# Design of Machine Elements - 1 - Mechanical Engineering (MCQ) questions and answers for Q. 10361

Q.  Determine number of coils in a helical compression spring, if modulus of rigidity is 80 Gpa and spring stiffness is 50 N/ mm. Assume wire diameter and spring index as 8 mm and 5 respectively
- Published on 14 Sep 15

a. 11.8 turns
b. 12.8 turns
c. 13.3 turns
d. None of the above

#### Discussion

• MEGHASHYAM NARHARI BHAWE   -Posted on 31 Jul 19
Can you give similar formula for double enveloping worm set.
• Sravanthi   -Posted on 06 Nov 15
- The coils which twist or wind in up or down direction in torsion spring are called as active coils. They are present within springs and inactive coils are present at the end of the coil.

Given: Modulus of rigidity = 80 Gpa, spring index (C) = 5, wire diameter = 8 mm,

Formula: 1)Spring stiffness (K) = Fmax / δmax

2) Spring stiffness (K) = Gd / 8 C3 n

here, n = number of coils, C = spring index, G = modulus of rigidity, K = spring stiffness

Solution:

Substituting the given values we get,

Spring stiffness (K) = Gd / 8 C3 n

50 = (80 x 103 x 8) / (8 x 53 x n)

Number of coils (n) = 12.8

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