Springs can be divided into static springs and dynamic springs according to their operating conditions. Static springs refer to springs that have a limited number of vibrations during the service period, such as safety valve springs, spring washers, weighing pan springs, constant load springs, mechanical springs, watch hair springs, etc. Springs with more than 1×106 vibrations during the service period, such as engine valve springs, vehicle suspension springs, anti-vibration springs, coupling springs, elevator buffer springs, etc. The selection of static springs mainly considers tensile strength and stability, and dynamic springs When selecting materials, fatigue, relaxation and resonance performance are mainly considered.
Springs can be divided into three states according to the load conditions: light load, general load and heavy load. Light load refers to springs that bear static stress, low stress, and small deformation, such as springs for safety devices and springs for vibration absorption. Design The service life is 103~104 times.
General load refers to a common spring with a design life of 105~106 times and a vibration frequency of 300 times/min. Within the allowable stress range, the life is guaranteed 1×106 times. The lower the load stress, the longer the life.
Heavy load refers to springs that work for a long time and frequently vibrate. For example, valve springs, air hammers, presses, and hydraulic controller springs have high loads, often used at about 10% below the allowable stress, and their service life is greater than 1×106 Times, usually 107 times.
The principle of spring material selection is: firstly meet the functional requirements, secondly the strength requirements, and finally consider the economy.
Carbon spring steel is the most widely used steel in spring steel. The steel contains 0.60%~0.90% carbon and 0.3%~1.20% manganese, no other alloying elements are added, and the use cost is relatively low. After proper processing or heat treatment, plain spring steel wire can obtain high tensile strength, sufficient toughness and good fatigue life. However, the hardenability of carbon steel wire is low, the relaxation resistance and corrosion resistance are poor, and the elastic modulus The temperature coefficient is large (up to 300×10-6/℃), which is suitable for manufacturing springs with small cross-section and low working temperature (120℃>).
Alloy spring steel generally contains 0.45% to 0.70% carbon and a certain amount of Si, Mn, Cr, V, W, and B and other alloying elements. The addition of alloying elements improves the relaxation resistance of spring steel, increases the toughness of steel, and shows In order to improve the hardenability and service temperature of steel, it is suitable for the manufacture of springs with larger sections and higher temperatures.