CHAPTER 5:- DESIGN OF SPRING
1.Write the equation of Wahl’s factor, used for design of helical coil spring. State the SI unit of each
term in the equation. ..............4 marks
Ans:-
2.Design of helical compression spring with ground ends. The spring index is 12. Maximum load on
the spring is 100N and deflection under maximum load is 15 mm. Allowable shear stress for
material is 100 MPa. And modulus of rigidity is 4 MPa. Find wire and spring diameters, number of
coils and stiffness of spring.
Ans:- Design of Helical Compression Spring:
Given Data: W=100 N , 𝛿 = 15 𝑚𝑚 , τ =100 N/mm2 , G= 84 x 103 N/mm2
(actually in question paper G= 4MPa is given , but it is not a correct value it could be a printing mistake)
C= 12
C= Dm/d =12,
3. State two application of leaf spring. Draw neat sketch of leaf spring.
Ans:-Application of Leaf spring ( Any Two )
Bus/truck/Car suspension springs, diving board,
Sketch of Leaf Spring of semi elliptical Type
4. State any four areas of application of spring.
An:- Four areas of application of springs.
(Any four applications of the following.1 mark each)
i) To absorb or control energy in automobiles suspension springs, vibration dampers, railway
buffers.
ii) To apply forces in brakes,clutches, valves of IC engines
iii) To store the energy in watches and toys.
iv) To measure forces in spring balances , gauges
iv) To provide clamping force in toolings like jigs and fixtures etc.
v) To control motion by maintaining contact between two elements.
5.At the bottom of mine shaft, a group of 10 identical close coil helical spring are set in parallel to
absorb the shock caused by the falling of cage of a failure. The loaded cage weighs 75KN while
counter wages weighs 15KN. If the loaded cage fall through a height of 59 meter from rest, find the
maximum stress induced in each spring? Each spring made up of 50mm diameter steel rod having
spring index of 6 and number of active turn in each spring is 20. Modulus of rigidity, G=80
KN/mm2.comment whether the spring design is safe or not if permissible shearing stress is 2800
N/mm2.
Ans:-
4. A close coil helical compression spring of 12 active coil has a spring stiffness k. It is cut into two
spring having 5 and 7 turns. Determine the spring stiffness of resulting spring.
Ans:-
5. Define the following term with respect to spring
1.spring index
2.spring stiffness
3.free length of spring
4.solid lenth of spring
Ans:- Terms w.r.t Springs:
1) Spring Index:It is a ration of mean diameter of coil to the diameter of spring wire.
Mathematically …………….1/2 mark
2) Spring stiffness: It is load required per unit deflection of the spring. …………….1/2 mark
3) Free length of spring : Length of spring when spring is free or unloaded condition
Lf= n’ x d + + 0.15 …… ……….1/2 mark
4) Solid Length of spring: it is the product of number of coils and diameter of wire
Or Length of spring when spring is fully loaded condition.
Ls= n’ x d …………….1/2 mark
6. A safety valve of diameter is to blow off at a pressure of 1.2N/mm2. It is held on it’s seat by a close
soiled helical spring. The maximum lift of the valve is 10mm. Design a suitable compression spring
of spring index 5 with an initial compression of 35mm. The shear stress for spring material is
limited to 500MPa. Take G=80KN/mm2.
Ans:-
7.A semi-elliptical carriage spring of 1200 mm lenth withstands a load of 60KN.with the maximum
deflection of 90mm. Assume breadth to thickness ratio as 8. Design the spring if bending stress of
spring material is 540MPa and E=2×105N/mm2.
Ans:- Central load on each spring = 2W =60KN
W= 30 KN =30X103 N, 2L= 1200, L= 600 mm, δ=90mm.
σb =540Mpa, E= 2 x 105 N/mm2
Here, b/t= 8 , thus b = 8t
The stress in leaf spring is given by
8.State any four application of spring.
Ans:- Application of spring: Any four …….1M each
1) To cushion, absorb or control energy to external load : Car springs, Railway buffers
2) To store Energy : Watches Toys
3) To Measure forces : Spring Balances, Gauges ,Engines
4) To provide clamping force in Jigs & fixtures.
5) To apply forces as in brakes, clutches & spring loaded valve.
9. A railway wagon having 1500Kg mass and moving at 1m/s velocity against a bumper consisting
of two helical springs of spring index 6. The spring which get compressed by 150mm while resisting
dash made of spring steel having allowable shear stress of 3600N/mm2 and modulus of rigidity
8.4×104N/mm2.design a helical coil spring with circular coil section of spring wire.
Ans:-
