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Spring material reasonable choice

- May 31, 2018 -

Spring material reasonable choice
 
The choice of spring material shall be determined according to the nature of the spring's load, stress state, stress magnitude, working temperature, environmental media, service life, requirements for conductive magnetic conductivity, process performance, material source, and price.
When determining the shape and size of the material section, the series of dimensions specified in national standards and ministry standards should be preferred, and non-standard series of materials should be avoided.

Medium and small springs, especially spiral tension springs, should be preferentially treated with steel wires reinforced with lead wire, isothermally drawn steel wire with lead bath and oil quenched and tempered steel wire, with high strength and good surface quality, and higher fatigue performance than normal quenching. Tempering wire, simple processing, good craftsmanship, stable quality.

Carbon spring steel wire and piano wire produce large residual stress after cold drawing. After machining the spring, there is a large residual stress, and the dimensional change after tempering is large, and it is difficult to control the dimensional accuracy. The oil quenched and tempered steel wire is modulated and strengthened after the steel wire is drawn to the specified size. There is basically no residual stress. After forming the gas spring, it is tempered at low temperature, the dimensional change is small, and the heat stability is better than the cold. Pull the reinforcement wire.

Large and medium-sized springs should be made of cold drawn material or polished steel after cold drawing for high load accuracy and stress. For springs with low load accuracy and stress, hot rolled steels can be used.
Leaf springs are generally selected from flat steels such as 55Si2Mn, 60Si2MnA, 55SiMnVB, 55SiMnMoV, 60CrMn, and 60CrMnB.

For the spiral spring material section, circular section should be preferred. Square and rectangular cross-section materials have strong bearing capacity, good impact resistance, and small springs, but the source of material is small. And the price is higher, except for special needs, generally try not to use this material.

Spring materials that work at high temperatures require good thermal stability, resistance to slack or creep, oxidation resistance, and resistance to certain media.

As the working temperature of the spring increases, the elastic modulus of the spring material decreases, resulting in a decrease in stiffness and a decrease in load carrying capacity. Therefore, the spring working at a high temperature must understand the rate of change of the elastic modulus, and calculate the effect of a decrease in the spring load carrying capacity on the use performance. According to the provisions of GB1239, when the working temperature of ordinary coil springs exceeds 60°C, the shear modulus should be corrected. The formula is: Gt = KtG, where the elastic modulus at G - normal temperature; Gt - shear at operating temperature t Modulus.

At low temperatures, the brittleness of the material is very sensitive to surface defects. Therefore, the surface quality of the material should be strictly required. At low temperatures, the environmental media erodes the material much less than in a greenhouse, and cadmium plating and galvanizing can cause cold brittleness. At low temperatures, the modulus of elasticity and the coefficient of expansion of the material do not change much and may not be considered in the design.
Spring made of spring steel, hardness (ie, strength) selection should be based on spring bearing properties and the size of the stress. However, the relationship between hardness and plane strain fracture toughness is extremely high. As the hardness increases, the plane strain fracture toughness (KIC) value decreases significantly. This means that in determining the hardness value of the spring, the hardness of the spring should be lower if the spring characteristic requirements are satisfied.

Spring materials used at low temperatures should have good low temperature toughness. Carbon spring steel wire, piano wire and 1Cr18Ni9 austenitic stainless steel spring wire, copper alloy, nickel alloy have good low temperature toughness and strength.
Spring selection, but also pay attention to the hardenability of steel. The extent to which the cross-section of the spring material is hardened and hardened is extremely relevant to the quality of the spring.

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