First, an overview of spring material selection
The choice of spring material should be determined according to the nature of the spring load, working temperature, stress state, service life, requirements for electrical and magnetic conductivity, process performance, stress, environmental medium, material source and price.
Second, several important points for attention when selecting spring materials
Ⅰ. Material factors
Leaf springs generally use flat steels of 55SiMnVB, 55SiMnMoV, 55Si2Mn, 60Si2MnA, 60CrMnB, 60CrMn, etc.
Medium and small springs, especially helical tension springs, should be given priority to using strengthened steel wire, lead bath isothermal cold drawn steel wire and oil quenched tempered steel wire. Its strength and surface quality are higher, and its fatigue performance is higher than that of ordinary quenching. Fire steel wire, with good manufacturability, simple processing, and stable quality. For large and medium-sized springs, cold drawn or cold drawn steel should be used for high load accuracy and stress; for low load accuracy and stress, it can be Use hot rolled steel.
Electrical springs that use the spring itself as a conductor or springs that work under variable humidity conditions, such as water (including sea water) and water vapor environments, generally use copper and gold steel.
Springs that work under acid contact with other corrosive media are generally made of corrosion-resistant materials such as stainless acid-resistant steel or nickel alloy. For springs used under general environmental conditions, ordinary spring steel is selected, and the spring is made on its surface Anti-rust coating or electroplating (zinc plating, cadmium plating, copper plating) method to prevent corrosion.
The springs used in weighing instruments and instruments, in order to meet the accuracy of not being affected by temperature changes, generally use constant elastic alloys with minimal changes in elastic modulus and expansion coefficient.
Reinforced plastic can be selected for special purpose springs such as light weight, insulation, anti-collision, anti-corrosion, etc., and vibration-proof rubber can also be used to make various types of rubber springs.
Ⅱ. Characteristic factors
Strength and hardness have a great relationship with plane strain fracture toughness. Therefore, its selection should be based on the spring bearing properties and stress.
Hardenability, whether the cross-section of the spring material is hardened and the degree of hardening, have a great relationship with the quality of the spring.
●Special type, the material cross section of the coil spring should be preferred to use the circular cross section. Although the square and rectangular cross-section materials have strong bearing capacity and good impact resistance, they have less material sources and higher prices. Except for special needs, generally Try not to choose this material.
Ⅲ. Temperature factor
Spring materials that work at high temperatures require good thermal stability, resistance to relaxation or creep, resistance to oxidation, and resistance to certain medium corrosion.
Spring materials used at low temperatures should have good low temperature toughness. Austenitic stainless steel spring steel wires such as carbon spring steel wire, piano wire and 1Cr18Ni9, copper alloys, and nickel alloys have good low temperature toughness and strength. Because in low temperature conditions The brittleness of the material is very sensitive to surface defects. The environmental medium is much less corrosive to the material than in the greenhouse, and cadmium and zinc plating are easy to cause cold brittleness. The elastic modulus and expansion coefficient of the material do not change much. It can be ignored in the design.
The working temperature of the spring increases, and the elastic modulus of the spring material decreases, resulting in a decrease in stiffness and a smaller load-bearing capacity. According to GB1239, when the working temperature of ordinary coil springs exceeds 60°C, the shear modulus should be corrected. The formula is: Gt=KtG where G–the modulus of elasticity at room temperature; Gt–the shear modulus at the working temperature t; Kt–the temperature correction coefficient is selected according to Table 2-98. Therefore, the spring that works at high temperature must It is very important to understand the rate of change (value) of the elastic modulus and calculate the impact of the decrease in spring load capacity on the performance.