Herical spring practical

                                     









Experiment : Axial deflection of a close coiled helical springs by loading


Aim           : To determine
                        (a)    The modulus of Rigidity of a  close coiled helical springs
                        (b)    Spring constant ( Stiffness )


Apparatus  : 1. close coiled herical springs
                   2. Loading frame
                   3.dial gauge
                   4.weights
                   5.Vernier caliper


Theory     : When a close coiled helical spring is loaded deflection is given by
                                          δ  = 64 WR²N
                                                    D⁴G
               Where,
                   δ = Axial  deflection due to load          W = Axial load
                  R = Mean radius of the coil                  N = Number of Coils
                  D = Diameter of spring wire                 G = Modulus of Rigidity



                      δ          =     64 R²N    W
                                        D⁴G
                    ^                   ^               ^
                    Y          =     m               x


    (1)   G can be calculated from the gradient (m) of the graph δ vs W
    (2)   Spring constant   = W / δ


Procedure :

• The spring was mounted to obtain the deflection due  to compressive load.
• The  load was applied in 1 KG steps and measure the corresponding deflection using a dial gauge
• This was repeated for unloading
• The internal and external diameter were mesured in directions perpendicular to one another at each end and a mean value of radius R was calculated using these values
• Two different spring were tested
• Modulus of rigidity and stiffness of spring were found for each spring.

Calculation :
   Spring 1 :
  From the graph m1 : 3.33 mm / Kg
Theoretical  Gradient : = 64 R³N
                                         D⁴ G
                  d = 48.11 mm , N = 7


Experimental gradient  = Theoretical  gradient
   3.33mm /kg       =  64 x (48.11)⁴ x 7
                                  (7.26) x 4x6x6
                 G       =   8.987 Kn /mm2


Spring constant   = 1
                            3.33
                          = 0.3003 N / mm
You can calculate G and spring constant   for 2 nd spring also same procedure.




Discussion :
                        In this experiment we noted the axial deflection of a closed coiled helical spring by loading and unloadimg.The aim of this experiment is to find the modulus of rigidity of a closed helical spring and to find spring constant .This is a very important experiment is engineering works because helical springs are used for various purpose in various places.There  are leaf springs , spiral springs, conical spring and helical springs


When we were doing this experiment by using closed coiled helical springs loading from dial gauge , weights and vernier caliper by doing this experiment . We also had to face for some difficulties and errors. We took the measurement  the diameter of spring wires and internal external diameter of coils by using the vernier caliper for reducing the errors. We got measurement at least three places in above points and got mean value.


When we talking about the dial gauge readings by loading and unloading weights. We have to take that readings from over eye level other wise we couldn't  get  that readings
from our eye level it occurred errors in readings. If we fail to get these readings correctly. It effect to our final calculations and final value of modulus of rigidity and spring constant.    


If we consider vehicles helical springs are used to absorb shocks. So we have to use a suitable spring for that other wise stability of vehicle was lost. If we have to fix a spring that has a low or high spring constant than required value. In earth quick occurring countries are used huge helical springs shock absorberbs in base of concreat beams for the safety of huge building engineers fix the suitable spring between the base of the 
building and the found action mostly that method use in japan. If they used the method building won't be distroyed. Before fix that spring we should know the spring constant of the springs.


This experiment is very important in practical usages. Therefore we have to learn this method correctly.