Spring is a very good elastic parts, it has easy to deformation, elasticity and other characteristics. In the spring limit of the range, the size of its elastic force with the spring elongation is proportional to the relationship between the amount of follow Hooke's law, F = KX, the following applications of the spring: mitigation of shock and vibration absorption: these springs have a greater elastic deformation capacity, can absorb vibration and shock. Such as automobiles, trains in the buffer springs, couplings in the vibration-absorbing springs and so on. Control the movement of institutions: these springs require a certain range of deformation within the force change is not large. Such as internal combustion engines in the valve spring, clutch control spring, automatic machine tool cam mechanism in the spring and so on. Stored energy: these springs require both greater elasticity, but also requires a more stable force. Such as clock springs, gun machine springs, automatic machine tools in the automatic return of the tool holder in the spring and so on. Measure the size of the force: these springs require a linear relationship between force and deformation. Such as force measuring instruments and spring scales in the spring and so on. There are many types of springs, according to the different loads can be divided into extension springs, compression springs, torsion springs and bending springs. According to the different shapes of springs can be divided into: coil springs, butterfly springs, ring springs, coil springs, leaf springs and so on. In a certain extension range spring, the spring can produce a large elastic deformation when loaded, the mechanical work or kinetic energy into deformation energy, and unloaded spring deformation disappears and return to its original state, the deformation energy into mechanical work or kinetic energy. In this process, the elongation length and the size of the elastic force into a fixed ratio k (depending on the spring itself) is called fully elastic deformation beyond this range, it will become generalized deformation, can not be recovered or can not be fully recovered.