Design of machine elements

1. Unit-4
Springs

2. Introduction
Spring is an elastic member which deflects
under the action of load and it regains its
original shape after the load is removed.

3. Application
• Automobiles
• Railway wagons
• Valves
• Watches

4. Functions of springs
• To provide cushioning effect
• Reduce the effect of shock or impact load
• To measure forces in spring balance
• To store energy such as in clocks, toys
• To apply forces and to control the motions as in brakes
and clutches.
• To control motions by maintaining contact between two
elements as in cam and followers

5. Types of Spring
• 1. Helical springs.
The helical springs are made up of a wire coiled in the
form of a helix and is primarily intended for
compressive or tensile loads.
The cross-section of the wire from which the spring is
made may be circular, square or rectangular. The two
forms of helical springs are compression helical spring
and tension helical spring.

6. Types of Helical spring
Helix angle more
than 10 degree
Helix angle less
than 10 degree
1)Closed coil helical or Tension spring
2)Open coil helical or Compression spring

7. Closed coil helical or Tension spring

8. Open coil helical or Compression spring

10. Spiral Spring

11. Leaf Spring

13. Disc or Belleville Spring

15. Conical Spring

16. Design of Helical Compression Spring

17. 1)Free length
2)Pitch
3)Endurance limit
4)Slenderness ratio
5)Pitch
6)Active coils
7)Solid length
8)Pitch angle
TERMINOLOGIES IN A COMPRESSION HELICAL SPRING
9)Hysterisis
10)Initial tension
11)Permanent set
12)Set
13)Spring rate
14)Spring index

22. Stresses in Helical Spring

23. Subjected to Axial Load

24. formulas
Torque, T = F X R
But , Torque =

25. Shear & Transverse Stresses

26. Transverse shear stress
Resultant
shear
stress

27. Wahl’s Stress Concentration Factor
• C should not be less than 3
• The value of C should be 5-12
• For industrial spring C= 6 -10

28. Deflection of the spring
C= D/d

29. Stiffness of the spring
C= D/d

30. Strain Energy Stored in Spring (U)
Also

31. Spring Under Impact Load
Energy Absorbed in Spring

32. End Conditions of Spring = Active coil + inactive coils
Poor Seating
Space
Better Seating
Space than
Plain
Better than
other types in
Seating Space
Its for high stress
model spring
application

33. Design Procedure of Helical Spring

34. The designers should find the
following basic things
• Pitch
• Diameter of the coil , D
• Wire Diameter, d
• Number of turns , n
• Free Length , Lf
• Solid Length, Ls
• Spring Stiffness, q
• Type of Ends

40. Condition of Natural Frequency

41. Stiffness – Springs in Series

42. Stiffness – Springs in Parallel

43. Helical Spring Subjected to
Variable Loading
Formulas
P 7.100 PSGDB

44. Helical Spring Subjected to
Variable Loading
• Spring subjected to fluctuating stresses are
designed on the basis of modified Soderberg
equation

45. Design of Belleville Spring

46. S.
NO
Springs in parallel Springs in Series
1
They have high load
capacity, this depends on
number of discs
The deflection is
proportional to the
number of discs

47. Formulas Axial Deflection

48. Constant

49. Maximum Stresses occurring at the edges

50. C1 & C2 - Constants

51. Constants finding graph
In general the ratio
of do / di should
be 1.5 - 5

52. Belleville Spring
Material
Chrome Vanadium Alloy
Steel
Allowable stress 1500 N/mm2
Young’s Modulus 2 x 105 N/mm2
Poisson’s Ratio 0.3
Thickness of spring 1 – 2 mm
Dia of disc at base 28 – 300 mm
h / t 0.4 – 0.75 for stiffness

53. t / do 0.03 – 0.06
Cone Angle 4 – 7 degree
Best value 6.5
Degree

54. INTRODUCTION

55. Formulas
7.131-PSGDB
7.131-PSGDB

56. LEAF SPRING

57. LEAF SPRING or FLAT SPRING
• The laminated or leaf spring (also known as
flat spring or carriage spring) consists of a
number of flat plates (known as leaves) of
varying lengths held together by means of
clamps and bolts

59. Arrangement of leaf Spring
• The design may be of cantilever type or simply
supported type.

60. Limitations in Leaf spring
They are stressed more at one specific location
and the other parts are stressed lightly
So some design considerations needed in this type.
So they increase the width of the plate and keep the
thickness as same

61. Material

62. Design Procedure

65. Check for Pin

66. Check for Pin

67. Length of Leaf Spring Leaves
Radius of Leaf Spring Leaves

68. FLY WHEEL

69. INTRODUCTION
Fly wheel is a heavy rotating member
placed between power source and
driving unit.
It act as a reservoir – for storing energy
(its an energy accumulator)

70. Functions of fly wheel
• It will absorb energy when the demand is less
than supply of energy.
• It will release it when the demand is more
than the supply of energy.

71. Two distinct Applications of Fly wheel

72. Types of fly wheels

74. Fly wheel effect and
co-efficient of fluctuation of speed

75. Maximum Fluctuation of speed
Co-Efficient of fluctuation of speed
The difference between maximum speed and
minimum speed during the cycle is called
maximum fluctuation of speed.

76. Value of Co-efficient of Fluctuation of
speed (Ks)
7.121-PSGDB

77. Mass of the fly wheel (m)

78. Co-efficient of fluctuation of energy (Ke)
The difference between maximum and minimum
energy during the cycle is called fluctuation of
energy

79. Values of Co-Efficient of Fluctuation of
Energy (Ke)

80. Stresses in Fly Wheel rim

81. Stresses in Fly Wheel
Tensile Stress
Due to Centrifugal Force

82. Cont..
Bending Stress
Due to Straining Effect of Arms

83. Cont..
Resultant Stress
In rim with the junctions of arms

84. Stresses in Rims
Tensile Stress
Due to Centrifugal Force

85. Cont..
Bending Stress
Due to Torque

86. Cont..
Belt Stress
Stress Due to Belt Tension

87. Design of flywheel shaft, Hub and Key
Shaft
Hub
di = d

88. Design of flywheel shaft, Hub and Key
Key

89. CONNECTING ROD

94. Formulas
7.122 - PSGDB
7.122 - PSGDB
7.122 - PSGDB

95. Formulas
7.122 - PSGDB

96. Formulas
7.122 - PSGDB

97. Formulas
7.122 - PSGDB
7.122 - PSGDB
7.122 - PSGDB

98. Whipping Stress

99. CRANK SHAFT

100. Introduction
• It’s a shaft used to convert a reciprocation
motion of piston into rotary motion

101. Types of crank shaft

102. Material of crank shaft
The crank shaft subjected to shock and fatigue loads.
so its should have more tough and fatigue strength

103. Stresses in Crank Shaft