Springs - Mechanical Elements Which Drives Many Jobs.

Introduction :

A spring is an elastic object that stores mechanicalenergy. Springs are typically made of spring steel. There are many spring designs. In everyday use, the term often refers to coil springs.

When a conventional spring, without stiffness variability features, is compressed or stretched from its resting position, it exerts an opposingforce approximately proportional to its change in length (this approximation breaks down for larger deflections).

The rate or spring constant of a spring is the change in theforce it exerts, divided by the change indeflection of the spring. That is, it is the gradient of the force versus deflection curve. Anextension orcompression spring's rate is expressed in units of force divided by distance, for example lbf/in or N/m.

Atorsion spring is a spring that works by twisting; when it is twisted about its axis by an angle, it produces atorque proportional to the angle. A torsion spring's rate is in units of torque divided by angle, such as N·m/rad or ft·lbf/degree.

The inverse of spring rate is compliance, that is: if a spring has a rate of 10 N/mm, it has a compliance of 0.1 mm/N. The stiffness (or rate) of springs in parallel isadditive, as is the compliance of springs in series.

Springs are made from a variety of elastic materials, the most common beingspring steel. Small springs can be wound from pre-hardened stock, while larger ones are made fromannealed steel and hardened after fabrication. Some non-ferrous metals are also used includingphosphor, bronze or aluminium for parts requiring corrosion resistance andberyllium copper for springs carrying electrical current (because of its low electrical resistance).

Types of Springs :

Let us know some of the types of springs which are used in our day to day life :

1. Tension/extension spring – the spring is designed to operate with atension load, so the spring stretches as the load is applied to it.

2. Compression spring – is designed to operate with a compression load, so the spring gets shorter as the load is applied to it.

3. Torsion Spring – unlike the above types in which the load is an axial force, the load applied to a torsion spring is atorque or twisting force, and the end of the spring rotates through an angle as the load is applied.

4. Constant spring - supported load remains the same throughout deflection cycle.

5. Variable spring - resistance of the coil to load varies during compression.

6. Variable Stiffness spring - resistance of the coil to load can be dynamically varied for example by the control system, some types of these springs also vary their length thereby providing actuation capability as well.

7.Volute Spring - a compression coil spring in the form of acone so that under compression the coils are not forced against each other, thus permitting longer travel.

8. Hairspring or Balance Spring – a delicate spiral spring used inwatches, galvanometers and places where electricity must be carried to partially rotating devices such assteering

wheels without hindering the rotation.

9.Leaf Spring – a flat spring used in vehicle suspensions, electrical switches andbows.

10. V-spring – used in antiquefirearm mechanisms such as thewheel lock,flintlock and percussion cap locks. Also door-lock spring, as used in antique door latch mechanisms.

11.Torsion Spring – any spring designed to be twisted rather than compressed or extended. Used intorsion bar vehicle suspension systems.

12.Wave Spring – any of many wave shaped springs, washers, and expanders, including linear springs—all of which are generally made with flat wire or discs that aremarcel led according to industrial terms, usually by die-stamping, into a wavy regular pattern resulting in curvilinear lobes. Round wire wave springs exist as well. Types include wave washer, single turn wave spring, multi-turn wave spring, linear wave spring, marcel expander, interlaced wave spring, and nested wave spring.

Helical Torsion Springs :

Helical Compression Springs and Helical Tension Springs are subjected to loads in the axial direction, while Helical Torsion Springs are subjected to loads in the circumferential direction. Many helical torsion springs are used in pedal and hand brake return devices for automobiles. Since the shapes are complicated and diverse, the introduction of automatic machines and the improvement of tools significantly enhance the quality and production capacity.

It is used in door hinges, levers, pawl ratchets & various other electrical devices where torque is required. It is wound similar to extension or compression springs but have the ends shaped to transmit torque.

The helical torsion resists the bending moment which tends to wind up the spring. The primary stresses in this springs are flexural in contrast with torsional shear stresses in compression or extension spring. The torsional moment on spring produces a bending stress in the wire, the bending moment being numerically equal to the torsional moment.

In addition to this stress there is direct there is direct tensile or compressive stress due to force F which is tangential to the coil. Each individual section of the torsion spring is considered as a curved beam. Therefore using curved beam principle bending stress in the torsion spring considering stress concentration factor is calculated.

Applications of Springs :

1. Clocks: Torsion springs are used in torsion pendulum clocks. In such clocks, a torsion spring is used to suspend a wheel-shaped weight from the centre of the clock.

2. Clothes Pins: This is one of the most common applications of these springs. The working of clothes pins is facilitated by the torsion springs.

3. Automotive: Torsion springs are known for providing even tension, along with smooth and frictionless motion.

4. Medical Equipment: In the medical industry, the torsion springs are used in a number of complex equipment.

5. Door Hinges: These springs are widely used in different types of door hinges.