A spring is a mechanical part that uses elasticity to work. Parts made of elastic material deformation under external force, remove the force and then restore the status quo ante. Generally made of spring steel. Spring types of complex and diverse, according to shape points, there are helical springs, scroll springs, leaf springs, 　　special-shaped springs.
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　　Most materials have different degrees of elasticity, if it is bent, will be a great strength to restore its prototype. In the history of mankind, it must have long been noted that the branches of saplings and saplings are very flexible, since many primitive cultures make use of this feature, wedge a stick in the tailor-made door or cage wedge, Set on a pole to pull down; once the release of tension, the stick or rod will go back. They use this approach to capture birds and beasts. In fact, the bow is in this way the use of young trees elastic spring; first pull back the bow, and then let go, let it rebound. In the Middle Ages, this idea began to appear in the machinery, such as textile machines, lathes, rigs, grinding machines and saws. The operator presses or pulls the working machine down by the hand or foot pedal, and then a rod fixed on the machine by the rope bounces back and forth to produce reciprocating motion.