Shafts

Shaft is a machine member is useful for power transmission by the rotation of own axis, usually of circular cross-section and transmit the power from one place to another. Shaft carries rotation parts like gears, pulleys, fly wheels, sprockets and those fixed through ‘Keys’. Splines and are subjected to torque due to transmitting the power and bending moment due to weight of pulley and gear, shafts are supported on bearing.
Types of cross sections of shafts
1) Cylindrical
2) Square
3) Elliptical
4) Spline shafts
These are solid as well as Hallow shafts.
* Hallow shafts usually used in merine works (automobile also), solid shafts are in automobile.*
* Hallow shafts are usually forged on mandrel, thus making more homogeneous than the solid shafts. 
* Spline shaft is applicable for high power transmissions shaft rotation.
   For transmitting power between two right angle arranged shafts by bevel gears, benchvice spindle manufactured with acme thread profile. 
 

Classification of shafts
1) Prime mover shaft:
e.g.: Turbine shaft, Motor shaft, Engine shaft
 

2) Power transmission shaft: These shafts are transmit power between the surface and the asorbing (using) power.
e.g.: Line shaft, Jack shaft, Counter shaft.
Line shaft: Long continuous shaft which received power from prime mover and transmits to the machines.
Jack shafts: Shaft directly connected to prime mover (or) source.
Counter shaft: Employed between line shaft and machine.
 

3) Machine shaft: Shaft is integral part of machine.
e.g.: Crack shaft
        The material used in ordinary shaft is mild steel, if strength of requires make alloy steel such as nickel, nickel chromium, chrome venadium steel is used.
   Shafts are formed by two process:
           1) Hot rolling
           2) Cold rolling
          *  Hot rolling shafts are turned to size and finished through grinding.
          *  Cold rolling stronger than the hot rolling due to residual stresses.
          *  Shafts larger size (special purpose) usually forged and then turned to size on a lathe.
          *  Standard length of shafts are 5 m, 6 m, 7 m. 

Torque: Twisting moment of the shaft
Torque (T) = Axial load (P) × Radius
                     = P × R
Designing of the shaft on the basis of strength
1) Shaft subjected to twisting moment (or) torque.
2) Shaft subjected to bending moment.
3) Shaft subject to both.
 

Designing of Shafts:

      
  θ  → Angle of twist  L
 J  → Polar moment of inertia n⁴

 D → Outer diameter m
 d → Inner diameter m


 (D → Diameter of shaft ‘m’)

work done = Torque × Angular Displacement

 
        
 Design of shaft subjected to bending moment
       Theory of simple bending

M →  Bending moment N - m 
I → Moment of Inertia of cross sectional area of shaft about the axis of Rotation m⁴   
F_b = Bending Stress N/m²
Y →  Distance from the Neutral axis, m 
E → Young modulus N/m²
R → Radius of curvature
 Radius curvature in no bending of shaft is neglected and it is less than that of distance from the Neutral axis.
*  At no load condition R < Y
*  At loading condition R > Y.
* Amount loading increase Radius of curvature also increases.

    Y =      distance from the neutral axis

for solid shaft  M = σb × Zsolid

   Y =  

  
 
  Guest’s theory

 (For solid shaft)

Ranking Theory