- 1. Unit 2 Design of Shafts, Keys & Couplings Prepared By Prof. M.C. Shinde [9970160753] Mech. Engg. Dept., JSCOE, Hadapsar
- 2. Unit 2 Design of Shafts ,Keys & Couplings Session 2.1 Introduction to Transmission Shaft Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 3. SPPU Syllabus Content â˘ Shaft design on the basis of strength, torsional rigidity and lateral rigidity, A.S.M.E. code for shaft design. Transmission shaft:- Theoretical treatment only. Design of keys and splines. Design of Flange Coupling and Flexible Bushed Pin Coupling.
- 4. Transmission Shafts â˘ Rotating member, usually of circular cross section used to transmit power or motion. â˘ supports transmission elements like gears, pulleys and sprockets. â˘ A transmission shaft supporting a gear in a speed reducer is shown in Fig. â˘ The shaft is always stepped with maximum diameter in the middle. â˘ portion and minimum diameter at the two ends, where bearings are mounted.
- 5. â˘ transmission shafts are made of medium carbon steels with a carbon content from 0.15 to 0.40 per cent such as 30C8 or 40C8. â˘ Commercial shafts are made of low carbon steels. â˘ produced by hot-rolling and finished to size either by cold-drawing or by turning and grinding. â˘ Steel bars up to 200 mm in diameter are commercially available.
- 6. Specific Categories Of Transmission Shafts â˘ Axle-supports rotating elements like wheels, hoisting drums. Used in rear axle of a railway wagon, automobile rear axle.
- 7. Specific Categories Of Transmission Shafts â˘ Spindle- A spindle is a short rotating shaft , used in all machine tools such as the small drive shaft of a lathe or the spindle of a drilling machine.
- 8. Specific Categories Of Transmission Shafts â˘ Countershaft It is a secondary shaft, driven by the main shaft and from which the power is supplied to a machine component. rotates âcounterâ to the direction of the main shaft. used in multi-stage gearboxes.
- 9. Stresses induced in the shaft â˘ Transmission shafts are subjected to axial tensile force, bending moment or torsional moment or their combinations. â˘ tensile stress â˘ bending stresses â˘ torsional shear stress When the shaft is subjected to combination of loads, the principal stress and principal shear stress are obtained by constructing Mohrâs circle
- 11. Shaft Design On Strength Basis 1. Design of shaft by theories of failures 2. Design of shaft by A.S.M.E. Code
- 12. 1.Shaft Design by theories of failures i] Maximum Shear Stress Theory:- the shaft is subjected to bending and torsional moments These equations are used to determine shaft diameter on the basis of maximum shear stress theory. The maximum shear stress theory is applicable to ductile materials. Since the shafts are made of ductile materials, it is more logical to apply this theory to shaft design.
- 13. ii] Maximum Principal Stress Theory:- the shaft is subjected to bending and torsional moments These equations are used to determine shaft diameter on the basis of principal stress theory maximum principal stress theory gives good predictions for brittle materials. Shafts are made of ductile material like steel and therefore, this theory is not applicable to shaft design.
- 14. iii] Distortion Energy Theory:- the shaft is subjected to bending and torsional moments These equations are used to determine shaft diameter on the basis of distortion energy theory. The maximum shear stress theory is applicable to ductile materials. The design of shaft by distortion energy theory is very accurate. Hence distortion energy theory is most widely theory used for shaft design.
- 15. 2. Shaft Design by A.S.M.E. CODE A.S.M.E. code used for design of shaft is based on maximum shear stress theory. According to A.S.M.E. code the values of allowable shear stress are as follows; [without keyway] take minimum of two values According to A.S.M.E. code the values of allowable shear stress are as follows; [with keyway] take minimum of two values Note :- the keyway on the shaft reduces the strength of the shaft. This is due to stress concentration near corners of keyway.
