Design of Machine Elements: Springs Interview Questions

Question No. 01
What is a spring?
Answer: A spring is an elastic member, which deflects, or distorts under the action of load and
regains its original shape after the load is removed.

Question No. 02
State any two functions of springs.
Answer:
1. To measure forces in spring balance, meters and engine indicators.
2. To store energy.


Question No. 03
What are the various types of springs?
Answer:
1. Helical springs
2. Spiral springs
3. Leaf springs
4. Disc spring or Belleville springs

Question No. 04
What are the requirements of spring while designing?
Answer:
1. Spring must carry the service load without the stress exceeding the safe value.
2. The spring rate must be satisfactory for the given application.

Question No. 05
Classify the helical springs.
Answer:
1. Close – coiled or tension helical spring.
2. Open –coiled or compression helical spring.

Question No. 06
Define Leaf springs
Answer: A leaf spring consists of flat bars of varying lengths clamped together and supported at both
ends, thus acting as a simply supported beam.

Question No. 07
What is spring index (C)?
Answer: The ratio of mean or pitch diameter to the diameter of wire for the spring is called the
spring index.

Question No. 08
Define Belleville Springs
Answer: They are made in the form of a cone disc to carry a high compressive force. In order to
improve their load carrying capacity, they may be stacked up together. The major stresses are
tensile and compressive.

Question No. 09
What is pitch?
Answer: The axial distance between adjacent coils in uncompressed state.


Question No. 10
What is solid length?
Answer: The length of a spring under the maximum compression is called its solid length. It is the
product of total number of coils and the diameter of wire.
Ls = nt × d
Where, nt = total number of coils.

Question No. 11
What are the end conditions of spring?
Answer:
1. Plain end.
2. Plain and ground end
3. Squared end
4. Squared and ground end.

Question No. 12
What is buckling of springs?
Answer: The helical compression spring behaves like a column and buckles at a comparative small
load when the length of the spring is more than 4 times the mean coil diameter.

Question No. 13
What is surge in springs?
Answer: The material is subjected to higher stresses, which may cause early fatigue failure. This
effect is called as spring surge.

Question No. 14
What is a laminated leaf spring?
Answer: In order to increase, the load carrying capacity, number of flat plates are placed and below
the other.

Question No. 15
What are semi elliptical leaf springs?
Answer: The spring consists of number of leaves, which are held together by U-clips.
The long leaf fastened to the supported is called master leaf. Remaining leaves are called as
graduated leaves.

Question No. 16
What is nipping of laminated leaf spring?
Answer: Pre-stressing of leaf springs is obtained by a difference of radii of curvature known as
nipping.

Question No. 17
What are the various applications of springs?
Answer: The springs are used in various applications, they are
1. Used to absorb energy or shocks (e.g. shock absorbers, buffers, etc.)
2. To apply forces as in brakes clutches, spring-loaded valves, etc.
3. To measure forces as in spring balances and engine indicators
4. To store energy as in watches


Question No. 18
Define free length.
Answer: Free length of the spring is the length of the spring when it is free or unloaded condition. It
is equal to the solid length plus the maximum deflection or compression plus clash allowance.
Lf = solid length + Ymax + 0.15 Ymax

Question No. 19
Define spring index.
Answer: Spring index (C) is defined as the ratio of the mean diameter of the coil to the diameter of
the wire.
C =D/d

Question No. 20
Define spring rate (stiffness).
Answer: The spring stiffness or spring constant is defined as the load required per unit deflection of
the spring.
K= W/y
Where, W - Load
y - Deflection

Question No. 21
Define pitch.
Answer: Pitch of the spring is defined as the axial distance between the adjacent coils in
uncompressed state. Mathematically Pitch=free length/n-1

Question No. 22
What are the points to be taken into consideration while selecting the pitch of the spring?
Answer: The points taken into consideration of selecting the pitch of the springs are
1. The pitch of the coil should be such that if the spring is accidentally compressed the stress
does not increase the yield point stress in torsion.
2. The spring should not be close up before the maximum service load is reached.

