MCQs on Efficiency of Screws
Efficiency of screw depends upon lead of the screw.
Explanation: Efficiency= WL/[Pπd].
Efficiency of the screw depends upon helix angle but does not depend on friction angle.
Explanation: Efficiency=tan(ἀ)/tan(Ǿ+ἀ) where ἀ=Helix angle and Ǿ=Friction angle.
Efficiency of the screw _______ with increase of coefficient of friction.
c) has no effect
d) cannot be determined
Explanation: Efficiency is inversely proportional to tan of the sum of helix and efficiency angle.
Maximum efficiency of a square threaded is given by
Explanation: Efficiency=Sin(2ἀ+Ǿ)-Sin Ǿ /Sin(2 ἀ+Ǿ+Sin Ǿ),For max efficiency, sin(2ἀ+ Ǿ)=1
If friction angle is 30’ then the maximum efficiency of the screw is
d) Noe of the mentioned
Explanation: Maximum efficiency=1-sinǾ/1+sinǾ.
Maximum possible efficiency of a self-locking screw is
Explanation: For self locking screw Ǿ(friction angle)>ἀ (helix angle), hence efficiency < tanǾ/tan(Ǿ+ἀ) or efficiency < tanǾ(1-tan²Ǿ)/2tanǾ.
In trapezoidal threads, f (coefficient of friction) can be taken as
a) f sec θ
b) f cos θ
c) f sin θ
d) f cosec θ
Explanation: The normal force acting on the thread is W sec θ therefore the effect of the thread angle is to increase the frictional force by a term sec θ.
Clutch and coupling can be considered to be same.
Explanation: Clutch is a temporary join while coupling is a permanent joint.
Cold rolled components have higher strengths and hardness than hot rolled components.
Explanation: During grain re-structuring, original strength of material is lost.
Which of the following are true?
a) Cold working reduces toughness and ductility
b) Cold worked components have poor resistance to shocks and vibrations
c) Tooling for cold working is cheaper as compared to hot working
d) All of the mentioned
Explanation: Properties of cold working.