- 16. Shaft Design On Rigidity Basis 1. Design of shaft based on Torsional Rigidity 2. Design of shaft based on Lateral Rigidity
- 17. 1. Design of shaft based on Torsional Rigidity Torsional rigidity is defined as â torque required to produce a torsional deflection or an angle of twist of one radian in the shaft.â This equation is used to design the shaft on the basis of torsional rigidity. The permissible angle of twist for machine tool applications is 0.25Â° per metre length. For line shafts, 3Â° per metre length is the limiting value. Modulus of rigidity for steel is 79 300 N/mm2
- 18. 2. Design of shaft based on Lateral Rigidity Lateral rigidity of the shaft at given location is âthe lateral force required to produce a lateral deflection of one unitâ. This equation is used to design the shaft on the basis of lateral rigidity. e.g. for cantilever beam maximum deflection is given by,
- 19. Q.1 What are different materials used for manufacturing of shafts. Q.2 What are stresses induced in the transmission shafts. Q.3 Write down formula to design shaft using ASME Code. Assignment 2.1
- 20. Unit 2 Design of Shafts ,Keys & Couplings Session 2.2 Numerical on Design of Shafts Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 21. Ex.1 A mild steel shaft transmits 20kW power at 200 r.p.m. If the allowable shear stress for shaft material in 42 Mpa , determine the diameter of shaft.
- 22. Ex. 2. A mild steel shaft transmits 20kW power at 200 r.p.m.it carries a central load of 1000 N and is simply supported between bearings 2.5m apart. The allowable shear stress for shaft material in 42 Mpa. If the shock & fatigue factors for bending and torsion are 1.5 and 1.0, determine the diameter of shaft by maximum shear stress theory.
- 23. A mild steel shaft transmits 40kW power at 400 r.p.m.it carries a central load of 2000 N and is simply supported between bearings 5m apart. The allowable shear stress for shaft material in 84 Mpa. If the shock & fatigue factors for bending and torsion are 1.5 and 1.0, determine the diameter of shaft by maximum shear stress theory Assignment 2.2
- 24. Unit 2 Design of Shafts ,Keys & Couplings Session 2.3 Numerical on Design of Shafts based on Maximum Shear Stress Theory Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 25. Ex. 3. A counter shaft with the bearings 800 mm apart receives 20kW power at 500 rpm through a pulley 300mm in diameter and mounted at an overhung of 200 mm. A 360 mm diameter pulley mounted midway between the bearings transmits torque to a shaft located below it. Both the pulleys have vertical belt tensions and the coefficient of friction between the bell and pulley is 0.3. if the required safety margin is 3. design the shaft using maximum shear stress theory Use the following properties for shaft material. 1. Ultimate tensile strength=700 N/mm2, 2. Yield strength in tension=460 N/mm2 Important : Keep Calculator with you for solve problem]
- 26. Step I Permissible shear stress
- 27. Step II Torque on Shaft
- 28. Total Load at Pulley B
- 29. Total Load at Pulley D
- 30. Support Reactions at A & C
- 31. Step III Bending Moment Note:- Bending Moment at A & D is zero
- 32. Step III Bending Moment Maximum Bending Moment is at C =
- 33. Step IV Maximum Shear Stress Theory Note:- Assume Kb = Kt = 1
- 35. A counter shaft with the bearings 1000 mm apart receives 220kW power at 1000 rpm through a pulley 600mm in diameter and mounted at an overhung of 400 mm. A 720 mm diameter pulley mounted midway between the bearings transmits torque to a shaft located below it. Both the pulleys have vertical belt tensions and the coefficient of friction between the bell and pulley is 0.6. if the required safety margin is 6. design the shaft using maximum shear stress theory . Use the following properties for shaft material. Ultimate tensile strength=800 N/mm2, Yield strength in tension=360 N/mm2 Assignment 2.3
