Answer to Question #268070 in Mechanical Engineering for Amat

Question

A rigid flange coupling is used to connect a 45KW 1440rpm electric motor to a centrifugal pump. The starting torque of the motor is 225% of the rated torque. There are 8 bolts and their pitch circle diameter is 150mm . The bolts are made of steel 45C8 (sigma yt 380N/mm2 ) the factor of safety is 2.5 . Determine the diameter of the bolts. Assume (sigma sy 0.577 sigma yt) . Assume that the bolts are finger tight is reamed and ground holes.

Answer 1

Permissible shear stress,$\tau=\frac{s_{Sy}}{FS}$

$=\frac{0.577s_{st}}{2.5}=87.7N/mm^2$

Direct shear stress in bolt

$P_1'=P_2'=\frac{P}{Number\ of\ bolts}$

$=\frac{45*10^3}{8}=5625N$

Shear area of 8 bolts=$8(\frac{πd^2}{4})mm^2$

P=$8(\frac{πd^2}{4})*\tau$

$d^2=\frac{45*10^3*4}{8*π*87.7}$

$d^2=81.664$

$d=9.03mm$

Hence standard size of bolt is M10