1. Find the torsional shear stress to which a screw of nominal diameter 22mm is subjected when the clamp exerts a force of 5kN on it. The screw is double threaded and pitch of screw is 5mm.Given: Coefficient of friction is 0.15.
a) 25.45N/mm²
b) 21.29N/mm²
c) 31.21N/mm²
d) 35.65N/mm²
Explanation: =16M/πd₂ᵌ where M=Wd₁ tan (Ǿ+ἀ)/2 where d₁=22-0.5 x 5,W=5000N,
tanἀ=2 x 5/[πx19.5] and d₂=19.5-0.5 x 5.
2. If bending stress in a screw is of magnitude 95N/mm² and torsional shear stress of magnitude 15N/mm², then what is the principal shear stress?
a) 48.7N/mm²
b) 54.3 N/mm²
c) 51.4 N/mm²
d) 49.8 N/mm²
Explanation: τ(max)=√(95/2)²+15².
3. The nominal diameter of the screw is 22mm and the allowable bearing pressure for the nut is 15N//mm². Find the length of the nut if pitch of the screw is
a) 15mm
b) 20mm
c) 25mm
d) 30mm
Explanation: z=4W/π S(d₁²-d₂²) where S=15N/mm²,d₁=22mm and d₂=17mm. Hencez=2.2 or z=3. Length of nut=zp or l=3 x 5= 15mm.
4. A but joint can be defined as a joint between two components lying approximately in a different plane.
a) True
b) False
Explanation: Butt joint is defined a joint between two plates lying in the same plane.
5. A fillet weld is an approximately triangular cross section joining two surfaces lying parallels to each other.
a) True
b) False
Explanation: Two surfaces lie perpendicular to each other.
6. How many types of jacks are there which can be used in a screw jack?
a) 2
b) 3
c) 4
d) 5
Explanation: Hydraulic jack and mechanical jack.
7. Which of the following does not form the important part of the screw jack?
a) Frame
b) Nut
c) Cup
d) Coupling
Explanation: There is no specific requirement of coupling in the screw jack.
8. The transverse shear stress at the root of the threads in the nut can be given by?(symbols have their usual meaning, z=number of threads in nut).
a) 4W/πdz²
b) W/πdtz
c) 4W/πtd²
d) None of the mentioned
Explanation: At root of threads, the area parallel to direction of force is considered which is equal to circumference x thickness x no. of threads.
9. What type of friction in cup design is recommended for the set screw?
a) Sliding
b) Rolling
c) Static
d) None of the mentioned
Explanation: Sliding friction, the total force require to raise the load is quite large as compared to that required in rolling friction. Hence length of handle in some cases becomes extremely large and thus it is impractical to use cups with sliding friction.
10. A differential screw is defined as a mechanical device consisting of two screws connected in parallel.
a) True
b) False
Explanation: The two screws are connected in series.