- 36. Unit 2 Design of Shafts ,Keys & Couplings Session 2.4 Numerical on Design of Shafts based on ASME Code Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 37. Ex. 5. A transmission shaft is supporting a spur gear B and pulley D, as shown in fig. The shaft is mounted on two bearings A & C. the diameter of pulley and gear are 500 mm and 350 mm respect. A 20kW power is transmitted at 500 r.p.m. from the pulley D to the gear B. F1 & F2 are the belt tensions in the tight and slack sides, while Ft & Fr are tangential and radial components of the gear tooth forces. Assume F1=3F2 and Fr=Ft tan 20. the gear and pulley are keyed to the shaft. If the material for the shaft is 50C4(Sut=700 N/mm2 and Syt= 460 N/mm2), determine the shaft diameter using ASME code, if Kb=Kt=1.5
- 38. Given To find the shaft diameter using ASME code
- 39. Step I Permissible shear stress [ASME] Note:- Given Shaft with keyway effect
- 40. Step II Torque on Shaft
- 41. Vertical forces at Pulley D
- 42. Forces on gear B
- 43. Vertical Support Reactions at A
- 44. Horizontal Support Reactions at A & C
- 45. Step III Vertical Bending Moment Note:- Bending Moment at A & D is zero
- 46. Step III Horizontal Bending Moment Note:- Bending Moment at A ,C & D is zero
- 47. Step III Resultant Bending Moment Note:- Bending Moment at A & D is zero
- 48. Step IV A.S.M.E. Code Note:- Kb =1.5, Kt = 1.5
- 49. Assignment 2.4 A transmission shaft is supporting a spur gear B and pulley D, as shown in fig. The shaft is mounted on two bearings A & C. the diameter of pulley and gear are 700 mm and 350 mm respect. A 40kW power is transmitted at 1000 r.p.m. from the pulley D to the gear B. F1 & F2 are the belt tensions in the tight and slack sides, while Ft & Fr are tangential and radial components of the gear tooth forces. Assume F1=3F2 and Fr=Ft tan 20. the gear and pulley are keyed to the shaft. If the material for the shaft is 50C4(Sut=500 N/mm2 and Syt= 260 N/mm2), determine the shaft diameter using ASME code, if Kb=Kt=1.0
- 50. Unit 2 Design of Shafts ,Keys & Couplings Session 2.5 Numerical on Design of Shafts Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 51. Ex. 6. The layout of an intermediate shaft of a gear box, supporting two spur gears B & C ,is shown in fig. the shaft is mounted on two bearings A & D. the pitch circle diameter of gears B & C are 900mm & 600mm respect. The material of the shaft is steel FeE 580(Sut=770N/mm2 & Syt=580N/mm2). The factors Kb & Kt are 1.5 & 2.0 respectively . Determine the shaft diameter using the ASME code. Assume that the gears are connected to the shaft by means of keys.
- 52. Given To find the shaft diameter using ASME code
- 53. Step I Permissible shear stress [ASME] Note:- Given Shaft with keyway effect
- 54. Step II Torque on Shaft
- 55. Vertical Support Reactions at A & D
- 56. Horizontal Support Reactions at A & D
- 57. Step III Vertical Bending Moment Note:- Bending Moment at A & D is zero
- 58. Step III Horizontal Bending Moment Note:- Bending Moment at A & D is zero
- 59. Step III Resultant Bending Moment
- 60. Step IV A.S.M.E. Code Note:- Kb =1.5, Kt = 2.0
- 61. Assignment 2.5 The layout of an intermediate shaft of a gear box, supporting two spur gears B & C ,is shown in fig. the shaft is mounted on two bearings A & D. the pitch circle diameter of gears B & C are 900mm & 600mm respect. The material of the shaft is steel FeE 580(Sut=770N/mm2 & Syt=580N/mm2). The factors Kb & Kt are 1.5 & 2.0 respectively . Determine the shaft diameter using the ASME code. Assume that the gears are connected to the shaft by means of keys.
- 62. Unit 2 Design of Shafts ,Keys & Couplings Session 2.6 Numerical on Design of Shafts Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 63. Ex. 4. The shaft shown in fig. is driven by pulley D from an electric motor, while another belt drive from pulley C is running a compressor. The belt tensions for pulley C are 1500 N & 600 N, while the ratio of belt tensions for pulley D is 3.5. find the shaft diameter by A.S.M.E. code. Yield strength and ultimate tensile strength for shaft material are 380 N/mm2 and 720 N/mm2 respectively. Take Kb=1.75 and Kt=1.25.
