(5) After more than 100 years of development, the technology of spring steel wire has experienced from lead quenching to oil quenching, and now to induction heating quenching. In addition, the process technology and equipment are constantly innovated and improved, and the variety and quality are constantly updated. Recently, the induction heating quenching and tempering treatment process for valve spring steel wire has been developed. The test results show that the plasticity, toughness, relaxation resistance, fracture toughness, delayed fracture resistance and fatigue life of the steel wire are greatly improved than those of the oil quenched and tempered steel wire due to its short induction heating time, fine quenching structure and almost no decarburization layer on the steel wire surface.
Another kind of ultra-fine grain thermomechanical treatment steel wire has been applied in the field. The ultra-fine grain thermomechanical treatment is a kind of composite strengthening and toughening process combining the ultra-fine structure and the thermomechanical treatment. It can not only improve the mechanical properties of steel wire, but also improve the surface quality of steel wire. The surface quality of materials has great influence on fatigue properties. In order to ensure the surface quality, the peeling process is adopted for the materials with special requirements, and the surface layer is removed by 0.1 mm. Eddy current inspection is used for defects with depth of 0.5mm. The surface roughness can be reduced to = (6.5 ~ 3.4) m by electrolytic grinding.
(6) The development of stainless steel wire in recent years, the production of stainless steel spring wire abroad has developed rapidly. 1Cr18Ni9 and 0cr17ni7ai were the main varieties with increased domestic demand.
The characteristics of advanced steel wire production process are that the wire rod is first peeled to remove the defects caused by hot working. Besides acid pickling after the first solution treatment, the whole cold working process keeps a bright surface.
With the development of technology, the production process of stainless steel wire is further simplified, and the quality control of some original metal products industry is simplified to the requirements of wire rod quality. After the roughing wire drawing machine, the surface coating and residual lubricating film shall be removed by wiping with cleaning ball and cleaning in water. Before the bright heat treatment, the electrolytic pickling, alkali neutralization, water washing and drying devices are equipped to completely remove the oil on the steel wire surface and improve the surface quality.
(7) Development of shape memory alloy (SMA), 50Ti and 50ni are the most promising unidirectional shape memory alloys. The spring made of shape memory alloy can stretch and stretch under the action of temperature. It is mainly used in the control system of constant temperature, constant load and constant deformation. Because the actuator is driven by spring expansion and contraction, the working stress of spring changes greatly.
(8) The application of ceramics has high elastic modulus and low fracture strength, which is suitable for small deformation. At present, we are developing ceramics with heat resistance, wear resistance and good insulation, and superplastic zinc alloy (SPZ) with high strength at room temperature. In addition, there is high strength silicon nitride, which can withstand high temperature, up to 1000 ℃. However, ceramic spring is not suitable for working under impact load.
(9) Glass fiber reinforced plastic (GFRP) leaf spring has been widely used in Britain, the United States and Japan. Besides the transverse suspension, it can also be used in special light vehicles, such as the longitudinal suspension of racing cars. At present, carbon fiber reinforced plastic (GFRP) suspension spring has been successfully developed, which is 20% lighter than metal leaf spring.