Subject :- Machine Design -I

Topic :- Spring

Difficulty :- Medium

• A concentric spring consists of two helical compression springs, one inside the other, having the same axis. It is also called a ‘nested’ spring.
• Two springs shown in Fig have opposite hand of helices. If the outer spring has a right-hand helix, the inner spring always has a left-hand helix and vice versa. Adjacent springs having opposite hands, prevent the locking of coils, in the event of axial misalignment or buckling of springs.

• In certain applications, concentric spring consists of three coaxial springs, namely inner, middle and outer springs.
• Concentric spring has the following advantages:

(a) Since there are two springs, the load carrying capacity is increased and heavy load can be transmitted in a restricted space.

(b) In concentric spring, the operation of the mechanism continues even if one of the springs breaks. This results in ‘fail safe’ system.

(c) In concentric spring, the spring vibrations called ‘surge’, are eliminated.