- 64. Step I Permissible shear stress [ASME] Note:- Assume Shaft with keyway effect
- 65. Step II Torque on Shaft
- 66. Total Load at Pulley C
- 67. Total Load at Pulley D
- 68. Vertical Support Reactions at A & B
- 69. Horizontal Support Reactions at A & B
- 70. Step III Vertical Bending Moment Note:- Bending Moment at A & B is zero
- 71. Step III Horizontal Bending Moment Note:- Bending Moment at A & B is zero
- 72. Step III Resultant Bending Moment Note:- Bending Moment at A & B is zero
- 73. Step IV A.S.M.E. Code Note:- Kb =1.75, Kt = 1.25
- 74. Assignment 2.6 The shaft shown in fig. is driven by pulley D from an electric motor, while another belt drive from pulley C is running a compressor. The belt tensions for pulley C are 3000 N & 1200 N, while the ratio of belt tensions for pulley D is 2.5. find the shaft diameter by A.S.M.E. code. Yield strength and ultimate tensile strength for shaft material are 420 N/mm2 and 720 N/mm2 respectively. Take Kb=1. 5 and Kt=1.05.
- 76. Unit 2 Design of Shafts ,Keys & Couplings Session 2.7 Design of Splined Shafts & Design of Keys Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 77. Splined Shaft
- 78. Splines â˘ Multiple keys which are made integral with the shaft. â˘ Prevent the relative rotary motion ,but permit the relative axial motion between the shaft and hub. â˘ Splines transmit much higher torque than the single key between the shaft and hub. â˘ Used in automobile gear boxes and machine tool gear boxes. â˘ Splines are designated as N*d*D; N- no. Of splines D- Major diameter of splined shaft(mm) d- minor diameter of splined shaft(mm)
- 79. Design of Splines â˘ As there exists a relative axial motion between the splined shaft and the hub, the bearing pressure between the external splines on shaft and the internal splines on hub must be considered.
- 80. Bearing Pressure between Splines(Pb)
- 81. Direct Shear Stress in Splines
- 82. Ex. 9. A standard splined connection 8*52*60mm is used for the gear and shaft assembly of gear box. A 20kW power at 300 r.p.m. is transmitted by the splines. If the normal pressure on the splines is limited to 6.5 N/mm2 and the coefficient of friction is 0.06. calculate: i) The length of hub of the gear ii) The force required to shift the gear Given
- 83. Torque to be transmitted to splined shaft
- 84. Bearing Pressure between Splines(Pb)
- 85. Tangential force to shift the gear
- 86. Frictional force to shift the gear
- 87. Design of Keys
- 88. Keys â˘ A machine element which is used to connect the transmission shaft to rotating machine elements like pulleys, gears, sprockets or flywheels. â˘ A keyed joint consisting of shaft, hub and key â˘ The primary function of the key is to transmit the torque from the shaft to the hub of the mating element and vice versa â˘ The second function of the key is to prevent relative rotational motion between the shaft and the joined machine element like gear or pulley. â˘ A recess or slot machined either on the shaft or in the hub to accommodate the key is called keyway
- 90. Sunk keys:- â˘ A sunk key is a key in which half the thickness of the key fits into the keyway on the shaft and the remaining half in the keyway on the hub. â˘ keyways are required both on the shaft as well as the hub of the mating element. â˘ In sunk key, power is transmitted due to shear resistance of the key. â˘ sunk key is suitable for heavy duty application, since there is no possibility of the key to slip around the shaft. â˘ A sunk key with rectangular cross-section is called a flat key. a) Rectangular key b) Square key c) Parallel key d) Gib headed key e) Feather key f) Woodruff key
- 91. Stresses induced in the Sunk Keys
- 92. Direct shear stress in key
- 93. Crushing or compressive stress in key Note:- compressive stress induced in a square key due to torque transmitted is twice the shear stress.
- 94. Ex. 7. A square key is to be used to fix a gear to a 35 mm diameter shaft. The hub length of the gear is 60mm. Both the shaft and key are to be made of the same material, having an allowable shear stress of 55 N/mm2. if the torque to be transmitted is 395 N-m. determine the minimum dimensions of key cross section. Given To find dimensions of key cross section.
