Question 10.15: A steam engine cylinder has an effective diameter of 370 mm ......
A steam engine cylinder has an effective diameter of 370 mm and the maximum steam pressure acting on the cover is 1.3 N/mm². Calculate the number and size of the studs required to fix the cylinder cover, assuming the permissible stress in the studs as 32 MPa.
Given that
D = diameter of the cylinder = 370 mm
p = internal fluid pressure = 1.3 MPa
\sigma_t=32 \mathrm{~MPa}
Now let us determine
d_r= root diameter of bolt or stud
and N_b= number of bolts or studs
Considering 12 number of studs in the joint
d_r=\sqrt{\frac{D^2 \times p}{N_b \times \sigma_t}}=\sqrt{\frac{370^2 \times 1.3}{12 \times 32}}=21.52 \mathrm{~mm}
Conisder the standard nominal diameter as 25 mm.
Assume the cylinder is made of steel with allowable strength as 32 MPa (as given for bolt material).
The thickness of the cylinder wall is obtained
t=\frac{p D}{2 \sigma_{\text {all }}}=\frac{1.3 \times 370}{2 \times 30}=8.02 \mathrm{~mm}
Taking the thickness of the cylinder wall as 10 mm, the bolt spacing diameter is obtained as
d_b=D+2 t+3 d
=370+20+75=465 \mathrm{~mm}
Verifying the bolt spacing as
3 \leq \frac{\pi d_b}{N_b d} \leq 6
\frac{\pi d_b}{N_b d}=\frac{\pi \times 465}{12 \times 25}=4.86
which is in between 3 and 6, hence safe.
The size of the stud is M25 and the number of studs is 12