How to design a reasonable extension springs?

With the development of extension springs application technology, more requirements are put forward for extension springs materials. The first is the forward fatigue life under high stress and the anti-slack function; the second is the corrosion resistance, non-magnetic, electrical conductivity, wear resistance, heat resistance and other aspects according to different uses. Therefore, in addition to the development of new varieties of extension springs materials, favorable results have been achieved in terms of strict control of chemical composition, reduction of non-metallic impurities, and improvement of surface quality and dimensional accuracy.

(1) Development of the production process of extension springs steel. In order to advance the quality of extension springs steel, the industry has generally selected out-of-furnace refining technology, continuous casting process, new rolling and online automatic detection and control equipment.

In order to ensure the chemical composition of steel and reduce the content of gases and various non-metallic inclusions, a large-capacity electric furnace or converter is used for smelting, and a ladle outside the furnace is used for refining to reduce the oxygen content (mass fraction) to (0.0021~0.0010)%. Produce ultra-pure steel, and then greatly advance the planning and operating stress of extension springs.

The continuous casting production process has been selected in the production of extension springs steel. Continuous casting can reduce the segregation of steel, reduce secondary oxidation, improve surface decarburization, and make the arrangement and function stable and uniform through techniques such as electromagnetic mixing and low-temperature casting.

The use of a split full continuous rolling mill can improve the dimensional accuracy and surface quality, and at the same time, the steel can be arranged uniformly along the length. In the rolling process, in order to ensure the surface quality of the product, online automatic detection and control are selected. In order to adapt to the production of variable cross-section extension springs flat steel, a new austenite rolling process has been developed, that is, the steel is heated and then rapidly cooled to the metastable austenite zone for plastic processing and quenching. This process allows the steel to advance its strength without reducing its plasticity. In addition, the function of extension springs steel is advanced by online heat treatment and surface hardening treatment after rolling.

(2) The development of alloy steel The primary function of alloying elements is to advance mechanical functions, improve process functions and give certain special functions. SiCr steel has been used for valve extension springs and suspension special-shaped springs. Si is an anti-stress slack alloy element. The addition of V and Mo to SiCr steel constitutes SiCrV and SiCrMo steels, which can improve fatigue life and anti-slack function. At the same time, the SiCr drawn wire has better anti-laundering function when working at high temperatures than piano wire and important-purpose carbon extension springs. With the high-speed miniaturization of engines, Ti alloys with good anti-vibration performance, light weight and small elastic modulus have been widely used, and their strength can reach 2000MPa.