produce bolts of uniform strength are
1. Reducing shank diameter equal to root diameter.
2. Drilling axial hole


Question No. 14
What stresses act on screw fastenings?
Answer: stresses act on screw fastenings are
1. Initial stresses due to screwing up
2. Stresses due to external forces
3. Combined stresses.

Question No. 15
What are the different applications of screwed fasteners?
Answer: 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


Question No. 16
What are the advantages of screwed fasteners?
Answer: 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.


Question No. 17
Define pitch.
Answer: Pitch is defined as the distance from appoint on one thread to the corresponding
on the adjacent thread in the same axis plane.

Question No. 18
Define lead.
Answer: Lead is defined as the distance, which a screw thread advances axially in one
rotation of the nut.

Question No. 19
What are the types of welded joints?
Answer: the types of welded joints are
1. Butt joint
2. Lap joint
3. T – joint
4. Corner joint
5. Edge joint.

Question No. 20
What are the different types of metric thread?
Answer: the different types of metric thread are
1. BSW (British standard Whit worth)
2. BSE (British standard End

Question No. 21
Define welding.
Answer: 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.

Question No. 22
What are the two types of stresses are induced in eccentric loading of loaded joint?
Answer: the two types of stresses are induced in eccentric loading of loaded joint are
1. Direct shear stress.
2. Bending or torsional shear stress.


Question No. 23
Define butt and lap joint.
Answer:
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.

Question No. 24
When will the edge preparation need?
Answer: If the two plates to be welded have more than 6mm thickness, the edge
preparation should be carried out.


Question No. 25
What are the two types of fillet weld?
Answer: Two types of fillet weld are
1. Longitudinal or parallel fillet weld
2. Transverse fillet weld

Question No. 26
State the two types of eccentric welded connections.
Answer: 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.


Question No. 27
What are the practical applications of welded joints?
Answer: It has employed in manufacturing of machine frames, automobile bodies, aircraft,
and structural works.

Question No. 28
What is bearing?
Answer: Bearing is a stationery machine element which supports a rotating shafts or axles
and confines its motion.


Question No. 29
Classify the types of bearings.
Answer: 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 Antifriction bearings.


Question No. 30
What are the required properties of bearing materials?
Answer: 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.

Question No. 31
What is a journal bearing?
Answer: A journal bearing is a sliding contact bearing which gives lateral support to the
rotating shaft.


Question No. 32
What is known as self – acting bearing?
Answer: The pressure is created within the system due to rotation of the shaft; this type of
bearing is known as self – acting bearing.

Question No. 33
What are the types of journal bearings depending upon the nature of contact?
Answer: The types of journal bearings are
1. Full journal bearing
2. Partial bearing
3. Fitted bearing.

Question No. 34
What are the types of journal bearing depending upon the nature of lubrication?
Answer: The types are
1. Thick film type
2. Thin film type
3. Hydrostatic bearings
4. Hydrodynamic bearing.

Question No. 35
What is flywheel?
Flywheel is a machine elements used to minimize the fluctuation of speed in a engine.


Question No. 36
What is the function of flywheel?
Answer: 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.

Question No. 37
Define the term ‘fluctuation of speed’ and ‘fluctuation of energy’.
Answer: 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.


Question No. 38
State the type of stresses induced in a rim flywheel?
Answer: 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.


Question No. 39
What are the stresses induced in flywheel arms?
Answer: 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.

Question No. 40
How does the function of flywheel differ from that of governor?
Answer: 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 const speed.