- 95. Direct shear stress in the key
- 96. Ex. 8. A 16*10 mm2 cross section parallel key is to be used to transmit 60kW power at 1440 rpm from a shaft of 45mm diameter. The key is made of plain carbon steel with yield strength of 300 N/mm2. if the required safety margin is 3, determine the key length. Given To find length of key cross section.
- 97. Allowable stresses in the key
- 98. Torque to be transmitted to the key
- 99. Shear stress in the key
- 100. Crushing stress in the key Ans:. Select larger value of l=35.36
- 101. Assignment 2.7 1. Explain Splined shaft with neat sketch 2. What is key? Explain different types of keys 3. Write stresses induced in the keys with equations. 4. A standard splined connection 4*26*30mm is used for the gear and shaft assembly of gear box. A 50kW power at 800 r.p.m. is transmitted by the splines. If the normal pressure on the splines is limited to 8.5 N/mm2 and the coefficient of friction is 0.06. calculate: a) The length of hub of the gear b) The force required to shift the gear
- 102. Unit 2 Design of Shafts ,Keys & Couplings Session 2.8 Introduction ,Classification of Couplings & Design of muff coupling Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 103. Couplings â˘ It is the mechanical element used to connect two shafts of a transmission system. â˘ The couplings are located as near as possible to bearing so as to minimize deflection. â˘ mechanical device that permanently joins two rotating shafts to each other.
- 104. Purposes of Couplings â˘ It provides for the connection of shafts of two different units such as an electric motor and machine. â˘ It makes the provision for disconnection of two units for repairs or alternations. â˘ It introduces mechanical flexibility between two connected units. â˘ It reduces the transmission of vibrations and shocks between two connected units.
- 105. Rigid Couplings Flexible Couplings Used to connect two shafts which are perfectly aligned Used to connect two shafts which are having small misalignment. Cannot tolerate any misalignment between two shafts Can tolerate small amount of lateral or and angular misalignment between two shafts Cannot absorb shock & vibrations Can absorb shock & Vibrations Less expensive More expensive e.g. muff coupling, split muff, rigid flange e.g. bushed pin type, oldham coupling and universal coupling
- 106. Couplings Rigid Couplings Muff/Sleeve Coupling Used for Line Shaft Split Muff/Clamp Coupling Used for Line Shaft Rigid Flange Coupling Used for connecting electric motor to pump Flexible Couplings Bushed Pin Type Used for connecting diesel engine to generator Oldham Coupling Used for connecting two eccentric shafts Universal Coupling Used between gear box and differential of automobile
- 107. Design of Muff (Sleeve) Couplings â˘ It is the simplest type of rigid coupling used to connect two shafts rigidly. â˘ Design of Muff coupling involve following steps 1. Design of Shaft 2. Dimensions of sleeve as standard proportions 3. Design of sleeve 4. Design of key
- 108. Design of Muff (Sleeve) Couplings Step 1: Design of Shaft â˘ Same as discussed in earlier session 2.1 & 2.2
- 109. Design of Muff (Sleeve) Couplings Step 2: Dimensions of sleeve as standard proportions â˘ Outside diameter of sleeve D=2d â˘ Length of Sleeve L=3.5d Where , d=diameter of shaft, mm
- 110. Design of Muff (Sleeve) Couplings Step 3: Design of Sleeve â˘ Torsional Shear Stress induced in Sleeve is given by Where ,k=d/D For the safety of sleeve against shear failure ,the torsional shear stress induced in a sleeve must be less than allowable shear stress for sleeve i.e.
- 111. Design of Muff (Sleeve) Couplings Step 4: Design of Key â˘ The key dimensions are calculated as discussed in design of key session â˘ For design purpose length of key is taken as l=L/2
- 112. Assignment 2.8 1. Give Classification of Couplings 2. Explain steps for design of muff couplings. 3. Differentiate between Rigid and Flexible Couplings
- 113. Unit 2 Design of Shafts ,Keys & Couplings Session 2.9 Design of Rigid Flange Coupling & Numericals Prepared By Prof. M.C. Shinde Mech. Engg. Dept., JSCOE, Hadapsar
- 114. Design of Rigid Flange Couplings A rigid flange coupling consist of two flanges one keyed to the driver shaft and other to driven shaft. Types of Rigid Flange Coupling 1.Unprotected type rigid flange coupling 2. Protected type rigid flange coupling 3. Marine type rigid flange coupling
- 115. Ex. A protected type rigid flange coupling is used to transmit 25kW power at 500 rpm from an engine to a machine. Design a coupling for an overload capacity of 25% .Assume following permissible stresses for components of coupling. Assume number of bolts as 6.
