Keys and Coupling

1
Keys and Coupling

• Many Types of Keys and couplings, however
  understand how Torque is transferred in between
  each, and forms shearing stresses

2
Shaft Coupling

• Sometimes, join 2 shafts together
• Flanged couplings
• Torque in Shaft ? Torque in Couplings ? Shear in
  bolts
• Similarly keys

Bolt circle
Flanged Couplings
Bolt
Shaft
3

• Design of Shaft Torque applied, TA ? t d3 /
  16
• Where, t shear stress in shaft d shaft
  dia.
• Design of bolts Torque resisted,
• TR Shear Stress Area x Radius of bolt circle
• TR n . (?/4) . db2 . t b . (D/2)
• Where, t b shear stress in bolt db
  bolt dia.
• D Diameter of bolt circle
• n number of bolts
• TA lt TR

4

• Design of Shaft Torque applied, TA ? t d3 /
  16
• Where, t shear stress in shaft d shaft
  dia.
• Design of keys
• Torque resisted,
• Tk Shear Stress Area x Radius of shaft
• Tk l b t k (D/2)
• Where, t k shear stress in key db
  bolt dia.
• D Diameter of bolt circle
• n number of bolts
• TA lt Tk

.
5
Springs and Stiffness

• Stiffness of spring
• Load required to produce a unit deflection in
  spring.
• K F/x
• xunit deflection
• Under gravity,
• W F

6
Springs

• Types of spring
• Bending / leaf / laminated spring
• Torsion / helical spring
• Close Coil helical spring
• Open Coil helical spring

7
Springs

• Uses of Springs
• Storing energy, used in watch
• Shock absorbers
• Seismic isolation
• Spring balance
• Cycle seats

8
Closed Coiled helical springs subjected to axial
loads

• R radius of the coil
• d Spring wire diameter
• W axial load on spring
• N number of coils/turns
• d deflection
• t, ?, G,
• Torque produced by axial load
• T W R
• Also T ? t d3/16
• Thus, ? t d3/16 W R

9

• Length of wire no. of coils x length of one
  coil
• Or, l n 2?R
• T G ?
• J l
• ? 64 WR2 n
• Gd4
• d R. ? 64 WR3 n
• Gd4
• Stiffness, s W Gd4
• d 64 R3 n
• Energy Stored in a spring, U (1/2) W d

10
Combined Bending and Torsion

• Find how Tan? 2 t / f T /M
• Where
• T Torsion,
• M Bending Moment
• t Shear Stress
• M Bending Stress

11
Tutorial- 2

1. Sketch 5 examples of use of springs
2. List differences between closed and open coil
   springs. Provide one sketch minimum
3. Answer Q.1. from Rethalias exercise on Helical
   Springs. pp. 72
4. Answer Q.1. to Q.7 from Rethalias example
   exercise