Question No. 23
Define active turns.
Answer: Active turns of the spring are defined as the number of turns, which impart spring action
while loaded. As load increases the no of active coils decreases.

Question No. 24
Define inactive turns.
Answer: Inactive turns of the spring are defined as the number of turns which does not contribute to
the spring action while loaded. As load increases number of inactive coils increases from 0.5 to 1
turn.

Question No. 25
What are the different kinds of end connections for compression helical springs?
Answer: The different kinds of end connection for compression helical springs are
1. Plain ends
2. Ground ends
3. Squared ends
4. Ground & square ends

Question No. 26
Write about the eccentric loading of springs?
Answer: If the load acting on the spring does not coincide with the axis of the spring, then spring is
said to be have eccentric load. In eccentric loading the safe load of the spring decreases and the
stiffness of the spring is also affected.

Question No. 27
Explain about surge in springs?
Answer: When one end of the spring is resting on a rigid support and the other end is loaded
suddenly, all the coils of spring does not deflect equally, because some time is required for the
propagation of stress along the wire. Thus a wave of compression propagates to the fixed end from
where it is reflected back to the deflected end this wave passes through the spring indefinitely. If the
time interval between the load application and that of the wave to propagate are equal, then
resonance will occur. This will result in very high stresses and cause failure. This phenomenon is
called surge.


Question No. 28
What are the methods used for eliminating surge in springs?
Answer: The methods used for eliminating surge are
1. By using dampers on the centre coil so that the wave propagation dies out
2. By using springs having high natural frequency.

Question No. 29
What are the disadvantages of using helical spring of non-circular wires?
Answer:
1. The quality of the spring is not good
2. The shape of the wire does not remain constant while forming the helix. It reduces the
energy absorbing capacity of the spring.
3. The stress distribution is not favourable as in circular wires. But this effect is negligible
where loading is of static nature.

Question No. 30
Why concentric springs are used?
Answer:
1. To get greater spring force within a given space
2. To insure the operation of a mechanism in the event of failure of one of the spring

Question No. 31
What is the advantage of leaf spring over helical spring?
Answer: The advantage of leaf spring over helical spring is that the end of the spring may be guided
along a definite path as it deflects to act a structural member in addition to energy absorbing device.

Question No. 32
Write notes on the master leaf & graduated leaf?
Answer: The longest leaf of the spring is known as main leaf or master leaf has its ends in the form
of an eye through which bolts are passed to secure the spring. The leaf of the spring other than
master leaf is called the graduated leaves.

Question No. 33
What is meant by nip in leaf springs?
Answer: By giving greater radius of curvature to the full length leaves than the graduated leaves,
before the leaves are assembled to form a spring thus a gap or clearance will be left between the
leaves. This initial gap is called nip.

Question No. 34
What is the application of leaf spring?
Answer: The leaf springs are used in automobiles as shock absorbers for giving suspension to the
automobile and it gives support to the structure.

Question No. 35
Define flat spiral spring.
Answer: A flat spiral spring is a long thin strip of elastic material wound like a spiral. These springs
are frequently used in watch springs, gramophones, etc

Question No. 36
What are the differences between helical torsion spring and tension helical springs?
Answer: Helical torsion springs are wound similar to that of tension springs but the ends are shaped
to transmit torque. The primary stress in helical torsion spring is bending stress whereas in tension
springs the stresses are torsional shear stresses.


Question No. 37
Define helical springs.
Answer: The helical springs are made up of a wire coiled in the form of a helix and are primarily
intended for compressive or tensile load.

Question No. 38
What are the different types of helical springs?
Answer: The different types of helical springs are
1. Open coil helical spring
2. Closed coil helical spring

Question No. 39
What is closed coil helical spring?
Answer:
1. The spring wires are coiled very closely, each turn is nearly at right angles to the axis of helix
2. Helix angle is small, i.e. less than 10 Degree.

Question No. 40
What is open coil helical spring?
Answer:
1. The wires are coiled such that there is a gap between the two consecutive turns.
2. Helix angle is large i.e. greater than 10 degree.