- 116. d-diameter of shaft, mm D-Outer diameter of hub ,mm D1- diameter of bolt circle ,mm D2- outer diameter of flange, mm D3- diameter of flange recess, mm l-length of hub, mm tf- thickness of flange, mm tp- thickness of protective flange, mm db- nominal diameter of bolt, mm N- no. of bolts
- 117. Given
- 118. Step 1 Torque Transmitted
- 119. Step 2. Design of Shaft
- 120. Step 3. Design of key Let us select square key.
- 121. Step 3. Design of key Considering crushing of key.
- 122. Step 3. Design of key Considering shearing of key.
- 123. Step 3. Design of key Selecting largest of three values of length(l)
- 124. Step 4. Design of hub Length of hub , l=79 mm Outer diameter of hub, D=2d= 2*45=90 mm Shear stress induced in hub given by Hence, hub is safe against shear failure
- 125. Step 5. Design of flange Thickness of flange, Thickness of protective flange, Diameter of bolt circle, Outer diameter of flange, Diameter of flange recess,
- 126. Step 5. Design of flange Direct shear stress induced in a flange at junction with hub is Hence flange is safe against shear failure
- 127. Step 6. Design of bolts a. Considering Shearing of bolt
- 128. Step 6. Design of bolts b. Considering Crushing of bolt
- 130. Assignment 2.9 1. Design a flange coupling for steel shaft transmitting 20kW power at 250 r.p.m. the maximum torque is 30% greater than full load torque. The material properties are as follow: â˘ Allowable shear stress for shaft and key =40MPa â˘ Allowable shear stress for bolts =30MPa â˘ Allowable crushing stress for shaft & key =80MPa â˘ Allowable shear stress for flange =14MPa â˘ Allowable compressive stress for bolts =60MPa â˘ Number of bolts =4
- 132. Ex.1 A transmission shaft supporting a helical gear B and an overhung bevel gear D is shown in Fig. The shaft is mounted on two bearings, A and C. The pitch circle diameter of the helical gear is 450 mm and the diameter of the bevel gear at the forces is 450 mm. Power is transmitted from the helical gear to the bevel gear. The gears are keyed to the shaft. The material of the shaft is steel 45C8 (Sut = 600 and Syt = 380 N/ mm2). The factors kb and kt of ASME code are 2.0 and 1.5 respectively. Determine the shaft diameter using the ASME code.
- 133. Ex.2. The armature shaft of a 40 kW, 720 rpm electric motor, mounted on two bearings A and B, is shown in Fig. The total magnetic pull on the armature is 7 kN and it can be assumed to be uniformly distributed over a length of 700 mm midway between the bearings. The shaft is made of steel with an ultimate tensile strength of 770 N/mm2 and yield strength of 580 N/mm2. Determine the shaft diameter using the ASME code if, kb = 1.5 and kt = 1.0 Assume that the pulley is keyed to the shaft.
- 134. Ex.3. It is required to design a square key for fixing a gear on a shaft of 25 mm diameter. The shaft is transmitting 15 kW power at 720 rpm to the gear. The key is made of steel 50C4 (Syt = 460 N/mm2) and the factor of safety is 3. For key material, the yield strength in compression can be assumed to be equal to the yield strength in tension. Determine the dimensions of the key. Ex.4. The standard cross-section for a flat key, which is fitted on a 50 mm diameter shaft, is 16 * 10 mm. The key is transmitting 475 N-m torque from the shaft to the hub. The key is made of commercial steel (Syt = Syc = 230 N/mm2).Determine the length of the key, if the factor of safety is 3.